Enhanced catalytic stability of non-stoichiometric Cu-Al spinel catalysts for dimethyl ether synthesis from syngas: Effect of coordination structure

Cu-Al spinel catalysts were synthesized by various preparation methods, and its CO hydrogenation performance was evaluated. Characterization results showed that different preparation methods can effectively regulate the coordination distribution of cations in surface spinel structure. The sustained release property of Cu-Al spinel was related to its coordination structure. The catalyst containing a large amount of octahedral spinel Cu2+ ions was capable of delaying the reduction of copper, and small Cu nanoparticles (Cu NPs) were produced and highly dispersed on the defective spinel surface, which may be that the vacancy derived on the surface of defective spinel anchored small Cu NPs, which was the key to improve catalytic stability. We also discussed the real reason for poor catalytic stability, and this was due to that the easily-reducible spinel possessed extensive tetrahedral spinel Cu2+, which accelerated the reduction and release of copper, resulting in that the formed copper was unstable and aggregated readily. The Cu-Al spinel catalyst prepared by the solid phase method included octahedral coordination Cu2+ ratio as high as 59%, and the corresponding average size of Cu particles produced from spinel was measured as about 11.3 nm by N2O titration method, exhibiting enhanced stability and excellent catalytic performance.