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Applied Catalysis A, General (v.297, #1)
Aerobic oxidation of glucose by Paolo Beltrame; Massimiliano Comotti; Cristina Della Pina; Michele Rossi (pp. 1-7).
The selective oxidation ofd-glucose tod-gluconic acid was performed in aqueous phase at atmospheric pressure, controlled pH value and different glucose and oxygen concentrations, in the temperature range from 303.2 to 333.2K, using a colloidal metal gold catalyst (average gold diameter 3.5nm). Initial rate was measured as a function of glucose and oxygen concentration: in the experimental conditions it was found that gluconic acid is produced together with hydrogen peroxide, which later decomposes in a fast way, due to the presence of alkali. The measurements were interpreted by considering different models based on different reaction pathways. Among the considered models, the experimental data fit with an Eley–Rideal mechanism where a glucose molecule, adsorbed on the catalyst, interacts with an oxygen molecule coming from the liquid phase. The model includes a kinetic parameter kcat and the equilibrium constant KG for the adsorption of glucose on the gold surface. The activation energy for kcat was found to be 47.0±1.7kJmol−1. It has been observed that KG decreases when temperature is increased, but the experimental uncertainty did not allow to obtain a precise value of the adsorption enthalpy. The values of the rate parameters here calculated for the colloidal gold catalyst have been compared with those previously obtained using the homogeneous enzymatic catalyst Hyderase under similar experimental condition. Considering geometric constraints, the specific activity of gold catalysis resulted quite similar to the enzymatic one.
Keywords: Gold catalyst; Glucose oxidation; Kinetic models; Eley–Rideal mechanism; Activation energy
Characterization and activity of zinc acetate complex supported over functionalized silica as a catalyst for the production of isopropyl palmitate by S.Y. Chin; A.L. Ahmad; A.R. Mohamed; S. Bhatia (pp. 8-17).
A hybrid silica gel-‘succinic acid-zinc acetate’ catalyst (SG-SAZnA) was synthesized for the esterification of palmitic acid with isopropanol. The scanning electron microscope (SEM) and X-ray diffraction (XRD) studies indicated the presence of a crystalline compound formed by the interaction of the surface succinic acid fragment and zinc acetate. The high thermal stability and catalytic activity of SG-SAZnA catalyst excluded the possibility of breaking of the bond between SA and the silica gel surface. The SG-SAZnA catalyst was mildly acidic, its surface area and average pore size were in the range of mesopores. The kinetics of the esterification of palmitic acid and isopropanol catalyzed by SG-SAZnA catalyst was studied in a stirred batch reactor for the synthesis of isopropyl palmitate. The effects of stirrer speed, reaction temperature, feed molar ratio, catalyst loading and reusability of the catalyst were evaluated. The SG-SAZnA catalyst activity was found to be higher compared to the hybrid silica gel–zinc acetate material (SG-ZnA) for the esterification reaction. The catalyst showed a long life and could be reused for various catalytic cycles without deactivation. The experimental reaction rates were correlated using different rate models. These models include the pseudo-homogeneous, Eley–Rideal and Langmuir Hinshelwood Hougen Watson models. The Langmuir Hinshelwood Hougen Watson (LHHW) model fitted the experimental kinetic data well over a wide range of operating conditions. The reaction parameters obtained from LHHW model were useful for the design of a catalytic distillation column for the production of isopropyl palmitate.
Keywords: Zinc acetate-supported catalyst; Catalytic activity; Esterification; Isopropyl palmitate; Characterization; Kinetic modeling
The activity of chromia-promoted skeletal copper catalysts for the oxidative dehydrogenation of ethanolamine to sodium glycinate based on measurements in a modified autoclave by Dongsheng Liu; Noel W. Cant; Andrew J. Smith; Mark S. Wainwright (pp. 18-23).
