Promoting effect of alkali metal cations on the catalytic performance of Pd/H-ZSM-5 in the combustion of lean methane

A series of alkali metal hydroxides (MeOH, Me = Li, Na, K and Cs) were used as the precipitant to prepare the Pd/H-ZSM-5-Me catalysts by deposition-precipitation; the effect of alkali metal cations on the catalytic performance of Pd/H-ZSM-5 in the combustion of lean methane was then investigated. The results indicate that in comparison with ammonia, alkali metal hydroxides as the precipitant can greatly enhance the catalytic performance of Pd/H-ZSM-5 in lean methane combustion and the extent of promoting effect follows the order of CsOH > KOH > NaOH > LiOH> > NH4OH. The alkali metal cations can enhance the dispersion of Pd on the H-ZSM-5 support and effectively reduce the size of Pd particles; in addition, the alkali metal cations may serve as an electron-donating component and endow the Pd species with a unique electronic characteristic, which can promote the activation of C-H bond of methane molecules.