Catalyst solid, hydrogenation

Suspension of fine solid particles m a liquid, such as m the catalytic hydrogenation of a liquid where solid catalyst and hydrogen bubbles are dispersed m the liquid. 

Figure 2. Hydrogen adsorption and desorption Isotherms for rhodium catalysts. Solid lines denote total adsorption and dashed lines denote reversible adsorption. The meaning of symbols Is as follows ...

Figure 47.2. (a) Effect of residence time 156 s, fresh catalyst (solid symbol) 80 s, catalyst used once (open symbol) and (b) effect of catalyst particle size in citral hydrogenation at 25°C, 6.1 bar total pressure, residence time 156 s, solvent ethanol, 0.1 g catalyst Ni/Si02, initial citral concentration 0.02 M. 

In order to increase the contact of a catalyst with hydrogen and the compounds to be hydrogenated platinum (or other metals) is (are) precipitated on materials having large surface areas such as activated charcoal, silica gel, alumina, calcium carbonate, barium sulfate and others. Such supported catalysts are prepared by hydrogenation of solutions of the metal salts, e.g. chloroplatinic acid, in aqueous suspensions of activated charcoal or other solid substrates [28. Supported catalysts which usually contain 5, 10 or 30 weight percent of platinum are very active, and frequently pyrophoric. 

These hydrogenations are rapid and quantitative. Conversely, the gas-solid hydrogenations of alkenes that were doped by platinum metal compounds on their recrystallization maybe incomplete as, for example, the hydrogenation of trans-cinnamic acid or N-vinylisatin [58,61], which should be milled for completion. Furthermore, the spillover technique by mixing powders of substrate and catalyst followed by application of hydrogen and several hours or days rest [69,70] appears inappropriate for quantitative conversions. Milling is, however, not applicable if volatile liquids have to be constantly pumped off [69] or if the products become liquid or sticky [70]. 

Microwave irradiation also shows a beneficial effect in the preparation of solid-supported palladium catalysts for hydrogenation reactions. Thus, alumina- and silica-supported palladium catalysts were synthesised by conventional and microwave heating, and their physical properties and catalytic activity in the hydrogenation of benzene were compared. The alumina-based system prepared under microwave conditions showed turnover numbers an order of magnitude higher than the conventionally prepared catalysts28. 

The product of step 2 (17 g) was dissolved in glacial acetic acid and hydrogenated in the presence of Adams catalyst until hydrogen uptake had ceased. The catalyst was filtered off through a keiselguhr filter and the filtrate was evaporated to leave 13.0 g of almost colorless solid. The mass and NMR spectra confirmed the structure of product. 

A mixture of 680 grams of 2-methyl-9-phenyl-2,3-dihydrol-pyridindene hydrobromide, 6,000 cc of water and about 100 grams of Raney-nickel catalyst is hydrogenated at room temperature and at about 1,000 lb pressure for a period of three hours. The catalyst is filtered. The clear filtrate is treated with a solution of 240 grams potassium thiocyanate in 400 cc of water. A heavy solid precipitates from which the supernatant liquid is decanted. 

New catalysts of hydrogen oxidation for low-temperature fuel cells are molybdenum and tungsten carbides [2, 3], For solid polymeric fuel cells the novel catalysts by plasma treatment of polymer membrane have been developed. The radicals at surface are generated. These radicals are catalysts of anodic reactions [4]... 

Nickel metal occurs as a lustrous, white, hard, ferromagnetic, metallic solid. Nickel is commonly used as a catalyst for hydrogenation reactions for food chemicals. Depending on the use, Nickel catalysts fall into two general categories Sponge Nickel Catalyst and Supported Nickel Catalyst. 

With this type of catalyst, the hydrogenation is usually carried out in the ranges 110-190°C, under 1-5 bar H2 with 0.01-0.15% Ni catalyst (w/w). The hydrogenation of fats is somewhat special due to the need to work in all three phases (gas, liquid, and solid, with corresponding mass and heat transfer problems), and since the natural feedstocks used show significant variations in composition. For these reasons batch reactors are still preferred because of their simplicity, lower cost, and since they have the flexibility to be adapted to different feedstocks or different end products. 

Fig. 13. Difference IINS spectrum (TOSCA, ISIS) ((catalyst + hydrogen)-(bare catalyst)) of hydrogen adsorbed on a Pt(40%)/C fuel cell catalyst (53) (crosses) and fits as a sum of components (solid line). The fundamentals are shown as individual Gaussians the remaining intensity is attributed to first overtones and binary combinations. The numbers indicate the hydrogen coordination number.

Ear greater yields were reported for the hydroxylation of benzene under the so-called triphasic conditions, that is with the solid catalyst, aqueous hydrogen peroxide and an immiscible aromatic phase [56]. Others, however, could not reproduce these results [54]. 

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