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Applied Catalysis A, General (v.355, #1-2)

Editorial Board (pp. co2).

Contents (pp. iii-viii).

Review on criteria to ensure ideal behaviors in trickle-bed reactors by Fabián S. Mederos; Jorge Ancheyta; Jinwen Chen (pp. 1-19).

Trickle-bed reactors are frequently used in bench scale and pilot plant experiments to determine reaction kinetics and generate data for commercial scale-up. Depending on experimental conditions, these reactors sometimes cannot produce reliable and repeatable data if the influences of three main factors (plug flow deviation, external wetting efficiency, and reactor wall effect) on reactor performance are not properly minimized or eliminated. Therefore, it is highly desirable to operate a trickle-bed reactor at conditions at which these effects can be neglected so that reliable and repeatable data can be obtained. There have been various criteria reported in the literature to theoretically determine the influence of these factors. The objectives of this work are to conduct an extensive review on the studies related to these criteria and to further make recommendations as how to use these criteria to provide guidelines for designing experiments.Trickle-bed reactors are frequently used in bench scale and pilot plant experiments to determine reaction kinetics and generate data for commercial scale-up. Depending on experimental conditions, these reactors sometimes cannot produce accurate data if the influences of three main factors (plug flow deviation, external wetting efficiency, and reactor wall effect) on reactor performance are not properly minimized or eliminated. Therefore, it is highly desirable to operate a trickle-bed reactor at conditions at which these effects can be neglected so that reliable and repeatable data can be obtained. There have been various criteria reported in the literature to theoretically determine the influence of these factors. The objectives of this work are to conduct an extensive review on the studies related to these criteria and to further make recommendations as how to use these criteria to provide guidelines for designing experiments.

Keywords: Trickle-bed reactor; Plug flow deviation; External wetting efficiency; Reactor wall effect

A new activation process of bimetallic catalysts and application to the n-hexane isomerization by Carlos M.N. Yoshioka; Maura H. Jordão; Daniela Zanchet; Teresita F. Garetto; Dilson Cardoso (pp. 20-26).

Bimetallic catalysts applied to the n-hexane isomerization reaction containing Ni and Pt were characterized by X-ray absorption near edge spectroscopy (XANES), transmission electron microscopy (TEM), temperature programmed reduction (TPR) and chemisorption. The metal sites were dispersed in a HUSY zeolite with metallic and acids. The activity was performed using the catalyst activated in different temperatures following a new activation process, named “fast activation method” and the behavior showed maximum catalytic activity at 400°C activation temperature.▪Bimetallic catalysts applied to the n-hexane isomerization reaction were prepared with a constant molar content of 130μmol Me/g_cat of Ni and Pt and characterized in its active form by X-ray absorption near edge spectroscopy (XANES), transmission electron microscopy (TEM), temperature programmed reduction and hydrogen chemisorption techniques. The metal was dispersed in a HUSY zeolite matrix in order to provide both types of sites, metallic and acid, to obtain a bifunctional catalyst. The catalytic activity was evaluated using the catalyst activated at different temperatures following a new activation process, named “fast activation method” and the profile pointed out a maximum catalytic activity when the catalyst was activated at 400°C. XANES results showed that all samples present similar electronic properties in the studied conditions, despite the differences found in the average particle diameter obtained by TEM, suggesting that the catalytic activity is related to the metal/acid balance.

Keywords: Bimetallic catalyst; Fast activation; n; -Hexane isomerization; XANES; TEM

Nickel catalyst activation in the carbon dioxide reforming of methane by J. Juan-Juan; M.C. Román-Martínez; M.J. Illán-Gómez (pp. 27-32).

The activation of a Ni/Al₂O₃during the CO₂ reforming reaction and the effects of calcination and reduction pretreatments on the catalytic properties have been studied. The results show that the activity is not affected by the pre-treatment but a noticeable effect on the amount of coke deposited has been observed. The following figure shows variations in the gas composition during a CH₄-TPR experiment corresponding to the reaction that produces the catalyst activation.A Ni/Al₂O₃ catalyst has been submitted to different treatments prior to catalytic test in the dry reforming of methane. The performed pretreatments are: (i)calcination+hydrogen reduction, (ii) direct hydrogen reduction and (iii) heat treatment up to the reaction temperature under inert atmosphere. The activity is not affected by the pretreatment carried out but a noticeable effect on the amount of deposited coke has been observed, probably related with an influence of the pretreatment on the size and structure of the nickel particles.

Keywords: Calcination; Reduction; Methane dry reforming; Nickel catalyst

Effect of pre-treatment on physico-chemical properties and stability of carbon nanotubes supported iron Fischer–Tropsch catalysts by Reza M. Malek Abbaslou; Ahmad Tavasoli; Ajay K. Dalai (pp. 33-41).

