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Applied Catalysis A, General (v.317, #2)

Editorial Board (pp. co2).

Contents (pp. iii-viii).

High surface area tin oxide by Alfred Hagemeyer www.symyx.com; Zach Hogan; Marco Schlichter; Birgit Smaka; Guido Streukens; Howard Turner; Anthony Volpe Jr.; Henry Weinberg; Karin Yaccato (pp. 139-148).

Proprietary recipes and optimized literature procedures for the synthesis of porous SnO₂ carriers were developed. Easily decomposed organic acid dispersants for inorganic tin precursors produce high surface areas (about 200m²/g). Tin oxides with BET surface areas >200m²/g were achieved by the hydrazine synthesis method. Several Pt-Ru-Co catalysts supported on tin oxides were tested for low temperature VOC combustion and CO oxidation in high-throughput reactors: C₃H₆, CO+O₂→CO₂+H₂O. ▪High surface area tin oxides are desirable catalyst carriers for emissions control including CO oxidation, VOC removal/methane combustion and NO_x abatement. We have optimized literature procedures as well as developed proprietary recipes for the synthesis of porous SnO₂ carriers. Precipitation of SnCl₄ from homogeneous solution by urea and by hydrazine, the dissolution of Sn metal powder in HNO₃, sol–gel routes from Sn alkoxides and inorganic Sn precursors, acid-induced gelation of K₂SnO₃, the Pechini method ex Sn(OAc)₄ using various organic acids as dispersants and dry and wet thermal decomposition of Sn carboxylates have been investigated and compared. BET surface areas >100m²/g have been achieved by a variety of methods after calcination in the temperature range 300–500°C. High surface area tin oxides with excellent sintering resistance (250, 228, 190 and 175m²/g after calcination at 300, 400, 500 and 600°C, respectively) have been synthesized by the hydrazine method. Pt/SnO₂ catalysts have been prepared by impregnation with Pt tetraamine hydroxide solution, and screened for propylene combustion and CO oxidation activity in a parallel 8×1 process optimization reactor. Light-off takes place at higher temperatures for CO oxidation than for propylene combustion due to Pt poisoning by CO at lower temperatures. High surface areas >200m²/g could also be achieved by a modified Pechini method using aqueous glyoxylic acid as dispersant for Sn(IV) acetate. Ce–Sn–Co mixed oxides have been synthesized by the glyoxylic acid method, impregnated with Pt–Ru and found to be more active than Pt/Al₂O₃ for CO oxidation when using CO-only feed, but inferior to the Pt standard when feeding a CO–propylene mixture.

Keywords: High surface area; Tin oxide; Carriers; Supports; Sol–gel; Pechini; Propylene combustion; VOC removal; CO oxidation; Combinatorial chemistry; Combinatorial catalysis; Heterogeneous catalysis; High-throughput synthesis; High-throughput screening

Synthesis of a bis(diketiminate)bromosamarium(III) complex and its activity in the polymerization of methyl methacrylate by Roberto Bineli Muterle; Fabio Fabri; Regina Buffon; Wanda de Oliveira; Ulf Schuchardt (pp. 149-153).

Bis(diketiminate)bromosamarium(III) was synthesized and shown to be active in the polymerization of methyl methacrylate. The catalyst shows in the first 30min an activity of 20.2kgPMMA(molSm)⁻¹h⁻¹, giving a polymer with a molar mass M_n>23.0kgmol⁻¹ and molar mass distribution ( M_w/ M_n)<1.4. ▪A bis(diketiminate)bromosamarium(III) complex was successfully synthesized and, after the activation with butyl lithium, was shown to be active in methyl methacrylate (MMA) polymerization. The effects of temperature, polymerization time and catalyst concentration were studied. Activities of ca. 16,000g of poly(methyl methacrylate) (PMMA) per mol of samarium and per hour were obtained under optimum conditions (0°C and a MMA/catalyst molar ratio of 90/1), providing a polymer with a molar mass M_n>23.0kgmol⁻¹ and a molar mass distribution ( M_w/ M_n)<1.4. After 1h of polymerization, conversions of MMA as high as 90% were observed.

Keywords: Methyl methacrylate polymerization; Samarium(III) complex; Diketiminate ligand

Oxidation of cyclohexane catalyzed by bis-(2-pyridylmethyl)amine Cu(II) complexes by Aires C. Silva; Tatiana Lopez Fernández; Nakédia M.F. Carvalho; Marcelo H. Herbst; Jairo Bordinhão; Adolfo Horn Jr; James L. Wardell; Enrique G. Oestreicher; O.A.C. Antunes (pp. 154-160).

