Low-temperature hydrogenation of dimethyl oxalate to ethylene glycol via ternary synergistic catalysis of Cu and acid−base sites

Abstract

Metal-support synergistic catalysis plays a crucial role in heterogeneous reaction processes from viewpoint of both fundamental research and practical applications. Herein, a series of Cu-based nanocatalysts were prepared by virtue of topotactic structure transformation from CuMgAl-layered double hydroxide (CuMgAl − LDH) precursors. Various in situ investigations including XRD, XPS, EXAFS and FTIR demonstrate that the structural transformation of CuMgAl − LDH results in well-dispersed Cu nanoparticles (metallic Cu° as the single species) supported on mixed metal oxides (MgO and Al2O3, denoted as Cu/MMO). The optimal catalyst (Cu/MMO−S3) exhibits an excellent catalytic performance toward hydrogenation of dimethyl oxalate (DMO) to ethylene glycol (EG) (yield: 94.4%) at an exceptionally low operation temperature (438 K). This is, to the best of our knowledge, at least 30―40 K lower than normally accepted temperature for Cu-based catalysts (above 473 K). Structure − property correlation investigations were performed via in situ FTIR, N2O pulse chemisorption, NH3−TPD and CO2−TPD, and the results revealed that a ternary synergistic catalysis of Cu and acid − base sites makes a predominant contribution: Lewis acid sites (Al3+) and medium-strong basic sites (Mg2+−O2− pair) of supports serve as active sites for adsorption of polarized CO/CO group in DMO molecule; while H2 undergoes dissociation adsorption on Cu° site. This precise control over metal and acid − base sites based on LDHs precursor approach would lead to new possibilities in rational design and preparation of heterogeneous catalysts for hydrogenation of CO/CO group.