Propane supported metal oxide catalyst

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. 

The characterization of the surface of supported metal oxide catalysts is vital to the understanding of many catalytic reactions. Supported chromium oxide catalysts are used for many industrial catalytic processes. Chromium oxide supported on alumina is used as a catalyst for propane and butane dehydrogenation. " Determination of the surface structure under reaction conditions is important for a complete understanding of the catalyst system. 

Metal oxide catalysts are extensively employed in the chemical, petroleum and pollution control industries as oxidation catalysts (e.g., oxidation of methanol to formaldehyde, oxidation of o-xylene to phthalic anhydride, ammoxidation of propylene/propane to acrylonitrile, selective oxidation of HjS to elemental sulfur (SuperClaus) or SO2/SO3, selective catalytic reduction (SCR) of NO, with NHj, catalytic combustion of VOCs, etc.)- A special class of metal oxide catalysts consists of supported metal oxide catalysts, where an active phase (e.g., vanadium oxide) is deposited on a high surface area oxide support (e.g., alumina, titania, ziiconia, niobia, ceria, etc.). Supported metal oxide catalysts provide several advantages over bulk mixed metal oxide catalysts for fundamental studies since (1) the number of surface active sites can be controlled because the active metal oxide is 100% dispersed on the oxide support below monolayer coverage,... 

Partial oxidation of propane with air in CO2 up to 400" C and 113 bar, over supported metal oxide catalysts in a flow reactor, revealed an increase in total... 

In the case of alumina (or other simple oxides), the reaction occurs at high temperatures and under low space velocity conditions. The activity was found to be improved by the addition of platinum group metals [13, 14] and of transition metal oxides [15], especially copper [16, 17, 18]. For alumina-supported copper oxide catalysts a maximum effect has been found by the addition of 0.3 wt % Cu and it has been considered that, for higher copper contents, the formation of cupric oxide would give a solid selective for the oxidation of the hydrocarbon by oxygen [16]. In the case of alumina-supported Cu-Cs oxide catalysts the formation of an isocyanate species has been evidenced by exposition to mixtures "nitric oxide/oxygen/propene (or acetylene)" but not with propane [18, 19], In fact the mechanism of the reaction and the nature of the active sites are still unknown. 

Catalysts based on other metals, such as gallium and vanadium oxides, can be also employed in DH processes [8, 9]. For example, silica-supported gallium oxide catalyst has been found to be moderately active, but quite selective in propane dehydrogenation (up to 80%) and results in much less coking, 1/10 of that using a silica-supported chromium oxide [8], There is an extensive research aimed to find new DH catalysts that will perform well at moderate temperatures, suffer less from coke deposition and maintain catalytic activity for long periods of time without regeneration. 

Improvements in acrylonitrile yield are also reported with other vapor phase promoters. A patent assigned to Monsanto Co. (125) describes the use of sulfur and sulfur-containing compounds in the feed gas mixture for production of acrylonitrile or methacrylonitrile from propane or isobutane over metal oxide catalysts. Examples of effective sulfur-containing compounds include alkyl or dialkyl sulfides, mercaptans, hydrogen sulfide, ammonium sulfide, and sulfiir dioxide. Best results are apparently achieved using a molar ratio of sulfur (or sulfur compound) to hydrocarbon of 0.0005 1 to 0.01 1. Nitric oxide has also been examined as a gas-phase promoter for propane and isobutane ammoxidation (126). However, it does not appear to be as effective as halogen or sulfur. Selectivities to acrylonitrile from propane are only about 30% over an alumina-supported chromium-nickel oxide catalyst. 

Propane Dehydrogenation over Supported Molybdenum Catalysts. The combined energy-dispersive (ED)-XAFS, UV-Vis, and Raman represents a powerful device that couples three spectroscopic techniques in one reactor, which probes the same part of a metal oxide catalyst under true reaction conditions and is capable of delivering subsecond time resolution. A scheme of the setup is given in Figure 32. 

Liu S, Xu L, Xie S, Wang Q, Xiong G (2001) Partial oxidation of propane to syngas over nickel supported catalysts modified by alkali metal oxides and rare-earth metal oxides. Appl Catal A-Gen 211 145-152... 

The physicochemical properties of potassium-, bismuth-, phosphorous- and molybdenum-doped (MeA7 atomic ratios of 0 to 1) V2O5/Y-AI2O3 catalysts and their catalytic behavior in the oxidative dehydrogenation of propane have been compared. The incorporation of metal oxides modifies the catalytic behavior of alumina-supported vanadia catalysts by changing both their redox and their acid-base properties. In this way, the addition of potassium leads to the best increase in the selectivity to propylene. This performance can be related to the modification of the acid character of the surface of the catalysts. The possible role of both redox and acid-base properties of catalysts on the selectivity to propylene during the oxidation of propane is also discussed. 

Supported vanadium oxides have been proposed as selective catalysts in partial oxidation reactions [1] and more specifically in the oxidative dehydrogenation (ODH) of short chain alkanes [2, 3]. However, it has been observed that the catalytic behavior of these catalysts during the oxidation of alkanes depends on the vanadium loading and the acid-base character of metal oxide support. In this way, alumina-supported vanadia catalysts with low V-loading are highly active and selective during the ODH of ethane [4-7] and propane [8] but they show a low selectivity in the ODH of n-butane [4, 5, 9, 10]. 

The catalytic behavior of vanadium-based catalysts can be generally modified with the addition of a second element which acts as promoter. In this paper we present a comparative study on the catalytic properties in the ODH of propane of undoped and Me-doped Al203-supported vanadium catalysts, in which metal oxides with redox and/or acid-base properties (K, Bi, Mo, P) have been used as potential promoters. 

In conclusion, this paper shows the effect of the addition of different metal oxides (K, Bi, P and Mo) on the catalytic behavior of an alumina-supported vanadia catalysts in the ODH of propane. In all cases, the addition of small amounts of metal oxide (MeA/ atomic ratio of 0.1) increases the selectivity to propylene, probably as a consequence of the elimination of non selective sites (Lewis acid sites) on the surface of the support. However, only in the case of K-doped catalysts the selectivity and the yield of propylene increases with the metal content. The varition of the acid-base character of catalysts and its influence on the adsorption/desorption of reactants and products could be responsible of the different performances obsen/ed. In this way. 

Reducing gas used for the treatment of metals in industry can be produced from propane in the presence of air or O2 over a supported metal catalyst with high selectivity towards CO+H2 formation. This process is performed at temperatures higher than 800°C. There are several different reactions for high temperature propane oxidation in the presence of air [1]. 

In order to stabilize noble metals during rich or lean excursions at high temperature, the role of three other supports have been studied. Tables 3 and 4 give the activities in oxidation and steam reforming of propane of PtRh bimetallic catalysts. 

The present work is concerned with the influence of the pretreatment of an alumina-aerogel supported Pd catalyst on its activity in propane oxidation. The state of Pd and the crystalline state of alumina aerogel were investigated by grazing-incidence X-ray diffraction (GIXD). To our knowledge, this method is applied for the first time to supported metal catalysts. In addition, a comparison of the structural and catalytic oxidation properties of Pd, Pt and Pt-Rh supported on alumina carriers was made. 

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