Highly Dispersed Ni⁰/Ni_<i>x</i>Mg_1–<i>x</i>O Catalysts Derived from Solid Solutions: How Metal and Support Control the CO₂ Hydrogenation

Abstract

Among the Ni-based catalysts studied for CO&lt;sub&gt;2&lt;/sub&gt; activation reactions, Ni&lt;sub&gt;x&lt;/sub&gt;Mg&lt;sub&gt;1-x&lt;/sub&gt;O solid solutions present advantageous characteristics, mainly linked with the homogeneous distribution of the Ni species inside the MgO structure, leading to highly dispersed Ni&lt;sup&gt;0&lt;/sup&gt; supported catalysts. In this work, we report on the preparation and characterization of Ni&lt;sub&gt;x&lt;/sub&gt;Mg&lt;sub&gt;1-x&lt;/sub&gt;O pre-catalysts calcined at different temperatures. The resulting Ni&lt;sup&gt;0&lt;/sup&gt;/Ni&lt;sub&gt;x&lt;/sub&gt;Mg&lt;sub&gt;1-x&lt;/sub&gt;O catalysts were tested for the methanation of CO&lt;sub&gt;2&lt;/sub&gt;. Following the structural, morphological and chemical changes during both the calcination and the reduction, we were able to observe clear correlations between the reactivity of the catalysts and their physical properties, leading to a better understanding of the reaction mechanism and the respective contributions of the metal and the support. While no change was observed in the formation of CH&lt;sub&gt;4&lt;/sub&gt; over the range of temperature tested, the CO formation as by-product clearly changed with the increasing temperatures. Our results are consistent with the hypothesis that two different CO formation mechanisms are occurring, but depending on the temperature, one dominates over the other. This study illustrates the importance of the complex interplay of metal particles and oxidic support (likely at the interface), both actively participating in the CO&lt;sub&gt;2&lt;/sub&gt; characterization of hydrogenation mechanism.