Vanadium oxide hydrogenation catalyst

Al-Shamma LM, Naman SA (1990) The production and separation of hydrogen and sulfur from thermal decomposition of hydrogen sulphide over vanadium oxide/sulphide catalysts. Int J Hydrogen Energy 15(1) 1-15... 

Clerici, M.G. and Kholdeeva, O.A. (eds) (2013) Liquid Phase Oxidation via Heterogeneous Catalysis Organic Synthesis and Industrial Applications, John Wiley Sons, Inc., Hoboken. Bruckner, A. and Baems, M. (1997) Selective gas-phase oxidation of polycyclic aromatic hydrocarbons on vanadium oxide-based catalysts. Appt Catal. A- Gen., 157 (1-2), 311-334. Corma, A., Esteve, P., and Martinez, A. (1996) Solvent effects during the oxidation of olefins and alcohols with hydrogen peroxide on Ti-beta catalyst the influence of the hydrophilicity-hydrophobicity of the zeolite. /. Catal, 161 (1), 11-19. 

Figure 2.8 The surface reaction between adsorbed carbon monoxide and hydrogen to methane over rhodium catalysts occurs at lower temperatures in the presence of a vanadium oxide promoter, which is known to enhance the rate of CO dissociation (from Koerts el al. 113]). 

The possibility of hydrogen activation on the surface of transition metal carbides has been supported by experiments in which WC was used as a promoter for the hydrogen oxidation reaction over the oxide catalyst V205.1 WC additions to V2O5 were shown to critically accelerate the reaction of H2 + 02 (so that under the same conditions the activities of V205 and WC were separately much lower). Moreover, WC additions to V205 boosted the reduction of vanadium oxide by hydrogen. Qualitatively,... 

Fig. 4 shows the TPR profiles of the fresh and spent catalyst. Curve C shows the desorption of hydrocarbons during reduction of the spent catalyst, formed by reduction of carbonaceous deposits on the catalyst surface. The hydrogen consumption profiles of the catalyst (see Curve A and B) show the two peaks, characteristic of palladium sulfate-based catalysts, with a vanadium oxide reduction peak at approximately 400 K and a sulfate reduction peak at 600 K [11,13,16]. The peak position of the sulfate reduction peak is comparable for both catalysts. For the spent catalyst, however, an additional small hydrogen consumption is observed at 700 K, which coincides with the large peak in the FID signal,... 

In heterogeneous catalysis the catalyst is present as a phase distinct from the reaction mixture. The most important case is the catalytic action of certain solid surfaces on gas-phase and solution-phase reactions. A critical step in the production of sulfuric acid relies on a solid oxide of vanadium (V2O5) as catalyst. Many other solid catalysts are used in industrial processes. One of the best studied is the addition of hydrogen to ethylene to form ethane ... 

Of more interest mechanistically though is the liquid nature of the molten phase present in the interstices of the inert porous support. It is now recognized that, deliberately or accidentally, a number of heterogeneously catalysed processes involve a supported liquid phase (SLP) rather than a solid catalyst. SLP catalysts are reviewed by Villadsen and Livbjerg. These include the vanadium-based sulphuric acid catalysts and, of comparable antiquity, the Deacon catalysts for oxidizing hydrogen chloride, where mixtures of copper and potassium chlorides can form melts in the catalyst support under reaction conditions. Thus in addition to diflfusional restrictions arising from pellet pore structure any... 

The TPR profiles of doped and undoped alumina supported vanadium oxide catalysts are shown in Figure 1, while the temperatures of the maximum hydrogen consumption, T, are shown in Table 1. One peak with a maximum at 465°C is observed in the undoped sample (Fig. la) in agreement with previous results [5]. 

The catalyst used is vanadium oxide or platinum. Platinum is good for N02 to become N2. Another catalyst, known as honeycat, will convert NOx to nitrogen when burnt with natural gas, hydrogen, naphtha, or LPG. 

It is clear that significant research efforts have been made in this subject and a few clear guidelines have been established including the roles of molybdenum and vanadium oxides as well as hydrogen modifiers to novel metal catalysts. 

Metal oxides such as iron oxide were first reported as catalysts for the hydrogenation of carboxylic acids to the corresponding aldehydes by GAP in 1935 [4]. A typical example was the production of benzaldehyde by hydrogenation of phthalic anhydride. After this discovery the success of this system, a variety of catalysts such as y-alumina [5], vanadium oxide [6], manganese oxide [7], yttrium oxide... 

The first reported hydrogenating action of vanadium oxide was the hydrogenolysis of cresol by Griffith (I). Vanadium pentoxide has also previously been classified by Sabatier 2) as a mixed dehydration-dehydrogenation catalyst. It was found however, in our laboratory that primary... 

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. 

Fig. 1. Comparison of hydrogenation curve for isobutylene and hydrogen adsorption curve vanadium oxide catalyst.

Chromium oxide was classified by Sabatier 2) as predominantly an alcohol-dehydration catalyst. It was found in our work that no water was formed when alcohols were contacted with this catalyst at elevated temperatures (200-400°). There was also no hydrogenolyzing activity when the same reaction was carried out in the presence of hydrogen in contrast with the action of vanadium oxide under similar conditions. 

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