Synthesis And Application Of Supported Metallic Catalyst For Hydrogenation

Hydrogenation plays an important role in the production of dyes, medicines, and functional intermedias, which has significant impacts on our daily life. Nowadays, the way that using metal reductants in acidic medium is still applied in the several hydrogenation process (e.g., synthesis of vitamin K4 from 2-methyl-1,4-naphthoquinone, production of 3,3’-dichlorobenzidine from o-chloronitrobenzene). This approach not only produces a lot of waste and by-products (such as nitroso-, azo-and hydrazine-compounds) during the reaction process, but also is time-consuming and has metal residues in the products. To avoid these situations, it is of great importance to design and develop some efficient heterogeneous catalysts for selective hydrogenation.At the same time, with the development of economy, the utilization of renewable resources has drawn a lot of attention. According to previous reports, it is possible to convert renewable materials (such as cellulose, glucose, sorbitol and glycerol) into C2 and C3 polyols (such as ethylene glycol, propanediol and propanol), which are crucial feedstocks in the manufacture of other chemicals, through hydrogenation process. Production of C2 and C3 polyols in this way would be more favorable in large-scale over cheap catalyst, which may hardly be realized using traditional catalysts and technology. Thus, it is great important to design and develop efficient heterogeneous catalysts for the conversion of renewable resources.According to those achievements in literatures, the aim of this dissertation is to design, synthesis and finding the application of highly efficient supported metallic heterogeneous catalyst for hydrogenation, and to find the relationship between the morphology, property of catalysts and its activity, mechanism for catalytic hydrogenation. The main contents and achievements of this work are:Novel Pt@MIL-101 catalyst was prepared via a simple colloid method. Characterizations disclosed that Pt adatoms were homogeneously dispersed in MIL-101. Pt@MIL-101 exhibited extremely high catalytic activity in the hydrogenation of nitroarenes under mild conditions. The turnover frequency of each Pt atom for nitrobenzene hydrogenation reached 1548 min-1 at 30℃. And the conversion of NB over Pt@MIL-101 remained stable even after five cycles, while the selectivity of AN decreased slightly to 86%.A magnetic Pt/Fe3O4 catalyst was prepared through a facile surfactant-free one-step approach to overcome the difficulties in recovery of the catalyst. Pt/Fe3O4 exhibited superior activity and extremely high selectivity for chloroaniline in the hydrogenation of chloronitrobenzene compared to free Pt NPs and MgO-, Al2O3- and SiO2-supported Pt catalysts. The specific activity of each Pt atom for m-chloronitrobenzene hydrogenation reached 45630.8 molcAN/(molpt-h) at 30℃. The high efficiency could be attributed to the well-dispersed Pt NPs on the Fe3O4 surface and the strong interaction between Pt NPs and Fe3O4, and the synergistic reaction between Pt and Fe3O4 may also promote the catalytic activity.A series of Mg-Al-Ox supported non-noble metal Ni catalysts were prepared through hydrotalcite-like precursors in order to decrease the cost for catalyst synthesis. It was disappointed to find these catalysts exhibited relatively lower catalytic activity in the hydrogenation of nitroarenes. Thus we applied these catalysts to the hydrogenolysis of D-sorbitol. Characterizations deduced that the conversion of D-sorbitol and the product distribution depends strongly on the basicity and surface area of Ni/Mg-Al-Ox. D-sorbitol converted mainly into erythritol and xylitol over M/Al2O3 and the conversion was relatively lower; while the main products over Ni/Mg1.22Al0.i2O1.40,Ni/Mg1.29Al0.06O1.38 and Ni/MgO were ethylene glycol, 1,2-propanediol and glycerol and the conversion increased. So it’s possible to control the conversion and product distribution of the hydrogenolysis of D-sorbitol via adjusting the composition of the catalysts.Different synthesis approach was applied in the preparation of Ni-Mg-Al layered double hydroxides. Mg-Al-Ox supported Ni catalysts mediated from these precursors still showed low catalytic activity in the hydrogenation of nitroarenes but it was active for the hydrogenolysis of D-sorbitol. Solvent-free approach was time-saving and avoided lots of wastes during the synthesis process. Compared to Ni-Mg-Al layered double hydroxides prepared via coprecipitation approach, Ni-Mg-Al layered double hydroxides prepared via solvent-free approach exhibited very different morphology (hexagonal plate-liked outline) under TEM observation and showed their superiority in specific surface area, surface basicity and Ni clusters distribution in their mediated catalysts. Thus Mg-Al-Ox supported Ni catalyst derived from solvent-free-prepared precursor exhibited superior catalytic activity to its counterpart.