Titanium Dioxide (Anatase and Rutile): Surface Chemistry, Liquid-Solid Interface Chemistry, and Scientific Synthesis of Supported Catalysts

摘要

Solid catalysts are very useful functional materials, which are used in 90% of industrial processes. The most important are the supported ones. In these catalysts, nanoparticles of an active element (metal, oxide, or sulfide) are dispersed on the surface of a carrier with high surface area. In most of the cases, the synthesis starts with the impregnation (immersion) of powder or preshaped bodies of a carrier with (inside) an electrolytic solution containing the precursor species of the active element to be deposited. The control of the impregnation step is, in effect, essential for preparing very active and selective catalysts. This control requires the understanding, at molecular level, of the deposition processes taking place at the interface developed between the carrier surface and the solution upon impregnation. The above can not be realized without the knowledge of the interface structure. Thus, interfacial chemistry can help toward a scientific synthesis of supported catalysts. On the other hand, the knowledge of the surface chemistry (surface science) of a solid used as a carrier is an essential prerequisite for understanding the relevant interfacial chemistry and then the fundamental deposition processes taking place upon impregnation. Thus, in view of the above requirement for a controlled synthesis of supported catalysts at molecular level, we realize that we need more chemistry to shift catalyst synthesis from the art to the science. We need three different disciplines to come in contact: surface chemistry, interface chemistry, and scientific synthesis of solid catalysts.