Layered and double perovskites as methane coupling catalysts

Abstract

Layered perovskites of the form A 2Ln 2Ti 3O 10 (A = K,Rb; Ln = La,Nd,Sm, Gd,Dy) and alkali carbonate promoted double perovskite LaCaMnCoO 6 were examined as methane oxidative coupling catalysts. The layered perovskites were of interest since they were reported to contain layers of alkali ions dispersed and sandwiched between lanthanide perovskite layers. The double perovskite, LaCaMnCoO 6, was of interest as a redox coupling catalyst due to its unique structure and redox properties. The material was reported to have an ordered perovskite structure showing multiple occupation of both A (La and Ca) and B (Mn and Co) sublattices. Layered perovskites of the form A 2Ln 2Ti 3O 10 gave coupling results comparable to many of the reported literature methane coupling catalysts. Trends observed upon changing temperature, CH 4/O 2 feed ratio or diluent amount in the feed were examined. Alkali carbonate doped LaCaMnCoO 6 were shown to be a unique class of sequential (redox) mode coupling catalysts. These catalysts showed very high initial C 2+ selectivities (>80%) and exhibited the unique characteristic that the CH 4 conversions and C 2 selectivities are at maximas during the early stages of the catalyst reduction. This characteristic has not been reported for any other sequential (redox) mode coupling catalysts.