Effect of promoters on the syngas production in the microwave-enhanced methane dry reforming over Ni-x/AC (x = Mg, Ca, La, Ce) catalysts

Capitalizing on the targeted energy transfer, microwave-enhanced dry reforming of methane (MW-DRM) is an attractive CO₂ valorization technology. However, this process coupled with carbon-based catalysts may suffer from rapid deactivation due to severe carbon deposition/loss or active metal sintering. In this study, activated carbon (AC)-supported Ni catalysts modified with different promoters (Mg, Ca, La, Ce) were investigated for MW-DRM process. As proved by the experiment results, Ca-promoted catalyst exhibited the worst reforming activity and stability in the MW-DRM and conventional heating DRM (CH-DRM) processes due to the severe carbon gasification of AC support and the severe sintering of the active metal. Compared to Mg, Ca, and La promoters, Ni-Ce/AC catalyst was demonstrated the optimum catalyst for MW-DRM process, which showed the most excellent stability with good reforming activity over 96 % and 98 % for CH₄ and CO₂ conversion rates, respectively. By converting MW energy attenuation into heat and plasma, the locally-formed high-energy active sites composed of adjacent Ni, CeO₂ and AC support of the Ni-Ce/AC catalyst could contribute to achieving the effective and localized activation of CH₄ and CO₂ molecules, thus leading to the enhancement of the reforming activity and the reduction of the loss of AC support due to CO₂ gasification. Moreover, MW heating method could avoid the excessive consumption of the AC support in Ni-Ce/AC by increasing the graphitization degree of AC, thus prolonging the lifetime of the AC-based catalysts. Above all, these findings provide new insights for the synergistic effect of MW with AC-based catalysts for syngas production.