Hirohumi Shinjoh

Effect of periodic operation over Pt catalysts in simulated oxidizing exhaust gas

Abstract The effect of periodic operation over Pt and Pt/Ba catalysts supported on γ-alumina under oxidizing conditions was investigated using simulated automotive exhaust gas from lean-burn combustion. The conversion of hydrocarbons and NOx was measured in cycled feedstream and steady feedstream under oxidizing conditions. The activities of the catalysts were improved in the cycled feedstream between oxidizing and reducing atmospheres under average oxidizing conditions. In particular, the NOx reduction on the Pt/Bt catalyst was higher than that on the Pt catalyst in the cycling operation. From the mass spectral analysis in streams of NO O2 C3H6 and NO O2 H2 (balance He) gas, it was found that NO was oxidized and stored on the Pt/Ba catalyst under oxidizing conditions, and that the stored NOx on the catalyst was subsequently reduced to N2 under reducing conditions.

Effect of Alkaline Addition on Hydrocarbon Oxidation Activities of Palladium Three-way Catalyst

The effect of alkaline addition on hydrocarbon oxidation activities of Pd catalyst supported on γ-alumina was investigated using simulated automotive exhaust gases. The hydrocarbon oxidation activity of the Pd catalyst with alkaline earth metal such as Mg, Ca, Sr, and Ba is higher than that with nothing added. On the other hand, the activity of the Pd catalyst with alkali metal such as K and Cs is lower than that with nothing added. From the results of the partial reaction orders in C3H6 oxidation, TPR, and XPS, it was concluded that the alkaline addition to the Pd catalyst increased electron density of Pd on the catalyst and weakened the adsorption strength of Pd with hydrocarbons. The addition of alkaline earth metal suppressed the hydrocarbon chemisorption on the Pd catalyst and therefore allowed the catalytic reaction to proceed smoothly. On the other hand, the addition of alkali metal caused such a strong oxygen adsorption on Pd that rejected the hydrocarbon adsorption and suppressed the reaction.

Study of the oxygen diffusion on three-way catalysts: a kinetic model

A computer model was developed to take into account all the phenomena that can occur in 18O/16O isotopic exchange over Pt/CeZrOx materials: adsorption/desorption on the metal, surface and bulk O diffusion. Discriminating each step of the exchange process is no longer necessary: kinetic parameters and O diffusivity can be calculated in a single experiment.

Comparative NOx reduction behavior of Pt, Pd, and Rh supported catalysts in simulated exhaust gases as a function of oxygen concentration

NOx reduction activity on Pt and Pd catalysts had a maximum for S value as stoichiometry number at a fixed temperature, and the S value at the maximum NOx conversion increased with decreasing temperature. NOx conversion on Rh catalyst increased with decreasing S value, but independent of temperature. As for the effect of HC on NOx reduction behavior, it was concluded that, for Pt and Pd catalysts, HC adsorbs strongly on the catalysts surface to cause the self-inhibition. Increasing O2 concentration lead to oxidation of HC, but decreased the value of NO/O2 ratio. The balance point of the two factors generated a maximum NOx conversion. For Rh catalyst, the strongly adsorbed oxygen is more reactive with decreasing S value, and thus NOx conversion is increased.

Effect of Ba Addition on Catalytic Activity of Pt and Rh Catalysts Loaded on γ-Alumina

The catalytic activity of Pt catalyst loaded on γ-alumina was improved by Ba addition in simulated automotive exhaust gases. On the other hand, the result of Rh catalyst was the opposite. From the results of the partial reaction orders in C3H6–O2 reaction and TPR, it was concluded that the Ba addition to Pt catalyst suppressed the hydrocarbon chemisorption on the Pt catalyst and therefore allowed the catalytic reaction to proceed smoothly. On the other hand, Ba addition to Rh catalyst caused such a strong oxygen adsorption on Rh that rejected the hydrocarbon adsorption and suppressed the reaction.

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.