Applied Catalysis A, General (v.377, #1-2)
Editorial Board (CO2).
Alkylation of isobutane/1-butene on methyl-modified Nafion/SBA-15 materials by Wei Shen; Yi Gu; Hualong Xu; David Dubé; Serge Kaliaguine (1-8).
Mesostructured SBA-15 was modified by OH capping and functionalized with Nafion resin. The resulting mesostructured materials (Nafion/Me-SBA-15) with strong acid sites and hydrophobic surface exhibited excellent activity and efficiency in the production of isooctane compared with Nafion/SBA-15 and commercial Nafion silica SAC-13. Capping of surface OH diminishes the surface silanol density and provides a hydrophobic environment for the isobutane/1-butene reaction.Hydrophobicity modification of the intrinsic polarity of the surface of SBA-15 mesoporous by ethoxytrimethylsilane was used in this work to make hybrid organic–inorganic mesoporous matrix. This matrix was functionalized with perfluorosulfonic acidic Nafion resin by a post-synthetic impregnation method. Characterized by N2-physisorption, XRD, and transmission electron micrographs (TEM), all the materials synthesized were highly ordered. Elemental analysis, 29Si MAS NMR, thermal gravimetric analysis (TGA), energy-dispersive X-ray (EDX) and potentiometric titration showed that trimethylsilane is grafted on the surface by capping the OHs and the Nafion resin was incorporated, revealing a strong solid acid with hydrophobic surface. The alkylation of isobutane/1-butene was thereafter evaluated on each material under specified conditions. Compared with the polar surface of conventional SBA-15 and commercial Nafion silica nanocomposite SAC-13, methyl-modified surface of SBA-15 material (denoted as Me-SBA-15) is a much better solid acid catalyst for isobutane/1-butene alkylation.
Keywords: Methyl modification; Silylation; Ethoxytrimethylsilane; Nafion; SBA-15; Alkylation of isobutane/1-butene;
Optimization of K–Ni/ α -Al2O3 catalyst for high-pressure oxidative reforming of methane by radial basis function network and multivariate analysis by Junpei Horiguchi; Seishiro Kobayashi; Yuichiro Yamazaki; Takayuki Nakanishi; Daisuke Itabashi; Kohji Omata; Muneyoshi Yamada (9-15).
In order to attain high activity of high-pressure oxidative reforming of methane, we optimized the preparation parameters of K–Ni/ α -Al2O3 catalyst. Parameters such as the calcination temperature of γ -Al2O3 and the amounts of NiO and K loading were designed by L9 orthogonal array; the catalysts were prepared by an impregnation method and activated by hydrogen reduction prior to the reaction. A radial basis function network (RBFN) was constructed using the experimental results of the L9 catalysts. The catalyst activity was expressed by the RBFN as functions of the catalyst preparation parameters. A grid search was conducted on the RBFN to find the optimum conditions of the catalyst preparation for the highest activity. The predicted catalysts were verified by experimental tests, and the best catalyst was determined to be 1.9 wt.%K–16.8 wt.%NiO on α -Al2O3 calcined at 1150 ° C. Temperature programed reduction (TPR) was conducted to characterize the NiO species contained in the L9 catalyst precursors. The amounts of NiO species were also expressed by RBFNs as functions of the catalyst preparation parameters. A part of the grid data was used for a multivariate analysis on the correlations between the activity and the amount of NiO species. The results suggested that the optimum catalyst precursor contains a large amount of NiO corresponding to the reforming activity.The calcination temperature of γ -Al2O3 and the amounts of NiO and K loading of K–Ni/ α -Al2O3 catalyst were designed by L9 orthogonal array. By use of the experimental results, radial basis function networks were constructed and a grid search was conducted to find the optimum conditions. A multivariate analysis suggested that CO yield could be expressed by a linear combination of the amounts of α -NiO and β -NiO in TPR, and that these are the main precursors for the reaction.
Keywords: Oxidative reforming of methane; TPR; Orthogonal array; Radial basis function network; Multivariate analysis;
Ni/CeO2-ZrO2 catalysts for the dry reforming of methane by A. Kambolis; H. Matralis; A. Trovarelli; Ch. Papadopoulou (16-26).
Ni/CeO2-ZrO2 catalysts (CeO2 molar content: 28–100%) were prepared, characterized and tested for the Dry Reforming of Methane (DRM). Compared to Ni/CeO2, the Ni/CeO2-ZrO2 catalysts exhibited much higher activity while the amount of carbonaceous deposits is related to the Ce/Zr ratio. This catalytic behaviour was accredited to the increase of the concentration of the active sites.Nickel catalysts supported on binary CeO2–ZrO2 carriers (28–100% CeO2 molar content) were prepared and evaluated regarding their catalytic performance for the CO2 reforming of CH4 (Dry Reforming of Methane, DRM). The textural and structural properties of catalysts and supports were studied in their calcined, reduced and used state by N2 adsorption–desorption, XRD, UV–vis DRS, TPR, SEM–EDS and TPH. Zirconium improves the textural properties of the CeO2–ZrO2 supports and the corresponding catalysts and enhances their textural stability under thermal reductive treatment. XRD analysis shows the formation of Ce x Zr1−x O2 solid solution for all Ce/(Ce + Zr) ratios. Considerable alterations in the electronic environment of the cations and increased lattice defects in the binary solid solutions were detected by UV–vis DR spectroscopy. A significant increase in the reducibility of both supports and catalysts is observed in the presence of Zr. Compared to the zirconia-free sample, the Ni/CeO2-ZrO2 catalysts exhibited much higher activity for the title reaction, accredited to the increase of the surface concentration of the active sites. However, the amount of carbonaceous deposits is not straightforward related to the activity but depends on the Ce/Zr ratio. Among the zirconium containing catalysts, the zirconium-rich one exhibited the higher activity and the stronger resistance to the formation of carbonaceous deposits.
