Applied Catalysis A, General (v.250, #1)


Study of metalloporphyrin covalently bound to silica as catalyst in the ortho-dianisidine oxidation by Flávio Luiz Benedito; Shirley Nakagaki; Adelir A. Saczk; Patricio Guillermo Peralta-Zamora; Creuza Maieru Macedo Costa (1-11).
The model compounds for horseradish peroxidase (HRP) is reported, based on the association of H2O2 with iron and manganese porphyrins immobilized onto a functionalized silica gel. The models were developed in an attempt to find a biomimetical compound for systems containing heme groups. The ortho-dianisidine is a useful substrate model compound for checking the ability of degradation promoted by delignificant natural enzymes. The heterogeneous catalysts were obtained by grafting of three metalloporphyrins: (Fe(TFPP)—iron porphyrin from the 5,10,15,20-tetrakis (pentafluorophenyl) porphyrin—and Mn(TCPP) and Fe(TCPP), iron and manganese porphyrins from the 5,10,15,20-tetrakis (4-carboxyphenyl) porphyrin), onto the modified surface of silica gel. The oxidation of ortho-dianisidine was monitored by UV-Vis spectroscopy at room temperature using different ratios of catalyst, oxidant and substrate. At high H2O2 concentration, the perhalogenated iron porphyrin Fe(TFPP) produced best results, showing a turnover number of about 1100. This value was higher than those obtained for Fe(TCPP) and Mn(TCPP) systems.
Keywords: Silica; Porphyrin; Catalysis; Supported catalysts; ortho-Dianisidine; Oxidation; Horseradish peroxidase;

Methane reforming with carbon dioxide to synthesis gas over Co-doped Ni-based magnetoplumbite catalysts by JunXia Wang; Yan Liu; TieXin Cheng; WenXing Li; YingLi Bi; KaiJi Zhen (13-23).
A series of Co-doped magnetoplumbite LaNi x Co1−x Al11O19+δ catalysts were prepared and characterized by XRD, UV-DRS, TPR, and DTA–TG techniques. The experimental results showed that the series of catalysts possessed the pure magnetoplumbite structure and exhibited similar reduction stability values. At x≤0.375, the activities of the catalysts apparently increased with the increase of x-value, while over 0.375≤x≤1.0, the activities of the catalysts remained almost constant. Thus, it can be concluded that the content of Ni that is between 0.375≤x≤0.50, is suitable for the titled reaction.
Keywords: Magnetoplumbite LaNi x Co1−x Al11O19+δ ; Methane; CO2-reforming; Synthesis gas;

Effect of support nature on WO3/SiO2 structure and butene-1 metathesis by Yangdong Wang; Qingling Chen; Weimin Yang; Zaiku Xie; Wei Xu; Deyin Huang (25-37).
Two series of silica-supported tungsten oxide catalysts were prepared by impregnation of ammonium metatungstate aqueous solution on two silica supports with different specific surface areas, followed by calcination in air at high temperature. The prepared catalysts were characterized by X-ray diffraction (XRD), Raman spectroscopy, nitrogen adsorption and NH3-TPD. Their catalytic performances in butene-1 metathesis reaction were also investigated. The results revealed that the interaction of tungsten oxide with silica was weaker and that tungsten oxide selectively dispersed on the surface of support with a dispersion capacity of 0.5 W6+  nm−2. The states of tungsten oxide species formed on the catalyst were dependent on the loading amount of tungsten oxide and on the nature of supports. When the loading amount of tungsten oxide was lower than the dispersion capacity, tungsten oxide species were mainly in the tetrahedrally coordinated states. With the increase of loading amount, the surplus tungsten oxide assembled to form the distorted octahedrally coordinated species on the surface of catalyst. NH3-TPD results suggested that loading of tungsten oxide on silica should introduce new acid sites on the centers of the metal. As for the reaction of butene-1, the catalytic activity of butene metathesis and that of double bond isomerization over WO3/SiO2 were related to the states of tungsten oxide species and to the acid nature of the catalyst, respectively. Tetrahedrally coordinated tungsten oxide species were suggested to be the active centers for metathesis, while acid sites on surface of catalyst should be active centers for double bond isomerization of butene-1.
Keywords: Silica; Tungsten oxide; Metathesis; Butene-1; Isomerization;