In this work, it is showed the cyclohexane oxidation catalyzed by the copper(II) complexes, [Cu(BMPA)Cl₂] (1) and {[Cu(BMPA)Cl₂][Cu(BMPA)(H₂O)Cl] [Cu(BMPA)Cl][CuCl₄]} (2), using hydrogen peroxide or tert-butyl hydroperoxide as terminal oxidants and acetonitrile as solvent. Although the complexes were previously reported, in the present paper it is disclosed an alternative method for the synthesis of the complex 2, as well as additional characterization data on these complexes including EPR and cyclic voltammetry. The complexes were able to oxidize cyclohexane into cyclohexanol, cyclohexanone, cyclohexyl hydroperoxide and adipic acid, in mild conditions. Complex2 exhibited the best results, reaching as high as 68.9% of total yield in 24h with H₂O₂. In general, H₂O₂ showed better results than tert-butyl hydroperoxide as terminal oxidant.In this work, it is showed the cyclohexane oxidation catalyzed by the copper(II) complexes, [Cu(BMPA)Cl₂] and {[Cu(BMPA)Cl₂][Cu(BMPA)(H₂O)Cl] [Cu(BMPA)Cl][CuCl₄]} (2), using hydrogen peroxide or tert-butyl hydroperoxide as terminal oxidants and acetonitrile as solvent. ▪

Keywords: Cu(II) enzymes; pMMO; Oxidation; Cu(II) complexes; Cyclohexanol; Cyclohexanone; Cyclohexyl hydroperoxide; Adipic acid; Hydrogen peroxide; tert-; Butyl hydroperoxide; EPR; Cyclic voltammetry

One-step methyl isobutyl ketone (MIBK) synthesis from 2-propanol: Catalyst and reaction condition optimization by G. Torres; C.R. Apesteguía; J.I. Di Cosimo (pp. 161-170).

The one-pot gas-phase synthesis of methyl isobutyl ketone (MIBK) from 2-propanol is studied using bifunctional catalysts under mild conditions. The effect of the catalyst copper content and acid–base properties as well as that of the operational conditions on the MIBK yield is investigated. Copper loadings of 2–6wt% and moderate catalyst Lewis acidity and Brönsted basicity are required to obtain MIBK yields of 27%, values comparable with the current commercial process from acetone (DMK) at high pressures. ▪A gas-phase process for methyl isobutyl ketone (MIBK) synthesis from 2-propanol in one-pot is studied as an alternative to the conventional technology for producing MIBK from acetone (DMK). Bifunctional copper/acid–base catalysts able to operate at mild temperatures and atmospheric pressure were prepared and characterized by measuring the acid and base properties as well as the metal dispersion. It was found that a Cu-Mg-Al mixed oxide catalyst gives high MIBK yields. In this catalyst, the metal fraction in loadings of 2–6wt% promotes the hydro-dehydrogenation steps at high rates whereas the surface acid–base sites of moderate acid and base properties favor the aldol condensation reaction.The effect of different operational conditions such as reaction temperature and reactant partial pressure was also investigated. The MIBK formation rate was enhanced by increasing 2-propanol partial pressure in a wide range, consistently with a positive 2-propanol reaction order in the overall kinetics whereas the presence of hydrogen in the reactant mixture inhibited MIBK synthesis due to a negative order with respect to H₂. An increase of the reaction temperature and the use of inert atmosphere improved the MIBK yield. By operation at 533K in N₂ the Cu-Mg-Al catalyst with 6.4wt% Cu, yields 27% MIBK in comparison to the 30% typically obtained in current commercial liquid-phase high-pressure processes from DMK.

Keywords: Methyl isobutyl ketone (MIBK); 2-Propanol; Aldol condensation; Bifunctional catalysis

Pd–heteropoly acid as a bifunctional heterogeneous catalyst for one-pot conversion of citronellal to menthol by Kelly A. da Silva Rocha; Patricia A. Robles-Dutenhefner; Edesia M.B. Sousa; Elena F. Kozhevnikova; Ivan V. Kozhevnikov; Elena V. Gusevskaya (pp. 171-174).

Pd–H₃PW₁₂O₄₀/SiO₂ catalyzes the one-pot transformation of (+)-citronellal to menthol via acid-catalyzed cyclization followed by Pd-catalyzed hydrogenation, with 92% yield of menthol at 100% citronellal conversion and 85% stereoselectivity for the desired (−)-menthol. ▪Pd–H₃PW₁₂O₄₀/SiO₂ catalyzes the one-pot transformation of (+)-citronellal to menthol via acid-catalyzed cyclization followed by Pd-catalyzed hydrogenation, with 92% yield of menthol at 100% citronellal conversion and 85% stereoselectivity for the desired (−)-menthol.

Keywords: Citronellal; Menthol; Heteropoly acid; Palladium; Bifunctional catalysis

Activation of Mo-based catalyst for paraffins isomerization by G. Boskovic; P. Putanov; K. Foettinger; H. Vinek (pp. 175-182).

