Applied Catalysis A, General (v.396, #1-2)
Editorial Board (CO2).
Stabilization of supported Pd particles by the application of oxide coatings by Axel Binder; Martin Seipenbusch (1-7).
Display Omitted► Novel experimental approach for stability investigations of supported catalysts. ► Synthesis of complex catalyst structures with high degree of process control. ► Stabilization of silica supported Pd by deposition of minute amounts of HfO x . ► Ostwald ripening could be identified as growth mechanism for immobilized Pd. ► Long-term stability on stream, minor loss of activity due to HfO x coating.The influence of an HfO x coating on the initial sintering rates of nearly monodisperse Pd model catalyst particles on silica was measured at well defined temperatures and residence times in the gas-phase.It was found that minute amounts of HfO x significantly retard the sintering of the Pd and at higher amounts the mean Pd size can even be maintained. Analysis of the Pd size distributions indicates an immobilization of the Pd particles and a growth by Ostwald ripening. The coated catalysts were extremely stable at reaction conditions and show only a negligible loss of activity in the hydrogenation of ethylene.
Keywords: Supported palladium catalysts; Sintering; Stabilization; Chemical vapour deposition (CVD); Chemical vapour synthesis (CVS);
Molybdenum oxide modified HZSM-5 catalyst: Surface acidity and catalytic performance for the dehydration of aqueous ethanol by Yuwang Han; Cuiyun Lu; Dongsheng Xu; Yelong Zhang; Yi Hu; He Huang (8-13).
.Display Omitted► 5 wt% Mo modified HZSM-5 calcined at 500 °C exhibited much better catalytic performance and anti-coking ability in ethanol dehydration reaction compared with HZSM-5. ► A correlation between the catalytic performance of Mo modified catalysts and the amount of weak and medium acidity was observed. ► The decrease of weak and medium acidity could be correlated with the reduction of Mo species.The catalytic dehydration of ethanol into ethylene was studied over 5 wt% Mo/HZSM-5 prepared by impregnation. The effect of calcination temperature on the structure, acidity and catalytic performance of the catalysts was investigated by XRD, N2 adsorption, NH3-TPD and TG. A correlation between the catalytic performance of Mo modified catalysts and the amount of weak and medium acidity was observed. It was found that 5 wt% Mo/HZSM-5 catalyst calcined at 500 °C exhibited the highest weak and medium acidity and much better catalytic performance in ethanol dehydration reaction compared with HZSM-5. TPR characterization showed that the Mo species on the external surface of HZSM-5 was easier to be reduced during the reaction. Combining quantitative analyses of NH3-TPD and H2-TPR profiles of fresh and used catalysts revealed that the decrease of weak and medium acidity could be correlated with the reduction of Mo species. It is proposed that reduction of Mo species caused the decrease of weak and medium acidity, which contributed to activity drop at the initial reaction stage.
Keywords: Ethanol dehydration; Mo/HZSM-5; Calcination temperature; Acidity; Reduction;
Kinetics of esterification of acetic acid with n-amyl alcohol in the presence of Amberlyst-36 by Elif Ödeş Akbay; Mehmet R. Altıokka (14-19).
Display Omitted► The kinetics of esterification of acetic acid with amyl alcohol in the presence of Amberlyst-36 in its H+ form. ► Homogeneous reversible reaction. ► Conversion–time curve in its linearized form based on the mechanism.The kinetics of esterification of acetic acid with amyl alcohol has been studied in the presence of Amberlyst-36 in its H+ form in a batch reactor. Experimental findings showed that the reaction is controlled by chemical step rather than external and internal mass transfer steps. Experimental data well fitted the kinetic model based on homogeneous reversible reaction. Temperature dependency of the equilibrium constant was found to be K e = exp(3.25 − 820/T) which indicates that the heat of reaction is 6.81 kJ/mol. It was also shown that the reaction rate can be given as − r A = ( k 1 + k ′ 1 C c ) C A C B − C E C W K where k 1 ( L mol − 1 min − 1 ) = exp 19.01 − 9620 T k ′ 1 ( min − 1 ) = exp 11.56 − 5990 T
Keywords: Esterification; Amyl acetate; Catalysis; Kinetic modeling; Amberlyst-36;
The new esterification catalysts and the nature of reactions proceeding at esterification of synthetic naphthenic acids in their presence by A.H. Azizov; G.I. Amanullayeva; R.V. Aliyeva; B.M. Aliyev; N.R. Bektashi (20-33).
Display Omitted► Heterogeneous catalysis. ► Synthesis and characterization of sulfocationites and their modification form with titanium compound. ► Esterification in the presence of sulfocationites. ► Studying of esterification mechanism. ► Cycle opening with formations of oxyacids and oxyesters, mediated by the “hard” protonic centers of the synthesized catalysts.There have been synthesized the novel sulfocationites on the basis of graft copolymers of polystyrene with oligostyrene, and their metal-polymer composites based on the titanium-containing compound with the grafted ionic-liquid type ligands. Esterifacation reaction of synthetic naphthen acid (SNA) fraction with heptyl alcohol as a model reaction has been investigated in the presence of the novel sulfocationites and Ti-containing metal-polymer composites on their basis. Structural group content and molecular mass characteristics of primary and end esterification products have been identified using PMR, NMR, IR-spectroscopy and gel-permeation chromotography methods, correspondingly. The results of the investigations carried out show that the esterification reactions of SNA with alcohols are complex process in the course of which the primary esterification reactions, opening of the five-membered cycles in the condensed naphthenic fragments with formation of oxy-ethers and/or oxy-acids, products of their polycondensation, lactone formation as well as decarboxylation reactions take place. The yields of the basic and side products strongly depend on the nature and method of the sulfocationite and their titanium-containing modificates type catalysts preparation.
