Applied Catalysis A, General (v.237, #1-2)
EDITORIAL BOARD (iii).
Living polymerizations of propylene and syntheses of atactic polypropylene-block-poly(ethylene-co-propylene) using metallocene catalyst systems by Yoshifumi Fukui; Masahide Murata (1-10).
Living propylene polymerizations were performed with various metallocene catalyst (Mt=Zr and Hf)/cocatalyst (organoborane)/trialkylaluminium systems at low temperatures, i.e. Cp2ZrR2 (Cp=cyclopentadienyl, R=Me and Cl)/B(C6F5)3/AlR3′ (R′=octyl and iso-butyl) at −78 °C, Cp2HfMe2/B(C6F5)3/AlOct3 at −50 °C and Cp 2 ∗ HfMe2 ( Cp ∗=pentamethylcyclopentadienyl)/B(C6F5)3/AlOct3 at −78 °C. The Cp 2 ∗ HfMe2 system showed a considerably higher propagation rate than the Cp2ZrR2 or Cp2HfMe2-based systems. With the above metallocene catalyst systems, atactic polypropylene-(ethylene-co-propylene) (ataPP/EP) block copolymers were prepared by the addition of ethylene monomer during the living polymerization of propylene at low temperature. By the addition of ethylene, the M n for the resultant copolymer showed a higher value than that of corresponding homopolypropylene while retaining the narrow molecular weight distribution. By the transmission electron microscopy (TEM) analysis, a microphase-separated morphology with ca. 50–100 nm dimension was observed in an iso-PP/PP-block-EP blend.
Keywords: Polypropylene; Block copolymer; Ethylene; Metallocene catalyst; Living polymerization; Microphase separation; Polymer blend;
Epoxidation of propylene on NaCl-modified silver catalysts with air as the oxidant by Jiqing Lu; Mengfei Luo; Hao Lei; Can Li (11-19).
Propylene epoxidation by air was carried out on NaCl-modified silver (NaCl/Ag) catalysts, and the catalysts were characterized by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The effects of NaCl loadings, propylene to oxygen ratio, and the reaction time on the catalytic performance were investigated. It was found that the addition of NaCl to silver significantly increases the propylene oxide (PO) selectivity. The PO yield has a maximum when the NaCl loading is about 10 wt.%. Also 12.4% conversion of propylene and 31.6% selectivity to PO are obtained on the NaCl/Ag (10 wt.%) catalyst at 350 °C, space velocity 1.8×104 h−1 and C3H6:O2=1:2. XPS and XRD characterizations show that AgCl formed on the silver catalyst was favorable to propylene epoxidation. A compound with highly oxidized Ag ion was also found, which may be effective for the reaction.
Keywords: Propylene; Epoxidation; Silver catalyst;
Sulfated zirconia supported in mesoporous materials by Yinyong Sun; Lei Zhu; Huijuan Lu; Runwei Wang; Sen Lin; Dazheng Jiang; Feng-Shou Xiao (21-31).
SO4 2−/ZrO2 (SZ) supported on ordered mesoporous hexagonal materials were prepared by dispersion of ZrOCl2·8H2O into the mesopores, followed by the hydrolysis and sulfation. These materials have been characterized by X-ray diffraction, nitrogen adsorption isotherms, infrared spectroscopy, and catalytic cracking of n-hexane, cumene and 1,3,5-triisopropylbenzene. The results show that SZ was successfully loaded into the inner pores of MCM-41; the as-synthesized catalyst showed favorable catalytic properties. The factors in the preparative process that affected the final activity were discussed.
Keywords: Sulfated zirconia; MCM-41; Cumene; 1,3,5-triisopropylbenzene; n-hexane; Cracking; Dispersion;
Dinitrogen production from ammonia by Nitrosomonas europaea by Niranjan Kumar Shrestha; Shigeru Hadano; Toshiaki Kamachi; Ichiro Okura (33-39).