Activation procedures of Mo-based catalysts were investigated in terms of their activity in reaction of n-hexane isomerization. Temperature programmed activation and oxidation (TPA/TPO) in different gaseous environments were used to correlate catalyst activity/selectivity properties with the nature of active phases and with activation procedures required for their formation. A beneficial activation procedure giving Mo-oxycarbide comprises very low ramping temperature of 1°C/min, 550°C as the final temperature and a flow of methane and hydrogen with a preferable ratio 1:4. In addition, some minimal time for keeping both initial and final temperature constant is required, indicating benefit of both periods of initialization and active phase slow aging. Neither different diluent (He) nor other gas as a C-source (CO, n-hexane) gives an active catalyst. The catalyst activity can be enhanced by exposing it to air at room temperature, and decayed in the same environment at 300°C.Activation procedures of Mo-based catalysts were investigated in terms of their activity in reaction of n-hexane isomerization. Temperature programmed activation and oxidation (TPA/TPO) in different gaseous environments were used to correlate catalyst activity/selectivity properties with the nature of active phases and with activation procedures required for their formation. A beneficial activation procedure giving Mo-oxycarbide comprises very low ramping temperature of 1°C/min, 550°C as the final temperature and a flow of methane and hydrogen with a preferable ratio 1:4.▪

Keywords: Mo-based catalysts; Activation; n; -Hexane isomerization; Activity–structure correlations

Effect of the temperature in the nature and extension of the primary and secondary reactions in the thermal and HZSM-5 catalytic pyrolysis of HDPE by M del Remedio Hernández; Amparo Gómez; Ángela N. García; Javier Agulló; Antonio Marcilla (pp. 183-194).

In this work, the pyrolysis temperature effect on the primary and secondary reactions of the thermal and HZSM-5 catalyzed pyrolysis of HDPE is reported and evaluated, in the range 500–800°C. For this purpose, two different equipments have been used, i.e. a flash coil pyrolyzer (pyroprobe 1000), that allows us to study the primary products and a fluidized bed reactor, where the extent of the secondary reactions is significant. The results show that in the catalytic pyrolysis it is observed a more similar effect of the primary and secondary reactions than in the thermal case. ▪Catalytic pyrolysis of plastic wastes is a promising recycling alternative to the disposal methods currently used for this type of residues (i.e. land filling or energetic valorisation). In order to optimize the yields of compounds obtained with this treatment, the knowledge of the parameters’ influence on the degradation process is of great interest.Pyrolysis temperature and volatiles residence time are the most influential variables in the process, since they affect the primary as well as the secondary reactions.In this work, the pyrolysis temperature effect on the primary and secondary reactions of the thermal and HZSM-5 catalyzed pyrolysis of HDPE is reported and evaluated, in the range 500–800°C. For this purpose, two different equipments have been used, i.e. a flash coil pyrolyzer (pyroprobe 1000), that allows us to study the primary products, since the extent of secondary reactions can be neglected, and a fluidized bed reactor, where the extent of the secondary reactions is significant.The results of the present study show that 1-hexene is the major product obtained when primary thermal cracking reactions are mainly taking place. However, the major compounds obtained when thermal secondary reactions are present in larger extension are propene at low temperatures and ethene at high temperatures. In catalytic pyrolysis, the effect of HZSM-5 is clearly evident at all temperatures evaluated, increasing the volatile yields in both equipments used. The influence of this catalyst is more significant in the primary cracking reactions showing an increase of the volatile compounds with the degradation temperature. In this case, propene is the main volatile product obtained reaching a yield of 30.6% at the highest temperature evaluated. When the presence of the secondary reactions is evident, using a fluidized bed reactor, the combined effect of generation and possible cracking reactions leads to a low-dependent product distribution on the degradation temperature, propene being the main volatile compound in the range of temperatures studied. It has been observed that branched hydrocarbons are formed mainly from secondary reactions and are quickly destroyed by increasing the temperature. In the zeolite catalyzed pyrolysis the differences between the yields obtained in both equipments are lower than in the thermal case.

Keywords: High density polyethylene; Zeolite; HZSM-5; Fluidized bed reactor; Pyroprobe equipment; Temperature; Residence time; Secondary reactions; Primary reactions

The preparation and study of sol–gel synthesized Co/Zn/TiO₂ Fischer–Tropsch catalysts by Nobuntu N. Madikizela-Mnqanqeni; Neil J. Coville (pp. 195-203).

The sol–gel method was used to prepare Co(10wt%)/Zn( x)/TiO₂ ( x=0, 1, 5 and 10wt%) materials that were tested as Fischer–Tropsch catalysts. While the influence of zinc was found to enhance FT activity, the poor reducibility of Co in these catalysts led to the generation of poor FT catalysts. ▪The sol–gel method was used to prepare Co(10wt%)/Zn( x)/TiO₂ ( x=0, 1, 5 and 10wt%) catalysts. Two methods were used to gel the catalyst precursors (Co, Zn, TiO₂): (i) co-gelling all the components and (ii) gelling the titania support alone followed by the impregnation of zinc and cobalt precursors. The catalysts prepared by co-gelling all the catalysts components together were tested for Fischer–Tropsch (FT) activity and <5% conversion was obtained using standard FT conditions. This finding correlates with the strong interaction between the support and the Co, even in the presence of zinc. Impregnation of the sol–gel prepared titania support with zinc and cobalt precursors resulted in different degrees of interaction between the support and cobalt catalysts (due to the presence of zinc) as determined from TPR and XPS measurements. However, the modified sol–gel prepared catalysts also showed low activity towards Fischer–Tropsch (FT) when compared to the catalysts prepared using Degussa titania as support.