Keywords: Esterification; Esters of synthetic naphthenic acids; Sulfocationites; Titanium-containing polymer catalysts;
Pd nanoparticles supported mesoporous γ-Al2O3 film as a reusable catalyst for reduction of toxic CrVI to CrIII in aqueous solution by Anirban Dandapat; Debrina Jana; Goutam De (34-39).
Display Omitted► Mesoporous γ-Al2O3 films using CTAB were synthesized. ► Pd NPs were incorporated within the mesopores of the γ-Al2O3 films. ► Toxic CrVI was reduced to CrIII by Pd−γ-Al2O3 film catalyst. ► The film catalyst can be reused several times.Pd nanoparticles (NPs) were generated inside the nanocrystalline mesoporous γ-Al2O3 films of thickness ∼2 μm. The support γ-Al2O3 films were prepared from boehmite sols derived from Al-alkoxide in presence of CTAB. The BET surface area (171 m2g−1) and pore size (4.3 nm) of the undoped γ-Al2O3 films were found to be decreased to 139 m2g−1 and 3.5 nm respectively after incorporation of Pd NPs. The films were characterized by GIXRD, cross-sectional FESEM, and TEM. TEM/GIXRD confirmed the existence of uniformly dispersed Pd NPs inside the γ-Al2O3 films. The Pd NPs (average size ∼4.1 nm)-incorporating mesoporous γ-Al2O3 films were used as catalyst to reduce toxic CrVI compounds to non-toxic CrIII in presence of formic acid as reducing agent at different temperatures (30, 40, 50 and 60 °C). This catalytic reduction process was monitored by UV–visible spectrometer. The rate constant value for the reduction was estimated to be 0.085 min−1 at 50 °C. The same catalytic film can be used for three consecutive cycles by simple washing with water. The catalytic property started to deteriorate after the third cycle. The original catalytic property can be restored fully after heat-treatment of the used films at 300 °C in nitrogen atmosphere.
Keywords: Pd NPs-incorporating mesoporous γ-Al2O3 films; Sol-gel; Film catalyst; CrVI reduction; Reuse of catalyst;
Comparison of metal and carbon catalysts for hydrogen production by methane decomposition by R. Guil-Lopez; J.A. Botas; J.L.G. Fierro; D.P. Serrano (40-51).
.Display Omitted► The first comparative study between metals and carbons as catalysts in CH4 decomposition to produce H2. ► The most active catalyst was Ni mixed oxides from hydrotalcites (Ni–ex LDHs). ► The most stable catalysts against deactivation were carbon blacks, mainly the CB-vulcan. ► Carbon vulcan produces 4 fold more H2 than the most active and stable metal catalysts (Ni–ex LDHs).The CO x -free hydrogen production by decomposition of methane was carried out over metal-free carbons and bulk and supported metal catalysts. Catalysts based on Ni or Fe (oxides, spinels and ex-hydrotalcite mixed oxides) and carbon-catalysts of different types (carbon black, activated carbon, carbon nanotubes and graphite) have been used and the performance of both different kinds of catalyst compared in the target reaction, focussing the comparative study on the initial activity and the resistance against deactivation. Catalytic results showed that activity of carbon catalysts is similar to that of the non-prereduced metal catalysts. Carbon blacks, and specifically vulcan-type, were found to be most resistant catalysts against deactivation, while the most active ones were nickel catalysts derived from hydrotalcite-like precursors (ex-LDH). It was also shown that pre-reduction treatment of nickel precursor to generate the metallic Ni0 phase before the reaction decreases the threshold temperature to generate hydrogen by about 200 °C.Along the course of the reaction, nanotubes and nanofibers are formed on the surface of metal catalysts. These carbon structures encapsulate metal particles and deactivate the catalysts. However, when carbons are used as catalysts, the nature of carbon deposits depends largely on the type of carbon material employed as catalyst in the methane decomposition. Thus, the use of carbon blacks and graphite yielded amorphous turbostratic carbon, whereas activated carbons mainly produced carbon, which showed the carbon black structure. Finally, the carbon by-product of the reaction, when carbon nanotubes were used bas catalysts, accumulates in the form of extra layers over the walls of carbon nanotubes thus increasing their wall thickness.
Keywords: CO x -free H2 production; CH4 decomposition; Ni-catalysts; Fe-catalysts; Hydrotalcites; Activated carbon; Carbon black; Carbon nanotubes;
Synthesis of carbon nanotubes by methane decomposition over Co–Mo/Al2O3: Process study and optimization using response surface methodology by Siang-Piao Chai; Kim-Yang Lee; Satoshi Ichikawa; Abdul Rahman Mohamed (52-58).
Display Omitted► The effects of process variables were examined using RSM three-level factorial design. ►TGA and HRTEM reveal that the CNTs had a high degree of crystallinity. ► TEM and SEM show that CNTs were densely grown and possessed open-tip morphology. ► The open tips had diameters in the range of 3.6–4.8 nm. ► Long CNTs entangled to form aggregated pores with pore sizes within 20–100 nm.Systematic studies of various process variables on the formation of carbon nanotubes (CNTs) by methane decomposition over a Co–Mo/Al2O3 catalyst were performed using a three-level factorial design in response surface methodology. A quadratic polynomial model for carbon yield was developed by multiple-regression analysis. The optimum conditions for CNT production within the experimental ranges were found at a reaction temperature of 761 °C, a methane partial pressure of 0.75 atm and a catalyst weight of 0.4 g. The carbon yield predicted at the optimum process conditions was 607%. Examination by electron microscopy revealed that the CNTs grown under optimum conditions had diameters of 11.8 ± 1.9 nm (average diameter ± standard deviation) and possessed an open-tip morphology.
