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Applied Catalysis A, General (v.343, #1-2)

Editorial Board (pp. co2).

Contents (pp. iii-vii).

Characterization and catalytic performance of ruthenium sulfide catalysts supported on H-BEA, Na– and Cs–H-BEA zeolites by Perla Castillo-Villalón; Jorge Ramírez; Catherine Louis; Pascale Massiani (pp. 1-9).

The behavior of Ru hydrodesulfurization (HDS) catalysts supported on a series of X-H-BEA (X=H⁺, Na⁺, Cs⁺) zeolites was studied. The catalysts tested in the thiophene HDS reaction to analyze the effect of zeolite acidity and nature of the alkaline cation on the acid properties, stability of the sulfided phase and HDS activity. ▪A series of Ru-X-H-BEA (X=H⁺, Na⁺, Cs⁺) catalysts sulfided at high temperature in H₂S (15%)/N₂ was characterized and tested in thiophene hydrodesulfurization (HDS) to analyze the effect of zeolite acidity and nature of the alkaline cation on the acid properties, stability of the sulfided phase and HDS catalytic activity. It is shown that after exchange of half of the zeolite protons by alkaline cations (Cs⁺, Na⁺) the acid properties of the zeolite are influenced by the nature of the cation suggesting the presence of a remote effect of the alkaline cation over the remaining sites and/or the disappearance of the most acidic sites. The activity of the catalysts and the product distribution in the HDS of thiophene are also influenced by the nature of the exchanged cation. Temperature-programmed reduction of the sulfided catalysts before and after thiophene HDS showed that a sulfided phase with low S/Ru ratio is obtained inside the zeolite channels.

Keywords: H-BEA; Na–H-BEA; Cs–H-BEA; RuS; ₂; Acid characterization; TPR-S; Thiophene HDS; Cumene cracking

Carbon dioxide reforming of methane over a metal modified Ni-Al₂O₃ catalyst by Adolfo E. Castro Luna; María E. Iriarte (pp. 10-15).

CO₂ reforming of methane over modified Ni-Al₂O₃ was studied. The influence of K, Sn, Mn and Ca on the behavior of a Ni-Al₂O₃ catalyst, prepared by a sol–gel method, was studied. For this purpose, catalytic activity and its resistance to coking were measured. The unmodified catalyst showed its effectiveness in the dry reforming reaction of methane with low carbon deposition and high and constant catalytic activity during over 30h of operation. The introduction of 0.5wt.% of the above mentioned metals showed, for the case of the K-modified catalyst, compared to the original catalyst, constant but slightly less activity, and a lower carbon deposition after the same operation period. In the case of Ca, Mn and Sn, a dramatic reduction of catalytic activity and a significant increase in carbon deposition were observed during the period of time under study.

Keywords: Methane dry reforming; Nickel-alumina catalyst; K-modified Ni-Al; ₂; O; ₃; catalyst

CuO and CeO₂ catalysts supported on Al₂O₃, ZrO₂, and SiO₂ in the oxidation of CO at low temperature by Gonzalo Águila; Francisco Gracia; Paulo Araya (pp. 16-24).

The effect of the support, Al₂O₃, ZrO₂, and SiO₂, on the activity for CO oxidation of a series of CuO and CeO₂ monometallic and bimetallic catalysts was studied. The catalysts were prepared by coimpregnation of the support with the adequate amount of Cu and Ce nitrates to obtain a loading of 2% Cu and/or 8% Ce. It was found that the support has a strong influence on the activity of the different bimetallic catalysts. Interestingly, the SiO₂ supported catalyst shows the higher activity. The bimetallic supported catalysts follow the activity sequence CuO–CeO₂/SiO₂>CuO–CeO₂/ZrO₂>CuO–CeO₂/Al₂O₃. In the absence of CeO₂, the most active monometallic catalyst was the CuO/ZrO₂ system. The different degree of interaction between CuO and CeO₂ particles, induced by the support, can explain the activity results for the bimetallic catalysts.▪The effect of the support, Al₂O₃, ZrO₂, and SiO₂, on the activity for CO oxidation of a series of CuO and CeO₂ monometallic and bimetallic catalysts was studied. The catalysts were prepared by coimpregnation of the support with the adequate amount of Cu and Ce nitrates to obtain a loading of 2% Cu and/or 8% Ce. It was found that the support has a strong influence on the activity of the different bimetallic catalysts. Interestingly, the SiO₂ supported catalyst shows the higher activity. The bimetallic supported catalysts follow the activity sequence CuO–CeO₂/SiO₂>CuO–CeO₂/ZrO₂>CuO–CeO₂/Al₂O₃. In the absence of CeO₂, the most active monometallic catalyst was the CuO/ZrO₂ system. The different degree of interaction between CuO and CeO₂ particles, induced by the support, can explain the activity results for the bimetallic catalysts.

