| p-Phenylenediamine and p-Chloroaniline are two kinds of important chemicalintermediates and fine chemical products. They are widely used in rubber, dyes,chemical reagents, and pharmaceutical industry. The current preparing ways of theseamino compounds include catalytic reduce reaction by ferrous powders, electrolyticprocess, catalytic hydrogenation, etc. Although industrial method is well-established,it has low conversion and poor selectivity and will cause severe environmentalcontamination as well. Au nanoparticles are newly arisen high efficient catalysts.They can catalyze selective oxidation of alcohol/aldehyde, sugar and its analogues, etc,as well as reduction of unsaturated aldehyde/acetone, nitro-compounds, etc. And itsapplication in catalyzing nitrobenzene compounds begins to be studied. The catalyticperformance of gold catalyst is affected by the particles size. With large particle size,the catalyst shows poor activity. The clotting and aggregation of gold particles duringpreparation also limit its further application. Therefore, the highly dispersing of goldnanoparticles on the support is the key point to guarantee high activity of gold catalyst.Currently, there are three common preparation strategies to obtain hybrid particles,including layer-by-layer self-assembling, impregnation, and seed-mediatedpreparation. Although these methods are simple and facile, they all involve theproblem of gold leakage which compromises the functional ability in application.To overcome problems mentioned above, we introduced a new method to preparegold-magnetic composites here. In this new template method, urea and formaldehyde(UF) condensed in acid condition, embedding gold nanoparticles, magnetic particlesand Si sols in it. After removal of UF by calcination, gold-magnetic composites wereobtained. Then as-prepared composites were applied to catalyze reduction ofnitrobenzene compounds. The research contents include3parts:1) preparation,characterization and stability study of gold nanoparticles;2) preparation andcharacterization of gold-magnetic composites;3) catalytic activity assessment ofgold-magnetic composites in reduction of nitrobenzene compounds.First, gold nanoparticles were prepared in two ways. One kind was obtained byreduction of citrate/tannin, whose size ranged from5-10nm. The second kind wasprepared with sodium borohydride as reductive agent and polyethylenimine as stabling agent, whose size was less than5nm. The as-prepared Au NPs had goodsphere shape and dispersibility. Compared to the first kind Au NPs, the second kindshowed good stability in both extreme acid and alkaline condition, which was moresuitable for the preparation of gold-magnetic composites by template method.Second, different gold-magnetic composites were prepared in layer-by-layerassembling, seed-mediated reduction and template method. Characterization ofas-prepared gold-magnetic composites included UV-Vis spectrum, high resolutiontransmission electron microscopy (HRTEM), energy spectrum analysis, and vibrationsample magnetometer. Results showed that the as-prepared gold-magnetic compositeshad good sphere shape and magnetic property. Gold nanoparticles were highlydispersed in the matrix without clotting and aggregation. What’s more, the porousstructure of composites facilitated mass transfer during the application.At last, the as-prepared gold-magnetic composites were applied to catalyzing thereduction of nitrobenzene compounds in liquid phase. The results showed that theyhad high catalytic activity and were convenient to separate and re-disperse inapplication. Particularly, gold-magnetic composites had better selectivity than Fe3O4particles, avoiding the generating of byproducts.In summary, gold-magnetic composites show high activity and selectivity incatalyzing reduction of nitrobenzene compounds, which indicates their promisingfuture in application. Meanwhile, template method provides a facilitatory andeffective way to prepare stable and high efficient supported gold catalyst. |
PDF Full Text Request