Applied Catalysis A, General (v.251, #1)
EDITORIAL BOARD (iii).
Three-phase hydrogenation of d-glucose over a carbon supported ruthenium catalyst—mass transfer and kinetics by Edwin Crezee; Bram W. Hoffer; Rob J. Berger; Michiel Makkee; Freek Kapteijn; Jacob A. Moulijn (1-17).
The catalytic hydrogenation of d-glucose to d-sorbitol over a 5% Ru/C catalyst was studied in a semi-batch slurry autoclave operating at 373–403 K and 4.0–7.5 MPa hydrogen pressure. The d-glucose concentration was varied between 0.56 and 1.39 mol/l. The kinetic experiments were carried out in the absence of mass transport limitations, which was verified by using measured gas–liquid mass transfer coefficients and estimated diffusion and liquid–solid mass transfer coefficients. Many literature reports suffer from transport limitations. In the operating regime studied the reaction rate showed a first order dependency with respect to hydrogen. A shift in the order of d-glucose was observed. At low d-glucose concentrations (up to ca. 0.3 mol/l) the reaction showed a first order dependency, while at higher concentrations this changed to zero order behavior. No inhibition by sorbitol or mannitol was observed. The kinetic data were modeled using three plausible rate models based on Langmuir–Hinshelwood–Hougen–Watson (LHHW) kinetics assuming that the surface reaction is rate-determining. Model 1 involves non-competitive adsorption of hydrogen and d-glucose. Hydrogen adsorption is either molecular or dissociative, but due to the weak adsorption it results in both cases in a linear hydrogen pressure dependency, i.e. the same rate expression; Model 2 is based on competitive adsorption of molecular hydrogen and d-glucose; and Model 3 assumes competitive adsorption of dissociatively chemisorbed hydrogen and d-glucose. All three models described the data satisfactorily and further statistic discrimination between these models was not possible.
Keywords: Ru/C; Kinetics; d-Glucose; Hydrogenation; Mass transfer; d-Sorbitol; Modeling;
Catalytic oxidation of trans-stilbene using pyrolysed manganese-loaded cation exchange resin by Philippe Trens; Valérie Caps; John W. Peckett (19-28).
The work presented in this paper describes a method for the preparation of supported metal catalysts on carbon matrix. Manganese used as metal catalyst was loaded onto an ion exchange resin and this precursor was calcined over a wide range of temperature between 600 and 900 °C. The final materials consist of discrete (typically 0.5–0.8 mm diameter) spherical particles of manganese-loaded carbon. Electron microscopy was performed, which demonstrated that the structural integrity of the particles is maintained after calcination. Textural characterisation evidenced a correlation between the temperature of calcination, the specific surface area and the density of the calcined materials. The chemical moieties present, as found by XRD analysis, have been established and the catalytic activity of the material for oxidation reactions has been tested.The catalytic activity of the calcined materials was examined in the case of the oxidation of trans-stilbene to trans-stilbene oxide for different calcination temperatures. trans-Stilbene oxide and benzaldeyde were found to be the major products of the oxidation reaction. Conversions of >50%, at all pyrolysis temperatures, were achieved at 55 °C in 144 h.
Keywords: trans-Stilbene; trans-Stilbene oxide; Ion exchange resin;
Oxidation of ethane and cyclohexane over vanadia-niobia-silica catalysts by Carlo Resini; Marta Panizza; Fabio Raccoli; Michela Fadda; Maria M. Carnasciali; Guido Busca; Enrique Fernandez Lopez; Vicente Sanchez Escribano (29-38).
The conversion of ethane and cyclohexane in the presence of oxygen has been investigated on vanadia-silica (VS), niobia-silica (NS) and 1:1 vanadia-niobia-silica (VNS) catalysts. Vanadia-silica is an active catalyst for the production of ethylene from ethane and of benzene from cyclohexane. Selectivity to ethylene near 60% is obtained at near 10% ethane conversion near 820 K. Selectivity to benzene declines from above 70 to 40% when conversion of cyclohexane grows up to 40%. Cyclohexene is produced only after total oxygen conversion. Niobia-silica is much less active than vanadia-silica, and the selectivities to ethylene and to benzene grow by increasing conversion up to approach those obtained in the empty reactor at very high temperatures (above 900–1000 K). The vanadia-niobia-silica catalyst behaves quite like the vanadia-silica catalyst.Raman, UV-Vis and XRD characterization experiments show that V2O5 particles are present both in vanadia-silica and in niobia-vanadia-silica. On the contrary niobium oxide is present as amorphous phase and traces of V-Nb mixed oxide are found in the V-Nb-silica catalyst.
