Metal oxides as promoters

Mn-promoted Fe-based Fischer-Tropsch Catalysts. 4.1.1 Unsupported Fe-Mn Fischer-Tropsch Catalysts. Iron-based F-T catalysts possess both hydrogenation and WGS activity, imposing a flexible option as a working catalyst for typically coal-derived CO-rich syngas conversion. Iron-based catalysts often contain small amounts of K and some other metals/metal oxides as promoters to improve their activity and selectivity. Mn has been widely used as one of the promoters for unsuppported Fe-based F T catalysts, particularly in promoting the production of C2 C4 olefins. ... 

The role of metal oxides as promoters of V2O5/Y-AI2O3 catalysts in the oxidative dehydrogenation of propane... 

Iron oxides with metal oxides as promoters can form two kinds of complex oxides ... 

Lopez Nieto, J. M., Coenraads, R., Dejoz, A., and Vazquez, M. I. The role of metal oxides as promoters of V Oj/y-AljOj catalysts in the oxidative dehydrogenation of propane. Stud. Surf. Sci. Catal. 110,443-452 (1997). 

Selective partial oxidation of hydrocarbons poses considerable challenges to contemporary research. While by no means all, most catalytic oxidations are based on transition-metal oxides as active intermediates, and the oxidative dehydrogenation of ethylbenzene to styrene over potassium-promoted iron oxides at a scale of about 20 Mt/year may serve as an example [1]. Despite this... 

Rhodium is a unique metal since it can catalyze several transformations.222,223 It is an active methanation catalyst and yields saturated hydrocarbons on an inert support. Methanol is the main product in the presence of rhodium on Mg(OH)2. Transition-metal oxides as supports or promoters shift the selectivity toward the formation of C2 and higher oxygenates. 

Therefore, at least on titania, transition metals promote the spillover of hydrogen to the support this is a necessary step in the reduction of the support (and hence modification of the global solid s catalytic properties). In other words, hydrogen spillover is a prerequisite in each of these recently recognized metal-support interactions (SMSI and IFMSI). Evidently these very specific metal-support interactions are, from the point of view of the spillover phenomena, merely the reduction of more or less easily reducible metal oxides, as mentioned in the preceding subsection. 

Interactions at oxide/salt contacts were suggested [61] to result in formation of a melt, which, after the initiation of decomposition, contained the ions Ca ", M", NO3, CF" and probably N02 . Reaction proceeds more rapidly in the liquid and the melting step was identified as exerting an important control on reactivity. The overall abilities of metal oxides to promote Ca(N03)2 decomposition decreased in the sequence ... 

This review analyzes the properties which are necessary for heterogeneous catalysts to promote the oxyfunctionalization of light paraffins to valuable chemicals. Three catalytic systems are discussed i) vanadium/phosphorus mixed oxide, the industrial catalyst for the oxidation of n-butane to maleic anhydride, which is here also examined for reactions aimed at the transformation of other hydrocarbons ii) Keggin-type heteropolycompounds, which are claimed for the oxidation of propane and isobutane, whose composition can be tuned in order to direct the reaction either to the formation of olefins or to the formation of oxygenated compounds iii) rutile-based mixed oxides, where rutile can act as the matrix for hosting transition metal ions or favour the dispersion of other metal oxides, thus promoting the different role of the various elements in the formation of acrylonitrile from propane. 

Catalysts considered in the present discussion cover a wide spectrum of solids reducible multivalent metal oxides as well as non reducible basic compounds Reducible metal oxides possess some inherent problems whereas these problems are less for the alkali ions promoted alkaline earth oxides. Alkaline earth oxides seem to be more suitable for working at low partial pressure of oxygen. By doping alkaline earth oxides with alkali metal compounds it is conceivable that O species can be stabilized for dissociative absorption of methane. Reducible metal oxides will tend to transform into lower valent oxides or even upto metallic state partly under applied reaction conditions specially at low partial pressure of O2. Both activity and selectivity will be deteriorated. But for the non reducible basic oxides structural changes will be quite different. They will tend to reach an equilibrium state in the surface level amongst the oxide, hydroxide and carbonate phases on reacting with evolved H2O and CO. Both the lattice distortion and the formation of O species can occur in the alkali earth oxides in doping with alkali ions as they can not build a mixed oxide lattice. 

Secondly, the topic addressed the quest for active and cost-effective noble-metal-free catalysts for DRM, an important reaction for mitigation of greenhouse effects and production of syngas. Manganese oxides as promoters for DRM catalysts showed superior promotional effects compared to other basic oxides and partially reducible oxides. Their role relied on the suppression of metal-catalyst deactivation and coke deposition. The use of manganese oxides as promotors for DRM is still growing, but the already obtained results anticipate great potential in their application. 

Other metals also have the abilities of adsorption of N2 without forming nitride. However, their capacity of chemisorption for nitrogen is so low that N2 cannot be activated. Copper has poor activity for N2, but copper surface can also chemisorbs N2 when the copper surface is activated by ion bombardment. In addition, CU3N is unstable. Reduced cobalt oxide as well as some noble metals (Ru, Rh, Os and Ir) can chemisorb nitrogen at room temperature in the presence of alkali oxides as promoters. ... 

Such compounds have two C-M bonds on the same carbon atom [3]. The first C-M bond serves to promote nudeophilic attack on the carbonyl compound, and the second fadlitates the subsequent j8-elimination of a metal oxide. As a result, an... 

While several of the oxidative techniques listed previously utilize transition metal complexes as promoters, the use of a completely organic photocatalyst for the oxidative synthesis of a-aminophosphonates has been reported (Scheme 4.108 and Example 4.27)... 

In contrast, numerous metal oxides—above all alumina (AI2O3) and magnesium oxide (MgO)—were identified as catalytic promoters. Moreover, combinations of several compounds may transform materials that by themselves have a neutral or even negative effect into promoters perhaps most notably, when combined with alumina, oxides of alkaline metals act as promoters. Appl marvels at how well Mittasch identified the optimal catalyst for ammonia synthesis for temperatures up to 530 °C and pressures up to 35 MPa. ° Most commercial catalysts on the market today are just slight variations on Mittasch s basic theme they use magnetite with 2.5-4% AI2O3, 0.5-f.2% K2O, 2.0-3.5% CaO, and 0-1.0% MgO (as well as 0.2-0.5% Si present as a natural impurity in the metal). ... 

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