Applied Catalysis A, General (v.349, #1-2)
Editorial Board (CO2).
Polyvalent-metal salts of heteropolyacid as catalyst for Friedel-Crafts alkylation reactions by Ken-ichi Shimizu; Kenjiro Niimi; Atsushi Satsuma (1-5).
Polyvalent transition metal salts of dodecatungstophosphate act as highly effective and recyclable heterogeneous catalysts for Friedel-Crafts alkylation with secondary alcohols and an alkene (cyclohexene). For Sn3/4PW12O40 as the most active catalyst, acetonitrile-temperature-programmed desorption (TPD) experiments show the relationship between the Lewis acidity and the catalytic activity.▪Dodecatungstophosphoric acid (HPW) and its metal salts (MPW) were tested for Friedel-Crafts alkylation of aromatics with alcohols and cyclohexene. The activity increased with the electronegativity of the cation. Sn4+ and Hf4+ salts (SnPW and HfPW) were among the most effective catalysts for alkylation of toluene with iso-propanol and cyclohexene. SnPW showed higher activity than the starting materials (HPW, SnCl4·6H2O) and Sc(OTf)3, and can be recycled without a marked loss in the activity. Temperature programmed desorption of acetonitrile showed the presence of Lewis acid due to Sn4+ cation in SnPW. The rate for the toluene alkylation with cyclohexene and the number of Lewis acid sites decreased when the number of water adsorbed on SnPW decreased with an increase in the dehydration temperature. The rate correlates well with the number of Lewis acid, indicating that Lewis acid site originated from the Sn4+ cation is responsible for the alkylation reaction.
Keywords: Friedel-Crafts alkylation; Solid acid; Lewis acid; Polyoxometalates;
Determining an optimum catalyst for liquid-phase dehydration of methanol to dimethyl ether by Nahid Khandan; Mohammad Kazemeini; Mahmoud Aghaziarati (6-12).
The liquid-phase dehydration of methanol to dimethyl ether was investigated. The results showed that the Mordenite zeolite exchanged with H+ exhibited the highest activity in dehydration of methanol. Ultimately, amongst all catalysts studied, Al-modified Mordenite zeolite exhibited optimum activity, selectivity and stability for methanol dehydration to dimethyl ether. ▪The liquid-phase dehydration of methanol to dimethyl ether was investigated over various materials including synthetic zeolites, namely, ZSM-5, Y, Mordenite, Ferrierite and Beta as well as silica and alumina. The key characters investigated were the Si/Al ratio and cation exchange. The results showed that the Mordenite zeolite exchanged with H+ exhibited the highest activity in dehydration of methanol. After finding the most active catalyst, the Mordenite zeolite was modified with Cu, Zn, Ni, Al, Zr, Mg and Na via wet-impregnation method to further improve its selectivity, and characterized by AAS, XRD, NH3-TPD, NH3-FT-IR and BET surface area techniques. It was found that these materials affected activity of HM zeolite by changing its acidity. Ultimately, amongst all catalysts studied, Al-modified Mordenite zeolite exhibited optimum activity, selectivity and stability for methanol dehydration to dimethyl ether.
Keywords: Dehydration; Methanol; Dimethyl ether; Zeolite; Mordenite;
High temperature stable mesoporous anatase TiO2 photocatalyst achieved by silica addition by P. Periyat; K.V. Baiju; P. Mukundan; P.K. Pillai; K.G.K. Warrier (13-19).
An aqueous sol–gel method was developed to synthesize the high temperature stable mesoporous anatase titania photocatalyst by doping with silica. Fully anatase phase was obtained at 900 and 1000 °C by the addition of 15 mol% silica. The photocatalytic study showed that 15 mol% sample calcined at 800 °C has a rate constant of 0.084 min−1, whereas the undoped sample shows only 0.022 min−1. ▪An aqueous sol–gel method was developed to synthesize a high temperature stable anatase titania photocatalyst by doping with silica. Doping was achieved in titania by the addition of silica sol prepared from tetra ethyl orthosilicate (TEOS). 1, 2, 5 and 15 mol% silica–titania mixed oxide were prepared and characterised by X-ray diffraction, Raman spectroscopy, surface area analysis and diffuse reflectance spectra. Fully anatase phase was obtained at 1000 °C by the addition of 15 mol% silica. The 15Si–Ti (15 denotes mol% of silica) had a specific surface area of 187.3 m2/g at 500 °C and it retains a value of 93.0 m2/g at 800 °C, whereas the undoped one shows 48.7 m2/g at 500 °C and zero value at 800 °C. Moreover, the 15Si–Ti composition retains the pore diameter in the mesoporous range (4.6 nm) at this high temperature of 800 °C. The photocatalytic analysis showed that the system with silica added possessed a higher activity than pure titania. The 15Si–Ti sample calcined at 800 °C decolourised the methylene blue dye within 30 min (rate constant 0.084 min−1), whereas the undoped sample decolourised the dye after 180 min (rate constant 0.018 min−1). The present method of preparation offers the advantages of inexpensive precursor, homogeneous distribution of the dopant over titania at nano-level and enables control over the powder characteristics of titania.
Keywords: Titania; Silica; Sol–gel; Anatase; Photocatalyst;
Copper-supported pillared clay catalysts for the wet hydrogen peroxide catalytic oxidation of model pollutant tyrosol by R. Ben Achma; A. Ghorbel; A. Dafinov; F. Medina (20-28).
The catalytic wet hydrogen peroxide oxidation of tyrosol, a major compound of the polyphenolic fraction present in olive oil mill wastewaters, was studied in batch and continuous reactors using copper-supported pillared clay catalysts under mild conditions. The catalysts were prepared by the solid-state reaction of Al-pillared clay synthesized with copper nitrate. The resultant materials were then calcined at 300 °C for 3 h under helium or oxygen. The catalytic activity of Cu-supported pillared clays was found to depend on the calcination method. The effects of several operating conditions were also studied. Our experimental results indicate that, under mild conditions and a stoichiometric amount of oxidant, the calcined material under helium (CuNHe catalyst) showed higher activity and stability (TOC abatement of roughly 80% and total elimination of tyrosol after 1 h reaction, without significant leaching of copper ions) than the calcined material under oxygen (CuNOxy). To better understand the catalytic behaviour of copper-supported pillared clay solids, fresh and used catalysts were characterized by X-ray diffraction, nitrogen adsorption, chemical analysis, temperature-programmed reduction (TPR), UV–visible diffuse reflectance spectroscopy, and transmission electron microscopy (TEM).A new and simple method to prepare Cu-pillared clays is described. These materials are active and stable catalysts, at mild reaction conditions, for catalytic wet hydrogen peroxide oxidation of organic compounds like tyrosol in aqueous solutions. These catalysts result in a promising alternative to the Fenton homogeneous system without significant catalyst leaching and deactivation.▪
Keywords: Copper; Pillared clay; Wet hydrogen peroxide catalytic oxidation; 2-(4-Hydroxyphenyl)ethanol;
Assessment of dominant factors affecting liquid phase hydroisomerization on bifunctional zeolites by A. Fúnez; J.W. Thybaut; G.B. Marin; P. Sánchez; A. De Lucas; J.L. Valverde (29-39).
