Hydrogen activating tungsten

The first suitable activated-alumina catalyst contained 10% M0O3 activated by addition of 3% nickel oxide. This catalyst was superseded by a more active tungsten catalyst containing 70% activated alumina, 27% tungsten sulfide, and 3% nickel sulfide. This catalyst is used in commercial plants for the prehydrogenation of middle oils and also for the direct hydrogenation of shale oil and lignite tar (TTH process). 

Tungsten-based hydrotreating catalysts have been studied much less than the classical molybdenum-based catalysts. It is expected, however, that phosphorus addition should lead to similar effects in both cases since tungsten is chemically similar to molybdenum. Atanasova et al. (101) reported that phosphorus increases the thiophene HDS activity, especially that of a sequentially impregnated NiW—P/Al catalyst. Halachev et al (135) found that a maximum hydrogenation activity for naphthalene conversion is attained when the catalyst contains 0.6 wt% P2O5. Cruz Reyes et al (58) reported that phosphorus on a W/Al catalyst notably enhances gas oil HDS and pyridine HDN. 

The horohydride reduction of a nickel salt solution containing small amounts of other metal salts can lead to co-reduced mixed metal borides that frequently have enhanced catalytic properties when compared to the unmodified nickel boride. The presence of about 2% chromium significantly increased the activity of a P-1 nickel boride toward aldehyde hydrogenation. Molybdenum, tungsten and vanadium modifiers were somewhat less effective than chromium while the presence of a small amount of cobalt had an inhibiting effect on the reaction.22 As the data in Fig. 12.2 show, the amount of chromium responsible for optimum P-1 nickel boride activity depends on the substrate being hydrogenated.39... 

The displacement reaction Although it is believed that the key reason for selectivity is the activated adsorption of hydrogen on tungsten there is obviously no tungsten available in the beginning of the deposition (in a contact to silicon). The first reaction which will occur is that between silicon and WF6, the so called displacement reaction [Broadbent et al.44] ... 

Strongly Acidic Catalysts with Mild Hydrogenation Activity. Reaction Mechanism. Typical catalysts with strongly acidic properties and relatively mild hydrogenation activity are metal sulfides such as nickel, tungsten, or cobalt sulfide on supports such as silica-alumina. 

Dybov A, Blacque O, Berke H (2010) Molybdenum and tungsten nitrosyl complexes in hydrogen activation. Eur J Inorg Chem 3328-3337... 

Aluminium and other metal alkyls also activate tungsten and molybdenum compounds (particularly oxychlorides), to generate homogeneous or supported olefin dismutation catalysts. It is now believed that an initial M-alkyl (M = W, Mo) group is converted to a metal alkylidene group by a-hydrogen abstraction. Coordinated olefin now gives a metallocyclobutane (isolable in some cases) ... 

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