Keywords: Dry reforming of methane; Ceria–zirconia binary oxides; Ni catalysts; BET; XRD; UV–vis DRS; TPH; SEM;
The effectiveness of ruthenium(II) complexes and ruthenium trichloride as pre-catalysts in solvent-free isomerization of model alkyl allyl ether by Magdalena Urbala (27-34).
The solvent-free isomerization of model alkyl allyl ether catalyzed by soluble ruthenium(II) complexes and ruthenium trichloride was investigated. The effectiveness of selected pre-catalysts (such as [RuClH(CO)(PPh3)3] [RuCl2(PPh3)3] and RuCl3) was examined in detail. The best results with high TOF (20,000/h) were obtained with [RuClH(CO)(PPh3)3] without any catalyst promoters.The isomerization of readily available allyl ethers catalyzed by soluble ruthenium complexes is an extremely versatile methodology for synthesis of O-1-propenyl systems—attractive monomers in cationic UV-radiation curing technology. From the process development perspective, the effectiveness of selected simple ruthenium catalyst precursors, mainly [RuClH(CO)(PPh3)3], [RuCl2(PPh3)3] and RuCl3·xH2O in the solvent-free isomerization of 1,4-bisallyloxybutane has been examined. The relationship between basic reaction parameters such as the reaction temperature, the amount of catalyst precursor, the promoters of non-hydride complexes (bases or alcohols), the ambient gas atmosphere and the reaction time allowing to achieve quantitative conversion of the model bisallyl ether to its 1-propenyl derivatives (τ 100%) has been presented. Particular attention has been paid to the use of lower loadings of [Ru] complex required for the completion of the reaction within the reasonable times. For the first time a detailed study on the effect of the presence and amount of allyl hydroperoxides on the course of isomerization has been done.
Keywords: Alkyl allyl ethers; Double-bond migration; Isomerization; 1-Propenyl ethers; Ruthenium complex;
Supported indium oxide as novel efficient catalysts for dehydrogenation of propane with carbon dioxide by Miao Chen; Jie Xu; Yong-Mei Liu; Yong Cao; He-Yong He; Ji-Hua Zhuang (35-41).
The dehydrogenation of propane over In2O3–MO x (M: Al, Zn, Zr, Ti, Fe, Mg, Si, and Ce) mixed metal oxide catalysts, which were prepared by a coprecipitation or sol–gel method, in the presence of CO2 was investigated. High activity and stability were achieved on the In2O3–Al2O3 catalyst with a 20 mol% indium content, giving a propylene yield of 27% without any observable trend of deactivation in 24 h.In2O3–MO x binary mixed metal oxide catalysts (M: Al, Zn, Zr, Ti, Fe, Mg, Si, and Ce) prepared by a coprecipitation or sol–gel method have been tested for the dehydrogenation of propane to propylene in the presence of carbon dioxide. Several techniques including N2 adsorption/desorption, X-ray diffraction, H2-temperature-programmed reduction and X-ray photoelectron spectroscopy were applied to characterize the physicochemical properties of the as-synthesized materials. Catalytic tests showed that all In-containing samples were active in the CO2-promoted dehydrogenation of propane with good propylene selectivity. Among the In2O3–MO x catalysts tested, the In2O3–Al2O3 sample containing a 20 mol% indium content showed the highest dehydrogenation activity with superior long-term stability. The specific interaction between In2O3 and Al2O3 leading to a high component dispersion is suggested to play a key role in regulating the redox and structural properties of surface indium species, which makes the In2O3–Al2O3 composite highly active and stable for the reaction.
Keywords: Indium oxide; Dehydrogenation; Propane; Propylene; Carbon dioxide;
Aerobic oxidation of glucose over gold nanoparticles deposited on cellulose by Tamao Ishida; Hiroto Watanabe; Takao Bebeko; Tomoki Akita; Masatake Haruta (42-46).
Small gold nanoparticles (Au NPs) (ca. 2 nm) could be deposited directly onto cellulose by the solid grinding method with volatile Me2Au(acac) followed by the reduction with H2. Gold NPs on cellulose exhibited high catalytic activity with a turnover frequency (TOF) of 11 s−1 for the aerobic oxidation of glucose to produce sodium gluconate at 60 °C and at pH 9.5.Gold nanoparticles (NPs) with mean diameters of around 2 nm could be deposited directly onto a bio-polymer, cellulose, by the solid grinding method with volatile dimethyl Au(III)acetylacetonate followed by the reduction with H2. Gold NPs on cellulose showed appreciably high catalytic activity with a turnover frequency (TOF) of 11 s−1 for the aerobic oxidation of glucose to produce sodium gluconate at 60 °C and at pH 9.5. The catalytic activity of Au/cellulose was comparable to that of Au/C provided the size of the Au particles was similar.
Keywords: Gold nanoparticles; Gold catalyst; Cellulose; Glucose oxidation; Gluconic acid;
Enhanced photocatalytic activity of indium and nitrogen co-doped TiO2–Pd nanocomposites for hydrogen generation by R. Sasikala; A.R. Shirole; V. Sudarsan; Jagannath; C. Sudakar; R. Naik; R. Rao; S.R. Bharadwaj (47-54).