Keywords: Al; ₂; O; ₃; SiO; ₂; ZrO; ₂; Copper; CeO; ₂; CO oxidation

Preparation of supported NbC catalysts from peroxoniobic acid and in situ XAFS characterization by Shun Kodama; Nobuyuki Ichikuni; Kyoko K. Bando; Takayoshi Hara; Shogo Shimazu (pp. 25-28).

Nb/Al₂O₃ and Nb/SiO₂ as niobium carbide precursors were prepared from peroxoniobic acid (PNA). Alumina-supported niobium carbide and silica-supported niobium carbide were prepared by temperature programmed reaction (TPR) method under CH₄–H₂ mixed gas passage. Both catalysts were characterized by X-ray absorption fine structure (XAFS) and Raman spectroscopy. Nb/Al₂O₃ was more efficiently carburized than Nb/SiO₂. The carbon deposition onto NbC occurred after the carburization completion of the Nb species.▪Nb/Al₂O₃ and Nb/SiO₂ as niobium carbide precursors were prepared from peroxoniobic acid (PNA). Alumina-supported niobium carbide and silica-supported niobium carbide were prepared by temperature programmed reaction (TPR) method under CH₄–H₂ mixed gas passage. Both catalysts were characterized by X-ray absorption fine structure (XAFS) and Raman spectroscopy. Nb/Al₂O₃ was more efficiently carburized than Nb/SiO₂. The carbon deposition onto NbC occurred after the carburization completion of the Nb species.

Keywords: NbC catalyst; XAFS; Carbon deposition

Methanol oxidation on LaBO₃ (B=Co, Mn, Fe) perovskite-type catalysts prepared by reactive grinding by B. Levasseur; S. Kaliaguine (pp. 29-38).

Perovskite-type mixed oxides LaBO₃ (with B=Co, Mn, Fe) with high specific surface area were prepared by reactive grinding. The catalytic performance of the samples for methanol oxidation was evaluated. The reaction rates were found to be strongly related to the amount of α-oxygen available and to the density of surface anion vacancies. A mechanism for this oxidation was proposed.▪Perovskite-type mixed oxides LaBO₃ (with B=Co, Mn, Fe) with high specific surface area were prepared by reactive grinding. These catalysts were characterized by N₂ adsorption, X-ray diffraction, H₂ temperature-programmed reduction (TPR-H₂), O₂-, CH₃OH- and CO₂-temperature-programmed desorption (TPD). The catalytic performance of the samples for methanol oxidation was evaluated. The reaction rates were found to be strongly related to the amount of α-oxygen available and to the density of surface anion vacancies. A mechanism for total oxidation of methanol into CO₂ was also proposed in which the amount of α-oxygen was an important parameter of the reaction rate. Indeed two kinds of reaction intermediates can be produced depending on the surface density of α-oxygen. Under an excess of α-oxygen the reaction intermediate was found to be a monodentate carbonate which decomposes into CO₂. However, as soon as a lack of α-oxygen was observed in the structure, the dominant reaction intermediate was a bidentate carbonate which induces a consumption of anion vacancies in spite of the production of CO₂. The differences observed between the three catalysts under study were discussed according to the observations of the characterization, the activity over methanol oxidation and the proposed mechanism.

Keywords: Perovskite; Methanol oxidation; Thermodesorption experiments; Carbonates

A continuous catalytic system for biodiesel production by Clayton V. McNeff; Larry C. McNeff; Bingwen Yan; Daniel T. Nowlan; Mark Rasmussen; Arlin E. Gyberg; Brian J. Krohn; Ronald L. Fedie; Thomas R. Hoye (pp. 39-48).

