Ethynylation of Formaldehyde over Binary Cu-Based Catalysts: Study on Synergistic Effect between Cu(+) Species and Acid/Base Sites

Most studies on the Cu-based catalysts in the ethynylation of formaldehyde are merely focused on the tuning of electronic configuration and dispersion of the Cu(+) species. So far, little attention has been paid to the synergy between Cu species and promoters. Herein, binary nano-CuO-MO(x) catalysts (M = Si, Al, and Mg) were synthesized and the effects of the promoter on the surface basicity/acidity were systematically studied as well as the ethynylation performance of the nano-CuO-based catalysts. The results show that the introduction of MgO provided a large number of basic sites, which could coordinate with the active Cu(+) species and facilitate the dissociation of acetylene as HC≡C(δ−) and H(δ+). The strongly nucleophilic acetylenic carbon (HC≡C(δ−)) is favorable to the attack at the electropositive carbonyl C(δ+) of formaldehyde. The MgO-promoted CuO catalyst showed the highest yield of BD (94%) and the highest stability (the BD yield decreased only from 94% to 82% after eight reaction cycles). SiO(2) effectively dispersed Cu species, which improved catalytic activity and stability. However, the introduction of Al(2)O(3) resulted in a large number of acidic sites on the catalyst’s surface. This led to the polymerization of acetylene, which covered the active sites and decreased the catalyst’s activity.