In this study, the conversion efficiency and optimal conditions of successive nitrification and denitrification were assessed for Nitrosomonas europaea, which uses ammonia monooxygenase (AMO), nitrite reductase and nitrous oxide reductase. In aerobic conditions, the first step of nitrification (i.e. NH4 +→NO2 −) occurred; under oxygen-limiting or oxygen free-conditions, however, there was denitrification, whereby nitrous oxide and dinitrogen were produced from nitrite (NO2 −). About 7% of the total ammonium was converted to dinitrogen following the successive nitrification and denitrification by N. europaea. During nitrification and denitrification, the optimal pH range for the production of nitrite and dinitrogen was found to be 7.0–8.0. A low partial oxygen pressure or oxygen-free conditions were favorable for the production of dinitrogen.
Keywords: Nitrification; Denitrification; Dinitrogen; Nitrosomonas europaea;
Plasma generation of supported metal catalysts by Hyunsup Shim; Jonathan Phillips; I.M Fonseca; S Carabinerio (41-51).
A novel method to prepare supported metal catalysts is described. A microwave frequency plasma torch was employed to create supported metal catalysts from physical mixtures of a metal (palladium, particles or molecular precursor) and a traditional support material (alumina). Specifically, an aerosol containing particles of metal and support was injected into the center of an atmosphere pressure plasma generated with a commercial microwave torch. Catalytic studies of the selective isomerization of 1-butene indicate that catalysts created in this novel fashion are more selective, but less active, than catalysts prepared on the same support by incipient wetness. Catalysts prepared by incipient wetness impregnation of alumina (no metal) pre-treated in the microwave torch were found to have both high activity and enhanced selectivity. Characterization studies suggest that the plasma generated catalysts consist of nano-scale metal particles on highly modified support material.
Keywords: Plasma; Palladium supported catalyst; Alumina; Selective hydrogenation; Double bond shift;
Direct synthesis of ethyl acetate from ethanol over Cu-Zn-Zr-Al-O catalyst by Kanichiro Inui; Toru Kurabayashi; Satoshi Sato (53-61).
Direct synthesis of ethyl acetate from ethanol is investigated over several copper catalysts. We clarified the role of additive metal oxides such as ZrO2, ZnO and Al2O3. An additive ZrO2 gives ester-formation activity to the pure copper catalyst. ZnO suppresses the formation of undesirable products such as methyl ethyl ketone (MEK) under the co-existence of ZrO2. Al2O3 enhances not only the conversion of ethanol but also the catalytic activity for the side reaction of aldol addition of acetaldehyde. Ethanol is converted into ethyl acetate with high selectivity over Cu-ZnO-ZrO2-Al2O3 catalyst, together with low selectivity to methyl ethyl ketone. Then we investigated the influence of copper content in the quaternary copper catalysts containing ZrO2, ZnO and Al2O3 on the catalytic performance. The ethyl acetate production ability of catalyst is roughly proportional to the Cu surface area of the Cu-ZnO-ZrO2-Al2O3 catalyst. The highest ethanol conversion, the highest ethyl acetate selectivity, and the highest space-time yield of ethyl acetate were achieved at Cu content of 70 mol%.
Keywords: Direct synthesis; Ethyl acetate; Cu-Zn-Zr-Al-O catalyst;
The structure and catalytic activity of the double oxide system Cu-Mn-O/MgF2 by Maria Wojciechowska; Agnieszka Malczewska; Bogdan Czajka; Michał Zieliński; Janina Goslar (63-70).
The paper presents the results of a study on the structure and catalytic activity of MgF2 supported binary copper and manganese oxides, prepared using a co-impregnation procedure, contrasted to the data obtained for Cu/MgF2 and Mn/MgF2. The catalysts were characterised by means of BET, X-ray diffraction (XRD), temperature-programmed reduction (TPR) and infrared (IR) methods. The results proved the presence of CuMn2O4 type spinel structures in the mixed systems CuO and MnO x supported on MgF2, forming already at 400 °C. The activity of the mixed copper-manganese oxides and single metal oxides supported on MgF2 has been studied in the reactions of 2-propanol decomposition, cyclohexene dehydrogenation, oxidation of CO and reduction of NO by C3H6. The double oxide systems were found more effective than the catalysts obtained on the basis of individual oxides.
Keywords: Copper-manganese oxide catalysts; MgF2; Spinel; XRD; TPR; IR;
Experimental determination of high-severity fluidized catalytic cracking (HS-FCC) deactivation constant by Mohammad A Abul-Hamayel; M.Abdul-Bari Siddiqui; Takashi Ino; Abdullah M Aitani (71-80).
