Applied Catalysis A, General (v.413-414, #C)
Editorial Board (CO2).
New efficient visible light photocatalyst based on heterojunction of BiOCl–bismuth oxyhydrate by Sanaa Shenawi-Khalil; Vladimir Uvarov; Ella Menes; Inna Popov; Yoel Sasson (1-9).
New efficient visible light photocatalyst based on heterojunction of BiOCl–bismuth oxyhydrate has been synthesized, its properties and photocatalytic activity have been studied.Display Omitted► Synthesis of new visible light sensitive photocatalysts based on heterojunction of BiOCl–bismuth oxyhydrate. ► 5 times higher photocatalytic activity compared to TiO2. ► Preliminary study of crystal structure and thermal behavior of synthesized bismuth oxyhydrate.A novel active photocatalyst, which is a heteroconjuction of a bismuth oxyhydrate and BiOCl, has been synthesized by a simple hydrothermal method. The photocatalytic activity of the new material was measured in the degradation of Rhodamine B (RhB) and Acetophenone (AP) and in the photocatalytic oxidation of iodide in water under UV–vis and visible light irradiations respectively. The heterojunction between bismuth oxyhydrate and BiOCl provided exceptional photocatalytic activity, whereas both the individual bismuth oxyhydrate and BiOCl showed a negligible efficiency. Compared to Degussa P25, the new composite material demonstrated 5 times higher activity in removing aqueous RhB under visible light (λ ≥ 420 nm) irradiation. The chemical composition and crystal structure were investigated using powder X-ray diffraction, scanning and transmission electron microscopy, and thermal methods. The preliminary study has revealed the bismuth oxyhydrate has tetragonal crystal structure with unit cell parameters a = b = 5.674 Å, c = 10.353 Å, unit cell volume V = 333.3 Å3 and possible P4/mmm (No. 123) space group. Temperature behavior of new photocatalyst has been investigated. It was found that at heating to 550 °C for 45 min the new phase transforms into well-known monoclinic Bi2O3.
Keywords: Visible light photocatalysis; Heteroconjuction; Bismuth oxyhydrate; Bismuth hydroxide; Bismuth oxychloride; Thermal decomposition;
Synthesis of hydrotalcite-supported shape-controlled Pd nanoparticles by a precipitation–reduction method by JunTing Feng; XiaoYan Ma; YuFei He; David G. Evans; DianQing Li (10-20).
Display Omitted► LDHs supported Pd catalysts were prepared by a precipitation–reduction method. ► Tetrahedral Pd nanoparticles were highly dispersed on the surface of LDHs. ► By adding CTAB as a capping agent, truncated octahedral particles were obtained. ► Specific Pd shapes lead to higher surface-to-volume ratio and catalytic activity. ► Pd (1 1 1) is regarded as the preferred facet in selective acetylene hydrogenation.A Pd catalyst supported on a layered double hydroxide (LDH or hydrotalcite-like material) has been synthesized in a one step reaction using a precipitation–reduction method in which hydrolysis of hexamethylenetetramine was used to both precipitate the LDH by virtue of the resulting increase in pH and provide formaldehyde which reduces the Pd2+ precursor to Pd0. The resulting Pd nanoparticles were mostly tetrahedral in shape, and were highly dispersed on the surface of the LDH. After introducing a capping agent during the synthesis, the morphology of the Pd particles changed to truncated octahedral, although a similar high degree of dispersion was obtained. Compared with a conventional impregnated catalyst composed of pseudo-spherical Pd particles, catalysts prepared by the new method showed both higher activity and selectivity in the hydrogenation of acetylene. The enhanced activity is due to the specific morphology of the Pd particles, which results in their higher dispersion, while the higher selectivity is attributed to the Pd–C phase formed in the catalyst during the reaction. Furthermore, compared with the truncated octahedral Pd particles enclosed by (1 1 1) and (1 0 0) facets, the tetrahedral particles with only (1 1 1) facets exposed showed higher ethylene selectivity, suggesting that the Pd (1 1 1) facet is the preferred facet in the selective hydrogenation of acetylene to ethylene.
Keywords: Supported metal catalyst; Pd morphology; Layered double hydroxide; Selective acetylene hydrogenation;
Synthesis of ethyl octyl ether from diethyl carbonate and 1-octanol over solid catalysts. A screening study by J. Guilera; R. Bringué; E. Ramírez; M. Iborra; J. Tejero (21-29).
.Display Omitted► Ethyl octyl ether is an interesting option to reformulate commercial diesel blends. ► Ethyl octyl ether can be obtained efficiently from diethyl carbonate and 1-octanol. ► Acidic ion exchangers are efficient catalysts for obtaining ethyl octyl ether. ► The zeolite H-BEA-25 are less active but more selective than acidic resins. ► Accessibility to acid sites is a key factor to explain the behavior of acidic resins.The synthesis of ethyl octyl ether (EOE) from a mixture of diethyl carbonate (DEC) and 1-octanol (1:2 molar ratio) over several solid catalysts was studied in batch mode at 150 °C and 25 bar. Catalyst screening revealed that EOE could be successfully obtained over some acid catalysts. In particular the highest yield was achieved over acid ion-exchange resins (33% after 8 h). A reaction scheme of the process is proposed. Selectivity to EOE was mainly affected by the production of diethyl ether (DEE) and di-n-octyl ether (DNOE). However, EOE was the main ether obtained (60 mol%), followed by DEE (20 mol%) and DNOE (20 mol%). By comparing the behavior of several acid resins, it was seen that the synthesis of EOE was highly related to the structural resin properties. It was found that the accessibility of DEC and 1-octanol to acid centers was improved over highly swollen and low polymer density resins. Thus, gel-type resins with low divinylbenzene content are the most suitable to produce EOE (e.g., Amberlyst 121, Dowex® 50Wx2-100 and CT224).
Keywords: Ethyl octyl ether; Diethyl carbonate; Ion-exchange resins; Diesel reformulation; Oxygenated compounds;
Metalloporphyrins immobilized on core–shell CeO2@SiO2 nanoparticles prepared by a double-coating method for oxidation of diphenyl methane by Xiang Guo; Yuan-Yuan Li; Dan-Hua Shen; Jie Gan; Mi Tian; Zhi-Gang Liu (30-35).
Display Omitted► Core–shell CeO2@SiO2 nanoparticles synthesized by a double-coating method. ► CeO2 modified by sodium citrate and coated with SiO2. ► Metalloporphyrin anchored onto CeO2@SiO2 nanoparticles by amide bond. ► Excellent catalytic performance for oxidation of diphenylmethane to diphenyl ketone. ► Remarkable reusability of the catalysts with high stability.Metalloporphyrins immobilized on CeO2@SiO2 core–shell nanoparticles were synthesized by a double-coating method and used for catalytic oxidation of diphenyl methane. A variety of characterization techniques including FT-IR, UV–vis, SEM, TEM, XRD, N2 adsorption–desorption and TGA were employed. The results show that the catalyst consists of regular nanoparticles (around 400 nm) with core–shell structure and metalloporphyrins were immobilized on CeO2@SiO2 core–shell nanoparticles via amide bonds. Moreover, these new developed catalysts for solvent-free selective oxidation of diphenyl methane exhibited an excellent catalytic activity, selectivity and stability. Furthermore, these catalysts could be reused 6 times without significant loss of their catalytic activity and the used catalysts maintained nearly the same physicochemical properties as the fresh.
Keywords: Metalloporphyrin; Silica; Ceria; Core–shell; Immobilization;
Catalytic dehydration of methanol to dimethyl ether over micro–mesoporous ZSM-5/MCM-41 composite molecular sieves by Qiang Tang; Hang Xu; Yanyan Zheng; Jinfu Wang; Hansheng Li; Jun Zhang (36-42).
Display Omitted► The ZSM-5/MCM-41 were synthesized in nano self-assembly method under an alkaline hydrothermal condition. ► Special acid distribution and micro–mesoporous structure of the ZSM-5/MCM-41 contribute to excellent catalytic performance. ► The combination of ZSM-5/MCM-41 and Cu/ZnO/Al2O3 was a promising catalyst for DME directly synthesis.A series of micro–mesoporous ZSM-5/MCM-41 composite molecular sieves were prepared by combining a microporous zeolite silica source with nano self-assembly methods, and characterized by SEM, TEM, XRD, N2 adsorption and desorption, TPD of ammonia, and their catalytic performance for the dehydration of methanol to dimethyl ether (DME) in a fixed bed microreactor at atmospheric pressure. Among these catalysts, the ZSM-5/MCM-41 sample alkali-treated with 1.5 mol/L NaOH solution, in which the relative crystallinity of ZSM-5 and MCM-41 are 54.5% and 30.5%, respectively, gave the best activity (X MeOH > 80%) with 100% selectivity and a long lifetime in a wide range of temperature from 190 °C to 300 °C. From the characterization and activity data, the formation mechanism of the micro–mesoporous composite molecular sieves was proposed to be a liquid-crystal templating mechanism.
Keywords: Dehydration; Micro–mesoporous; Composite molecular sieves; Methanol; Dimethyl ether;
Mechanism of complete n-hexane oxidation on silica supported cobalt and manganese catalysts by S. Todorova; A. Naydenov; H. Kolev; J.P. Holgado; G. Ivanov; G. Kadinov; A. Caballero (43-51).
