Methane Conversion to Ethylene and Aromatics on Ptsn Catalysts

Non-oxidative coupling of methane to ethylene and aromatics is a promising strategy for activation and conversion of methane into more valuable chemicals; however, this conversion suffers from coke deposition and catalyst deactivation at high operating temperatures (e.g., 970 K).¹ In this study, Pt and Pt-Sn catalysts supported on either SiO₂ or H-ZSM-5 supports are investigated for non-oxidative methane conversion. Pretreatment of silica-supported catalysts at 1123 K decreased the extent of coke formation. On both supports, PtSn catalysts showed higher activity than their monometallic counterparts. The ethylene formation rate was 20 times faster over a PtSn(1:3)/H-ZSM-5 catalyst with SiO₂:Al₂O₃ =280 in comparison to that over PtSn(3:1)/SiO₂. Using H-ZSM-5 supports with higher contents of framework Al (i.e., SiO₂:Al₂O₃ = 23, 50, 80) provided a significant increase in selectivity to aromatics. The most active and stable PtSn/H-ZSM-5 catalyst forms carbon products at a rate comparable to state-of-the-art Mo/H-ZSM-5 catalysts. STEM measurements suggest that the presence of smaller Pt nanoparticles on H-ZSM-5 supported catalysts is the primary source of their high activity. In parallel, results from density functional theory calculations and microkinetic modelling for methane conversion on Pt and PtSn surfaces predict higher coupling rates on bimetallic and stepped surfaces, rationalizing the experimental observations.²

References:

(1) Xu, Y.; Lin, L. Appl. Catal., A 1999, 188, 53−67.

(2) Gerceker, D.; Motagamwala, A. H.; Rivera-Dones, K. R.; Miller, J. B.; Huber, G. W.; Mavrikakis, M.; Dumesic, J. A. ACS Catal. 2017, 7 (3), 2088–2100.