This paper presents the effects of acid treatment on the activity, product selectivity and life span of iron Fischer–Tropsch (FT) catalysts supported on carbon nanotubes (CNTs). Two different types of CNTs with low surface area (∼30m²/g) and high surface area (∼180m²/g) were prepared and treated with 35wt% HNO₃ at 25°C and 110°C for 16h. Fe/CNTs were prepared using incipient wetness impregnation method with iron loading of 10wt%. The CNT supports and catalysts were characterized by nitrogen adsorption, ICP, TPR, XRD, SEM, TEM and Raman spectroscopy. The FT synthesis was carried out in a fixed-bed microreactor (275°C, 2MPa, CO/H₂=2) for 120h. Among the catalysts studied, Fe catalyst supported on pre-treated CNTs at 110°C was stable and active while, the other catalysts experienced rapid deactivations. The Fe catalyst supported on CNTs low surface area and larger diameter showed much lower CH₄ and higher C₅⁺ selectivities.This paper presents the effects of acid treatment on the activity, product selectivity and life span of iron Fischer–Tropsch (FT) catalysts supported on carbon nanotubes (CNTs). Two different types of CNTs with low surface area (∼25m²/g) and high surface area (∼170m²/g) were prepared and treated with 35wt% HNO₃ at 25°C and 110°C for 16h. Fe/CNTs were prepared using incipient wetness impregnation method with iron loading of 10wt%. The CNT supports and catalysts were characterized by nitrogen adsorption, ICP, TPR, XRD, SEM, TEM and Raman spectroscopy. The acid treatments at 25°C and 110°C increased the BET surface area by 18% and 31%. The results of Raman analysis revealed that the acid treatment increased the number of defects which are considered as anchoring site for metal particles. TEM analysis showed that the major parts of the iron particles were homogenously distributed inside the acid treated nanotubes. According to the XRD analysis, the acid treatment on both families of CNTs resulted in decrease in metal particle sizes. The FT synthesis was carried out in a fixed-bed microreactor (275°C, 2MPa, CO/H₂=2) for 120h. Among the catalysts studied, Fe catalyst supported on pre-treated CNTs at 110°C was stable and active while, the other catalysts experienced rapid deactivations. The Fe catalyst supported on CNTs low surface area and larger diameter showed much lower CH₄ and higher C₅⁺ selectivities.

Keywords: Fischer–Tropsch synthesis; Iron catalyst; Carbon nanotubes; Acid treatment; Activity; Stability

Octahedral molecular sieves of the type K-OMS-2 with different particle sizes and morphologies: Impact on the catalytic properties in the aerobic partial oxidation of benzyl alcohol by Fanny Schurz; Jörg M. Bauchert; Thorsten Merker; Thomas Schleid; Hans Hasse; Roger Gläser (pp. 42-49).

Crystalline, manganese-oxide-based octahedral molecular sieves of the type K-OMS-2 with different particle size and morphology were studied as catalysts in the selective liquid-phase oxidation of benzyl alcohol. A systematic comparison of these materials with both crystalline and amorphous manganese oxides proofs the superior activity of the K-OMS-2 catalysts. The catalytic conversion is shown to occur predominantly on the outer surface of the crystallites.▪Manganese-based octahedral molecular sieves of the type K-OMS-2 (cryptomelane structure) with different morphologies and specific surface areas in the range of 20–135m²g⁻¹ were prepared via synproportionation of KMnO₄ and Mn²⁺ salts, either in acidic aqueous suspension (reflux method) or by a solid-state reaction, and via oxidation of MnSO₄ either by K₂Cr₂O₇ or by molecular oxygen in aqueous solution. For the reflux method, the influence of K⁺ cations for the formation of the OMS-2 structure was proven. When KMnO₄ is replaced by Ba(MnO₄)₂, the anion in the Mn²⁺ salt exerts a strong influence on the synthesis product. All materials were characterized by elemental analysis (ICP-OES), XRD, nitrogen sorption, scanning electron microscopy and TGA.For the oxidation of benzyl alcohol with molecular oxygen in liquid toluene at 110°C, the catalytic activity of the K-OMS-2 materials is directly correlated to their specific surface area A_BET. Since A_BET increases with decreasing average crystallite diameter, the catalytic conversion presumably occurs at the outer crystallite surface. These relations are independent of morphology or synthesis procedure. The K-OMS-2 materials are more active than crystalline manganese oxides (MnO, Mn₂O₃, Mn₃O₄, β-MnO₂), but less active than amorphous MnO₂. Regeneration of deactivated K-OMS-2 catalysts can be achieved by calcining at 300°C in air, partly due to the reversible desorption of water.

Keywords: Octahedral molecular sieves; K-OMS-2; Partial oxidation; Benzyl alcohol; Manganese oxides

Selective hydrogenation of ethyl-benzoylacetate to 3-hydroxy-3-phenyl-propionate catalyzed by Pd/C in EtOH as a solvent in the presence of KOH: The role of the enolate ion on the reaction mechanism by L. Ronchin; A. Vavasori; D. Bernardi; G. Cavinato; L. Toniolo (pp. 50-60).

The selective hydrogenation of ethyl-benzoylacetate to 3-hydroxy-3-phenyl-propionate catalyzed by Pd/C in a solution of KOH in EtOH has been investigated. A Langmuir–Hinshelwood type kinetics gives the best fit of the experimental data. The consecutive hydrogenolysis of the C–OH bond of the product is inhibited due to the low hydrogen coverage and the fast desorption of the product, thus achieving selectivity close to 100%. ▪The selective hydrogenation of ethyl-benzoylacetate to 3-hydroxy-3-phenyl-propionate catalyzed by Pd/C in EtOH in a solution of KOH has been investigated. Mass transfers as well as adsorption and desorption stages do not influence reaction kinetics. A kinetic model is proposed based on the best fitting of the experimental data with Langmuir–Hinshelwood type kinetics equation. The mechanism implies that the enolate of the ethyl-benzoylacetate adsorbs strongly on two sites, thus occupying a large part of the surface Pd atoms without any reaction. The ethyl-benzoylacetate adsorbs also on two sites but with adsorption equilibrium constant almost three order of magnitude lower than that of the enolate anions. Also the hydrogen is poorly adsorbed, however, it forms Pd–H and reacts with the adsorbed keto-ester by a step hydrogenation mechanism in which the first hydride insertion is the rate-determining step. Furthermore, due to the low surface Pd–H availability and the fast desorption of the 3-hydroxy-3-phenyl-propionate the consecutive hydrogenolysis of the C–OH bond of the product is practically suppressed, thus achieving selectivity close to 100%.

