An Effective CuZn–SiO₂ Bimetallic Catalyst Prepared by Hydrolysis Precipitation Method for the Hydrogenation of Methyl Acetate to Ethanol

Abstract

A highly active CuZn–SiO2 catalyst with excellent stability in hydrogenation of methyl acetate (MA) was fabricated by the hydrolysis precipitation (HP) method. The HP method caused notable high dispersion of both copper and zinc species due to the strong interaction between metal species and silica support caused by the pseudo-homogeneous reaction during the mixing process. According to the linear correlation between the TOF (Cu+) and Zn/Cu ratio, the Cu+ was considered the predominant active site, and the Cu+ site derived from the strong interaction between copper and zinc species has higher activity than those Cu+ species generated from copper phyllosilicate. Compared to the CuZnO/Al2O3 and Cu–SiO2 catalysts, the Cu9Zn1–SiO2 catalyst displayed the highest catalytic activity on account of the high dispersion of active species and the enhanced ability of Cu+ species on ester adsorption by stronger Cu-ZnO interaction.

Highly active Ce, Y, La-modified Cu/SiO2 catalysts for hydrogenation of methyl acetate to ethanol

“…4a, all the calcined catalysts show typical IV type isotherms, indicating the existence of a mesoporous structure. 24 Aer introducing the rare earth element into the Cu/ SiO 2 system, the shape of the hysteresis loop changes to some extent but the distributions of pore size of all the samples are concentrated at about 3 nm (in Fig. 4b), suggesting that the addition of Ce, Y, and La has no signicant change on the pore structure.…”

“…The Cu/SiO 2 catalyst (30 wt% Cu) was prepared using the hydrolysis precipitation method (HP), as reported previously. 21,24 Briey, an appropriate amount of TEOS mixed ethanol solution was rst added in the Cu(NO 3 ) 3 $3H 2 O aqueous solution and then stirred for 1 h. Subsequently, 0.25 M ammonium carbonate was used as a precipitant and added dropwise to the above solution under vigorous stirring. The pH of the mixed solution was maintained at about 7 and the resultant mixture was aged at 80 C for 18 h. Aer ltering, washing, and drying, the dried Cu/SiO 2 was obtained.…”

“…As reported previously, it was assumed that Cu + ions and Cu 0 atoms occupy the same area (1.47 Â 10 19 copper atoms per m 2 ). 24,33 The detailed process is shown in the ESI. † X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (XAES) measurements were performed on an ESCA Lab220i-XL electron spectrometer (VG Scientic) with an Al Ka X-ray radiation source (hy ¼ 1486.6 eV).…”

“…Some researchers have found that more Cu + content on the surface would improve the catalytic activity in hydrogenation esters, such as dimethyl oxalate and MA. 21,24,31 They pointed out that Cu + species could polarize C]O bond in the esters since they act as electrophilic or Lewis acidic sites, which was the key factor and the rate-controlling step. Moreover, it is noteworthy that Cu/SiO 2 -5La has a large Cu + surface area but the lowest surface area of Cu 0 (Fig.…”

“…22,23 In previous studies, it has been shown that adding a second metal such as Zn, Ni, B, In, Ag, Mn, or Mg to the Cu/SiO 2 catalyst could improve the catalytic activity. 17,[24][25][26][27][28][29] The promotion is attributed to the enhancement in copper species dispersion and the appropriate Cu + /(Cu + + Cu 0 ) ratio on the surface of the catalyst. However, there are still many challenges in Cu-based catalysts that need to be overcome, especially their short lifespan.…”