Ag/La0.6Sr0.4MnO3 catalysts for deep oxidation of CH4 and CH3OH at low concentrations

Abstract

Ag-modified La(0.6)SrO(4)rMnO(3) catalysts were prepared and their catalytic performance for deep oxidation of CH4 and CH3OH at low concentrations were investigated. The results showed that the La0.6Sr0.4MnO3 host catalyst with the perovskite-type nano-crystallite structure displayed considerably high catalytic activity for deep oxidation of CH4 and CH3H at low concentrations. Ag-modification to the La0. 6Sr0.4MnO3 host catalyst resulted in significant enhancement of the catalyst activity, making the T-95 (the reaction temperature needed for conversion of 95% of CH4 or CH3OH) lowered down to 735K (for CH4) and 421K (for CH3OH) from 813 and 465 K over the Ag-free system under the reaction conditions: 0.1MPa, CH4/O-2/N-2 =2/12/86 (molar ratio), GHSV =45000 h(-1) and CH3OH/O-2/N-2 = 0.2/1.0/98.8 (molar ratio), GHSV = 58000 h(-1), respectively. The carbon-containing product was almost CO2 and the contents of HCHO and CO in the reaction-exit gas were both under GC-detectable limit in both cases. The results of spectroscopic characterization indicated that modification by proper amount of Ag-dopant did not change the perovskite structure of the La0.6Sr0.4MnO3 host catalyst as a whole. Interaction of Ag-dopant with the surface of the host catalyst, La0.6Sr0.4MnO3, was in favor of high dispersion of the Ag component at the catalyst surface and led to the oxidation of part of the Mn3+ species to Mn4+, resulting in an increase of amounts of the reducible Mn+ species and a decrease of their reduction temperature. On the other hand, this interaction led also to enhancement of adsorption ability of the catalyst toward O-2 at relatively low temperature. High activity of the Ag-modified La0.6Sr0.4MnO3 catalyst for CH4 and CH3OH complete oxidation was closely related to high redox-activity of the catalyst and its prominent adsorption-activation ability to O-2 at relatively low temperatures.