.Display Omitted► Oxi-redox (Mars–van Krevelen) mechanism on the single manganese sample. ► Associative (Langmuir–Hinshelwood) mechanism is more probable for Co sample. ► Mars–van Krevelen predominates on CoMn bi-component catalysts. ► The highest activity of the catalyst prepared from a mixed solution Co(NO3)2 and Mn(NO3)2.Mono- and bi-component cobalt and manganese samples were prepared by impregnation of silica with aqueous solutions of Co(NO3)2·6H2O and/or Mn(NO3)2·6H2O. The bi-component samples were obtained by a common solution of Co- and Mn nitrates (CoMn-MS) or by deposition of cobalt on calcined Mn sample (Co + Mn). The catalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), temperature programmed reduction (TPR), Fourier transformed infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), elemental analysis and tested in reaction of complete n-hexane oxidation. It was observed that the well crystalline cobalt oxide partially covers poorly crystalline manganese oxide in the Co + Mn catalysts, while finely divided oxides (MnO2 and Mn2O3, Co3O4) are present on the surface of the (CoMn-MS) sample. Four Langmuir–Hinshelwood and two Mars–van Krevelen models were fitted with the experimental data from the catalytic tests. According to the model calculations and results from instrumental methods, the reaction pathway over single component manganese and bi-component Co-Mn catalysts proceeds through Mars–van Krevelen mechanism (the oxidation of the catalyst surface being the rate determining step), while Langmuir–Hinshelwood mechanism is more probable for the Co sample. A considerable increase in activity for the sample obtained from a mixed solution is explained by low crystallinity, simultaneous presence of Mn4+–Mn3+ and enrichment of the surface in oxygen species.
Keywords: n-Hexane complete oxidation; Kinetics models; Supported Co-Mn oxide catalysts;
Styrene epoxidation over V-SBA-15 with alkaline-earth metal ion promotion under photo-assisted conditions by Guangjian Wang; Shuai Zhang; Yanhong Huang; Fangfang Kang; Zhenxing Yang; Yajie Guo (52-61).
Display Omitted► V-SBA-15 with alkaline-earth metal ion was synthesized. ► Catalysts with low acidic sites avoided the ring opening reaction. ► Addition of alkaline-earth metals favor of dispersion of V5+ species. ► Possible mechanism for styrene epoxidation was discussed.The photo-assisted epoxidation of styrene over V/SBA-15 modified by alkaline-earth metal ions was investigated with hydrogen peroxide at room temperature. The results indicated that the isolated VO4 tetrahedron dispersed on the SiO2 was the photo-assisted catalytic active site for the formation of styrene oxide, while V5+ polymer species in V/SBA-15 with highly loaded V species caused deep oxidation of styrene oxide. Among the catalysts modified by alkaline-earth metal ions, Mg–V/SBA-15 displayed the best catalytic performance. It was probably due to the fact that the metallic character of Mg was weaker in alkaline-earth metals, so it was easier to disperse V5+ polymer species and the dispersion effect was especially obvious in the comparatively high loading weight of vanadium oxide. Moreover, addition of alkaline-earth metals decreased the acidic sites of V/SBA-15, inhibiting the ring-opening reaction on which the deep oxidation occurred. The structures of all catalysts were thoroughly investigated using different characterization techniques, including X-ray diffraction (XRD), transmission electron microscopy (TEM), NH3-temperature programmed desorption (TPD), H2 temperature-programmed reduction (TPR) and X-ray photoelectron spectroscopy (XPS), etc. A possible catalytic mechanism was proposed.
Keywords: V/SBA-15; Alkaline-earth metal promotion; Styrene; Photo-assisted epoxidation;
Low temperature conversion of linear C4 olefins with acid ZSM-5 zeolites of homogeneous composition by M. Henry; M. Bulut; W. Vermandel; B. Sels; P. Jacobs; D. Minoux; N. Nesterenko; S. Van Donk; J.P. Dath (62-77).
Display Omitted► n-Butenes dimerization at 220 °C with H-ZSM-5: dimerization–cracking–alkylation. ► Linear correlation between acid sites amounts and framework aluminum concentration. ► Presence of aromatic coke on Al-rich H-ZSM-5 fills the intracrystalline voids. ► On Al-rich catalysts, complete pore blockage with coke: extra-crystalline chemistry. ► On Al-poor ZSM-5, shape selective product distributions: intracrystalline catalysis.Conversion of linear butenes over ZSM-5 zeolites leads to a large variety of products, from olefins to aromatics. At low temperature, these products are mainly olefins from C3 = to C13 =, with a predominance of dimeric products. The analysis of the product stream obtained by the reaction of n-butenes over several materials with MFI topology, but with different aluminum content provides evidence for an oligomerization–cracking–realkylation mechanism. The reactions occur predominantly in the catalyst bulk or at the external surface, depending on the amount of coke developed inside the catalyst. This behavior is determined by the concentration of framework Al and associated silanol groups, inducing coking. For Al-rich MFI samples, the amount of hard coke is sufficient to block the access of reactants to internal acid sites. As a result, extra-crystalline catalysis dominates, while the appearance of the individual products is consistent with that predicted by classical carbocation theory. For siliceous samples, hard coke formation is less pronounced, and evidence for shape selective product formation is present. Expected relations among structural, morphological and acidic properties of all MFI materials have been confirmed by XRD, SEM and BET and by 27Al MAS NMR, NH3-TPD and FTIR.
Keywords: n-Butenes; ZSM-5; Dimerization; Oligomerization; Coke; External surface; Shape-selectivity;
Guaiacol transformation over unsupported molybdenum-based nitride catalysts by I.T. Ghampson; C. Sepúlveda; R. Garcia; B.G. Frederick; M.C. Wheeler; N. Escalona; W.J. DeSisto (78-84).
Display Omitted► Mo2N catalysts prepared under different synthesis conditions. ► The catalysts were characterized and evaluated for hydrodoxygenation of guaiacol. ► Single phase γ-Mo2N had the highest activity for guaiacol conversion. ► Single phase γ-Mo2N had the highest phenol to catechol ratio in the products. ► Co addition increased hydrodeoxygenation products.Unsupported Mo2N catalysts were prepared by thermal decomposition of ammonium heptamolybdate to form MoO3 followed by nitridation in either flowing ammonia or a N2/H2 mixture. The nitridation was achieved at two different space velocities for each reaction mixture. This resulted in Mo2N catalysts with different surface areas as well as different phases present as were determined by X-ray diffraction (XRD). The activity and selectivity of the catalysts were evaluated for hydrodeoxygenation (HDO) of guaiacol in a batch autoclave at 300 °C and 5 MPa hydrogen pressure. The catalyst prepared with flowing ammonia and a space velocity of 29 h−1 displayed the highest activity (guaiacol conversion) and highest phenol/catechol ratio within the products indicative of HDO activity. This highest activity was attributed to the catalyst containing only γ-Mo2N phase (as measured by XRD) and having the highest N/Mo atomic ratio. An initial attempt to promote this catalyst with Co, similar to that done for hydrodesulfurization and hydrodenitrogenation catalysts was unsuccessful in forming a single phase cobalt molybdenum nitride, however did show modest improvements in the production of deoxygenated compounds, and suggests further studies into this material for HDO catalysis.
Keywords: Hydrodeoxygenation; Guaiacol; Metal nitrides; Activity;
Study of La2−x Ca x CuO4 perovskites for the low temperature water gas shift reaction by S.S. Maluf; P.A.P. Nascente; C.R.M. Afonso; E.M. Assaf (85-93).
Display Omitted► La2−x Ca x CuO4 samples were synthesized. ► This perovskites are active for the gas shift reaction at 290 °C. ► A promoter effect of Ca was observed. ► The best catalytic performance was obtained for the La1.85Ca0.15CuO4 catalyst. ► La1.85Ca0.15CuO4 catalyst presented the highest content of surface calcium and the reducible species Cu0 and Cu1+.The effects of small fractions of calcium (x = 0, 0.05, 0.1, 0.15, and 0.20) on the structure and the catalytic properties of La2−x Ca x CuO4 peroviskites have been investigated. The samples have been synthesized using the co-precipitation method. Perovskite-type oxides were characterized by XRD, TPR, XPS, XANES, SEM, and TEM. Catalytic tests for the water gas shift reaction (WGSR) were carried out in a tubular reactor at 290 °C. All samples showed a well-defined perovskite structure with surface areas between 6 and 18 m2 g−1. The partial substitution of La by Ca enhanced the stability of the perovskites and increased their reduction temperature. All catalysts were actives for WGSR, and the best catalytic performance was obtained for the La1.85Ca0.15CuO4 catalyst, but the samples with 5 and 10% of Ca had the best TOF values for reaction. These results can be associated to promoter effect of calcium, the high surface area, and the reducible species Cu0 and Cu1+.
Keywords: Water gas shift reaction; Perovskites; Catalysts;
Anionic iron(III) porphyrins immobilized on zinc hydroxide chloride as catalysts for heterogeneous oxidation reactions by Guilherme Sippel Machado; Fernando Wypych; Shirley Nakagaki (94-102).