Indium and nitrogen co-doped TiO2, indium- or nitrogen-doped TiO2 and undoped TiO2 were synthesized by polyol method. A clear red shift of the absorption edge and highest photocatalytic activity were observed for the co-doped TiO2. The enhanced activity of the co-doped TiO2 is attributed to the enhanced light absorption resulting from the narrowing of the band gap.Indium and nitrogen co-doped TiO2, indium- or nitrogen-doped TiO2 and undoped TiO2 were synthesized by polyol method and studied their photocatalytic activity for hydrogen generation from water. Crystalline nanoparticles of predominantly anatase phase of TiO2 were obtained by this method. A clear red shift of the absorption edge and stronger absorption in the visible region was observed for indium and nitrogen co-doped TiO2 compared to the other samples. The presence of bonded nitrogen in the N-doped samples was evidenced from their N 1s X-ray photoelectron spectra. Photocatalytic activity for hydrogen generation using sunlight type radiation showed enhanced activity for the doped samples compared to pristine TiO2. The photocatalytic activity of different samples decreased in the following order: N and In co-doped TiO2 > In-doped TiO2 > N-doped TiO2 > undoped TiO2. The enhanced photocatalytic activity of the In and N co-doped TiO2 for hydrogen generation is attributed to the enhanced light absorption resulting from the narrowing of the band gap caused by the contribution of 5s5p orbitals of In to the conduction band and 2p orbitals of N to the valence band of TiO2. A pronounced enhancement of photocatalytic activity was observed for all catalysts when Pd metal was present as co-catalyst due to the efficient separation of photogenerated charge carriers in this nanocomposite system.
Keywords: Nanoparticles; Photocatalysis; Polyol method; Co-catalyst; Palladium; Anatase TiO2; Water; Sacrificial reagent;
Dehydrogenation of ethylbenzene with CO2 to produce styrene over Fe-containing ceramic composites by Jesuina C.S. de Araujo; Charllys B.A. Sousa; Alcemira C. Oliveira; Francisco N.A. Freire; Alejandro P. Ayala; Alcineia C. Oliveira (55-63).
The preparation of ceramic composites, as well as the Fe3+ environments (Mössbauer spectra), exerts a significant influence on the catalytic activity for the dehydrogenation of ethylbenzene with CO2 to produce styrene. The high catalytic activity of Cr0.75Fe1.25O3 was a result of the optimal balance between Fe2+ and Fe3+, which are continuously oxidized by the CO2.The activity of Fe-containing ceramic composites for the dehydrogenation of ethylbenzene in the presence of CO2 was studied. Ceramic composites containing Fe, Cu, Cr, Pb and/or Ti were obtained by solid-state reaction method. The materials were characterized by XRD, textural properties, chemical analysis, SEM, Mössbauer spectroscopy, TPR, CO2-TPD analyses and electrical measurements. A low conversion was obtained using CaTiO3, due to the loss of the Ca species and coke production. The improvement of styrene selectivity with iron content, as well as the high stability of Cr0.75Fe1.25O3, resulted in a better activity when using this solid. Fe2+ is continuously reoxidized to Fe3+ by CO2 in the Fe–Ti active phase from the Fe0.5Cu0.75Ti0.75O3 sample. The latter catalyst exhibited high selectivity but limited stability towards styrene production. The ceramic composites appeared to be quite promising candidates for the dehydrogenation of ethylbenzene under CO2, in comparison with the conventional Fe–K doped catalysts, due to the highly stable Fe3+ in a ceramic matrix.
Keywords: Catalysts; Ethylbenzene; Ceramic composites; CO2;
Sulfonic acid supported on hydroxyapatite-encapsulated-γ-Fe2O3 nanocrystallites as a magnetically Brønsted acid for N-formylation of amines by Leila Ma’mani; Mehdi Sheykhan; Akbar Heydari; Mohammad Faraji; Yadollah Yamini (64-69).
Treatment of aqueous formic acid with structurally diverse amines in the presence of a catalytic amount of sulfonic acid supported on HAp-encapsulated-γ-Fe2O3 as a heterogeneous, reusable and highly efficient catalyst gave the corresponding formamides. The magnetically catalytic system was recovered by-passing time consuming filtration operation by using an external magnet device.Treatment of aqueous formic acid (85%) with structurally diverse amines in the presence of a catalytic amount of sulfonic acid supported on hydroxyapatite-encapsulated-γ-Fe2O3 [HAp@-γ-Fe2O3] (0.9 mol.%) as a heterogeneous, reusable and highly efficient catalyst gave the corresponding formamides in good to excellent yields at room temperature. The magnetically catalytic system was recovered by-passing time consuming filtration operation by using an external magnet device. In addition to facility, this methodology, it also enhances product purity and promises economic as well as environmental benefits.
Keywords: Magnetically catalytic system; Sulfonic acid; Hydroxyapatite-encapsulated-γ-Fe2O3; Formylation;
Screening of Supported Ionic Liquid Phase (SILP) catalysts for the very low temperature water–gas-shift reaction by Sebastian Werner; Normen Szesni; Agnes Bittermann; Martin J. Schneider; Peter Härter; Marco Haumann; Peter Wasserscheid (70-75).
