The importance of copper-phyllosilicate formed in CuO/SiO2 catalysts in the ethynylation of formaldehyde for 1,4-butynediol synthesis

Abstract

Ethynylation of formaldehyde for 1,4-butynediol synthesis catalyzed by a Cu-based catalyst is an attractive technology in the chemical industry field related to 1,4-butanediol. The stabilization of Cu⁺ species under a reducing atmosphere is still extremely challenging. Herein, a series of CuO/SiO₂ catalysts were prepared by a hydrolysis–precipitation method using ethyl orthosilicate as a silicon source and applied in the ethynylation of formaldehyde. The influence of active Cu species contents and catalyst calcination temperatures on Cu-based catalyst structures and performances are all investigated carefully. All catalysts are characterized through N₂ physical adsorption–desorption, X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and thermogravimetric analysis. The results show that catalyst's Cu loading and calcination temperatures affect CuO dispersibility and lamellar copper-phyllosilicate formation. The CuO/SiO₂ catalysts with highly dispersed CuO and large amounts of lamellar copper-phyllosilicate exhibit high ethynylation performance. The highly dispersed CuO usually provides initial activity, while the copper-phyllosilicate contributes to the stability of catalysts. It is ascribed to copper-phyllosilicate with the strong interaction between CuO and SiO₂, thus generating a stable and active Cu₂C₂ complex. Furthermore, the obvious reduction of copper-phyllosilicate and the increase of CuO sintering result in ethynylation performances decreasing with catalyst calcination temperature increasing from 450 °C to 850 °C.