Display Omitted► Immobilization of anionic iron(III) porphyrins on hydroxide salt. ► Catalyst solids for heterogeneous catalysis with reuse capacity. ► Efficiency and selectivity in oxidation reaction. ► Comparison of layered hydroxide salts as support to catalysts. ► Similar layered matrixes, presented opposite selectivity results.This work describes the immobilization of an anionic iron(III) porphyrin (FePor) family on zinc hydroxide chloride (ZHC), a layered hydroxide salt prepared by reacting an aqueous zinc chloride solution with an ammonium hydroxide solution. The FePor immobilization was performed at room temperature under magnetic stirring, under air atmosphere, of each complex ethanol solution and the ZHC solid support suspension. The materials obtained were characterized by X-ray powder diffraction (XRPD), ultraviolet-visible spectroscopy (UV–vis) (solid samples), Fourier transform infrared spectroscopy (FTIR) and electron paramagnetic resonance (EPR). The catalytic activity of the solids was investigated in cyclooctene, cyclohexane and n-heptane heterogeneous catalytic oxidation reactions with iodosylbenzene as the oxygen donor. The solid catalyst's reutilization capacity was also investigated and the heterogeneous character of the catalytic process was confirmed. The compounds and the catalytic activity of FePor-ZHC were compared with the synthesis and catalytic activity of the same FePor immobilized on zinc hydroxide nitrate (ZHN). Though the matrixes are similar, the results obtained were exactly the opposite when the selectivity was analyzed.
Keywords: Porphyrin; Zinc hydroxide chloride; Heterogeneous catalyst; Oxidation;
Photocatalytic reduction of CO2 to methane over HNb3O8 nanobelts by Xiukai Li; Huiqi Pan; Wei Li; Zongjin Zhuang (103-108).
.Display Omitted► HNb3O8 with nanobelt-like morphology was prepared by hydrothermal synthesis. ► HNb3O8 nanobelts exhibited high activity for CO2 photoreduction to methane. ► The photocatalytic activity of HNb3O8 is higher than that of KNb3O8. ► The protonic acidity contributes to the high activity of HNb3O8 nanobelts. ► The nano-structure contributes to the high activity of HNb3O8 nanobelts.KNb3O8 and HNb3O8 nanobelts were prepared by hydrothermal synthesis. The characteristics of samples were investigated by XRD, SEM, and UV–vis diffuse reflectance spectroscopy. The KNb3O8 and HNb3O8 nanobelts exhibited much higher activities for CO2 photoreduction to methane than commercial TiO2 (Degussa P25), and the KNb3O8 and HNb3O8 particles prepared by conventional solid state reaction. It was also found that either the HNb3O8 nanobelts or the HNb3O8 particles performed better than the corresponding KNb3O8 counterpart. It is proposed that the nanobelt-like morphology and the protonic acidity contribute to the higher photocatalytic activity of the HNb3O8 nanobelts.
Keywords: Niobic acid; Nanobelt; CO2; Photoreduction; Methane;
Direct conversion of glycerol to acrylic acid via integrated dehydration–oxidation bed system by Ayut Witsuthammakul; Tawan Sooknoi (109-116).
Display Omitted► Over HZSM-5, glycerol dehydrated to acrolein then oxidized to acrylic acid over VMoO x . ► Complete glycerol conversion required over HZSM-5 to avoid decomposition over VMoO x . ► Selective oxidation obtained over highly dispersed VMoO x with <20 mol%V content ► Acrylic acid selectivity in 2nd bed, determined by acrolein selectivity in 1st bed. ► Diluted feed (<30%) at 300 °C, 0.2 atm O2 provides optimal dehydration–oxidation.Acrylic acid can be successfully produced in a single reactor via subsequent oxidation of the glycerol-dehydrated products. Selective dehydration of glycerol to acrolein was studied at 275–400 °C over HZSM-5, HBeta, HMordenite and HY. The V–Mo oxides (15–70 mol%V) on silicic acid support (20–100 wt% mixed oxides loading) were then included as a second bed for subsequent oxidation of the dehydrated products. Over the acid zeolites, acrolein and acetol are mainly generated, together with acetaldehyde, propionaldehyde, pyruvaldehyde and other oxygenates as secondary products. A complete conversion of glycerol with high selectivity to acrolein (up to 81 mol%) can be obtained when medium pore zeolites (HZSM-5) and low glycerol concentration (10–30 wt%) was used at 300 °C. A separated-sequential bed system provides high selectivity for acrylic acid with small amount of acetic acid and acetaldehyde (∼15 mol%). The catalyst with high V content promotes total oxidation of the dehydrated products to CO while that with highly dispersed V–Mo–O phases affords 98% selectivity to acrylic acid with 48% acrolein conversion.
Keywords: Glycerol; Acrolein; Acrylic acid; HZSM-5; Vanadium–molybdenum oxides; Dehydration; Oxidation;
Nitrates and nitrous oxide formation during the interaction of nitrogen oxides with Cu-ZSM-5 at low temperature by L. Lisi; R. Pirone; G. Russo; N. Santamaria; V. Stanzione (117-131).
Display Omitted► Cu-ZSM-5 adsorbs large amounts of NO in the temperature range 25–225 °C which undergo surface transformations. ► Reduced Cu+ sites are quickly re-oxidized by NO producing large amounts of N2O. ► Adsorbed NO slowly reacts with gaseous NO giving surface nitrates and N2O regardless the Cu oxidation state. ► Both mechanisms could involve either Cu monomers or copper pairs.The interaction of NO with Cu-ZSM-5 has been investigated in a temperature range (25–225 °C) in which no steady-state reactions occur. The study has been conducted by performing adsorption tests at variable exposure times and analysing the phenomena that occur by continuous monitoring of the gaseous effluents as well as by performing a subsequent TPD. The effect of temperature, catalyst pre-treatment and composition of the adsorbing mixture (NO/He, NO/O2/He, N2O/He and N2/He) have been evaluated. In situ FTIR experiments have been also carried out under similar conditions.The main observed phenomena are: (i) reduced Cu+ sites are quickly re-oxidized by NO producing large amounts of N2O; (ii) adsorbed NO slowly reacts with gaseous NO to give surface nitrates and still N2O in the gas phase regardless the copper oxidation state. A mechanism of copper re-oxidation and nitrates formation under the different conditions explored has been proposed on the basis of these findings.
Keywords: Cu-ZSM-5; NO adsorption; TPD; Copper; Redox chemistry; Nitrogen oxides;
The effect of potassium on Ni/Al2O3 catalyst in relation to CO/H2 reaction by Leszek Znak; Jerzy Zieliński (132-139).
Display Omitted► Potassium does not affect dispersion of nickel supported on alumina. ► Potassium hardly promotes CO dissociation on Ni/Al2O3 catalyst. ► Potassium strongly retards reduction of carbon preadsorbed on Ni/Al2O3 catalyst.The effect of potassium on nickel/alumina catalysts in relation to CO/H2 reaction was studied. The examinations were performed on the samples containing 90 wt.% of nickel and up to 6.0 mol% of potassium. XRD studies and adsorption measurements (H2, O2 and CO) showed a small effect of potassium on nickel dispersion; at the same time potassium enhanced heat of CO adsorption, which implies that the promoter locates on Ni surface. Temperature-programmed (TP) studies showed that potassium significantly retards the hydrogenation of pre-adsorbed CO and these results were confirmed by steady state tests of CO/H2 reaction. TP desorption of pre-adsorbed CO provided ambiguous view on the effect of potassium on CO dissociation. Instead, it was revealed that potassium strongly retards hydrogenation of carbon species adsorbed on nickel, which shed a new light on the effect of potassium on CO/H2 reaction.
Keywords: Nickel/alumina catalyst; Nickel dispersion; Effect of potassium; CO hydrogenation;
Benzene reduction in gasoline by alkylation with olefins: Comparison of Beta and MCM-22 catalysts by Georgina C. Laredo; J. Jesus Castillo; Juan Navarrete-Bolaños; Patricia Perez-Romo; Flavio A. Lagos (140-148).
.Display Omitted► Propylene alkylation of the benzene present in a real feed was successfully attained. ► MCM-22 presented a lower deactivation rate than Beta catalyst. ► MCM-22 presented higher yield and higher IPB selectivity than Beta catalyst. ► MCM-22 outstanding behavior may relay on its Brønsted and Lewis acid ratio. ► MCM-22 open crystalline framework may facilitate the diffusion process.The study compares the performance of Beta and MCM-22 zeolites as catalysts for propylene alkylation of benzene present in an enriched sample of reformate heart cut (20 wt% benzene). The experiments were carried out in a batch system with a 2/1 mole ratio of benzene/propylene at 220 °C for 1 h. An MCM-22 zeolite that contained Brønsted/Lewis acid sites in a 2–3/1 ratio proved to be much more resistant to deactivation during these real feed benzene alkylation experiments when compared with the Beta catalyst (Brønsted/Lewis acid site ratio of 0.1–0.3/1). MCM-22 with a 45 wt% benzene conversion presented higher i-propylbenzene selectivity than Beta (38 wt% benzene conversion) by reducing the formation of by-products. The outstanding behavior of MCM-22 may be explained by its particular Brønsted to Lewis acid ratio, which could help in the carbonium-ion formation and in the activation of the benzene ring toward electrophilic attack, and to its open crystalline framework that facilitates diffusion of reactants, products and coke precursors. Additional studies regarding experimental conditions for the preparation of MCM-22 and alkylation procedures are required for optimization.
Keywords: Gasoline; Benzene; Alkylation; Propylene; IPB; Zeolite Beta; Zeolite MCM-22;
Catalytic fluorination of 2-chloropyridine over metal oxide catalysts in gas phase in the presence of HF by Cindy Cochon; Thibaut Corre; Stéphane Celerier; Sylvette Brunet (149-156).
