Effects of Co/Al molar ratio in CoAPSO-34 catalysts on the physicochemical property and catalytic performance in the chloromethane to light olefins reaction

Abstract

In this work, a series of CoAPSO-34(cobaltsilicoaluminophosphate, X = Co/Al, X = 0, 0.02, 0.05, 0.07, and 0.10) catalysts with different Co/Al molar ratio(X) were prepared for use in the chloromethane to olefin (CMTO) reaction to produce light olefins, such as ethylene and propylene. The CMTO reaction at 450 °C showed that CoAPSO-34(0.05) catalyst had the highest chloromethane conversion among the catalysts with a conversion of 78.75 % at the reaction time of 250 min. The catalytic lifetime increased with increasing Co/Al molar ratio up to 0.05 and then decreased with increasing Co/Al molar ratio up to 0.10. The deposition of coke originating from polymethylbenzene species is thought to be the main reason for deactivation of the catalysts. As the molar ratio of Co/Al increased from 0 to 0.05, the amount of acid site increased, although the textural property did not change. However, as the molar ratio of Co/Al increased from 0.05 to 0.10, the BET surface area and pore volume of the catalysts decreased sharply, in addition to the amount of acid sites. Hence, it is concluded that both the acidic properties and textural properties of the catalysts play a crucial role in determining the catalytic activities in the chloromethane to olefin reaction, resulting in the highest chloromethane conversion and light olefin selectivity over CoAPSO-34(0.05).