Several homogeneous transition metal complexes were immobilized in the ionic liquid [BMMIM][OTf] on Silica 100 using the Supported Ionic Liquid Phase (SILP) technology and tested in the water–gas shift reaction (WGSR) in a continuously operated fixed-bed reactor at temperatures between 120 and 160 °C and ambient pressure. Best activities and stabilities were found for ruthenium-based systems.Screening of transition metal complexes typically involves elaborative experiments in batch reactors in organic solvents under non-steady-state conditions. In contrast, screening of immobilized catalysts in a fixed-bed continuous gas-phase reactor enables highly efficient and precise investigations on activity and stability under steady-state. In this work we present a technique to immobilize numerous homogeneous transition metal complexes (Ru, Ir, Os, Fe, Cu, Mo, Pd Re, Rh) in the ionic liquid [BMMIM][OTf] on the highly porous support Silica 100 using the Supported Ionic Liquid Phase (SILP) technology. All prepared SILP catalysts were investigated in the water–gas shift reaction (WGSR) in a continuously operated fixed-bed reactor at temperatures between 120 and 160 °C and ambient pressure. Best activities and stabilities were found for ruthenium-based systems.
Keywords: Water–gas-shift reaction; Homogeneous catalysis; Immobilization; Supported ionic liquid phase; Screening;
Comparison of the catalytic performance of the metal substituted cage type mesoporous silica catalysts in the alkylation of naphthalene by Robert Brzozowski; Ajayan Vinu; Barbara Gil (76-82).
Alkylation of naphthalene with propylene to diisopropylnaphthalenes (DIPN) for the use as a high-quality solvent was studied over mesoporous AlSBA-1, GaSBA-1 and FeSBA-1 catalysts. The AlSBA-1 and GaSBA-1 catalysts proved to be promising for this purpose due to their high alkylation activity and a low 2,6-DIPN selectivity.Alkylation of naphthalene with propylene to diisopropylnaphthalenes (DIPN) for the use as a high-quality solvent was carried out over mesoporous AlSBA-1, GaSBA-1 and FeSBA-1 catalysts. The AlSBA-1 and GaSBA-1 catalysts were very active in alkylation while the FeSBA-1 samples, although initially active, deactivated quickly. Activity of the SBA-1 catalysts increased with the amount of Al, Ga or Fe incorporation into the silica framework. Regardless of the alkylation activity, all SBA-1 catalysts showed rather low isomerization activity and as a result low 2,6-DIPN selectivity was observed. The AlSBA-1 and GaSBA-1 catalysts proved to be promising for DIPN solvent synthesis due to their high alkylation activity and stability together with low 2,6-DIPN selectivity.
Keywords: Alkylation; Naphthalene; Diisopropylnaphthalene; SBA-1 mesoporous material;
Aromatization of methane on Mo modified zeolites: Influence of the surface and structural properties of the carriers by A. Smiešková; P. Hudec; N. Kumar; T. Salmi; D.Yu. Murzin; V. Jorík (83-91).
Aromatization of methane on MoZSM-5 and MoMCM-22 catalyst having comparable Mo content and Si/Al was investigated. Deep bed treatment (MoZSM-5/1DB), low resistance towards coking (MoMCM-22) and a nanoscale particle size (MoZSM-5/2) are not advantageous for catalyst performance. Microscale MoZSM-5/1 shows significantly higher activity indicating an importance to optimize the external surface of ZSM-5 for minimizing the localization of Mo outside the channels.Mo/zeolite type catalysts based on ZSM-5 and MCM-22 type carriers having a comparable amount of Mo (4.67 wt%) were investigated in methane conversion. The effect of the different structure and surface properties of zeolite samples has been studied. XRD, FTIR, TPDA, SEM and model reaction measurement were applied for the catalysts characterization. It has been revealed that deep bed treatment (DBT) of ZSM-5 has a negative effect as regards the catalyst performance in methane conversion. Results obtained on MoMCM-22 showed a lower resistance of this catalyst towards coking compared with MoZSM-5 type catalyst probably due to the channel system of MCM-22 forming supercages. Catalytic results on two MoZSM-5 catalysts which differ only in particle size of the ZSM-5 samples showed that Mo catalyst based on microsized ZSM-5 is significantly more active, selective and stable in methane conversion compared with catalyst based on ZSM-5 sample having particle size in nanosized region. Physico-chemical measurements indicated that Mo is located preferentially on high external surface area in nanosized catalyst, while Mo species in microsized HZSM-5 interact with the internal Brönsted acid sites probably due to its smaller external surface area. It is generally accepted that these species are the precursors for the formation of the most active carburized Mo sites. Mo does not have inorganic salts which are in the state of isolated cations so a wet impregnation with the solution of ammonium heptamolybdate (AHM) is usually used for Mo incorporation into zeolite resulting in the localization of large AHM molecules mainly on the external surface. The results that indicate probably the decrease of external surface supports the migration of Mo oxide species, forming during the activation of the catalyts, into intracrystalline space of zeolite crystals, where they interact with the internal Brönsted acid sites.
Keywords: Methane; Aromatization; Zeolite; Molybdenum; Surface characteristics;
Dehydration of 1,3-butanediol over rare earth oxides by Hiroshi Gotoh; Yasuhiro Yamada; Satoshi Sato (92-98).