Keywords: Ethyl-benzoylacetate; 3-Hydroxy-3-phenyl-propionate; Selective hydrogenation kinetics; Enolate adsorption

Fischer–Tropsch synthesis on a Co/Al₂O₃ catalyst with CO₂ containing syngas by Carlo Giorgio Visconti; Luca Lietti; Enrico Tronconi; Pio Forzatti; Roberto Zennaro; Elisabetta Finocchio (pp. 61-68).

Hydrogenation of CO, CO₂ and their mixtures has been comparatively studied in this work on a representative cobalt-based catalyst under typical Fischer–Tropsch synthesis conditions. In addition, the interactions of the adopted catalyst with CO, CO₂ and their mixtures have been studied by FT-IR spectroscopy. When used alone, both CO and CO₂ are easily hydrogenated over the adopted catalyst, but the selectivity of the two processes is extremely different. In the presence of CO, CO₂ is hardly hydrogenated and behaves essentially as an inert species.Hydrogenation of CO, CO₂ and their mixtures has been comparatively studied in this work on a representative cobalt-based catalyst under typical Fischer–Tropsch synthesis conditions ( T=220°C, P=20bar, GHSV=4800cm³(STP)/h/g_cat, H₂/CO_x=2.45–4.9mol/mol). In addition, the interactions of the adopted catalyst with CO, CO₂ and their mixtures have been studied by FT-IR spectroscopy. When used alone, both CO and CO₂ are easily hydrogenated over the adopted catalyst, with CO₂ showing a reactivity higher then CO. However the selectivity of the two processes is extremely different, with over 90% of the products represented by methane in the case of CO₂ hydrogenation. No evidence has been found for the involvement of different surface species in CO and CO₂ hydrogenation, suggesting that the observed reaction products originate from the same intermediate. It is speculated that the different reactivity of the mixtures CO/H₂ and CO₂/H₂ is due to the different adsorption ability of CO and CO₂, which strongly affects the H/C atomic ratio on the catalyst surface. The higher H/C ratio resulting upon CO₂ hydrogenation inhibits the chain growth, hence favoring the methanation reaction. In the presence of CO, CO₂ is hardly hydrogenated and behaves as an inert species: this has been ascribed to a competition between CO and CO₂ for the adsorption on the catalyst active sites.

Keywords: Fischer–Tropsch synthesis; CO; ₂; effect; FT-IR characterization; Cobalt catalysts

Metallic phases of cobalt-based catalysts in ethanol steam reforming: The effect of cerium oxide by Sean S.-Y. Lin; Do Heui Kim; Su Y. Ha (pp. 69-77).

The catalytic activity of cobalt to produce hydrogen via ethanol steam reforming has been investigated in relating to the crystalline structure of metallic cobalt. According to this figure, at reaction temperature of 350°C, cobalt in hexagonal close-packed (hcp) structure possesses higher conversion and hydrogen production rate as compared with cobalt in face-centered cubic (fcc) structure (O/C=6.5 and WHSV=0.8h⁻¹).The catalytic activity of cobalt in the production of hydrogen via ethanol steam reforming has been investigated in its relation to the crystalline structure of metallic cobalt. At a reaction temperature of 350°C, the specific hydrogen production rates show that hexagonal close-packed (hcp) cobalt possesses higher activity than face-centered cubic (fcc) cobalt. However, at typical reaction temperatures (400–500°C) for ethanol steam reforming, hcp cobalt is transformed to less active fcc cobalt, as confirmed by in situ X-ray diffractometry (XRD). The addition of CeO₂ promoter (10wt.%) stabilizes the hcp cobalt structure at reforming temperatures up to 600°C. Moreover, during the pre-reduction process, CeO₂ promoter prevents sintering during the transformation of Co₃O₄ to hcp cobalt. Both reforming experiments and in situ diffuse-reflectance infrared Fourier transform spectroscopy (DRIFTS) showed that the surface reactions were modified by CeO₂ promoter on 10% Ce–Co (hcp) to give a lower CO selectivity and a higher H₂ yield as compared with the unpromoted hcp Co.

Keywords: Ethanol steam reforming; Hydrogen production; Metallic cobalt; CeO; ₂; promoter; In situ; X-ray diffractometry (XRD); In situ; diffuse-reflectance infrared Fourier transform spectroscopy (DRIFTS)

Co-TUD-1 catalysed aerobic oxidation of cyclohexane by Anand Ramanathan; Mohamed S. Hamdy; Rudy Parton; Thomas Maschmeyer; Jacobus C. Jansen; Ulf Hanefeld (pp. 78-82).

Co-TUD-1 was shown to be a very active and selective catalyst for the aerobic oxidation of cyclohexane. Additionally, the decomposition of CHHP was carried out over Co-TUD-1, resulting in a complete conversion of CHHP with excellent selectivity towards cyclohexanol and cyclohexanone. For the continuous decomposition of CHHP, a virtually undiminished high performance of Co-TUD-1 was observed over a period of one week in our rigorous leaching experiments. ▪Co-TUD-1, an amorphous sponge-like mesoporous cobalt-containing silicate, was shown to be a very active and selective catalyst for the aerobic oxidation of cyclohexane. In addition, the decomposition of cyclohexyl hydroperoxide (CHHP) was carried out over Co-TUD-1 and it catalysed complete conversion of CHHP with excellent selectivity towards cyclohexanol and cyclohexanone. A stable activity over a period of one week was established for Co-TUD-1 in our rigorous leaching experiments during the continuous decomposition of CHHP. No leaching of the metal could be detected proving the catalyst to be truly heterogeneous.

