Precious metals definition

Interactions between the precious metal and support influence the performance of the catalyst. Beil (1987) has defined metal-support interaction as depending on contact between the metal particle and the support which can be a dissolution of the dispersed metal in the lattice. The interaction could also depend on the formation of a mixed metal oxide, or the decoration of the metal particle surface with oxidic moieties derived from the support. It is possible that in this study, the differences in catalytic performance of the same active material supported on different washcoats can be attributed to any of these phenomena. Another explanation could be that the support materials exhibit different acid-base properties. According to the Bronsted and Lewis definitions, a solid acid shows a tendency to donate a proton or to accept an electron pair, whereas a solid base tends to accept a proton or to donate an electron pair. The tendency of an oxide to become positively or negatively charged is thus a function of its composition, which is affected by the preparation method and the precursors used. Refer to the section Catalyst characterization for further discussion on the influence of support material on catalyst performance. To thoroughly examine the influence of the support... 

The specific influence of non-precious metal oxide additives which definitely influence A/F windows will be reported in another study. 

The essential importance during stage of impregnation of SAPO material with precious metal is an origin of the latter. Usually tetraammine complexes of Pd or Pt are used for that purpose. Tetraammine complexes have definite composition and their water solution have practically neutral pH value. For the case of palladium loading we have checked the influence of another form of palladium, namely palladium dichloride, water solution of which possesses slightly acidic reaction. Catalytic data are presented in Table 4. 

It is perhaps not immediately obvious that the precious-metal catalysts that are employed for use in PEM fuel cells will be subject to degradation, agglomeration, and even dissolution. Most of us are familiar with platinum as an example of a noble metal, which, according to its definition, means that it resists chemical action and does not corrode. Yet there is compelling evidence that platinum can degrade under conditions experienced in the fuel cell operating environment. Within the catalyst and separator of the fuel cell, the conditions are quite acidic, and the presence of oxygen results in an environment that is extremely oxidative. 

The productivity is sometimes also related to the total mass of the catalyst, that is, to support plus active metal, but we recommend the definition according to Eq. (2.3.4) as the price of a catalyst is dominated by the metal that is used. The price of metals varies strongly over time. Thus, for a comparison, the actual prices should be used. In September 2010, the prices for some precious metals were 41 gpt, 14gpd 20gir 59gRh and 5 gR ... 

Supported noble-metal catalysts are still regarded as the most active systems for oxidation reactions when compared to transition-metal oxides, despite being more expensive and more sensitive to poisoning. A definite target of research in this field is the development of active catalysts using a combination of transition-metal oxides with the smallest possible amount of a precious metal. 

Gold is used in a wide range of industrial and medical applications and accounts for over 10 percent of the annual demand for metal, worth billions of dollars annually. While much has been written about the mystique and trade of gold, very little has been written about the science and technology in which it is involved. Edited by two respected authorities from the World Gold Council, Gold Science and Applications provides researchers with the definitive handbook on the current science and practical applications of this valuable and beautiful precious metal. 

In catalytic reactions with very expensive catalyst metals, for example, ruthenium, iridium, or platinum, it is of special interest to know how much mass of product, tttproduct, can be produced with a given mass of the precious catalyst metal, meat, metal, pct reaction time t. This important aspect leads to the definition of catalyst productivity according to Eq. (2.3.4) ... 

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