Liquid phase n-octane hydroisomerization was investigated over a series of zeolites containing 1 wt% Pt. PtBETA was the most active catalyst followed by PtMOR and PtUSY. The isomer yields on PtMOR were somewhat lower than on PtBETA and PtUSY. A kinetic model fitted adequately the experimental data on PtBETA and PtUSY, while more dispersion was observed with catalyst PtMOR. These modelling results were related to pore sizes and geometry and average acid strength.▪The hydroisomerization of n-octane in the liquid phase was investigated over beta, USY and mordenite zeolites loaded with 1 wt% Pt in a stirred semi-batch microautoclave. The total pressure ranged form 5 to 9 MPa and the temperature from 523 to 563 K with an initial catalyst/n-octane ratio of 7 g catalyst /mo l n - C 8 . PtBETA was the most active catalyst at all operating conditions, followed by PtMOR and PtUSY. The isomer yields on PtMOR were somewhat lower than on PtBETA and PtUSY. Increasing the total pressure always resulted in a decrease in the n-octane conversion, which is indicative of so-called ideal hydroisomerization. The n-octane hydroisomerization experiments were simulated with a kinetic model based on a parallel/consecutive reaction scheme involving reversible mono- and multibranching and irreversible cracking from mono- as well as multibranched isomers. The model fitted adequately the experimental data on PtBETA and PtUSY. However, more dispersion was observed with catalyst PtMOR. The ratio of the composite rate coefficients for cracking to that for monobranching was significantly higher on PtMOR than on PtUSY and PtBETA. The composite activation energy for monobranching was 20 kJ mol−1 higher on USY if compared to that of mordenite and beta. These modelling results were related to pore sizes and geometry and average acid strength.
Keywords: n-Octane; Hydroisomerization; Liquid phase conditions; Experimental investigation; Kinetic model; Zeolite; USY; Beta; Mordenite;
Selective heterogeneous catalytic hydrogenation of nitriles to primary amines in liquid phase by László Hegedűs; Tibor Máthé; Tamás Kárpáti (40-45).
Benzyl cyanide (BC) was hydrogenated to 2-phenylethylamine (PEA) under mild reaction conditions (40 °C, 6 bar), over a carbon supported palladium catalyst, in a mixture of two immiscible solvents (e.g. water/dichloromethane) and in the presence of an acidic additive (e.g. NaH2PO4). The effects of amount and type of the acidic additives, solvents, catalyst/substrate ratio on the selectivity to PEA, as well as on the conversion and the rate of the hydrogenation of BC were discussed. ▪A method for selective liquid-phase heterogeneous catalytic hydrogenation of nitriles to primary amines has been developed. Benzyl cyanide (BC) was hydrogenated under mild reaction conditions (40 °C, 6 bar), over a carbon supported palladium catalyst, in a mixture of two immiscible solvents (e.g. water/dichloromethane) and in the presence of an acidic additive (e.g. NaH2PO4). Complete conversion, but lower isolated yield (40%) and selectivity (45%) to primary amine could be achieved by using this process than in the hydrogenation of benzonitrile (BN) reported previously. A comparison concerning the reactivities and adsorption abilities of these substrates (BC and BN) was also made.
Keywords: Palladium; Benzyl cyanide; Selective hydrogenation; Primary amine;
The effect of platinum in Cu-Ce-Zr and Cu-Zn-Al mixed oxide catalysts for water–gas shift by Florian Huber; John Walmsley; Hilde Venvik; Anders Holmen (46-54).
Pt was wet-impregnated on Cu-Ce-Zr and Cu-Zn-Al mixed oxide catalysts prepared by homogeneous co-precipitation with urea. Low-temperature WGS activity of Cu-Ce-Zr and Cu-Zn-Al mixed oxides correlates with low-temperature Cu reducibility. Pt had little effect on Cu-Ce-Zr. Pt addition shifted the Cu reduction to lower temperatures of Cu-Zn-Al, indicating interaction between Pt and Cu. The effect on WGS activity and stability depended on pre-treatment and reaction conditions. ▪Cu-Ce-Zr and Cu-Zn-Al mixed oxide catalysts were prepared by homogeneous co-precipitation with urea. Pt was wet-impregnated on the mixed oxide catalysts. The WGS activity of Cu-Ce-Zr and Cu-Zn-Al mixed oxide catalysts can be related to the Cu reducibility in these catalysts. Low-temperature reducibility correlates with low-temperature activity. Pre-reduction is not absolutely necessary when performing the WGS reaction above the Cu reduction temperature of the catalyst. An adequate reduction procedure may, however, be applied in order to optimize the CO conversion. Pt had no significant effect on the Cu-Ce-Zr mixed oxide catalyst, but altered the properties of the Cu-Zn-Al mixed oxide catalyst. Pt shifted the Cu reduction to lower temperatures, indicating the existence of an interaction between Pt and Cu in the bimetallic catalyst. The effect of Pt on the WGS activity and stability was dependent on the pre-treatment procedure as well as the reaction conditions.
Keywords: Homogeneous alkalinization; Urea; Cu-Ce-Zr; Cu-Zn-Al; Mixed oxide; Bimetallic catalyst; Platinum; Pre-reduction; Cu reducibility; Water–gas shift;
Production of ethanol by vapor phase hydration of ethene over tungsta monolayer catalyst loaded on titania by Naonobu Katada; Yohei Iseki; Akira Shichi; Nobuo Fujita; Iwao Ishino; Kazuhiro Osaki; Tatsuya Torikai; Miki Niwa (55-61).
High catalytic activity and selectivity for vapor phase hydration of ethene (ethylene) into ethanol under practical conditions were observed on a tungsta monolayer loaded on titania. Brønsted acidity generated on the monolayer is suggested to be the origin of such activity. The activity and the selectivity to desired product of tungsta monolayer loaded on titania were comparable to those of a silica-impregnated phosphoric acid catalyst, which has been utilized for a conventional process but has disadvantages from a view of environmental protection. The selectivity was higher than that of a WO3–TiO2 mixed oxide, possibly due to the co-presence of Brønsted and Lewis acid sites.Conversion of ethene (▴), and selectivity of ethanol + diethyl ether (▵) on WO3/TiO2 (support A) calcined at 873 K at W / F = 15 g cat h mo l C 2 H 4 + H 2 O − 1 .▪
Keywords: Ethanol production; Hydration of ethylene; Tungsta monolayer loaded on titania; Solid acid catalyst;
Chromium oxide supported on MCM-41 as a highly active and selective catalyst for dehydrogenation of propane with CO2 by Piotr Michorczyk; Jan Ogonowski; Piotr Kuśtrowski; Lucjan Chmielarz (62-69).
