Role of oxygen vacancies in dendritic fibrous M/KCC-1 (M = Ru, Pd, Rh) catalysts for methane partial oxidation to H2-rich syngas production

Abstract

The fibrous M/KCC-1 (M = Ru, Pd, Rh) catalysts prepared by microwave-assisted hydrothermal approach were investigated for methane partial oxidation (MPO) reaction at stoichiometric CH4/O2 feed ratio and temperature of 500–800 °C. A drop in BET surface area with metal oxide addition suggesting the successful embedment of metal oxides on KCC-1. Low-angle XRD, FTIR and TEM analyses confirmed the formation of bicontinuous concentric lamellar morphologic structure, typical fingerprint of fibrous KCC-1. The H2-TPR and ESR studies revealed that oxygen vacancy (OV) of KCC-1 not only beneficial for the metal-support interactions of catalysts but also strongly and dissociately bind with O2, CO2 and H2O promoting the syngas formation rate. The post-reaction Raman spectroscopy measurement corroborated the M/KCC-1 catalysts hindered the graphitic carbon formation during reaction. The Rh/KCC-1 appeared to be the optimum catalyst as it exhibited the TOF of both CH4 consumption and H2 formation about 2-fold higher to other catalysts meanwhile achieving H2/CO ratio about 2.16 that applicable for industrial applications. Based on the experimental MPO evaluation, post-reaction Raman spectroscopy and the in-situ ESR studies, the synergistic effects of metals and OV from fibrous KCC-1, where metal dissociates CH bonds in CH4 molecules whilst OV generates activated O2− species from oxidants at the OV sites, are determined as the key factors for the enhancement in MPO activity.