Vanadia-alumina catalyst

Table 15.1 Extent of oxygen removal during reduction of vanadia/alumina catalysts.

Figure 15.8 Desorption of butane at room temperature in a flow of 2% 02/Ar from vanadia/alumina catalysts after butane dehydrogenation at 873 K and 1 bar.

Nam, Eldridge and Kittrell studied the pore size distribution for vanadia/alumina catalysts for the removal of NOx by reaction with ammonia. The pore size distributions are found to change dramatically as sulfur poisons the de-NOx reaction. The smallest pores (<10 nm in radius) are found (by porosimetry) to be filled first. As a result the surface decreases by up to 90% with 12% sulfur content, although the pore volume decreased by only 20%. The associated de-NOx activity decreased substantially. It was proposed that ammonium sulfate, bisulfate, or aluminum sulfate formed on the surface to deactivate the catalyst. 

Since exploratory experimental work on the interaction of NO with NH3 in air using vanadia-alumina catalyst indicated a large catalyst bed temperature rise, effort was concentrated on this system. Other oxidation catalysts appeared less attractive than vanadia because their known activity for CO and H2 oxidation could cause interference from these... 

Studies were made over a range of temperatures, flow rates, and NH3/NO ratios. The position of the thermocouple probe tip in the catalyst bed was fixed at 0.125 in. of catalyst ahead of the tip. Catalyst bed diameter was 0.128 in., the volume 0.026 cm3. The vanadia-alumina catalyst was the same used for prior work on HC oxidation (I). Am-... 

Since vanadium oxide had been used as an effective catalyst for the dehydrogenation of hydrocarbons, it was expected from purely thermodynamic considerations that conditions could be found for the reverse reaction of hydrogenation to take place. Experiments carried out in our laboratory with coprecipitated vanadia-alumina catalyst showed this to be true. 

The x-ray diffraction pattern of the coprecipitated vanadia-alumina catalyst 6) showed that the amount of vanadium trioxide formed by the reduction of the pentoxide increases rapdily as the temperature of reduction approaches 400°. In fact all three phenomena, the absorption of hydrogen. 

Oxidation of benzothiophene by tert-butyl hydroperoxide over vanadia-alumina catalyst... 

Gomez-Bernal, H., Cedeno-Caero, L., Finocchio, E., et al. (2009). Oxidation of benzothio-phene by tert-butyl hydroperoxide over vanadia-alumina catalyst An FTIR study at the vapour-solid interface, Catal, Commun., 10, pp. 1629-1632. 

Shiju, N., Anilkumar, M., Mirajkar, S., ef al. (2005). Oxidative dehydrogenation of ethylbenzene over vanadia-alumina catalysts in the presence of nitrous oxide structure-activity relationship, J. Catal., 230, pp. 484-492. 

Other metal oxide catalysts studied for the SCR-NH3 reaction include iron, copper, chromium and manganese oxides supported on various oxides, introduced into zeolite cavities or added to pillared-type clays. Copper catalysts and copper-nickel catalysts, in particular, show some advantages when NO—N02 mixtures are present in the feed and S02 is absent [31b], such as in the case of nitric acid plant tail emissions. The mechanism of NO reduction over copper- and manganese-based catalysts is different from that over vanadia—titania based catalysts. Scheme 1.1 reports the proposed mechanism of SCR-NH3 over Cu-alumina catalysts [31b],... 

Under these conditions an average yield of 43% was obtained. Increased yields (50-69%) were found with the use of a coprecipitated vanadia-alumina (35 % V2O6-65 % AI2O3) catalyst and with 40-atm. pressure of hydrogen in a continuous high-pressure flow system. The general utility of this reaction was demonstrated by the conversion of n-butyl, f-butyl, n-hexyl, and n-octyl alcohols to corresponding paraffin hydrocarbons. Recently, this work was extended to secondary aliphatic, as well as aromatic alcohols, with similar results (4)-... 

