Showing papers in "Catalysis Surveys From Asia in 2003"

Oxide semiconductor gas sensors

Abstract: Semiconductor gas sensors utilize porous polycrystalline resistors made of semiconducting oxides. The working principle involves the receptor function played by the surface of each oxide grain and the transducer function played by each grain boundary. In addition, the utility factor of the sensing body also takes part in determining the gas response. Therefore, the concepts of sensor design are determined by considering each of these three key factors. The requirements are selection of a base oxide with high mobility of conduction electrons and satisfactory stability (transducer function), selection of a foreign receptor which enhances surface reactions or adsorption of target gas (receptor function), and fabrication of a highly porous, thin sensing body (utility factor). Recent progress in sensor design based on these factors is described.

Photocatalyst Materials for Water Splitting

Abstract: Various photocatalyst materials developed by the group of the present author are described. Alkali and alkaline earth tantalates have arisen as a new group of photocatalyst materials for splitting of water into H2 and O2 under ultraviolet irradiation. They showed activities even without co-catalysts such as Pt, being different from titanate photocatalysts. When NiO co-catalysts were loaded on the tantalate photocatalysts, the photocatalytic activities were markedly increased. Among the tantalates, NiO/NaTaO3 doped with La showed the highest activity. BiVO4, AgNO3, and TiO2 co-doped with Cr and Sb photocatalysts showed high activities for O2 evolution in the presence of a sacrificial reagent (Ag+) under visible light irradiation (λ > 420 nm). Pt/SrTiO3 co-doped with Cr and Sb or Ta, Pt/NaInS2, and Pt/AgInZn7S9 photocatalysts showed high activities for H2 evolution from aqueous solutions containing reducing reagents under visible light irradiation. Furthermore, Cu- or Ni-doped ZnS photocatalysts showed H2 evolution activities even without co-catalysts such as Pt.

Oxygen Storage Materials for Automotive Catalysts: Ceria-Zirconia Solid Solutions

Abstract: This paper reviews progress in the development of oxygen storage materials for automotive exhaust catalysts. The research was mainly conducted as a study and development exercise in the author's laboratory in Japan. Ceria-lanthana solid solutions (CL) and the first generation of ceriazirconia solid solutions (CZ) were developed as excellent oxygen storage materials for automotive catalysts in the 1980s. These materials consist of ceria doped with less than 20 mol% of La4+ or Zr4+. An increase in oxygen defects in CL and CZ under reductive conditions is responsible for an enhanced oxygen storage capability on the cerium atoms. An accurate measure of the oxygen storage capacity (OSC) per cerium is very important for theoretical and practical treatments of the catalyst. The term “partial OSC” was introduced to describe this capacity and to differentiate it from the usual definition of the OSC, known also as the “total OSC”. After the development of CL and CZ, a new technology was developed to dissolve more than 20 mol% of zirconia in the ceria, allowing second generation CZ and third generation CZ (known as ACZ, which is doped with alumina) to be successfully developed in the 1990s. The partial OSC of these materials increases with increasing amounts of zirconia dissolved in the ceria, and also with decreasing material particle size after an engine durability test. In the case of ACZ, alumina was added to CZ based on the “diffusion barrier concept”, in which a diffusion barrier layer inhibits the coagulation of CZ and A when the material is required for duty at high temperature in air. Furthermore, the relationship between the total or partial OSC and the structure of the ceriazirconia solid solutions is explained in this paper. For ceriazirconia solid solutions composed of equimolar CeO2 and ZrO2(Ce/Zr=1), the total or partial OSC of the κ-phase CeZrO4, in which the cerium and zirconium ions are regularly distributed, was about twice as large as that of a ceriazirconia solid solution with a relatively irregular distribution of cerium and zirconium ions, and about five times larger than that of a mixture of ceria powder and zirconia containing only a small amount of ceriazirconia solid solution. It corresponds to about 89% of the theoretical maximum value. For a ceriazirconia solid solution composed of non-equimolar CeO2 and ZrO2(Ce/Zr ≠ 1), the partial OSC of a ceria-κ-phase solid solution with a zirconia content of between 30 and 50mol% is much higher than that of a ceriazirconia solid solution of the same zirconia content. The partial OSC of a κ-phase and zirconia mixed oxide, which is formed by reducing the material at 1200 °C, reaches a value above 0.20 mol-O2/mol-Ce (about 80% of the theoretical maximum value of the partial OSC), when the zirconia content is between 50 and 80 mol%. The Toyota Motor Corp. has put automotive three-way catalysts containing the first, second and third generations of CZ into practical use on a global basis.

