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

Abstract

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-MOx 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 ≡ Cδ− and Hδ+. The strongly nucleophilic acetylenic carbon (HC≡Cδ−) is favorable to the attack at the electropositive carbonyl Cδ+ 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). SiO2 effectively dispersed Cu species, which improved catalytic activity and stability. However, the introduction of Al2O3 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.

Walter Reppe Revival – Identification and Genesis of Copper Acetylides Cu2C2 as Active Species in Ethynylation Reactions

“…W. Reppe proposed that Bi inhibit the formation of cuprene which plugs the pipes in the industrial process [7] . A relationship between catalytic activity and unspecified Cu(I) surface centers (amorphous active cuprous species) was derived from infrared spectroscopic experiments (CO adsorption), one of the very few studies of spent catalysts in the literature proposing a reaction mechanism [8] …”

“…[7] A relationship between catalytic activity and unspecified Cu(I) surface centers (amorphous active cuprous species) was derived from infrared spectroscopic experiments (CO adsorption), one of the very few studies of spent catalysts in the literature proposing a reaction mechanism. [8] In all former experimental studies, the focus was on the characteristics of the pre-catalysts only (supported copper(II) oxides). The present study shall bridge the gap between these pre-catalysts and catalysis by focusing on the active species "Cu 2 C 2 " formed under activation conditions.…”

Application of CuxO-FeyOz Nanocatalysts in Ethynylation of Formaldehyde

“…The introduction of MgO enhances the surface alkalinity of the catalyst. The synergistic effect of a Cu center and a base center promotes the activation and adsorption of acetylene, and it makes the catalyst show higher catalytic activity [19]. The activation and adsorption of formaldehyde molecules has been realized by introducing copper centers and zinc oxide.…”

Importance of Zinc Oxide in Cu-Based Catalysts for the Ethynylation of Formaldehyde to 1,4-Butynediol

“…The catalyst is a key element in the synthesis of BD via the ethynylation of formaldehyde. At present, CuO–Bi 2 O 3 catalysts loaded on SiO 2 –MgO and Cu-based basic carbonate catalysts are used for this reaction. − It is generally believed that Cu 2+ in the initial CuO or Cu 2 (OH) 2 CO 3 is controllably reduced to Cu + , which is then converted to cuprous acetylide, which acts as the active species during the reaction. − In previous reports, copper species were stabilized to inhibit the reduction of Cu 2+ species to Cu metal and the side-reaction of acetylene polymerization by introducing Bi 2 O 3 , FeO x , and other promoters into the catalyst, regulating and controlling the valence, grain size of the initial Cu species, and with the help of a carrier effect. In this way, the initial Cu species were converted into highly dispersed cuprous acetylide species that improved the catalytic activity; , however, the catalytic activity of the ethynylation reaction using only single-component cuprous acetylide as the active species was low.…”