Bimodal porous Pd-silica for liquid-phase hydrogenation

Palladium catalysts loaded on bimodal porous silica were examined in the liquid-phase hydrogenation of 2-butenal at 0 °C and a hydrogen pressure of 1.1 MPa. The sizes of mesopores and macropores of the silica support are controllable in the range of 4-23 nm and 0.5-25 μm, respectively. The macropores provide effective paths of mass transfer, and the mesopores present effective surfaces for dispersion of metals. The catalytic activity of Pd-silica with bimodal porous structure depends on the size of mesopores and macropores as well as on the particle size of the support silica. The most active Pd-silica catalyst, with mesopores of 12 nm and macropores of 2 μm, shows much higher activity than does a commercial palladium carbon catalyst without macropores. The results indicate that the diffusion process inside the catalyst particles dominantly determines the reaction rate in the hydrogenation.