Keywords: Alkane; Oxidation; Cobalt; Air; Heterogeneous catalysis

Hydrogen production by ethanol steam reforming over Ni catalysts derived from hydrotalcite-like precursors: Catalyst characterization, catalytic activity and reaction path by Carlo Resini; Tania Montanari; Luca Barattini; Gianguido Ramis; Guido Busca; Sabrina Presto; Paola Riani; Rinaldo Marazza; Michele Sisani; Fabio Marmottini; Umberto Costantino (pp. 83-93).

Ni–Zn–Al and Ni–Mg–Al hydrotalcites have been prepared and characterized as precursors of mixed oxide catalysts for ESR reaction which has been investigated with flow reactor and IR experiments. Methane is the byproduct limiting hydrogen production above 773. A mechanism with a key step involving acetate ions decomposition is proposed for ethanol steam reforming. ▪The urea hydrolysis method has been applied to prepare Ni–Zn–Al and Ni–Mg–Al layered double hydroxides (LDHs) to be used as precursors of mixed oxide catalysts for the ethanol steam reforming (ESR) reaction. Well crystallized hydrotalcite-like LHDs have been prepared for both systems. IR spectroscopy provides evidence of the carbonate/nitrate copresence and of the additional presence, in the case of the NiMgAl system, of a Mg-free Ni hydroxide phase.The calcinations of the layered precursors give rise to high surface area mixed oxides which essentially retain the lamellar morphology of the precursors. However, the mixed oxides obtained from Ni–Zn–Al LDHs are definitely polyphasic, being actually a mixture of a rock salt phase (NiO), a wurtzite phase (ZnO) and a spinel phase (likely mostly ZnAl₂O₄). On the contrary, the mixed oxides obtained from Ni–Mg–Al LDHs are essentially monophasic, being mostly constituted by a rock salt NiO–MgO solid solution. IR data show the incorporation of tetrahedrally coordinated Al ions in such a rock salt phase.The steam reforming of ethanol has been investigated over these catalysts with flow reactor and IR experiments. All these catalysts are active for ESR with slight differences with Mg/Zn incorporation and Ni loading. It has been found that, above 750–800K it is only possible to have the products H₂, CO₂, CO and CH₄. The formation of CO and methane limits the yield to hydrogen to no more than 90% in the best conditions. In fact, working at high temperature water gas shift equilibrium does not allow such a yield to increase, while at lower temperature the yield is limited also by the methane steam reforming equilibrium. IR spectroscopy suggests that the decomposition of acetate ions is the main source of methane. A mechanism via adsorbed oxygenate species is proposed for ethanol steam reforming.

Keywords: Ethanol steam reforming; Hydrogen production; Nickel catalysts; Hydrotalcite catalyst precursors; Steam reforming; Reaction mechanism

Heterogeneous catalysis of calcium oxide used for transesterification of soybean oil with refluxing methanol by Masato Kouzu; Shin-ya Yamanaka; Jyu-suke Hidaka; Michito Tsunomori (pp. 94-99).

Calcium oxide has the great advantage of the enhanced catalytic activity, but the soluble substance is leached away from the solid base catalyst during the vegetable oil transesterification. We investigated the leaching of solid base catalyst by performing the heterogeneous catalytic transesterification of soybean oil under reflux of methanol. When calcium oxide was employed for the reaction, the amount of the soluble substance reached 10.5wt%. The solid base catalyst was reused with the result that the leaching of the solid base catalyst was mitigated. The catalytic activity of the soluble substance was also measured. From the experimental results, the heterogeneous catalysis of calcium oxide was discussed.Much interest has been taken in finding a solid base catalyst for a reaction to produce biodiesel. Calcium oxide has the great advantage of the enhanced catalytic activity, but the soluble substance is leached away from the solid base catalyst during the reaction. In this paper, the leaching of solid base catalyst was investigated on the basis of data from the heterogeneous catalytic transesterification of soybean oil at reflux of methanol. When calcium oxide was employed for the reaction, the calcium contents of the produced oil and glycerol were 139 and 4602ppm, respectively. This data indicated that the amount of the soluble substance corresponded to 10.5wt% of the employed catalyst. Since calcium oxide was transformed into calcium diglyceroxide at the beginning of the reaction, many of the soluble substances derived from calcium diglyceroxide. Also, the soluble substances were rather active in the soybean oil transesterification. On the other hand, calcium diglyceroxide was employed for the reaction, with the result that the amount of the soluble substance was only 4.0wt%. In this case, the soluble substance did not catalyze the conversion of soybean oil into its methyl esters. Based on the experimental results, the heterogeneous catalysis of calcium oxide was discussed. Additionally, removal of the soluble substance by cation-exchange resin was tested in order to purify the produced oil.

Keywords: Solid base catalyst; Biodiesel; Calcium oxide; Calcium diglyceroxide; Transesterification

Deoxygenation of palmitic and stearic acid over supported Pd catalysts: Effect of metal dispersion by Irina Simakova; Olga Simakova; Päivi Mäki-Arvela; Andrey Simakov; Miguel Estrada; Dmitry Yu. Murzin (pp. 100-108).