Vapor-phase catalytic dehydration of 1,3-butanediol to produce 3-buten-2-ol and 2-buten-1-ol was investigated over rare earth oxides (REOs) calcined at different temperatures. In the dehydration of 1,3-butanediol, CeO2 showed the highest formation rate with the highest selectivity to the unsaturated alcohols among REOs. C-type REOs, such as Ho2O3, Er2O3, Tm2O3, Yb2O3, Lu2O3, and Y2O3, also selectively produced the unsaturated alcohols. The formation rates of the unsaturated alcohols over CeO2 and Er2O3 were suppressed in CO2 and NH3 carrier gas flows.Vapor-phase catalytic dehydration of 1,3-butanediol was investigated over rare earth oxides (REOs) calcined at different temperatures. In the dehydration of 1,3-butanediol over REOs such as Dy2O3, Ho2O3, Er2O3, Tm2O3, Yb2O3, Lu2O3, and Y2O3, 3-buten-2-ol and 2-buten-1-ol were preferentially produced. REOs exhibited different catalytic activities in the dehydration of 1,3-butanediol depending on their crystal structures. CeO2 showed the highest formation rate with the highest selectivity to the unsaturated alcohols among the REOs. Cubic REOs also selectively produced the unsaturated alcohols: cubic Er2O3, Yb2O3, and Lu2O3 showed high formation rate of the unsaturated alcohols. Since the formation rates of the unsaturated alcohols over Er2O3 and CeO2 were suppressed in CO2 and NH3 carrier gas flows more than in H2 flow, it is probable that the acid–base sites play a major role of the formation of the unsaturated alcohols.
Keywords: Unsaturated alcohols; 3-Buten-2-ol; 1,3-Butanediol; Dehydration; Rare earth oxide; Acid–base property;
Transalkylation of toluene with trimethylbenzenes over large-pore zeolites by Andrea Krejčí; Sulaiman Al-Khattaf; Muhammad Ashraf Ali; Martina Bejblová; Jiří Čejka (99-106).
The effect of channel architecture with optimized acidity of zeolite Beta to achieve high trimethylbenzene and toluene conversions and xylene yields is reported. Equimolar ratio of toluene and trimethylbenzenes was found as the optimum while any shift from this value leads to a decrease in xylene yield.Zeolites Beta, mordenite and Y were evaluated for their activity in transalkylation reaction of toluene with trimethylbenzenes. Zeolite Beta was found to possess the highest conversion in toluene–trimethylbenzene transalkylation as well as a higher stability in time-on-stream compared with mordenite and zeolite Y. The effect of Si/Al ratio in zeolite Beta was evaluated and it was found that transalkylation activity and xylene yields increase with decreasing Si/Al ratio. Zeolite Beta with the lowest Si/Al ratio of 12.5 (the highest concentration of active sites) exhibited the highest 1,2,4-trimethylbenzene (124TMB) conversion and maximum xylene yield. The highest xylene yield was obtained at optimum equimolar ratio (1:1) of 124TMB to toluene. With increasing 124TMB concentration in the feed, the conversion of 124TMB and xylene yield decreased while toluene conversion simultaneously increased. The increase in the concentration of toluene in the feed resulted in the increase in the conversion of 124TMB. However, addition of higher concentrations of toluene led to a significant decrease in xylene yield.
Keywords: Transalkylation; Toluene; Zeolites Beta; Mordenite; Zeolite Y; Si/Al ratio; Large-pores zeolites; 1,2,4-Trimethylbenzene;
Fluorine-modified Mg–Al mixed oxides: A solid base with variable basic sites and tunable basicity by Gongde Wu; Xiaoli Wang; Wei Wei; Yuhan Sun (107-113).
Some fluorine-modified Mg–Al mixed oxides could be prepared by thermal decomposition of the fluorine-containing Mg–Al hydrotalcite. The weak, moderate and strong basic sites were all produced in the as-prepared samples. Moreover, the amount of basic sites could be controlled by the changes of decomposition temperature and fluorine content.The fluorine-modified Mg–Al mixed oxides were synthesized by thermal decomposition of the fluorine-containing Mg–Al hydrotalcites, and their physicochemical properties were characterized by ICP, TGA, XRD, FTIR, CO2-TPD and N2 adsorption/desorption techniques. It was found that weak basic sites were gradually transformed into moderate and strong basic sites during thermal decomposition, and thus weak basic sites (OH− groups), moderate basic sites (Mg–O, Mg–F and Al–O pairs) and strong basic sites (coordinatively unsaturated F− and O2− ions) were all produced in the as-prepared samples. Furthermore, the basicity of moderate basic sites could be controlled by the change of fluorine content, which caused the change in the amounts of Mg–F pairs. In the synthesis of propylene glycol methyl ether from methanol and propylene oxide, the base-catalytic performance of the obtained samples was shown to be closely associated with their moderate basic sites.
Keywords: Hydrotalcite; Mg–Al mixed oxides; Fluorine; Tunable basicity; Propylene oxide; Methanol;
Substrate influences on activity and stability of SBA-15–Pr-anchored Rh–P complex catalysts for olefin hydroformylation by Wei Zhou; Yuming Li; Dehua He (114-120).
Rhodium chloride (RhCl3) was immobilized to diphenylphosphinopropyl (–PrPPh2)-modified mesoporous silica SBA-15 with or without externally adding PPh3, and the prepared immobilized catalysts were employed in hydroformylation of higher olefins with different lengths, different C＝C bond positions or different structures. The substrate influences on the activity and recycling stability of the catalysts were investigated.RhCl3 was immobilized to diphenylphosphinopropyl (–PrPPh2)-modified mesoporous silica SBA-15 through a multi-step-assembly process. The prepared catalyst was characterized with reference to bulky and surface properties by X-ray diffraction (XRD), infrared spectroscopy (FT-IR), isothermal nitrogen sorption analysis and X-ray photoelectron spectroscopy (XPS). The metal content was determined by inductive coupling plasma-atomic emission spectroscopy (ICP-AES). The prepared rhodium-immobilized catalyst was employed in hydroformylation of several higher olefins of different lengths (C6, C8, and C10), different C＝C bond positions (terminal or internal) or different structures (linear or branched). The substrate influences on the activity and recycling stability of the immobilized catalyst were investigated and are discussed. Shorter linear olefin substrates were more easily activated with higher catalyst specific activity, while the catalyst showed recycling stability in hydroformylation of longer and branched olefin substrates. For comparison, PPh3 was externally added to immobilize RhCl3 to –PrPPh2-modified SBA-15. The immobilized catalyst so prepared showed a more flexible immobilizing structure and revealed a promoted turnover number of substrates.