A novel continuous fixed bed reactor process has been developed for the production of biodiesel using a metal oxide-based catalyst. Porous zirconia, titania and alumina micro-particulate heterogeneous catalysts are shown to be capable of continuous rapid esterification and transesterfication reactions under high pressure (ca. 3000psi) and elevated temperature (300–450°C). The continuous transesterification of triglycerides and simultaneous esterification of free fatty acids with contact times as low as 5.4s is described. Biodiesel produced from a variety of lipid and alcohol feedstocks using this new process pass all current ASTM testing specifications. Furthermore, the economics of this novel process is much more cost competitive due to the use of inexpensive lipid feedstocks that often contain high levels of free fatty acids. The process has been shown to easily scale up a factor of 49 for more than 115h of continuous operation without loss of conversion efficiency. The increased use of biodiesel world-wide could help reduce the emission of greenhouse gases.▪A novel continuous fixed bed reactor process has been developed for the production of biodiesel using a metal oxide-based catalyst. Porous zirconia, titania and alumina micro-particulate heterogeneous catalysts are shown to be capable of continuous rapid esterification and transesterfication reactions under high pressure (ca. 2500psi) and elevated temperature (300–450°C). The continuous transesterification of triglycerides and simultaneous esterification of free fatty acids with residence times as low as 5.4s is described. Biodiesel produced from soybean oil, acidulated soapstock, tall oil, algae oil, and corn oil with different alcohols to make different alkyl esters using this new process pass all current ASTM testing specifications. Furthermore, the economics of this novel process is much more cost competitive due to the use of inexpensive lipid feedstocks that often contain high levels of free fatty acids. The process has been shown to easily scale up a factor of 49 for more than 115h of continuous operation without loss of conversion efficiency. The increased use of biodiesel world-wide could help reduce the emission of greenhouse gases that are linked to the progression of global warming.

Keywords: Biodiesel; Esterification; Transesterification; Alumina; Titania; Zirconia; Heterogeneous fixed bed catalyst; Alkyl alcohols

A new chemical process for catalytic conversion ofd-glucose into lactic acid and gluconic acid by Ayumu Onda; Takafumi Ochi; Koji Kajiyoshi; Kazumichi Yanagisawa (pp. 49-54).

The conventional alkaline degradation ofd-glucose into lactic acid involves large amounts of by-products including unidentified compounds. In contrast, a new one-pot reaction ofd-glucose resulted in yielding about 45C-% of lactic acid and about 45C-% of gluconic acid using Pt/C catalysts with a 1.0molL⁻¹ of sodium hydroxide aqueous solution at 353K under flowing air.▪In this work, the catalytic conversion of monosaccharides, such asd-glucose,d-fructose,d-mannose,d-galactose, andd-xylose, into lactic acid and aldonic acid in an alkaline media using supported noble metal catalysts under flowing air was investigated. Thus far, the conventional chemical conversions ofd-glucose into lactic acid, such as alkaline degradations and hot water reactions, involved large amounts of by-products including unidentified compounds. To improve the atom economy for thed-glucose conversion, we examined a one-pot reaction ofd-glucose into lactic acid and gluconic acid with the alkaline degradation and the air oxidation using supported metal catalysts. It succeeded in yielding about 45C-% of lactic acid and about 45C-% of gluconic acid fromd-glucose using Pt/C catalysts with a 1.0molL⁻¹ of sodium hydroxide aqueous solution at 353K under flowing air.

Keywords: Lactic acid; Gluconic acid; Glucose; Alkaline degradation; Pt/C

Enhancement in microporosity and catalytic activity on grafting silica and organosilica moieties in lamellar titanium phosphate framework by Krishanu Sarkar; Mahasweta Nandi; Asim Bhaumik (pp. 55-61).