Keywords: Vanadium oxide; Niobium oxide; Ethane oxidation; Cyclohexane oxidation; Catalysts characterization;
Selective oxidation of styrene over nanosized spinel-type Mg x Fe3−x O4 complex oxide catalysts by Ning Ma; Yinghong Yue; Weiming Hua; Zi Gao (39-47).
Nanosized spinel-type Mg x Fe3−x O4 complex oxide catalysts were prepared by coprecipitation and citrate gel methods and were characterized. The crystallization temperature of spinel particles prepared by citrate gel method is about 300 °C lower than that of those prepared by coprecipitation method. Mg x Fe3−x O4 catalysts prepared by citrate gel method have higher dispersity and smaller particle size, leading to higher activity for styrene oxidation with H2O2 as oxidant. The nonstoichiometric Mg x Fe3−x O4 catalysts (x<1) are more active for styrene oxidation than the pure spinel MgFe2O4. The major reaction (∼65–70 mol%) is oxidative CC cleavage into benzaldehyde, and the minor reaction (10 mol%) is epoxidation and its further isomerization into phenylacetaldehyde. The effects of solvent, styrene:H2O2 molar ratio, reaction temperature and time on the conversion and product distribution were also studied.
Keywords: Nanosized Mg x Fe3−x O4 spinel; Styrene oxidation; Hydrogen peroxide; Benzaldehyde;
Cr/V/Sb mixed oxides, catalysts for the ammoxidation of propane to acrylonitrile by N Ballarini; F Cavani; M Cimini; F Trifirò; R Catani; U Cornaro; D Ghisletti (49-59).
Rutile-type, Cr/V/Sb mixed oxides having different atomic ratio between components were studied as catalysts for propane and propylene ammoxidation to acrylonitrile. Catalysts were more active than Cr/Sb and V/Sb mixed oxides; this was attributed to (i) the higher specific surface area of Cr/Sb/O and Cr/V/Sb/O with respect to V/Sb/O, and (ii) the preferential formation of V4+ in Cr/V/Sb/O. The nature of the V species and the catalytic performance of Cr/V/Sb/O samples were functions of the (Cr+V)/Sb atomic ratio. When the latter was higher than ≈1, the prevailing species was V4+; the catalysts were very active but poorly selective to acrylonitrile (selectivity lower than 20%) because of the prevailing formation of carbon oxides and propylene. This was due to the absence of sites able to transform the unsaturated intermediate to acrylonitrile. When the (Cr+V)/Sb ratio was between ≈1 and ≈0.5, catalysts reached a selectivity to acrylonitrile between 20 and 30%, and to propylene lower than 10%. In these samples, the presence of intra-crystalline Sb gradients in the rutile lattice provided a Sb surface enrichment and the development of allylic ammoxidation sites, able to transform the unsaturated intermediate to acrylonitrile. When the (Cr+V)/Sb ratio was lower than ≈0.5, i.e. in systems having excess Sb, the prevailing species was V3+; the selectivity to acrylonitrile was higher than 30%, with low formation of carbon oxides and of propylene. In this case additional sites for allylic ammoxidation were provided by excess antimony oxide dispersed over the rutile surface.
Keywords: Ammoxidation of propane; Ammoxidation of propylene; Acrylonitrile; Chromium, antimony, vanadium oxides;
RE0.6Zr0.4−x Y x O2 (RE = Ce, Pr; x = 0, 0.05) solid solutions: an investigation on defective structure, oxygen mobility, oxygen storage capacity, and redox properties by H He; H.X Dai; K.W Wong; C.T Au (61-74).