A series of silicoaluminophosphate (SAPO)-11 molecular sieve samples by using various raw materials and process parameters was prepared. Two of the selected SAPO structure materials were formed in extrudate supports, impregnated with platinum acid solution, thermally treated and tested in hydroisomerization process of so-called “cetane fraction” (mixture of n-C13n-C20 hydrocarbons). It was found that the preferred parameters of SAPO-11 crystallization are: time, 20 h; temperature, 473 K, with use of n-propylamine as a pore shaping reagent. The obtained SAPO-11 samples were micro-porous materials, micropores consists of ca. 65% of total pore volume and 85% of total specific surface area. Application of Pt catalysts supported on SAPO-11 and alumina binder containing carrier (weight ratio 1:1) enabled hydroisomerization of cetane, n-paraffins fraction, with selectivity of 80–84%. At the low conversion levels the main product of isomerization were mono-branched paraffins while higher process temperature and the increase in conversion favoured obtaining of di- and poly-branched isomers.
Keywords: SAPO-11; Hydroisomerization; Cetane fraction;

Acetylene cyclotrimerization over Ni/SiO2 catalysts in hydrogen atmosphere by Abdel-Ghani Boudjahem; Serge Monteverdi; Michel Mercy; Mohammed M Bettahar (49-64).
Non-conventional Ni catalysts supported on low surface area SiO2 were prepared by reduction of nickel acetate by aqueous hydrazine, characterized by XRD and H2 chemisorption properties or TPSR and tested in acetylene cyclotrimerization in the presence of hydrogen. Their performances were compared with those of classical catalysts supported on silica of low or high surface area.Hydrogen TPD profiles exhibited the presence of active sites involving nickel or nickel in interaction with the support. Hydrogen storage increased for non-classical catalysts or low surface area support.Under the reaction conditions used, no cyclotrimerization of acetylene was observed in the absence of hydrogen, probably as a result of strong adsorption of benzene precursor species. In the presence of hydrogen, benzene and ethylene were the main products in the low reaction temperature regime (<80 °C) whereas ethane predominated in the higher temperature domain. Butane and higher hydrocarbons were also formed but in small amounts or as traces. Decreasing the nickel loading increased acetylene conversion and benzene selectivity to some extent but diminished selectivity of ethylene and ethane in the same proportions. A non-classical catalyst and a low surface area support favoured acetylene trimerization whereas a classical catalyst and a high surface area silica preferentially formed ethane. Increasing the hydrogen partial pressure increased conversion and C2 and C4 hydrogenation products at the expense of cyclotrimerization to benzene. Increasing the partial pressure of acetylene strongly deactivated the catalyst but favoured selectivity of both benzene and ethylene. The presence of both water vapour and hydrogen improved cylotrimerization to benzene at the expense of hydrogenation products, notably at low reaction temperatures.The effect of the different parameters on the sorptive and catalytic properties of the nickel catalysts prepared are discussed, notably the role of hydrogen and water in the determination of activity and reaction paths.
Keywords: Catalyst; Nickel; Silica; Acetylene; Cyclotrimerization; Hydrogenation;