New silica- and organosilica-grafted analogues of lamellar semicrystalline titanium phosphate (sc-TiOP) have been synthesized hydrothermally. N₂ adsorption studies revealed that the surface area increased significantly when the Si- and Si–CH₂CH₂–Si-moieties were grafted into the titanium phosphate framework. These materials showed excellent catalytic activity and selectivity in epoxidation and ammoximation reactions using dilute aqueous H₂O₂ as an oxidant vis-à-vis sc-TiOP.▪New silica-grafted analogs of lamellar semicrystalline titanium phosphate (sc-TiOP), silicotitanium phosphate (STP) and organic–inorganic hybrid silicotitanium phosphate (HSTP) have been synthesized under hydrothermal condition without the assistance of any template or structure-directing agent under acidic pH conditions. These materials were characterized by elemental analysis, powder XRD, field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), N₂ sorption and spectroscopic studies. N₂ adsorption studies revealed that the surface area increased significantly when the Si atoms were incorporated into the layered titanium phosphate framework. The surface area improves further with the grafting of organosilane moiety in HSTP material. Fourier-transformed infrared (FT IR), UV–vis and X-ray photoelectron spectroscopic (XPS) results suggested the presence of Si–O–P, Ti–O–Si bonds and octahedral coordination of Ti(IV) in these novel microporous materials. Si- and Si–CH₂CH₂–Si-grafted materials showed considerable enhancement in catalytic activity towards the liquid phase partial oxidation of styrene, α-methyl styrene, cyclohexene and acrylic acid using dilute H₂O₂ as an oxidant. These materials also showed excellent catalytic activity and selectivity in ammoximation of cyclohexanone to cyclohexanone oxime in the presence of aqueous ammonia and dilute aqueous H₂O₂ with reference to the silica-free sc-TiOP analogue.

Keywords: Microporous materials; Titanium phosphate; Organic–inorganic hybrid materials; Partial oxidation; Ammoximation

Acid phosphate-impregnated titania-catalyzed nitration of aromatic compounds with nitric acid by Saitanya K. Bharadwaj; Sahid Hussain; Manoranjan Kar; Mihir K. Chaudhuri (pp. 62-67).

Solid acid catalysts containing 84.5% of TiO₂ and 15.5% of [Ti₄H₁₁(PO₄)₉] xH₂O ( x=1–4) have been prepared by heating a mixture of titania and phosphoric acid (88%) in the molar ratio of 1:1 at 200–220°C on a sand bath. They serve as efficient catalysts for nitration of a wide range of aromatic compounds with nitric acid (70%). ▪Solid acid catalysts containing 84.5% of TiO₂ and 15.5% of [Ti₄H₁₁(PO₄)₉]· nH₂O ( n=1–4) have been prepared by mixing titania and phosphoric acid (88%) in the molar ratio of 1:1 and heating at 200–220°C on a sand bath. Each catalyst has been characterized by IR spectroscopy, XRD, SEM/EDAX, TG and BET surface area analysis. The catalysts work very efficiently for nitration of a wide range of aromatic compounds with nitric acid (70%).

Keywords: Acid phosphate-impregnated titania; Solid acid; Nitration; Nitric acid

Understanding the relationship between composition and hydrodesulfurization properties for cobalt phosphide catalysts by Autumn W. Burns; Kathryn A. Layman; Denise H. Bale; Mark E. Bussell (pp. 68-76).

Silica-supported cobalt phosphide (Co_xP_y/SiO₂) catalysts, prepared from precursors having P/Co molar ratios in the range 0.50–2.0, were characterized and evaluated for thiophene hydrodesulfurization (HDS). The HDS activities of the Co_xP_y/SiO₂ catalysts varied nearly four-fold depending on the composition of the Co phosphide phase, with the most active Co_xP_y/SiO₂ catalyst corresponding to the precursor composition having just enough P to ensure formation of phase-pure CoP on the silica support. The maximum in HDS activity observed for this Co phosphide composition can be correlated with a balance between site density (as measured by O₂ chemisorption) and resistance to S incorporation (as measured by S analysis of catalysts subjected to an H₂S/H₂ treatment).Co_xP_y/SiO₂ catalysts were prepared and evaluated for thiophene hydrodesulfurization (HDS). The HDS activities of the catalysts varied nearly four-fold depending on the composition of the Co phosphide phase. The most active Co_xP_y/SiO₂ catalyst corresponded to the precursor composition having just enough P to ensure formation of phase-pure CoP on the silica support.▪

Keywords: Hydrodesulfurization; Cobalt phosphides

Mesoporous titanosilicates synthesized from TS-1 precursors with enhanced catalytic activity in the α-pinene selective oxidation by Griselda A. Eimer; Isabel Díaz; Enrique Sastre; Sandra G. Casuscelli; Mónica E. Crivello; Eduardo R. Herrero; Joaquín Perez-Pariente (pp. 77-86).