The activity of promoted and unpromoted skeletal copper catalysts for the oxidative dehydrogenation of ethanolamine to sodium glycinate in strong NaOH solutions has been studied using a modified stirred autoclave that allows the reactants to be brought to the reaction temperature of 160°C separately prior to mixing. This enables the study of activity and kinetics without complication from partial reaction and catalyst deactivation at lower temperatures. First order plots based on the continuous measurement of hydrogen evolution are close to linear throughout reaction. Unpromoted catalysts show substantial deactivation in repeated experiments but this can be eliminated by pretreatment in NaOH alone at temperatures above that used for reaction. This lowers the initial activity but helps the stability with treatment at 200°C in 9.7M NaOH being particularly effective. Small amounts of Cr2O3, deposited from sodium chromate included in the NaOH solution used to prepare the catalysts by leaching of a CuAl2 alloy, are a highly effective promoter. Catalysts containing 1–1.5wt.% Cr2O3, pretreated in 9.7M at 200°C, are several times as active as their unpromoted counterparts through the course of six successive reaction cycles. The promoted catalysts exhibit a much higher surface area, which correlates with the retention of aluminium in used catalysts, but the connection to the improved activity is complex.
Keywords: Raney copper; Dehydrogenation; Ethanolamine; Glycine; Deactivation; Chromia promotion
Hydrogenations of nitrate and nitrite in water over Pt–promoted Ni catalysts by Ikkou Mikami; Reo Kitayama; Toshio Okuhara (pp. 24-30).
Hydrogenations of nitrate (NO3−) and nitrite (NO2−) in water were studied with 40–5000ppm of the reactant at 333K using a gas–liquid flow reactor over Pt–promoted Ni catalysts. Porous Ni was highly active for hydrogenation of NO3− to form NH3 exclusively, but rapid deactivation was observed during the reaction. It was found that the addition of a small amount of Pt to the porous Ni greatly enhanced the stationary activity. The loading amount of Pt was sensitive to the activity; 1wt.% Pt–Ni exhibited the maximum activity. XPS measurements revealed that Pt suppressed the oxidation of the Ni0 atoms on the surface. The kinetic equation,v= k[NO3−]0.8 PH20.8, was obtained for the hydrogenation of NO3− over 1wt.% Pt–Ni. Results showed that 1wt.% Pt–Ni was highly active and stable even for 5000ppm of nitrate without the dissolutions of Pt and Ni. The product was mainly NH3 over Pt–Ni, independent of the concentration of NO3− or NO2−, the pressure of hydrogen or the reaction temperature.
Keywords: Hydrogenation; Nitrate; Nitrite; Porous Ni; Pt–Ni; Water-treatment
Surface and catalytic properties of pure CeO2 and MoO3-doped NiO/TiO2 system by N.R.E. Radwan; H.G. El-Shobaky; S.A. El-Molla (pp. 31-39).
Isopropanol conversion was carried out over TiO2 and pure and variously MoO3- and CeO2-doped NiO/TiO2 solids calcined at 300 and 500°C. The concentration of NiO was varied between 9 and 23mol% and those of dopants were changed within 1–6mol%. The effects of calcination temperature, dopant concentration and NiO content on the activity and selectivity of various solids were investigated. The techniques employed were XRD, nitrogen adsorption at −196°C and isopropanol conversion at 200–300 and 200–350°C for the solids heated at 300 and 500°C, respectively, using flow method. The results revealed that TiO2 (anatase) existed as major phase besides TiO2 (rutile), nickel titanate (major phase), NiO and NiMoO3 (minor phase) in heavily MoO3–NiO/TiO2 system. The rutile/anatase ratio was varied between 18% and 36% depending on calcination temperature and dopant concentration. Doping NiO/TiO2 decreased the crystallite size of anatase phase which varied between 7 and 23nm depending on the amount of dopant added and calcination temperature of doped solids. The catalytic activity of TiO2 much decreased by increasing its calcination temperature from 300 to 500°C. Opposite trend manifested in case of NiO/TiO2 solids. All solids investigated were selective in isopropanol conversion which proceeds, mainly, via dehydration yielding propene. Small amounts of acetone were produced via dehydrogenation of alcohol investigated specially at reaction temperature below 250°C. MoO3 and CeO2 doping of the system investigated resulted in a considerable increase in its catalytic activity. The increase was, however, more pronounced in case of MoO3-doping. The selectivity of various solids was only influenced by the reaction temperature reaching >90% at temperatures ≥250°C.
