Photothermocatalytic Dry Reforming of Methane for Efficient CO2 Reduction and Solar Energy Storage

Energy shortage and global warming owing to greenhouse gas (CO2) discharge in enormous quantities are two major global strategic issues. Photocatalytic solar fuel production (e.g., CO2 reduction, H2O splitting, etc.) by utilizing inexhaustible solar energy is very appealing and promising for addressing the two issues. Low light-to-fuel efficiencies (η) and fuel production rates (rfuel) are the impassable challenges in the view of the photocatalytic principle. Therefore, it is imperative and a great challenge to develop a new strategy of significantly increasing η and rfuel. Recently, a novel strategy of photothermocatalytic dry reforming of methane (DRM, CO2 + CH4 = 2CO + 2H2, ΔH298 = 247 kJ mol–1) has been reported. By the strategy, very high η and rfuel values have been simultaneously achieved merely using focused illumination based on nanostructured group VIII metal catalysts. The photothermocatalytic DRM abides by a mechanism of light-driven thermocatalysis. A novel photoactivation, quite different from conventional photocatalysis on semiconductor photocatalysts, is found to considerably promote light-driven thermocatalysis. In this Perspective, the light-driven thermocatalytic DRM mechanism, light-to-fuel conversion, and the photoactivation will be discussed. The major challenge for the photothermocatalytic DRM is the quick deactivation of the catalysts (especially nonprecious group VIII metal catalysts) due to thermodynamically inevitable side reactions of coke formation accompanying DRM. The strategies of kinetically inhibiting coke formation by designing nonprecious group VIII metal catalysts such as the surface modification of Ni nanoparticles by oxide clusters, loading Ni or Co nanoparticles on oxides with active oxygen, forming NiCo alloy nanoparticles, forming a CO2 molecular fence around Ni nanoparticles, and so on, will be discussed.