Keywords: Fischer–Tropsch catalysis; Zinc; Cobalt; XPS; Sol–gel

Long-term stability of a 0.45% Au/TiO₂ catalyst in the selective oxidation of glucose at optimised reaction conditions by Agnes Mirescu; Heinz Berndt; Andreas Martin; Ulf Prüße (pp. 204-209).

The use of gold catalysts in the oxidation of glucose resulted in high selectivities (>95%) and very high activities. The optimisation of the reaction conditions revealed that best results were obtained at 40–60°C and a pH value of 9. A 0.45% Au/TiO₂ catalyst showed the best performance. It can be re-used at least 17 times without loss of activity or a change in gold particle size. ▪The use of gold catalysts in the oxidation of glucose resulted in high selectivities (>95%) with respect to gluconic acid and very high catalytic activities were obtained. A catalyst with 0.45wt.% Au supported on titania showed the best performance. The optimisation of the reaction conditions revealed that best results were obtained at a reaction temperature in a range of 40–60°C and a pH value of 9. The Au/TiO₂ catalyst can be re-used at least 17 times without loss of activity or change of the gold particle size.

Keywords: Gold catalysts; Au/TiO; ₂; Long-term stability; Selective oxidation; Glucose; Gluconic acid; TEM

Ni-nanoparticles: A mild chemo-selective catalyst for synthesis of thioethers by Amit Saxena; Ajeet Kumar; Subho Mozumdar (pp. 210-215).

A novel method for selective oxidative coupling of a thiol with an alcohol to form the corresponding thioether in the presence of other functional groups, viz. –NH₂, –X, –NO₂, –OCH₃, etc., under air atmosphere using Ni-nanoparticles is described. Ni-nanoparticles act as a novel selective catalyst, which efficiently reduces the reaction time and increases the yield without producing any side products. Ni-nanoparticles have high TON and TOF so they can be easily recycled. ▪A novel method for selective oxidative coupling of a thiol with an alcohol to form the corresponding thioether in the presence of other functional groups, viz. –NH2, –X, –NO2, –OCH3, etc., under air atmosphere using Ni-nanoparticles is described. Ni-nanoparticles act as a novel selective catalyst, which efficiently reduces the reaction time and increases the yield without producing any side products. Ni-nanoparticles have high TON and TOF so they can be easily recycled.

Keywords: Oxidative coupling; Thiols; Thioether; TON and TOF

Spectroscopic studies on NiO supported on ZrO₂ modified with MoO₃ for ethylene dimerization by Jong Rack Sohn; Si Hyon Kwon; Dong Cheol Shin (pp. 216-225).

NiO supported on zirconia modified with MoO₃ for ethylene dimerization was prepared by drying powdered Ni(OH)₂–Zr(OH)₄ with ammonium heptamolybdate aqueous solution, followed by calcining in air at high temperature. The characterization of prepared catalysts was performed using FTIR, Raman, XRD, and DSC. MoO₃ equal to or less than 15wt% was dispersed on the surface of catalyst as two-dimensional polymolybdate or monomolybdate, while for MoO₃ above 15wt%, a crystalline orthorhombic phase of MoO₃ was formed, showing that the critical dispersion capacity of MoO₃ on the surface of catalyst is 0.18g/g NiO–ZrO₂ on the basis of XRD analysis. From 600°C of calcination temperature, zirconium molybdenum oxide, Zr(MoO₄)₂ was formed due to the reaction between ZrO₂ and MoO₃; its amount increased with the calcination temperature. The acid amount and the catalytic activity of catalysts increased with the amount of dispersed MoO₃. The high acid strength and acid amount was responsible for the MoO bond nature of the complex formed by the interaction between MoO₃ and ZrO₂. The catalytic activity for ethylene dimerization was correlated with the acid amount of the catalysts measured by the ammonia chemisorption method.NiO supported on zirconia modified with MoO₃ for ethylene dimerization was prepared by the impregnation method using an aqueous solution of ammonium heptamolybdate. MoO₃ equal to or less than 15wt% was dispersed on the surface of catalyst as two-dimensional polymolybdate or monomolybdate. The acid amount and the catalytic activity of catalysts increased with the amount of dispersed MoO₃. The high acid strength and acid amount was responsible for the MoO bond nature of the complex formed by the interaction between MoO₃ and ZrO₂. ▪

Keywords: NiO–ZrO; ₂; /MoO; ₃; catalyst; Ethylene dimerization; Acidic properties; MoO; ₃; dispersion; Modification with MoO; ₃

Preparation and activity of Cu/ZnO-CNTs nano-catalyst on steam reforming of methanol by Hung-Ming Yang; Ping-Heng Liao (pp. 226-233).

