Koji Yokota

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.

Research on new DeNOx catalysts for automotive engines

Abstract The performance and durability of Cu-ZSM-5 catalysts for selective reduction of NOx in an oxidizing atmosphere were studied. These catalysts exhibited substantial NOx conversion performance in a leanburn engine exhaust and the simulated gas. However, the temperature dependence, SV performance, and thermal stability must still be improved.

Catalytic removal of nitric oxide with hydrogen and carbon monoxide in the presence of excess oxygen

Catalytic NOx removal with H2 in the presence of an excess of oxygen was studied. A Pt/zeolite catalyst has a high NOx conversion efficiency, but has the disadvantages of being strongly poisoned by CO and HCs such as C3H6 and the formation of N2O as a byproduct from NOx. By reducing the oxidation efficiency of Pt, we have developed an improved catalyst, Pt-Mo-NaSiO2, which has a higher temperature range of NOx conversion and a lower N2O byproduct formation, than conventional Pt catalysts. This idea was supported by IR and XPS data of the catalyst.

Nitric oxide reduction performance of automotive palladium catalysts

Reduction of nitric oxide over palladium catalysts under reducing conditions was examined by using cycled feeds and steady non-cycled feeds. The effects of lanthanum(III) oxide on the catalytic properties of α-alumina-supported palladium for the reduction of nitric oxide were studied by X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR) and chemisorption of propene. The reduction of nitric oxide on palladium catalysts is significantly inhibited by hydrocarbon. However, the reduction activity is improved by both the periodic operation effect and the addition lanthana to the catalyst. The mechanism of the periodic operation effect is interpreted in terms of the strong adsorption of hydrocarbons. The addition of lanthana to the catalyst substantially moderated this hydrocarbon poisoning. The conversion of nitric oxide on the Pd/La2O3 catalyst with cycled feeds was similar to that on a rhodium catalyst. The XPS, TPR and hydrocarbon chemisorption studies showed that the presence of lanthana provided palladium oxide in a hardly-reduced state and suppressed the chemisorption of hydrocarbons on the palladium oxide.

Effect of the addition of Mo and Na to Pt catalysts on the selective reduction of NO

The selective reduction of NOx by reductants such as C3H6 and CO in oxidizing feedstreams simulated exhaust from automobile engine and three-way behavior around the stoichiometric point have been investigated on trimetallic PtMoNa/SiO2 catalysts, over a wide range of temperatures compared with bimetallic PtMo/SiO2 catalyst and monometallic Pt/SiO2 catalyst. The simultaneous addition of Mo and Na to Pt catalysts has been found to improve the following reaction characteristics on selective reduction of NOx and three-way activity of conventional Pt catalyst. The temperature window on selective reduction of NOx on trimetallic PtMoNa/SiO2 catalysts was found to be wider and to shift at higher temperature than that on bimetallic PtMo/SiO2 and monometallic Pt/SiO2 catalysts under lean static conditions. The redox ratio window, in which three-way activity occurred on trimetallic PtMoNa/SiO2 catalysts, was also found to be wider than that on bimetallic PtMo/SiO2 catalysts and monometallic Pt/SiO2 around stoichiometric point. On the other hand, XPS, IR and CO adsorption data indicated that the oxidation of Pt on PtMoNa/SiO2 catalysts was depressed by the added Mo and Na even under excess oxygen conditions, so that the reaction characteristics of trimetallic PtMoNa/SiO2 catalysts was improved.

Synthesis of Novel Structured TiO2 with Mesopores by Anodic Oxidation

In this study, a simple anodic oxidation process resulted in the successful synthesis of novel N-ion-doped TiO(2) with one-dimensionally aligned and large-sized mesopores. TiO(2) obtained by this anodic oxidation process possessed the high values of specific surface area and a large amount of one-dimensional mesopores with 30-50 nm diameter. Furthermore, X-ray photoelectron spectroscopy and UV-vis results suggested the possibility that these TiO(2) products were composed of a N-ion-doped powder. Thus, novel structured TiO(2) with large-sized mesopores was simply synthesized by an anodic oxidation of Ti metal in a nitric acid solution. These uniquely nanostructured mesoporous TiO(2) products will expand possibilities for applying mesoporous TiO(2) in new fields.

Application of numerical modeling of selective NOx reduction by hydrocarbon under diesel transient conditions in consideration of hydrocarbon adsorption and desorption process

Abstract A model of NO x selective reduction by hydrocarbon (HC) was developed, which takes into account the adsorption and desorption of HC. The model was applied for predicting the performance of a De–NO x catalytic reactor, working under transient conditions such as a legislative driving cycle. Diesel fuel was used as a supplemental reductant. The behavior of HC and NO x reactions and HC adsorption and desorption has been simulated successfully by our numerical approach under the transient conditions of the simulated Japanese 10–15 driving cycle. Our model is expected to optimize the design of selective diesel NO x reduction systems using a diesel fuel as a supplemental reductant.

NOx Reduction Behavior on Catalysts With Non-Thermal Plasma in Simulated Oxidizing Exhaust Gas

NOx reduction activity in an oxidizing exhaust gas was significantly improved by discharging non-thermal plasma and catalysts (plasma assisted catalysis). We investigated effective catalyst for plasma assisted catalysis in view of hydrocarbon-selective catalytic reduction(HC-SCR). Plasma assist was effective for γ-alumina and alkali or alkaline earth metals loaded zeolite and γ-alumina showed the highest NOx conversion among these catalysts. On the other hand, Plasma assist was not effective for Cu-ZSM-5 and Pt loaded catalyst. The NOx conversion for the plasma assisted γ-alumina decreased by formation of a deposit on the catalyst below 400°C. It is shown that indium loading on γ-alumina improved the NOx reduction activity and suppressed the degradation of the NOx reduction activity at 300°C with plasma assist.