Platinum black, hydrogenation catalyst

Figure 1. Reduced-minus-oxidized difference absorption spectrum of Ps. aeruginosa azurin. Sample and reference cell contained 6.8 X 10 5 M solutions of reduced and oxidized protein, respectively. Hydrogen, with platinum black as catalyst, was used as reductant (1). Medium ...

De Wilde Hydrogenated acetylene and ethylene at 20 C Berichte 7,352 (1874) using platinum black. Regenerated catalyst to recover activity. 

Aqueous solutions of hydrogen peroxide decompose slowly the decomposition is catalysed by alkalis, by light and by heterogeneous catalysts, for example dust, platinum black and manganese... 

G. Vavon has examined the hydrogenation of carvone, in presenc of platinum black as a catalyst, and shown that it takes place in three entirely distinct phases. Carvone fixes successively three molecules of hydrogen, giving dextro-carvotanacetone, then tetrahydrocarvone, and finally carvomenthol. 

A solution of 20 g of 1 -isonicotinyl-2-isopropy lidene hydrazine in 1 50 cc of methanol was reduced with hydrogen at room temperature and 50 psi using 300 mg of platinum black as a catalyst. 

The brown oxide is a heavy granular powder which settles to the bottom of the solution in the bottle in which the reduction is carried out (p. 10). It must be reduced to platinum black before it becomes a catalyst for the reduction. When the hydrogen is admitted and the bottle shaken the brown oxide becomes black and whips up into a fine suspension. The time necessary for the change of the oxide to platinum black is called the lag. The time of lag varies usually from several seconds to two or three minutes, depending upon the conditions under which... 

In certain reductions it is an advantage to reduce the platinum oxide to platinum black by shaking with hydrogen in the presence of solvent only, before the substance to be reduced is added to the mixture. More often the catalyst is reduced in the presence of the substance to be reduced with aldehydes for example the platinum black is usually more finely divided and generally more active if prepared in presence of the aldehyde. 

It was found in the 1960s that disperse platinum catalyst supported by certain oxides will in a number of cases be more active than a similar catalyst supported by carbon black or other carbon carrier. At platinum deposits on a mixed carrier of WO3 and carbon black, hydrogen oxidation is markedly accelerated in acidic solutions (Hobbs and Tseung, 1966). This could be due to a partial spillover of hydrogen from platinum to the oxide and formation of a tungsten bronze, H WOj (0 < a < 1), which according to certain data has fair catalytic properties. 

Addition of platinum-black catalyst to ethanol caused ignition. Pre-reduction with hydrogen and/or nitrogen purging of air prevented this. 

Tetrahydropyrane has been prepared by hydrogenation of dihydropyrane using a platinum black catalyst 1 by heating pen-tamethylene bromide with water 2 3 or with water and zinc oxide in a sealed tube 4 or by heating pentamethylene glycol with three volumes of 60 per cent sulfuric acid in a pressure tube.5... 

Fig. 2. The selectivity of saturated products (2MP + 3MP + MCP) and benzene produced from n-hexane (total conversion = 100%) as a function of the final hydrogen pressure. Thick full lines represent calculated equilibrium concentrations. Dashed lines denote experimental data with respect to benzene (x ) and saturated Cg products (O). Pulse system, catalyst 1.0 g platinum black, T = 327 3°C ( 600 K) (31).

Fig, 6. Rates of methylcyclopentane formation from 3-methylpentane, as a function of hydrogen pressure. Static-circulation system catalyst, 0.16 g platinum black hydrocarbon pressure, 5 Torr (77). 

Fig. 7, Percent selectivity of hydrogenative C, ring closure as a function of the hydrogen content of the carrier gas. Pulse system catalyst, 0.4 g platinum black T = 360°C. Starting hydrocarbons ( ) 3-methylpentane ( ) 3-methyl-1-pentene (T) tra . -3-methyl-2-pentene (A) di-2-methyl-2-pentene. Selectivity is expressed as methylcyclopentane (MCP) % in the total C5 cyclic product (MCP + MCPe) (55).

Platinum (IV) oxide (Pt" + 20 —> Pt O ) is also known as platinum dioxide. It is a dark-brown to black powder known as Adams catalyst that is used as a hydrogenation catalyst. 

A catalytic agent can alter the speed of a chemical action, bat it cannot alter the condition of equilibrium.—Although the speed of a chemical reaction is modified by the presence of a catalytic agent, the final state of equilibrium is not affected. If otherwise, J. H. van t Hoff showed that we could allow these substances to react alternately with and without the catalytic agent this would involve a change in the quantity combined, and the energy thus obtained could be made to do work. This would lead to perpetual motion, which is assumed to be impossible. This deduction has been confirmed experimentally with hydrogen iodide with and without platinum black. Hence, adds W. Nernst, the catalyst must always affect... 

Over the alumina-supported metals, the activity sequences for isomerisation and hydroisomerisation were observed to be similar. With these catalysts, the results were interpreted in terms of a H-atom addition-abstraction mechanism involving an adsorbed but-2-yl intermediate the importance of the alumina support as a source of hydrogen atoms to initiate the isomerisation was stressed [130,133]. It was suggested that, with platinum black, isomerisation occurred by both an addition—abstraction and an abstraction—addition mechanism, the relative contributions of each depending upon the experimental conditions [135]. 

There have been used essentially only three catalysts foi the hydrogenation of ethylene oxides nickel, palladium on charcoal, and platinum black. Solvent normally employed include ethanol wait nickel, and ethanol, ethyl acetate, or acetic acid with the other. Reduction over platinum or palladium catalysts is usually conducted at room temperature and low pressure, whereas nickel catalysth Imvi-been employed in autoclaves at temperatures ranging from 3fT to nearly 200° and high pressures. For excellent general discussions ol catalytic redaction any of several outstanding sources14" 11-ltni m.i> be consulted. 

Platinum in a finely divided form is obtained by the in situ reduction of hydrated platinum dioxide (Adams catalyst) finely divided platinum may also be used supported on an inert carrier such as decolourising carbon. Finely divided palladium prepared by reduction of the chloride is usually referred to as palladium black. More active catalysts are obtained however when the palladium is deposited on decolourising carbon, barium or calcium carbonate, or barium sulphate. Finely divided ruthenium and rhodium, usually supported on decolourising carbon or alumina, may with advantage be used in place of platinum or palladium for some hydrogenation reactions. 

To solubilise a dialkylmethylamine during oxidation to the V-oxide with hydrogen peroxide, methanol was used as diluent in place of water. After oxide formation was complete, platinum black was added to decompose excess peroxide, and an explosion occurred. This was attributed to ignition of the methanol vapour—oxygen mixture by glowing catalyst particles. 

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