Catalytic deoxygenation of palmitic and stearic acids mixture was studied over four synthesized Pd catalysts supported on synthetic carbon (Sibunit) in a semibatch reactor and dodecane as a solvent at 260–300°C. The catalysts were prepared by precipitation deposition method using Pd chlorides as metal precursors. All catalysts contained 1wt.% Pd, however, the metal dispersion was systematically varied. An optimum metal dispersion giving the highest reaction rate was observed. The main liquid phase products were n-heptadecane and n-pentadecane, which were formed parallel.Catalytic deoxygenation of palmitic and stearic acids mixture was studied over four synthesized Pd catalysts supported on synthetic carbon (Sibunit) in a semibatch reactor and dodecane as a solvent at 260–300°C. The catalysts were prepared by precipitation deposition method using Pd chlorides as metal precursors. All catalysts contained 1wt.% Pd, however, the metal dispersion was systematically varied. An optimum metal dispersion giving the highest reaction rate was observed. The main liquid phase products were n-heptadecane and n-pentadecane, which were formed in parallel. In addition to the particle size effect the impact of mass transfer was elucidated and a detail discussion on temperature programmed desorption of CO from the fresh and spent samples was provided.

Keywords: Deoxygenation; Fatty acid; Palladium

Decolouration of Orange II solutions by TiO₂ and ZnO active layers screen-printed on ceramic tiles under sunlight irradiation by E. Rego; J. Marto; P. São Marcos; J.A. Labrincha (pp. 109-114).

In this work TiO₂ and ZnO layers have been deposited by screen-printing in common ceramic tiles. These layers were characterized and tested for the photocatalytic degradation of organic dye Orange II in aqueous solutions, under direct exposure to the sunlight.Optimal processed layers showed an interesting decolourisation performance, as denoted by an attenuation degree of 90% and decolouration rate, assuming an apparent first order reaction, reaching 2.9×10⁻³min⁻¹. In the actual conditions, TiO₂ layers show superior performance than ZnO. The previous alkalinisation of the dye solution is not recommended, since better performance is achieved under the naturally resulting pH (6.7) of the solution (20g/L).Thus these layered ceramic tiles can be regarded as an alternative to photocatalytic suspensions of the same material with the advantage of avoiding the removal of the photocatalyst at the end of the process.TiO₂ and ZnO layers have been deposited by screen-printing in common ceramic tiles. These layers were characterized and tested for the photocatalytic degradation of organic dye Orange II in aqueous solutions, under direct exposure to the sunlight. Optimal processed layers showed an interesting decolourisation performance, as denoted by an attenuation degree of 90% and decolouration rate of 2.9×10⁻³min⁻¹.

Keywords: TiO; ₂; and ZnO; Screen-printed layers; Orange II decolouration; Sunlight irradiation

Properties of Pt/C catalysts prepared by adsorption of anionic precursor and reduction with hydrogen. Influence of acidity of solution by L.B. Okhlopkova (pp. 115-122).

Effect of acidity of the solution on the dispersion and activity in cyclohexene hydrogenation of Pt/C catalysts was investigated. Differences in catalytic activity are ascribed to variation in the extent of Pt particles blocking in the carbon pores. The effect proved to be larger on activated carbons with the smaller micropores and higher concentration of the oxygen-containing groups.Carbon-supported Pt/C catalysts prepared with H₂PtCl₆ as metal precursor have been studied by temperature-programmed reduction (TPR), transmission electron microscopy (TEM) and CO chemisorption in order to investigate the effect of acidity of the solution on the catalyst properties. The catalytic activity of the samples has been tested in structure insensitive reaction of cyclohexene hydrogenation. The catalysts were prepared by adsorption of platinum precursor on activated carbons with different pore structure followed by drying and reduction in flowing hydrogen at 523K. The use of acidic and highly basic solution during the impregnation of microporous carbons led to highly dispersed catalysts with low activity. It has been suggested that a part of the supported metal became inaccessible to the organic substrate due to localization of metal particles in narrow pores of the support. However, in the range of intermediate solution pH, the activity per surface metal atom remained at a high level. Such phenomenon is attributed to the formation of bulky species of platinum precursor, which hardly penetrates into the small pores of the support, thus preventing a blocking effect. Effect of acidity of the solution proved significant for Pt/C catalysts on the activated carbons with the smaller micropores and higher concentration of oxygen-containing groups.

Keywords: Platinum; Activated carbons; Acidity; Cyclohexene hydrogenation; CO chemisorption; TEM; Blocking effect

Silica supported tungsta-zirconia catalysts for hydroisomerization–cracking of long alkanes by Mariana Busto; María E. Lovato; Carlos R. Vera; Kiyoyuki Shimizu; Javier M. Grau (pp. 123-131).