Kinetic study of hydrogen adsorption on Pt/WO3-ZrO2 and WO3-ZrO2 by Sugeng Triwahyono; Takashi Yamada; Hideshi Hattori (65-73).
Rates of hydrogen adsorption on Pt/WO3-ZrO2 and WO3-ZrO2 were measured in the adsorption temperature range 323–573 K and the hydrogen pressure range 20–70 Torr (1 Torr = 133 Pa) to elucidate the rate-controlling step involved in the hydrogen adsorption, the corresponding energy barrier, and the heat of adsorption. The hydrogen adsorption was faster on Pt/WO3-ZrO2 than on WO3-ZrO2. On both Pt/WO3-ZrO2 and WO3-ZrO2, the adsorption continued for a long time. The adsorption continued for more than 10 h for Pt/WO3-ZrO2 below 373 K and for WO3-ZrO2 below 473 K. The adsorption of hydrogen involved the surface diffusion of hydrogen atoms for both adsorbents. For WO3-ZrO2, each hydrogen molecule was dissociated on a specific site of WO3-ZrO2 to form hydrogen atoms, which undergo surface diffusion over the surface of WO3-ZrO2. The rate-controlling step was the surface diffusion of hydrogen atoms. The activation energy was 25.9 kJ/mol for the surface diffusion. For Pt/WO3-ZrO2, two routes were operating. One route was same as that for WO3-ZrO2, and the other route involved dissociation of hydrogen molecules on the Pt sites to form hydrogen atoms that undergo spillover onto the WO3-ZrO2 surface, followed by surface diffusion. For the latter route, the rate-controlling step was the spillover step; its activation energy was 35.5 kJ/mol. The isosteric heats of adsorption of hydrogen on Pt/WO3-ZrO2 were obtained as 11.6–8.0 kJ/mol for the hydrogen uptake range 2–3×1019  atom H/g cat. Similarities and differences in hydrogen adsorption between SO4 2−-ZrO2 and WO3-ZrO2 types are discussed.
Keywords: Pt/WO3-ZrO2; WO3-ZrO2; Hydrogen adsorption; Spillover; Surface diffusion;

IR study of acid sites on WO3-ZrO2 by Sugeng Triwahyono; Takashi Yamada; Hideshi Hattori (75-81).
The mechanism of the generation of protonic acid sites from molecular hydrogen on WO3-ZrO2 was studied by IR spectroscopy. The spectral changes in the WO stretching and the OH stretching regions were observed in response to the exposure to hydrogen and the removal of hydrogen. By heating in the presence of hydrogen, the WO stretching bands at 1021 and 1014 cm−1 eroded and a broad band around 980 cm−1 was developed. The peaks at 1021, 1014 and 980 cm−1 restored to their original intensities on heating in a vacuum. A broad OH stretching band around 3600 cm−1 was intensified by heating in the presence of hydrogen and restored to its original intensity by removal of the hydrogen from a gas phase. Pyridine adsorption caused essentially the same changes in the WO stretching region as hydrogen adsorption. Based on the spectral changes, the changes in the structure of acid sites caused by hydrogen adsorption are proposed.
Keywords: WO3-ZrO2; Protonic acid site; IR;

Catalytic pyrolysis and partial oxidation of methane and liquefied petroleum gas (LPG) were studied using a novel wire-mesh reactor (WMR) and a quartz tubular reactor. A non-porous nickel mesh was used as a catalyst to avoid the complexity of internal pore diffusion. The catalyst activities were stable even for the pyrolysis of pure methane and LPG when short gas–catalyst contact times were used. The desorption of radicals from the mesh catalyst surface into the gas phase at short gas–catalyst contact time was an important process for the radicals, competing well even with the oxidation of these radicals by oxygen on the catalyst surface. The desorption of radicals plays an important role for the formation of reaction products, e.g. ethane from the pyrolysis and oxidation of methane. Scanning electron microscope (SEM) images and EDX analysis of the used mesh catalyst indicate that the desorption of radicals greatly limits the successive dehydrogenation of radicals on the catalyst surface and therefore greatly limits or eliminates the formation of coke on the surface of non-porous mesh catalyst. Our results have implications for the understanding of coke formation in a porous pellet catalyst.
Keywords: Radical desorption; Coke formation; Methane; LPG; Pyrolysis; Oxidative coupling; Mesh/gauze catalysts; Wire-mesh reactor; Short residence time;

