Effect of molecular structure on pyrolysis coking performances of hydrocarbons at different temperatures

•Compared with nC7, MCH has lower heat sink at low temperature and higher coking rate at high temperature.•The unique unimolecular demethylation and intramolecular stepwise dehydrogenation reactions of MCH caused its coking rate to be higher than that of nC7.•An experimental parameter for evaluating coking active site density for irregular coke morphology was proposed.•Some five-membered ring hydrocarbons such as cyclopentenes and PAHs such as A3-A5 components were considered as possible additional coking precursors.•The wall coking can be divided into several steps, in which the filamentous coke produced by catalytic coking provides the initial coking sites.