Effect of pH value of impregnating solution on the performance of Co/TiO2 catalyst for Fischer-Tropsch synthesis
浸渍溶液pH值对Co/TiO2催化剂F-T反应性能的影响

A series of Co/TiO_2 catalysts were prepared by incipient wetness impregnation. The pH value of the impregnation solution was adjusted by using nitric acid and urea. The XRD, TPR and XPS characterization results indicate that the change of the pH value of the impregnation solution is correlated with the crystal particle size of cobalt oxide species (Co_3O_), dispersion behavior and metal-support interaction. When the pH value of the solution is higher than the IEP (ion equipotential point) of titania, the larger Co_3O_4 particle size could be obtained on the surface of the catalyst. High pH value favores the adsorption and dispersion of active cobalt species over the titanium dioxide, and facilitates the interaction between cobalt and titania, and depresses the reduction degree of the catalyst. In the F-T reaction, catalysts prepared at high pH value have low activities and high methane selectivities. When the pH value of the solution is lower than the IEP of titania, the Co_3O_4 particle size is small, the interactions between cobalt species and support are weak and the reduction degrees are high, which further enhance the F-T reaction activity and suppress methane selectivity.