Oxidative coupling of methane over alkaline earth oxides deposited on commercial support precoated with rare earth oxides

Abstract

A number of supported catalysts, prepared by depositing alkaline earth (viz. Mg, Ca, Sr and Ba) oxides on a commercial support (SA-5205) precoated with various rare earth (viz. La, Ce, Nd, Sm, Gd, Er and Yb) oxides have been evaluated for their surface properties and activity/selectivity in oxidative coupling of methane (OCM) at low contact time (GHSV=1.02×10⁵ cm³ g^-1 h^-1). The catalysts have been characterized for their basicity and acidity distributions by temperature programmed desorption (TPD) Of CO₂ and ammonia from 50°C to 950°C, respectively, and for their oxygen chemisorption sites by TPD of O₂. The OCM activity of the catalysts has been correlated with their basic sites measured in terms of the CO₂ desorbed between 500°C and 950°C. The catalysts with La₂O₃ and/or Nd₂O₃, showing good OCM activity, have been compared for their performance in the OCM process at different temperatures (750°C-850°C), and CH₄/O₂ ratios (4.0-20.0) in the feed. At 850°C, the catalyst with SrO deposited on the support precoated with mixed La₂O₃-Nd₂O₃ shows best performance in the OCM process.