Keywords: Methane decomposition; Co–Mo/Al2O3; Carbon nanotubes; Response surface methodology;
Utilization of biomass: Conversion of model compounds to hydrocarbons over zeolite H-ZSM-5 by Uffe V. Mentzel; Martin S. Holm (59-67).
Display Omitted► Different conversion capacities are seen when co-feeding structural isomers in MTH. ► Methanol dilution increases conversion capacity of the additive by up to 10 times. ► Acids and esters favor deoxygenation through CO/CO2 dissociation over dehydration. ► 13C labeling indicates that additives are incorporated via the aromatic products.Zeolite catalyzed deoxygenation of small oxygenates present in bio-oil or selected as model compounds was performed under Methanol-to-Hydrocarbons (MTH) like reaction conditions using H-ZSM-5 as the catalyst. Co-feeding of the oxygenates with methanol generally decreases catalyst lifetime due to coking and results in higher selectivity towards aromatics compared to conversion of pure methanol. The reaction pattern of the different oxygenates did not simply follow the effective H/C ratio of the additives since structural isomers with identical effective H/C ratios showed significant differences with respect to catalyst lifetime and product selectivity. A distinct positive effect on catalyst lifetime was observed for methanol dilution. Thus, the conversion capacity of the catalyst was up to 10 times higher when the reactant was diluted in methanol. We observe that in particular acid/ester functionalities favor oxygen removal through decarbonylation over dehydration which preserves hydrogen in the hydrocarbon product mixture. By employing 13C labeled substrates we confirmed the incorporation of carbon into the hydrocarbon products as well as a pronounced preference of the additive carbon towards incorporation into aromatic compounds.
Keywords: Zeolite; ZSM-5; Methanol-to-Hydrocarbons (MTH); Bio-oil; Biomass-to-liquids (BTL);
Methanol oxidation catalysis and substructure of PtRu/C bimetallic nanoparticles synthesized by a radiolytic process by Takao A. Yamamoto; Satoru Kageyama; Satoshi Seino; Hiroaki Nitani; Takashi Nakagawa; Ryo Horioka; Yuji Honda; Koji Ueno; Hideo Daimon (68-75).
Display Omitted► Highly active PtRu/C nanoparticle catalysts are synthesized by a radiolytic process, which is a simple one-pot process without any use of surfactant, solvent or heating. ► The mixed state of PtRu is controlled by using high dose rates and additives to the synthetic solution. ► A correlation between the substructure of the catalysts and the activity of methanol oxidation was found.Nanoparticle catalysts of PtRu/C for the direct methanol fuel cell anode were synthesized by a radiolytic process. Bimetallic substructures were controlled by varying irradiation dose rate and by addition of NH4OH or NaH2PO2. Material characterization was performed with the transmission electron microscopy, the X-ray diffraction, the X-ray fluorescence spectroscopy and the X-ray absorption fine structure techniques. Methanol oxidation activity was evaluated by the linear sweep voltammetry. We concluded that the structure of the radiolytically synthesized catalysts has a Pt-rich core/Ru-rich shell structure or incomplete alloy structure. A correlation between the substructures and catalytic activities was found by using a pairing factor defined from coordination numbers determined by the extend X-ray absorption fine structure analysis, which indicates the validity of the bifunctional mechanism in the PtRu nanoparticle system. This radiolytic process is promising for synthesizing advanced PtRu/C catalysts with well-mixed bimetallic substructures enhancing methanol oxidation.
Keywords: Methanol oxidation; Bimetallic catalyst; Radiolytic process; Platinum; Ruthenium;
Characterization of the acidic sites in organic acid functionalized mesoporous silica in an aqueous media by Basak Cinlar; Brent H. Shanks (76-84).
Display Omitted► Method developed to characterize the aqueous phase acidity of solid acid catalysts. ► Bulk aqueous phase pKa of solid Brönsted acid catalysts can be reliably determined. ► Appropriate titration conditions are established for solid acid characterization. ► Method validated by measuring pKas of tethered organic acid functional groups. ► Improved acid characterization method over gas phase surrogate measurement.Exploring the catalytic potential of organic acid functionalized mesoporous silica in condensed phase necessitates characterization of their acidic properties in a similar environment. In this study, potentiometric titration is used as a direct measurement technique to determine the acidic strength and total acid capacity of propylsulfonic, arenesulfonic, ethylphosphonic, and butylcarboxylic functionalized mesoporous silica catalysts in water. While the method can provide direct insight into the acidic properties of the materials the characterization conditions must be carefully chosen to yield reliable results. The addition of salts are required for enhancing the ion-exchange in the titration procedure, but their over-addition leads to significant deviation of the activity coefficients leading to incorrect results. Titrations, which are performed under reliable characterization conditions, demonstrate that network interactions can exist between the organic acid functional groups, but their interaction with surface silanols does not appear to play a significant role on acidic properties. While the strongest acidity is observed for the arenesulfonic acid functionalized material, none of the acidic materials are leveled in an aqueous solvent.
Keywords: Acidity characterization; Solid acid catalysts; Condensed phase acidity measurement; pKa determination;
On the nature of the deactivation of supported palladium nanoparticle catalysts in the decarboxylation of fatty acids by Eric W. Ping; John Pierson; Robert Wallace; Jeffrey T. Miller; Thomas F. Fuller; Christopher W. Jones (85-90).