MCM-supported chromium oxide materials with a Cr loading ranging from 0.7 to 13.7 wt% were investigated in the dehydrogenation of propane with CO2. All the tested catalysts exhibited a good catalytic performance. The best results were achieved over the sample containing 6.8 wt% of Cr. In this case, the selectivity to propene was above 80%, while the conversion of propane increased from 21% (at 773 K) to 62% (at 923 K). The promoting effect of CO2 on the yield of propene was found for all the studied catalysts. This effect was discussed on the basis of temperature-programmed reaction of CO2 with H2 as well as H2-TPR experiments after regeneration of the reduced catalyst with pure CO2.▪Incipient wetness technique was used for a preparation of MCM-supported chromium oxide materials with a Cr loading ranging from 0.7 to 13.7 wt%. The obtained samples were characterized by XRD, UV–vis-DRS, H2-TPR and BET, and tested as catalysts in dehydrogenation of propane with CO2. The catalytic reaction was studied in a flow apparatus at 773–923 K. All the tested catalysts exhibited a good catalytic performance in the dehydrogenation of propane with CO2. The best results were achieved over the sample containing 6.8 wt% of Cr. In this case, the selectivity to propene was above 80%, while the conversion of propane increased from 21% (at 773 K) to 62% (at 923 K). The promoting effect of CO2 on the yield of propene was found for all the studied catalysts. This effect was discussed on the basis of temperature-programmed reaction of CO2 with H2 as well as H2-TPR experiments after regeneration of the reduced catalyst with pure CO2. It was suggested that one of reasons of a higher yield of propene observed in the presence of CO2 compared to that measured in the absence of CO2 was coupling of the dehydrogenation of propane with the reverse water–gas shift reaction.
Keywords: Dehydrogenation; CO2; Propene; Chromium oxide catalysts; MCM-41; TPSR of CO2 with H2;
Development of metal cation compound-loaded S-doped TiO2 photocatalysts having a rutile phase under visible light by Teruhisa Ohno; Naoya Murakami; Toshiki Tsubota; Hitoshi Nishimura (70-75).
Rutile S-doped TiO2 loaded with metal ion compounds (Fe3+, Rh3+, Cu2+, Co3+, Ni2+, Cr3+) have been prepared (S-doped TiO2-M n+). The metal ions were adsorbed on the surfaces of S-doped TiO2 nanoparticles. The photocatalytic activities of S-doped TiO2 for oxidation of acetaldehyde in gas phase were drastically improved after adsorbing treatment of metal ions under a wide range of incident light wavelengths.▪We have synthesized S (S4+)-doped TiO2 photocatalysts having a rutile phase. Rutile S-doped TiO2 photocatalysts loaded with metal ion compounds (Fe3+, Rh3+, Cu2+, Co3+, Ni2+, Cr3+) have also been prepared (S-doped TiO2-M n+). The metal ions were adsorbed on the surfaces of S-doped TiO2 nanoparticles by impregnation methods (IM) or photodeposition methods (PH). The photocatalytic activities of S-doped TiO2 for oxidation of acetaldehyde in gas phase were drastically improved after adsorbing treatment of metal ions under a wide range of incident light wavelengths. Under photoirradiation at wavelengths longer than 350 or 420 nm, S-doped TiO2-Cu2+ (PH) shows the highest level of activity among the metal ions. S-doped TiO2-Fe3+ (IM) shows the highest level of activity for oxidation of acetaldehyde in gas phase compared to the activity levels of S-doped TiO2 with loading of other metal ions such as Rh3+, Cu2+ Co3+, Ni2+, and Cr3+ under a wide range of incident light wavelengths. The optimum amount of metal ion compound nanoparticles adsorbed on S-doped TiO2 was 0.1 wt%. In order to elucidate the role of metal ions adsorbed on the surface of S-doped TiO2, we measured the double beam photoacoustic spectra (DB-PA). The amount of Ti3+ generated as a result of the reaction between Ti4+ and photoexcited electrons was analyzed by this spectroscopy. The relationship between the reaction rate of photocatalytic oxidation of acetaldehyde on S-doped TiO2 adsorbed with metal ions and the charge separation between photoexcited electrons and holes is discussed.
Keywords: S-doped TiO2; Loading of metal ions compounds; Degradation of acetaldehyde; Improvement of charge separation;
Product selectivity and catalytic deactivation of MOR zeolites with different acid site densities in methanol-to-olefin (MTO) reactions by Ji Won Park; Sun Jung Kim; Myungeun Seo; Sang Youl Kim; Yoshihiro Sugi; Gon Seo (76-85).
The IR spectra recorded in situ during the MTO reaction over four kinds of MOR zeolites with different Si/Al ratios clearly exhibited some differences in the formation of active intermediates (1465 cm−1) and in the accumulation rate of polycyclic aromatic hydrocarbons (1570 cm−1) in pores according to their acid site density. ▪The effects of the acid site densities of MOR zeolites on their product selectivity and deactivation were investigated in the methanol-to-olefin (MTO) reactions. The MOR zeolites showed a high conversion and high yield of the lower olefins at the initial time of the MTO reaction, regardless of their acid site density. However, the conversion and the yield of the lower olefins over them rapidly decreased in the order of MOR(103) < MOR(55) < MOR(12) < MOR(5), where the numbers in parenthesis represent their Si/Al ratios. The materials occluded on the MOR zeolites during the MTO reaction were investigated by the IR, 13C NMR and UV–vis spectroscopic methods. A large amount of polycyclic aromatic hydrocarbons (PAHs) with 3–4 fused aromatic rings was occluded on the MOR(5) zeolite with the highest acid site density. However, alkylbenzenes and alkylnaphthalenes were the major components of the materials occluded on the MOR(103) zeolite with the lowest acid site density. The IR spectra recorded in situ during the MTO reaction over the MOR zeolites clearly exhibited the differences in the accumulation rates of PAH on their pores according to the acid site density. The rapid accumulation of PAH on the MOR zeolites with high acid site densities leads to the loss of the active alkylbenzene intermediates as well as to the blockage of the pores, resulting in their rapid deactivation. The sparse distribution of acid sites in the pores of the MOR zeolites suppresses the condensation of alkylbenzenes in their pores and lengthens their catalyst lifetime.
Keywords: Methanol to olefin (MTO); MOR zeolite; Acid site density; Deactivation;
Selective oxidation of alcohols to aldehydes and ketones over TiO2-supported gold nanoparticles in supercritical carbon dioxide with molecular oxygen by Xueguang Wang; Hajime Kawanami; Sudhir E. Dapurkar; Natarajan S. Venkataramanan; Maya Chatterjee; Toshirou Yokoyama; Yutaka Ikushima (86-90).
Selective oxidation of alcohols to aldehydes or ketones has been investigated over nano Au catalysts using molecular oxygen in supercritical carbon dioxide (scCO2). TiO2-supported nano Au catalysts prepared by a deposition–precipitation method show unprecedented catalytic performance for selective oxidation of alcohols compared to the other Au catalysts reported so far. The results show that the selective oxidation of benzyl alcohol to benzaldehyde in scCO2 could be accomplished with a high conversion of 97% and a selectivity of 95% at 70 °C in the presence of TiO2-supported nano Au catalyst. Carbon dioxide (CO2) medium enhances the oxidation of benzyl alcohol to benzaldehyde, and inhibits the ester formation and the over-oxidation of aldehyde to the corresponding acid. The oxidation of various alcohols has also been examined and related aldehydes were obtained with good yields and selectivities.TiO2-supported nano Au (2.7 ± 0.8 nm) catalyst has been developed by a deposition–precipitation method. Our catalyst shows unprecedented catalytic performance for the oxidation of variety of alcohols with molecular oxygen in scCO2 at a low temperature of 70 °C with a good yield and a high selectivity of aldehydes.▪
Keywords: Selective oxidation; Alcohol; Aldehyde; Gold catalyst; Supercritical carbon dioxide;
Highly active and selective copper-containing HMS catalyst in the hydrogenation of dimethyl oxalate to ethylene glycol by Anyuan Yin; Xiuying Guo; Wei-Lin Dai; Hexing Li; Kangnian Fan (91-99).
