Takeshi Tabata

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.

A study on selective reduction of NOx by propane on Co-Beta

Selective catalytic reduction of NOx by propane was investigated on Co-Beta to clarify the loaded states of cobalt and their role in catalytic activity. At low ion exchange levels less than 100%, loaded cobalt is highly dispersed, which has a high selectivity for NOx reduction. At ion exchange levels much higher than 100%, Co3O4 appears as identified by Raman spectroscopy, and it contributes to propane oxidation by oxygen and lowers the selectivity especially at high temperatures.

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.

Relationship between methane adsorption and selective catalytic reduction of nitrogen oxide by methane on gallium and indium ion-exchanged ZSM-5

Abstract Methane adsorption on Ga ion-exchanged ZSM-5 (Ga-ZSM-5) and In ion-exchanged ZSM-5 (In-ZSM-5) was investigated by temperature-programmed desorption in ultra high vacuum (UHV-TPD) to clarify the difference in the influence of water vapor on the selective catalytic reduction of NOx by methane. Methane was adsorbed on Ga-ZSM-5 and In-ZSM-5, and the adsorption heats of methane were estimated to be − 98 kJ/mol and − 132 kJ/mol for Ga-ZSM-5 and In-ZSM-5, respectively. The amount of methane adsorbed on Ga-ZSM-5 decreased considerably after the preadsorption of water, while little decrease was observed on In-ZSM-5. These results suggest that one of the reasons that the suppression of HC-SCR activity by water vapor is less severe on In-ZSM-5 than on Ga-ZSM-5, may be that competitive water adsorption is much more inhibiting to methane adsorption on Ga-ZSM-5 than it is on In-ZSM-5.

Study on patent literature of catalysts for a new NOx removal process

Abstract Catalysts for selective catalytic reduction of NO x by hydrocarbons (HC-SCR) have been reviewed from the patent literature. The problems to be solved for practical applications of the HC-SCR process and the method to solve them found in the patent literature are discussed. 198 references cited.

Adsorption properties of oxygen and methane on Ga-ZSM-5; the origin of the selectivity of NOx reduction using methane

The adsorption properties of oxygen and methane on Ga-ZSM-5 and Cu-ZSM-5 catalysts were examined by a TPD method to clarify the extraordinary selectivity of HC-SCR using methane on Ga-ZSM-5. It was observed that Ga-ZSM-5 did not adsorb oxygen but adsorbed methane dissociatively, while on Cu-ZSM-5 oxygen was dissociatively adsorbed and reacted with adsorbed ethylene.

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.

Deactivation by poisoning of three-way catalyst for natural gas-fuelled engines

Abstract A Pt Rh three-way catalyst used in natural gas-fuelled engine systems for 21 000 h was investigated employing chemical analyses, EPMA, surface area measurements, catalytic activity tests, as well as tests using model poisoned catalysts. Specific deactivation characteristics, such as the decrease in the selectivity of nitric oxide reduction, which cannot be reproduced by heat treatment nor explained by physical poisoning such as blockage of micropores, were observed on the used catalyst. P, Ca, Zn, Fe and trace amounts of Pb were detected as elements which increased in the used catalyst, and Zn, Fe and Pb were observed in the wash coat layer of the catalyst, while P and Ca existed on the surface of the wash coat. Of the model Zn-, Fe-, and Pb-poisoned catalysts prepared by dipping heat-treated catalysts into an aqueous solution of metal salt, only model Pb-poisoned catalyst showed a considerable decrease in the selectivity of nitric oxide reduction. Further, all the characteristics of the deactivation on the used catalyst were qualitatively reproduced by the measurement of the activity of the model Pb-poisoned catalyst at high space velocity. From these results, it is concluded that the selectivity of nitric oxide reduction is decreased by chemical poisoning due to trace amounts of Pb on the used catalyst, and that the absolute rates of nitric oxide reduction as well as the other reactions are additionally reduced by an decrease in the effective surface area of the catalyst due to the covering the surface of the wash coat layer by accumulated compounds consisting of P, Ca, Zn and Fe. Therefore, trace amounts of Pb as well as ash derived from oil additives become an issue even in natural gasfuelled engine systems when a Pt Rh three-way catalyst is used for more than several ten thousand hours.

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.

Deterioration mechanism of Cu÷ZSM-5 as a catalyst of selective reduction of NOx by hydrocarbons from the exhaust of stationary natural gas-fuelled engine

The durability of Cu-ZSM5 as a catalyst of selective reduction of NOx by hydrocarbons from the exhaust of stationary natural gas engines was examined. Even 100% ion-exchanged Cu-ZSM5 also showed a deterioration tendency at 773 K under wet conditions simulating lean-burning gas engine exhaust. From the results of the durability test of SOx concentration dependence, SOx was not considered to be the cause of the deterioration. The deteriorated Cu-ZSM5 was characterized by the measurements of BET surface area, CO adsorption, XRD, NMR, EXAFS, XANES as well as carbon analysis. Neither dealumination, carbon deposition nor loss of micropore was observed in the deteriorated sample, and CuO cluster formation and resultant loss of surface area of copper were clearly shown, therefore, the CuO cluster formation is considered to lead to deterioration of the activity of Cu-ZSM5.