Keywords: SBA-15; Rh–P complex; Hydroformylation; Olefin; Aldol condensation;
The synergetic mechanism between copper species and ceria in NO abatement over Cu/CeO2 catalysts by Jinfa Chen; Yingying Zhan; Junjiang Zhu; Chongqi Chen; Xingyi Lin; Qi Zheng (121-127).
The fresh and nitric acid treated Cu/CeO2 catalysts were characterized. The results indicated that three crucial copper species interacting with CeO2 change the surface structure of ceria, facilitating the relative free movement of oxygen from ceria to supported copper. This synergy between ceria and different copper species endows Cu/CeO2 with excellent activity for NO + CO reaction.Copper supported on ceria prepared by the impregnation method was used as a model catalyst to investigate the synergetic mechanism between copper species and ceria for NO reduction by CO. To identify the copper species in the catalyst, we treated the as-synthesized Cu/CeO2 by 30 wt.% nitric acid solution. Fresh and nitric acid treated Cu/CeO2 catalysts were characterized and compared with AAS, XRD, TPR, EPR, Raman and NO-TPD techniques. It is found that, after nitric acid treatment, there is only 0.27 wt.% Cu left (vs. 5 wt.% Cu in fresh sample); this is present in the following forms: (1) isolated copper ions in octahedral sites of ceria, (2) copper oxide clusters and (3) copper ions in ceria lattice. The residual small amount of Cu has a significant effect on surface structure, redox property and catalytic behavior of ceria, indicating that these copper species are crucial copper species inducing copper–ceria interactions. Moreover, it is suggested that the relative free movement of oxygen from ceria to supported copper, caused by the three copper species, leads to oxygen vacancies in ceria, significantly enhancing the NO conversion of Cu/CeO2 during NO + CO reaction.
Keywords: Copper–ceria interaction; NO reduction by CO; Copper species; Oxygen vacancy; Oxygen transfer; Active site;
Influence of copper precursors on the structure evolution and catalytic performance of Cu/HMS catalysts in the hydrogenation of dimethyl oxalate to ethylene glycol by Anyuan Yin; Xiuying Guo; Kangnian Fan; Wei-Lin Dai (128-133).
High copper contented Cu–HMS catalyst prepared by an ion exchange method using Cu(NH3)4(NO3)2 as the copper precursor exhibited high ethylene glycol yield (98%) with 100% conversion and 98% selectivity to ethylene glycol in the hydrogenation reaction of dimethyl oxalate under these optimal reaction conditions: 2.5 MPa, 473 K, H2/dimethyl oxalate (mol/mol) = 50, and LHSV = 0.7 h−1.Cu/HMS catalysts synthesized with different copper precursors via the ion exchange method have been systematically characterized, focusing on the influence of copper precursors. It is found that the texture, surface composition and the surface structure of the dried, calcined and reduced Cu/HMS materials were profoundly affected by the kinds of copper precursors. Based on the characterizations, the copper species on dried, calcined and reduced samples were assigned. Proper copper precursor could be beneficial for the generation of active copper species; enhanced catalytic performance could thus be obtained. By optimizing the gas-hydrogenation reaction conditions, an ethylene glycol yield of 98% could be obtained via the Cu–HMS catalyst using Cu(NH3)4(NO3)2 as the copper precursor.
Keywords: Cu/HMS catalysts; Ion exchange method; Copper precursors; Hydrogenation; Ethylene glycol;
Reversible promotional effect of SiO2 modification to Co/Al2O3 catalyst for Fischer–Tropsch synthesis by Xiaoyu Sun; Xuejun Zhang; Yi Zhang; Noritatsu Tsubaki (134-139).
The addition of a small amount of SiO2- to Al2O3-supported cobalt catalyst significantly increased the reduction degree of the supported cobalt oxides and the metallic cobalt surface area, as a result of remarkable enhancement of the Fischer–Tropsch synthesis (FTS) activity in the slurry-phase reaction, attributing to the improved bridge-type CO adsorption on metallic cobalt surface.The addition of a small amount of SiO2- to Al2O3-supported cobalt catalyst significantly increased the reduction degree of the supported cobalt oxides and the metallic cobalt surface area, as a result of remarkable enhancement of the Fischer–Tropsch synthesis (FTS) activity in the slurry-phase reaction. Properties of various catalysts were characterized by in situ DRIFT, XRD, TPR, N2 physisorption and H2 chemisorption. Furthermore, properties and reaction performances of the present catalyst system were compared with those of Al2O3-promoted Co/SiO2 catalyst.
Keywords: Fischer–Tropsch synthesis; Reversible promotional effect; SiO2; Co/Al2O3 catalyst;
Adsorbent as an essential participant in photocatalytic processes of water and air purification: Computer simulation study by D.S. Selishchev; P.A. Kolinko; D.V. Kozlov (140-149).