Display Omitted► Highly dispersed palladium nanoparticles supported on silica mesoporous foam. ► Severe deactivation after one cycle in decarboxylation of stearic acid to n-C17. ► Deactivation caused by deposition of reactants and products—no measurable coking. ► Catalyst regains substantial activity after extraction of residual organics.Supported palladium catalysts are effective catalysts for the hydrogen-free decarboxylation of fatty acids. However, the catalysts deactivate severely after one use. Here, the recyclability of a well-defined, mesoporous silica-supported palladium nanoparticle catalyst is evaluated in the batch decarboxylation of stearic acid at 300 °C under inert atmosphere, producing n-heptadecane. The nature of the catalyst deactivation is examined in detail via an array of characterization techniques. X-ray photoelectron spectroscopy (XPS) demonstrates that little palladium surface oxidation occurs over the course of the reaction, and a combination of X-ray absorption spectroscopy and transmission electron microscopy (TEM) suggests negligible particle sintering or agglomeration. Physisorption and chemisorption measurements demonstrate substantial loss in total surface area and porosity as well as accessible palladium surface area with these losses attributed to significant organic deposition on the catalyst, as verified via thermogravimetric analysis. High temperature calcination is applied to combust and remove these residues, but resultant nanoparticle agglomeration is significant. Solid state nuclear magnetic resonance spectroscopy (NMR), Fourier transform infrared spectroscopy (FT-IR) and solid dissolution followed by organic extraction methodologies demonstrate that the carbonaceous deposits are not coke but rather strongly adsorbed reactants and products. Detrimental coke formation, as suggested by prior literature, is verified to be absent, as extraction of the surface-deposited organic species yields nearly complete recovery of the total surface area, pore volume, and active palladium surface area. Furthermore, the regenerated catalyst exhibits a corresponding significant recovery of decarboxylation activity.
Keywords: Diesel; Bio-fuel; Deactivation; Fatty acid; Bio-diesel;
Hydrotalcite supported Co catalysts for CO hydrogenation by Yu-Tung Tsai; Xunhua Mo; Andrew Campos; James G. Goodwin; James J. Spivey (91-100).
.Display Omitted► Co on hydrotalcite results in a highly active Fischer–Tropsch synthesis catalyst. ► Co/hydrotalcite exhibited higher activity for CO hydrogenation than Co/Al2O3. ► This high activity for Co/hydrotalcite does not require a reduction promoter. ► Co/HT exhibited its highest activity at an intermediate reduction temperature.It is well known that the catalytic performance of Co catalysts depends on supports and promoters. The focus of this work was to investigate the catalytic activities for CO hydrogenation of Co catalysts supported on the solid base, hydrotalcite (HT), and to probe the role of support in the reaction. A cobalt catalyst containing 10 wt% cobalt supported on HT was prepared using the incipient wetness impregnation method. Pre-calcined HT (CHT), alumina and magnesium oxide were also employed as supports for comparison purposes. Catalysts were characterized by surface area and porosity analysis, XRD, TEM/STEM/EDX, TPR and H2 chemisorption. The catalytic activity was tested using a fixed-bed reactor at 230 °C, 1.8 atm, and H2/CO = 2. It was found that the hydrotalcite supported catalyst showed the highest steady-state reaction rates. The activities of Co/HT reduced at different reduction temperatures (from 300 to 600 °C) were also compared. Reduction at 500 °C resulted in the highest activity; however, CH4 selectivity was also enhanced as the reduction temperature increased. The product distributions for Co/HT obeyed an Anderson–Schulz–Flory distribution. The α values were not impacted by the different reduction temperatures for Co/HT. The characterization and reactivity results suggest that the thermal stability properties of hydrotalcite, BET surface area, particle size of Co, the interaction between Co and the support, and the reducibility of Co were all important in governing the catalytic performance of the Co catalysts for CO hydrogenation. Our study suggests that HT is a promising support for Co for Fischer–Tropsch synthesis because it gives high activity (higher than Co/Al2O3) without the need for a reduction promoter.
Keywords: Fischer–Tropsch synthesis; CO hydrogenation; Co catalysts; Hydrotalcite; MgO; Al2O3;
Catalytic oxygenation of dibenzothiophenes to sulfones based on FeIII porphyrin complex by Xinrui Zhou; Shuang Lv; Hui Wang; Xiuna Wang; Jihong Liu (101-106).
Display Omitted► FeIII porphyrins are particularly active in the oxygenation of dibenzothiophenes. ► These aerobic catalytic oxidations occur in non-polar hydrocarbons. ► The parameters influencing the stability of the porphyrin catalyst were studied. ► A mechanism involving a two-step process has been proposed.FeIII porphyrin complexes as biomimetic catalysts display remarkable activity in the oxidation of dibenzothiophenes (DBTs) to the corresponding sulfones, in the absence of co-reductants or sacrificial agents, for deep desulfurization. The influence of the reaction conditions on the catalytic oxygenation was investigated. UV–vis spectra of FeIII porphyrin complexes under various reaction conditions revealed that temperature was a vital factor for the catalyst's lifetime. However, catalyst decomposition was not caused by thermal self-destruction but by oxygenation at high temperatures. The FeIII porphyrin complex was decomposed partly during the oxygenation, which was retarded by adding carbazole (CAR) to the reaction medium. FeIII porphyrins, substituted with electron-withdrawing groups (–Cl), showed higher efficiency than electron-donating groups (–OH). Radical scavenging experiments demonstrated that the oxygenation catalyzed by the FeIII porphyrin complex was not a free-radical reaction. Based upon the DBTs’ concentrations, obtained by gas chromatography, the catalytic oxygenation can be treated kinetically as a first-order reaction. Finally, a mechanism involving a two-step nucleophilic addition was proposed for the oxygenation.