Copper-containing mesoporous silica HMS catalysts prepared by an impregnation method exhibit excellent activity (100% conversion) and selectivity (>92%) in the selective hydrogenation of dimethyl oxalate (DMO) to ethylene glycol (EG) under mild condition of a reaction temperature of 473 K and a system pressure of 2.5 MPa.▪Copper-containing mesoporous silica HMS catalysts were prepared by an impregnation method. The surface structures of these catalysts were characterized by N2-physisorption, X-ray diffraction, transmission electron microscopy, H2 temperature-programmed reduction, Fourier transform infrared spectroscopy, N2O titration and X-ray photoelectron spectroscopy. The results show that the copper-containing HMS catalysts exhibit superior catalytic performance in the selective hydrogenation of dimethyl oxalate to ethylene glycol compared to the commercial silica-supported ones obtained by the same method. The dimethyl oxalate conversion can reach 100% and the ethylene glycol selectivity can reach 92% at 473 K with 2.5 MPa H2 pressure and 0.2 h−1 liquid hour space velocity of dimethyl oxalate over the 5 wt.% Cu-HMS catalyst. The enhanced catalytic performance of copper-HMS catalysts may be attributed to the homogeneous dispersion and uniformity of the active copper species and to the larger copper surface areas attained on the HMS supports with large pore diameters and surface areas.
Keywords: Cu/HMS catalysts; Hydrogenation of dimethyl oxalate; Ethylene glycol; Wet impregnation method;
Catalytic and kinetic study of the liquid-phase hydrogenation of acetophenone over Cu/SiO2 catalyst by Nicolás M. Bertero; Carlos R. Apesteguía; Alberto J. Marchi (100-109).
The liquid-phase hydrogenation of acetophenone (AP) to 1-phenylethanol (PhE) was studied on Cu(6.8%)/SiO2 catalyst. Catalytic tests were carried out in a batch reactor by varying temperature, total pressure and AP initial concentration between 353–373 K, 5–20 bar, and 0.038–0.251 M, respectively, and using four different solvents: isopropylic alcohol (IPA), cyclohexane, toluene and benzene. The selectivity to PhE was about 100% irrespective of the solvent used, but the initial AP conversion rate followed the order IPA > cyclohexane > toluene > benzene. The differences in catalyst activity when changing the solvent were interpreted by considering the effect of the solvent–metal interaction on the relative coverage of adsorbed reactant species. Experimental data were well interpreted by kinetic modeling only when assuming that: (i) the adsorption of AP and H2 is competitive; (ii) AP adsorption is strong; (iii) copper surface is saturated in AP; (iv) the PhE coverage on the catalyst is negligible. These assumptions were consistent with the fact that the reaction was negative order with respect to AP and first order in H2. The highly selective AP hydrogenation to PhE was explained by considering that the strong electrostatic repulsion between metallic Cu and the phenyl group tilts the AP molecule thereby favoring its adsorption via the carbonyl group and the formation of the unsaturated alcohol. Also, PhE was not consecutively converted via hydrogenolysis or other acid catalyzed reactions since the support was inert.The liquid-phase hydrogenation of acetophenone into 1-phenylethanol over Cu/SiO2 catalyst was studied. Results obtained in different conditions were interpreted by kinetic modeling employing heterogeneous Langmuir–Hinshelwood–Hougen–Watson (LHHW)-type and non-stationary models. A reaction mechanism (see pictogram), based on the interactions acetophenone-Cu0 explains: (1) the high selectivity to 1-phenylethanol; (2) the negative order respect to acetophenone and first order in H2; (3) solvent influence.▪
Keywords: Selective hydrogenation; Acetophenone; Copper-based catalyst; Kinetic modeling;
Columnar support structures for oxygen reduction electrocatalysts prepared by glancing angle deposition by Arman Bonakdarpour; M.D. Fleischauer; M.J. Brett; J.R. Dahn (110-115).
Columnar titanium structures were fabricated on smooth glassy carbon (GC) disks using the glancing angle deposition (GLAD) physical vapour deposition technique. This catalyst support consists of 500 nm long posts with a nominal cross-sectional diameter of 100 nm. They have a number density of about 10 billion per cm2 which increases the effective surface area of the GC disks by a factor of 13. Platinum films ranging from 10 to 90 nm in thickness (planar equivalent) were deposited onto these posts by magnetron sputtering. The oxygen reduction activity and H2O2 release of these electrocatalysts were measured by the rotating ring-disk electrode method in O2-saturated 0.1 M HClO4 at room temperature. The electrochemical surface area of the catalysts, obtained from Hupd cyclic voltammograms, is about 10–15 times higher than smooth Pt films. The supports can be fabricated from most vacuum-compatible materials and should be stable over a wide range of processing, annealing, and operating conditions.Columnar titanium structures were fabricated on smooth glassy carbon (GC) disks using the glancing angle deposition (GLAD) physical vapour deposition technique. This catalyst support consists of 500 nm long posts with a nominal cross-sectional diameter of 100 nm. They have a number density of about 10 billion per cm2 which increases the effective surface area of the GC disks by a factor of 13. Platinum films ranging from 10 to 90 nm in thickness (planar equivalent) were deposited onto these posts by magnetron sputtering. The oxygen reduction activity and H2O2 release of these electrocatalysts were measured by the rotating ring-disk electrode method in O2-saturated 0.1 M HClO4 at room temperature. The electrochemical surface area of the catalysts, obtained from Hupd cyclic voltammograms, is about 10–15 times higher than smooth Pt films. (a) Oxygen reduction curves. Anodic sweep rates are shown for 400, 900, and 2500 rpm (grey). A full cycle is shown for 1600 rpm (black). (b) Oxygen reduction curves from the four different Pt loadings at 900 rpm. (c) % H2O2 released in the electrolyte for the four different Pt loadings.▪
Keywords: Glancing angle deposition; O2 reduction; Rotating ring-disk electrode; Catalyst support;
Methane decomposition and catalyst regeneration in a cyclic mode over supported Co and Ni catalysts by Jerry Li; Kevin J. Smith (116-124).
CH4 decomposition (CH4 → C + 2H2) and catalyst regeneration by reaction of the deposited carbon with O2 or CO2 are reported for repeated CH4 decomposition–carbon oxidation cycles. At the chosen conditions, Ni was more active and more stable than Co over several cycles. However, catalyst regeneration resulted in oxidation of the catalysts and CO contamination of the H2 in subsequent CH4 decomposition steps. ▪CH4 decomposition (CH4 → C + 2H2) on supported Co and Ni catalysts has been studied using a fixed-bed, oscillating microbalance reactor and a 5% CH4 in He feed reacted at 773 K and 101 kPa. After 45 min reaction the catalysts were regenerated by reaction of the deposited carbon with O2 or CO2 at 773 K and 101 kPa. The effect of repeated CH4 decomposition–carbon oxidation cycles is reported. At the chosen conditions, Ni was more active and more stable than Co during the CH4 decomposition step. Although >90% of the carbon deposited on both Co and Ni was removed by reaction with O2, an oxidation of the active metal also occurred. In subsequent CH4 decomposition steps, an induction period was necessary to re-reduce the Co. Furthermore, the oxidized metal reacted with CH4 producing CO and CO2 as an impurity in the H2. Removal of the carbon deposit by reaction with CO2 rather than O2 significantly decreased the CO contamination of the produced H2 on the Ni catalyst. However, the carbon removal rate was 20×'s slower with CO2 compared to O2. Several CH4 decomposition–carbon oxidation cycles were completed on the Ni catalyst without a significant loss in activity, whereas the Co catalyst deactivated.