Photocatalytic reactions were simulated with the assumption that there exist an adsorbent in the system which could adsorb substrates and intermediates according to Langmuir mechanism. Both static and flow reactors were simulated and results demonstrate that adsorbent could strongly influence the kinetics of photocatalytic reactions.The influence of adsorbent on the kinetics of (photo)catalytic oxidation processes was studied using the simple single and double stage reaction mechanisms with the adsorption stages corresponding to Langmuir model. It was found that in the static reactor in all cases the usage of adsorbent leads to the prolongation of substrate (A) removal and product (P) accumulation kinetic curves but the substrate concentration becomes lower during almost all (photo)catalytic process. Fitting of experimental data points of acetone photocatalytic oxidation reaction demonstrated a good correlation with proposed reaction mechanism. Calculated adsorption constants values are close to those reported in literature.The using of adsorbent in flowing conditions leads to the decrease of maximum outlet substrate concentration in the case if the inlet substrate concentration is too high to be oxidized completely for one run.Kinetics simulation in the case of (photo)catalytic reaction with intermediate demonstrates that adsorbent could accumulate additional intermediate quantity thus keeping catalyst surface more active and contributing to faster substrate (A) removal.
Keywords: Photocatalysis; Titanium dioxide; Adsorption; Activated carbon; Reaction kinetics simulation;
Indium as a chemical promoter in Fe-based Fischer-Tropsch synthesis by Wonga M. Hexana; Neil J. Coville (150-157).
The ‘Knight's move’ relationship suggests that indium, like copper, should promote iron Fischer-Tropsch catalysts. Addition of indium to Fe and to Fe/SiO2/K2O catalysts revealed that while In did promote Fe reduction under H2, presumably by a spill-over mechanism, the FT activity decreased substantially in the presence of low melting In.The ability of indium to act as a chemical promoter in Fe-based FTS reaction was evaluated and compared to that of copper. Indium was chosen for study due its relationship to Cu through the ‘Knight's Move’relationship. N2 physisorption, temperature programmed reduction (TPR), X-ray diffraction (XRD) and diffuse reflectance infrared fourier transform spectroscopy (DRIFTS) were employed to characterise the catalysts. “In situ” Fischer-Tropsch synthesis (FTS) reactions were also performed in a DRIFTS reactor. It was found via TPR studies that indium exhibited a similar ability to reduce Fe as found for copper. Results obtained from XRD and N2 physisorption experiments showed indium promoted catalysts give comparable results to those of copper promoted catalysts. However, indium decreased the % reducibility and CO adsorption ability of the Fe catalyst. Indium also lowered the FTS activity of the Fe-based catalyst, an effect ascribed to be associated with the low melting point of In. The effect of adding indium to a multi-promoted Fe-based FTS catalyst was also investigated. The addition of indium suppressed the reduction properties of the catalyst when H2 was employed as a reductant. When CO was employed as a reductant, the reduction/carburization properties were improved and resulted in a selectivity shift to heavy weight hydrocarbons during the FTS reaction. Adding indium to the multi-promoted catalyst also lowered the catalyst surface area which resulted in a decrease to the FTS activity. It appears that while the ‘Knight's Move’relationship is consistent with Cu and In both acting to enhance Fe reduction, the low In melting point determines the poor activity of the FT catalysts.
Keywords: Fischer-Tropsch synthesis (FTS); Fe-based catalyst; Indium promoter; Copper promoter;
Steam and CO2 reforming of methane over a Ru/ZrO2 catalyst by Jon Geest Jakobsen; Tommy L. Jørgensen; Ib Chorkendorff; Jens Sehested (158-166).
Modeling of methane steam reforming at 1.3 bar and 425–575 °C on a Ru/ZrO2 catalyst have shown that CO and H adspecies partly block the active sites. This reduces the activity significantly at low temperature (<500 °C) methane steam reforming experiments. For characterization in situ TEM is advised due to surface oxidation of the ruthenium particles at ambient conditions.The kinetics of methane steam reforming over a Ru/ZrO2 catalyst was studied at 1.3 bar total pressure and in the temperature range 425–575 °C. These data were fitted by combining a reactor model with a series of kinetic models. The best fit was obtained by a model with methane dissociative adsorption as the rate limiting step and with CO and H adspecies partly blocking the active sites. The Ru/ZrO2 catalyst was characterized by TEM and H2 chemisorption. By comparison of ex situ and in situ TEM, it is evident that Ru particles with diameters of <2 nm are difficult to observe with ex situ TEM due to oxidation when exposed to air.
Keywords: Methane steam reforming; TEM; Kinetics; Ruthenium;
Probing metal substrate interaction of Pt nanoparticles: Structural XRD analysis and oxygen reduction reaction by Walter Vogel; Laure Timperman; Nicolas Alonso-Vante (167-173).
Platinum nanoparticles were selectively deposited on titania via a photochemical method. The structural studies via XRD in the as prepared and heat-treated samples were evaluated and compared to the substrate without oxide. A metal nanoparticle–oxide interaction, which is favorable for electrocatalysis, is observed.Platinum nanoparticles were selectively deposited on titania via a facile photochemical method. The anatase-type TiO2 nanostructure, prepared by sol-gel, is in intimate contact with the carbon (Vulcan XC-72) used as supporting material. The structural studies via XRD in the as prepared and heat-treated samples were evaluated and compared to the substrate without oxide. The lattice constant of platinum was found 0.6% less than the value in the bulk. This observation is accompanied by high internal strains, which are not present on the Pt/C system. A healing of such defects is achieved by the thermal treatment. The consequence of such observations is discussed in terms of a strong-metal nanoparticle oxide interaction, which is favorable for electrocatalysis. These studies suggest that Pt–TiO2–C might serve as an element of response to lower the amount of utilized platinum in low temperature H2/O2 fuel cells cathodes.