Keywords: Iron tetra-(2-chlorophenyl) porphyrin chloride; Oxygenation; Dibenzothiophene;
Ethylbenzene dehydrogenation over Mg3Fe0.5−x Co x Al0.5 catalysts derived from hydrotalcites: Comparison with Mg3Fe0.5−y Ni y Al0.5 catalysts by Luqman A. Atanda; Rabindran J. Balasamy; Alam Khurshid; Ali A.S. Al-Ali; Kunimasa Sagata; Makiko Asamoto; Hidenori Yahiro; Kiyoshi Nomura; Tsuneji Sano; Katsuomi Takehira; Sulaiman S. Al-Khattaf (107-115).
Display Omitted► Styrene production by ethylbenzene dehydrogenation. ► Mg3Fe0.25Co0.25Al0.5 catalyst derived from hydrotalcites. ► Fe3+–Co2+ (1/1) active species.► Comparison with Mg3Fe0.25Ni0.25Al0.5 catalyst. ► Synergy observed on Mg3Fe0.25Co0.25Al0.5 catalyst.A series of Mg3Fe0.5−x Co x Al0.5 (x = 0–0.5) catalysts were prepared from hydrotalcite precursors and their activities in the dehydrogenation of ethylbenzene were compared with those of a series of Mg3Fe0.5−y Ni y Al0.5 (y = 0–0.5) catalysts also derived from hydrotalcite. The hydrotalcites prepared by co-precipitation were calcined at 550 °C to the mixed oxides with a high surface area of 150 – 240 m 2 g cat − 1 ; they were composed of Mg(Fe,Me,Al)O periclase and Mg(Me)(Fe,Al)2O4 spinel (Me = Co or Ni). Bimetallic Fe3+–Co2+ system showed a synergy, i.e., an increase in the activity, whereas Fe3+–Ni2+ bimetallic system showed no synergy. The high styrene yield was obtained on Mg3Fe0.1Co0.4Al0.5; however, a large substitution of Fe3+ with Co2+ caused a decrease in styrene selectivity along with coking on the catalysts, due to an isolation of CoO x on the catalyst surface. The highest yield as well as the highest selectivity for styrene production was obtained at x = 0.25 at time on stream of 30 min. The coprecipitation at pH = 10.0 and the composition of Mg3Fe0.25Co0.25Al0.5 were the best for preparing the active catalyst. This is partly due to the formation of a good hydrotalcite structure. On this catalyst, the active Fe3+ species was reduced at a low temperature by the Fe3+–Co2+ bimetal formation, leading to a high activity. Simultaneously, the amount of reducible Fe3+ was the smallest, resulting in a high stability of the active Fe3+ species. It is likely that the dehydrogenation was catalyzed by the reduction–oxidation between Fe3+ and Fe2+ and that Co2+ assisted the reduction–oxidation by forming Fe3+–Co2+ (1/1) bimetallic active species.
Keywords: Ethylbenzene dehydrogenation; Styrene; Mg3Fe0.25Co0.25Al0.5 catalyst; Fe3+–Co2+ active species; Hydrotalcite;
Fischer–Tropsch synthesis over one eggshell-type Co/SiO2 catalyst in a slurry phase reactor by Chun Chen; Hisashi Yuuda; Xiaohong Li (116-122).
Display Omitted► Eggshell Co/SiO2 catalyst was prepared by spray method. ► Cobalt was deposited on the external surface of silica gel in the eggshell catalyst. ► The catalyst was conducted FT synthesis in a slurry phase reactor. ► The high TOF value of eggshell catalyst indicated good performance of FT synthesis.The eggshell type cobalt catalyst (Co/SiO2) was prepared via a spray method. Characterization of surface information between cobalt and the support of silica gel was obtained by SEM and EPMA techniques. The discrete cobalt particle sizes were calculated based on XRD analysis. The prepared eggshell Co/SiO2 catalysts were investigated for Fischer–Tropsch (FT) synthesis in a slurry-phase reactor and compared with conventional impregnated catalyst under the conditions of P = 1.0 MPa, T = 503 K, W/F = 5.0 g-cat h/mol and H2/CO = 2. Results indicated that eggshell Co/SiO2 catalyst was inclined to generate long chain hydrocarbons and had relatively low CH4 selectivity. The parameters that respond to the performance of FT synthesis had been upgraded when compared with those of a conventional impregnated catalyst. In generated hydrocarbons for 1800 μm supported catalyst, CH4 selectivity decreased from 22.98% to 9.68%, and C5+ selectivity increased from 61.66% to 79.45%. Meanwhile, the chain growth probabilities (α) also increased from 0.84 to 0.90. According to H2-chemisorption and space-time yield (STY), the turnover frequency (TOF) of each catalyst was calculated. The higher TOF value of eggshell catalyst means better FT synthesis performance than is available using conventional impregnated catalyst.
Keywords: Eggshell; Cobalt; Spray method; Fischer–Tropsch synthesis;
Syntheses and characterizations of cobalt doped mesoporous alumina prepared using natural rubber latex as template and its catalytic oxidation of tetralin to tetralone by Yongping Ma; Muling Zeng; Jiao He; Lina Duan; Jianfei Wang; Junjie Li; Jiaqiang Wang (123-128).
