Hirofumi Ohtsuka

Study on catalysts of selective reduction of NOx using hydrocarbons for natural gas engines

Abstract The effect of water on selective catalytic reduction of NOx using hydrocarbons (HC-SCR) on Cu- and Co-ZSM-5 was investigated. Co-ZSM-5 showed a higher HC-SCR activity and selectivity using C3H8 than Cu-ZSM-5 at temperatures above 400°C in the presence of water. On Co-ZSM-5, C3H8 oxidation by O2 was slow and severely inhibited by water due to Co-ZSM-5s poor ability to adsorb O2 dissociatively, and the capacity for NO adsorption was large enough to supplement the poor NO oxidation activity. These adsorption properties are therefore considered to contribute to the high activity and selectivity observed on Co-ZSM-5. Among the Co-based catalysts, Co-Beta showed higher HC-SCR activity and was more durable than Co-ZSM-5.

The selective catalytic reduction of nitrogen oxides by methane on noble metal-loaded sulfated zirconia

Abstract The selective catalytic reduction of NO x by methane on noble metal-loaded sulfated zirconia (SZ) catalysts was studied. Ru, Rh, Pd, Ag, Ir, Pt, and Au-loaded sulfated zirconia catalysts were compared with the intact sulfated zirconia. For the NO–CH 4 –O 2 reaction, Ru, Rh, Pd, Ir, and Pt showed promotion effect on NO x reduction, while for the NO 2 –CH 4 –O 2 reaction, only Rh and Pd showed promotion effect. Over intact and Rh, Pd, Ag, and Au-loaded sulfated zirconia, NO x conversion in NO 2 –CH 4 –O 2 reaction was significantly higher than that in NO–CH 4 –O 2 reaction, while clear difference was not observed over Ru, Ir, and Pt-loaded sulfated zirconia. Comparison of [NO 2 ]/([NO]+[NO 2 ]) in the effluent gases in NO–O 2 and NO 2 –O 2 reactions showed that Ru, Ir, and Pt has high activity for NO oxidation under the reaction conditions. These facts suggest that effects of these metals toward NO x reduction by methane can be categorized into the following three groups: (i) low activity for NO oxidation to NO 2 , and high activity for NO 2 reduction to N 2 (Pd, Rh); (ii) high activity for NO oxidation to NO 2 , and low activity for NO 2 reduction to N 2 (Ru, Ir, Pt); (iii) low activity for both reactions (Ag, Au). To confirm these suggestions, combination of these metals were investigated on binary or physically-mixed catalysts. The combination of Pd or Rh with Pt or Ru gave high activity for the selective reduction of NO x by methane.

Selective catalytic reduction of NOx by propane on Co-loaded zeolites

Abstract To ascertain the reason of the superiority of cobalt ion-exchanged BEA (Co-BEA) in the selective catalytic reduction of NOx by hydrocarbons (HC-SCR) using propane, the dependence of the catalytic performance of Co-loaded zeolite (Co-zeolite) in the HC-SCR reaction using propane on zeolite species was examined using IR and catalytic activity tests. The order of catalysts according to their initial activity in the absence of sulfur dioxide (SO2) was BEA>MFI>MOR≫FER≫FAU. In the presence of SO2, only Co-BEA exhibited stable activity, whereas the activities of Co-MOR and Co-MFI rapidly decreased, although no tendency to clogging of micropores nor decrease in dispersion of Co were observed. On the other hand, there was no obvious difference in the IR spectra of adsorbed NOx species between Co-BEA and Co-MFI. Since in the presence of SO2 the crystal size effect on catalytic performance was observed even with Co-BEA, intracrystalline diffusion is considered to control the overall reaction rate under such conditions. Thus, it is concluded that the micropore structure of BEA, advantageous to intracrystalline diffusion, is considered to be one of the reasons for the superiority of Co-BEA in the HC-SCR reaction using propane.

Roles of palladium and platinum in the selective catalytic reduction of nitrogen oxides by methane on palladium–platinum-loaded sulfated zirconia

Abstract The selective reduction of nitrogen oxides by methane on Pd–Pt/sulfated zirconia (SZ) was investigated. The activity of Pd–Pt/SZ was noticeably higher than that of either Pd/SZ or Pt/SZ. The cooperative effect of Pd and Pt, Pd acting as sites for the reaction of NO 2 with methane and Pt catalyzing NO oxidation to NO 2 , was suggested. The addition of Pt to Pd/MOR showed a similar improvement, but the effect was much more prominent for Pd/SZ.

Influence of Si/Al ratio on the activity and durability of Pd-ZSM-5 catalysts for nitrogen oxide reduction by methane

Abstract The selective reduction of NO by methane on Pd-ZSM-5 catalysts with different Si/Al and Pd loadings was examined in the presence and absence of water vapor. At low Si/Al, NO reduction activity was high and stable, while at higher Si/Al, activity was lower and deactivation was significant. The deactivated samples showed PdO bands in the Raman spectra, which indicated that dispersed Pd cations play a key role in NO reduction. The influence of Si/Al on the stability of dispersed Pd cations suggested the importance of Al site pairs for the stable dispersion of Pd cations.

Advanced catalyst for NOx reduction using hydrocarbons from lean-burning gas engine

Abstract For a catalytic NOx reduction process for natural gas-fueled lean-burning engines, selective catalytic reduction of NOx by propane was studied on metal ion-exchanged zeolite catalysts. A comparative study on Cu- and Co-ZSM-5 showed the superiority of Co-based catalysts for C3H8-SCR in the presence of water vapor. Investigation into various Co-zeolite catalysts showed that Co-Beta has superior activity and selectivity for NOx reduction. Durability tests of the catalyst in a model gas simulating gas engine exhaust showed that the activity of Co-Beta is sufficient even in the presence of SOx after 5000 h of operation, whereas Co-Mordenite and Co-ZSM-5 lost their activity in several hundred hours of operation.

Theoretical study of NO decomposition on Cu-ZSM-5 catalyst models

Abstract The decomposition mechanism of NO on Cu-ZSM-5 catalyst models was investigated using ab initio molecular orbital calculations with Huzinagas MIDI-P basis set [see S. Huzinaga, Gaussian Basic Sets for Molecular Calculations, Elsevier, Amsterdam, 1984]. Two reaction routes were assumed for each model and the geometry of all molecules was optimized.