We have examined the crystal structures, surface textures, oxygen mobility, oxygen storage capacity, and redox behaviors of RE0.6Zr0.4−x Y x O2 (RE=Ce, Pr; x=0, 0.05) solid solutions. According to the results of X-ray diffraction (XRD) studies, there are two cubic phases (Ce0.75Zr0.25O2, major; ZrO1.87, minor) in Ce0.6Zr0.4O2 (denoted as CZ hereafter) and Ce0.6Zr0.35Y0.05O2 (CZY), but only one cubic phase in Pr0.60Zr0.40O2 (PZ) and Pr0.60Zr0.35Y0.05O2 (PZY). These nanosized materials are porous and have large surface areas. As revealed by the Ce 3d and Pr 3d results of X-ray photoelectron spectroscopic (XPS) investigations, the doping of Y3+ ions into the CZ and PZ lattices resulted in an increase in concentration of oxygen vacancies and Ce3+ and Pr4+ ions. The results of H2 (or CO)–O2 titration and temperature-programmed reduction (TPR)–reoxidation experiments indicate the presence of a reversible redox behavior of Ce4+/Ce3+ in CZY and Pr4+/Pr3+ in PZY. The results of 18 O/16 O exchange studies show that, with the presence of oxygen vacancies, the lattice O2− mobility on/in CZY and PZY enhanced. Based on such outcomes, we conclude that, by incorporating Y3+ ions into CZ and PZ, one can enhance (i) lattice oxygen mobility, (ii) Ce3+ and Pr4+ concentrations, and (iii) oxygen uptake capacity. We observed that PZY is superior to CZY in redox behavior, oxygen mobility, and oxygen storage capacity.
Keywords: CeO2–ZrO2; PrO2–ZrO2; RE0.6Zr0.4−x Y x O2 (RE=Ce, Pr; x=0, 0.05); Yttrium-incorporated CeO2–ZrO2 and PrO2–ZrO2 solid solutions; Redox property; Lattice oxygen mobility; Oxygen storage capacity; 18 O/16 O isotope exchange;
Selective low temperature carbon monoxide oxidation in H2-rich gas streams over activated carbon supported catalysts by Şeyma Özkara; Ahmet Erhan Aksoylu (75-83).
Selective oxidation of CO in a H2-rich gas stream was investigated over a series of Pt-Ce and Pt-Sn catalysts supported on activated carbon (AC). In order to study the effect of AC surface chemistry on the catalytic performance of AC supported catalysts, three types of activated carbon, namely (i) grinded and HCl washed activated carbon (AC1), (ii) air-oxidized form of AC1 (AC2), and (iii) HNO3 oxidized form of AC1 (AC3), were prepared and used as catalyst supports.The results have shown that the activities of AC supported catalysts increased with the increase in reduction temperature. Higher conversion levels were observed for 1% CeO x -1% Pt/AC and 0.25% SnO x -1% Pt/AC catalysts supported on oxidized AC supports compared to those prepared on non-oxidized support. Between these catalysts, the highest activity, ca. 80% CO conversion, is obtained on 0.25% SnO x -1% Pt/AC2.
Keywords: Selective CO oxidation; Activated carbon; Pt-Sn catalysts; Pt-Ce catalysts;
Deactivation of Mo/Al2O3 and NiMo/Al2O3 catalysts during hydrodesulfurization of thiophene by Bas M. Vogelaar; Petr Steiner; A. Dick van Langeveld; Sonja Eijsbouts; Jacob A. Moulijn (85-92).
A Mo/Al2O3 and a NiMo/Al2O3 catalyst were subjected to the gas-phase hydrodesulfurization (HDS) of thiophene. The mechanism of catalyst deactivation was investigated. Sintering or modification of the active phase and blocking of the active sites or the pore structure by coke deposition were considered as possible causes. The freshly sulfided and the spent catalysts were characterized by quasi in situ TEM, IR spectroscopy on adsorbed CO, total carbon analysis, N2 chemisorption and Hg porosimetry. For the NiMo/Al2O3 catalyst the main cause for deactivation is loss of sulfur during the reaction. This process is fully reversible by H2S/H2 treatment. In contrast coke deposition on the active sites is a major cause for deactivation of the Mo/Al2O3 catalyst.
Keywords: Hydrodesulfurization; NiMo/Al2O3; Thiophene HDS; Deactivation; Infra-red spectroscopy; FTIR;
Hydroisomerization of n-heptane and dehydration of 2-propanol on MoO2(H x )ac. catalysts by A Benadda; A Katrib; A Barama (93-105).
