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.
Highlights
1,4-butynediol (BD) contains both electron-rich –C≡C– and polar –OH groups and has many excellent properties
BD can be used as a critical C4 feedstock for the synthesis of the important downstream chemicals with high added value, such as 1,4-butanediol (BDO), 1,4-butenediol (BED), tetrahydrofuran (THF), γ-butyrolactone (GBL), polytetramethylene ether glycol (PTMEG), polyurethane (PU), polybutylene terephthalate (PBT), and polybutylene succinate (PBS) [4,5,6,7,8,9]
In order to further unfold the catalytic mechanism of ethynylation reaction, it is very necessary to study the synergistic effect between the active Cu species and other components
Summary
1,4-butynediol (BD) contains both electron-rich –C≡C– and polar –OH groups and has many excellent properties. For the reactants in the ethynylation reaction of formaldehyde, the terminal ≡C–H of the acetylene molecule is acidic, while the O in the C=O unit of the formaldehyde molecule has two lone pairs of electrons Based on these characteristics of the reactant molecules, homogeneous-phase catalysts such as NaOH, KOH, organic Li, and Lewis acids have successfully been used to prepare alkynals by reacting acetylene with carbonyl compounds bearing a variety of functional groups [27,28,29]. In the Cu-based heterogeneous catalytic systems, the adsorption and activation of acetylene or formaldehyde by the introduction of promoters, and synergistic catalysis involving active cuprous species during the reaction of formaldehyde with acetylene has not been reported. The effects of the promoter on the texture, structure, surface property, and ethynylation activity of the nano CuO-based catalysts were studied, and the structure-performance relationships of the catalysts were analyzed, which provided important inspiration for the development of highly active ethynylation catalysts
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