Study On Pd-Based Catalyst For Anthraquinone Hydrogenation Reaction

Hydrogen peroxide?H₂O₂? is a popular oxidizing agent widely used in the industry of electron, pharmaceutical, papermaking, wastewater treatment and so on, for its efficient oxidizing and its significant environmental friendliness as the by-product of oxidation reactions is water. The main industrial synthesis method for H₂O₂ is anthraquinone process. In the whole process, anthraquinone hydrogenation reaction is the key step. Therefore, the development of a highly active catalyst with high selectivity to active quinones is one of the priority issues of process improvement, since the excellent catalyst will possibly lead to a reaction process with higher safety and lower cost. In this dissertation, we made attempts to develop high-performance Pd catalysts through three ways, namely, modification of supports, control of Pd dispersion and exposed facets, and incorporation of a second metal.The surface properties of ?-Al₂O₃ were regulated through modification with Si. The Si species existed as an amorpnous phase and covered partial medium acid sites, which resulted in the decrease of surface acid sites. The activity of prepared catalyst declined because of the reduced catalyst surface acid sites and dispersion of Pd. However, the production of degradation products was also suppressed due to the reduced acidity of catalysts.The effect of pH in the impregnation process on the chemical composition, Pd dispersion and acidity of catalysts synthesized by the impregnation method was evaluated. The optimum pH value of the impregnation process was about 3. Then we prepared Pd nanocrystals with exposed?100? and?111? facets by controlling the growth of cubic seeds and their catalytic performance were compared in anthraquinone hydrogenation reaction through immobilization on ?-Al₂O₃ as catalysts. Our experimental results combined with the density functional theory calculations showed that Pd?100? facet was more active than Pd?111? in the C=O hydrogenation but less active in the saturation of aromatic ring. Their abilities in C?O hydrogenolysis reactions were almost the same. Directed by this result, a high-performance of Pd nanocrystals/Al₂O₃ was successfully prepared using one-step synthesis method, which could not only control the exposure of Pd?100? facet but also increase the stability of Pd components. Its catalytic performance was superior to that of prepared by traditional impregnation method.A series of bimetallic PdAu catalysts with different structures were prepared by changing the loading sequence of Pd and Au. High-performance PdAu catalyst was obtained by loading Pd on Au particles deposited on an Al₂O₃ support. The popcorn structure and unique electronic properties of the Pd species resulted in the highest content of surface metallic Pd, which was the most active component for the reaction. What is more, the addition of Au can effectively reduce the amount of degradation products via suppressing the side reactions.