Toward a molecular understanding of catalyst preparation
- 出版日期：2004.
- 页数：1 v. :
- 第一责任说明：Marc R. Schreier.
- 分类号：a873
- ISBN：0496149601(ebk.) :
MARC全文
02h0031094 20120912143255.0 cr un||||||||| 120629s2004 xx ||||f|||d||||||||eng | 3154475 0496149601(ebk.) : CNY371.35 NGL NGL NGL a873 Schreier, Marc R. Toward a molecular understanding of catalyst preparation [electronic resource] / Marc R. Schreier. 2004. 1 v. : digital, PDF file. Adviser: Regalbuto, John R.,eadvisor. Thesis (Ph.D.)--University of Illinois at Chicago, 2004. Among the simplest, least expensive, and most prevalent preparation methods in the manufacture of heterogeneous catalyst is the process of impregnation, whereby high surface area porous supports such as silica and alumina are contacted with aqueous solutions containing dissolved metal complexes. Much recent progress in the "transformation of the art of catalyst preparation into a science" has been made in catalyst preparation through fundamental studies of the adsorption process. A landmark work is the postulation of Brunelle that the adsorption of noble metal complexes onto common oxide supports was essentially coulombic in nature. The hydroxyl groups which populate the oxide surface become protonated and so positively charged or deprotonated and negatively charged above and below a characteristic pH value. This pH value, at which the surface is neutral, is termed the point of zero charge PZC). By understanding the nature of the charging mechanism of the oxide, adsorption of cationic and anionic metal complexes can be predicted by the revised physical adsorption RPA) model. The RPA model and more recently the simplified RPA model are based solely on electrostatic interactions between the oxide surface and metal complexes in solution. In this study, experimental adsorption data of platinum tetraamine PTA, PtNH3)4＋2) and chloro-platinic acid CPA, PtCl6-2) onto silica, ceria, titania and zirconia as a function of pH is presented. Comparisons between control experiments platinum free) and adsorption experiments, ability to simulate adsorption and pH shift data with one set of parameters using the RPA and pH shift models, suggest that the majority of the adsorption processes over such oxide supports are essentially electrostatic in nature. In an effort to obtain fundamental charging parameters of the oxide surface, such as the PZC, intrinsic surface acidity constants K1 and K 2) and the hydroxyl density on the surface, an optimization procedure was developed to determine such parameters from titration data, using the previously mentioned pH shift model. These parameters, obtained independent of adsorption experiments, when used in the RPA model, provide reasonable fits to platinum adsorption data over alumina and silica. Lastly, comparisons between the adsorption of platinum and copper tetraammine complexes over silica and zeolites are made to identify the "over exchange" nature of the Cu/ZSM5. Zeolites are well known to be able to exchange ＋2 charged cations into their cage like structure in a ratio of 1:2 due to substituted alumina. This study found that not only do zeolites have the ability to exchange cations in the acidic region, but found that they also have the ability to attract cations through electrostatic mechanisms in the basic region, above the 100% exchange level. Catalysts Synthesis. aeBook. aCN bNGL http://pqdt.bjzhongke.com.cn/Detail.aspx?pid=w1HoMZ%2byYww%3d NGL Bs1648 rCNY371.35 ; h1 bs1205