Catalytic hydroisomerization of n-heptane was carried out following the reduction by hydrogen of bulk MoO3, MoO3/TiO2, as well as MoO3 were present on the surface of commercial bulk MoO2. A conversion of 55% and a selectivity of more than 90% in isomerization products, mainly 2- and 3-methyl hexanes, were obtained at 573 K using the supported system. The major hydrocracking products obtained are C3 and C4 with a ratio C3/C4=1.2. Modifications of the reactant flow rate as well as the catalyst mass, enabled us to increase the conversion to 74% with a selectivity of 82% in isomerization products at 573 K reaction temperature. The catalytic active phase is attributed to the bifunctional MoO2(H x )ac. single phase. The metallic function is assured by MoO2 delocalized π electrons as identified by XPS–UPS in terms of density of state (DOS) at the Fermi-level. The Brönsted acidic functional group(s), (H x )ac. were deduced from the adsorption of ammonia, the isomerization of olefins at relatively low reaction temperatures in comparison to alkanes and the dehydration of 2-propanol.
Keywords: XPS and XRD of MoO3 and MoO2; Hydroisomerization of n-heptane; Dehydration of 2-propanol;
Effect of H2–O2 pre-treatments on the state of gallium in Ga/H-ZSM-5 propane aromatisation catalysts by Izabela Nowak; Juliette Quartararo; Eric G Derouane; Jacques C Védrine (107-120).
The state and local environment of gallium species in Ga/H-ZSM-5 zeolites prepared by ion-exchange have been identified by various techniques. Small GaO(OH) particles (diameter ∼4–5 nm) were present after synthesis at the outer surface of the zeolite crystals together with some isolated large particles (needles 0.5–1.5 μm long and 0.1–0.2 μm wide) of Ga2O3. Upon calcination at 823 K both were transformed into small Ga2O3 particles (diameter ∼4–5 nm), still at the outer surface of the zeolite crystals, while the needles disappeared almost completely. Reducing–oxidising cycles at 823 K enable the migration of these gallium species into the zeolite, most likely as ion-exchanged Ga species. The latter enhance the bifunctional (dehydrogenating and acidic) catalytic properties of the Ga-modified zeolite for the aromatisation of propane and it appears that maintaining those in the GaI oxidation state may enhance the aromatic yield.
Keywords: Ga/H-ZSM-5 zeolite; Propane aromatisation; Location Ga species; Effect H2/O2 treatment;
Wustite as a new precursor of industrial ammonia synthesis catalysts by N. Pernicone; F. Ferrero; I. Rossetti; L. Forni; P. Canton; P. Riello; G. Fagherazzi; M. Signoretto; F. Pinna (121-129).
Contradictory results about the best oxidic precursor of Fe ammonia synthesis catalyst prompted the present comparative investigation on wustite- and magnetite-based catalysts. Many physical (density, porous texture, crystalline phases, reduction rate, metal surface, abrasion loss) and catalytic (kinetic constants, thermoresistancy) properties have been determined on both catalysts. The wustite-based catalyst proved to be much more active, especially at lower temperatures, approaching the performances of Ru/C catalyst, except at high conversion. Possible reasons for such a behavior of the wustite-based catalyst are discussed, suggesting that a reconsideration of the present consolidated knowledge on Fe ammonia synthesis catalyst might be convenient.
Keywords: Ammonia synthesis; Wustite catalyst; Magnetite catalyst;
Novel supported Rh, Pt, Ir and Ru mesoporous aluminosilicates as catalysts for the hydrogenation of naphthalene by Mélanie Jacquin; Deborah J Jones; Jacques Rozière; Simone Albertazzi; Angelo Vaccari; Maurizio Lenarda; Loretta Storaro; Renzo Ganzerla (131-141).
Rh, Pt, Ir and Ru have been directly incorporated in mesoporous aluminosilicates prepared using direct liquid crystal templating with a non-ionic surfactant via addition of the corresponding metal complexes to the synthesis gel. In this approach, the non-ionic surfactant plays the role both of porogen and dispersant for the metal ions throughout the aluminosilicate, leading to controlled metal particle formation. Chemical–physical characterisation, simulated coking and regeneration tests, and catalytic behaviour towards naphthalene hydrogenation and ring opening are described. The catalyst activity in the hydrogenation of naphthalene has been studied at atmospheric pressure at 200 and 300 °C, and at 6 MPa between 220 and 340 °C. At atmospheric pressure, all four catalysts give a naphthalene conversion in the range of 95–96% at 200 °C, while at 300 °C, the Rh and Ru catalysts have the highest selectivity to high molecular weight (HMW) hydrogenolysis and/or ring-opening products, as shown by the relatively high formation of alkylbenzenes and decadiene. The effect of parameters such as temperature, contact time and H2/naphthalene ratio on conversion and selectivity to partially or fully hydrogenated products, HMW products and low molecular weight gases, was investigated under 6 MPa for the supported Rh catalyst. It provides a naphthalene conversion up to 98–99% and interesting selectivity, with a high proportion of HMW products between 260 and 300 °C, and a good thermal stability.
