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Pt and PtSn catalysts supported on SiO₂ and H-ZSM-5 were studied for methane conversion under nonoxidative conditions. Addition of Sn to Pt/SiO₂ increased the turnover frequency for production of ethylene by a factor of 3, and pretreatment of the catalyst at 1123 K reduced the extent of coke formation. Pt and PtSn catalysts supported on H-ZSM-5 zeolite were prepared to improve the activity and selectivity to non-coke products. Ethylene formation rates were 20 times faster over a PtSn(1:3)/H-ZSM-5 catalyst with SiO₂:Al₂O₃ = 280 in comparison to those over PtSn(3:1)/SiO₂. H-ZSM-5-supported catalysts were also active for the formation of aromatics, and the rates of benzene and naphthalene formation were increased by using more acidic H-ZSM-5 supports. These catalysts operate through a bifunctional mechanism, in which ethylene is first produced on highly dispersed PtSn nanoparticles and then is …