Ti-containing mesoporous catalysts have been prepared using zeolite precursors as building blocks of the mesoporous network. These materials were catalytically tested in the oxidation of α-pinene with aqueous H₂O₂, showing an enhanced activity when compared to a conventional mesoporous titanosilicate. This feature can be attributed to a chemical environment of the Ti species very close to that in titanosilicalite and clearly distinguishable from that in a conventional mesoporous catalyst.▪Ti-containing mesoporous catalysts have been successfully prepared using zeolite precursors as building blocks of the mesoporous network. Tetrapropylammonium (TPA) cations were used as structure directing agent in the TS-1 precursor solutions. The assembly of the polymeric zeolite precursor species into a mesophase was carried out at room temperature assisted by cetyltrimethylammonium bromide as surfactant. Various techniques including XRD, diffuse reflectance UV–vis (DRUV–vis), N₂ adsorption, SEM, transmission electron microscopy (TEM) and thermogravimetric analysis (TGA) were employed for the materials characterization. Ti was incorporated into the silica framework in isolated sites, anatase phase was not observed. These materials were catalytically tested in the oxidation of α-pinene with aqueous H₂O₂, showing an enhanced activity when compared to a conventional mesoporous titanosilicate. Both a catalyst obtained from a precursor gel containing Na and aged at 80°C for 1 day and one obtained from a precursor gel without Na but aged for 2 days at 80°C showed the highest activity and selectivity to products arising from epoxidation mechanism. This feature can be attributed to a chemical environment of the Ti species very close to that in titanosilicalite and clearly distinguishable from that in a conventional mesoporous catalyst. An addition of peroxide after the first reaction hour allowed us to increase the conversion values in ∼30%.

Keywords: Zeolite precursors; TS-1; Mesoporous materials; Titanosilicates; Epoxidation; α-Pinene

Selective hydrogenation of 1,5,9-cyclo-dodecatriene towards cyclo-dodecene by J. Gaube; W. David; R. Sanchayan; S. Roy; F. Müller-Plathe (pp. 87-94).

A cyclo-dodecene yield ≥90% can be attained in liquid phase hydrogenation of 1,5,9- cis, trans, trans-cyclo-dodecatriene on Pd catalysts of eggshell type if the hydrogen concentration is kept at a low level. Ab initio Hartree–Fock calculations of the molecular structures of cyclododecadienes have pointed at the crucial role of both cyclododecadienes and hydrogen adsorption on nanostructured surfaces of palladium. ▪The liquid phase hydrogenation of 1,5,9- c, t, t-cyclo-dodecatriene (CDT) and of cyclododecadienes (CDD) towards cyclo-dodecene (CDE) using a Pd/Al₂O₃ catalyst of egg-shell type has been studied in discontinuous operation at different hydrogen pressures and for stepwise reduced hydrogen pressure. The yield of CDE is considerably increased if the hydrogen concentration and consequently the rate of hydrogenation are markedly reduced. By this means a CDE yield of 93% at a (CDT+CDD) conversion of 98% could be reached. Because of the low hydrogenation rate the conversion is not influenced by mass transfer effects.For discussion the partial hydrogenation of CDT is compared with the hydrogenation of cyclo-octadiene for which a cyclo-octene yield of >99% is attainable at a much higher reaction rate. In order to understand the partial hydrogenations of cyclo-octadiene and of CDD ab initio Hartree–Fock calculations have been carried out to study the structure of these molecules. On this basis a hypothesis for the lower selectivity of CDT-hydrogenation towards CDE compared to that of cyclo-octadiene towards cyclo-octene is presented. The increase of CDE selectivity with decreasing hydrogen pressure is traced back to the increased rate of the isomerization of t, t- and c, t-CDDs towards the more strongly adsorbed c, c-CDDs.The results of the presented study clearly show that the realization of an industrial process of the selective hydrogenation of CDT towards CDE using a simple catalytic reactor is possible. Concepts are proposed for discontinuous and for continuous procedure.

Keywords: Hydrogenation; 1,5,9-Cyclo-dodecatriene; Cyclo-dodecene; Kinetics; Reaction engineering

Mechanism of thiophene hydrodesulfurization on clean/sulfided β-Mo₂C(001) based on density functional theory— cis- and trans-2-Butene formation at the initial stage by Hiroyuki Tominaga; Masatoshi Nagai (pp. 95-103).

