Catalysts for hydrogen

Hot spot formation witliin tlie reactor can result in catalyst breakdown or physical deterioration of tlie reactor vessel." If tlie endothermic cyanide reaction has ceased (e.g., because of poor catalyst performance), the reactor is likely to overheat. Iron is a decomposition catalyst for hydrogen cyanide and ammonia under the conditions present in the cyanide reactor, and e. posed iron surfaces in the reactor or reactor feed system can result in uncontrolled decomposition, which could in turn lead to an accidaital release by overheating and overpressure. 

A variety of catalysts including copper, nickel, cobalt, and the platinum metals group have been used successfully in carbonyl reduction. Palladium, an excellent catalyst for hydrogenation of aromatic carbonyls is relatively ineffective for aliphatic carbonyls this latter group has a low strength of adsorption on palladium relative to other metals (72,91). Nonetheless, palladium can be used very well with aliphatic carbonyls with sufficient patience, as illustrated by the difficult-to-reduce vinylogous amide I to 2 (9). 

Ruthenium dioxide or ruthenium-on-carbon are effective catalysts for hydrogenation of mono- and dicarboxylic acids to the alcohol or glycol. High pressures (5,000-10,000 psig) and elevated temperatures (130-225 C) have been used in these hydrogenations 8,12,24). Yields of alcohol tend to be less than perfect because of esterification of the alcohol. Near quantitative yields of alcohol can be obtained by mixing ruthenium and copper chromite catalysts so as to reduce the ester as formed. 

The rhodium complexes are excellent catalysts for hydrogenation of NBR. At low temperature and pressure, high catalyst concentrations are used to obtain a better rate of reactions. Due to higher selectivity of the reaction, pressure and temperature can be increased to very high values. Consequently the rhodium concentration can be greatly reduced, which leads to high turnover rates. The only practical drawback of Rh complex is its high cost. This has initiated the development of techniques for catalyst removal and recovery (see Section VU), as well as alternate catalyst systems based on cheaper noble metals, such as ruthenium or palladium (see Sections IV.A and B). 

These pentahydrides have attracted attention as catalysts for hydrogenation of the double bond in alkenes. IrH5(PPr3)2 catalyses vinylic H-D exchange between terminal alkenes and benzene, the isomerization of a,f3-ynones, isomerization of unsaturated alcohols and dehydrogenation of molecules such as secondary alcohols [176],... 

Shatenshtein et a/.S19 have also measured the effect of boron trifluoride as a catalyst for hydrogen exchange in acetic acid and have compared it with stannic chloride (Table 157). The logarithm of the rate coefficient was linearly related to... 

Hydrogen iodide has also been used as a catalyst for hydrogen exchange581, rate coefficients (lO7 ) at 25 °C for reaction with [2H]C6H4R being (R =) 2,3-benzo(l position of naphthalene), 500 4-Me, 40 2-Me, 21 4-Ph, 42 2-Ph, 10. The reaction was catalysed by added iodine, the rate being directly proportional to the concentration of this, and for the latter compound rates were measured... 

Neopentyl alcohol, 40, 76 Nickel catalyst for hydrogenation of resorcinol, 41, 56, 57 Nitramines from amines and acetone cyanohydrin nitrate, 43, 84 Nitration, of amines to nitramines by acetone cyanohydrin nitrate, 43, 83... 

The performance of the catalysts doped with transition metals on 20 mol% NiO/Ti02 catalyst for hydrogen production at 998 K and GHSV of 2700 h" at steady state. 

Palladium is used as a catalyst for hydrogenation reactions in the food industry, and a rhodium catalyst is used in... 

Raney nickel is a useful catalyst for hydrogenations at mild conditions. It is, however, sensitive to poisoning and not very stable at high temperatures. Another disadvantage is that regeneration is not always possible in many cases the catalyst must be melted with aluminium until the right Al-Ni alloy is formed. Then the preparation procedure has to be repeated again. Moreover, the preparation procedure is not very reproducible. 

Hinnemann B, Moses PG, Bonde J, Jorgensen KP, Nielsen JH, Horoh S, Chorkendorff I, Nprskov JK. 2005. Biomimetic hydrogen evolution M0S2 nanoparticles as catalyst for hydrogen evolution. J Am Chem Soc 127 5308-5309. 

It is very well known that Pt is one of the best metal catalysts for hydrogen as well as for organic oxidations. Nevertheless, a comparison of the electrochemical behavior of hydrogen and any of these organic substances shows large differences. While hydrogen establishes its reversible thermodynamic potential with platinum in an aqueous acidic solution very quickly, the reversible potential of the other fuels could never be experimentally observed. 

Rossi, L.M., Silva, F.P., Vono, L.L.R., Kiyohara, P.K., Duarte, E.L., Itri, R., Landers, R. and Machado, G. (2007) Superparamagnetic nanopartide-supported palladium a highly stable magnetically recoverable and reusable catalyst for hydrogenation reactions. Green Chemistry, 9 (4), 379-385. 

Laska, U., Frost, C.G., Plucinski, P.K. and Price, G.J. (2008) Rhodium containing magnetic nanoparticles effective catalysts for hydrogenation and the 1 4-addition of boronic acids. Catalysis Letters, 122 (1-2), 68-75. 

Mevellec, V., Roucoux, A., Ramirez, E., Philippot, K. and Chaudret, B. (2004) Surfactant-stabilized aqueous iridium(O) colloidal suspension an effident reusable catalyst for hydrogenation of arenes in biphasic media. Advanced Synthesis and Catalysis, 346 (1), 72-76. 

S. V. (2007) Pd on amine-terminated ferrite nanopartides a complete magnetically recoverable facile catalyst for hydrogenation reactions. Organic Letters, 9 (7), 1419-1421. 

Jacinto, M.J., Landers, R. and Rossi, L.M. (2009) Preparation of supported Pt(0) nanopartides as efficient recyclable catalysts for hydrogenation of alkenes... 

Baruwati, B., Polshettiwar, V. and Varma, R.S. (2009) Magnetically recoverable supported ruthenium catalyst for hydrogenation of alkynes and transfer... 

Major work on zinc chloride catalysts for hydrogenation and hydrocracking of coal has been carried out by Zielke, Gorin, Struck and coworers at Consolidation Coal (now Conoco Coal Development Co.) (1). The emphasis there has been on a full boiling-point range of liquid product, from treatment at temperatures between 385 and 425°C and hydrogen pressures of 140 to 200 bars. 

A variety of Group VIII transition metal phosphine complexes are shown to be active catalysts for hydrogenation of aliphatic nitro compounds. However, chiral phosphines have been found to be noneffective to induce asymmetric induction.110... 

The most commonly used catalysts for hydrogenation (finely divided platinum, nickel, palladium, rhodium, and ruthenium) apparently serve to adsorb hydrogen molecules on their surface. 

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