This paper presents the results of an investigation carried out to experimentally determine the deactivation constant of a fluid catalytic cracking (FCC) process. Kinetic modeling was performed using a four-lump model and an experimentally determined deactivation constant. Significant improvement was achieved in predicting the product gasoline, gas and coke yields compared to the yields predicted by models using a theoretical deactivation constant. Activation energies for each reaction are reported and compared with the literature values.
Keywords: Fluidized catalytic cracking; Kinetic modeling; Vacuum gas oil (VGO); Deactivation;
Oxidative decomposition of o-dichlorobenzene over V2O5/TiO2 catalyst washcoated onto wire-mesh honeycombs by Ki-Suk Chung; Zhidong Jiang; Bong-Seok Gill; Jong-Shik Chung (81-89).
A novel wire-mesh (WM) honeycomb reactor was developed and tested for the oxidative decomposition of 1,2-dichlorobenzene (o-DCB) in air over V2O5/TiO2 catalyst. The WM-honeycomb substrate had triangle-shaped channels and was fabricated from flat and corrugated carbon steel wire-meshes (20 Taylor mesh). The geometric surface area of the substrate is similar to that of a ceramic honeycomb module with square channels of size 3 mm. The optimal loading of powder catalyst on the WM-honeycomb module was determined experimentally. This loading was adopted thereafter in experiments probing the effect of changes in the working conditions. The influences of temperature, flow rate and o-DCB concentration on the conversion of o-DCB by the reactor were investigated. Results were compared with those for similar wash-coated ceramic honeycomb modules. WM-honeycombs were characterized by much higher conversion than ceramic honeycomb modules, which can be attributed to radial mixing across the mesh screen pores. The performance gap between the two types of reactor was enhanced on going to higher values of the o-DCB concentration, flow rate or temperature, or in circumstances where external mass transfer or radial mixing was important to the overall reaction rate. The stability of both honeycomb reactors was examined by running them for 50 h at 900 ppm, 3000 cm3/min and 270 °C. The WM-honeycomb module showed only small fluctuations in the conversion over the course of the run and good reproducibility. The WM-honeycomb exhibits higher efficiency and much lower cost than the ceramic honeycomb, so the WM-honeycomb is a promising option for use in a variety of industrial applications.
Keywords: o-Dichlorobenzene; Oxidative decomposition; Wire-mesh; Monolithic reactor; V2O5/TiO2;
Catalytic behavior of O2-pretreated Ni3(SbTe3)2 catalyst in oxidative coupling of methane by Sung Han Lee; Jin-Seung Jung; Jae-Uk Joo; No-Seung Myung; Jong Ho Jun; Joong-Gil Choi (91-101).
Amorphous Ni3(SbTe3)2 was prepared from a metathesis between K3SbTe3 and NiBr2 solution and was examined as a catalyst for the oxidative coupling of methane in a single-pass flow reactor system using on-line gas chromatography at atmospheric pressure. Catalytic reaction was performed by feeding the reaction mixture containing CH4/O2/He in the temperature range of 600–750 °C. Although amorphous Ni3(SbTe3)2 showed no catalytic activity for the oxidative coupling of methane, the O2-pretreated Ni3(SbTe3)2 was found to be active and selective for the reaction. Its C2 selectivities were in the range of 45–79% in the temperature range of 600–750 °C. The best C2-yield was 11% with a selectivity of 79% at 650 °C. X-ray powder diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses were performed for the O2-treated Ni3(SbTe3)2 catalyst before and after the catalytic reaction to characterize the catalyst. Thermogravimetry (TG) analysis was performed for amorphous Ni3(SbTe3)2 in a flow of O2/Ar mixture. Electrical conductivity of amorphous Ni3(SbTe3)2 was measured as a function of temperature in the range of 400–800 °C at both P O2 ’s of 0.01 and 0.20 atm. The results suggest that NiTeO3 formed on the surface by the O2-pretreatment of catalyst is active and is the selective phase for the oxidative coupling of methane.
