Hydrogenation Of Isoprene Research Articles

Raney metal catalysts: I. comparative properties of raney nickel proceeding from Ni-Ai intermetallic phases

Raney nickel catalysts, prepared from well defined pure phases, have been characterised by bulk composition, total and nickel surface areas, structure, activity and sensitivity to sulfur compounds. The catalyst formed from the Ni 2Al 3 phase has 3 times more residual aluminium than that obtained from the NiAl 3 phase and it also develops the highest surface areas. Raney nickel prepared from a commercial 50–50 wt% Ni-AI alloy is a mixture of the samples obtained from the two pure phases. The origin of the catalyst has no effect upon either its activity and selectivity to benzene and isoprene hydrogenation or its catalytic properties in presence of thiophene or t-butyl mercaptan.

Calorimetric studies of the properties of Pd/Al2O3 with different metal contents

Hydrogen on Pd/Al2O3 catalysts (1,2,4% Pd) is sorbed in three forms with a heat of 152.6–2.1 kJ/mol. Metallic surface of the catalysts has been measured by the amount of adsorbed oxygen, whose adsorption heat varies in the range of 313.7–3.4 kJ/mol. Catalytic activity and selectivity of Pd/Al2O3 was studied in isoprene hydrogenation.

Hydrogenation reactions over alkali metal doped MgO, II

The hydrogenation of benzene, styrene and isoprene over magnesia doped with sodium and potassium vapors has been studied. Neither system displays a catalytic activity towards benzene hydrogenation. The initial rate, turnover number and time of halfdecay for styrene and isoprene hydrogenation have been determined.

Selective hydrogenation of diene C5 hydrocarbons on Pd-Ru membrane catalysts

1. Isoprene and 1,3-pentadiene can be hydrogenated to olefins, without paraffin formation, on a palladium alloy containing 9.8% ruthenium. 2. The rate of 1,3-pentadiene hydrogenation is higher when hydrogen feed is by diffusion through the membrane catalyst than when the hydrogen is fed as part of a mixture with the hydrocarbon vapors. With the partial pressures of hydrogen and 1,3-pentadiene each greater than unity, the principal hydrogenation product is cis-2-pentene, with mixture hydrogen feed, and 1-pentene, with hydrogen feed through the membrane catalyst. 3. Although the rate of isoprene hydrogenation also increases as one passes from mixture to diffusion hydrogen feed, the effect is not as pronounced as in the 1,3-pentadiene hydrogenation.

Isoprene hydrogenation in the presence of cobalt pohosphine complexes

The influence of the type of phosphine on the yield of methylbutenes in isoprene hydrogenation with complex cobalt catalysts has been studied. The complex H3Co[P(n-C4H9)3]3 has been identified by the NMR method in the catalytic system Co(C5H7O2)2+P(n-C4H9)3+Al(C2H5)3. A mechanism of isoprene hydrogenation is suggested.

Synthesis of isoprene from isobutene and methanol over supported silver catalysts.

One-step synthesis of isoprene from isobutene and methanol over suppsoilrvterd catalysts was investigated. Among the various metal oxides, SiO2 was found to be most suitable as catalyst carrier.Highly dispersed Ag on SiO2 produced acid sites of H0>-3.0 at which isoprene was thought to be formed by condensation of isobutene with the formaldehyde produced from methanol by the action of the Ag component. Only a small amount of isoprene was obtained at 280°C in the absence of oxygen; however, at higher temperatures, a considerable amount of isoprene was obtained even in the absence of oxygen, while isopentenes were co-produced probably by alkylation of isobutene with methanol and by hydrogenation of isoprene.

The poisoning effect of group V triphenyl compounds on the selective hydrogenation of isoprene with palladium(O) on carbon

A series of heterogeneous catalysts, based on Pd nanoparticles encapsulated into the networks, obtained from poly(propylene imine) (PPI) dendrimers, has been synthesized. Dendritic networks were designed using bi- and ter-functional coupling agents of various size, rigidity and polarity, influencing the catalyst morphology and hydrogenation activity. The catalysts obtained have demonstrated significant increase in selectivity on styrene in comparison with traditional Lindlard catalyst, maintaining at prolonged reaction time and quantitative conversions achieved. A positive dendritic effect was revealed when passing from dendrimers of the 1st generation in the carrier to those of the 3rd generation. The best results were obtained for the catalyst, synthesized using 3,3′-dimethoxy-4,4′-diphenyl diisocyanate in the presence of polymeric template (the selectivity of 90–95% at conversion of 98–100% and surface turnover frequency, TOFs, of 160–300 s−1). The same catalyst has demonstrated the best stability at recycling.

