Hirofumi Shinjoh

The new concept 3-way catalyst for automotive lean-burn engine : NOx storage and reduction catalyst

The new concept 3-way catalysts for a lean-burn engine have been developed, and their NOx purification mechanisms have been studied. The catalysts consist of precious metals, aluminum oxide and some other metal compounds such as NOx, storage compounds. NOx is oxidized over the precious metals and stored as nitrate ion combined with NOx storage compounds under oxidizing conditions. The stored NOx, is reduced to N2 under stoichiometric and reducing conditions. The NOx, storage capacity is deteriorated by sulfur. The improved catalysts showed sufficient NOx, conversion durability in the Japanese 10–15 mode test.

Extra-Low-Temperature Oxygen Storage Capacity of CeO2 Nanocrystals with Cubic Facets

Herein we demonstrate the extra-low-temperature oxygen storage capacity (OSC) of cerium oxide nanocrystals with cubic (100) facets. A considerable OSC occurs at 150 °C without active species loading. This temperature is 250 °C lower than that of irregularly shaped cerium oxide. This result indicates that cubic (100) facets of cerium oxide have the characteristics to be a superior low-temperature catalyst.

In Situ Redispersion of Platinum Autoexhaust Catalysts: An On-Line Approach to Increasing Catalyst Lifetimes?†

Supported precious metals, such as platinum (Pt), rhodium (Rh), and palladium (Pd), are used to facilitate many industrial catalytic processes. Pt in particular is found at the core of catalysts used throughout the petrochemical industry: from bifunctional catalysts (isomerization/dehydrogenation) used for refining of hydrocarbon fuel stocks, to three-way (CO and hydrocarbon oxidation/NOx reduction) conversions within car exhausts. In this latter, ubiquitous application— commercialized in the USA and Japan in 1977—Pt has always been a pivotal component in the abatement of harmful gas emissions from gasolineor diesel-driven engines. The ever-increasing appreciation of the damage that noxious gas emissions are doing to our environment and the finite availability of noble metals provide strong drivers for the continued study and optimization of the behavior of Pt-based three-way catalysts (TWCs). Central to technological progress in this area is a fundamental understanding of how these materials behave, which may allow us to stop them degrading or deactivating during operation. A longstanding problem, affecting many applications that use highly dispersed metal nanoparticles, is loss of active surface area in the metal components as a result of “sintering”. This is a particularly pernicious problem in applications in which catalysts have to experience high temperatures—in excess of 800 8C in the case of modern car catalysts. This deleterious process causes the particle size of the metal to increase massively—through either particle diffusion or agglomeration or through “ripening” processes. The result is that a large fraction of the active metal is effectively “hidden away” within the bulk of these larger particles where it cannot be used to affect the desired chemical conversions that occur on the particle surface. This central issue of exhaust catalyst deactivation has long been recognized in the hydrocarbon reforming and emission abatement industries. In the former industry, “oxidative redispersion” has been utilized to reverse the effects of sintering and regenerate spent Pt-based reforming catalysts. However, whereas other noble metal particles such as Pd or Rh can be effectively redispersed by gaseous oxygen at certain temperatures, this method is efficient for Pt catalysts only when Cl is present either in the catalyst formulation or as an adjunct added during the redispersion process: in the absence of Cl, redispersion in Pt/Al2O3 by oxygen is limited both to a narrow temperature window (of around 500 8C) and a low level of redispersion. 6] Further, a continuous oxidative treatment over time is required for this redispersion process. Exhaust gases exiting from gasoline engines change quickly and dramatically during operation. Temperatures can rise transiently to around 1000 8C, and the exhaust gas composition itself fluctuates quickly between oxidative and reductive compositions. Clearly, the conventional approach to redispersion and reactivation is highly unsuitable on many counts for “on-board” redispersion and regeneration of TWCs. Other regeneration phenomena have recently been shown in some related cases. The “intelligent” catalyst system of Daihatsu shows in-built structural reversibility of the noble metal component. In this case, it is the structure of the perovskite support that provides the foundation for this extremely elegant piece of applied catalyst design. The possibility of forming very large particles is intrinsically reduced and, under some circumstances, this technology has been successfully commercialized. However, this approach is very much dependent upon the structure of a particular and low surface area support material and is limited in this sense. [*] Dr. Y. Nagai, K. Dohmae, T. Tanabe, Dr. H. Shinjoh TOYOTA Central R&D Labs., Inc. Nagakute, Aichi 480-1192 (Japan) Fax: (+ 81)561-63-6150 E-mail: e1062@mosk.tytlabs.co.jp

Nanostructured Ceria-Silver Synthesized in a One-Pot Redox Reaction Catalyzes Carbon Oxidation

We introduce a new concept for a nanomaterial in terms of both synthesis and properties. The nanomaterial, aggregates of ceria particles around central silver metal (CeO(2)-Ag), was fabricated by a one-pot selective redox reaction using cerium(III) and silver(I) autocatalyzed by silver metal without the need for surfactants or organic compounds. This unique nanostructure is suitable as a catalyst, in contrast to core-shell materials wherein the shell deactivates the catalyst metal. The material was developed to be intimately related to catalytic carbon oxidation.