Keywords: X-ray structure; Metal–support interaction; Oxide; Oxygen reduction; Composites; Carbon;
Analysis of selective CO oxidation over promoted Pt/Al2O3 catalysts using modular neural networks: Combining preparation and operational variables by M. Erdem Günay; Ramazan Yildirim (174-180).
The effects of preparation (Pt wt.%, promoter type) and operational (reaction temperature, feed composition, time on stream) variables on CO conversion were modeled by using modular neural networks for the selective CO oxidation over promoted Pt/Al2O3 catalysts. As a novel approach to modeling of the catalytic performance, the preparation and the operational variables were processed differently to improve the accuracy of the model.In this work, modular neural network modeling was applied to analyze the experimental data for the selective CO oxidation over promoted Pt/Al2O3 catalysts. The effects of preparation (Pt wt.% and promoter type) and operational (reaction temperature, feed composition and time on stream) variables on CO conversion were modeled. As a novel approach to neural network modeling of the catalytic performance, the preparation and the operational variables were used together but processed differently in the network so that the accuracy of the model could be improved since the nature of these two variables are quite different although they are both important. Similarly, the continuous (like Pt wt.%) and categorical (like promoter type) variables were also treated in different manner. After the most successful network structure was determined, the relative importances of the preparation and the operational variables as well as their effects on CO conversion were analyzed in detail. It was found that modular neural networks used this way are quite successful in predicting and explaining the experimental results, and they are superior to the monolithic neural network models.
Keywords: Selective CO oxidation; Promoted Pt/Al2O3; Catalyst modeling; Partially connected neural networks; Modular neural networks;
Evaluation of the performance of Ni/La2O3 catalyst prepared from LaNiO3 perovskite-type oxides for the production of hydrogen through steam reforming and oxidative steam reforming of ethanol by Sania M. de Lima; Adriana M. da Silva; Lídia O.O. da Costa; José M. Assaf; Gary Jacobs; Burtron H. Davis; Lisiane V. Mattos; Fábio B. Noronha (181-190).
DRIFTS spectra recorded as a function of time on stream under the reaction mixture ethanol + water at 773 K (Figure below) showed that the coverage of carbonate species on the catalyst surface remained constant and could not be responsible for the deactivation observed. Catalyst deactivation was determined to be due to the deposition of carbon.This paper studies the performance of LaNiO3 perovskite-type oxide precursor as a catalyst for both steam reforming and oxidative steam reforming of ethanol. According to results of temperature-programmed desorption of adsorbed ethanol and by carrying out diffuse reflectance infrared Fourier transform spectroscopy analyses of ethanol steam reforming, ethanol decomposes to dehydrogenated species like acetaldehyde and acetyl, which at moderate temperatures, convert to acetate by the addition of hydroxyl groups. Demethanation of acetate occurs at higher temperatures, leading to a steady state coverage of carbonate. Catalyst deactivation occurs from the deposition of carbon on the surface of the catalyst. Both thermogravimetric and scanning electron microscopy analyses of postreaction samples indicate that lower reaction temperatures and lower H2O/EtOH ratios favor the deposition of filamentous carbon. However, less carbon formation occurs when the H2O/EtOH ratio is increased. Increasing reaction temperature or including O2 in the feed suppresses filamentous carbon formation.
Keywords: Perovskite-type oxides; Hydrogen production; Ethanol steam reforming; Ethanol oxidative steam reforming; Deactivation mechanism; Nickel catalyst;
Improved Pt-Ni nanocatalysts for dry reforming of methane by M. García-Diéguez; I.S. Pieta; M.C. Herrera; M.A. Larrubia; L.J. Alemany (191-199).
Pt-Ni nanocatalysts prepared by the reverse microemulsion method and supported on a nanofibrous alumina were studied for the CO2 reforming of methane. Preparing the catalysts by microemulsion inhibits global carbon formation, promotes the relative content of active species and avoids metal sintering, as well as improves considerably the catalysts’ stability.Nanostructured PtNi catalysts, prepared by the reverse microemulsion method (ME) and supported on a nanofibrous alumina were studied for the CO2-reforming of methane. Monometallic (Ni and Pt) and bimetallic (PtNi) supported catalysts were synthesized, characterized (XRD, TEM, Elemental Analysis, Raman, XPS and temperature-programmed reduction (TPR)) and tested under CO2-reforming reaction conditions. Catalysts prepared by wetness impregnation (IM) of the support were also synthesized for comparative purposes. Characterization results showed that Pt addition and the preparation of the catalysts by ME promoted the formation of NiO, instead of NiAl2O4, and facilitated its reduction to Ni0 during the catalysts pre-treatment. It was also observed that the Ni and Pt ensembles were modified when the catalysts were prepared by the reverse microemulsion method, reducing the global carbon formation. From activity tests it can be concluded that catalysts prepared by the reverse microemulsion method are less sensitive to coke deposition and more stable under CO2-reforming conditions. Besides, in the bimetallic catalysts, there is a Pt-Ni interaction between metallic centers, which enhances the catalyst stability and selectivity towards H2 and CO.
Keywords: Dry reforming; Methane; Nickel; Platinum; Reverse microemulsion;