Basic Sites Promoted Highly Dispersed Cu-Based And Ni-Based Nano-Catalysts And Performances

Transition metal catalyst is one kind of common catalysts, especially cobalt, nickle, copper and chromium, are widely used as active site or promoter in catalysts. The most outstanding advantage is much cheaper than noble-metal catalysts. With the development of industry, catalysts with poisonous Cr ion are eliminated by human. In this case, as a kind of green catalyst, transition metal catalyst is used more often because its feature of environmental friendly. However, in most cases, low performances, harsh reaction conditions, small surface areas and particles agglomeration are the main defects of these catalysts. Therefore, how to prepare a well-dispersed transition metal catalyst with a large surface area, and a high efficiency is the common goal of many scientists. Traditional methods like impregnation method and deposition-precipitation method, have such defects mentioned above, a new preparation method is the key to preparing a good catalyst.In this passage, well dispersed basic catalysts with large surface areas were prepared by using a non-traditional method, and showed high performances in several reactions which could be promoted by basic sites. Synergistic effect between active sites and basic sites were inferred according to some characterizations.(1) Cu/MgO catalysts with different copper loading were prepared by separate nucleation and aging step method, using in the hydrogenation of DMCD to CHDM and the hydrogenation of FAL to FOL. After a series of characterizations we found that the role of basic sites was the most significant factor to promote the catalytic performances. Among the different Cu/MgO catalysts, sample 2 with a copper loading of 25% showed a higher performance and efficiency with a conversion and a selectivity both more than 95%, as well as a highest TOF. The large amount of strong basic sites, which had a strong interaction with the active sites Cu0 and produced a kind of Cu0(B) which was more efficient than the normal Cu0(A), was the main reason why this sample was the best one.(2) Well dispersed nickel-based catalysts were prepared through a Ni-Mg-Al LDH precursor, which were used in the hydrogenolysis of sorbitol. XRD, H2-TPR, CO2-TPD, XPS were tested on these catalysts. According to the results of reactions, the sample with Ni:Mg:Al ratio of 4:8:6 showed highest productivity, with a relatively low selectivity which should be improved further. Therefore, cobalt was induced into this catalyst to be a assistant to nickle. By changing the ratio of Ni:Mg:Al:Co, we found that sample Co-2 with a ratio of 4:8:4:2 showed the highest selectivity up to more than 40% to 1,2-propylene glycol, which has never been reported in the literature. This is because the introduction of Co changed the chemical circumstance in the catalyst, and produce a kind of super strong basic sites. Moreover, the interaction between Co and Ni confined the growth of Ni particles. Thus, the strength and number of basic sites were both improved and route of’retro-aldol’was promoted by these basic sites, a route could lead to a high selectivity of the main products.