Heterogeneous catalyst supported metal catalysts

XPS is the most commonly used and most useful surface analysis method in catalyst characterization. It can be used for both qualitative and quantitative analysis for almost all kinds of catalysts used in heterogeneously catalyzed reactions. XPS studies of oxide, sulfide, fluoride, halide, etc., catalysts,. supported metal catalysts, Raney or gauze metal catalysts and zeolite catalysts are all possible. The samples can be studied in any of the precursor, calcined, reduced, activated, deactivated, aged or poisoned states. Real industrial catalysts can be analyzed as well as fundamental model systems. Quantitative analysis is possible either with the help of empirical sensitivity factors or by standard-free methods. In the latter case appropriate theoretical models are u.sed with photoionization cross-section tables, inelastic mean free path (X.) data and individ-... 

Heterogeneous vapor-phase fluorination of a chlorocarbon or chlorohydrocarbon with HP over a supported metal catalyst is an alternative to the hquid phase process. Salts of chromium, nickel, cobalt or iron on an A1P. support are considered viable catalysts in pellet or fluidized powder form. This process can be used to manufacture CPC-11 and CPC-12, but is hampered by the formation of over-fluorinated by-products with Httle to no commercial value. The most effective appHcation for vapor-phase fluorination is where all the halogens are to be replaced by fluorine, as in manufacture of 3,3,3-trifluoropropene [677-21 ] (14) for use in polyfluorosiHcones. 

These were prepared by tethering Rh and Pt complexes to silica-supported metal catalysts (metal = Pd, Ni, Ru, Au). The catalysts are very active in the hydrogenation of benzene derivatives to the corresponding substituted cyclohexanes under mild conditions. The activities are higher than those of the separate homogeneous complexes, complexes just tethered to silica, or the silica-supported heterogeneous catalysts. When the sol-gel-entrapped [Rh2Co2(CO)12] complex was heat-treated at 100°C, immobilized metallic nanoparticles were formed.425 The catalyst thus prepared efficiently catalyzed substituted benzene derivatives. 

As for hydrogenation, heterogeneous catalytic oxidation of carbohydrates was essentially performed in the presence of carbon-supported metal catalysts, namely Pt, Pd or Bi-doped Pd.[57] Oxidation of glucose into gluconic acid, the worldwide production of which is around 60000 tons year 1,[52] is used in the food and pharmaceutical industry, and is produced today by enzymatic oxidation of D-glucose with a selectivity in gluconic acid close to 100%. 

Since the late 1960s there has been some interest in the concept of a structure-sensitive reaction in heterogeneous catalysis (177, 178). In the case of supported metal catalysts, structure sensitivity is visualized as a dependence of metal particle size and catalytic behavior in a given reaction (activity and selectivity). Almost all of the possible kinds of relationships were reported in the past. Recently, Che and Bennett reviewed this problem (161). Our intention here is not to repeat most of their analysis, rather we shall try to present our view on the general characteristics of palladium versus other platinum metals. 

We report here some results of an exploratory project on the HDN activity of [M(PC) ] where M represents a variety of metals. We have chosen first to study the model compound quinoline. The [M(PC)] catalyst were supported on high surface area inorganic oxides to produce heterogenized catalysts. The solid catalysts are convenient to study because of the ease of separation and process adaptability. Further, due to the low solubility of [M(PC)] in almost all solvents, the high surface area supported catalysts are expected to have a considerably higher effective concentration of [M(PC)] than the small portion of [M(PC)] that is in homogeneous solution or the low surface area solid [M(PC)]. 

The complexity of many heterogeneous systems used in multi-phase reactions, the use of a solid support, the difficulty in analyzing highly dispersed active sites and the bifunctional nature of many solid supported metal catalysts, make a detailed and complete study challenging. The simpler homogeneous systems teach many of the principles of catalysis active sites, reaction mechanisms, reaction kinetics and catalytic cycles, which can often be applied elsewhere. 

Strength (FLS) empirical approach are discussed in Section 3 as methods for determining the molecular structures of metal-oxide species from their Raman spectra. The state-of-the-art in Raman instrumentation as well as new instrumental developments are discussed in Section 4. Sampling techniques typically employed in Raman spectroscopy experiments, ambient as well as in situ, are reviewed in Section S. The application of Raman spectroscopy to problems in heterogeneous catalysis (bulk mixed-oxide catalysts, supported metal-oxide catalysts, zeolites, and chemisorption studies) is discussed in depth in Section 6 by selecting a few recent examples from the literature. The future potential of Raman spectroscopy in heterogeneous catalysis is discussed in the fmal section. 

This work demonstrates that supported heterogeneous Platinum Group Metal catalysts are very effective for the selective oxidation of primary alcohols to aldehydes and secondary alcohols to ketones using air as the oxidant. 

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