Regulating local electron density of Cu active site by the lamellar structure of hydrotalcite for selective-hydrogenation of furfural

Abstract

Rational modulation of the local electron density of Cu active site is the key to improve the efficient transfer hydrogenation (CTH) of furfural (FF) on the surface of catalysts with low Cu-loadings. In this paper, a CuMgAl/LSC catalyst with lower Cu content (<3.5 %wt) was prepared by using porous biochar as a carrier and exploiting the local dispersion and electron-modulation effects of structural elements of hydrotalcite laminates. CTH experiments showed that the conversion of FF and the selectivity of FA could reach more than 99.0 % in isopropanol solution at 170 °C and within 1 h. Catalyst characterization and density functional theory (DFT) calculations demonstrated that the Cu(I) species was the main active site during the CTH process of FF. Doping laminate metals (i.e., Mg, Al) can not only form electron-rich centers by local electron modulation of the active site through the coordination structure of Cu-O-M, lowering its D-band center and achieving higher catalytic activity; Due to the Jahn-Teller effect, the local spatial misalignment of Cu sites formed, which can reduce the risk of over-hydrogenation and improve the FA selectivity. In addition, it can be also found that the Coulomb tractive force of reactive intermediates can lead to the crystal surface reconstruction and structure deterioration of Cu species. The new discovery of the deactivation mechanism can provide a reference for the future design of copper-based catalysts in CTH process of FF.