Study on mechanical properties and damage mechanism of recycled concrete containing silica fume in freeze-thaw environment

Hydrogenation of CO2 to methane is a promising prospect for the utilization of carbon dioxide. Ni-Mg-Al mixed oxides have been reported as a catalyst for this process. Their promotion with cobalt allows to improve Ni reducibility, enhances surface basicity, electronic and textural properties. Solution combustion synthesis was used to optimize the introduction of cobalt to the Ni-Mg-Al oxide matrix. Three synthesis strategies were applied to obtain different morphologies and study their catalytic performance. Characterization techniques (ICP-MS, XRD, low-temperature N2 sorption, H2-TPR, CO2-TPD, TEM, XAS) showed that simultaneous combustion of all the precursors (Ni, Mg, Al, and Co) led to dissociation of nickel and cobalt to the support which resulted in the reduction of catalytic activity and blockage of active centers. The separation of the synthesis into two steps increased the availability of active centers, improved surface properties, and catalytic performance. Furthermore, it led to a decrease in the coordination number of nickel, due to higher contribution of cobalt in the metal crystallites, which resulted in improved catalytic activity. Our findings showed that the addition of cobalt in the second step, in the NiCo-D catalyst, enhanced the CO2 and H2 conversions for methane production compared to the other applied synthesis strategies.