Keywords: NiO/TiO; 2; Isopropanol conversion; MoO; 3; CeO; 2; -doping
Factors influencing the catalytic activity of SBA-15-supported copper nanoparticles in CO oxidation by Cai-Hua Tu; Ai-Qin Wang; Ming-Yuan Zheng; Xiao-Dong Wang; Tao Zhang (pp. 40-47).
Copper nanoparticles were deposited onto mesoporous SBA-15 support via two different routes: post-grafting method and incipient wet impregnation method. Both XRD and TEM reveal that the post-grafting can make Cu particles very small in size and highly dispersed into channels of SBA-15, while the impregnation method mainly forms large Cu particles on the external surface of SBA-15. TPR experiments show that CuO species formed by the post-grafting method is more reducible than that prepared by the impregnation method. The catalytic activity tests for CO oxidation manifests that the sample prepared by the post-grafting method has a much higher activity than that prepared by the impregnation method, with a lowering of 50°C for T50, showing a strong dependence of catalytic activity on the size and dispersion of Cu particles. Besides the preparation procedure, other factors including calcination temperature, reduction treatment, copper loading as well as the feed composition, have an important effect on the catalytic activity. The best performance was obtained when the catalyst was calcined at 500°C and reduced at 550°C. The calcination and reduction treatment at high temperature have been found to be necessary to completely remove the organic residue and to generate active metallic copper particles.
Keywords: Copper nanoparticle; SBA-15; Catalysis; CO oxidation
Pt/CeO2 catalysts in crotonaldehyde hydrogenation: Selectivity, metal particle size and SMSI states by Mohamed Abid; Valerie Paul-Boncour; Raymonde Touroude (pp. 48-59).
Pt/CeO2 catalysts with different metal particle sizes were prepared by impregnation of chlorine-free precursor, Pt(NH3)4(NO3)2, with different Pt loadings (1, 3, 5, 10wt%), on a commercial ceria. These catalysts and a CePt5 powder, which was regarded as a reference catalyst, were tested in the hydrogenation of crotonaldehyde as a function of the reduction treatment (from 473–973K). A dramatic difference in the influence of the reduction temperature on the reactivity was observed between the high and low loaded metal catalysts: after reduction at 973K, high selectivity to crotyl alcohol (83%) was observed on the high loaded catalyst while on the 1% Pt/CeO2, crotyl alcohol selectivity was below 35%. Characterization by TEM, XPS and XRD showed differences in the particle size distributions and the presence of various nanostructural modifications during the increase of the reduction temperature. On the other hand, the reactivity of CePt5 powder indicates no ability of this compound for the carbonyl bond hydrogenation. The different SMSI states which could influence the reactivity are discussed: formation of epitaxial Pt (111) layer on CeO2 instead of Pt–CeO x interfacial sites or CePt5 sites, has been retained to be responsible for the increase in crotyl alcohol selectivity.
Keywords: Selective crotonaldehyde hydrogenation; Crotyl alcohol selectivity; Pt (1; 1; 1) epitaxy on ceria; SMSI states; Metal particle size effects; Structure sensitivity
Hydrogen production by oxidative reforming of hexadecane over Ni and Pt catalysts supported on Ce/La-doped Al2O3 by R.M. Navarro; M.C. Álvarez-Galván; F. Rosa; J.L.G. Fierro (pp. 60-72).
