Abstract
Direct non-oxidative methane conversion (DNMC) converts methane (CH(4)) 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 SrCe(0.8)Zr(0.2)O(3-δ) (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.