The Catalysis of Vapor-Phase Beckmann Rearrangement for the Production of ε-Caprolactam

Abstract: Recently, Sumitomo Chemical Co., Ltd. developed the vapor-phase Beckmann rearrangement process for the production of e-caprolactam. In the process, cyclohexanone oxime is rearranged into e-caprolactam using a zeolite as a catalyst instead of sulfuric acid. EniChem in Italy developed the ammoximation process that involves the direct production of cyclohexanone oxime without producing any ammonium sulfate. Sumitomo Chemical Co., Ltd. has commercialized the combined process of vapor-phase Beckmann rearrangement and ammoximation in 2003. In this paper, the authors focus on some aspects of the vapor-phase Beckmann rearrangement catalysis. A solid catalyst that is mainly composed of a high-silica MFI zeolite (Silicalite-1) has been developed for the vapor-phase Beckmann rearrangement. This catalyst does not possess acidity that can be detected by ammonia TPD. Methanol fed into the reactor with cyclohexanone oxime improves the yield of caprolactam. Methanol reacts with terminal silanols on the zeolite surface and converts them to methoxyl groups. The modification of the catalyst by methanol has an important role for the Beckmann rearrangement reaction. Nest silanols located just inside the pore mouth of the MFI zeolite are supposed to be the active sites of the catalyst. We propose that the coordination between the NOH group of cyclohexanone oxime molecule and the nest silanols through hydrogen bonding is responsible for the reaction. The reaction mechanism of Beckmann rearrangement under vapor-phase conditions is the same as in the liquid phase, namely, the alkyl group in anti-position against the hydroxyl group of the oxime migrates to the nitrogen atom's position.

Photocatalytic Organic Syntheses : Selective Cyclization of Amino Acids in Aqueous Suspensions

Abstract: Photocatalytic reactions occurring at semiconductor particles/solution interfaces can be applied to organic syntheses. In this review article, examples of photocatalytic syntheses of cyclic amino acids by suspended semiconductor particles, e.g., titanium(IV) oxide or cadmium(II) sulfide are introduced and interpreted. Different from the photocatalytic decomposition of pollutants under aerobic conditions, selective conversion of organic compounds can be driven by the photocatalytic reactions under deaerated conditions.

Photoredox Chemistry of Polyoxometalates as a Photocatalyst

Abstract: The photocatalytic action of polyoxometalates (PMs), which is initiated by the photoexcitation of the oxygen-to-metal charge-transfer (O → M LMCT) bands of PM, is based on the electron–hole pair separation followed by reductive and oxidative reactions with surrounding molecules. It is shown that the O → M LMCT triplet states are involved in the photoredox reactions in which the significance of the highly negative oxidation potential for the photoreduced PMs can be considered in connection with the photocatalytic H2 formation from a great variety of organic substrates with their dehydrated oxidation. When the reaction of the photoreduced PMs with the electron acceptor hardly occurs kinetically or thermodynamically, they undergo self-assembled organization to nanosized supramolecules (as a result of photoencapsulation of small molecules and ring cluster formation). Some typical examples for the electron–hole pair separation and the photoredox reactions developed in our laboratory are discussed.

Biomimetic Oxidations Using Transition Metal Complexes Encapsulated in Zeolites

Abstract: An account of biomimetic oxidations by metal phthalocyanines, tri- and tetra-aza macrocycles, Schiff bases (salen and saloph), dimeric Cu-acetate and Co-Mn-acetate complexes encapsulated in zeolite-Y and molecular sieves is reported. The selective oxidation reactions investigated include epoxidation of styrene, hydroxylation of phenol, oxidation of p-xylene to terephthalic acid, ethylbenzene to acetophenone and cyclohexane, cyclohexanol and cyclohexanone to adipic acid. In all these reactions, the encapsulated metal complexes exhibit enhanced activity or selectivity compared to the “neat” complexes. The reasons for the enhanced activity of metal complexes upon encapsulation in zeolites are reported.

SK Hydrodesulfurization (HDS) Pretreatment Technology for Ultralow Sulfur Diesel (ULSD) Production

Abstract: SK Corporation of Korea has developed a unique process, SK hydrodesulfurization (HDS) pretreatment technology, to produce ultralow sulfur diesel (ULSD) with pretreatment of the middle-distillate-range petroleum fractions. This technology has been successfully demonstrated through a 1000 barrel/day (B/D) demonstration plant, which has been running since May 2002. This technology is based on the adsorptive removal of a small amount of nitrogen-based natural polar compounds (NPC). Dramatic improvement in deep HDS efficiency is observed with the removal of NPC from the feedstock.