The mechanism of thiophene hydrodesulfurization (HDS) on clean/sulfided β-Mo₂C(001) slabs was studied based on density functional theory (DFT) calculations with different thiophene configurations. Self-consistent, gradient-corrected, periodic DFT calculations were performed. The η⁵-configuration of thiophene on the Mo atom of Mo carbide preferred the η¹-configuration of the adsorption of the thiophene sulfur atom and induced the subsequent scission of the C–S bonds. The addition of hydrogen atoms to the adsorbed C4 species led to the formation of trans-2-butene and S–Mo bonding on the clean β-Mo₂C(001) slab, while cis-2-butene was formed as a result of hydrogen addition on the sulfided β-Mo₂C(001) slab. The difference between the formation of trans-2-butene for the β-Mo₂C(001) slab and cis-2-butene for the sulfided β-Mo₂C(001) was discussed.▪The mechanism of thiophene hydrodesulfurization (HDS) on clean/sulfided β-Mo₂C(001) slabs was studied based on density functional theory (DFT) calculations with different thiophene configurations. Self-consistent, gradient-corrected, periodic DFT calculations were performed. The η⁵-configuration of thiophene on the Mo atom of Mo carbide preferred the η¹-configuration of the adsorption of the thiophene sulfur atom and induced the subsequent scission of the C–S bonds. The addition of hydrogen atoms to the adsorbed C4 species led to the formation of trans-2-butene and S–Mo bonding on the clean β-Mo₂C(001) slab, while cis-2-butene was formed as a result of hydrogen addition on the sulfided β-Mo₂C(001) slab. The difference between the formation of trans-2-butene for the β-Mo₂C(001) slab and cis-2-butene for the sulfided β-Mo₂C(001) was discussed.

Keywords: Density functional theory; Adsorption; η; ⁵; -Configuration; Hydrodesulfurization; trans-; or; cis-; 2-Butene; Molybdenum carbide; Sulfide; Thiophene

Reversible deactivation of TiO₂ in CS₂ conversion associated with Claus reaction by P.D. Clark; N.I. Dowling; M. Huang (pp. 104-108).

A reversible deactivation over titania in CS₂ conversion has been found in this laboratory. This deactivation is closely related to the presence of Claus reaction. The key intermediate species of Claus reaction is thiosulfate anion, S₂O₃²⁻, which further reacts with Bronsted acid of titania to form surface polythionates. The long S chain of the latter would shield the active centers responsible for CS₂ conversion.▪CS₂ destruction is an important reaction in industrial Claus process. A reversible deactivation over titania in CS₂ conversion has been found in this laboratory. This deactivation is closely related to the presence of Claus reaction. The key intermediate species of Claus reaction is thiosulfate anion, S₂O₃²⁻, which further reacts with Bronsted acid of titania to form surface polythionates. The long S chain of the latter would shield the active centers responsible for CS₂ conversion and causes the deactivation, while these polythionates can be easily destroyed by heating at 330°C, which is finally accompanied by a recovery of catalytic activity in CS₂ conversion.

Keywords: Titania; CS; ₂; conversion; Reversible deactivation; Claus reaction

Preparation, characterization and catalytic activity of tin oxide-supported 12-tungstophosphoric acid as a solid catalyst by Abd El Rahman S. Khder (pp. 109-116).

