Catalytic CO2 reforming of CH4 over Cr-promoted Ni/char for H2 production

•CH4–CO2 reforming over Cr-modified Ni/char catalyst has been studied.•Impregnation sequence has impacted on the activity of catalyst.•The optimal Cr loading could improve the dispersion of Ni and the affinity to CO2.•Nickel carbide was formed in situ during reforming and played as active species for catalysis.

The objective of the study is to investigate the catalytic performance of Cr-promoted Ni/char in CO2 reforming of CH4 at 850 °C. The char obtained from the pyrolysis of a long-flame coal at 1000 °C was used as the support. The catalysts were prepared by incipient wetness impregnation methods with different metal precursor doping sequence. The characterization of the composite catalysts was evaluated by XRD, XPS, SEM-EDS, TEM, H2-TPR, CO2-TPD, CH4-TPSR, and CO2-TPO. The results indicate that the catalyst prepared by co-impregnation of Ni and Cr possess higher activity than those by sequential impregnation. The optimal loading of Cr on 5 wt% Ni/char is 7.8 wt‰. Moreover, the molar feed ratio of CH4/CO2 has a considerable effect on both the stability and the activity of Cr–Ni/char. The main effect of Cr is the great enhance of the adsorption to CO2. It is interesting that the conversions of CH4 and CO2 over Cr-promoted Ni/char and Ni/char decrease initially, following by a steady rise as the reaction proceeds with time-on-stream (TOS). In addition, cyclic tests were conducted and no distinct deterioration in the catalytic performance of the catalysts was observed. On the basis of the obtained results, nickel carbide was speculated to be the active species which was formed during the CO2 reforming of CH4 reaction.