Chemisorbed Oxygen Species over the (110) Face of SnO2

Abstract: The electronic states of chemisorbed oxygen species on the (110) face of SnO2 and their variations caused by heat treatments and/or O2 exposure have been investigated. The reactivities of the chemisorbed oxygen species for methane oxidations were also examined. Four different chemisorbed oxygen species (O2 2-, O2-, O-, Ob) were observed, in addition to the lattice oxygen (O2-), on the surface of the stabilized (110) surface of SnO2 after O2 exposure. The Ob species was assumed to be the bridging oxygen at the topmost layer of the SnO2 (110) surface having no neighboring oxygen vacancies. The electronic state of Ob was converted to O- upon CH4 exposure at 473 K by coupling with newly produced vacancies at the bridging site of the SnO2 (110) surface.

Diffusion mechanisms of zeolite catalysts

Abstract: The diffusion mechanisms within zeolite catalysts, such as resistance to diffusion at pore mouths, configurational diffusion, adsorption-controlled diffusion, influence of co-existing molecules and pore blocking, were overviewed. Two kinds of diffusivities, the intracrystalline diffusivity and the effective diffusivity, were discussed separately to clarify the diffusion mechanism.

Novel Catalysts for Gasification of Biomass with High Conversion Efficiency

Abstract: We have developed catalysts for the gasification of biomass with much higher energy efficiency than the conventional methods (noncatalyst, dolomite, and commercial steam reforming Ni catalyst). In our investigation, the Rh/CeO2 gave high yields of syngas for cellulose gasification using a fluidized-bed reactor with batch feeding of cellulose. However, the catalyst was deactivated because of sintering of CeO2 during the reaction. To prevent the CeO2 sintering, we have further improved the catalyst and found that Rh/CeO2/SiO2 was quite stable for the gasification of cellulose. It was demonstrated that Rh/CeO2/SiO2 gave almost complete gasification of real biomass (wood powder) at 873 K. These results indicate that the combination of this kind of catalyst and fluidized-bed reactor can realize the energy-efficient biomass gasification.

Ultradeep Hydrodesulfurization of Dibenzothiophene (DBT) Derivatives over Mo-Sulfide Catalysts Supported on TiO2-Coated Alumina Composite

Abstract: The present paper reviews in detail the different studies now being conducted by our research team concerning the ultradeep hydrodesulfurization (HDS) of dibenzothiophene (DBT) derivatives over Mo/TiO2 and Mo/TiO2–Al2O3 catalysts. First, a detailed characterization of Mo/TiO2 (P-25 Degussa, 50 m2/g) catalysts prepared by equilibrium adsorption technique shows that Mo- species are highly and uniformly dispersed on the surface of titania up to 6.6 wt% MoO3 loading. Above this value, some aggregation of Mo occurs, leading to the formation of bulk MoO3. Below 6.6 wt% MoO3 loading, the Raman spectroscopy data of the calcined samples show that the supported Mo-species possess a highly distorted octahedral MoO6 structure. TiO2–Al2O3 composites were prepared by chemical vapor deposition (CVD) using TiCl4 as a precursor. Using several characterization techniques, we demonstrated that the support composite presents a high dispersion of TiO2 over γ-Al2O3 without forming precipitates up to ca. 11 wt% loading. Moreover, the textural properties of the composite support are comparable to those of alumina. Under the present sulfidation conditions (673 K, 5%H2S/95%H2), Mo-species supported on TiO2 are better sulfided than on alumina, as demonstrated using XPS. This can be attributed to the relatively lower interaction between Mo-species and titania. The state of sulfide species supported on the composite support can be considered as a transition state between TiO2 and Al2O3. However, at relatively higher TiO2 loadings (ca. 11 wt%), Mo/TiO2–Al2O3 catalysts exhibit sulfidability similar to that of Mo/TiO2. The HDS tests conducted in both the laboratory and in industry show that sulfide catalysts supported on TiO2–Al2O3 (ca. 11 wt% TiO2) are more active than those supported on TiO2 or Al2O3.