Display Omitted► Heterogeneous catalytic process with HF gas used to prepare 2-fluoropyridine. ► Initial basic oxides used as precursors of catalysts for a Cl/F exchange reaction to form 2-chloropyridine. ► Activation by HF gas of basic oxide leading to the formation of fluorides or oxyfluorides with a moderate Lewis acidity. ► Fluorination of 2-chloropyridine involving unsatured metals as active sites with a moderate Lewis acidity.The fluorination of 2-chloropyridine to produce selectively 2-fluoropyrydine by Cl/F exchange at 300 or 380 °C with HF as the fluorinating agent and a metal oxide as precursor of catalyst was investigated. The influence of the activation step under HF gas on the structural, microstructural and physico-chemical properties of various oxides such as MgO, CeO2, Ce0.5Zr0.5O2, LaFeO3, Cr2O3, were studied. This activation step by HF led to the formation of the corresponding fluorides and/or oxyfluorides materials which were the active catalysts for the Cl/F exchanges. Moreover, this activation step modified strongly the initial properties of the starting materials. This corresponded to a strong decrease of the initial specific surface area and of the basic properties. In the same time, an increase of Lewis acid properties measured by FTIR with pyridine as probe molecule was noticed. MgO, which was initially the most basic oxide studied was also the most active for the fluorination of the 2-chloropyridine after its transformation into fluoride solid which was the active catalyst. This could be due to a lower strength Lewis acidity of the active sites formed by the activation step by HF directly correlated to the basic properties of the initial oxides. A mechanism of the 2-chloropyridine fluorination involving Lewis acid unsaturated metal site was proposed.
Keywords: Basic metal oxides; Fluoride metal catalyst; Fluorination; 2-Chloropyridine; 2-Fluoropyridine;
Highly active and selective C-alkylation of p-cresol with cyclohexanol using p-TSA treated clays under solvent free microwave irradiation by S. Ramesh; B.S. Jai Prakash; Y.S. Bhat (157-162).
Display Omitted► p-Toluene sulphonic acid and a mineral acid hydrochloric acid to activate clay under MW. ► Mild acid treatment can generate materials of different surface characteristics. ► The efficiency of p-TSA treated clays was probed in the alkylation under solvent free MW. ► Alkylation of p-cresol yielded 89% conversion with 98% selectivity towards C-alkylation.The efficiency of p-TSA treated clays was probed in the alkylation of p-cresol under solvent free microwave irradiation. The different aspects of the reaction studies include variation of temperature, duration of contact between the reactants, mole ratio of cresol to cyclohexanol and the clay treated with p-TSA to different extent. The acid strength as well as reaction parameters such as temperature and time were found to be the main factors controlling the reactivity and selectivity. The reaction was carried out in the temperature range 413–443 K. Lower temperature range favoured O-alkylation and higher temperatures yielded C-alkylated p-cresol. The catalyst retained its catalytic activity even after three consecutive runs. The results obtained with clays were compared with other solid acid catalysts such as aluminium exchanged clay, hydrochloric acid treated clay and K-10.
Keywords: p-TSA treated clay; Solid acid catalyst; Microwave irradiation; Solvent free alkylation;
Studies on stability and coking resistance of Ni/BaTiO3–Al2O3 catalysts for lower temperature dry reforming of methane (LTDRM) by Xiancai Li; Quanhong Hu; Yifeng Yang; Yan Wang; Fei He (163-169).
Display Omitted► The dispersion of BaTiO3 on γ-Al2O3 enlarges the specific surface area of BaTiO3. ► The strong electronic donor intensity of Ni/BaTiO3 catalyst results in heavy coking. ► The ideal electronic donor intensity of the synthesized catalyst was proved by XPS.Wt.%BaTiO3–Al2O3 (wt.%BaTiO3 = 0–100%) composite supports were synthesized through varying the BaTiO3 content by the “sol–(xero)gel” method. Ni/wt.%BaTiO3–Al2O3 nickel-based catalysts prepared by incipient wetness method were evaluated for dry reforming of methane carried out between 690 °C and 800 °C. Characterizations using XRD, IR, N2 adsorption–desorption, H2-TPR, SEM, and XPS were conducted to investigate the structure or properties of the wt.%BaTiO3–Al2O3 composite supports as well as the Ni/wt.%BaTiO3–Al2O3 catalysts. The results demonstrate that BaTiO3 particles are discontinuously dispersed on the surface of γ-Al2O3 in the form of individual isolated particles for the wt.%BaTiO3–Al2O3 composite supports. Meanwhile, it is probably that the coexistence of BaAl2O4 spinel phase with the BaTiO3 phase on the surface of γ-Al2O3 inhibits the Ni/wt.%BaTiO3–Al2O3 catalysts from the formation of NiAl2O4 spinel phase, improving the catalytic performance of the catalysts. The Ni/BaTiO3 catalyst showed poor stability and severe coke formation in the dry reforming of methane tested at 690 °C, which was thought to be mainly originated from the excessive strong electronic donor intensity of Ni/BaTiO3 catalyst as well as the resulted CO disproportionation reaction. Compared with the Ni/BaTiO3 catalyst, the Ni/wt.%BaTiO3–Al2O3 catalysts with the addition of BaTiO3 had a higher dispersion of active nickel and a weakened electronic donor intensity of the NiO x species. As a result, the synthesized Ni/32.4%BaTiO3–Al2O3 catalyst exhibited a high catalytic activity, excellent stability as well as coking resistance for lower temperature dry reforming of methane.
Keywords: Ni/BaTiO3–Al2O3 catalyst; Dry reforming of methane; Barium titanate; Nickel; Coking resistance;
Facile synthesis of silver-deposited silanized magnetite nanoparticles and their application for catalytic reduction of nitrophenols by Kuan Soo Shin; Young Kwan Cho; Jeong-Yong Choi; Kwan Kim (170-175).
Display Omitted► Silica was coated on Fe3O4 particles to avoid the aggregation of the particles. ► Ag was deposited by soaking the particles in the solutions of AgNO3 and butylamine. ► Fe3O4/SiO2@Ag particles were effective for the catalytic reduction of nitrophenols. ► Fe3O4/SiO2@Ag particles, separated using a neodium magnet, could be recycled.We have demonstrated a facile fabrication of silver-deposited silanized magnetite (Fe3O4/SiO2@Ag) beads, along with their catalytic performance in the reduction of nitrophenols. Initially, 283 ± 40 nm sized spherical magnetite (Fe3O4) particles composed of ∼13 nm superparamagnetic nanoparticles were synthesized, and then they were silanized following the modified Stöber method. Silica-coated magnetic (Fe3O4/SiO2) nanoparticles are then resistant to oxidation and coagulation. In order to deposit silver onto them, Fe3O4/SiO2 nanoparticles were dispersed in a reaction mixture consisting of ethanolic AgNO3 and butylamine. With this simple and surfactant-free fabrication method, we can avoid any contamination that might make the Fe3O4/SiO2@Ag particles unsuitable for catalytic applications. The as-prepared Fe3O4/SiO2@Ag particles were accordingly used as solid phase catalysts for the reduction of 4-nitrophenol (4-NP) in the presence of sodium borohydride. The reduction of other nitrophenols such as 2-nitrophenol (2-NP) and 3-nitrophenol (3-NP) were also tested using the Fe3O4/SiO2@Ag nanoparticles as catalysts, and their rate of reduction has been found to follow the sequence, 4-NP>2-NP>3-NP. The Fe3O4/SiO2@Ag particles could be separated from the product using an external magnet and be recycled a number of times after the quantitative reduction of nitrophenols.
Keywords: Fe3O4 particle; Silanization; Silver deposition; Catalytic reduction; Nitrophenol;
Study of the interaction between hydrogen and the MoO3–ZrO2 catalyst by Nurun Najwa Ruslan; Sugeng Triwahyono; Aishah Abdul Jalil; Sharifah Najiha Timmiati; Nur Hazirah Rozali Annuar (176-182).
Display Omitted► H2-adsorbed IR results confirmed the formation of hydrogen-bonded OH groups. ► Decrease in the ESR signals indicated the formation of electrons from H2. ► Protons and electrons from H2 participated in the isomerization of n-heptane. ► H2 adsorption involves 2 successive steps: H2 dissociation and H surface diffusion. ► The rate-controlling step was the surface diffusion of H with the Ea = 62.8 kJ/mol.The interaction of molecular hydrogen with the surface of MoO3–ZrO2 was observed using infrared IR and electron spin resonance (ESR) spectroscopy, and the hydrogen adsorption was quantitatively evaluated in the temperature range of 323–573 K. The hydrogen adsorbed IR results confirmed the formation of a new broad band in the range of 3700–3400 cm−1, which corresponds to hydrogen-bonded OH groups. A decrease in the ESR signals indicated the formation of electrons that have been trapped by the electron-deficient metal cations and/or oxygen radicals. The hydrogen adsorbed IR and ESR results suggested that the protons and electrons were formed on the surface of MoO3–ZrO2 from molecular hydrogen enhancing the isomerization of n-heptane. A quantitative study of the hydrogen adsorption showed that the rate of hydrogen uptake was high for the first few minutes at 473 K and above, and the rate reached an equilibrium value within 10 h. At 423 K, different features of the hydrogen adsorption were observed on MoO3–ZrO2, where the hydrogen uptake increased slowly with time and did not reach equilibrium after 10 h. The rate of hydrogen adsorption increased slightly at 373 K and below. Hydrogen adsorption on MoO3–ZrO2 involves two successive steps. The first step involves hydrogen dissociation on a specific site on the MoO3–ZrO2 catalyst to form hydrogen atoms, and the second step involves the surface diffusion of the hydrogen atoms on the MoO3–ZrO2 surface. Then the hydrogen atom becomes a proton by donating an electron to an adjacent Lewis acid site. The rate-controlling step involves the surface diffusion of hydrogen atoms and has an activation energy of 62.8 kJ/mol. A comparison of the hydrogen adsorption on SO4 2−–ZrO2, WO3–ZrO2 and MoO3–ZrO2 catalysts is discussed.
