Hydrogenation of unsaturated hydrocarbons

Soluble Rh and Ru nanoparticles are commonly used as catalysts in olefin and alkyne hydrogenation reactions. Various catalytic systems are investigated, depending on the metal precursor and the stabilizer. 

Organic polymers are very often used for the protection of metal nanopartides, providing a steric stabilizing effect. Due to this embedding effect, it is generally considered that the diffusion of the substrates through the polymer matrix can be limited. However, interesting results have been obtained. 

1 Hydrogenation of Compounds with C=C Bonds Hirai and Toshima have published several papers on the synthesis of transition metal nanopartides by alcoholic reduction of metal salts in the presence of a polymer such as polyvinyl alcohol (PVA), poly(methyl vinyl ether) (PMVE) or polyvinylpyrrolidone (PVP) in methanol (or ethanol) /water mixtures or in pure alcohols. This simple and reproducible process has been applied for the preparation of rhodium nanopartides from rhodium (III) trichloride [15]. The particles size of metallic fee rhodium is distributed in a narrow range, 3-7nm and the average diameter is 4nm. The PVP-stabilized Rh nanoparticies are more stable. These nanomaterials are effident catalysts for olefin and diene hydrogenation in rruld conditions (30 C PH2=lbar) as shown in Table 11.1. 

AH the three tested colloidal dispersions exhibited roughly the same catalytic activity for hydrogenation of terminal olefins but differences were observed for internal and cyclic olefins. 

Delmas et al. produced PVP-stabihzed rhodium nanopartides following the method reported by Hirai performing catalytic hydrogenation of oct-l-ene in a two liquid phase system [16].They investigated the effect of various parameters on their stability and activily under more or less severe conditions. They have shown that PVP/Rh colloids could be reused twice or more without loss of activity. 

When unsaturated hydrocarbons (alkenes and alkynes) are saturated, alkanes are produced. In this type of reaction, Ni, Pt or Pd are used as a catalyst. 

2 moles of a mixture of ethane (C2Hg) and propene (C3Hg) is treated with excess H2 gas. 0.5 mole of H2 is used and all the mixture becomes saturated. What is the mass of propene in the original mixture  

Ethane is a saturated hydrocarbon and propene is an unsaturated one. So, when this ethane - propene mixture is treated with H2, only propene reacts with the hydrogen. 

1 mole C3Hg reacts with 1 mole H2 X mole C3Hg reacts with 0.5 mole H2 

The reactions of ethylene and ethyne with hydrogen are as follows. 

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The Mechanism of the Hydrogenation of Unsaturated Hydrocarbons on Transition Metal Catalysts G. C. Bond and P. B. Wells... 

J. P. Boitiaux, J. Cosyns, and E. Robert, Hydrogenation of unsaturated hydrocarbons in liquid phase on palladium, platinum and rhodium catalysts, Appl. Catal. 35, 193 (1987). 

Although reference is made to other kinds of information pertinent to the mechanistic problems which are considered, the discussion emphasizes the stereochemical contributions to mechanism. The recent review of the Mechanism of the Hydrogenation of Unsaturated Hydrocarbons on Transition Metal Catalysts by Bond and Wells (5) may be consulted for a more detailed analysis of the kinetic and exchange data which are available as well as a briefer, and in some respects different, evaluation of the stereochemistry of these reactions. 

Stereochemistry and the Mechanism of Hydrogenation of Unsaturated Hydrocarbons Samuel Siegel... 

The reactions studied were the catalytic formation of methane from carbon monoxide and hydrogen (according to Sabatier (34), normal pressure), the catalytic hydrogenation of unsaturated hydrocarbons and also of unsaturated fatty acids ( fat hardening according to Normann (35)). Here again, a certain analogy was established between... 

Trickle-bed reactors are often employed in highly exothermic reactions such as the hydrogenation of unsaturated hydrocarbons. However, they exhibit poor capability of removing the excess heat of the reaction. Since the gas has low heat capacity, the liquid is responsible for removing this heat. If the generated heat is not adequately removed, hot spots may be created. These hot spots may lead to sintering of catalyst particles, with an... 

An early and popular complex, [IrCl(CO)(PPh3)2], called the Vaska complex,113 and its derivatives can be used for the hydrogenation of unsaturated hydrocarbons.26,31... 

The type of catalyst most commonly used in studies of the hydrogenation of unsaturated hydrocarbons is one in which the metal is dispersed upon a support such as alumina or silica. Although for many years it was generally thought that the support was catalytically inert, studies over the past few years have suggested that this may not be the case and there is a growing body of evidence to suggest that the support may influence the... 

In the foregoing sections, the various aspects of the metal-catalysed hydrogenation of unsaturated hydrocarbons have been discussed. In this final section, it is appropriate to attempt to summarise, in a general way, the current state of knowledge of the subject and to make suggestions as to possible future developments. 

Reductions. Hydrogenation of Mono- and Polyolefins and Acetylenes. Catalysis of hydrogenation of unsaturated hydrocarbons has been studied widely. Catalysis by a variety of metal complexes including those... 

Smits HA, Stankiewicz A, Glasz WC, Fogl THA, Moulijn JA. Selective three-phase hydrogenation of unsaturated hydrocarbons in a monolithic reactor. Chem Eng Sci 1996 51 3019-3025. 

As an example of low-temperature catalytic reactions, hydrogenation of unsaturated hydrocarbons is the most important industrial application. Chemical industrial needs are mainly for unsaturated hydrocarbons, which have reactivities that enable polymer or petrochemical product development. All the processes developed for the production of olefins, diolefins, and aromatics give a mixture of unsaturated hydrocarbons, which are not valuable as such further hydrogenations are necessary to obtain usable products for refining and chemical industry. Sulfur is generally considered to be a poison of hydrogenation catalysts. But in the case of hydrodehydrogenation reactions, this compound can also be used as a modifier of selectivity or even, in some cases, as an activator. 

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