Keywords: Methane decomposition; Partial oxidation; Carbon; Catalyst; Cobalt; Nickel; Cyclic reaction;
Laboratory set-up to pilot plant investigations on vapour phase ammoxidation of 2,6-dichlorotoluene by N. Dropka; Q. Smejkal; V.N. Kalevaru; A. Martin (125-132).
The scaling-up of the gas phase catalytic ammoxidation of 2,6-dichlorotoluene (DCT) to 2,6-dichlorobenzonitrile (DCBN) over VPO catalysts in a pilot plant was investigated. The focus was led on the process variables that might be critical to the design of a commercial manufacturing facility. Furthermore, catalyst scale-up, catalyst stability and a development of a product separation section particularly for the solid reaction products was studied.▪The scaling-up of the gas phase catalytic ammoxidation of 2,6-dichlorotoluene (DCT) to 2,6-dichlorobenzonitrile (DCBN) over vanadium phosphate catalyst in a pilot plant was investigated. The focus was led on the process variables that might be critical for designing a commercial manufacturing unit, in particular on evaluation of reaction temperature that may cause hot spots, temperature gradients, etc. Furthermore, catalyst scale-up, catalyst stability and a development of a product separation section particularly for the solid reaction products was studied. The up-scaling of the process using 100 ml of catalyst was investigated both by reactor simulations and catalytic experiments. For reactor simulations, a pseudo-homogeneous model of a fixed bed tubular reactor with negligible axial and radial diffusion operating in the steady-state was applied. The kinetic model based upon the Langmuir–Hinshelwood mechanism was used. The results showed that the temperature control will be crucial in scaling-up of the process. The influence of the reactor geometry, reactor operating conditions and catalyst stability on the reactor performance is discussed. The possibility of an appearance of hot spots in the reactor is addressed. High selectivity of DCBN (85%) can be achieved for an extended period of time. A good agreement between experimental and simulation results is observed.
Keywords: Scale-up; Pilot plant experiments; Reactor simulation; VPO catalyst; Ammoxidation; 2,6-Dichlorotoluene; 2,6-Dichlorobenzonitrile; Temperature profile;
Catalytic hydrogen transfer over magnesia by Marek Gliński (133-139).
Moderately high yields of phenylalkanols (60–80%) were obtained in the vapour and liquid modes of transfer hydrogenation in the presence of MgO as the catalyst. The causes of the exceptions were explained based on X-ray diffraction studies. The liquid phase reduction over MgO is the more structure sensitive of the two.▪A comprehensive study of the reactivity of a series of mono-, di- and trisubstituted aralkyl ketones (Me, i-Pr or OMe as substituents) with straight- or branched acyl groups in the hydrogen transfer reaction over magnesium oxide as the catalyst, either in vapour or liquid phase (VP or LP) has been performed.In the VP mode of reaction, most of the studied ketones gave good conversions (60–65%), which slightly decreased with the increase of crowding in the carbonyl group region. There were five exceptions, namely isopropylphenyl and tertbutylphenyl ketones, whose conversions were very high (74–82%) and all trisubstituted ketones, in which both ortho positions were occupied, whose conversions were very low (<22%). In the reduction of most of the monosubstituted aralkyl ketones high selectivities towards alcohols (98%) under optimal conditions have been observed.Based on single crystal X-ray diffraction data for some ketones and the corresponding alcohols a parameter, ΔL, has been proposed to describe the shortest intramolecular interactions between hydrogen atoms in the aforementioned molecules. This parameter was used to show that the changes in the reactivity of ketones in transfer hydrogenation might be attributed to an increase or decrease of steric strains in the appropriate alcohols.In the LP mode of reaction, 12 aliphatic alcohols have been used as hydrogen donors and the dependence of the conversion of acetophenone on their structure and boiling point has been determined. The influence of the amount of catalyst and donor–acceptor molar ratio on the conversion of the ketone has also been studied. Under optimal conditions yields of alcohols exceeding 80% and selectivity higher than 99% after 6 h of the reduction of acetophenone and its 4- and 3-alkyl derivatives have been reached. It has been found that the liquid phase mode of reaction is much more structure sensitive than the gas phase mode; only residual reactivity has been noted for all studied monortho- or diorthosubstituted acetophenones and pivalophenone.
Keywords: Hydrogen transfer; Magnesia; Aralkyl ketones; Reactivity; Structure analysis;
Reaction mechanism of cyclohexane selective photo-oxidation to benzene on molybdena/titania catalysts by Paolo Ciambelli; Diana Sannino; Vincenzo Palma; Vincenzo Vaiano; Roger I. Bickley (140-147).
Photo-induced oxidative dehydrogenation of cyclohexane has been investigated in an annular gas–solid continuous flow reactor on molybdenum-based catalysts as a function of the molybdenum loading. The formation of polymolybdate species on the anatase support surface increased with increasing molybdenum load up to that corresponding to monolayer formation, resulting in a high selectivity to benzene formation, while with titania alone the process was 100% selective to forming carbon dioxide. After monolayer formation, segregation of MoO3 crystallites has been observed, with a significant loss in photo-oxidative dehydrogenation activity. A mechanism for the photo-induced oxidative dehydrogenation of cyclohexane, based upon consecutive oxy-dehydrogenation steps occurring on active molybdenum sites in competition with total oxidation on bare titania, has been proposed. This mechanism considers the oxy-dehydrogenation of cyclohexane to cyclohexene, followed by its further oxy-dehydrogenation to benzene occurring on the molybdenum oxide active sites.Gas phase cyclohexane selective photo-oxidation has been investigated on MoO x /TiO2 catalysts. Polymolybdate species were responsible of the high selectivity to benzene, while on titania alone, only carbon dioxide was formed. A mechanism for the photo-oxidative dehydrogenation of cyclohexane, consisting of consecutive oxy-dehydrogenation steps on active molybdenum sites in competition with total oxidation on bare titania has been proposed.▪
Keywords: Photocatalytic oxidative dehydrogenation; Cyclohexane; Cyclohexanol; Cyclohexene; Benzene; MoO x /TiO2; Dark adsorption; Reaction mechanism;
Activity of Gallium and Aluminum SBA-15 materials in the Friedel–Crafts alkylation of toluene with benzyl chloride and benzyl alcohol by Maria J. Gracia; Elia Losada; Rafael Luque; Juan M. Campelo; Diego Luna; Jose M. Marinas; Antonio A. Romero (148-155).