Keywords: Mesoporous aluminosilicates; Noble metal supported catalysts; Naphthalene hydrogenation/ring opening/hydrogenolysis;
Catalytic carbon monoxide oxidation over CoO x /CeO2 composite catalysts by Min Kang; Min Woo Song; Chang Ha Lee (143-156).
CoO x /CeO2 composite catalysts of different cobalt/ceria ratios have been prepared and tested for carbon monoxide oxidation in mixtures of carbon monoxide and oxygen. The small activity decay observed for them is due to carbon dioxide retention. The CoO x /CeO2 composite catalyst showed good resistance to water vapor poisoning. The catalysts were investigated by X-ray diffraction (XRD), temperature-programmed reduction (TPR), CO-TPD and XPS. The CoO x /CeO2 composite catalysts exhibit high catalytic activity in carbon monoxide oxidation, showing markedly enhanced catalytic activities due to the combined effect of cobalt oxide and ceria. Combining the results of XRD, TPR and XPS, we propose that the finely dispersed and higher valence state CoO x species mainly contribute to the catalytic activity.
Keywords: Ceria; Cobalt oxide; Composite catalyst; Carbon monoxide oxidation;
A study of CO removal on an activated Ru catalyst for polymer electrolyte fuel cell applications by Mitsuaki Echigo; Takeshi Tabata (157-166).
The influence of pre-treatment of a Ru/Al2O3 catalyst on the CO preferential oxidation activity was studied for the residential polymer electrolyte fuel cell (PEFC) cogeneration system. When a Ru/Al2O3 catalyst was heated in a H2/N2 mixed gas flow as the pre-treatment, the CO oxidation activity was highly improved at a low temperature range. When an activated Ru/Al2O3 catalyst was used with the pre-treatment, CO was removed from the simulated reformed gas to less than 6 ppm at [O2]/[CO]=1.0 and to less than 0.5 ppm at [O2]/[CO]=1.5. However, CO was not removed to below 10 ppm at [O2]/[CO]=1.5 on a non-activated Ru/Al2O3 catalyst without the pre-treatment. The temperature window, where CO was removed to below 10 ppm, of the activated Ru/Al2O3 catalyst was between ca. 90 °C and ca. 140 °C at [O2]/[CO]=1.0 and between ca. 85 °C and ca. 170 °C at [O2]/[CO]=1.5, while that of the non-activated Ru catalyst was between ca. 155 °C and ca. 180 °C at [O2]/[CO]=3.0.
Keywords: CO removal; Preferential oxidation; Reformed gas; Ru catalyst; Polymer electrolyte fuel cell; Residential use;
Kinetics of homo- and copolymerizations of ethylene by zirconocarborane catalyst cocatalyzed by AlR3 or methyl aluminoxane by Il Kim; Chang-Sik Ha (167-180).
Homo- and copolymerizations of ethylene have been carried out by zirconocarborane [Cp∗(C2B9H11)Zr(Me)] n (Cp∗: C5Me5, Me: methyl) catalyst in the presence of common alkylaluminum or methyl aluminoxane (MAO) as a cocatalyst. The polymerization rate was not proportional to the concentration of catalyst and was strongly dependent upon the type and amount of cocatalyst used for activation. The catalytic activity was sensitive to the polymerization temperature, due to the complicated equilibrium of the cyclopentadienyl dicarbollide complexes formed at different temperatures. Copolymerizations of ethylene and 1-hexene or 1-octene showed rate enhancement behavior, while the catalyst system was characterized by negligible comonomer reactivity. The multiple melting peaks of polyethylenes that can be fractionated demonstrated that the active sites are not uniform. End group analysis of the polymer showed that β-hydride elimination is a main chain transfer process, but the chain transfer to cocatalyst becomes dominant as the cocatalyst concentration increases.
Keywords: Kinetics; Ethylene; Polymerization; Zirconocarborane catalyst;
Hydroformylation of 1-butene catalyzed by water-soluble Rh-BISBIS complex in aqueous two-phase catalytic system by Maolin Yuan; Hua Chen; Ruixiang Li; Yaozhong Li; Xianjun Li (181-185).
