NixAl1O2-δ mesoporous catalysts for dry reforming of methane: The special role of NiAl2O4 spinel phase and its reaction mechanism

The structure evolution of surface NiAl2O4 spinel phase in NixAl1O2-δ mesoporous catalysts, synthesized by the citric acid sol-gel method, was systematically investigated. Small-size Ni nanoparticles, obtained by partial reduction from NiAl2O4 spinel in NixAl1O2-δ catalysts with low Ni contents at high temperature, can effectively inhibit the carbon formation from kinetics, while the irreducible NiAl2O4 counterpart can participate in elimination of carbon deposition. The constructed structure of Ni0-NiAl2O4 interfaces, produced by exsolution of Ni from NiAl2O4 spinel, is responsible for its high long-term stability and excellent resistance to coking and sintering for dry reforming of methane (DRM) reaction. The structure sensitivity and kinetic compensation effect of CH4 dissociation on Ni0 active sites are observed. DRM reaction proceeds via a Langmuir-Hinshelwood mechanism accompanied by an additional redox mechanism. It is noteworthy that the active oxygen species generated by filling the oxygen vacancies of NiAl2O4 spinel by CO2 provide another rapid redox route to eliminate carbon species.