A series of solid acid catalysts were synthesized by incipient wetness impregnation method by varying the wt% of 12-tungstophosphoric acid (TPA) on tin oxide. The acidity measurements showed that the total acidity increases with the rise of TPA content up to 20wt% (monolayer coverage) and decreases thereafter. FT-IR spectra of pyridine adsorbed on the catalysts showed the presence of both Brønsted and Lewis acidities. Material with 20wt% TPA on tin oxide having high surface area and acid sites acts as the better catalyst for esterification reaction. For the material that exhibits the optimum catalytic activity, selective poisoning of the potential catalytic centers revealed that Brønsted sites play the major role in carrying out the reaction. ▪A series of solid acid catalysts were synthesized by incipient wetness impregnation method by varying the wt% of 12-tungstophosphoric acid (TPA) on tin oxide. The prepared catalysts were characterized by thermal analysis, XRD, FT-IR and BET surface area. The acidity of the catalyst was measured by different techniques. The suitability of the materials was studied for acid-catalyzed esterification reaction using acetic acid and amyl alcohol. The acidity measurements showed that the total acidity increases with the rise of TPA content up to 20wt% (monolayer coverage) and decreases thereafter. FT-IR spectra of pyridine adsorbed on the catalysts showed the presence of both Brønsted and Lewis acidities. Material with 20wt% TPA on tin oxide having high surface area and acid sites acts as the better catalyst for esterification reaction. For the material that exhibits the optimum catalytic activity, selective poisoning of the potential catalytic centers revealed that Brønsted sites play the major role in carrying out the reaction. The straight-line plots of −ln(1-ester formed) versus catalyst weights support that the esterification reaction obeys first-order kinetics. The reusability study justifies that the catalyst is stable and active.

Keywords: Tin oxide; 12-Tungstophosphoric acid; Surface acidity; Esterification reaction; Amyl acetate; Reaction mechanism; Selective poisoning

Preferential CO oxidation in hydrogen-rich stream over Pt catalysts modified with alkali metals by Hisanori Tanaka; Masatoshi Kuriyama; Yoichi Ishida; Shin-ichi Ito; Keiichi Tomishige; Kimio Kunimori (pp. 117-124).

In preferential CO oxidation in H₂-rich stream (PROX), the additive effect of potassium to Pt/Al₂O₃ was more effective than other alkali metals. The PROX activity of K-Pt/Al₂O₃ was much higher than that of Pt/Al₂O₃ under the presence of steam, and the effect of steam addition over K-Pt/Al₂O₃ suggests that the active site can be Pt surface modified with potassium ions.▪In preferential CO oxidation in H₂-rich stream (PROX), the additive effect of potassium on Pt catalysts was more remarkable over Al₂O₃ than over SiO₂, ZrO₂, Nb₂O₅ and TiO₂. The additive effect of potassium to Pt/Al₂O₃ was more effective than other alkali metals. Especially, the presence of H₂ drastically promoted CO oxidation over Pt/Al₂O₃ modified with potassium. On the other hand, the suppressing effect of steam on the PROX was more significant over K-Pt/Al₂O₃ than over Pt/Al₂O₃, although the PROX activity of K-Pt/Al₂O₃ was much higher than that of Pt/Al₂O₃ even under the presence of steam. The different effect of steam addition to the PROX over K-Pt/Al₂O₃ suggests that the active site can be Pt surface modified with potassium ions.

Keywords: Preferential CO oxidation; Platinum; Alkali metal ions; Potassium; Presence of H; ₂

Preferential CO oxidation in hydrogen-rich stream over Pt catalysts modified with alkali metals by Hisanori Tanaka; Masatoshi Kuriyama; Yoichi Ishida; Shin-ichi Ito; Takeshi Kubota; Toshihiro Miyao; Shuichi Naito; Keiichi Tomishige; Kimio Kunimori (pp. 125-133).

The promoting and negative effects of addition of alkali metals over Pt/Al₂O₃ in preferential CO oxidation in H₂-rich stream (PROX) were investigated in this work. The addition of alkali metals strongly influences the state of Pt metal particles, and coadsorbed species originating from H₂ and O₂ under the PROX condition can be found on highly active catalysts.▪The addition of alkali metals over Pt/Al₂O₃ has both promoting and negative effects on the catalytic performance in the preferential CO oxidation in H₂-rich stream (PROX), therefore there is an optimum amount of alkali metal. The Pt/Al₂O₃ catalysts modified with Na, K, Rb and Cs were characterized by means of transmission electron microscopy (TEM), extended X-ray absorption fine structure (EXAFS), X-ray absorption near-edge structure (XANES), and Fourier transform infrared spectroscopy (FTIR). The results show that the addition of larger amount of alkali metals with stronger basicity causes the aggregation of Pt metal particles. The Pt particles on Pt/Al₂O₃ modified with alkali metals are more electron-deficient than those on Pt/Al₂O₃, and this weakens the strength of CO adsorption on Pt/Al₂O₃ modified with alkali metals, which is related to the enhancement of turnover frequency of the PROX. In addition, in situ FTIR observation suggests that the coadsorbed species originating from H₂ and O₂ (e.g., the OH species) under the PROX condition, which promote the CO oxidation, can be found on highly active catalysts.

