Comparison of the surface and catalytic properties of rare earth-promoted CaO catalysts in the oxidative coupling of methane

✍ Scribed by Vilas H Rane; Sopan T Chaudhari; Vasant R Choudhary

• Publisher: Wiley (John Wiley & Sons)
• Year: 2006
• Tongue: English
• Weight: 141 KB
• Volume: 81
• Category: Article
• ISSN: 0268-2575
• DOI: 10.1002/jctb.1387

✦ Synopsis

Abstract

Rare earth (viz. La, Ce, Sm, Nd and Yb) promoted CaO catalysts have been investigated, comparing their surface properties (viz. surface area and basicity/base strength distribution) and catalytic activity/selectivity in the oxidative coupling of methane at different reaction conditions (temperatures, 650–800 °C, CH~4~/O~2~ ratios, 2.0–8.0 and space velocity, 51 360 cm^3^ g^−1^ h^−1^). The surface properties and catalytic activity/selectivity are strongly influenced by the rare earth promoter and its concentration. Apart from the Sm‐promoted CaO catalyst, both the total and strong basic sites (measured in terms of CO~2~ chemisorbed at 50° and 500 °C respectively) are decreased due to the promotion of CaO by rare earth metals (viz. La, Ce, Nd and Yb). The catalytic activity/selectivity is strongly influenced by the temperature, particularly below ⩽700 °C, whereas at higher temperature no further effect is seen. The La~2~O~3~CaO, Nd~2~O~3~CaO and Yb~2~O~3~CaO catalysts showed high activity and selectivity, and also their results are comparable. Among the catalysts, Nd‐promoted CaO (with Nd/Ca = 0.05) showed the best performance (19.5% CH~4~ conversion with 70.8% C~2+~ selectivity) in the oxidative coupling of methane. A close relationship between the surface density of total and strong basic sites (measured in terms of CO~2~ chemisorbed at 50° and 500 °C respectively) and the C~2+~ selectivity and/or C~2+~ yield has been observed. Copyright © 2005 Society of Chemical Industry