Understanding the Impact of Hydrogen Activation by SrCe0.8Zr0.2O3-delta Perovskite Membrane Material on Direct Non-Oxidative Methane Conversion

Direct non-oxidative methane conversion (DNMC) converts methane (CH4) in one step to olefin and aromatic hydrocarbons and hydrogen (H-2) co-product. Membrane reactors comprising methane activation catalysts and H-2-permeable membranes can enhance methane conversion by in situ H-2 removal via Le Chatelier's principle. Rigorous description of H-2 kinetic effects on both membrane and catalyst materials in the membrane reactor, however, has been rarely studied. In this work, we report the impact of hydrogen activation by hydrogen-permeable SrCe0.8Zr0.2O3-delta (SCZO) perovskite oxide material on DNMC over an iron/silica catalyst. The SCZO oxide has mixed ionic and electronic conductivity and is capable of H-2 activation into protons and electrons for H-2 permeation. In the fixed-bed reactor packed with a mixture of SCZO oxide and iron/silica catalyst, stable and high methane conversion and low coke selectivity in DNMC was achieved by co-feeding of H-2 in methane stream. The characterizations show that SCZO activates H-2 to favor "soft coke" formation on the catalyst. The SCZO could absorb H-2 in situ to lower its local concentration to mitigate the reverse reaction of DNMC in the tested conditions. The co-existence of H-2 co-feed, SCZO oxide, and DNMC catalyst in the present study mimics the conditions of DNMC in the H-2-permeable SCZO membrane reactor. The findings in this work offer the mechanistic understanding of and guidance for the design of H-2-permeable membrane reactors for DNMC and other alkane dehydrogenation reactions.