The activity and selectivity to hydrogen of alumina-supported nickel or platinum catalysts doped with Ce and La for the oxidative reforming of hexadecane were studied. The influence of both thermal stabilizer and activity promoter, such as lanthanum and cerium oxide, respectively, over hydrogen yield and catalyst durability was investigated. Catalytic activity was found to depend strongly on the type of metal, platinum showing lower specific activities per atom of metal exposed and a higher selectivity to combustion products than the Ni counterparts. The characterization results achieved with H2 chemisorption, XRD, TPR and XPS showed differences in surface metal concentrations and metal–support interactions which depend on the presence of cerium and/or lanthanum in the support composition. For both based metal catalysts higher reforming activities were found when active metals were deposited on Ce–La–Al2O3 substrate. For Pt-based catalysts, the increase in activity observed for the sample using Ce–La-modified alumina as support is suggested to be related with a participation of lanthanum in the reaction more than modifications on coke resistance or dispersion and state of platinum-induced by lanthanum. In the case of Ni-based catalysts, a lower carbon deposition and a higher thermal stability of metallic Ni particles under reaction conditions were observed for catalyst using Ce–La-modified alumina as support. It is suggested that the higher number of Ni–Ce and Ni–Al surface interactions developed Ce–La–Al2O3-supported Ni catalysts are responsible of the better catalytic behaviour of this sample in the oxidative reforming of hexadecane.
Keywords: Alumina-supported platinum and nickel catalysts; Cerium; Lanthanum; Hydrogen production; Hexadecane; Reforming; Oxidative reforming
Effect of water vapor on the transformation of VOHPO4·0.5H2O into (VO)2P2O7 by Naonori Ryumon; Hiroyuki Imai; Yuichi Kamiya; Toshio Okuhara (pp. 73-80).
The transformation of VOHPO4·0.5H2O to (VO)2P2O7 has been studied in the absence and presence of water vapor (0−40vol%) using small (340nm×40nm) and large (10,000nm×410nm) VOHPO4·0.5H2O crystallites. The small VOHPO4·0.5H2O crystallites were transformed into a single-phase of well-crystallized (VO)2P2O7 within 5h under a reactant gas (0.9% n-butane, 10% O2 and He(balance)) containing 40% water vapor, whereas the transformation took more than 100h in reactant gas without water vapor. In the large-sized VOHPO4·0.5H2O crystallites, (VO)2P2O7 was the main phase formed in the presence of reactant gas containing 40% water vapor, whereas αII-VOPO4 was the main product in the absence of water vapor. It was found that, under the reaction conditions, water vapor accelerated two processes in the transformation of VOHPO4·0.5H2O to (VO)2P2O7; the crystallization of the amorphous VP phase containing V4+ and V5+ to (VO)2P2O7 and δ-VOPO4, and the transformation of δ-VOPO4 to (VO)2P2O7. On the other hand, water vapor inhibited the topotactic transformation of VOHPO4·0.5H2O to (VO)2P2O7. The two processes accelerated by water vapor resulted in the rapid transformation of VOHPO4·0.5H2O to (VO)2P2O7 under the reactant gas. The catalyst obtained in the presence of water vapor gave stationary conversion and selectivity for MA from immediately after the beginning of the reaction. This catalyst showed a high selectivity for MA in comparison to the catalyst transformed in the absence of water vapor. Furthermore, over the catalyst formed in the absence of water vapor, it took more than 100h to reach stationary conversion and selectivity.
Keywords: Crystallization; Water vapor; Selective oxidation of; n; -butane; (VO); 2; P; 2; O; 7
The effect of voids and dilution on n-hexane oxidation over a VMgO catalyst by Holger B. Friedrich; Nishlan Govender; Mfanwenkosi R. Mathebula (pp. 81-89).
The conversion of n-hexane has been studied over magnesium orthovanadate (Mg3V2O8). This work illustrates some of the problems associated with alkane activation and subsequent conversion to more valuable products with respect to location of voids and the catalyst in the reactor. The effect of differently packed reactors and dilution factors on the product profile was investigated at a constant gas hourly space velocity (GHSV) of 3000h−1. The products included propane, propene, butane, benzene, carbon oxides and isomers of butene and hexene. Cracked products, propane and propene were favored in an empty reactor. Benzene production in an empty steel and glass reactor suggested that its formation was non-catalytic. Benzene production below 400°C was catalytically driven, whilst production above 400°C was thermodynamically driven. The product-selectivity profile was investigated with respect to catalytic products from the conversion of n-hexane over Mg3V2O8 and non-catalytic products from blank reactor and inert packed reactor experiments.
