Effect of Ce on 5 wt% Ni/ZSM-5 catalysts in the CO2 reforming of CH4 reaction

The aim of this study is to investigate the promotional effect of Ce on Ni/ZSM-5 catalysts in the CO2 reforming of CH4 reaction. The evaluation of the catalytic performances of the composite catalysts was conducted in a fixed-bed reactor at atmospheric pressure. The influencing factors, including temperature, Ni and Ce loadings, molar feed ratio of CO2/CH4, and time-on-stream (TOS), were investigated. The characteristics of the catalysts were checked with Brunauer-Emmett-Teller (BET) analysis, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). The reduction and the basic properties of the composite catalysts were elucidated by temperature-programmed reduction by H-2 (H-2-TPR) and temperature-programmed desorption of CO2 (CO2-TPD), respectively. The reactivity of deposited carbon was studied by sequential temperature-programmed surface reaction of CH4 (CH4-TPSR) and temperature-programmed oxidation using CO2 and O-2 (CO2-TPO and O-2-TPO). Results indicate that higher CH4 conversion, H-2 selectivity, and desired H-2/CO ratio for 5 wt% Ni & 5 wt% Ce/ZSM-5 could be achieved with CO2/CH4 feed ratio close to unity over the temperature range of 500-900 degrees C. Moreover, the addition of Ce could not only promote CH4 decomposition for H-2 production but also the gasification of deposited carbon with CO2. The dispersion of Ni particles could be improved with Ce presence as well. A partial reduction of CeO2 to CeAlO3 was observed from XPS spectra over 5 wt% Ni & 5 wt% Ce/ZSM-5 after H-2 reduction and 24 h CO2 CH4 reforming reaction. Benefiting from the introduction of 5 wt% Ce, the calculated apparent activation energies of CH4 and CO2 over the temperature range of 700-900 degrees C could be reduced by 30% and 40%, respectively. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.