ZnO-Al2O3-promoted CuO/ZrO2 catalyst prepared by oxalate gel-coprecipitation for the conversion of water-bearing materials

Generally, ZrO2 facilitates the reactions of O-containing species, which result in the loss of activity or the sintering of Cu species via intimate interaction between water and CuO/ZrO2 catalysts. Indeed, the CuO/ZrO2 catalysts (CZo) prepared by oxalate gel-coprecipitation technique possessed a high dispersion of Cu and a certain degree of alkalinity. Unfortunately, it exhibited inferior catalytic activity in conversion of bio-ethanol (37.6% conversion). In contrast, the CuO–ZnO–Al2O3–ZrO2 catalysts (CZAZo) with extra addition of ZnO and Al2O3 showed a good catalytic performance and stability (>600 h on line). For example, the 92.5% selectivity of ethyl acetate based on 62.2% conversion of ethanol, was achieved. Besides, it performed better in hydrogenation of hydrous ethyl acetate than CZo. Evidently, the excellent performance in conversion of water-bearing materials was mainly due to the addition of ZnO and Al2O3 to CuO/ZrO2 catalysts. Besides, the uniform combination of each component could be achieved successfully by the employment of oxalate gel-coprecipitation. As a result, the surface electronic properties are tuned effectively and the affinity for water decreases sharply. Most importantly, the associated loss of active sites could be effectively avoided because of the reduced water coverage over CZAZo.