Solid P-W Keggin Heteropoly Compounds as Effective Catalysts for the Sorption-decomposition of NO_x

摘要

Several new heteropoly compounds catalysts with pronounced activities in NO_x conversion via adsorption-decomposition process in a fixed-bed reactor were evaluated concerning the principal internal and external factors having marked effects on the process of adsorption. Results showed that substitution of H~+ in HPW (H_3PW_(12)O_(40).6H_2O) by NH_4~+ results in marked enhancement of the catalyst activity, however, substitution of coordination atom W in the [PW_(12)O_(40)]~(3-) anion by one or more Mo atoms tends to lower the catalyst activity and such tendency deepens with the increase in the Mo atom numbers introduced. It is for the first time that the nano-effect was observed with nano (NH_4)_3PW_(12)O_(40) catalyst, in which a 1.6% to 10.6% enhancement in NO_x adsorption efficiency was obtained in comparison with the same catalyst in normal particle size. By IR analysis, NO was found to be adsorbed via interaction with the proton of HPW structure. With the aid of GC-MS analysis, the process effectiveness for NO_x decomposition into N_2 was confirmed.