A novel Cu/ZnO-CNTs (carbon nano-tubes) nano-catalyst was prepared by chemical reduction and wet impregnation method, and was applied to catalyze the steam reforming reaction of methanol.CH₃OH+H₂O⇌CO₂+3H₂XRD analysis of 23wt% Cu/ZnO-CNTs catalysts; (▾) CNT, (▿) CuO, (♦) ZnO, (●) Cu. ▪A novel Cu/ZnO-CNTs (carbon nano-tubes) nano-catalyst was prepared by a chemical reduction and wet impregnation method, and was applied to catalyze the steam reforming reaction of methanol. If one uses CNT as the support, the CNTs should be pre-treated by nitric acid and sulfuric acid at 60°C for 24h to create defects on its surface; the hydrophilicity of CNTs was improved by adding a suitable amount of ethanol. The catalysts were characterized by TEM, XRD, FTIR and TGA. A good dispersion of Cu nano-particles on the surface of CNTs with particle size about 10nm is identified by TEM analysis. Using 23wt% Cu₈₀ZnO₂₀-CNTs as the catalyst, we obtained the hydrogen yield for steam reforming of methanol of 83% at 280°C and near 100% at temperatures higher than 320°C with 1.5 of molar ratio of water to methanol. The higher hydrogen production (larger than 400mmol/(skgcat)), higher selectivity of CO₂ and lower CO concentration were also observed.

Keywords: Carbon nano-tubes; Nano-catalyst; Chemical reduction method; Methanol steam reforming

Formation from direct oxidation of H₂ and destruction by decomposition/hydrogenation of H₂O₂ over Pd/C catalyst in aqueous medium containing different acids and halide anions by Vasant R. Choudhary; Chanchal Samanta; Prabhas Jana (pp. 234-243).

The H₂O₂ formation activity of Pd/C catalyst in the H₂-to-H₂O₂ oxidation in an aqueous acidic medium is drastically increased because of the addition of chloride or bromide promoter (at optimum concentration) in the medium. ▪Direct oxidation of H₂ by O₂ to H₂O₂ and decomposition/hydrogenation of H₂O₂ (at 27°C and atmospheric pressure) over Pd/C catalyst in an aqueous acidic reaction medium have been thoroughly investigated using different mineral acids (viz. 0.1N H₂SO₄, H₃PO₄, H₃BO₃, HNO₃, HCl, HBr or HI) and/or halide anions (viz. F⁻, Cl⁻, Br⁻ or I⁻), covering their wide concentration range (0–24mmol/dm³), in the reaction medium. In the absence of any externally added halide, appreciable H₂O₂ formation in the H₂ oxidation occurred only when the medium contained HCl. However, the rates of H₂O₂ decomposition and hydrogenation are greatly reduced because of the presence of any acid; the influence on the H₂O₂ decomposition was, however, much larger for the halo acids. In the presence of acid (0.1N H₃PO₄ or H₂SO₄), the H₂-to-H₂O₂ formation reaction is greatly enhanced by the externally added halide anions up to their optimum concentrations. However, above the optimum halide anion concentration, it is inhibited more than the H₂-to-water formation (parallel) reaction, causing a decrease in both the H₂O₂ yield and selectivity. Whereas, the H₂ conversion and H₂O₂ destruction activities of the catalyst are decreased continuously with increasing the halide anion (except F⁻) concentration. Among the halides, chloride is the best halide promoter for Pd/C catalyst in the H₂-to-H₂O₂ oxidation. At the optimum Cl⁻ concentration (5.4mmol/dm³), both the H₂ conversion and H₂O₂ yield are passed through a maximum and the H₂O₂ decomposition is greatly inhibited with increasing the phosphoric acid concentration. In the absence of either the chloride anions or the acid (or both) in the reaction medium, only a little or no H₂O₂ is formed in the H₂ oxidation and also the rate of H₂O₂ destruction is very fast, particularly in the presence of H₂; the rapid destruction of H₂O₂ is mainly due to its decomposition rather than its hydrogenation. The best H₂-to-H₂O₂ oxidation results are obtained at the optimum concentrations of both the acid and halide anions. In the presence of acid and chloride (or bromide) promoter, the H₂O₂ hydrogenation dominates the H₂O₂ destruction and hence the net H₂O₂ formation is mainly controlled by the H₂O₂ hydrogenation.

Keywords: Oxidation of H; ₂; -to-H; ₂; O; ₂; Hydrogen peroxide; H; ₂; O; ₂; decomposition; H; ₂; O; ₂; hydrogenation; Halide anion promoters; Pd/C catalyst

Catalytic performance of bismuth molybdate catalysts in the oxidative dehydrogenation of C₄ raffinate-3 to 1,3-butadiene by Ji Chul Jung; Heesoo Kim; Yong Seung Kim; Young-Min Chung; Tae Jin Kim; Seong Jun Lee; Seung-Hoon Oh; In Kyu Song (pp. 244-249).

