Preparation Of Supported Palladium-based Catalysts And Study Of Their Performance In Selective Hydrogenation

Supported Pd catalysts have been widely used in selective hydrogenation due to their unique catalytic properties, which can be tuned by selectively distributing the active phase, changing the properties of the supports, and introducing the second metal. This thesis investigated the influence of the eggshell distribution of active phase on the support, the surface defects of the support, and the introduction of the second metal, such as Fe and Re, on the structure and catalytic hydrogenation performance of the supported Pd-based catalysts. The main contents are as follows:The eggshell Pd/SiO2-Al2O3catalysts have been prepared through the rapid reduction of Pd2+by CO. The influence of H2O content and Pd2+concentration on the thickness of the Pd shell has been investigated. And the catalytic performance of the catalyst has been tested by liquid phase hydrogenation of phenylacetylene. The results indicated that, the fast reduction of Pd2+by CO was efficient and simple for generating the eggshell Pd catalyst, which displayed high activity and high selectivity to styrene in the hydrogenation of phenyl acetylene. In the hydrogenation of phenylacetylene in the presence of excess styrene, the eggshell Pd catalyst showed a better performance with comparison to the uniformly supported Pd catalyst, generating little ethylbenzene before the complete conversion of phenylacetylene.The stucture of CNFs with a high external surface area is similar to the stucture of the eggshell catalyst. The defects were introduced to the surface of CNFs by steam treatment at high temperature. Pd nanoparticles were synthesized through the reduction of Pd(OAc)2in ethylene glycol by ultrasonic-assisted method, and were deposited on the treated CNFs. The catalytic performance of the Pd/CNFs catalysts in the hydrogenation of phenyl acetylene has been investigated. The results indicated that the terrace-and hole-like defects could be introduced on CNFs by changing the temperature of the treatment. The former had small impact on the structural order of CNFs, while the latter would bring serious damage to the structural order of CNFs. Similar to the eggshell catalyst, the prepared Pd/CNFs catalysts showed high selectivity to styrene in the hydrogenation of phenylacetylene. However, they suffered from poor stability. The introduction of terrace-like defects could alleviate the deactivation the Pd/CNFs catalysts, while the presence of hole-like defects was against the improvement of the catalyst activity. The bimetallic Pd-Fe catalysts supported on activated carbon were synthesized through the replacement reaction between Fe colloid and Pd2+. A series of characterizations including XRD, TPR, TEM and EDX were used to investigate the structure of Pd-Fe catalysts. The results indicated that, the bimetallic Pd-Fe catalysts prepared by replacement reaction had a relatively low alloying, accompanying with the formation of metallic Pd. The bimetallic Pd-Fe catalyst with Pd/Fe molar ratio of3showed the high activity in the hydrogenation of phenylacetylene. Meanwhile, phenylacetylene had almost completely converted to styrene and more ethylbenzene was produced. Further increasing the content of Fe led to the decrease of the activity.A series of bimetallic Pd-Re catalysts supported on activated carbon were prepared by impregnation method and microwave-assisted pyrolysis method and their catalytic properties were systematically investigated in the aqueous phase hydrogenation of succinic acid. The main reaction pathway of the aqueous phase hydrogenation of succinic acid has been studied. The results indicated that, monometallic Pd catalyst showed a relatively low activity in the hydrogenation of succinc acid, with γ-butyrolactone being the main product. Introducing small amount of Re could significantly improve the activity of the catalyst and enhance the selectivity to tetrahydrofuran. Compared to the bimetallic Pd-Re catalyst prepared by the impregnation method, the catalyst obtained through microwave-assisted pyrolysis exhibited a higher conversion of the succinc acid but a slightly decreased selectivity to tetrahydrofuran. The hydrogenation pathway has been implemented through the investigation on the hydrogenation of the intermediate products.