Design, Synthesis And Catalytic Performance Of Nanocrystal Catalysts

The development of efficient catalysts is important for promoting technological innovation, changing the industrial landscape and raising labor productivity. Heterogeneous catalysts are applied widely in the production of bulk chemicals. The two most important factors determining catalytic performance of heterogeneous catalysts are their electronic and structural properties. In the traditional research of heterogeneous catalysts, we often use electronic aids, such as alkaline compounds, to regulate the electronic properties of catalysts, and use different carriers or change the preparation methods to adjust the structural properties of catalysts. In recent years, the study of inorganic nanocrystals has developed rapidly. The electronic properties of nanocrystals may be different from those of traditional materials, as the geometry and size of nanocrystals can regulate the electronic properties. Furthermore, the small size of nanocrystals readily excludes impurities, allowing easy formation of a single crystal structure. This makes the surface a relatively simple structure, allowing specific catalytic reactions brought about by structural match between the surface and the reactants. Both of them are needed for the development of new heterogeneous catalysts. Therefore, the studies of the synthesis, properties and catalytic performances of nanocrystals may bring new opportunities for the development of new heterogeneous catalysts. The purpose of this paper is to develop nanocrystals preferentially exposing high activity crystal faces and to study their properties and examine their catalytic performance.(1).γ-Al2O3 is the most important and widely used industrial catalyst carrier. When prepared using traditional techniques, γ-Al2O3 preferentially exposes the most thermodynamically stable (110) planes. The (111) planes of γ-Al2O3 have higher atomic density, higher surface energy and stonger surface acidity compared with its (110) planes. According to γ-Al2O3 crystal structure analysis and density functional quantum chemical calculation, using it as a carrier may produce a new type of catalyst. According to the pseudomorphism rules, (101) planes of boehmite correspond with the (111) planes of γ-Al2O3. AlOOH nanotubes preferentially exposing (101) planes were prepared using oleic acid root as a protective agent of high energy (101) planes of AlOOH and a structural assembly agent of AlOOH colloidal particles. Then, γ-Al2O3 nanotubes preferentially exposing (111) planes were obtained by annealing AlOOH nanotubes preferentially exposing (101) planes at high temperature. The examination of surface structure and catalytic performance of γ-Al2O3 nanotubes preferentially exposing (111) planes confirms that γ-Al2O3 nanotubes preferentially expose the (111) planes, which have higher density of hydroxyl, higher acidic density and higher strength of acid compared with (110) planes. Thus, they have better catalytic performance for ethanol dehydration to ethylene. (2). A series of supported catalysts (CuO/γ-Al2O3, Pd/γ-Al2O3, etc.) with different loadings were made using the above-prepared γ-Al2O3 nanotubes with preferentially exposed (111) planes and the conventional γ-Al2O3 with preferentially exposed (111) planes as carriers, respectively. The detailed measurements of the dispersion state of the active component, the interactions of carrier and active component and the catalytic performance for the two kinds of catalyst indicated that γ-Al2O3 (111) planes disperse the active component more readily and have stronger interactions with the active component compared with γ-Al2O3 (110) planes, and the catalytic performance of supported copper catalyst for oxidation and supported Pd catalyst for hydrogenation using γ-Al2O3 nanotubes as carriers are different from the corresponding catalysts that use conventional γ-Al2O3 as carriers. (3). A simple process is designed to prepare ceria nanocubes covered by oleic acid with exposed (100) faces using oleic acid root as a protective agent. This catalyst is applied to liquid phase selective oxidation of toluene under mild reaction conditions and it has a particularly high selectivity for benzaldehyde. Thus, this paper presents a novel reaction mechanism for nano-scale catalytic phase transfer.