Consequence of heterogeneity of active sites for reactivity mechanism of n -butane isomerization over SO 4 2− /ZrO 2 -Al 2 O 3 catalyst

•Incomplete removal of coke leads to a decrease in overall activity without the reduction in the isobutane formation rate.•Peaks in NH3-TPD profiles at 500-700°C are caused by a redox reaction between strongly adsorbed NH3 and superacid sites.•Incomplete removal of coke and appropriate decrease in the density of SO42− selectively promoted monomolecular pathway.