Nonoxidative Methane Conversion with C5-Hydrocarbons of Different Classes

The target of this work is to investigate the co-conversion directions of chemisorbed methane with C₅-hydrocarbons of different classes (pentane, pent-1-ene, cyclopentane) over 0.5wt.% Pt/γ-Al₂O₃ catalyst at temperature range of 748-823 K under non-oxidative conditions. The synthesized sample was characterized by nitrogen adsorption-desorption, atomic emission analysis with inductively coupled plasma, IR-spectroscopy of adsorbed CO, temperature programmed reduction and others. The chemisorption experiments conditions: temperature range of 298-823 K and molar ratio of CH₄:Pt=10:1. After formation of adsorbed methane forms (H-deficient hydrocarbon fragments CH_х) on the catalyst surface to estimate the catalytic activity of the catalyst in CH₄ co-conversion and C₅-hydrocarbons one of model C₅-hydrocarbon was fed into the reactor at molar ratio of C₅H₁₂:Pt=1:1 and temperatures of 748, 773, 798 or 823K. It was shown that quantity of methane chemisorbed was 0.4 mol/mol Pt at 748K and 1.7 mol/ mol Pt at 823 K. The composition of surface CH_x-particles (H/C atomic ratio) was 3.1 at 748 K and 1.1 at 823 K. The qualitative and quantitative composition of the conversion products was determined by gas chromatography-mass-spectrometry method. An increase in the conversion of C₅-hydrocarbon during co-conversion of chemisorbed methane with model hydrocarbons over the Pt/Al₂O₃ at 748-823 K occurs in the series: pentane (61.8% at 823 K) – cyclopentane (75.3% at 823 K) – pent-1-ene (83.7% at 823 K). The largest yield of aromatic hydrocarbons (35.2 wt.% at 823 K) was recorded in the joint conversion of chemisorbed methane with pent-1-ene compared with the methane conversion with pentane (22.2wt.% at 823 K) and cyclopentane (16.1 wt.% at 823 K). The reactivity of the methane chemisorbed on the surface of the platinum-alumina catalyst was estimated by isotope ratio mass spectrometry using enriched methane (¹³CH₄).

This work was carried out within the state task of the Boreskov Institute of Catalysis (project AAAA-A17-117021450095-1).