Keywords: MoO3–ZrO2; Proton; Electron; Surface diffusion; n-Heptane isomerization;
The effect of ZSM-5 zeolite acidity on the catalytic degradation of high-density polyethylene using simultaneous DSC/TG analysis by A. Coelho; L. Costa; M.M. Marques; I.M. Fonseca; M.A.N.D.A. Lemos; F. Lemos (183-191).
Display Omitted► Acidity of the zeolite influences the degradation temperature. ► Increase in acidity implies a decrease in the computed activation energy. ► Catalytic degradation is related to internal acid strength.In the present work, simultaneous thermogravimetric (TG) and differential scanning calorimetric (DSC) analyses were used to investigate the effect of the acidity of HZSM-5 zeolites on the catalytic degradation of high-density polyethylene (HDPE). The acidity of the zeolite was modified by ion exchange with sodium. The results obtained using HZSM-5 zeolites of varying acid strengths show the effect of increasing the acidity on the reduction of the degradation temperature. The addition of sodium to HZSM-5, by ion exchange, results in a decrease of the acid strength of the catalyst and an increase in the observed degradation temperature from 402 to 465 °C.The simultaneous use of the signals from the TG and DSC allowed the development of a kinetic model that is able to accurately describe all the runs performed, both the thermal and the catalytic degradation of the polymer. The kinetic parameters obtained clearly revealed the reduction in the activation energy due to the presence of the catalyst and its relation to the overall acidity of the samples. The gases evolved from the pyrolysis of polyethylene were also analysed using gas chromatography, and it was also found that volatile product selectivity changes with the catalyst acidity.The fact that the overall activity for the catalytic cracking of HDPE on these zeolites varies with internal acid strength of the zeolite indicates that the inner surface of these zeolites participates in this reaction despite the fact that the reactant molecules are extremely large.
Keywords: High-density polyethylene (HDPE); ZSM-5 zeolite; Kinetic modelling; Acid catalysis; Catalytic degradation; Differential scanning calorimetry (DSC); Thermogravimetry (TG);
Alkylation of 3-methylthiophene by 2-methyl-1-pentene over HY, HBEA and HMCM-22 acidic zeolites by Benoit Dupuy; Sébastien Laforge; Cláudia Morais; Christian Bachmann; Patrick Magnoux; Frédéric Richard (192-204).
Display Omitted► HBEA the most stable in alkylation of 3-methylthiophene with 2-methyl-1-pentene. ► HMCM-22 the most selective in alkylation compared to olefin dimerization. ► Alkylation by an Eley–Rideal mechanism. ► Stabilities of the intermediate carbocations. ► Inhibiting effect of toluene.The alkylation of 3-methylthiophene with 2-methyl-1-pentene was investigated over acidic zeolites at 85 °C under atmospheric pressure in a fixed bed reactor. Three zeolites were tested, HY, HBEA and HMCM-22, which presented different pore systems but the same Brønsted acidity. Over these zeolites, 3-methylthiophene was only transformed by alkylation whereas 2-methyl-1-pentene underwent isomerization, alkylation and dimerization. No effect of the zeolite pore architecture on the initial activity was noted, but differences in stability and selectivity were observed. Indeed, HBEA was the most stable whereas HMCM-22 was the most selective in alkylation compared to olefin dimerization. The addition of toluene led to a decrease of the initial activity and the stability for all zeolites, due to competitive adsorption and coke formation. An Eley–Rideal mechanism was proposed for the alkylation reaction, where the thiophenic molecule reacts with the protonated olefin. The product distribution obtained experimentally was explained on the basis of the calculated B3LYP/cc-pVDZ stabilities of the intermediate carbocations involved in the steps proposed as rate determining.
Keywords: Zeolites; HY; HBEA; HMCM-22; 3-Methylthiophene; 2-Methyl-1-pentene; Alkylation;
Imidazolium chloride immobilized SBA-15 as a heterogenized organocatalyst for solvent free Knoevenagel condensation using microwave by Mst. Nargis Parvin; Hua Jin; Mohd. Bismillah Ansari; Soon-Moon Oh; Sang-Eon Park (205-212).
.Display Omitted► Microwave mediated morphosynthesis of ILS SBA-15. ► The ILS SBA-15 short channel, platelet morphology and high pore size distribution. ► Microwave mediated Knoevenagel condensation reaction was carried within 6 min. ► The reaction proceeded under solvent free conditions.Heterogeneous organocatalyst, 1-methyl-3-[(3-triethoxysilyl) propyl] imidazolium chloride [MTESPImCl] immobilized SBA-15 (ILS) was synthesized by co-condensation method using microwave irradiation in which 1-methylimidazole (Im) was modified by organosilane (3-chloropropyl triethoxysilane). The ILS was thoroughly characterized by small angel XRD, N2 adsorption desorption isotherms, TEM, SEM, TGA and FT-IR. The ILS showed 2D hexagonal short channeled disk type mesostructure which can provide facile to-and-from diffusion of substrates and products with enhanced activity. This heterogenized organocatalyst ILS had been investigated for the Knoevenagel condensation reaction of different aromatic and heteroaromatic aldehyde with ethyl cyanoacetate in solvent free conditions. The catalyst ILS was found to be efficient to catalyze the condensation effectively leading the completion of the reaction within 6 min using single mode microwave irradiation.
Keywords: Ionic liquid; 1-Methyl-3-[(3-triethoxysilyl) propyl] imidazolium chloride; Mesoporous SBA-15; Heterogeneous organocatalyst; Green method;
Mesoporous nitrogen doped nano titania—A green photocatalyst for the effective reductive cleavage of azoxybenzenes to amines or 2-phenyl indazoles in methanol by K. Selvam; S. Balachandran; R. Velmurugan; M. Swaminathan (213-222).
Display Omitted► High surface area N-doped TiO2 was synthesized by a simple wet impregnation method. ► N-TiO2 is used for cleavage of azoxybenzenes into amines or 2-phenylindazoles. ► In both conversions, mesoporous N-TiO2 is more effective than prepared TiO2. ► Our reaction conditions provide selective conversion of anilines. ► Easy product isolation and catalyst reusability make this reaction eco-friendly.A new nitrogen precursor, hydrazine hydrate was used in the synthesis of nano-sized, N-doped TiO2 photocatalyst by a simple wet impregnation method. This photocatalyst was characterized by X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), High resolution transmission electron microscope (HR-TEM), UV–vis diffuses reflectance spectra (DRS), photoluminescence (PL) and X-ray photoelectron spectroscopy (XPS). XRD patterns show that the crystal structure of N-TiO2 resembles anatase phase of TiO2. The UV–vis spectra indicate an increase in absorption of visible light when compared to TiO2. Furthermore XPS analysis reveals the presence of the N atom as O–Ti–N linkage substituting the O atom in the TiO2 lattice and this causes a decrease in oxygen vacancies. N-TiO2 nanoparticles were used as a green and recyclable heterogeneous photocatalyst for rapid and efficient reductive cleavage of azoxybenzene into their corresponding amines or 2-phenylindazoles with methanol at room temperature under N2 atmosphere. Azoxybenzenes in neat methanol afforded anilines, while in aqueous methanol (20% water–80% methanol) they formed corresponding 2-phenyl indazoles. In both reductive cleavages, nano N-TiO2 is more effective than prepared TiO2, showing that the nitrogen doping could be an excellent choice to improve the photoactivity of TiO2.
Keywords: Azoxybenzene; Aniline; 2-Phenylindazole; Photocatalytic cyclization; N-TiO2; Reductive cleavage;
Promotion of Co/carbon sphere Fischer–Tropsch catalysts by residual K and Mn from carbon oxidation by KMnO4 by Mahluli Moyo; Myriam A.M. Motchelaho; Haifeng Xiong; Linda L. Jewell; Neil J. Coville (223-229).
Display Omitted► Carbon spheres (CSs) preparation by a direct chemical vapour deposition method. ► CSs functionalisation by KMnO4 and HNO3 functionalising agents. ► 5% Co/CS KMnO4 functionalised and 5% Co/CS HNO3 functionalised catalyst evaluation in FTS. ► Investigation of K and Mn promoter effects on 5% Co/CS HNO3 catalysts in FTS.The effect of functionalising agents (KMnO4 and HNO3) on the surface properties of carbon spheres (CSs) produced from acetylene gas by a chemical vapour deposition method, was examined. Cobalt was loaded onto the differently functionalised CSs using the deposition precipitation (DPU) method and the Co/CS catalysts were tested for Fischer–Tropsch (FT) activity. FT studies, revealed differences in activity and selectivity for the HNO3 and KMnO4 functionalised catalysts. Investigation of the role of Mn (0.05%) and K (0.05%) on Co/CS FT catalysts functionalised with HNO3 revealed that these differences were due to the presence of residual MnO4 − ions remaining after the surface functionalisation reaction.
Keywords: Fischer–Tropsch synthesis; Cobalt; Manganese; Carbon spheres; Potassium;
Polypyrrole nanotube-supported gold nanoparticles: An efficient electrocatalyst for oxygen reduction and catalytic reduction of 4-nitrophenol by Lihua Qiu; Yingjing Peng; Baoqiang Liu; Bencai Lin; Yu Peng; Muhammad J. Malik; Feng Yan (230-237).
