A nickel−magnesia solid solution Ni−Mg−O was examined as a catalyst for solar CO2 reforming of methane. The activity was tested in a laboratory-scale transparent (quartz) reactor under direct irradiation of the catalyst by high-flux visible light from a sun-simulator. The 8−11 wt % Ni−Mg−O catalyst gave the high reforming activity or about 100% of chemical conversion, with little coking, under a high-flux irradiation of 890 kW m-2 and at a short residence time of about 0.15 s while passing a 1:1 CH4−CO2 gas mixture at 1 atm. The comparison of the activity data with those obtained in a light-irradiated, nontransparent (steel) reactor showed that the intensification of heat supply by the direct light irradiation of the Ni−Mg−O catalyst leads to considerable reaction rate enhancement. Applying this Ni−Mg−O catalyst, a new type of “catalytically activated” ceramic (alumina) foam absorber was prepared and tested on activity in a laboratory-scale volumetric receiver-reactor using the sun-simulator. This new abs...