This paper reports the hydroformylation of 1-butene catalyzed by RhCI(CO)(TPPTS)2 (TPPTS: P(m-C6H4SO3Na)3) and BISBIS (sodium salt of sulfonated 2,2′-bis(diphenylphosphinomethyl)-1,1′-biphenyl) in aqueous/organic two-phase catalytic system. The effects of reaction parameters on the catalytic activity and regioselectivity were investigated under the optimum reaction conditions: 130 °C, 2.5 MPa (syngas pressure), [BISBIS]/[Rh]=5, [1-butene]/[H2]/[CO]=1:1:1, [1-butene]/[Rh]=10 400, TOF and the regioselectivity for n-valeraldehyde were 2987 h−1 and 98%, respectively.
Keywords: Hydroformylation; 1-Butene; Water-soluble rhodium complex; Two-phase catalysis;
Radioisotopic study of (Co)Mo/Al2O3 sulfide catalysts for HDS by V.M Kogan; R.G Gaziev; S.W Lee; N.N Rozhdestvenskaya (187-198).
By using radioisotopic testing technique a poisoning effect of N-containing compounds on sulfided-( 35 S ) (Co)Mo catalysts in the reaction of thiophene hydrodesulfurization (HDS) has been studied. In the course of the experiments the number, distribution and reactivity of surface SH groups of various types and related functioning vacancies as well as catalytic activity of poisoned and non-poisoned Mo and CoMo catalysts have been measured. It has been shown that desulfurization (DS) and hydrogenation (HYD) reactions mostly proceed on the same sites. These sites are attributed as “rapid” and belong to Mo. The results have been compared with the literature data of the HDS of dibezothiophene (DBT) and its methyl derivatives. The comparison has shown that in the course of the HDS of thiophene and 4-methyl- and 4,6-dimethyldibenzothiophenes CoMoS catalysts demonstrate stronger resistance to poisoning in HYD reactions than DS ones. In the course of dibezothiophene HDS, catalysts demonstrate the opposite trend. It has been suggested that the DS of thiophene and alkyl derivatives of DBT and all the HYD reactions should proceed on Mo related sites while the DS of DBT—on Co related sites. The HYD reactions of the DS products of DBT should take place on Mo related sites. A method to evaluate the efficiency of (Co)MoS catalysts for HDS of various types of crudes has been developed.
Keywords: Active sites; Aniline; Catalysis; CoMo/Al2O3; CoMoS; DBT; 4-MDBT; 4,6-DMDBT; Efficiency of HDS catalysts; HDS; Poisoning by N-containing compounds; Pyridine; 35 S ; Sterically hindered adsorption; Radioisotopic methods; Reaction mechanisms; Residual oils; Thiophene; Quinoline; Vacancies;
Acetylene hydrogenation over Ni–Si–Al mixed oxides prepared by sol–gel technique by Claude Guimon; Aline Auroux; Enrique Romero; Antonio Monzon (199-214).
The effect of the support (here silica and silica-alumina) and of the composition of Ni-based hydrogenation catalysts, elaborated by sol–gel method, on their physico-chemical characteristics and on their activity and selectivity (towards ethylene) for acetylene hydrogenation has been studied with the help of temperature programmed reduction (TPR) and oxidation (TPO), X-ray photoelectron spectroscopy (XPS) and reaction tests (acetylene to ethylene hydrogenation). These techniques have shown the existence of two different types of sites. Firstly, the hydrogenolytic (naked) metallic centres, corresponding to nickel without (or little) interaction with the support, are responsible for a large part of the coke and are active for side-reactions. Secondly, the hydrogenating sites correspond to nickel in interaction with the support and are active for the main reaction. Three types of coke have been detected: filaments, amorphous coke, and partially hydrogenated carbons strongly adsorbed on the surface. The latter are facilitated by the acidity of the silica-alumina. Because the metal–support interactions related to a better dispersion of reduced nickel, silica-alumina-based catalysts produce a much smaller amount of coke than silica-based catalysts.
Keywords: Sol–gel Ni catalysts; Acetylene hydrogenation; Coking; TPR; TPO; XPS;
INSTRUCTIONS TO AUTHORS (217-221).
CONTENTS CONTINUED (223).