Display Omitted► We fabricate polypyrrole nanotube/Au nanoparticle hybrids. ► We characterize the catalytic performances of resultant nanoparticle hybrids. ► The synthesized nanoparticle hybrids are effective for dioxygen electroreduction. ► The resultant nanoparticle hybrids are effective in the reduction of 4-nitrophenol.Polypyrrole nanotubes (PPyNTs)/Au nanoparticle hybrids were synthesized by using covalently attached imidazolium-type ionic liquids (ILs) as linkers. The approach involves the surface functionalization of PPyNTs with ILs, anion-exchange with Au precursor and followed by the reduction of metal ions to produce the Au nanoparticles. The surface functionalized ILs on the PPyNTs surface play an important role in the formation of Au/ILs/PPyNTs hybrids. The synthesized Au nanoparticles supported on the ILs/PPyNTs surface have a smaller particle size and better dispersion than those on pristine PPyNTs surface. The morphology and optical properties of the produced nanohybrids were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectrometer, X-ray diffraction (XRD) and UV–vis spectroscopy. The catalytic performances of Au/ILs/PPyNTs hybrids were evaluated for both the electrocatalytic oxygen reduction and catalytic reduction of 4-nitrophenol in the presence of NaBH4. The results revealed that the Au/ILs/PPyNTs hybrids are effective electrocatalysts for dioxygen reduction and for the reduction of 4-nitrophenol.
Keywords: Polypyrrole nanotubes; Ionic liquids; Gold nanoparticles; Oxygen reduction; 4-Nitrophenol;
Hydrothermal synthesis and photocatalytic performance of metal-ions doped TiO2 by Huajun Feng; Min-Hong Zhang; Liya E. Yu (238-244).
Display Omitted► We synthesized six metal-ions doped TiO2 photocatalysts by a hydrothermal method. ► Mn-TiO2 shows the best photocatalytic activity under both solar and visible light. ► Hydrothermal parameters of Mn-TiO2 are optimized. ► Particle surface area is critical to the photocatalytic property of doped TiO2. ► Crystal structure and visible-light response of doped TiO2 are secondary important.Metal-ions doped TiO2 (M-TiO2) were synthesized using a hydrothermal method with a post-annealing process, including individual Ag+, Cu2+, Mn2+, Ce3+, Fe3+ and Zr4+ ions. Physical properties of the synthesized M-TiO2 were characterized including XRD pattern, BET surface area, diffuse reflectance spectra and visible-light photoactivity tests. Total photocatalytic performances of M-TiO2 were evaluated by degrading rhodamine b under whole solar-light irradiation with manganese-ions doped TiO2 (Mn-TiO2) showing the highest degradation efficiency. Compared to crystalline structure and visible-light photoactivity, BET surface area of M-TiO2 particles exhibits the most significant impacts, showing a positive correlation with the total photocatalytic performance of M-TiO2. Total photocatalytic efficiencies of Mn-TiO2 were further optimized through synthesis with 3% of Mn doping concentration, 180 °C of hydrothermal treatment and 450 °C of post-annealing temperature.
Keywords: Metal-ions doped TiO2; Photocatalytic performance; Solar-light irradiation; Hydrothermal synthesis;
Liquid phase catalytic oxidation of benzyl alcohol to benzaldehyde over vanadium phosphate catalyst by Gobinda Chandra Behera; K.M. Parida (245-253).
Display Omitted► VO(H2PO4)2 as catalyst precursor. ► The adsorption of polar molecules on the catalyst surface is usually temporary. ► The present catalyst VO(PO3)2 has shown remarkable catalytic activity. ► The influence of reaction temperature on benzyl alcohol conversion is very strong.Vanadium phosphate (VPO) is well known as a heterogeneous catalyst in gas phase oxidation reactions. Till date, this material has not drawn much attention for its application in liquid phase reactions. This paper briefly highlights our recent research on vanadyl metaphosphate concerning its fabrication, characterization and application towards liquid phase oxidation of benzyl alcohol to benzaldehyde using tert-butyl hydroperoxide (TBHP) as the oxidant. In our preliminary catalytic studies, we find that the VO(PO3)2 exhibits extraordinarily high activity and selectivity in oxidation of benzyl alcohol under mild conditions. The benzyl alcohol conversion is largely increased but the selectivity for benzaldehyde is slightly decreased with the increase in reaction period or temperature. The present catalyst VO(PO3)2 showed remarkable catalytic activity with respect to other catalytic system; conversion and selectivity with respect to aldehyde is 97 and 99%, respectively.
Keywords: Vanadium phosphate; Benzyl alcohol; Benzaldehyde; tert-Butyl hydroperoxide; Vandyl metaphosphate;
High silica REHY zeolite with low rare earth loading as high-performance catalyst for heavy oil conversion by Xionghou Gao; Zhengxing Qin; Baojie Wang; Xiaozheng Zhao; Jiangcheng Li; Hongjuan Zhao; Honghai Liu; Baojian Shen (254-260).
Display Omitted► The Si/Al ratio of zeolite determines the utilization efficiency of rare earth (RE). ► The higher the Si/Al ratio, the less selective the zeolite to RE. ► The higher the Si/Al ratio, the more difficult to remove residual sodium. ► High silica NaY derived REHY zeolite with low RE loading is stable and able.Study on the rare earth exchange performance was carried out with high silica, normal silica and low silica NaY zeolites with framework SiO2/Al2O3 ratios of 5.8, 4.8 and 4.6, respectively. It is found that the silicon content of the starting NaY zeolite is one of the significant factors in determining the ion exchange efficiency. The higher the framework SiO2/Al2O3 ratio is, the less selective to the rare earth ions the zeolite will be. However, the efficiency of the use of rare earth ions are comparable to each other when the concentration of rare earth in the ion exchange solution is less than 6 wt.%, no matter the level of the framework SiO2/Al2O3 ratio of the starting zeolites. Comparison of the hydrothermal stability of the rare earth and ammonium exchanged zeolites (REHY) indicates that the REHY sample prepared from the high silica NaY and with the lowest rare earth loading (2.9 wt.%) exhibits the best hydrothermal stability. The reaction studies indicate that the catalyst containing this REHY zeolite shows much better activity and product selectivity in the catalytic conversion of heavy oil than another REHY zeolite prepared from the normal silica NaY zeolite and having a rare earth loading as high as 6.6 wt.%, which is highly probably due to the superior hydrothermal stability of the former zeolite. It is suggested that the REHY zeolite with a low level of rare earth loading prepared from the high silica NaY can be considered as an alternative catalyst for the catalytic conversion of gas oil.
Keywords: Y zeolite; Rare earth ions; Ion exchange; Stability; Catalytic cracking;
Support effects of metal oxides on gold-catalyzed one-pot N-alkylation of amine with alcohol by Tamao Ishida; Rena Takamura; Takashi Takei; Tomoki Akita; Masatake Haruta (261-266).
Display Omitted► Supported gold nanoparticles catalyzed one-pot N-alkylation of aniline with alcohol. ► Gold on ZrO2 exhibited the best catalytic activity and the selectivity. ► Zirconia might assist alcohol dehydrogenation, aniline adsorption, and hydrogen transfer.Gold nanoparticles supported on metal oxides catalyzed the N-alkylation of aniline with benzyl alcohol to produce secondary amine under the equimolar amounts of substrates without additives under mild conditions. Selectivity to secondary amine was changed by the kinds of supports. Gold on ZrO2 exhibited the highest catalytic performance and achieved 94% selectivity to secondary amine. Surface hydroxyl groups of ZrO2 played important roles in the deprotonation of alcohol in the alcohol dehydrogenation step, as the adsorption sites of aniline, and as a proton source in the hydrogen transfer step.
Keywords: Gold nanoparticles; Supported gold catalyst; N-Alkylation; Dehydrogenation;
Coupling reactions of aromatic halides with palladium catalyst immobilized on poly(vinyl alcohol) nanofiber mats by Linjun Shao; Weixin Ji; Pengdu Dong; Minfeng Zeng; Chenze Qi; Xian-Man Zhang (267-272).
Display Omitted► Nanoporous poly(vinyl alcohol) (PVA) nanofiber mats were prepared by electrospinning. ► The prepared PVA nanofiber mats were used to immobilize palladium catalyst. ► The morphology of the PVA nanofiber mats was examined by SEM images. ► The palladium oxidation states were examined by XPS analysis. ► The catalytic activity and recyclability were examined for different coupling reactions.Nanoporous poly(vinyl alcohol) (PVA) nanofiber mats prepared by means of electrospinning have been used for the immobilization of palladium catalyst. Thermal treatment of the palladium-loaded PVA nanofiber mats results in the cross-linking of the matrix PVA molecules as well as the reduction of the divalent palladium (Pd2+) into zerovalent palladium (Pd0) species. The palladium oxidation states were examined by X-ray photoelectron spectroscopic (XPS) analysis. The PVA nanofiber morphology was characterized by scanning electron microscopy (SEM). The catalytic activity and recyclability of the prepared heterogeneous palladium catalysts have been evaluated for the Ullmann, Heck–Mizoroki and Sonogashira coupling reactions of aromatic halides. The large structure of the Pd/PVA nanofiber mats can greatly facilitate its separation and recycling, and the high catalytic activity and stability of the prepared Pd/PVA nanofiber mats have been attributed to the chelation of palladium species with the abundant hydroxyl functional groups on the PVA matrix surface area.
Keywords: Poly(vinyl alcohol) (PVA) fiber mats; Heterogeneous palladium catalyst; Ullmann homocoupling; Heck–Mizoroki and Sonogashira cross-couplings;
Biphasic hydroformylation of 1-octene catalyzed by cobalt complex of trisulfonated tris(biphenyl)phosphine by Aasif A. Dabbawala; Hari C. Bajaj; Hervé Bricout; Eric Monflier (273-279).
