Oxidative catalytic materials applied

Catalysts were some of the first nanostructured materials applied in industry, and many of the most important catalysts used today are nanomaterials. These are usually dispersed on the surfaces of supports (carriers), which are often nearly inert platforms for the catalytically active structures. These structures include metal complexes as well as clusters, particles, or layers of metal, metal oxide, or metal sulfide. The solid supports usually incorporate nanopores and a large number of catalytic nanoparticles per unit volume on a high-area internal surface (typically hundreds of square meters per cubic centimeter). A benefit of the high dispersion of a catalyst is that it is used effectively, because a large part of it is at a surface and accessible to reactants. There are other potential benefits of high dispersion as well— nanostructured catalysts have properties different from those of the bulk material, possibly including unique catalytic activities and selectivities. 

Photoluminescence techniques will be applied to a broader range of systems, particularly oxide-supported sulfides (because of their important role in hydrotreating catalysis) as well as unsupported or oxide-supported (oxi)carbides or (oxi)nitrides (because of their growing importance as substitutes for noble metals and because they have metallic and acidic functions). Moreover, improved procedures for preparing catalytic materials will enable the design of tailored oxides with better defined characteristics, such as size, composition, and structure. The accumulation of data concerning the behavior of surface anions will also lead to a more refined view of the coordination chemistry of anions of nontransition elements. 

In the review by Armor [1] a variety of pollutants are discussed with a focus on commercially applied processes using catalysis as a solution. Issues such as the removal of NO.v, SO.v, chlorofluorohydrocarbons (CFC), VOC, carbon monoxide, auto exhaust emission, ozone, nitrous oxide, byproducts from chemicals production, odor control, and toxic gas removal are discussed. In another review Armor [2] discusses specific topics such as monolith technology, new catalytic materials, and specific processes. Additionally, key suggestions for future research effort are given. 

Decreasing operation temperature of solid oxide fuel cells (SOFCs) and electrocatalytic reactors down to 800-1100 K requires developments of novel materials for electrodes and catalytic layers, applied onto the surface of solid electrolyte or mixed conducting membranes, with a high performance at reduced temperatures. Highly-dispersed active oxide powders can be prepared and deposited using various techniques, such as spray pyrolysis, sol-gel method, co-precipitation, electron beam deposition etc. However, most of these methods are relatively expensive or based on the use of complex equipment. This makes it necessary to search for alternative synthesis and porous-layer processing routes, enabling to decrease the costs of electrochemical cells. Recently, one synthesis technique based on the use... 

Excellent summary lists of publications where the TAP technique is applied to different catalytic systems can be found in [79, 80]. These lists include the many types of catalytic materials that are studied including supported metals, mixed metal oxides, zeolites, metal particles, metals deposited on screens, catalytic monoliths, and nanoparticles or atoms deposited on microparticles, single crystals, and other model catalysts. 

Here the role of the particle is to couple the anodic oxidation of the reduced relay with H2 generation from water. The choice of the catalytic material may be based on the same considerations which apply for electrocatalytic reagents used on macroelectrodes the exchange current densities for the anodic and cathodic electron transfer steps must be high. Colloidal platin xm would then appear to be a suitable candidate to mediate reaction (6o). This fact was recognized already at the end of the last century when numerous examples for the intervention of finely divided Pt in the process of water reduction by agents such as Cr and V appeared in the german colloid literature. ... 

Depending on the mode of feeding of methane and oxidant, different catalytic materials are applied. When the OCM reaction is performed with cofed CH4 and O2, nonreducible metal oxides show higher C2 selectivity than reducible metal oxides. Promoting with alkaline earth and alkali metal oxides significantly enhances the selectivity to C2 hydrocarbons of reducible and nonreducible metal oxides [8,10-12]. Very recently, Ivanov et al. [22] demonstrated that MgO and SrO formed under reaction conditions and stabilized on the surface of Mg-, A1-,... 

Reducible metal oxides, which are able to provide their lattice oxygen for methane activation, are potential catalytic materials for alternating feeding of CH4 and O2. Mn- and Co-based perovskites were identified as effective catalysts for such OCM operation [24]. At best, the yield of C2 hydrocarbons of 20% with the corresponding selectivity of 73% was obtained at 1073 K over S1C0O3 doped with the oxides or hydroxides of K and Na applying a 1.5-min cycle of methane. However, the catalyst productivity remained still low. 

Over the past two decades, Raman spectroscopy has been extensively applied during catalytic oxidation reactions by mixed-metal oxides and metals under in situ and operando spectroscopy conditions, which has allowed the direct identification of the catalytic active sites involved in the oxidation reactions. Among the multiple spectroscopic techniques that can provide information about the catalytic active sites under oxidation reaction conditions, Raman spectroscopy is unique because of its ability to directly provide molecular level information that allows discrimination among the different catalytic active sites which may be present in the oxidation catalyst. This chapter provides a snapshot of the types of fundamental information obtainable by Raman spectroscopy, and the different types of catalytic materials and oxidation reactions that have been reported, especially under oxidation reaction conditions. 

Very different catalytic materials have been tested in the selective oxidation of propane, which includes vanadium phosphorous oxide (VPO) catalysts, industrially applied for w-butane oxidation to maleic anhydride. The other catalysts systems include Keggin structure heteropolyoxometalUc compounds (HPCs) and multicomponent mixed oxides (MMOs). These materials have different structure and properties, but have something in common they contain reducible metal 0x0 species. 

---