New acidic materials with uniform mesoporous texture were synthesized by dispersion of tungsten promoted zirconia over a wide pore silica carrier. The catalysts showed both an activation temperature and a coke deactivation pattern in acid catalyzed isomerization similar to bulk tungsten-zirconia catalysts. On a mass basis of active tungsten-zirconia phase some supported catalysts had a higher activity than bulk tungsten-zirconia. Their open pore structure made them more suitable for the reaction of bulky molecules.New acidic materials with fairly uniform mesoporous texture were synthesized by deposition of tungsten promoted zirconia (WZ) over a wide pore silica carrier (SiO₂). High dispersion of the tungsten-zirconia crystallites was achieved by a two-step controlled impregnation procedure. A first deposition of zirconia was performed by controlled hydrolysis of alkoxide. Impregnation of tungstate was performed by incipient wetness impregnation of ammonium metatungstate.The catalysts show an activation pattern for the reaction of 1-butene similar to bulk tungsten-zirconia catalyst, with an optimum at a calcination temperature of 750°C. Supported zirconia crystallizes almost exclusively as tetragonal crystallites.The catalysts were tested in the reaction of hydroisomerization–cracking of n-octane (300°C, 1atm, WHSV=1h⁻¹ and H₂/ n-C₈=6mol/mol) for the production of light isoalkanes (isobutane, isopentane, isohexane) of high octane number. The tried catalysts had a high catalytic activity and this result was related to the high surface area of the supported catalyst. Both bulk and supported catalysts deactivated rapidly if they did not contain Pt. Impregnation with Pt and the use of H₂ in the reaction medium enable the hydrogenation of coke precursors and the stabilization of the catalyst. A stable performance was obtained at a moderate activity level. This was attributed to the presence of Pt/SiO₂ particles with a stronger metal function than Pt/WZ due to a lower metal–support interaction. Silica supported catalysts would have a higher hydrogenating activity and this would be crucial for enhancing their stability in comparison to bulk Pt/WZ catalysts.Tungsten addition to supported zirconia in amounts greater than 7.5% produced segregation of a WO₃ phase in the form of crystallites that plugged pores and produced a reduction of the available area and hence of the overall catalytic activity.For the WZ supported catalysts activity as a function of calcination temperature had a pattern similar to that of bulk WZ catalysts. Supported WZ catalysts were more stable in the n-octane isomerization reaction and reached a pseudo steady state even at very low H₂ partial pressures while bulk WZ catalysts deactivated continuously and stabilized only at high H₂ partial pressures. On a mass basis of active WZ phase some supported catalysts had a higher activity than bulk WZ. They also have a more open pore structure more suitable for the reaction of bulky molecules. However the dilution effect of silica produces catalysts with a relatively low activity per unit volume.

Keywords: Supported zirconia; Silica; Tungsten-zirconia; Hydroisomerization; Hydrocracking; Long alkanes

Characterization of nitric acid functionalized carbon black and its evaluation as electrocatalyst support for direct methanol fuel cell applications by Marcelo Carmo; Marcelo Linardi; João Guilherme Rocha Poco (pp. 132-138).

This study presents results on PtRu electrocatalysts supported on functionalized carbon black. Cyclic voltammetric curves showed higher activity for the PtRu supported on functionalized carbon black. Such an enhanced performance is related to a better PtRu nanoparticle distribution and can also be inferred by the better nanoparticles utilization, nanoparticles that are outside from the carbon pore structure.This study presents results on PtRu electrocatalysts supported on both as received and functionalized carbon black. The electrochemical properties of both home-made and commercial PtRu electrocatalysts were compared to PtRu supported on functionalized carbon black. The PtRu nanoparticles were synthesized by the impregnation method and subsequent alcohol reduction. Transmission electron microscopy experiments revealed that the PtRu electrocatalysts supported on functionalized carbon black are more homogeneously distributed than all other studied materials. Cyclic voltammetric electrocatalyst curves experiments showed higher activity for the PtRu supported on functionalized carbon black. This enhanced performance is related to the better nanoparticle distribution on functionalized carbon black. The better performance can also be inferred by the better nanoparticles utilization. The nanoparticles are now located outside from the pore structure of the carbon black. Hence, the nanoparticles are more exposed and available to the reactants, enhancing the catalyst performance and avoiding the waste of noble catalysts.

Keywords: Carbon functionalization; HNO; ₃; Electrocatalysis; Fuel cell; PEMFC; DMFC

Synthesis, characterization and reactivity of Lewis acid/surfactant cerium trisdodecylsulfate catalyst for transesterification and esterification reactions by Grace Ferreira Ghesti; Julio Lemos de Macedo; Vicente Cavalcanti Ibiapina Parente; José Alves Dias; Sílvia Cláudia Loureiro Dias (pp. 139-147).

The Lewis acid/surfactant cerium trisdodecylsulfate catalyst was prepared, characterized, and applied in the production of alkyl esters by solvent-free transesterification and esterification reactions. High catalytic activities were found for the reaction of soybean oil and oleic acid with light alcohols. The recovered catalyst was recycled without loss of catalytic activity.This article reports the synthesis, characterization and application of cerium(III) trisdodecylsulfate trihydrate (Ce[OSO₃C₁₂H₂₅]₃·3H₂O) as a Lewis acid-surfactant-combined catalyst for the production of alkyl esters by solvent-free transesterification and esterification reactions. The new material presents a bilayer lamellar arrangement with an interplanar spacing of d₀₀₁=3.76nm, and the dodecylsulfate headgroup in a C_2v symmetry. The reaction of soybean oil and oleic acid with light alcohols (methanol and ethanol) was used as model reactions and high catalytic activity (TOF=57.4molh⁻¹mol_cat⁻¹) was observed. The catalyst converted the used feedstocks to esters in less than 4h with yields greater than 95%. In addition, it can be used to produce biofuels from unrefined and waste oils in which both triacylglyceride and free fatty acid molecules are present. After reaction, the recovered catalyst maintained its activity (≥95%) for three cycles. The catalyst was characterized by elemental analysis, X-ray powder diffraction (XRD), thermal analysis (thermogravimetry (TG)/derivative thermogravimetry (DTG)/differential thermal analysis (DTA)), pyridine adsorption, and spectroscopic analysis (FTIR and NMR).

Keywords: Cerium trisdodecylsulfate; Lewis acid-surfactant-combined catalyst; Transesterification; Esterification; Biodiesel

Metathesis of fluorinated olefins by ruthenium alkylidene catalysts. Fluorine substituent effects on a Ru-carbene (alkylidene) complex stability: A computational study by Serguei Fomine; Mikhail A. Tlenkopatchev (pp. 148-155).