Ga-, Al- and AlGa-SBA-15 mesoporous materials synthesized via a direct sol–gel hydrothermal protocol were found active and selective in the Friedel–Crafts alkylation of toluene with benzyl chloride (promoted by Lewis acidity) and benzyl alcohol (promoted by Brönsted acidity). The solid acids were also highly reusable preserving almost their initial catalytic activity after five reuses.▪Ga-, Al- and AlGa-SBA-15 mesoporous materials were synthesized via a direct sol–gel hydrothermal protocol. The SBA-15 materials were characterized using X-ray fluorescence (XRF), X-ray diffraction (XRD), N2 physisorption, transmission electron microscopy (TEM) and pyridine and 2,6-dimethylpyridine titration. The activity of the Ga- and AlGa-SBA-15 was investigated in the Friedel–Crafts alkylation of toluene with benzyl chloride (promoted by Lewis acidity) and benzyl alcohol (promoted by Brönsted acidity). Quantitative conversion of the starting material was found for all Ga- and AlGa-SBA-15 after a few hours of reaction at 110 °C in the alkylation of toluene with benzyl chloride. The mesoporous acidic materials provided very poor activities in the alkylation of toluene with benzyl alcohol, with the exception of the Al-SBA-15. The activities of the Ga- and AlGa-SBA-15 were correlated to the higher proportion of Lewis compared to Brönsted acid sites. The solid acids were also highly reusable preserving almost their initial catalytic activity after five reuses.
Keywords: Ga- and AlGa-SBA-15; Heterogeneous catalysis; Friedel–Crafts alkylation; Alkylation of toluene;
Transient kinetic modelling of propane dehydrogenation over a Pt–Sn–K/Al2O3 catalyst by M.P. Lobera; C. Téllez; J. Herguido; M. Menéndez (156-164).
A complete kinetic model of propane dehydrogenation to produce propene over a Pt–Sn–K/Al2O3 catalyst was obtained. This has been investigated over the temperature range of 460–540 °C at atmospheric pressure. A Langmuir–Hinshelwood mechanism provides the best fit for propane dehydrogenation, while a monolayer–multilayer mechanism is proposed for modelling the coke formation. In addition, the reaction rate of coke formation and its influence on catalyst deactivation and subsequent regeneration have been studied. Finally, a suitable mathematical model is developed for simulating the process behaviour in a two-zone fluidized bed reactor (TZFBR).▪A complete kinetic model of propane dehydrogenation to produce propene over a Pt–Sn–K/Al2O3 catalyst was obtained. This has been investigated over the temperature range of 460–540 °C at atmospheric pressure. A Langmuir–Hinshelwood mechanism provides the best fit for propane dehydrogenation, while a monolayer–multilayer mechanism is proposed for modelling the coke formation. In addition, the reaction rate of coke formation and its influence on catalyst deactivation and subsequent regeneration have been studied. Finally, a suitable mathematical model is developed for simulating the process behaviour in a two-zone fluidized bed reactor (TZFBR).
Keywords: Reaction mechanism; Propane dehydrogenation; Pt–Sn–K/Al2O3 catalyst; Catalyst deactivation; Coke formation rates; Reactor simulation;
Pt/Ta2O5–ZrO2 catalysts for vapour phase selective hydrogenation of crotonaldehyde by E.V. Ramos-Fernández; B. Samaranch; P. Ramírez de la Piscina; N. Homs; J.L.G. Fierro; F. Rodríguez-Reinoso; A. Sepúlveda-Escribano (165-169).
This paper reports a study on the effect of the support composition in Pt/Ta2O5–ZrO2 in regard to their catalytic behaviour in the vapour phase hydrogenation of crotonaldehyde. Two Ta2O5–ZrO2 supports with different Ta/Zr ratios and a pure Ta2O5, were prepared by a sol–gel route. The Pt catalysts were characterized by CO chemisorption, infrared spectroscopy of adsorbed CO and X-ray photoelectron spectroscopy. The best catalyst in terms of activity and selectivity to crotyl alcohol was Pt/Ta2O5, and this has been related to the metal–support interaction. On the other hand, under the experimental conditions used, the acidity properties of supports do not significantly influence the catalytic behaviour of materials. ▪This paper reports a study on the effect of the support composition in Pt/Ta2O5–ZrO2 catalysts in regard to their catalytic behaviour in the vapour phase selective hydrogenation of crotonaldehyde (2-butenol). Two Ta2O5–ZrO2 supports with different Ta/Zr ratios and a pure Ta2O5 were prepared by a sol–gel route. The platinum catalysts were characterized by CO chemisorption, infrared spectroscopy of adsorbed CO and X-ray photoelectron spectroscopy (XPS). The best catalyst in terms of activity and selectivity to crotyl alcohol (2-butenol) was Pt/Ta2O5, and this behaviour is tentatively related to the metal–support interaction. On the other hand, under the experimental conditions used, the acidic properties of the supports could not be correlated to the catalytic behaviour of these materials.
Keywords: Crotonaldehyde hydrogenation; Ta2O5–ZrO2; Pt; SMSI;
Heteropoly acids as catalysts for liquid-phase esterification and transesterification by Ali Alsalme; Elena F. Kozhevnikova; Ivan V. Kozhevnikov (170-176).
Esterification of hexanoic acid and transesterification of ethyl propanoate and ethyl hexanoate with excess methanol are tested at 60 °C and ambient pressure with a range of heteropoly acid (HPA) catalysts in homogeneous and heterogeneous systems in comparison with conventional acid catalysts such as H2SO4, Amberlyst-15 and zeolites HY and H-Beta. The turnover frequency of HPA catalysts is significantly higher than that of the conventional acid catalysts in these reactions. ▪Esterification of hexanoic acid and transesterification of ethyl propanoate and ethyl hexanoate with excess methanol (1:20 molar ratio) are tested at 60 °C and ambient pressure with a range of HPA catalysts in homogeneous and heterogeneous systems in comparison with conventional homogeneous and solid acid catalysts such as H2SO4, Amberlyst-15 and zeolites HY and H-Beta. The intrinsic catalytic activity (turnover frequency, TOF) of HPA catalysts is significantly higher than that of the conventional acid catalysts in these reactions. The TOF values decrease with decreasing catalyst acid strength in the order: H3PW12O40 ≈ Cs2.5H0.5PW12O40 > H4SiW12O40 > 15%H3PW12O40/Nb2O5, 15%H3PW12O40/ZrO2, 15%H3PW12O40/TiO2 > H2SO4 > HY, H-Beta > Amberlyst-15. The activity per unit catalyst weight falls in a different order: H2SO4 > H3PW12O40 ≈ H4SiW12O40 > Amberlyst-15 ≥ Cs2.5H0.5PW12O40 > supported H3PW12O40 > HY, H-Beta. Bulk cesium salt Cs2.5H0.5PW12O40 exhibits high catalytic activity as well as high stability to leaching. Supported HPA catalysts suffer from leaching and exhibit significant contribution of homogeneous catalysis by the leached HPA.
Keywords: Biodiesel; Esterification; Transesterification; Heteropoly acid; Catalysis;
Biomimetic oxidation of sulfides with sodium periodate catalyzed by polystyrene-bound manganese (III) tetrapyridylporphyrin by Majid Moghadam; Shahram Tangestaninejad; Valiollah Mirkhani; Iraj Mohammadpoor-Baltork; Ali Akbar Abbasi-Larki (177-181).