Keywords: Magnesium orthovanadate catalyst; VMgO; n; -Hexane oxidation; Voids; Dilution
Catalytic cracking of thiophene and benzothiophene: Mechanism and kinetics by J.A. Valla; A.A. Lappas; I.A. Vasalos (pp. 90-101).
The scope of the present study is to describe the cracking behavior of sulfur compounds during the fluid catalytic cracking (FCC) process. Specifically, the cracking mechanism of thiophene and benzothiophene molecules was investigated using model compounds. Experiments were performed in a fixed bed reactor unit, short contact time-microactivity testing (SCT-MAT) using a commercially available FCC catalyst deactivated with two different methods: steam deactivation with no metals using a laboratory fluid bed reactor and deactivation occurring in an industrial FCC unit (equilibrium). The latter represents a relatively slow deactivation in the presence of metals deposited from the feedstock and it was used in order to investigate the impact of Ni and V on the reaction mechanism. The model compounds were run in small concentrations either with hexadecane or with FCC gas oil. The experimental results indicated that thiophene is a very stable molecule, which undergoes mainly desulfurization reactions (leading to H2S and S deposition in coke), while alkylation and saturation reactions take place to a lower extent. It was found that the equilibrium catalyst (Ecat) promotes the deposition of S in coke while steamed deactivated catalyst favors the alkylation and saturation reactions. Benzothiophene is more reactive than thiophene and it participates in alkylation reactions resulting in heavier sulfur compounds with a boiling point outside the gasoline range. The above reactions are mainly promoted using the steamed catalyst. Based on the experimental results, reaction networks were proposed for both model compounds and the reaction rate parameters were estimated. Parity plots of experimental and predicted yields, as well as statistical analysis of the estimated kinetic parameters indicated that the suggested models simulated satisfactorily the cracking behavior of the specific sulfur compounds under the FCC conditions.
Keywords: Thiophene; Benzothiophene; FCC gasoline; Kinetic lumps
Effect of hydrochlorination and hydrofluorination of H-ZSM-5 on the catalytic hydroconversion reactions of cyclohexene by Ahmed K. Aboul-Gheit; Sameh M. Aboul-Fotouh; Sohair M. Abdel-Hamid; Noha A.K. Aboul-Gheit (pp. 102-110).
Modifying the acid sites (number and strength) of H-ZSM-5 zeolite via doping with 3.0wt.% HCl or HF for being used as catalysts for the hydroconversion of cyclohexene (CHE) in a flow-type fixed-bed reactor operated atmospherically in H2 carrier gas at temperatures of 50–400°C. The acid sites strength distribution in these zeolite forms was evaluated using temperature programmed desorption (TPD) of presorbed ammonia in a differential scanning calorimeter (DSC). Either HCl or HF incorporation has increased both acid sites number and strength in the zeolite to varying extents. Hydrochlorination enhanced the acid sites number in the zeolite to a larger extent than hydrofluorination, whereas, the latter enhanced the acid sites strength to a larger extent than hydrochlorination. Nevertheless, not only the acid catalysed reactions; i.e., isomerisation of the six-membered-ring of CHE to the five-membered ring compounds (methylcyclopentenes (MCPEs) plus methylcyclopentane (MCPA)) and hydrocracking reactions to lower molecular weight components, were enhanced via both hydrohalogenation treatments of the zeolite, but also hydrogenation of CHE to cyclohexane and MCPEs to MCPA and dehydrogenation of CHE to cyclohexadienes (CHDEs) plus benzene were also enhanced.
Keywords: Cyclohexene; Hydroconversion; H-ZSM-5; Zeolitel; Catalyst