Hydrodesulphurisation catalysts supported on alumina-titania by Jolanta R. Grzechowiak; Iwona Wereszczako-Zielińska; Jacek Rynkowski; Maria Ziółek (95-103).
Reducibility, sulphidability and hydrodesulphurisation (HDS) activity of molybdenum and molybdenum-nickel catalysts are related to the preparation method of alumina-titania supports. Supports containing 15 wt.% of titanium dioxide were prepared by hydrolysis of TiCl4 on alumina surfaces (impregnation method) and by the coprecipitation method. The activity of the catalysts was investigated for the HDS of diesel oil fraction (1.05 wt.% S).The molybdenum distribution and the effect of nickel on the reducibility and sulphidability of the molybdenum catalysts depends on the Al2O3-TiO2 supports preparation method. It was found that the formation of NiAl2O4 spinel was observed only on the support prepared by the coprecipitation method. The support obtained by this method is found to be of lower utility in the preparation of hydrodesulphurisation catalysts.
Keywords: Alumina-titania support; Molybdenum catalyst; Molybdenum-nickel catalyst; Hydrodesulphurisation; Sulphidability; TPR; SEM; HRTEM;

The different catalytic sites involved in hydrodenitrogenation (HDN) over supported sulfided Ni-Mo and Rh catalysts were investigated by means of four model reactions, the hydrodenitrogenation of methylcyclohexylamine (MCHA) and o-toluidine and the hydrogenation of cyclohexene (CHE) and toluene (TOL). By comparing the effects of the silica–alumina support and fluorination on the activity of these reactions, at least four sites were identified. The active site for C(sp3)N bond cleavage involves neighbouring acid and base sites. The site for C(sp2)N bond cleavage is highly unsaturated and accommodates aromatic amines in a flat adsorption mode. Hydrogenation of aromatics is favoured by high stacking of the MoS2 slabs with more edge and corner sites, whereas the hydrogenation of alkenes is favoured on catalysts with better dispersion and lower stacking of MoS2 slabs.
Keywords: Active sites; Hydrodenitrogenation; Hydrogenation; Alkenes; Aromatics; Toluidine; Ni-Mo; Rh; Alumina; Silica–alumina;

The catalytic hydrogenation of aqueous solutions of 3-hydroxypropanal (3-HPA) to 1,3-propanediol (1,3-PDO) was conducted at 40–60 °C and 40 bar hydrogen with heterogeneous ruthenium catalysts in a trickle-bed reactor. Catalysts were optimized to obtain stable activity and selectivity as a function of time on stream. Catalyst deactivation was attributed to the deposit of heavy organic impurities on the catalyst surface blocking the reactant access to the active ruthenium particles. The pore structure of the catalyst had a significant influence on the catalytic results. The most stable catalysts were supported on low surface area macroporous titania (rutile, ca. 1 m2  g−1), whereas mesoporous TiO2, and particularly microporous SiO2 supports deactivated because of surface blockage by organic impurities.
Keywords: 3-Hydroxypropanal hydrogenation; 1,3-Propanediol; Ruthenium catalysts; Titania support; Stability;

A theoretical analysis of thermal processes in liquid–gas exothermic reactions in a porous catalyst shows the existence of the alternating motion of liquid in the pore. According to this model, if the released heat in the pore exceeds a certain critical value, the alternating motion of the liquid driven by the formation of the bubble takes place in the pore. Specifically, because of the heating of the liquid in the pore, the partial pressure of vapor saturated in liquid increases until the total pressure of the saturated gas and vapor becomes greater than the maximum possible pressure in the pore (equal to the sum of capillary pressure and pressure in the reactor) and the bubble thereby comes into being. The growing bubble pushes the liquid out of the pore. Since the reagent(s) is no longer in the pore, the reaction ceases and the generated heat dissipates. The liquid penetrates into the pore due to capillary force and the process of bubble formation occurs once again. A detailed analysis of this non-stability is undertaken. This paper seeks to show how this theory can explain some dependencies of the reaction rate observed in practice, mass and heat transfer in the fixed and suspended catalyst as well as some practical recommendations for catalyst development and process intensification. Analogy between oscillation behaviour and the boiling process is considered.
Keywords: Multiphase exothermic reactions; Oscillation model; Catalysis; Mass and heat transfer; Kinetics; Effective diffusion;

