Microenvironment of the HMOR catalyst leads to high ethylene selectivity from ketene conversion: Insights from ab initio molecular dynamics simulations

The origin of high ethylene selectivity in ketene conversion with the HMOR catalyst is revealed using ab initio molecular dynamics simulations, and the microenvironment of catalyst pores of 8-member ring (8MR) and 12MR are found to be playing a crucial role. The higher activity of ketene conversion in 8MR than that in 12MR is because the 8MR side pocket pore microenvironment has a better stabilization effect on reaction intermediates. In addition, the free energy barrier of methylation of ethylene is higher than that of ketene in 8MR, which is due to the stronger interaction between hydrogen in ethylene and the framework of 8MR side pocket, resulting in relatively high C2 selectivity in 8MR. Similarly, the microenvironment of 12MR would facilitate the further methylation of CH3CH2CO+ to isopropyl, decreasing the selectivity of ethylene. These results strengthen the importance of understanding microenvironment of HMOR catalyst in improving ethylene selectivity from ketene conversion.