Efficient oxidation of sulfides with sodium periodate catalyzed by manganese (III) tetrapyridylporphyrin supported on chloromethylatedpolystyrene is reported. This catalyst shows high activity in the oxidation of various sulfides to their corresponding sulfoxides and sulfones at room temperature. The effect of different axial ligands, oxidants, solvents, and catalyst amount was also investigated in this catalytic system. This heterogeneous catalyst can be reused five times without significant loss of its activity.▪Efficient oxidation of sulfides with sodium periodate catalyzed by manganese (III) tetrapyridylporphyrin supported on chloromethylatedpolystyrene is reported. This catalyst shows high activity in the oxidation of various sulfides to their corresponding sulfoxides and sulfones at room temperature. The effect of different axial ligands, oxidants, solvents, and catalyst amount was also investigated in this catalytic system. This heterogeneous catalyst can be reused five times without significant loss of its activity.
Keywords: Biomimetic oxidation; Supported metalloporphyrin; Sulfide; Sulfoxide; Sulfone;
Photocatalytic oxidation of aromatic alcohols to aldehydes in aqueous suspension of home-prepared titanium dioxide by Vincenzo Augugliaro; Horst Kisch; Vittorio Loddo; María José López-Muñoz; Carlos Márquez-Álvarez; Giovanni Palmisano; Leonardo Palmisano; Francesco Parrino; Sedat Yurdakal (182-188).
Home-prepared (ex TiCl4) and commercial TiO2 catalysts were used for carrying out the oxidation of benzyl alcohol and 4-methoxybenzyl alcohol. The HP catalysts exhibited selectivity towards the aldehyde up to four times higher than those of commercial TiO2. The addition of an aliphatic alcohol in small amounts enhanced the selectivity for aldehyde formation up to 1.5 times. ▪Oxygenated aqueous suspensions of home-prepared (HP) and commercial TiO2 catalysts were used in a batch photoreactor for carrying out the oxidation of benzyl alcohol (BA) and 4-methoxybenzyl alcohol (MBA) under different operative conditions. HP catalysts were synthesized from TiCl4 and underwent a hydrolysis treatment of different times under mild conditions. The textural characterization of catalysts was carried out with XRD, SEM observations, BET surface area and porosity measurements. For both alcohols the main oxidation products were the corresponding aromatic aldehydes and CO2. The HP catalysts exhibited selectivity values towards the aldehyde production up to 28% (BA conversion: 50%) and 41% (MBA conversion: 65%), about four times higher than those of commercial TiO2. The addition of an aliphatic alcohol (methanol, ethanol, 2-propanol or tert-butanol) in small amounts with respect to water decreased the overall oxidation rate of aromatic alcohols but enhanced the selectivity for aldehyde formation up to 1.5 times. The reactivity results suggest that: (i) the aromatic alcohol molecules interact with the TiO2 surface in different ways that eventually determine two parallel reaction pathways (partial oxidation or mineralization); (ii) the aliphatic alcohols preferentially compete with aromatic alcohols for the mineralizing pathway.
Keywords: Photocatalysis; TiO2; Aromatic alcohols; Aliphatic alcohol; Selective oxidation;
Photocatalytic oxidation of aromatic alcohols to aldehydes in aqueous suspension of home prepared titanium dioxide by Vincenzo Augugliaro; Horst Kisch; Vittorio Loddo; María José López-Muñoz; Carlos Márquez-Álvarez; Giovanni Palmisano; Leonardo Palmisano; Francesco Parrino; Sedat Yurdakal (189-197).
In this paper some intrinsic electronic properties of home prepared (HP) TiO2 catalysts were investigated by diffuse reflectance spectroscopy and quasi-Fermi level measurements. These powders were used for carrying out the photocatalytic oxidation of benzyl alcohol to benzaldehyde and CO2 in water; the selectivity for aldehyde formation was enhanced by the addition of small amounts of ethanol, a typical hole trap. The values of band gap, valence band and conduction band edges are almost identical for all the HP samples in which anatase phase is predominant, whereas appreciable differences can be noticed for an HP sample containing high amount of rutile phase. A comparative ATR-FTIR study of the HP catalyst showing the highest selectivity and the commercial titania showing the highest activity towards benzyl alcohol oxidation (Degussa P25 TiO2) was carried out. The ATR-FTIR results indicate that HP and Degussa P25 surfaces show a very dissimilar hydrophilicity and different ability for adsorbing the organic compounds deriving from benzyl alcohol photocatalytic oxidation. Results show moreover that the improved selectivity to aldehyde by adding ethanol is due to competition between the substrate and the hole trap for adsorption on reactive sites.Home prepared TiO2 powders were used for carrying out the photocatalytic oxidation of benzyl alcohol in water, in the presence of ethanol. Catalysts characterization was carried out through XRD, SEM, TG, BET and porosity measurements. Diffuse reflectance spectroscopy and quasi-Fermi level measurements were also performed. An ATR-FTIR study of catalysts showed that HP and Degussa P25 surfaces hold very different hydrophilicity and ability for adsorbing the intermediates deriving from benzyl alcohol oxidation. ▪
Keywords: Photocatalysis; TiO2; In situ ATR-FTIR analysis; Aromatic alcohols; Selective oxidation; Aliphatic alcohol;
Transesterification of vegetable oils promoted by poly(styrene-divinylbenzene) and poly(divinylbenzene) by Simone M. de Rezende; Michele de Castro Reis; Marcelli Garcia Reid; Paulo Lúcio Silva; Fernanda M.B. Coutinho; Rosane Aguiar da Silva San Gil; Elizabeth R. Lachter (198-203).
Ion-exchange resins based on styrene (S) and divinylbenzene (DVB) were prepared and characterized by surface area, pore volume and surface morphology. Their activities were evaluated in vegetable oil transesterification with methanol and compared with the performance of a commercial sulfonic resin. The synthesized resin presented better results than the commercial one representing a convenient route for biodiesel production.▪Ion-exchange resins based on styrene (S) and divinylbenzene (DVB) were prepared by aqueous suspension polymerization using toluene and n-heptane as diluents for the monomers. The different morphological structures were characterized by surface area, pore volume, optical appearance and surface morphology. Sulfonic catalysts were prepared from these resins in the presence of solvents with solvating and non-solvating characteristics. These catalysts were characterized and their activities were evaluated in vegetable oil transesterification with methanol and compared with the performance of a commercial sulfonic resin. The synthesized resin presented better results than the commercial one representing a convenient route for biodiesel production.
Keywords: Transesterification; Biodiesel; Vegetable oil; Ion-exchange resins; Morphology structure;
Vapor-phase hydrogenolysis of biomass-derived lactate to 1,2-propanediol over supported metal catalysts by Long Huang; Yulei Zhu; Hongyan Zheng; Mingxian Du; Yongwang Li (204-211).