Oxidative conversion of isobutane to isobutene over V-Sb-Ni oxide catalysts by V.P. Vislovskiy; N.T. Shamilov; A.M. Sardarly; R.M. Talyshinskii; V.Yu. Bychkov; P. Ruiz; V. Cortés Corberán; Z. Schay; Zs. Koppany (143-150).
Insertion of proper amounts of nickel oxide into alumina-supported V-Sb oxide catalyst for the oxidative dehydrogenation of isobutane substantially increases isobutane conversion (from 36 to 42–44%) at selectivity to isobutene ∼70%. Fresh and used catalysts (including reference bulk V-Sb-O and V-Sb-Ni-O systems) were characterised by BET, XRD, XPS and H2-TPR. Formation of new phase of nickel vanadate NiV2O6 at the expense of free VO x -phase leads to more reducible catalyst with increased amounts of mobile lattice oxygen. The facile redox cycle of vanadium species is considered to improve the catalyst activity.
Keywords: Isobutane; Oxidative dehydrogenation; Isobutene; Nickel oxide; Vanadium-antimony oxide catalysts;

Potassium fluoride doped fluorapatite and hydroxyapatite as new catalysts in organic synthesis by Abdellatif Smahi; Abderrahim Solhy; Hanane El Badaoui; Abderrahim Amoukal; Abdellatif Tikad; Mostafa Maizi; Saı̈d Sebti (151-159).
Fluorapatite (FAP) and hydroxyapatite (HAP) were prepared and doped with potassium fluoride. KF/FAP and KF/HAP were prepared by usual impregnating method. The doped materials were characterised by X-ray diffraction, BET surface area, BJH total pore volume and scanning electron microscopy (SEM). All this data were compared to that of unimpregnated apatites. Some modifications in the particles morphology were observed by doping apatites with KF. The comparison of the catalytic activity of KF, FAP, HAP, KF/FAP and KF/HAP indicate clearly the positive effect of the doping apatites by KF in the Knoevenagel condensation used as model reaction. In this work, KF/FAP and KF/HAP were prepared and used for the first time as new and efficient catalysts in heterogeneous solid–liquid synthesis.
Keywords: Heterogeneous catalysis; Fluorapatite; Hydroxyapatite; Potassium fluoride;

A mathematical model was developed in the framework of the process simulator Aspen Plus® in order to describe the reaction kinetics and performance of a fuel processor used for autothermal reforming of liquid hydrocarbons. Experimental results obtained in the facilities of Argonne National Laboratories (ANL) when reforming isooctane using a ceria-oxide catalyst impregnated with platinum were used in order to validate the reactor model. The reaction kinetics and reaction schemes were taken from published literature and most of the chemical reactions were modeled using the Langmuir–Hinshelwood–Hougen–Watson (LHHW) formulation to account for the effect of adsorption of reactants and products on the active sites of the catalyst. The water-gas-shift (WGS) reactor used to reduce the concentration of CO in the reformate was also modeled. Both reactor models use a simplified formulation for estimating the effectiveness factor of each chemical reaction in order to account for the effect of intraparticle mass transfer limitations on the reactor performance. Since the data in the literature on kinetics of autothermal reforming of liquid hydrocarbons using CeO2-Pt catalyst is scarce, the proposed kinetic model for the reaction network was coupled to the sequential quadratic programming (SQP) algorithm implemented in Aspen Plus® in order to regress the kinetic constants for the different reactions. The model describes the trend of the experimental data in terms of hydrogen yield and distribution of products with a relative deviation of ±15% for reforming temperatures between 600 and 800 °C and reactor space velocities between 15 000 and 150 000 h−1.
Keywords: Kinetic modeling; Reactor modeling; Reforming; Gasoline; Hydrogen;