α-Bi₂Mo₃O₁₂ and γ-Bi₂MoO₆ were prepared by a co-precipitation method, and were applied to the oxidative dehydrogenation of C₄ raffinate-3 to 1,3-butadiene. Both α-Bi₂Mo₃O₁₂ and γ-Bi₂MoO₆ catalysts were thermally and structurally stable during the catalytic reaction. They exhibited a stable catalytic performance in the oxidative dehydrogenation of C₄ raffinate-3 without catalyst deactivation. However, the catalytic performance of γ-Bi₂MoO₆ was superior to α-Bi₂Mo₃O₁₂ due to the facile oxygen mobility of γ-Bi₂MoO₆. The reactivity of n-butene isomers in the C₄ raffinate-3 decreased in the order of 1-butene> trans-2-butene> cis-2-butene over both α-Bi₂Mo₃O₁₂ and γ-Bi₂MoO₆ catalysts. Steam played an essential role in suppressing CO₂ formation, and furthermore, served as a heat sink for preventing hot spots or reactor run-away. In the catalytic reaction with respect to reaction temperature, the maximum conversion of n-butene (ca. 66%) and the maximum yield for 1,3-butadiene (ca. 60%) were achieved at 440°C over the γ-Bi₂MoO₆ catalyst ( n-butene:oxygen:steam=1:0.75:15).In the oxidative dehydrogenation of C₄ raffinate-3 to 1,3-butadiene, the maximum yield for 1,3-butadiene (ca. 60%) was achieved at 440°C over γ-Bi₂MoO₆ catalyst ( n-butene:oxygen:steam=1:0.75:15). ▪

Keywords: Bismuth molybdate; C; ₄; raffinate-3; 1,3-Butadiene; Oxidative dehydrogenation; Catalyst stability; Effect of steam; Effect of reaction temperature

Acylation of anisole with long-chain carboxylic acids over wide pore zeolites by S.G. Wagholikar; P.S. Niphadkar; S. Mayadevi; S. Sivasanker (pp. 250-257).

The acylation of anisole with long-chain carboxylic acids (hexanoic, octanoic and decanoic) has been studied over three large pore zeolites—beta (BEA), faujasite (FAU) and mordenite (MOR). The acylation of anisole with the long chain acids produced mainly the ketone (4-methoxy phenyl alkyl ketone) and small amounts of the ester (phenyl alkanoate). The results revealed the reaction to be influenced by the type of zeolite and its Si/Al ratio (acidity) besides the chain length (carbon number) of the carboxylic acid. In the acylation of anisole with hexanoic acid, the activity of the zeolites increased with dealumination as it led to the generation of mesopores that resulted in a decrease in diffusion resistance of the zeolites. The reactivity of the acids in the acylation reaction was found to decrease with increase in the carbon number. The experimental data have been fitted into a pseudo first order kinetic model.Acylation of anisole with long-chain carboxylic acids (hexanoic, octanoic and decanoic) was studied over three large pore zeolites—beta, faujasite and mordenite. Acylation produced mainly 4-methoxy phenyl alkyl ketone and small amounts of phenyl alkanoate. The reaction was influenced by the zeolite type, Si/Al ratio and the chain length of the acid. The reaction followed a pseudo first order kinetics. ▪

Keywords: Acylation; Anisole; Hexanoic acid; Octanoic acid; Decanoic acid; Zeolites

Evaluation of multiphase microreactors for the direct formation of hydrogen peroxide by Xu Wang; Yuntong Nie; Jasmine L.C. Lee; Stephan Jaenicke (pp. 258-265).

The formation of hydrogen peroxide by the direct reaction of hydrogen and oxygen in a microchannel reactor requires the presence of a catalyst and a liquid phase. The mass transport in this three-phase system is greatly enhanced under the prevailing Taylor flow conditions. ▪The direct production of hydrogen peroxide from H₂ and O₂ has been investigated in two types of microreactors: (1) a single-channel microreactor with a washcoat of catalyst and (2) a multichannel microreactor with eight parallel channels, where the catalyst was grown as a thin film. The multichannel microreactor mimics features of a monolith reactor, where the catalyst is contained in a structured honeycomb. The Taylor (slug) flow in a microchannel reactor under three phase (gas–liquid–solid) conditions enhances the mass transfer over the phase boundaries. The influence of liquid and gas flow rate, pressure drop, solvents, support materials and metal dispersion on the reaction were investigated in order to screen for optimal operation conditions. The productivity in the microchannel reactors increases approximately with the square root of the liquid flow rate, verifying the Taylor-flow model.

Keywords: Hydrogen peroxide; Microreactor; Heterogeneous catalysis; Multi-phase flow; Taylor flow; Pd–Pt bimetallic catalysts

Hydrothermal post-synthesis of HZSM-5 zeolite to enhance the coke-resistance of Mo/HZSM-5 catalyst for methane dehydroaromatization reaction: Reconstruction of pore structure and modification of acidity by Y. Song; C. Sun; W. Shen; L. Lin (pp. 266-274).