Periodic operation effects in propane and propylene oxidation over noble metal catalysts

Abstract It had been observed that under cycling conditions, the catalytic activities of three-way automotive catalysts are superior to those under static conditions, and that catalyst performance depends on the cycling period and feedstream conditions. The oxidation of propylene and propane over platinum, palladium and rhodium catalyst under static and periodic conditions was therefore investigated. The results were as follows; (i) the order of catalytic acitivities was Pd>Pt>Rh for propylene—oxygen and Pt>Rh>Pd for propane-oxygen; (ii) the periodic operation effect is dependent on both catalyst species and reaction temperature; (iii) the optimum period for the maximum conversion decreases with increasing temperature; and (iv) from results of the partial reaction order and evolution pattern analysis, either hydrocarbons or oxygen self-poison the reaction on the catalysts. The order of sensitivity to self-poisoning corresponds to the order of the periodic operation effect.

Effect of lanthanum on the no reduction over palladium catalysts

Abstract A palladium-lanthanum (Pd-La) catalyst was found to be more active for NO reduction than a palladium (Pd) catalyst under the reducing conditions found in engine exhaust gas. Both the Pd-La and Pd catalysts had same activities for the NO reduction with CO. However, in the presence of hydrocarbons, the NO reduction activity of a Pd-La catalyst was much better than that of a Pd catalyst. The NO reduction of the Pd catalyst was significantly inhibited by hydrocarbons. The behavior of the adsorbed hydrocarbons on the both catalysts were studied by means of the transient response method. The hydrocarbon was more strongly adsorbed on the Pd catalyst than on the Pd-La catalyst. Also, the partial oxidation activity of hydrocarbon for the Pd-La catalyst was much better than that for the Pd catalyst. The presence of lanthanum in the Pd-La catalyst perhaps weakens the adsorption strength of hydrocarbons.

Effect of Severe Thermal Aging on Noble Metal Catalysts

Abstract Both sintering and activity behaviours over noble metal catalysts aged in oxidative atmospheres with various O 2 contents at 1100°C (or 1000° C) for 5 h were systematically characterized. With increasing O 2 contents, catalytic activities over aged Pt, Rh, and Pt/Rh catalysts decreased, and, in contrast, those over aged Pd and Pd/Rh catalysts increased. While, an order of sintering for the noble metal particles on aged catalysts agreed closely to that of the each percentage conversions as well as to that of vapour pressures of respective catalyst species, such as noble metals or their oxides. Selectivity profiles of the aged catalysts for converting NO and O 2 in a simulated exhaust gas were characteristic ones. It is confirmed through the above results that the performance of aged catalysts are tightly governed by the properties of noble metals and the selectivity data are also important for exploring the catalytic activities, in particular, over multi-functional catalysts such as automotive exhaust ones.

Periodic Operation Effects on Automotive Noble Metal Catalysts — Reaction Analysis of Binary Gas Systems

Catalytic activities and periodic operation effects in various binary gas systems (CO-O2, NO-CO, NO-H2, C3H6-O2, and C3H8-O2) over Pt, Pd, and Rh/α-Al2O3 were compared. In all reaction systems, periodic operation effects were found to some extent. That is, the conversion improved in the cycling feed compared to the static one. The periodic operation effects occurred most noticeably for catalysts having lower catalytic activity as a result of the difference of adsorption capability between the two reactants.

Dynamic behavior and characterization of automobile catalysts

Abstract Automotive catalyst technology is now faced with very difficult problems. The recent progress of research on the dynamic behavior and characterization of automobile catalysts, and their development to solve these problems are reviewed in this chapter. The oxygen storage and release phenomena under the non-steady atmosphere are investigated in terms of the oxygen storage capacity, the oxygen mobility and the local structure of oxygen storage materials. These parameters are in good correlation with each other. The sintering and re-dispersion phenomena of Platinum Group Metals (PGM) on metal oxides are studied by X-ray absorption analysis. The sintering of Pt is suppressed by making a bond between Pt and surface oxygen of oxides such as CeO 2 under the oxygen rich atmosphere, and sintered Pt particles on CeO 2 are re-dispersed under appropriate conditions. The NO x storage-reduction (NSR) catalyst, which was developed for automotive lean-burn engines, can reduce NO x under the oxygen-rich atmosphere. The NO x reduction phenomena are investigated by four steps. NO is oxidized on Pt under the oxygen-rich atmosphere. NO 2 reacts with basic materials and then is stored in the NSR as nitrate. The stored NO x is released after the decomposition of nitrate under the oxygen deficient atmosphere. The released NO x is reduced into N 2 on PGM by the reaction with a reducing component such as HC, CO and H 2 . The main cause of deterioration for the NSR is sulfur poisoning. The sulfur-poisoning mechanism and the way for an NSR with high tolerance to sulfur poisoning is studied in storage materials, support materials, substrate structures and the arrangement of catalysts.

Real-Time Observation of Platinum Redispersion on Ceria-Based Oxide by In-situ Turbo-XAS in Fluorescence Mode

A real‐time observation of the redispersion behavior of sintered Pt on ceria‐based oxide was made possible by in‐situ time‐resolved Turbo‐XAS in fluorescence mode. 2 wt% Pt/Ce‐Zr‐Y mixed oxide samples were prepared, and then treated under an aging condition. The average Pt particle size measured by CO absorption method after aging was 7 nm. Redispersion treatments of the previously aged catalyst were carried out at 600°C within an in‐situ XAS cell in a cyclical flow of reducing/oxidizing gases. Pt L3‐edge XANES spectra were collected every 1.1 second under in‐situ conditions. From a change in the XANES spectra, we observed that the Pt particle size of the aged catalyst decreased from 7 to 5 nm after 60 seconds and then to 3 nm after 1000 seconds.