Pretreatment as the crucial step for biogas reforming to hydrogen over Ni–Co bimetallic catalyst: Effect of CO2 pretreatment time

γ-Al2O3 pellets supported Ni–Co bimetallic catalyst prepared by excessive impregnation was employed for biogas reforming to hydrogen. H2 and CO2 pretreatment of the catalyst was investigated under different conditions in order to enhance the performance of the catalyst. CO2 pretreatment was performed at 850 °C and 0.1 MPa under different times (0, 0.25, 0.5, 1, 2 and 6 h). The activity is significantly increased by the pretreatment and has a close relationship with CO2 pretreatment time. No initial activation period was detected for catalyst with CO2 pretreatment for more than 0.5 h. The final conversion of methane increased from 87 to 95% and carbon dioxide from 95 to 99%, respectively, with increasing the CO2 pretreatment time from 0 to 1 h. Further increasing the pretreatment time from 1 to 6 h, the catalyst activity has a slight decrease. Characterizations revealed that catalyst pretreated for 0.5 h showed the strongest resistance to coking and catalyst pretreated for 1 h exhibited the greatest resistance to sintering. Catalyst pretreated for 0.5 h showed no sign of deactivation during a 511 h test with very low carbon deposition rate. With all factors considered, the optimum CO2 pretreatment time should be 0.5 h–1 h.