The SiO2 supported cobalt catalysts are active for vapor-phase hydrogenolysis of ethyl lactate to 1,2-propanediol at mild conditions. Interestingly, a quasi-linear correlation is observed between average reaction rate and the percentage of the bulk-like Co3O4 phase precursors, suggesting that the metallic cobalt from the bulk-like Co3O4 phase precursor is more active.▪Vapor-phase hydrogenolysis of ethyl lactate to 1,2-propanediol was performed over a series of SiO2 supported metal (Fe, Co, Ni, Ru, and Pd) catalysts in a fixed-bed reactor. Among them, the Co/SiO2 and Cu/SiO2 catalysts exhibit promising performance, and the Co/SiO2 were more active than the traditional copper catalysts under mild conditions. Effects of support, metal loading and preparation method were investigated to optimize the performance of the Co-based catalysts. Over the optimal catalyst (a 10 wt.% Co/SiO2 catalyst prepared via rotary evaporation drying method), the 1,2-propanediol selectivity was in excess of 98% at 90.2% lactate conversion, 2.5 MPa and 160 °C. The cobalt catalysts were characterized by X-ray diffraction (XRD) and temperature programmed reduction by H2 (H2-TPR) and temperature programmed desorption of H2 (H2-TPD). Interestingly, a quasi-linear correlation is observed between the average reaction rate and the percentage of bulk-like Co3O4 phase precursors, suggesting that the metallic cobalt from the bulk-like Co3O4 phase precursor is more active than that from the cobalt surface support species. The emerging technologies for production of low-cost lactate ester, make this high-yield route a sustainable benign process for 1,2-propanediol.
Keywords: Ethyl lactate; 1,2-Propendiol; Co/SiO2; Hydrogenolysis;
Significant effect of acidity on catalytic behaviors of Cs-substituted polyoxometalates for oxidative dehydrogenation of propane by Miao Sun; Jizhe Zhang; Chuanjing Cao; Qinghong Zhang; Ye Wang; Huilin Wan (212-221).
Two series of Keggin-type polyoxometalates (i.e., Cs x H3−x PMo12O40 and Cs x H4−x PVMo11O40) with different cesium contents have been studied for the oxidative dehydrogenation of propane at a mild temperature (653 K). The conversion of propane decreases while the selectivity to propylene increases with increasing cesium content, and the yield of propylene reaches a maximum at appropriate cesium content for either series of catalysts. The best yield of propylene (9.3%) has been achieved over the Cs x H3−x PMo12O40 catalyst with an x value of 2.56, and the vanadium substitution cannot enhance the maximum yield of propylene. The correlation between catalytic behaviors and physicochemical properties of the catalysts suggests that the acidity of the present catalysts plays crucial roles in the oxidative dehydrogenation of propane. It is clarified that the rate of propane conversion increases proportionally to the concentration of Brønsted acid sites, whereas the selectivity to propylene decreases with increasing the surface acidity.Propane conversion decreases while propylene selectivity increases with increasing cesium content in the Cs x H3−x PMo12O40 (x = 2–3) and Cs x H4−x PVMo11O40 (x = 2–4) catalysts with different cesium contents. We have clarified that the rate of propane conversion increases proportionally to the concentration of surface Brønsted acid sites, whereas the selectivity to propylene decreases with increasing the surface acidity.▪
Keywords: Oxidative dehydrogenation; Propane; Propylene; Polyoxometalate; Acidic property;
Redox properties of H3PMo x W12−x O40 and H6P2Mo x W18−x O62 heteropolyacid catalysts and their catalytic activity for benzyl alcohol oxidation by Dong Ryul Park; Ji Hwan Song; Sang Hee Lee; Sun Ho Song; Heesoo Kim; Ji Chul Jung; In Kyu Song (222-228).
Reduction potentials and UV–visible absorption edge energies of H3PMo x W12−x O40 Keggin heteropolyacid (HPA) and H6P2Mo x W18−x O62 Wells-Dawson HPA catalysts were measured to probe their oxidation catalysis for benzyl alcohol oxidation. Yield for benzaldehyde increased with increasing reduction potential and with decreasing absorption edge energy of the HPA catalyst, regardless of the identity of the catalyst.▪Reduction potentials of H3PMo x W12−x O40 (x = 0, 3, 6, 9, and 12) Keggin heteropolyacid (HPA) and H6P2Mo x W18−x O62 (x = 0, 3, 9, 15, and 18) Wells-Dawson HPA catalysts were measured by an electrochemical method in solution. UV–visible spectra of H3PMo x W12−x O40 and H6P2Mo x W18−x O62 catalysts in solution were then obtained in order to explore the reduction potentials of the HPA catalysts. Reduction potentials increased and UV–visible absorption edge energies shifted to lower values with increasing molybdenum substitution in both families of H3PMo x W12−x O40 and H6P2Mo x W18−x O62 catalysts. It was revealed that the lower absorption edge energy corresponded to the higher reduction potential of the HPA catalyst. In order to correlate the redox property (reduction potential and absorption edge energy) with the catalytic oxidation activity of H3PMo x W12−x O40 and H6P2Mo x W18−x O62 catalysts, vapor-phase oxidation of benzyl alcohol was carried out as a model reaction. Yield for benzaldehyde increased with increasing reduction potential and with decreasing absorption edge energy of the HPA catalyst, regardless of the identity of HPA catalyst (without HPA structural sensitivity). The absorption edge energies measured by UV–visible spectroscopy could be utilized as a correlating parameter for the reduction potentials (oxidizing powers) of H3PMo x W12−x O40 and H6P2Mo x W18−x O62 catalysts, and furthermore, as a probe of oxidation catalysis of the HPA catalysts.
Keywords: Heteropolyacid catalyst; Reduction potential; UV–visible absorption edge energy; Benzyl alcohol oxidation;
Highly enhanced hydrogen-transfer hydrodechlorination and hydrogenation reactions in alkaline 2-propanol/methanol over supported palladium catalysts by Yuji Ukisu (229-232).
Hydrodechlorination of organic chlorides and hydrogenation of an unsaturated hydrocarbon were performed in a solution of 2-propanol/methanol (99:1, v/v) containing NaOH over a supported palladium catalyst (Pd/C, Pd/TiO2, or Pd/Al2O3) at 30 °C. The added methanol greatly enhanced the reaction rates. In these catalytic reactions, the hydrogen in 2-propanol was efficiently transferred to the organic compounds over the Pd catalysts.▪Hydrodechlorination of organic chlorides and hydrogenation of an unsaturated hydrocarbon were performed in a solution of 2-propanol/methanol (99:1, v/v) containing NaOH in the presence of a supported palladium catalyst (Pd/C, Pd/TiO2, or Pd/Al2O3) at 30–40 °C. p-Chloroanisole, 2-chloronaphthalene, and (2-chloroethyl)benzene were successfully dechlorinated to anisole, naphthalene, and ethylbenzene, respectively. For all combinations of the substrates and the catalysts, the reaction rates were much higher (>3 times) than those in the absence of 1% methanol, indicating that the catalytic reactions were greatly enhanced by the addition of a small amount of methanol. However, the dechlorination rate of 1-chlorodecane, which has no aromatic ring, was not enhanced by the addition of 1% methanol. The hydrogenation of 1,1-diphenylethylene to 1,1-diphenylethane was also enhanced by the addition of 1% methanol to an alkaline 2-propanol solution. These catalytic reactions did not require H2 gas and a high operating temperature, because the hydrogen from the alcohol solvent molecules was efficiently transferred to the organic compounds over the Pd catalysts even at 30 °C.
Keywords: Organic chlorides; Unsaturated hydrocarbon; 2-Propanol; Methanol; Sodium hydroxide;