Keywords: Amorphous Ni3(SbTe3)2; Oxidative coupling of methane;
Catalytic and direct synthesis of dimethyl carbonate starting from carbon dioxide using CeO2-ZrO2 solid solution heterogeneous catalyst: effect of H2O removal from the reaction system by Keiichi Tomishige; Kimio Kunimori (103-109).
CeO2-ZrO2 solid solution catalysts are very effective in the selective synthesis of dimethyl carbonate (DMC) from methanol and CO2. The methanol conversion is very low because the DMC formation is limited by the reaction equilibrium. For the removal of H2O from the reaction system, the reaction between 2,2-dimethoxy propane (DMP) and H2O can be utilized. The addition of the DMP to the reaction system of DMC synthesis from methanol and CO2 is very effective for the increase of the conversion. However, the addition of larger amounts of DMP is not suitable because of the decrease of DMC formation rate and the by-production of the dimethyl ether (DME). The combination of this selective catalyst with an effective H2O removal system can provide a novel process of selective DMC production starting from CO2 with high efficiency.
Keywords: Dimethyl carbonate; CeO2-ZrO2; Solid solution; CO2; Methanol;
High-throughput experimentation in multicomponent bulk mixed metal oxides: Mo-V-Sb-Nb-O system for selective oxidation of propane to acrylic acid by Jamal N Al-Saeedi; Vadim V Guliants (111-120).
The bulk mixed Mo-V-Sb-Nb oxides, which is a candidate catalytic system for the selective oxidation of propane to acrylic acid, were prepared using an automated synthesis workstation. Two catalyst compositions, Mo0.3V0.3Sb0.125Nb0.125 and Mo1.0V0.3Sb0.125Nb0.125, were characterized by XRD and Raman spectroscopy and shown to contain Mo6V9O40, Mo0.61–0.77V0.31–0.19Nb0.08–0.04O x (a niobium-stabilized defect phase of a vanadium-rich molybdate), Mo3Nb2O11, and MoO3 as the major phases. The results of the structural characterization and kinetic screening demonstrated good reproducibility of the phase compositions and catalytic properties of the model Mo-V-Sb-Nb-O system and provided new insights into the transformation processes that occur in these mixed oxides with time on stream. These results suggest the promise of emerging high-throughput in situ characterization techniques for establishing fundamental structure–activity/selectivity relationships and developing novel multicomponent mixed metal oxides for selective oxidation of lower alkanes.
Keywords: Propane; Partial oxidation; Mixed metal oxides; High-throughput experimentation;
Isopropanol oxidation by pure metal oxide catalysts: number of active surface sites and turnover frequencies by Deepak Kulkarni; Israel E. Wachs (121-137).
The objective of the present study was to determine the number of active surface sites and their nature, redox or acidic, for bulk metal oxide catalysts using isopropanol as a chemical probe molecule. Isopropanol oxidation activity on the following metal oxides was investigated: MgO, CaO, SrO, BaO, Y2O3, La2O3, CeO2, TiO2, ZrO2, HfO2, V2O5, Nb2O5, Ta2O5, Cr2O3, MoO3, WO3, Mn2O3, Fe2O3, Co3O4, Rh2O3, NiO, PdO, PtO, CuO, Ag2O, Au2O3, ZnO, Al2O3, Ga2O3, In2O3, SiO2, SnO2 and Bi2O3. On average, the number of active surface sites for isopropanol dissociative adsorption on these catalysts was ∼2–4 μmol/m2. The number of active surface sites enabled quantification of the turnover frequency (TOF) for these catalysts. The TOF values for the various pure metal oxides were normalized at 200 °C. The TOFs of catalysts showing redox activity vary by six-orders of magnitude (102 to 10−4 s−1). For catalyst showing acidic activity, the TOFs varied by over eight-orders of magnitude (101 to 10−7 s−1). The reaction products from isopropanol oxidation at low conversions reflected the nature of the active surface sites, redox or acidic, on these catalysts. Redox surface sites yield acetone and acidic surface sites yield propylene. Small amounts of isopropyl ether formation are sometimes also observed via bimolecular recombination of surface isopropoxide species on acidic surface sites. All catalysts with the exception of Fe2O3 and TiO2, exhibited extremely high selectivity to either redox or acidic products. Except for the sharp decrease in TOFs towards redox products with increasing bulk M–O heats of formation at low −ΔH f, no correlations were found between the TOFs and bulk metal oxide properties (TPR–H2 and −ΔH f). However, an inverse relation was found between the TOFs (redox) and the surface isopropoxide intermediate decomposition temperature at low decomposition temperatures. At moderate and high decomposition temperatures, the TOFs (redox) were almost independent of the surface isopropoxide decomposition temperature. The selectivity of the metal oxide catalysts was found to be independent of the TOFs.