Tishchenko reaction over solid base catalysts

Abstract: Catalytic behavior of solid bases for mixed Tishchenko reaction in which an equimolar mixture of two different aldehydes is allowed to react was investigated employing the combinations of benzaldehyde and pivalaldehyde, pivalaldehyde and cyclopropanecarbaldehyde, and cyclopropanecarbaldehyde and benzaldehyde. The reactions were performed at 353 K for 4 h in vacuo without solvent using 5 mmol of each aldehyde and 100 mg of solid base catalyst. For all the combinations, the catalytic activity of alkaline earth oxides increased in the order of BaO≪MgO

Design and Development of Zeolite-Based Catalytic Processes for Aromatics Production

Abstract: Processes for the production of xylenes, which occur in an integrated aromatic complex, are discussed. A brief overview of the work carried out at Indian Petrochemicals Corporation Limited for the development of zeolite-based catalytic processes for the production of aromatics is presented. This includes xylene isomerization, transalkylation and disproportionation of C7 and C9 aromatics for maximization of xylenes, selective disproportionation of toluene and selective alkylation of mono-alkylaromatics to p-dialkylbenzene. Achievements in the commercialization of zeolite-based catalysts and processes for isomerization of m-xylene to p- and o-xylene along with dealkylation of ethylbenzene, and for selective ethylation of ethylbenzene to produce p-diethylbenzene are highlighted.

Structure and function of a multidomain alkaline xylanase from alkaliphilic Bacillus sp. strain 41M-1

Abstract: Xylanase is an enzyme that catalyzes the hydrolysis of xylan, a β-1,4-linked xylose polymer Alkaliphilic Bacillus sp strain 41M-1 secretes a xylanase (xylanase J) that has an alkaline pH optimum Xylanase J is a multidomain enzyme and consists of two functional domains: a family 11/G catalytic domain and a non-catalytic xylan-binding domain The xylan-binding domain bound to xylan and enhanced catalytic activity of the adjacent catalytic domain Mutational analyses revealed some amino acid residues that contribute to catalytic activity, alkaliphily and xylan-binding activity of xylanase J

Recent developments in the in situ XAFS and related work for the characterization of catalysts in Japan

Abstract: This short review deals with some recent XAFS (X-ray absorption fine structure) applications to catalysts in Japan. The high transmission ability of X rays makes it possible to carry out in situ work on catalysts. First, in situ XAFS works under flow and high-pressure reaction conditions will be described. The time-resolved XAFS work will be another important topic because it can provide the possibility of observing the change of the reaction active site and the reaction intermediate. Finally, PTRF-XAFS will be described, which is a unique technique and provides three-dimensional local structures of highly dispersed surface species.

In Situ IR Spectroscopic Studies on Molybdenum Nitride Catalysts: Active Sites and Surface Reactions

Abstract: Recent IR spectroscopic studies on the surface properties of fresh Mo2N/γ-Al2O3 catalyst are presented in this paper. The surface sites of fresh Mo2N/γ-Al2O3, both Moδ+ (0<δ<2) and N sites, are probed by CO adsorption. Two characteristic IR bands were observed at 2045 and 2200 cm-1, due to linearly adsorbed CO on Mo and N sites, respectively. The surface N sites are highly reactive and can react with adsorbed CO to form NCO species. Unlike adsorbed CO on reduced passivated one, the adsorbed CO on fresh Mo2N/γ-Al2O3 behaves similarly to that of group VIII metals, suggesting that fresh nitride resembles noble metals. It is found that the surface of Mo nitrides slowly transformed into sulfide under hydrotreating conditions, which could be the main reason for the activity drop of molybdenum nitride catalysts in the presence of sulfur-containing species. Some surface reactions, such as selective hydrogenation of 1,3-butadiene, isomerization of 1-butene, and hydrodesulfurization of thiophene, were studied on both fresh and reduced passivated Mo2N/γ-Al2O3 catalysts using IR spectroscopy. The mechanisms of these reactions are proposed. The adsorption and reaction behaviors of these molecules on fresh molybdenum nitride also resemble those on noble metals, manifesting the unique properties of fresh molybdenum nitride catalysts. Mo and N sites are found to play different roles in the adsorption and catalytic reactions on the fresh Mo2N/γ-Al2O3 catalyst. Generally, Mo sites are the main active sites for the adsorption and reactions of adsorbates; N sites are not directly involved in catalytic reactions but they modify the electronic properties of Mo sites.

Electrocatalytic Oxidation of Methanol and Related Chemical Species on Ultrafine Pt and PtRu Particles Supported on Carbon

Abstract: Well-homogenized PtRu/C electrocatalysts possessing high specific activity for methanol electro-oxidation were prepared by a co-impregnation method from carbon black and ethanolic solutions of Pt(NH3)2(NO2)2 and RuNO(NO3) x . The specific activity for methanol electro-oxidation increased with an increase in the PtRu particle size. A similar size effect was observed for Pt/C electrocatalysts. The size effect was discussed by considering a model catalyst method.

