Masayoshi Hayashi

Reduction of nitric oxide with methane on Pd/Co/H-ZSM-5 catalysts: cooperative effects of Pd and Co

Reduction of low concentration of nitric oxide (NO) with methane as a reductant under wet conditions has been investigated using Pd/Co/H-ZSM-5 catalysts and the effects brought about by coexistence of Pd and Co are discussed. The role of Co is attributed to the acceleration of oxidation of NO to NO2, which is the necessary species for reduction of NO with CH4 on Pd sites. A Pd/H-ZSM-5 loading of 1 wt% Co shows a maximum activity for NO reduction as well as for NO oxidation. Excess loading of Co led to a decrease in activity for NO reduction. An XPS study shows that Pd and Co are well dispersed inside the zeolite when the concentrations of Pd and Co are less than 1 wt%. Loading of excess Co, however, causes aggregation of Pd on the surface of ZSM-5.

Role of zeolite structure on reduction of NOx with methane over In- and Pd-based catalysts

Abstract Catalytic performances of ZSM-5 based catalysts containing indium or palladium were examined for NO reduction with CH 4 and NO x chemisorption. The amounts of NO x chemisorbed on In/H-ZSM-5 were well proportional to the catalytic activities for NO x reduction. Pd/H-ZSM-5, on the other hand, hardly chemisorbed NO 2 , while the catalytic activity for NO 2 reduction with CH 4 is very high. Furthermore, Pd loaded on SiO 2 showed comparably high catalytic activity for NO 2 reduction with CH 4 at 400°C in the absence of oxygen as Pd/H-ZSM-5. CH 4 combustion during NO x reduction with CH 4 in the presence of oxygen significantly occurred over PdO on SiO 2 , while less over Pd/H-ZSM-5. The role of zeolite might be slightly different between In/H-ZSM-5 and Pd/H-ZSM-5: the zeolitic porous structure is needed for In/H-ZSM-5 in order to concentrate NO 2 adspecies on InO + sites, which is important for NO reduction with CH 4 on In/H-ZSM-5 based catalysts, while the ion-exchangeable ability of zeolite is needed for Pd/H-ZSM-5 in order to make Pd 2+ located in a highly dispersed state, on which NO is strongly chemisorbed.

Intrapore catalysis in reduction of nitric oxide with methane

Abstract Catalytic activities of In/H-ZSM-5 and Ir/In/H-ZSM-5 for selective reduction of NO with methane were investigated with in situ measurements of NOx adspecies by FT-IR method under reaction conditions. The reaction proceeded in the following two stages: NO was oxidized to NO2 on Ir and NO2 was reduced to N2 by CH4 on InO+. Studies on chemisorption of NOx indicated that NO2 chemisorbed on InO+ sites is important for this reaction. Two intense NO2 adspecies were observed at 1610 and 1575xa0cm−1 under the reaction conditions: one of these species at 1610xa0cm−1 is reactive with CH4. These adspecies are assigned to nitro or nitrite species. Nitrates adsorbed on InO+ (1450xa0cm−1) and zeolite acid sites (1635xa0cm−1) cannot consume CH4. Chemisorption of NO2 on InO+ sites were shown by IR measurements to be a slow step on In/H-ZSM-5, while Ir accelerated the chemisorption of NO2 on InO+ not only on the outer surface but also in the pores of ZSM-5. It is concluded that bifunctional catalysis in identical zeolite pores, named “intrapore catalysis”, brings forth high catalytic activity and selectivity.

Determination of active palladium species in ZSM-5 zeolite for selective reduction of nitric oxide with methane

Abstract The active site in ZSM-5 zeolite-supported palladium, which shows the catalytic activity for NO reduction with methane as a reducing agent, has been investigated qualitatively and quantitatively by means of NO chemisorption and NaCl titration, comparing with PdO supported on silica. Palladium species in 0.4xa0wt.% Pd loaded H-ZSM-5 can adsorb NO equimolarly after calcination at 773xa0K, and almost all the NO was desorbed at around 673xa0K, while the palladium species on PdO/SiO2 hardly adsorbed NO. The palladium species in Pd(0.4)/H-ZSM-5 are ion-exchangeable with Na+ in NaCl solution, indicating that they exist in a cationic state of an isolated Pd2+. This method for quantitative analysis of the isolated Pd2+ cations is named as ‘NaCl titration’. The amount of the isolated Pd2+ cationic species increased with increasing palladium content on Pd/H-ZSM-5, and PdO co-existed above 1xa0wt.%. The amount of the isolated Pd2+ cation was unchanged after the reaction of NO2–CH4, NO2–CH4–O2, or CH4–O2 at 673xa0K, while the adsorbed amount of NO per the Pd2+ as determined by NO-TPD decreased after the NO2–CH4–O2 reaction. It was found by NaCl titration that the catalytic activity of Pd/H-ZSM-5 for NO2–CH4–O2 reaction increased with increasing amount of the isolated Pd2+ cationic species up to 0.7xa0wt.%, while the increase in the amount of PdO led to decrease in selectivity towards NO2 reduction. The palladium species that are active and selective for NO reduction with CH4 will be proposed.

Remarkable enhancement in durability of Pd/H-ZSM-5 zeolite catalysts for CH4-SCR

Abstract Effect of second components on the catalytic performance of Pd/H-ZSM-5 zeolite (Pd: 0.4xa0wt.%) was evaluated by a durability test of NO reduction with CH4 at a relatively high temperature of 500°C in the presence of water vapor for a prolonged period. The Pd/H-ZSM-5 showed high stable activity for this reaction without H2O in the reactant feed, while immediate and irreversible deactivation was observed in the presence of H2O, resulting in no activity after 7xa0h. The second components such as Co, Rh, Ag, Ce, and Fe introduced individually to the Pd/H-ZSM-5 enhanced the durability, and in particular the addition of 3.3xa0wt.% Co led to a stable NO conversion for more than 40xa0h in the presence of H2O.

Inefficiency and Self-Determination: Simulation-based evidence from Meiji Japan

We consider a model in which the arrangement of political boundaries involves a tradeoff between efficiencies of scale and geographic heterogeneity. If jurisdiction formation is decentralized, the model corresponds to a fractional hedonic game. We show how mixed integer programming can be used to calculate core partitions for fractional hedonic games via a sequence of myopic deviations. Using historical data from Japan regarding a set of centralized boundary changes, we estimate parameters using moment inequalities and find that core partitions always exist. In a counterfactual world in which there are no between-village income differences, these core partitions are extremely close to the partition that would be chosen by a utilitarian central planner. When actual cross-village income differences are used, however, sorting on income results in mergers that are both smaller and geographically bizarre.