Keywords: 2-Propanol oxidation; Metal oxides; Turnover frequency; Active sites;
The support effect on platinum catalyst under oxidizing atmosphere: improvement in the oxidation-resistance of platinum by the electrophilic property of support materials by Yoshiteru Yazawa; Hisao Yoshida; Tadashi Hattori (139-148).
The support effect on platinum catalyst for low temperature propane combustion was investigated by using a series of platinum catalysts with different acid strengths support materials and different platinum dispersions. The catalytic activity of platinum catalyst varied with both the acid strength of support materials and the platinum dispersion. On each support material, the turnover frequency increased with the decrease in platinum dispersion. This variation in the turnover frequency is attributed to the variation in the oxidation state of platinum, since it was clarified by Pt LII and LIII-edge XAFS that platinum with small dispersion is less oxidized than that with large dispersion. The turnover frequency also varied with the acid strength of support materials; the turnover frequency increased with the increase in the acid strength of support materials at the same dispersion. The Pt LII and LIII-edge XAFS investigation clearly indicated that platinum on the acidic support material is less oxidized than that on basic material. Thus, it is clearly shown that the support materials affect the catalytic activity of platinum through the control of the oxidation-resistance of platinum by its electrophilic/electrophobic property, demonstrating that the electrophilic/electrophobic property of support materials is an important factor for the design of platinum catalyst under the oxidizing atmosphere.
Keywords: Electrophilic/electrophobic property of the support materials; Oxidation-resistance of platinum; Platinum dispersion; Propane combustion; Supported platinum catalyst; Support effect;
Butene skeletal isomerization over H-ferrierite: a TEOM and in situ IR study on the role of carbonaceous deposits and the location of Brønsted acid sites by Sander van Donk; Eveline Bus; Alfred Broersma; Johannes H Bitter; Krijn P de Jong (149-159).
Butene skeletal isomerization over H-ferrierite (H-FER) is monitored in a catalysis set-up including a tapered element oscillating microbalance (TEOM) and using in situ infrared (IR) spectroscopy. For the first time the location and number of vacant Brønsted acid groups sited in the 10, 8, 6, and 5 membered rings (MRs) of the H-ferrierite framework are established as a function of time-on-stream (TOS). By deconvolution of the acid site-band, it is determined that with proceeding reaction the 8 MR channels are blocked and the available micropore volume and Brønsted acidity on the aged H-ferrierite will be primarily located inside the 10 MR channels. When a maximum amount of hydrocarbons is deposited on the catalyst, vacant Brønsted acid sites are still present. Additionally, IR spectroscopy shows that with TOS carbonaceous deposits are slowly converted from hydrogen-rich alkyl-aromatics into hydrogen-poor cyclopenta-fused-alkyl-aromatics, reducing by-product formation and therefore enhancing isobutene selectivity.
Keywords: n-Butene skeletal isomerization; Isobutene; Ferrierite; H-FER; Carbonaceous deposits; Coke; Oscillating microbalance; Infrared spectroscopy;
Radioisotopic study of CoMo/Al2O3 sulfide catalysts for HDS by V.M. Kogan (161-169).
Using 35 S , reaction temperature effects within the range of 300–400 °C on the number and reactivity of active sites of sulfidized Mo/A2O3 catalysts (non-) promoted by Co in thiophene hydrodesulfurization (HDS) have been studied. On the basis of the results of the radioisotopic tests of the catalysts, changes in the number and mobility of the surface SH groups, as well as relationships between them and the coordinatively unsaturated sites (CUS) have been evaluated. Estimated dependencies have been explained in the terms of the “forcing out” mechanism.