Manganese-Catalyzed Carbomagnesation of Alkynes

Abstract: The development of manganese-catalyzed carbomagnesation of alkynes is reviewed. Manganese salts mediate the efficient addition of a variety of Grignard reagents to alkynes. Allyl, aryl, and alkyl Grignard reagents participate in these reactions. In many cases, a hetero atom such as oxygen or nitrogen in substrates facilitates the addition reaction. Stoichiometric carbometalation reactions with manganese ate complexes are also discussed, as is cyclization of 1,6-diynes and 1,6-enynes via carbometalation with triallylmanganate.

The Formation and Reactions of Hydrogen Cyanide During Isobutane-SCR over Fe-MFI Catalysts

Abstract: The extent to which HCN is produced as a significant product during isobutane-SCR over Fe-MFI catalysts has been investigated together with its origin and further conversion. Catalysts made by both vapor-phase sublimation and solid-state ion exchange can produce well over 100-ppm HCN, which is a major intermediate for N2 production, but the peak concentration is less with the former material due to a higher oxidation activity. HCN production is confined to temperatures giving partial conversion of isobutane, when deposited material suppresses the very high intrinsic activity of Fe-MFI for the further conversion of HCN to N2, largely via hydrolysis to ammonia and NH3-SCR. Activity for the oxidation of NO to NO2 is similarly suppressed. This oxidation step is likely to be the rate determining one in isobutane-SCR rather than the activation of the alkane since there is no deuterium kinetic isotope effect. Decomposition of isobutyronitrile, formed by dehydration of a primary nitroso species via its oxime tautomer, is a possible source of HCN. This decomposition gives propene as a coproduct, which reacts completely during isobutane-SCR and may also be a source of deposits through oligomerization. Secondary and tertiary nitroso intermediates cannot react in this way and, based on the reactions of nitroanalogues, are more likely to undergo elimination to form alkenes. The overall effect is to convert alkane-SCR to SCR with alkenes containing the same number or one less carbon atom.

New industrial process of PTMG catalyzed by solid acid supported on mesoporous material

Abstract: Polymerization of tetrahydrofuran (THF) catalyzed by solid acid in the presence of acetic anhydride was studied. Moderate Lewis acid catalyst produces PTME (PTMG-diacetate) having appropriate molecular number (Mn). Mixed oxide materials show good performance. Mass transfer study suggests the importance of pore size of the support and of the location of active sites. They affect the Mn and the polydispersity (Mw/Mn) strikingly. The commercial technology has established by utilizing these results.

Living Polymerization of Propene with Alkyltitanium-Based Catalysts

Abstract: Living polymerization of propene with alkyltitanium-based catalysts is described with emphasis on the role of the activators employed. (η1 : η3-tert-Butyl(dimethylfluorenylsilyl)amido)dimethyltitanium activated by tris(pentafluorophenyl)borane (B(C6F5)3) catalyzes the living polymerization at -50 °C. The use of dried methylaluminoxane (MAO) in place of B(C6F5)3 raises the living polymerization temperature to 0 °C and improves the syndiospecificity. A chelating diamide dimethyltitanium activated by dried modified MAO (MMAO) catalyzes the living polymerization at 0 °C to give a statistically atactic polymer. The heterogenization of the living systems is attempted by supporting MAO, MMAO and dried MMAO on SiO2 as solid activators.

Effect of Acidic and Basic Species on the Hydrodesulfurization of Methyl-Substituted Dibenzothiophenes

Abstract: Acidic components when added to Mo-based catalysts enhance the activity of the catalysts for the hydrodesulfurization (HDS) of methyl-substituted dibenzothiophenes (DBTs), the major refractory compounds included in gas oil. However, the enhancing effect of the acidic species is frequently retarded by impurities present in the gas oil, particularly by basic nitrogen compounds. Accordingly, evaluations of the performance of such acid-modified catalysts in HDS should take into account the combined effects of acidic and basic components. The performance is strongly dependent on the types of DBT compounds, acidic and basic species involved in the reaction, and promoters of the Mo-based catalysts.

Rhodium–Aluminum-Mixed Oxide Catalysts for Selective Reduction of NO x by Hydrocarbons

Abstract: Rhodium—alumina-mixed oxides have been investigated as catalysts for selective catalytic reduction of NO x by propene, as a part of the R&D Project of Next Generation Catalysts Research Institute. The results indicated that the NO x reduction activity increases with a decrease in the reducibility of rhodium, suppressing wasteful consumption of propene by the reaction with oxygen. Coprecipitation method for the preparation of Rh-alumina catalysts was effective for the formation of the less-reducible rhodium sites, and the addition of zirconium and gallium further enhanced the formation of those sites and increased the selectivity of NO x reduction.