Display Omitted► Water-soluble ligand, BiphTS applied in Co catalyzed biphasic hydroformylation. ► Conversion and the aldehydes selectivity depended on the ligand/Co ratio. ► Employed various mass transfer promoters to enhance conversion and selectivity. ► The catalytic system can be easily recovered and recycled.The aqueous biphasic hydroformylation of 1-octene catalyzed by cobalt complex of the water-soluble ligand trisulfonated tris(biphenyl)phosphine (BiphTS) was investigated in the absence and presence of various mass transfer promoters (co-solvents, surfactants, cyclodextrins and activated carbon). In the presence of cetyltrimethylammonium bromide, methylated β-cyclodextrin or activated carbon, the Co/BiphTS system allowed the hydroformylation of 1-octene with high conversion (92–95%) and aldehydes selectivity (85–90%). Moreover, the catalytic system could be easily reused in the presence of activated carbon as a mass-transfer promoter. In all cases, the conversion and the aldehydes selectivity were found to depend strongly on the ligand/cobalt ratio.
Keywords: Aqueous biphasic catalysis; Hydroformylation; Higher olefin; Cobalt; Water-soluble phosphine; Activated carbon;
Influence of the Cr loading in Cr/MCM-41 and TiO2/Cr/MCM-41 molecular sieves for the photodegradation of Acid Orange 7 by Verónica Elías; Ema Sabre; Karim Sapag; Sandra Casuscelli; Griselda Eimer (280-291).
Display Omitted► MCM-41 materials were modified with different Cr loading and with Ti. ► High Cr loading results in the presence of inactive Cr3+ species. ► Cr6+ highly dispersed on MCM-41 is responsible for the azo-dyes photodegradation. ► A heterojunction effect between Cr6+ and Ti is observed for low Cr loading samples. ► The synergism between Cr6+ and Ti allows the (OH)• formation and the AO7 degradation.MCM-41 materials were modified with different Cr contents and then loaded with Ti by the wet impregnation method. The samples were characterized by XRD, XRF, N2 adsorption, UV–vis DR and TPR. Their photocatalytic activity was evaluated for the degradation of an Acid Orange 7 (AO7) aqueous solution irradiated by UV–vis and only visible light. The presence of Cr6+ species highly dispersed on the MCM-41 structure had a significant influence on the photoactivity. With respect to the samples only loaded with Cr, a theoretical loading of 3.5 wt.% allowed an AO7 degradation percentage of around 70%. Higher loadings result in the incremented presence of Cr3+ inactive species, as clusters or α-Cr2O3 nano-particles, producing no notable increase in the photoactivity. For its part, the presence of Ti in the samples with lower Cr loadings causes an increase in the AO7 degradation which could be associated to a heterojunction effect between active Cr6+ species and the titania. For the samples with higher Cr loadings, the lack of synergism could be due to the increased presence of inactive Cr3+ species that avoid this expected interaction.
Keywords: Heterogeneous photocatalysis; Azo-dyes; MCM-41; Cr-species;
Effects of preparation and structure of cerium-zirconium mixed oxides on diesel soot catalytic combustion by Claudinei F. Oliveira; Fillipe A.C. Garcia; Daniel R. Araújo; Julio L. Macedo; Sílvia C.L. Dias; José A. Dias (292-300).
Display Omitted► Preparation of nanostructured materials. ► Mixed oxides of cerium-zirconium have distorted structures from cubic ceria. ► Raman spectra confirmed cell contraction as a result of zirconium insertion. ► Ce0.8Zr0.2O2 was the most acidic and had the best performance for soot combustion. ► Ce0.8Zr0.2O2 can be reutilized, with no loss of activity and maintenance of structure.Mixed oxides of Ce x Zr1−x O2 (0.1 ≤ x ≤ 0.9) were prepared by sol–gel method, in aqueous ammonia solution with CeCl3·7H2O and ZrOCl2·8H2O as precursors, and employed in diesel soot combustion. The catalysts were characterized by XRF/EDX, nitrogen adsorption, TGA/DTG, powder XRD, FTIR/DRIFTS and Raman. In addition, the acidity was evaluated by adsorption and desorption of pyridine. XRD indicated the formation of solid solutions that progressively distorted from cubic into tetragonal lattices. Raman studies confirmed that the Ce–O bonding was stronger in the mixed oxide series because of the cell contraction, as a result of the zirconium insertion. Ce0.8Zr0.2O2 was the most acidic and active material, shifting the combustion temperature (T m) from 622 to 547 °C (loose contact) or 404 °C (tight contact). The calculated activation energy for the catalytic combustion of this optimized oxide attested that the combustion temperature was lower under all conditions, compared to the thermal process. The catalyst was utilized five times without any appreciable loss of activity and maintained its structural properties.
Keywords: Cerium-zirconium mixed oxide; Sol–gel method; Diesel soot combustion; Zirconia; Ceria;
Pillared montmorillonite supported ferric oxalate as heterogeneous photo-Fenton catalyst for degradation of amoxicillin by O.B. Ayodele; J.K. Lim; B.H. Hameed (301-309).
Display Omitted► Intercalation of Al and inclusion of Fe into acid treated montmorillonite clay. ► Formation of highly porous inorganic pillared and lipophilic organo-clay catalyst. ► The catalyst compete favorably well with the homogeneous processes in literature. ► High stability and reusability was observed for the developed catalyst.Degradation of amoxicillin (AMX) was achieved using pillared montmorillonite ferric oxalate (PMFeOx) catalyst in photo-Fenton process. The catalyst was prepared by aluminum pillaring of mild acid treated montmorillonite (MATM) clay followed by incorporation of ferric oxalate. The PMFeOx catalyst produced was characterized. XRD results revealed the intercalation of aluminum with an increase in basal spacing from 1.24 to ∼1.69 nm, the specific surface area also increased from 164.94 to 211.61 m2 g−1. SEM images of PMFeOx showed the formation of irregular flaky morphology with random orientation. The FTIR profile at relevant wavenumbers detected intercalation of aluminum and incorporation of iron. The optimum condition that achieved 99.65% and 84.26% initial concentration reduction and COD removal respectively, for 40 ppm AMX solution was 15% excess H2O2 and 2.0 g PMFeOx catalyst loading at 40 °C in 10 min. The catalyst displayed good efficiency in degrading amoxicillin.
Keywords: Pillared montmorillonite; Ferric oxalate; Amoxicillin; Mineralization; Heterogeneous catalyst;
Crucial factors for catalyst aggregation and deactivation on Co/Al2O3 in a slurry-phase Fischer–Tropsch synthesis by Seon-Ju Park; Jong Wook Bae; Gyu-In Jung; Kyoung-Su Ha; Ki-Won Jun; Yun-Jo Lee; Hae-Gu Park (310-321).
Display Omitted► The catalyst deactivation by forming the aggregated FTS catalyst lumps were investigated in a slurry-phase reaction. ► It is related with the amount of adsorbed water and the deposited hydrocarbons. ► The phase transformation of γ-Al2O3 to pseudo-boehmite accelerates the aggregation.The different behaviors for catalyst deactivation by forming aggregated catalyst lumps were investigated on the phosphorous-modified Co/P–Al2O3 and the unmodified Co/Al2O3 Fischer–Tropsch synthesis (FTS) catalysts in a slurry-phase continuous stirred tank reactor. The lower catalytic activity at steady-state with a fast deactivation rate was observed on the phosphorous-unmodified Co/Al2O3 catalyst due to the facile formation of aggregated catalyst lump with a high hydrophilic property of support and a significant hydrocarbon deposition on catalyst surface. The amount of adsorbed water and the deposited hydrocarbons are strongly related with aggregated catalyst lump formation. The adsorbed water could possibly transform the local γ-Al2O3 surface to pseudo-boehmite (Bronsted acidic Al2OH sites) material which is characterized as a low attrition resistance and accelerates the formation of fine powders during FTS reaction. The formed fine powder during FTS reaction could be easily aggregated and it is resulted in catalyst deactivation due to the difficult intraparticular diffusion of reactants. The possible mechanisms of phase transformation of γ-Al2O3 to pseudo-boehmite and formation of aggregated catalyst lump were suggested by measuring the deposited hydrocarbons and the concentration of adsorbed water on catalyst surface with the help of the characterizations such as X-ray photoelectron spectroscopy, temperature-programmed surface reaction, diffuse reflectance infrared Fourier transform and water-sorption method.
Keywords: Fischer–Tropsch synthesis; Deactivation; Aggregation; Hydrophilicity; Cobalt; Phosphorous-modification; Alumina;
Monoglyceride synthesis by glycerolysis of methyl oleate on MgO: Catalytic and DFT study of the active site by C.A. Ferretti; S. Fuente; R. Ferullo; N. Castellani; C.R. Apesteguía; J.I. Di Cosimo (322-331).