Keywords: Active sites; Catalysis; CoMo/Al2O3; 3 H ; 35 S ; Radioisotopic methods; Reaction mechanisms; SH groups; Temperature effects; Thiophene; Vacancies;
Dehydrogenation of methanol over copper-containing catalysts by T.P. Minyukova; I.I. Simentsova; A.V. Khasin; N.V. Shtertser; N.A. Baronskaya; A.A. Khassin; T.M. Yurieva (171-180).
The catalytic properties in methanol dehydrogenation of copper metal formed as a result of reduction by hydrogen of copper-containing oxides with different structure: copper chromite (tetragonally distorted spinel), copper hydroxysilicate (Chrysocolla), and copper-zinc hydroxysilicate (Zincsilite) have been studied. This process proceeds via successive reactions: (I) 2CH3OH=CH3OOCH+2H2 and (II) CH3OOCH=2CO+2H2.The methyl formate selectivity for the catalysts studied was close to 1.0 at low methanol conversion, X≤0.1, where the dehydrogenation process is represented by reaction (I), occurring far from its equilibrium. At 0.2≤X≤0.55, the selectivity decreases with increasing conversion, and the ratio of the activities in successive reactions may serve as a comparative characteristic for the catalysts. At high conversions, when reaction (I) is close to its equilibrium, selectivity is independent of the properties of studied catalysts and depends on the methanol conversion.Reaction (I) shows low sensitivity to the state of metal copper of reduced catalysts and, hence, low sensitivity to the composition and structure of oxides-precursors. The catalysts’ activity in reaction (II) greatly depends on the state of metal copper in the catalysts. It was assumed that the catalyst activity in methyl formate conversion to CO and H2 and, hence, the selectivity of methanol dehydrogenation with respect to methyl formate in the region of moderate methanol conversion depends on the strength of interaction between metal copper particles and catalyst oxide surface, which is determined by the composition and structure of oxide-precursor.
Keywords: Methanol dehydrogenation; Methyl formate; Cu-containing catalysts;
Liquid phase hydrogenation of citral: suppression of side reactions by Päivi Mäki-Arvela; Lasse-Pekka Tiainen; Ahmad Kalantar Neyestanaki; Rainer Sjöholm; Tiina-Kaisa Rantakylä; Ensio Laine; Tapio Salmi; Dmitry Yu Murzin (181-200).
Selective hydrogenation of citral was investigated at 70 °C in four different alcohols over Ru, Rh and Ni supported catalysts. The main aim was to suppress the side reaction, like acetalization and cyclization of citronellal. Acetalization could be suppressed either by using chloride-free catalyst precursors and other supports than active carbon or by using longer chained alcohols, like 2-pentanol and 2-methyl-2-propanol as solvents. The highest maximum selectivity to citronellol (92%) was obtained in citral hydrogenation in ethanol over Ni/Al2O3 catalyst, which was pre-reduced ex situ at 350 °C and in situ at 350 °C for 2 h in ethanol. The acidic alumina support was covered by spillover hydrogen, suppressing the acetalization reaction. Citronellal cyclization increased with the increasing solvent hydrophobicity and was also larger over active carbon supported Ru catalyst.
Keywords: Citral hydrogenation; Acetalization; Cyclization; Nickel;
Competitive reactions in alkyne hydrogenation by Christine A Hamilton; S.David Jackson; Gordon J Kelly; Ron Spence; David de Bruin (201-209).
Competitive hydrogenation reactions between alkynes have been studied over a palladium/carbon catalyst. The competitive reactions of 1-pentyne, phenyl acetylene, 2-pentyne, and 1-phenyl-1-propyne have been examined. The results show that in general, the competitive reaction results in a reduction of the hydrogenation rate for both alkynes. However, the 1-pentyne/2-pentyne couple revealed a rate enhancement for both alkynes. This is thought to be due to enhanced hydrogen transfer on the surface. Terminal alkynes reduced the rate of hydrogenation of a competing alkyne more effectively than internal alkynes. Phenyl acetylene was very sensitive to the presence of the second alkyne with its hydrogenation rate being reduced proportionately more than the aliphatic alkyne. This may be related to a disruption of its π–π stacking ability. Competitive hydrogenation increased selectivity to the respective alkenes but had no effect on the cis:trans ratio.