Keywords: Preferential CO oxidation; Platinum; Alkali metals; Potassium; OH group; FTIR; X-ray absorption fine structure

Preparation and characterization of Fe/Cu/Al₂O₃-composite granules for SO₃ decomposition to assist hydrogen production by Haznan Abimanyu; Kwang-Deog Jung; Ki-Won Jun; Jinsoo Kim; Kye Sang Yoo (pp. 134-141).

Cu/Al₂O₃-, Fe/Al₂O₃- and Cu/Fe/Al₂O₃-composite granules were prepared by a combination of the Yoldas sol–gel process and the oil-drop method for SO₃ decomposition. The catalysts showed high catalytic activities and reached the highest SO₃ conversion for the optimum metals (Cu and Fe) loading in the alumina granules with a ratio of [Cu]/[Fe]=1/2 and [Cu]+[Fe]=0.125M.▪In this work, the activity values of Cu/Al₂O₃-, Fe/Al₂O₃- and Cu/Fe/Al₂O₃-composite granule catalysts prepared by a combination of Yoldas-process and oil-drop method were studied in an attempt to find some suitable catalysts for the decomposition of sulfur trioxide as the oxygen-generating reaction in the thermo-chemical water splitting process. The SO₃ decomposition was performed in the temperature range of 750–950°C at a space velocity of 72,000mL/gcat.h in a fixed bed reactor. The catalytic activity of Cu/Fe/Al₂O₃-composite granule catalyst was better than that of Cu/Al₂O₃- and Fe/Al₂O₃-composite granule catalysts. The composite of Cu and Fe in the alumina granules increased the catalytic activity and found the optimum ratio of [Cu]/[Fe]=1/2 with [Cu]+[Fe]=0.125M.

Keywords: Metal oxide; Composite granule; SO; ₃; decomposition

Oxidative coupling of methane for the production of ethylene over sodium-tungsten-manganese-supported-silica catalyst (Na-W-Mn/SiO₂) by Yen Thien Chua; Abdul Rahman Mohamed; Subhash Bhatia (pp. 142-148).

Sodium-tungsten-manganese (Na-W-Mn)-supported SiO₂ catalyst has been studied for the production of ethylene in a OCM reaction. Na, W and Mn play important roles during the OCM reaction, in providing the stability and activity of the catalyst system. The interaction effects of the component–component and component–support on the methane conversion and C₂₊ yield are reported using different characterization techniques.▪Sodium-tungsten-manganese (Na-W-Mn)-supported SiO₂ catalyst is one of the widely studied catalysts in oxidative coupling of methane (OCM) reaction. Na, W and Mn have individual roles during the OCM reaction, in providing the stability and activity of the catalyst system. The interaction effects of the component–component and component–support on the methane conversion and C₂₊ yield were investigated with the aid of thermal gravimetric analysis (TGA), X-ray diffraction (XRD), Raman spectroscopy, Fourier transformed infrared (FTIR) spectroscopy, nitrogen adsorption analysis and catalytic activity tests. The catalyst performance was studied at an operating temperature of 850°C, a gas hourly space velocity (GHSV) of 23,947cm³/gh, a catalyst pretreatment period of 2h, a dilution ratio of 0.2, and a CH₄/O₂ ratio of 7. During the stability test, methane conversion was maintained at 40–50% throughout a 30h run. The catalyst was regenerated by allowing oxygen flow through the catalyst bed for 3–5h once the catalyst was deactivated. C₂₊ selectivity was recovered to almost 60%, whereas methane conversion did not change after the regeneration. Both Na₂WO₄ and Mn₂O₃ crystalline phases contributed to achieving high selectivity of C₂₊ products. The catalyst activity dropped due to the phase transformation of the support from α-cristobalite to quartz and the loss of manganese oxide from the catalyst surface.

Keywords: Oxidative coupling of methane (OCM); Na-W-Mn/SiO; ₂; C; ₂₊; selectivity; Stability; Catalyst regeneration

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Applied Catalysis A, General (v.343, #1-2)

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Applied Catalysis A, General (v.343, #1-2)