Sustainable hydrogen production via dry reforming of biogas using M−Ni/NiAl2O4 (M = Na, K, Ca, Mg) catalysts prepared by the combustion method: Effect of alkaline and alkaline-earth promoters

In this study, the insertion of alkaline metals (Na, K) and alkaline-earth metals (Ca and Mg) as promoters of NiO-Al 2 O 3 catalysts, prepared by the combustion synthesis method, was studied. The catalysts were active during 8 h of reaction and with high resistance to coke deposition when compared to other catalysts in the literature, and the best results obtained were for the Ca-Ni/NiAl 2 O 4 catalyst operating with a molar ratio CH 4 /CO 2 = 1. The simulated biogas composition was varied (CH 4 /CO 2 = 1, 1.5, 2) showing that the increased CH 4 /CO 2 molar ration favors methane decomposition reaction, resulting in increased coke formation, especially for K-promoted catalyst. The characterization of the catalysts revealed that the combustion method was highly efficient to produce Ni catalysts with good stoichiometric control, and highly dispersed nickel with crystallite sizes smaller than 15 nm. The insertion of alkaline and alkaline-earth promoters result in a decrease of nickel dispersion, but no activity loss was detected. The associative mechanism was proposed by DRIFTS in situ .