Clorine and especially fluorine substituents at carbene atom stabilize ruthenium-carbene complexes by the electron density transfer to Ru center from lonely pairs of halogen atom through p_z orbital of carbene carbon. ▪Cross-metathesis reaction pathways of ethylene (2a), trans-1,2-dichloro-ethylene (2b) and fluorinated olefins trans-1,2-difluoro-ethylene (2c) and tetrafluoro-ethylene (2d), with norbornene (NB) using a (1,3-diphenyl-4,5-dihydroimidazol-2-ylidene) (PCy₃)CI₂Ru=CHPh (I) have been studied at B3LYP/LACVP* level of theory. The calculated Δ G of reactions for olefins2a,2b,2c and2d were of 2.5, −2.0, −11.9 and −31.6kcal/mol, respectively. The calculations show that the natural charge at a Ru center is strongly dependent on substituent nature and can be a measure of the carbene stability. The stabilization of a metallacarbene is due to the stabilization of the metal center and not a carbene carbon itself.

Keywords: Olefin metathesis; Ruthenium; Density functional theory; Carbene stability

Highly stable dealuminated zeolite support for the production of hydrogen by dry reforming of methane by Antonio N. Pinheiro; Antoninho Valentini; José M. Sasaki; Alcineia C. Oliveira (pp. 156-168).

Dealumination improved the accessibility and increased the stability of BEA supports, generating better catalytic activity. Dealuminated BEA zeolite containing 1wt% of Pt appeared to be a very promising candidate for dry reforming of methane, in comparison with other zeolite supports.Dealuminated FAU type Y and BEA zeolites were used as supports for the dry reforming of methane. Ni and Pt (1 or 0.5wt%) were impregnated on these carriers to produce both monometallic and bimetallic catalysts. The catalysts were characterized before and after exposure to reaction conditions by XRD, X-ray fluorescence, N₂ adsorption, TGA, TPR, SEM, TEM and XPS analyses. The acidity of the fresh solids was also evaluated by TPD of ammonia and FT-IR measurements. The improvement of the accessibility with dealumination of the supports, as well as the high stability of the BEA zeolite support, generated high dispersion of the metals and improved catalytic activity of this solid. The FAU type Y supports show much more total acidity compared to that of BEA, which possess acid sites of medium strength. The results demonstrated that the bimetallic Ni–Pt/zeolite catalyst showed lower activity (e.g., NiPtY and NiPtβ activities were 1.70 and 1.90g_metal⁻¹h⁻¹, respectively) than that of the monometallic Pt/zeolite catalyst (e.g., PtY and Ptβ activities were close to 2.0 and 3.20g_metal⁻¹h⁻¹, respectively). NiY and Niβ were practically inactive, which could be attributed to the formation of deactivating whisker-like carbon deposits (approximately 60wt%) on the metal particles, combined with the high acidity of the support, which was measured by FT-IR analysis. In the case of Pt dispersed on BEA zeolite, it produced lower carbon deposition (16wt%) and this coke was easily removed by CO₂. Dealuminated BEA zeolite appeared to be a promising candidate for dry reforming of methane application due to its high stability and selectivity during 24h of time on stream, in comparison with alumina (activity=0.90molg_metal⁻¹h⁻¹), active carbon (activity=2.30g_metal⁻¹h⁻¹), and other zeolites.

Keywords: Dealuminated zeolite; Reforming; Platinum; Stability; Coke

γ-MnO₂ octahedral molecular sieve: Preparation, characterization, and catalytic activity in the atmospheric oxidation of toluene by Lei Jin; Chun-hu Chen; Vincent Mark B. Crisostomo; Linping Xu; Young-Chan Son; Steven L. Suib (pp. 169-175).

A synthesized γ-MnO₂ octahedral molecular sieve was characterized and used to catalyze solvent-free atmospheric oxidation of toluene with molecular oxygen. The γ-MnO₂ showed excellent catalytic activity and good selectivity under the mild atmospheric reflux system at a low temperature (110°C). Under optimized conditions, a 47.8% conversion of toluene, along with 57% selectivity of benzoic acid and 15% of benzaldehyde were obtained. The effects of reaction time, amount of catalyst and initiator, and the reusability of the catalyst were investigated.Atmospheric oxidation of toluene with molecular oxygen has been reported for the first time using easy synthesized γ-MnO₂ octahedral molecular sieve as the catalyst. Under optimized conditions, a 47.8% conversion of toluene, along with 57% selectivity of benzoic acid and 15% of benzaldehyde were obtained. The effects of reaction time, amount of catalyst and initiator, and the reusability of the catalyst were investigated.▪

Keywords: Toluene; OMS; Reflux; γ-MnO; ₂; Oxygen; Benzoic acid

Recyclable Au⁰, Ag⁰ and Au⁰–Ag⁰ nanocolloids for the chemoselective hydrogenation of α,β-unsaturated aldehydes and ketones to allylic alcohols by Pascal G.N. Mertens; Pieter Vandezande; Xingpu Ye; Hilde Poelman; Ivo F.J. Vankelecom; Dirk E. De Vos (pp. 176-183).

