A comparative study of Ni/Al2O3–SiC foam catalysts and powder catalysts for the liquid-phase hydrogenation of benzaldehyde

Abstract

In this study, Al2O3-washcoated SiC (Al2O3–SiC) foams and Al2O3 powder were employed as the supports of a Ni catalyst for the liquid-phase hydrogenation of benzaldehyde. A series of Ni/Al2O3–SiC foam catalysts and Ni/Al2O3 powder catalysts with a Ni loading from 10 wt% to 37 wt% of the weight of Al2O3 were first prepared by a deposition–precipitation (DP) method. The catalytic activity and recyclability of both kinds of catalysts were then compared. Although it had a smaller accessible surface area with the reactant, the foam catalyst with a Ni loading of 16 wt% exhibited a slightly higher conversion of benzaldehyde after 6 h (of 99.3%) in comparison with the Ni/Al2O3 catalyst with identical Ni loading (conversion of 97.5%). When the Ni loading increased from 16 wt% to 37 wt%, the reaction rate obtained with the foam catalyst increased significantly from 0.108 to 0.204 mol L−1 h−1, whereas the reaction rate obtained with the powder catalyst increased from 0.106 to 0.123 mol L−1 h−1. Furthermore, the specific activity (moles of benzaldehyde consumed by 1 g min−1 of Ni) of the foam catalyst with a Ni loading above 30 wt% was superior to that of the powder catalyst because of its smaller Ni-particle size and higher mass-transfer rate. The foam catalyst displayed a high recyclability as a function of run times owing to the strong interaction between the Ni component and the Al2O3 coating. The conversion of benzaldehyde over the foam catalyst remained almost unchanged after being used 8 times. In comparison, a drop of 43% in the conversion of benzaldehyde with the powder catalyst was observed after being used 7 times due to the leaching of the Ni component.