Molecular-size selective H-β zeolite-encapsulated Ce-Zr/Ni-Mg catalysts for steam reforming

Abstract

A composite H-β zeolite membrane encapsulated 1.6%Ni/1.2%Mg/Ce0.6Zr0.4O2 steam reforming catalyst was prepared by a physical coating method using silica sol as a binder between the H-β zeolite shell and steam reforming catalyst core. Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) analyses indicated that H-β zeolite was coated successfully on the core reforming catalyst and the shell thickness was at least 100nm. The pore size of H-β zeolite shell was between 0.43 and 0.57nm, as measured by the HK method. Steam reforming of CH4 and C7H8 (as a tar model) were conducted with the composite H-β zeolite coated reforming catalyst, the two components individually, and physical mixtures of the two components as a function of temperature (780–840°C). CH4 conversion was enhanced by a factor of 2–3 (depending on temperature) for the composite catalyst as compared to the core reforming catalyst individually even though the zeolite did not have any activity alone. Possible reasons for the enhanced CH4 conversion include confined reaction effects (increase residence time within pores) of the catalyst containing the zeolite coating and/or Al3+ promotion of the active sites. Alternatively, due to molecular-size selectivity, the composite H-β zeolite coated reforming catalyst demonstrated a decrease in C7H8 conversion when compared to the uncoated reforming catalyst. The results validate the use of size selective catalysts to control molecular traffic and enhance the reforming reactant selectivity.