Selective catalytic oxidation materials

Attempts to achieve selective oxidations of hydrocarbons or other compounds when the desired site of attack is remote from an activating functional group are faced with several difficulties. With powerful transition-metal oxidants, the initial oxidation products are almost always more susceptible to oxidation than the starting material. When a hydrocarbon is oxidized, it is likely to be oxidized to a carboxylic acid, with chain cleavage by successive oxidation of alcohol and carbonyl intermediates. There are a few circumstances under which oxidations of hydrocarbons can be synthetically useful processes. One group involves catalytic industrial processes. Much effort has been expended on the development of selective catalytic oxidation processes and several have economic importance. We focus on several reactions that are used on a laboratory scale. 

The need to conserve raw materials and enhance the yield of high-value products has led the petrochemical industry to rely increasingly on processes that involve catalytic selective oxidation. In turn, this reliance has led to the emergence of important new technologies in the past decade—processes that use selective catalytic oxidation now generate almost a quarter of all organic chemicals produced worldwide. 

Nassos S, Svensson EE, Boutonnet M, Jaras SG (2007) The influence of Ni load and support material on catalysts for the selective catalytic oxidation of ammonia in gasified biomass. Appl Catal B Environ 74 92... 

Selective catalytic oxidations using oxygen as terminal oxidant is a topic of much current interest due to the cost-effectiveness and greenness of these processes compared to the use of other chemicals as oxidants. In this regard aerobic oxidation of benzylic alcohols in addition of being an important process from the industrial point of view has become a preferred test reaction to rank the catalytic activity of various materials. Palladium NPs... 

Temperature-programmed oxidation (TPO) is an equally valuable technique for investigating the oxidation kinetics and mechanisms of reduced materials. The cyclic application of TPR and TPO provides information on the redox behavior of catalytic materials, for example, of catalysts for selective catalytic oxidations. 

A new material based on Pt and Co exdianged in NaMordenite for the selective catalytic reduction (SCR) ofnitiic oxide with methaneinthepresence of excess oxygen is studied. The incorporation of... 

A wide range of catalytic materials have been investigated for the selective catalytic reduction of NOx. For stationary emissions, NH3-SCR using vanadium-tungsten oxides supported on titania is the most used method however, when there is a simultaneous emission of NO and NOz (in tail gas from nitric acid plants), copper-based zeolites or analogous systems have been proven to be preferable [31b], In fact, there are two main reactions for NH3-SCR ... 

As in other fields of nanosdence, the application of STM techniques to the study of ultrathin oxide layers has opened up a new era of oxide materials research. New emergent phenomena of structure, stoichiometry, and associated physical and chemical properties have been observed and new oxide phases, hitherto unknown in the form of bulk material, have been deteded in nanolayer form and have been elucidated with the help of the STM. Some of these oxide nanolayers are and will be of paramount interest to the field of advanced catalysis, as active and passive layers in catalytic model studies, on the one hand, and perhaps even as components in real nanocatalytic applications, on the other hand. We have illustrated with the help of prototypical examples the growth and the structural variety of oxide nanolayers on metal surfaces as seen from the perspective of the STM. The selection of the particular oxide systems presented here refleds in part their relevance in catalysis and is also related to our own scientific experience. 

In catalytic processes, such as CO conversion (CO + H20 —> C02 + H2), selective methanisation (CO + 3 H2 —> CH4 + H20) or selective CO oxidation (CO + Vi 02 —> C02), the achievable efficiencies depend on reaction parameters, such as temperature, pressure, volume flow, raw gas concentration and catalyst material. These are capable of achieving contamination levels from 1 % down to a few ppm. The selection of different reaction paths is based on the use of different types of catalyst. 

The calcined iron-grafted materials exhibit high selectivity as catalysts for oxidations of alkanes, alkenes and arenes with H2O2 as the oxidants [13a]. A similar method has been used by Tilley et al. to prepare a pseudotetrahedral (Co(II) [Co(4,4 -di Bu-bipy) OSi(0 Bu)3 2]) complex grafted onto the SBA-15 surface and subsequently use it in catalytic oxidation of alkylaromatic substrates with tert-butyl hydroperoxide [14]. Unfortunately, neither iron nor cobalt surface organometaUic compounds have been tested in the recycled catalytic system. 

The present chapter will primarily focus on oxidation reactions over supported vanadia catalysts because of the widespread applications of these interesting catalytic materials.5 6,22 24 Although this article is limited to well-defined supported vanadia catalysts, the supported vanadia catalysts are model catalyst systems that are also representative of other supported metal oxide catalysts employed in oxidation reactions (e.g., Mo, Cr, Re, etc.).25 26 The key chemical probe reaction to be employed in this chapter will be methanol oxidation to formaldehyde, but other oxidation reactions will also be discussed (methane oxidation to formaldehyde, propane oxidation to propylene, butane oxidation to maleic anhydride, CO oxidation to C02, S02 oxidation to S03 and the selective catalytic reduction of NOx with NH3 to N2 and H20). This chapter will combine the molecular structural and reactivity information of well-defined supported vanadia catalysts in order to develop the molecular structure-reactivity relationships for these oxidation catalysts. The molecular structure-reactivity relationships represent the molecular ingredients required for the molecular engineering of supported metal oxide catalysts. 

Partial oxidation of cyclohexane at the cathode of an 02/H2 fuel cell takes place at ambient temperature.197 Catalytic oxidation with 100% selectivity of the formation of cyclohexanol and cyclohexanone is achieved. Of the cathode materials comprising a mixture of alkaline-earth or rear-earth metal chlorides and graphite, the one which contains SmCl3 exhibits the highest activity. 

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