Keywords: Hydrogenation; Alkynes; Competitive reactions; Palladium; 1-Pentyne; 2-Pentyne; Phenyl acetylene; 1-Phenyl-1-propyne;
Transalkylation of toluene with trimethylbenzenes catalyzed by various AFI catalysts by E Dumitriu; C Guimon; V Hulea; D Lutic; I Fechete (211-221).
Substitution of transition metals in the AlPO4-5 framework was found to afford novel heterogeneous catalysts for the transalkylation of toluene (T) with trimethylbenzenes (TMBs). The activity of MeAPO-5 catalysts follows the order of SiAPO>MgAPO>MnAPO>ZnAPO>CoAPO which can be correlated with the acid properties of catalysts. The same correlation was found for MeAPSO-5 catalysts. The strength of acid sites of the catalyst influences the competition among various reactions that occur during the transalkylation process. Generally, the transalkylation and/or disproportionation reactions occur on stronger acid sites, while the isomerization of xylenes (Xs) and TMBs predominate on weaker acid sites.
Keywords: SiAPO-5; MeAPO-5; MeAPSO-5; Transalkylation of toluene; Trimethylbenzenes;
Ammonia decomposition over the carbon-based iron catalyst promoted with potassium by Anna Jedynak; Zbigniew Kowalczyk; Dariusz Szmigiel; Wioletta Raróg; Jerzy Zieliński (223-226).
Kinetics of NH3 decomposition over the K+-promoted iron catalysts supported on graphitized carbon (surface area=440 m2/g) have been studied under 1 bar pressure. Both the ammonia partial pressure dependence (5–20% NH3 in the H2:N2=3:1 mixture) and temperature dependence of the reaction rates have been determined. The studies demonstrate that the rate of ammonia decomposition (TOF) over K+-Fe/C is influenced by the size of iron particles: smaller particles exhibit higher TOF. The apparent energy of activation for K+-Fe/C (166 kJ/mol) proved to be similar to that for the fused iron catalyst (167 kJ/mol) and significantly higher than the activation energy for K+-Ru/C (139 kJ/mol). The Langmuir–Hinshelwood modeling based on the NH3 decomposition data obtained and corresponding data for NH3 synthesis suggest that the Fe surfaces of the K+-Fe/C catalyst are strongly covered with atomic nitrogen when operating under the high pressure NH3 synthesis conditions.
Keywords: Ammonia decomposition; Iron catalysts; Carbon support; Potassium promotion;
(Ni)W/ZrO2 hydrotreating catalysts prepared in molten salts by P Afanasiev; M Cattenot; C Geantet; N Matsubayashi; K Sato; S Shimada (227-237).
(Ni)W/ZrO2 oxide catalysts have been prepared using reactions in molten Na(K)NO3 fluxes at different temperatures ranging from 350 to 500 °C. The solids were characterized using X-ray diffraction (XRD), textural measurements and X-ray photoelectron spectroscopy (XPS). Highly dispersed zirconia with tungstate species grafted on its surface was formed at 450–500 °C. At 350–400 °C tungsten oxide or crystalline intermediate polytungstates of K and Na were observed in the products. Specific surface areas of the solids were high, up to 250 m2/g, due to stabilizing effect of tungstate species. After sulfidation, the catalysts were studied by XPS in situ, and tested in the model reactions of hydrodesulfurisation (HDS) and hydrogenation (HYD). XPS study reveal incomplete sulfidation of tungsten even at 500 °C, suggesting some persistent Zr–O–W bonds. Compared with conventional impregnation NiMo/Al2O3 systems, the (Ni)W/ZrO2 solids showed increased hydrogenating activity.
Keywords: Zirconia; Molten nitrate; Tungsten; Nickel; Hydrotreating;
On the applicability of membrane technology to the catalysed dry reforming of methane by P Ferreira-Aparicio; I Rodrı́guez-Ramos; A Guerrero-Ruiz (239-252).
