浸渍溶液pH值对Co/TiO2催化剂F-T反应性能的影响

Fischer—Tropsch合成（简称F—T合成）是煤和天然气转化制取液体燃料的重要途径，催化剂的研制与开发是该过程实现工业化的关键步骤。钻基催化剂以其较高的加氢反应活性、较高的长链烃选择性和较低的水煤气变换活性而成为F—T合成中最有前途的催化体系之一。钴基催化剂的制备通常采用浸渍法。除了能够提高催化剂的比表面积和分散度，载体可以与金属发生相互作用而改变活性金属组分的结构组成、电子状态等，从而影响催化剂的催化反应性能。TiO2作为F—T合成的载体近年来受到普遍的关注。文献7，8]是针对TiO2载体的低表面有针对性地添加无机氧化物黏接剂，提高金属钴的负载量，从而改进催化剂的反应性能；或者是添加助剂及第二金属组分以提高催化剂分散与还原性能。本文通过调节浸渍液pH值控制钻钛的相互作用并与催化剂反应性能关联，以期为催化剂制备条件的选择提供参考。

Effect of pH value of impregnating solution on the performance of Co/TiO2 catalyst for Fischer-Tropsch synthesis

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.