Au⁰ and Ag⁰ based nanocolloids emerge as superior quasihomogeneous metal catalysts for the amide-phase hydrogenation of α,β-unsaturated carbonyl compounds, owing to their pronounced preference for CO reduction. Colloidal Au⁰–Ag⁰ alloy clusters with optimized composition and size lead to the highest allylic alcohol yields and can be recycled efficiently by solvent-resistant nanofiltration over custom-made polyimide membranes with unaffected hydrogenation chemoselectivity. ▪A high-throughput evaluation of polymer-stabilized metal clusters, with varying composition and size, as unpromoted quasihomogeneous catalysts for the amide-phase hydrogenation of α,β-unsaturated aldehydes and ketones, allowed to identify the most appropriate metal clusters to achieve a high selectivity to allylic alcohols. Au⁰ and Ag⁰ based nanocolloids proved superior owing to their pronounced preference for CO reduction over CC saturation. Optimization of the metal nanoclusters in terms of size and composition led to exceptionally high allylic alcohol selectivities. These robust metal nanocolloids could be recycled efficiently from the amidic reaction media by solvent-resistant nanofiltration over cross-linked polyimide membranes. The catalytic activity of the optimized bimetallic nanocolloids consisting of alloyed Au and Ag was well preserved in successive hydrogenation runs while the chemoselectivity was unaffected. The wide substrate scope enabled to study the effect of the CCCO substitution pattern on the substrate reactivity and the allylic alcohol selectivity.

Keywords: Chemoselective hydrogenation; Unsaturated ketone; Allylic alcohol; Gold; Silver; Quasihomogeneous catalyst; Bimetallic catalyst; Alloy catalyst; Solvent-resistant nanofiltration

Ethylation of coking benzene over nanoscale HZSM-5 zeolites: Effects of hydrothermal treatment, calcination and La₂O₃ modification by Linping Sun; Xinwen Guo; Min Liu; Xiangsheng Wang (pp. 184-191).

The objective of this work is to study some post-treatment effects, including hydrothermal treatment, calcination and La₂O₃ modification, on the catalytic performance of a nanoscale HZSM-5 zeolite for ethylation of coking benzene. The nanoscale HZSM-5 zeolite was treated by hydrothermal treatment, calcination and La₂O₃ modification in series, and the prepared catalysts were evaluated in a fixed-bed down-flow reactor. The catalyst samples were also characterized by XRD, SEM, NH₃-TPD, IR, N₂ adsorption–desorption isotherms, cyclohexane adsorption isotherms and TG. The results showed that both the hydrothermal treatment and the calcination led to a drastic decrease in the total amount of acid sites, while the subsequent La₂O₃ modification resulted in only a slight increase in the number of acid sites. These post-treatments led to a decrease in the Brönsted/Lewis ratio of the nanoscale HZSM-5 zeolites. The hydrothermal treatment followed by the La₂O₃ modification created new large micropores on the nanoscale HZSM-5 zeolites, which results in the coexistence of micropores and large micropores. The increase in the catalyst lifetime can be attributed to both suppression of carbon deposit formation and partial accommodation of the formed carbon deposit in La-C-HT-HZSM-5 catalyst with lower acidity, lower ratio of B/L and complicated pore structure. The prepared La-C-HT-HZSM-5 catalyst showed good catalytic stability within 1500h of time on stream in the ethylation of coking benzene containing high sulfur content (375ppmw) with ethylene under industrial reaction conditions.The objective of this work is to study some post-treatment effects, including hydrothermal treatment, calcination and La₂O₃ modification, on the catalytic performance of a nanoscale HZSM-5 zeolite for ethylation of coking benzene in a fixed-bed down-flow reactor. The prepared La-C-HT-HZSM-5 catalyst showed good catalytic stability within 1500h of time on stream in the ethylation of coking benzene containing high sulfur content (375ppmw) with ethylene under industrial reaction conditions.

Keywords: Coking benzene; Nanoscale HZSM-5; Hydrothermal treatment; Calcination; La; ₂; O; ₃; modification

Preparation, characterization, and catalytic activity of chromia supported on SBA-15 for the oxidative dehydrogenation of isobutane by Guozhi Wang; Lei Zhang; Jiguang Deng; Hongxing Dai; Hong He; Chak Tong Au (pp. 192-201).

Mesoporous SBA-15 and 1–12wt% CrO_x/SBA-15 have been prepared by triblock copolymer P123-templated hydrothermal synthesis and incipient wetness impregnation method, respectively. The materials were characterized by means of a number of analytical techniques and their catalytic activities were evaluated for the oxidative dehydrogenation (ODH) of isobutane. It is found that with rise of chromia loading, the morphology of SBA-15 changed from long interconnected chains to short banana-like rods, and finally changed to spheres with wormholes. The results of Raman and X-ray photoelectron spectroscopic investigations reveal that the surface Cr species are mainly Cr⁶⁺ in mono- and polychromate, with a minor amount of Cr³⁺ due to α-Cr₂O₃ formation. The H₂ temperature-programmed reduction study demonstrates that the catalysts at chromia loading of 6–10wt% are more reducible. The 10wt% CrO_x/SBA-15 catalyst exhibits the best activity, showing 79% C₄-olefin selectivity and 11% C₄-olefin yield at 540°C. One monolayer CrO_x coverage on SBA-15 occurs at Cr surface density=1.05–1.43Cr-atom/nm². We conclude that factors such as (i) presence of active Cr⁶⁺ in mono- and polychromate, (ii) strong redox ability of Cr species, and (iii) good dispersion of CrO_x on banana-like rods of well-ordered mesoporous SBA-15 are responsible for the good performance of the SBA-15-supported chromia in isobutane ODH.Loaded chromia exists in mono- and polychromate forms on SBA-15 surfaces. Isobutane interacts with the lattice oxygen of CrO_x/SAB-15 to generate isobutanoxide adspecies that decompose to give isobutene, and the reduced catalyst is re-oxidized by gas-phase oxygen. The well-dispersed CrO_x and its strong redox ability account for the excellent catalytic performance of the SBA-15-supported chromia.

Keywords: Mesoporous silica; SBA-15-supported chromia catalyst; Oxidative dehydrogenation of isobutane; Surface chromia species; Reducibility

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Applied Catalysis A, General (v.355, #1-2)