Insight to structure-activity relationship of non-stoichiometric CuMgAl spinel catalysts for CO hydrogenation to dimethyl ether: Effect of MgO doping amount

Abstract

Understanding the structure-activity relationship of catalysis is of critical importance for the design and modulation of catalysts. Herein, Cu-Al spinel catalysts with varied Mg doping levels were synthesized and investigated for CO hydrogenation to dimethyl ether (DME). The results revealed that the coordination distribution of cations in catalysts was effectively regulated by controlling Mg content. Increasing the Mg content facilitated the migration of Cu2+ ions in catalysts from tetrahedral to octahedral sites, enhancing the sustained release performance of copper, and further promoting the stabilization role of Cu nanoparticles by spinel. Importantly, suitable Mg content enhanced the synergistic effect between Cu nanoparticles and spinel active sites, which was conducive to improving DME selectivity. However, excessive Mg doping suppressed the reduction of copper species, and also adversely generated excessive strong base sites. Consequently, an optimal Mg/(Mg+Cu) mole ratio of 0.15 over the C0.85M0.15A2 catalyst exhibited superior selectivity to DME at 64.2 % (at 48 h) and excellent stability during the continuous testing for 120 h. The In-situ DRIFTS experiment confirmed that this reaction involved CH3O* intermediates, and the pathway was elucidated as the hydrogenation of CH3O* to form CH3OH and further dehydration to generate CH3OCH3.