Oxidative coupling of methane on fluorite-structured samarium–yttrium–bismuth oxide

Abstract

The catalytic properties of dense fluorite-structured Bi 1.5Y 0.3Sm 0.2O 3– δ (BYS) pellets for oxidative coupling of methane (OCM) to ethane and ethylene (C 2 products) were studied in a packed-bed reactor in co-feed mode. The effects of temperature, feed flow rate, CH 4/O 2 and He/(CH 4+O 2) ratios on the OCM performance over BYS were systematically investigated. The appropriate operating conditions were found to be: temperature, 900–1000°C; total flow rate, 90–150 ml (STP)/g min; CH 4/O 2 ratio, 2–3.5; He/(CH 4+O 2) ratio, 0.75–1.75. Under these conditions, C 2 yields of 20–27%, C 2 selectivities of 50–62% and C 2 space–time yield of up to 6.9 μmol/g s were achieved. The good OCM catalytic properties of BYS are believed to be related to its fluorite-type phase structure and large oxygen ion mobility at high temperatures. OCM kinetics of BYS oxide was studied with the assumption that no C 2 products were converted to CO x under low to medium methane conversion range. Lumped rate equations for C 2 and CO x formation were obtained as functions of temperature, O 2 and CH 4 partial pressures. The solid phase oxygen ions are responsible for the C 2 formation, while the gas phase oxygen molecules enhance the CO x formation.