Hydrothermal post-synthesis of a commercial HZSM-5 zeolite in Al(NO₃)₃ aqueous solution resulted in the creation of a uniform microporous network and the formation of Brönsted acid sites with suitable acidic strengths through the dynamic extraction and incorporation of aluminum species between the solution and the framework. NMR and N₂ adsorption–desorption isotherms measurements revealed that a dynamic extraction and incorporation of aluminum from the framework occurred during the post-synthesis treatment. X-ray powder diffraction (XRD), X-ray photoelectron spectra (XPS) and temperature-programmed reduction (TPR) measurements of the resulting Mo/HZSM-5 catalyst indicated that the dispersion of Mo species was greatly promoted over the post-synthesized HZSM-5 zeolite, significantly facilitating the migration of Mo species into the channels. As a result, the Mo/HZSM-5 catalyst showed rather high methane conversion and selectivity of aromatics by effectively inhibiting the formation of coke during the methane dehydroaromatization reaction.▪Hydrothermal post-synthesis of a commercial HZSM-5 zeolite in Al(NO₃)₃ aqueous solution resulted in the creation of a uniform microporous network and the formation of Brönsted acid sites with suitable acidic strengths through the dynamic extraction and incorporation of aluminum species between the solution and the framework. NMR and N₂ adsorption–desorption isotherms measurements revealed that a dynamic extraction and incorporation of aluminum from the framework occurred during the post-synthesis treatment. XRD, XP spectra and TPR measurements of the resulting Mo/HZSM-5 catalyst indicated that the dispersion of Mo species was greatly promoted over the post-synthesized HZSM-5 zeolite, significantly facilitating the migration of Mo species into the channels. As a result, the Mo/HZSM-5 catalyst showed rather high methane conversion and selectivity of aromatics by effectively inhibiting the formation of coke during the methane dehydroaromatization reaction. Comparatively, the Mo/HZSM-5 catalyst, where the HZSM-5 zeolite was obtained by conventional hydrothermal post-synthesis, exhibited lower methane conversion and heavy coke deposits, apparently due to the substantial loss of the Brönsted acid sites and the creation of secondary pores.

Keywords: Hydrothermal post-synthesis; Al(NO; ₃; ); ₃; aqueous solution; HZSM-5 zeolite; Methane dehydroaromatization

Thermal stability of alumina aerogel doped with yttrium oxide, used as a catalyst support for the thermocatalytic cracking (TCC) process: An investigation of its textural and structural properties by N. Al-Yassir; R. Le Van Mao (pp. 275-283).

Undoped and yttria doped alumina aerogel are prepared by the (solution) sol–gel method using a supercritical drying technique. The doping concentrations are in the range of 2.5–20.0wt.% Y₂O₃, using yttrium(III) nitrate as a precursor. The effect of yttria doping on the structural and textural properties of alumina aerogel is investigated by BET surface area measurement, X-ray diffraction (XRD), TEM and²⁷Al MAS NMR.This method of preparation of alumina aerogel provides the most important increases in surface area at 750°C and up to 1000°C, when compared to conventional alumina that is obtained via thermal dehydration of boehmite. These results show that the much smaller size of crystallites of alumina aerogel is quite efficient to retard the sintering occurring at these high temperatures.Further improvements in thermal stability are obtained by incorporation of yttrium species during the aerogel preparation. The stabilizing effect goes through a maximum with a yttrium content of ca. 10wt.%. The presence of yttrium significantly delays the lattice rearrangement into new phases, as normally experienced by the conventional alumina when the temperature increases. These yttrium species induce the formation of distorted tetrahedral Al sites. Such binding effect of Y to Al is clearly detected by²⁷Al MAS NMR already at 750°C. However, at 1200°C, even the doped aerogel cannot withstand the combined effect of sintering and α-phase transformation, so that extremely low surface areas corresponding to those of alumina α-phase and segregated Y-Al₂O₃ are obtained.Increase in the thermal stability.▪

Keywords: Yttria doped alumina aerogel; Conventional Al; ₂; O; ₃; Thermal stability; BET surface area; XRD; ²⁷; Al MAS NMR

Carbon deposition on Ni/YSZ composites exposed to humidified methane by Hongpeng He; Josephine M. Hill (pp. 284-292).