Display Omitted► MgO basicity can be tuned by changing the calcination temperature. ► MgO strong base site density decreases with increasing calcination temperature. ► Methyl oleate (FAME) glycerolysis is promoted on strong base sites. ► DFT calculations corroborate that glycerol O–H bond breaking occurs on strong base sites. ► DFT calculations show FAME adsorption on MgO is much weaker than that of glycerol.The synthesis of monoglycerides by glycerolysis of methyl oleate, a fatty acid methyl ester (FAME), was efficiently promoted on strongly basic MgO. The chemical nature of the base sites responsible for the catalytic activity was investigated, both experimentally and by density functional theory (DFT). MgO catalysts stabilized at different temperatures were used to control the distribution of surface base sites. The nature, density and strength of the catalyst base sites were characterized by TPD and FTIR of CO2. Catalytic results suggested that the synthesis of monoglycerides was promoted mainly on strongly basic low coordination O2− surface sites.The molecular modeling of glycerol (Gly) and FAME adsorptions was carried out using terrace, edge and corner sites for representing the MgO surface. Results indicated that Gly was more strongly adsorbed than FAME. Dissociative chemisorption of Gly with O–H bond breaking was favored on low coordination O2− surface sites such as those on edges, in agreement with the experimental results. Thus, the proton abstraction from the OH groups of Gly, a necessary step in the reaction mechanism, would take place on unsaturated oxygen anions and the resulting glyceroxides would react with weakly adsorbed FAME molecules.
Keywords: Glycerol; Monoglyceride; DFT; Base catalysis; Glycerolysis; Fatty acid methyl ester;
Room temperature aerobic oxidation of alcohols using CuBr2 with TEMPO and a tetradentate polymer based pyridyl-imine ligand by Zhenzhong Hu; Francesca M. Kerton (332-339).
Display Omitted► Polydimethylsiloxane-bis(pyridylimine) forms active catalyst for alcohol oxidation. ► PDMS-derived ligand is soluble in supercritical carbon dioxide. ► Good yields of aldehyde/ketone from challenging substrates (1-alkanols and 1-phenylethanol). ► Dicopper complexes were identified in catalytic reaction through mass spectrometry. ► Tetradentate ligands afford higher TOF and TON catalysts than bidentate versions.A series of tetradentate pyridyl-imine terminated Schiff-base ligands has been investigated for their ability in the catalytic oxidation of alcohols when combined with copper bromide (CuBr2) and 2,2,6,6-tetramethylpiperidyl-1-oxy (TEMPO). Analogous bidentate ligands showed poorer catalytic activity and the ratio of Cu:ligand was of crucial importance in maintaining high yields. The polydimethylsiloxane (PDMS) derived pyridyl-imine terminated ligand combined with copper(II) ions affords an effective and selective catalyst for aerobic oxidations of primary and secondary alcohols under aqueous conditions. Preliminary mechanistic studies suggest that bimetallic complexes may be playing a role in the catalytic transformation.
Keywords: Aerobic oxidation; Polydimethylsiloxane (PDMS); Tetradentate; 2,2,6,6-Tetramethylpiperidyl-1-oxy (TEMPO); Copper; Green chemistry;
Selective ring opening of methylcyclopentane over Pt/γ-Al2O3, Ir/γ-Al2O3 and Pt-Ir/γ-Al2O3 catalysts with hydrogen at atmospheric pressure by Amel Djeddi; Ioana Fechete; François Garin (340-349).
Display Omitted► The most active catalyst in the conversion of MCP was Ir/γ-Al2O3. ► Ir/γ-Al2O3 showed the ability to open MCP with an atom economy of 100 at 180 °C. ► On Ir/γ-Al2O3 opening occurred at the secondary–secondary positions. ► Pt/γ-Al2O3 and Pt-Ir/γ-Al2O3 opened MCP at 220 °C in the secondary–tertiary positions.Pt/γ-Al2O3, Ir/γ-Al2O3 and Pt-Ir/γ-Al2O3 were prepared by incipient wetness impregnation and co-impregnation methods. The catalysts were characterised by the classical physico-chemical techniques of SEM, TEM, XRD, N2-sorption, H2-TPR and elemental analysis. The metallic particles were highly dispersed on the support, assuming the presence of an icosahedral Mackay structure, which is a limited only by (1 1 1) face. The performances of the catalysts were investigated in the conversion of methylcyclopentane (MCP) with hydrogen at atmospheric pressure at temperatures between 180 and 400 °C. At low temperature, only Ir/γ-Al2O3 showed the ability to open MCP with an atom economy (S RO = 100%) and without by-products from cracking and ring enlargement reactions. Ir/γ-Al2O3 opened the MCP ring at the secondary–secondary positions. The Pt/γ-Al2O3 and Pt-Ir/γ-Al2O3 catalysts opened MCP starting at 220 °C, in the secondary–tertiary positions, with atom economy (S RO = 100%). The synergistic effect between Ir and Pt was observed in our conditions, but the Pt and Ir particles existed also as individual entities on the support. At high temperature, all the catalysts were inactive in MCP ring opening. Cracking reactions became more pronounced with increasing temperature and parallel decreases in ring opening selectivities. The formation of benzene was observed at high temperatures only on Pt/γ-Al2O3.
Keywords: Ring opening; Monometallic catalysts; Bimetallic catalysts; Atom economy; Icosahedral structure;
Nickel nanoparticles embedded in the framework of mesoporous TiO2: Efficient and highly stable catalysts for hydrodechlorination of chlorobenzene by Ye Xu; Jinqiang Ma; Yuanfeng Xu; Hui Li; Hexing Li; Ping Li; Xinggui Zhou (350-357).
Display Omitted► Here a novel nickel nanoparticles embedded within the framework of mesoporous TiO2 were prepared. ► An optimum Ni loading is detected. ► These catalysts exhibited much higher activity and stability than the conventionally prepared reference catalyst. ► These performances were related to the electronic structure of Ni and the strong Ni–support interaction.Mesoporous TiO2-supported metallic Ni catalysts were prepared through a multicomponent assembly approach, where surfactant, titania, and nickel precursor were cooperatively assembled in a one-pot process. With the characterization of transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, N2 physisorption, hydrogen temperature-programmed reduction, and hydrogen temperature-programmed desorption, the resultant Ni nanoparticles were identified to be homogenously embedded within the framework of TiO2 ranging in size from 1 to 6 nm. The embedment of Ni within the framework of support resulted in larger interface between Ni and support and thus stronger Ni–TiO2 interaction. During the gas-phase hydrodechlorination of chlorobenzene reaction, the as-prepared 0.23%-Ni/TiO2-DS delivered turnover frequency up to 1.5 times greater than that associated with the reference Ni/TiO2 catalyst prepared by conventional incipient-wetness impregnation method. Meanwhile, the as-prepared 0.23%-Ni/TiO2-DS also exhibited much improved stability for a continuous reaction of 30 h than the reference catalyst. The remarkable enhancement of the catalytic performances was found to depend on the strong metal–support interaction.
Keywords: Nickel; Mesoporous titania; Embedment; Hydrodechlorination; Chlorobenzene; Metal–support interaction;
Liquid phase selective hydrogenation of cinnamaldehyde over copper supported catalysts by Victoria Gutierrez; Mariana Alvarez; María A. Volpe (358-365).
Display Omitted► In this study a series of Cu catalysts are evaluated for the selective hydrogenation of cinnamaldehyde. ► Cu1+ species are stabilized on MCM-48, turning Cu/MCM-48 a selective catalysts. ► Hydrogen transfer from isopropanol is achieved under certain experimental conditions. ► Some copper catalysts are more selective than noble based ones.The selective hydrogenation of cinnamaldehyde is carried out in a batch reactor, at 100 °C and 1 MPa of H2 using isopropyl alcohol as the solvent, over a series of copper supported catalysts: Cu/Al2O3, Cu/SiO2 Cu/MCM-48, Cu/CeO2 and Cu/α-Fe2O3. The selectivity of the samples is compared with that corresponding to Pti/SiO2. Reduced Cu/Al2O3 and Cu/SiO2 showed lower selectivity to the cinnamyl alcohol (16–22%) than Pt/SiO2 (35%), at 15% of conversion. Following a calcination at 300 °C both, activity and selectivity of copper catalysts were increased. The calcined surface would hydrogenate C＝O bond by hydrogen transfer from the solvent. TPR, XRD and FTIR of adsorbed CO showed that Cu (I) species are stabilized on the mesoporous structure of MCM-48. This particular feature renders Cu/MCM-48 a selective catalyst, reaching high selectivity values (51%, at 15% of conversion). Cu/CeO2 and Cu/α-Fe2O3 showed higher selectivity than Pt based catalyst due to a promotion of the catalytic properties of copper by reduced support species.
Keywords: Supported copper; Selective hydrogenation; Conjugated carbonyl; Ceria; Copper oxide; α,β-Unsaturated aldehydes;
Kinetic analysis of the Ru/SiO2-catalyzed low temperature methane steam reforming by M.A. Soria; C. Mateos-Pedrero; P. Marín; S. Ordóñez; A. Guerrero-Ruiz; I. Rodríguez-Ramos (366-374).
Display Omitted► A mechanistic model is proposed for methane steam reforming on Ru/SiO2. ► The model considers that rate determining steps are the reaction between dissociatively adsorbed CH4 and H2O molecule. ► Data modeling has considered both mass-transfer effect and equilibrium limitations.The performance of a Ru/SiO2 catalyst for methane steam reforming at 450–550 °C is studied in the present. These conditions are suitable for coupling the fixed-bed reactor with a hydrogen-selective membrane for hydrogen recovery, with the subsequent equilibrium shift. A reaction mechanism based on the dissociative adsorption of steam and methane has been proposed (from a total of six possible mechanisms compared), in terms of the statistical analysis of reaction data obtained at different temperatures and contact times in an integral, lab-scale reactor.The proposed model shows that hydrogen inhibition plays an important role in the reaction. Finally, the Ru/SiO2 catalyst prepared in this work is found to be one of the most active catalysts, among other Ru-based catalysts reported in the literature.
Keywords: Hydrogen production; Steam reforming; Kinetic mechanism; Model discrimination;