A possible mechanism for the effect of vanadia is suggested by the observation that vanadium oxide severely reduces the propensity of a Pt/alumina catalyst to store sulfate. It seems reasonable to speculate that SO2 oxidation on Pt/alumina involves adsorption of SO2 onto the alumina surface, with migration ( spillover ) of a sulfite species onto neighboring Pt crystallites and/or of oxygen atoms from the Pt onto the support. Coverage of alumina with high-valent vanadia can, because of its acidic nature, reduce affinity for SO2 and thereby disrupt the mechanism. 

Examples of space velocities used for heavy-duty diesel applications with vanadia SCR catalysts are in the range 20,000-70,000 h [6, 18, 34, 35]. Havenith et al. [6] used 51 dm of washcoated vanadia/alumina SCR catalyst volume, corresponding to a space velocity of 28,000 h for a 12 1 heavy-duty engine, van Helden et al. [35] used 34 dm of washcoated vanadia SCR catalyst volume (space velocity 45,000 h ) for a 12.0 and a 12.6 1 heavy-duty engine. Hofmann et al. [36] used the same SCR catalyst volume (34 dm ), but with a fully extruded vanadia SCR catalyst for a 12 1 heavy-duty diesel engine. 

In 1975, Ohloff etal. studied the gas-phase oxidation of ot-isophorone to KIP over a vanadia/pumice catalyst modified with 1 wt% of hthium phosphate at 230°C. Under these conditions, simultaneous formation of KIP and formylisophorone occurred. More than 20 years later, Baiker et al. revisited the catalytic gas-phase oxidation of isophorone. At 200-250°C, 75% combined yields of KIP and formyhsophorone were obtained at 17% ot-isophorone conversion over vanadia/pumice impregnated with hthium phosphate j6-isophorone was found as a major by-product (18%). Bismuth molybdate or vanadium phosphate showed poor selectivity and rapid deactivation. The Ag/y-alumina-catalysed oxidation was unselec-tive and resulted mainly in isomerisation to j6-isophorone. Chromia-based catalysts led to an increased formation of 3,5-xylenol. To efficiently remove coke deposits and to re-oxidise vanadium oxides to vanacha, temperatures higher than 300°C would be needed however, under these conditions isophorone and KIP are not stable. Thus, highly selective catalysts would be required which are active at lower temperatures. 

Planar model catalysts with similar compositions (such as vanadia-silica, vanadia-alumina on NiAl(l 10), and vanadia on Ce02(l 11) monocrystal faces) have been recently investigated with surface science techniques such as infrared reflection absorption spectroscopy Although the authors claim that these studies... 

Active heterogeneous catalysts have been obtained. Examples include titania-, vanadia-, silica-, and ceria-based catalysts. A survey of catalytic materials prepared in flames can be found in [20]. Recent advances include nanocrystalline Ti02 [24], one-step synthesis of noble metal Ti02 [25], Ru-doped cobalt-zirconia [26], vanadia-titania [27], Rh-Al203 for chemoselective hydrogenations [28], and alumina-supported noble metal particles via high-throughput experimentation [29]. 

DeNOx (3) A Denox process for removing nitrogen oxides from the gaseous effluents from chemical plants. The catalyst is vanadia on alumina. Developed by Rhone-Poulenc in the 1970s and used in 25 plants by 1994. 

Standard Oil A process for polymerizing ethylene and other linear olefins and di-olefins to make linear polymers. This is a liquid-phase process, operated in a hydrocarbon solvent at an intermediate pressure, using a heterogeneous catalyst such as nickel oxide on carbon, or vanadia or molybdena on alumina. Licensed to Furukawa Chemical Industry Company at Kawasaki, Japan. 

Surface vanadium appears to be most stable (to reduction) at low (<1%) V concentration when present as monomeric vanadyl units. Its stability decreases with increasing V levels. It is least stable (to reduction) at high (5%) V levels when present as a supported Vanadia phase. This difference in reactivity with V concentrations is believed responsible for the rapid decline in cracking activity observed in dual function cracking catalysts containing alumina when V start to exceed the 1.0-1.25 wt.% level (4). Further details of the mechanism of catalyst deactivation by V age the subject of continuing investigations 1n our laboratories by 31V solid state NMR, XPS, and Raman spectroscopy. 

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