Display Omitted► Natural rubber latex templated cobalt doped mesoporous alumina. ► High activity for the oxidation of tetralin to 1-tetralone. ► Heterogeneous catalyst can be used several times without losing its activity. ► A new method for the syntheses of mesoporous alumina.Natural rubber latex, one of the most important biosynthesized polymers, was successfully used as template in the syntheses of cobalt doped mesoporous alumina. The synthesized cobalt doped mesoporous alumina was characterized by a combination of various physicochemical techniques; N2 adsorption/desorption, diffuse reflectance UV–vis, X-ray diffraction and FT-IR. It was used as an efficient catalyst for the oxidation of tetralin to 1-tetralone under mild conditions for the first time. The catalyst exhibited high substrate conversion (80.3%) and good product (1-tetralone) selectivity (74.5%). Fast hot catalyst filtration experiments proved that the catalyst acted as a heterogeneous one; it can be reused three times without losing its activity. By contrast, undoped alumina synthesized using rubber latex as template, cobalt-doped alumina synthesized by a using traditional chemical template: poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (P123) as template, and cobalt-doped mesoporous silica synthesized by using natural rubber latex as template exhibited much lower activities.
Keywords: Cobalt doped mesoporous alumina; Natural rubber latex template; Oxidation of tetralin; 1-Tetralone;
Liquid-phase dehydration of 1-octanol, 1-hexanol and 1-pentanol to linear symmetrical ethers over ion exchange resins by C. Casas; R. Bringué; E. Ramírez; M. Iborra; J. Tejero (129-139).
Display Omitted► Dehydration of 1-octanol, 1-hexanol and 1-pentanol over ion exchange resins. ► Synthesis of di-n-octyl ether, di-n-hexyl ether and di-n-pentyl ether. ► Polystyrene di-vinyl benzene microporous and macroporous resins. ► Effect of polymer density distribution of resins on alcohol dehydration.Dehydration of 1-octanol, 1-hexanol and 1-pentanol to di-n-octyl ether (DNOE), di-n-hexyl ether (DNHE) and di-n-pentyl ether (DNPE), respectively, has been studied in the liquid phase at 423K in a batch reactor on ion exchange resins as catalysts. Tested catalysts were the macroporous resins Amberlyst 15, Amberlyst 35, CT175, CT275 and CT276 (high crosslinking degree); Amberlyst 16, Amberlyst 36 and CT252 (medium crosslinking degree); Amberlyst 39 and Amberlyst 70 (low crosslinking degree), and the gel type ones CT224, Amberlyst 31, Amberlyst 121 and Dowex 50Wx4-50. Amberlyst 46, an ion-exchange resin sulfonated only at the polymer surface and Nafion NR50 were also tested for comparison purposes. Data show that the yield of linear symmetrical ethers (DNOE, DNHE and DNPE) highly depends on the resin structure so that best results are obtained on Amberlyst 121, Amberlyst 31 and Dowex 50Wx4-50 (the most swollen resins in reaction medium). The high ether yields are due both to the high alcohol conversions and especially to the very high selectivity to ethers (≥94%) shown by that resins. Finally, by comparing initial reaction rates of ether formation with those obtained on Amberlyst 46 an estimation of the fraction of sulfonic groups that take part in the reaction is given.
Keywords: Alcohol dehydration; Di-n-octyl ether (DNOE); Di-n-hexyl ether (DNHE); Di-n-pentyl ether (DNPE); Ion-exchange resin catalysts;
Performance of γ-Ga2O3-Al2O3 solid solutions prepared by spray pyrolysis for CH4-SCR of NO by Tsunenori Watanabe; Yoshihisa Miki; Takeo Masuda; Hiroyoshi Kanai; Saburo Hosokawa; Kenji Wada; Masashi Inoue (140-147).
Display Omitted► Precursor particles for γ-Ga2O3-Al2O3 solid solutions were prepared by spray pyrolysis. ► An adequate temperature in ovens and residence time for the mists in spray pyrolysis were required. ► The concentration of HNO3 or of metal nitrates in the starting solution affected the performance.Precursor particles for γ-Ga2O3-Al2O3 solid solutions were prepared by spray pyrolysis of aqueous solutions of mixtures of Ga(NO3)3, Al(NO3)3, and HNO3, and the performance of the γ-Ga2O3-Al2O3 solid solutions obtained by calcination thereof at 800 °C was investigated for the selective catalytic reduction of NO with methane as a reducing agent. The precursor prepared with a temperature gradient from 200 to 700 °C and with a total residence time of 23 s in the ovens had a high performance. The concentration of HNO3 or of metal nitrates affected the performance. The precursor prepared from Al(NO3)3 or Al(acac)3 as an aluminum source exhibited high performance; however, the precursor prepared from pseudoboehmite resulted in a lower activity.
Keywords: Selective catalytic reduction; NO x ; γ-Ga2O3-Al2O3; Solid solution; Spray pyrolysis;
Enantioselective hydrogenation of dimethyl itaconate with immobilised rhodium-duphos complex in a recirculating fixed-bed reactor by M.A. Al Herz; A.N. Tsoligkas; M.J.H. Simmons; J. Wood (148-158).
