Methane formation mechanism in methanol to hydrocarbon process: A periodic density functional theory study

Methane is an important product in methanol to hydrocarbon (MTH) process and its formation mechanism over HZSM-5 was investigated by applying periodic density functional theory. The results show that the carbocations of C7H9+-C12H19+ are important intermediates in MTH process and methane is formed via one intramolecular hydrogen transfer reaction of these intermediates from ring carbon to the carbon of methyl group. The activation energies for methane formation increase from 101 to 174 kJ/mol with increasing methyl groups in protonated methylbenzenes. The data indicate that methane has similar formation mechanism as ethene and propene, i.e. via hydrocarbon pool mechanism. (C) 2015 Elsevier B.V. All rights reserved.