Oxidative Coupling of Methane over Calcined Coral-Sands: Their Catalytic Property and Comparison with Other Natural Calcium Carbonates

Article abstract of DOI:10.1246/bcsj.67.2278

Coral sands calcined at high temperatures of 800 and 1000 deg C were found to be an effective catalyst for the oxidative coupling of methane to C2 hydrocarbons, especially with high selectivity.The coral-sand catalyst was almost composed of calcium oxide; however, it also contained small amounts of Na, Sr, Mg ions etc., and had a characteristic structure with many small pores of 2-8 μm in diameter, which were formed during calcination.In order to investigate the role of their components in C2 formation, nine kinds of catalysts were prepared from other natural calcium carbonates, such as turbo shell, short-necked clam shells, and marbles; their catalytic properties were compared with that of the coral-sand catalyst.Consequently, it seemed that the C2 yield was related to the bulk and surface concentrations of sodium in catalyst, while the maximum-C2 selectivity at 700-800 deg C was related to those of strontium.The catalysts of corals and coral sands showed the highest maximum-C2 selectivity as well as the highest strontium-content (about 1.2wtpercent).It was considered that the strontium ions are well-dispersed in the catalyst and that they enhance the basicity in combination with sodium ions (main active species), leading to the high C2 selectivity.