Carbon formation on Ni/YSZ cermets in high-temperature processes involving hydrocarbons can be a severe problem. Understanding the mechanisms of carbon formation is necessary for developing strategies to avoid or minimize the problem. In this study, Ni/YSZ pellets (70/30 NiO/YSZ) have been exposed to humidified methane at temperatures between 773K and 1073K. The carbon formed on these pellets and/or any structural changes in the pellets was studied with X-ray diffraction (XRD), scanning electron microscopy (SEM) and temperature-programmed oxidation (TPO). At temperatures below 873K, carbon fibres dominated. At higher temperatures, the majority of the carbon dissolved into the Ni particles. After TPO and removal of the carbon, the Ni structure was damaged to various extents depending on the exposure temperature. The amount of carbon deposited was significantly reduced by placing zirconia-doped ceria pellets on each side of the Ni/YSZ pellet. The addition of a ceria layer did not completely eliminate the carbon formation but the carbon that was formed was weakly attached to the Ni/YSZ such that the structure was not irreversibly changed. The role of the ceria is beyond simply reforming the methane.Characterization of carbon deposition on Ni/YSZ at different conditions in humidified methane is presented. The type of carbon changes with exposure temperature. Carbon fibres dominate at temperatures up to 873K while at higher temperatures the carbon dissolves into the Ni particles. Physically placing Zr-doped ceria pellets on each side of the Ni/YSZ significantly reduced the carbon formation. ▪

Keywords: Ni/YSZ; Carbon deposition; Ceria; TPO; SEM; XRD

Stable nickel catalysts with alumina-aluminum phosphate supports for partial oxidation and carbon dioxide reforming of methane by Luc Pelletier; Dirkson D.S. Liu (pp. 293-298).

Under dry reforming conditions, impregnated nickel catalysts with both γ-Al₂O₃ and alumina-aluminum phosphate (AAP) supports deactivated quickly. Co-precipitated nickel catalysts showed no sign of deactivation. Characterization shows that stability of the co-precipitated nickel catalysts was due to strong metal–support interactions. Increased nickel loadings and higher reforming temperatures enhanced catalytic activity, while maintaining stable a performance. ▪Alumina-aluminum phosphate (AAP) materials were prepared as mesoporous catalyst supports for methane partial oxidation and dry reforming. Average pore size is substantially reduced when nickel is impregnated on the support. Large pores and adequate surface area are maintained when the nickel is co-precipitated with AAP. Impregnated nickel catalysts with γ-Al₂O₃ and AAP supports were tested for methane partial oxidation. Catalytic activity and selectivity was similar with both supports and performance was stable for over 100h on stream. Under dry reforming conditions, impregnated nickel with both γ-Al₂O₃ and AAP supports deactivated quickly. Conversely, co-precipitated nickel catalysts showed no sign of deactivation. XRD and TPR analysis shows that stability of the co-precipitated nickel catalysts was due to strong metal–support interactions such as in the NiAl₂O₄ spinel structure. However lower concentrations of surface nickel and the demand for higher reduction temperatures resulted in lower conversions with the co-precipitated catalyst. Increased nickel loadings and higher reforming temperatures enhanced catalytic activity, while maintaining a stable performance for over 250h on stream.

Keywords: Nickel catalyst; Co-precipitation; Methane reforming; Catalyst stability

Methane dry reforming on Ni loaded hydroxyapatite and fluoroapatite by Zouhair Boukha; Mohamed Kacimi; Manuel Fernando R. Pereira; Joaquim L. Faria; José Luís Figueiredo; Mahfoud Ziyad (pp. 299-309).

Calcium-hydroxyapatite and calcium-fluoroapatite loaded with different amounts of nickel were synthesized and characterized by several techniques including scanning electron microscopy, temperature programmed reduction (TPR), UV–visible–NIR and XPS spectroscopy. Three types of nickel species were detected in the two series of catalysts (i) Ni²⁺ ions exchanged with Ca²⁺ ions of the apatite framework. This Ni²⁺/Ca²⁺ exchange seems to be restricted to nickel loadings inferior to 1wt% Ni, (ii) small particles of NiO exhibiting strong interactions with the carriers (for x>1wt% Ni) and (iii) large particles of NiO which appear at high loadings. The distribution of the nickel between these three hosting sites depends on the nature of the apatite. For instance the amount of exchanged Ni²⁺ ions in Ni(1)/CaHAp is twice more important than in Ni(1)/CaFAp.The Ni( x)/CaHAp and Ni( x)/CaFAp catalysts were tested in methane dry reforming with CO₂. Methane conversion at 600°C, increases with the nickel loading up to x=4 where the activity is around the thermodynamic equilibrium (78%) and H₂/CO ratio close to 1. These results were confirmed by the investigation of the catalysts activity versus the temperature. Carbon deposition on the catalysts was found to also increase with nickel loading but without provoking any significant decay of the activity after 4h on stream. The encouraging results achieved were attributed to the synergy between the basic properties of the apatites, their aptitude to chemisorb CO₂ and the catalytic features of the supported nickel.Ni( x)/CaHAP and Ni( x)/CaFAP were prepared and characterized using electron microscopy, TPR, UV–visible–NIR and XPS spectroscopy. Three species of nickel were identified and their distribution in the catalysts varied with the nature of the apatite. At all temperatures, the catalysts performance in methane dry reforming, was managed by thermodynamics and appeared as good as that of Mg–Ni/Al₂O₃.▪

Keywords: Methane dry reforming; Ni loaded calcium-hydroxyapatite; Ni loaded calcium-fluoroapatite; XRD; IR; DRS; XPS and TPR

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Applied Catalysis A, General (v.317, #2)

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Applied Catalysis A, General (v.317, #2)