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 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 and H. The strongly nucleophilic acetylenic carbon (HC≡C) is favorable to the attack at the electropositive carbonyl C 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 effectively dispersed Cu species, which improved catalytic activity and stability. However, the introduction of AlO 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.