Catalytic Pyrolysis of Methane on Mo/H-ZSM5 with Continuous Hydrogen Removal by Permeation Through Dense Oxide Films

Abstract

A dense SrCe_0.95Yb_0.05O_{3 - α} thin film (∼2μm) was used to remove H₂ during non-oxidative conversion of methane to higher hydrocarbons on Mo/H-ZSM5 in order to overcome kinetic and thermodynamic constraints. At 950 K, these films removed only a small fraction of the H₂ produced and hydrocarbon synthesis rates were unaffected by H₂ removal. Higher temperatures led to a modest increase in CH₄ conversion rates, but also to slightly lower C₂–C_{12} hydrocarbon selectivities and to higher catalyst deactivation rates. These undesired effects were eliminated by the addition of small amounts of CO₂ to the CH₄ reactants. The combination of dense SrCe_0.95Yb_0.05O_3-α thin films, chain-limiting catalytic pyrolysis reactions on Mo/H-ZSM5, and CO₂ co-reactants led to stable catalyst performance and modestly higher hydrocarbon synthesis rates than in conventional reactors. The improvements achieved by continuous H₂ removal are in agreement with predictions of kinetic-transport model simulations in tubular reactors with permeable walls.