.Display Omitted► Selectivity of dimethyl itaconate hydrogenation assessed in a trickle bed reactor. ► Osborn–Wilkinson kinetics showed complexation before reaction with hydrogen. ► Using trilobe alumina support gave high enantioselectivities in the TBR. ► Changing hydrodynamics affected both reaction rate and enantioselectivity.The catalytic hydrogenation of dimethyl itaconate was studied in lab-scale shake flask and transferred to continuous flow with recirculation in a trickle bed reactor. All experiments were performed under ambient conditions (20 °C and atmospheric pressure). The catalyst complex [Rh((R,R)-Me-DuPhos)(COD)]BF4 was anchored to powder and trilobe alumina supports using phosphotungstic acid (PTA) as an anchoring agent. For the powder alumina, tests were conducted in the shake flask to ensure that the reaction was not influenced by mass transfer limitations by varying the stirrer speed and catalyst mass, thus ensuring the reported data are in the kinetic regime. In the shake-flask [substrate to catalyst molar ratio of 60, atmospheric pressure (101,317 Pa), room temperature (293.15 K), H2 flow rate of 100 ml min−1 (1.7 × 10−6 m3 s−1) and agitation speed of 200 rpm], a turnover frequency (TOF) of 50 h−1 (1.4 × 10−2 s−1) was achieved with powder alumina support in comparison to a TOF of 20 h−1 (5.6 × 10−3 s−1) obtained with the trilobes. Under these conditions, the enantioselectivities obtained from immobilising the catalyst complex onto the powder and trilobe supports were 96% and 97%, respectively. Fitting Osborn–Wilkinson kinetics to the concentration profiles indicated that complexation with the olefin before reaction with hydrogen was the preferred path. The trickle bed reactor (TBR) was operated in the trickle flow regime using the trilobe support. Optimal gas and liquid flow rates were selected which were found to have a noticeable effect on initial reaction rate and enantioselectivity. Under optimized conditions in the TBR [substrate to catalyst molar ratio of 223, atmospheric pressure (101,317 Pa), room temperature (293.15 K), gas flow rate of 100 ml min−1 (1.7 × 10−6 m3 s−1) and liquid flow rate of 20 ml min−1 (3.3 × 10−7 m3 s−1)], 99% conversion and enantioselectivity of up to 99.9% were achieved.
Keywords: Anchored homogeneous catalyst; [Rh ((R,R)-Me-DuPhos)(COD)]BF4; Dimethyl itaconate hydrogenation; Shake-flask reactor; Trickle bed reactor;
Monodispersed and nanostructrured Ni/SiO2 catalyst and its activity for non oxidative methane activation by Silvia. F. Moya; Ruth L. Martins; Martin Schmal (159-169).
.Display Omitted► Preparation of NiB/SiO2 and Ni-O x /SiO2 for non oxidative methane activation. ► Chemisorption of CH4 in the temperature range 473–773 K, followed by hydrogenation. ► Ni-O x /SiO2 evidenced great ability for methane coupling in chemisorption to C2. ► XPS and TEM results evidence metallic Ni particles of 3.5 nm at surface.In this paper, we prepared nickel nanoparticles for the non oxidative methane activation. A nickel acetate solution was impregnated on silica support and then reduced with NaBH4 (NiB/SiO2) exhibiting only small metallic Ni0 particles of the order of 15 nm. Part of this solid was then oxidized under mild conditions, where Ni ions were re-structured and redistributed as a Ni-O x /SiO2 oxide solid that after reduction with hydrogen favored the formation of smaller Ni particles. XPS spectra of the Ni-O x /SiO2 sample before the reduction showed that NiO is the predominant species at the surface and after reduction it indicates the presence of small metallic nickel particles at the surface interacting with the SiO2 support. XRD and DRIFTS results confirm the structural interaction of metal-support after the mild oxidation and TEM images indicate small particles of the order of 3.5 nm and surface defects. The non oxidative methane activation evidenced significant formation of methane coupling products over the Ni-O x /SiO2 catalyst during methane chemisorption. Chemisorption of methane on the NiB/SiO2 showed ethane formation only. The temperature programmed surface hydrogenation (TPSH) results suggested the formation of carbidic species at lower temperatures of adsorption.
Keywords: Nickel nanostructure; Methane activation; Boron; Non oxidative process;
Hept-1-yne partial hydrogenation reaction over supported Pd and W catalysts by Cecilia R. Lederhos; M. Juliana Maccarrone; Juan M. Badano; Gerardo Torres; Fernando Coloma-Pascual; Juan C. Yori; Mónica E. Quiroga (170-176).
Display Omitted► Cheaper catalysts based in low Pd and W loading were prepared. ► Low-loaded palladium catalyst showed high selectivity but was the least active. ► Tungsten catalyst proved to be an active but low selective catalytic system. ► Bimetallic catalysts PdW or WPd were more active than classical Lindlar catalyst. ► Bimetallic WPd reduced at 393 K had the highest activity and selectivity values.In order to increase the production of olefins the partial hydrogenation of alkynes has achieved industrial importance. In this sense catalysts with selective hydrogenation properties may be of potential interest. In this work mono and bimetallic Pd and W catalysts supported on γ-alumina with low metal content (2.4% W and 0.4% Pd) were prepared. XPS, XRD, TPR and hydrogen chemisorption techniques were used for the characterization. The effect of metallic precursor incorporation order and of the reduction temperature, on the activity and selectivity for the partial hydrogenation of hept-1-yne at mild reaction conditions, were evaluated.Low-loaded palladium monometallic catalyst showed a high selectivity but it was the least active. Moreover, bimetallic catalysts proved to be more active than the classical Lindlar catalyst. The addition of Pd to the W/γ-Al2O3 catalyst greatly improved the total conversion and the selectivity to the desired product. XPS results suggest electronic effects between Pd and W metals. The bimetallic W-Pd catalyst treated in hydrogen at low temperature conditions (393 K) showed the highest activity and selectivity values.
Keywords: Bimetallic catalysts; Palladium; Tungsten; Selective hydrogenation; Hept-1-yne; Lindlar;
Investigating the performance and deactivation behaviour of silica-supported copper catalysts in glycerol hydrogenolysis by E.S. Vasiliadou; A.A. Lemonidou (177-185).
