Correlating NEXAFS characterization of Co-W and Ni-W bimetallic carbide catalysts with reactivity for dry reforming of methane

摘要

The effect of temperature on the structure and performance of Co-W-C and Ni-W-C catalysts for dry reforming of methane(DRM)has been investigated using both reactors and near-edge X-ray absorption fine structure(NEXAFS)spectroscopy.For Co-W-C,the DRM reactivity is greatly improved after being exposed to methane at 850 °C.For Ni-W-C,however,the catalytic performance before such exposure is good,although no obvious difference has been found in the catalytic performance before and after exposure to methane at 850 °C In this work,NEXAFS has been applied to characterize the fresh and spent catalysts,both before and after exposure to the reactants at 850 °C,for both Co-W-C and Ni-W-C.Three NEXAFS regions have been investigated for each catalyst:the carbon K-edge,the oxygen K-edge and the L-edge of either cobalt or nickel.NEXAFS results provide insights into the possible origins for the different performance of those two different carbides.To exhibit reasonable reactivity for DRM,Ni-W oxide and Co-W oxide are required to be reduced,and the active stable catalysts must contain large amounts of carbon so that WC and either Ni or Co are seen in the bulk.NEXAFS results indicate that Ni-W-C can be reduced to a greater extent and at a lower temperature than Co-W-C.In addition,NEXAFS measurements reveal the formation of graphitic carbon at or near the surface region.This species can play a critical role in the reactivity and stability of the catalysts for DRM.