The coupling of a catalytic reactor and a separator in the same unit is an attractive concept which still entails complex technological problems caused by the generally severe conditions at which a large part of heterogeneous catalytic reactions take place. The application of this technology to the conversion enhancement in reversible chemical reactions with high reaction enthalpies can provide interesting advances in the methane conversion processes. This paper analyses the applicability of mesoporous ceramic filters in a membrane reactor to carry out the reforming of methane with carbon dioxide. The effect of the variation of the sweep gas flow rate as compared to the feed rate of reactants has been studied. It has been observed that, even for membranes in which the main mechanism for the gas transport is the Knudsen diffusion, high sweep gas flows rates induce large changes in the distribution of species at both sides of the membrane. This change is dependent on the membrane permeance and gives place not only to a moderate conversion enhancement but also to maximise selectivity to hydrogen by hindering the progress of the secondary reverse water gas shift reaction.
Keywords: Carbon dioxide reforming of methane; Membrane reactor; Porous ceramic membrane; Syngas production;
Influence of oxidizing and reducing treatments on the metal–metal interactions and on the activity for nitrate reduction of a Pt-Cu bimetallic catalyst by Florence Epron; Florence Gauthard; Jacques Barbier (253-261).
Bimetallic Pt-Cu/γAl2O3 catalyst has been prepared by controlled deposition of copper onto platinum particles according to a redox reaction between hydrogen, pre-adsorbed on metallic platinum, and Cu2+ ions in water. This catalyst has been submitted to either oxidizing or reducing treatments, at ambient temperature or at 400 °C. The interaction between copper and platinum in the bimetallic catalysts was estimated from temperature-programmed reduction (TPR) profiles, determined after various pre-treatments, and compared to that of a fresh catalyst. It was demonstrated that reducing and oxidizing pre-treatments noticeably affect the interactions between platinum and copper and consequently the catalytic activity for nitrate reduction in water.
Keywords: Nitrate; Nitrite; Pt-Cu catalysts; Catalytic reduction; TPR; Morphological modifications; Pre-treatment effect;
V2O5–SmVO4 mechanical mixture: oxidative dehydrogenation of propane by Bibiana P. Barbero; Luis E. Cadus (263-273).
V2O5, SmVO4 and the mechanical mixtures of them in two different mass ratios were studied in the reaction of oxidative dehydrogenation of propane to propene. The results of the catalytic activity indicate the presence of a synergy effect in the yield to propene at reaction temperatures lower than 450 °C. This synergy effect disappears when the reaction temperature increases. When the catalysts tested at 500 °C were re-evaluated at low temperatures (350–400 °C), a significant decrease in yield to propene was observed. By the results of physicochemical characterization (BET, X-ray diffraction (XRD), temperature programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS)), it can be inferred that the synergy would be due to a transient state of the catalytic system. In it, surface vanadium species adsorbed on the SmVO4 and originated by V2O5 migration would constitute active and selective centers for the oxidative dehydrogenation of propane. The reason for the loss of synergy when the reaction temperature increases would be that the transformation of the catalytic system continues towards the coverage of SmVO4 phase by V2O5. Thus, the surface of SmVO4 is covered by conglomerates of surface VO x species and even recrystallized V2O5. This surface transformation modifies the catalytic performance of the system.
Keywords: Oxidative dehydrogenation of propane; Vanadium pentoxide; Samarium orthovanadate; Mechanical mixtures; Synergy effect;
Heterogeneous asymmetric reactions by Kornél Szöri; Mária Sutyinszki; Károly Felföldi; Mihály Bartók (275-280).
α-Ketoesters (1–11: MeCOCOOR1, R1=Me, Et, i-Pr, i-Bu, t-Bu, neo-pentil, and RCOCOOEt, R=i-Pr, i-Bu, t-Bu, Ph, PhCH2CH2) can be hydrogenated with high enantioselectivity under mild experimental conditions (0 °C and room temperature, H2 pressure 1–25 bar) on Pt-alumina catalyst modified with cinchona alkaloids. In this way α-hydroxy esters that are important building blocks in organic syntheses can be produced in high optical yield (>90%).
Keywords: Enantioselective; Hydrogenation; Pt-alumina; Cinchonidine–cinchonine; α-Ketoesters; α-Hydroxy esters;
AUTHOR INDEX (283-284).
SUBJECT INDEX (285-289).
CONTENTS CONTINUED (291-292).