Display Omitted► Cu is associated with high selectivity to propylene glycol. ► Silica type used affects copper dispersion and hence the active copper metal area. ► Increased activity and selectivity are obtained over 20 wt%Cu/HMS catalyst. ► TOF increases as the d Cu decreases providing evidence of structure sensitivity. ► Cu on mesoporous silica showed deactivation caused by various factors examined.Selective hydrogenolysis of glycerol to propylene glycol was performed over monometallic (5 and 20 wt%Cu) and a bimetallic (5 wt%Ru–Cu) catalyst. The catalytic materials used, were supported on commercial silica and synthesized hexagonal mesoporous silica (HMS). The catalysts (fresh and used) were characterized employing XRD, ICP, BET surface area, N2O chemisorption, TEM, TGA and TPR techniques. The performance of 5 wt%Cu monometallic catalysts is characterized by high propylene glycol selectivity (>90%) and relatively low activity. Increase of Cu loading to 20 wt% results in satisfactory activity. At 240 °C and 8 MPa hydrogen pressure, the 20 wt%Cu/HMS catalyst exhibits 43% glycerol conversion along with 91% propylene glycol selectivity and TOF 148 h−1. The bimetallic Ru–Cu catalyst supported on silica combines both good selectivity and activity providing evidence for synergetic effect between the two metals. Silica type (commercial or mesoporous) affects mainly the dispersion and hence the active copper metal area with the HMS supported monometallic catalysts exhibiting higher activity than those supported on commercial silica. Present results indicate that glycerol hydrogenolysis over Cu catalysts is a structure sensitive reaction. Partial loss of activity in consecutive glycerol hydrogenolysis tests was observed with the best performing 20 wt%Cu/HMS catalyst. Based on characterization results of the reused catalyst, the deactivation was attributed to a number a factors like partial collapse of the mesoporous network, agglomeration of the active metallic phase, presence adsorbed species on the catalytic surface and/or formation of coke during the reaction. No indication of Cu leaching to the liquid phase was provided.
Keywords: Glycerol hydrogenolysis; Cu catalysts; Ru–Cu catalysts; Deactivation; HMS support;
Hydrogenation of aniline to cyclohexylamine in supercritical carbon dioxide: Significance of phase behaviour by M. Chatterjee; M. Sato; H. Kawanami; T. Ishizaka; T. Yokoyama; T. Suzuki (186-193).
Display Omitted► An example of tunability, the most claimed advantage of scCO2. ► High conversion and exceptionally high selectivity of cyclohexylamine. ► Phase behaviour has strong impact on the activity and selectivity. ► Temperature played a complex role to achieve high selectivity of the product.Hydrogenation of aniline to cyclohexylamine was carried out in supercritical carbon dioxide using a variety of noble metal (Pt, Pd and Rh) catalysts. At 80 °C and 8 MPa of CO2 pressure, >95% of aniline conversion with 93% selectivity to cyclohexylamine was achieved on 5% Rh/Al2O3. A strong influence of phase behaviour related to the CO2 pressure was found on the conversion and selectivity. Optimization of reaction parameters resulted in a higher overall activity in the biphase (liquid substrate + gaseous H2 and CO2) than in the single phase (liquid substrate–CO2–H2) condition. It has been found that the interaction of CO2 with amine leads to the formation of solid carbamic acid, which enhanced the selectivity of cyclohexylamine, but reduced the conversion significantly. Furthermore, reaction temperature played a crucial role in preventing the formation of carbamic acid and also maintained a reasonably high reaction performance in terms of conversion and selectivity.
Keywords: Supercritical carbon dioxide; Phase behaviour; Heterogeneous catalysis; Hydrogenation; Aniline; Cyclohexylamine;
Efficient and selective conversion of methyl lactate to acrylic acid using Ca3(PO4)2–Ca2(P2O7) composite catalysts by Ju Hyeong Hong; Jong-Min Lee; Hyungrok Kim; Young Kyu Hwang; Jong-San Chang; Shiva B. Halligudi; Yo-Han Han (194-200).
Display Omitted► Ca3(PO4)2–Ca2(P2O7) [50–50 wt%] was an efficient catalyst in methyl lactate (ML) conversion. ► ML conversion (91%) resulted in the highest selectivity (80%) for acrylic acid (AA) and methyl acrylate (MA). ► Catalysts of moderate acid–base strength gave higher conversions and product selectivities.Calcium phosphate Ca3(PO4)2 and calcium pyrophosphate Ca2(P2O7) composite catalysts of different weight ratios were prepared by a slurry-mixing method. These composite catalysts were calcined at 500 °C in air and characterized by N2 sorption for specific surface area by XRD for crystal phases and by TPD-NH3 (acidity), TPD-CO2 (basicity) and SEM for morphological features. All the Ca3(PO4)2–Ca2(P2O7) composite catalysts were found to be active in the vapor phase conversion of methyl lactate (ML) to give mainly acrylic acid (AA) and methyl acrylate (MA) as products. The catalyst Ca3(PO4)2–Ca2(P2O7) of 50:50 wt% ratio was the most efficient and selective catalyst in the conversion of ML, which gave 91% conversion of ML with selectivity for AA (75%) and MA (5%) together (80%) under optimized reaction conditions. The higher conversion of ML and formation of AA by Ca3(PO4)2–Ca2(P2O7) [50:50 wt%] composite catalyst has been attributed to moderate acid–base strength regulated with surface properties.
Keywords: Methyl lactate; Acrylic acid; Methyl acrylate; Ca3(PO4)2; Ca2(P2O7);