Synthesis, Modification And HDS/HDN Of Transition Metal Phosphides Catalysts

Hydrodesulfurization (HDS) and hydrodenitrogeneration (HDN) are the most effective processes for clean fuel production. In recent years, transition-metal phosphides became a field of research hot spots in hydrofining due to their high activity and stability under working conditions. This thesis mainly focused on studying the relationship between the structure and activity in preparation and modification of transition metal phosphide catalyst. The catalytic activities of nickel phosphide (Ni2P), molybdenum phosphide (MoP) and tungsten phosphide (WP) promoted by titanium dioxide (TiO2) and cerium dioxide (CeO2) were investigated; The different ways of preparation and passivation for supported nickel phosphide catalysts were elaborated. Meanwhile, a new method was proposed based on studying the non-calcination silica-based supported Ni2P. The content mainly includes:TiO2and CeO2were effective electronic and structure-forming promoters based on the XAFS results of the passivated catalysts. TiO2and CeO2not only affected the oxidability of Ni2P, also led to the formation of metallic Ni. These two factors may contribute both to the enhancement of hydrogenation, desulfurization and denitrogenation ability. The changes of DDS pathway activities of Ti-Ni2P(x) were in agreement with the changement of the oxidation state of the catalysts, whereas metallic Ni was usually considered to be the active center for hydrogenation.The promoting effect of TiO2/CeO2could be related to the electronic interactions between surface TiO2/CeO2and Ni2P species and the presence of Ni. The HDS/HDN performance of the Ti-Ni2P(0.03) and Ce-Ni2P(0.25) were much higher than the performance of unmodified Ni2P catalyst. As for the bulk MoP and WP in HDN, TiO2and CeO2are also promising promoters. The best Ti/Mo and Ti/W molar ratio is0.1, while the best Ce/Mo and Ce/W molar ratio is0.3. The HDS and HDN performance of promoted MoP and WP catalysts are much higher than the performance of MoP and WP catalysts, respectively.Several catalysts were synthesized by different preparation and passivation methods. With the characterization of X-ray Absorption Fine Stucture (XAFS), the relationship between the catalytic performance, the structure and electronic property of the catalysts were investigated. Ni2P catalysts were prepared by hydrogen plasma reduction (PR) and conventional temperature-programed reduction (TPR) method. The influences of preparation method toward the catalytic performance was expound. In the aspect of passivation, different passivation atmosphere were used inorder to study the influences on catalyst structure. The results showed that Ni-P bond of Ni2P was more sensitive to O2than the Ni-Ni bond, while H2S mainly attacked the surface Ni-Ni site. This led to different performance after passivation.The results showed that Ni2P/SiO2catalysts with good activity and stability can be prepared by non-calcination method. The performance of the non-calcination catalysts was not lower than conventional catalysts. Compared to conventional method, non-calcination method was more simple and convenient.