Hydrogenation of dienes and the selectivity for partial hydrogenation on a molybdenum disulfide catalyst

The reaction of butadiene with hydrogen/deuterium on molybdenum disulfide (MoS/sub 2/) proceeded via the sec.-butyl intermediate and yielded only 1-butene-3,4-d/sub 2/ and 1-butene-d/sub 0/. The hydrogenation of isoprene on MoS/sub 2/ yielded 2-methyl-1-butene about four times as fast as it gave 3-methyl-1-butene, as previously found for other heterogeneous catalysts and in opposition to available results for homogeneous catalysts, which have a high selectivity for 3-methyl-1-butene. Isomerization of 2-methyl-1-butene to 2-methyl-2-butene occurred via the carbonium ion mechanism. Deuteriation of isoprene yielded 2-methyl-1-butene-d/sub 2/ and 3-methyl-1-butene-d/sub 2/ in a process in which the adsorption of isoprene molecules with the double bond adjacent to the methyl group was apparently loose compared with the adsorption on the other side of the double bond. Deuteriation of pentadiene also showed the weakened adsorption at the double bond adjacent to the alkyl group. The steric effect in the selectivity of isoprene hydrogenation was confirmed by molecular orbital calculations. Graphs, tables, and 20 references.

Hydrogenation of isoprene, hept-1-yne and cyclopentadiene on modified palladium catalysts

PALLADIUM catalysts are widely used for hydrogenation of diene and acetylene hydrocarbons [1]. Palladium is selected as an active catalytic phase for the hydrogenation of these hydrocarbons most probably because on palladium hydrogen is added to dienes and acetylenes in stages [2]. The type of carrier and modifying additive has a marked effect on the reduction of hydrocarbons, thus changing the activity and selectivity of the catalyst [3, 4]. This study is aimed at comparing the effect of modifying additives on the activity and selectivity of action of palladium catalysts during hydrogenation of hydrocarbons with different unsaturated bonds (isoprene, hept-l-yne and cyclopentadiene). Lanthanum, zinc, cadmium, lead and barium compounds were used as modifying additives and were introduced into the palladium catalyst during preparation.

Supported transition metal complexes: V. Liquid phase catalytic hydrogenation of hexene-1, cyclohexene and isoprene under continuous flow conditions

Three complexes of rhodium and one of iridium of the type MX(phosphine) n , where X = halide and n = 2 or 3, have been chemically bonded to silica. The resulting materials have been shown to catalyze the hydrogenation of hexene-1, cyclohexene, and isoprene in the liquid phase under a variety of continuous flow conditions (15–50 atm H 2 , 20–160 °C). n -Butyl mercaptan in the feedstock reduces the activity, but increases the thermal stability of the catalysts. Continuous flow operation for 70 hr without loss of activity in the hydrogenation of hexene-1 and cyclohexene has been demonstrated for the heterogeneous complex RhBr(SIL CH 2 CH 2 PPh 2 ) 2 . (SIL CH 2 CH 2 PPh 2 represents the phosphine ligand linked to the surface of silica.) Rhodium elution from the catalysts was extremely small, generally below the limit of detection (0.2 ppm).

A kinetic model of the selective hydrogenation of isoprene on a palladium-lead catalyst in the vapor phase

1. The kinetics of the selective hydrogenation of isoprene to isoamylenes in a circulation-flow system in the vapor phase on a palladium-lead catalyst was studied; the results indicate a sequential mechanism of selectivity. An equation was derived describing the kinetics of the process. 2. A kinetic model of the process was proposed, satisfying the aggregate of data obtained.

Mechanism of isoprene hydrogenation on palladium

The reaction for the selective hydrogenation of isoprene on a palladium catalyst at low temperatures is accomplished mainly on a small portion of the surface via the rapid formation of the surface isoprene compound in the undissociated form, with the subsequent slow steps of its conversion to the semihydrogenated form, and then to isopentenes.

Hydrogenation by cyanocobaltate. Part IV. Hydrogenation of conjugated dienes by 2,2′-bipyridinetricyano-, tricyano(ethylenediamine)-, and tricyano(1,10-phenanthroline)-cobaltate(II) complexes

Hydrogenation of butadiene and isoprene catalysed by aminetricyanocobaltate(II) ions [amine = ethylenediamine (en), 2,2′-bipyridine (bipy), and 1,10-phenanthroline (phen)] has been studied. The effect of the CN : Co ratio on the selectivity and the optical, e.s.r., and n.m.r. spectra suggests that the active species is [Co(CN)3(am)]–. Intermediate complexes have been detected by n.m.r. spectroscopy, and a high-field shift by the ‘ring current’ observed with the bipy and phen complexes indicated that the am ligands co-ordinate to the cobalt atom in the cis-configuration with respect to an alkenyl ligand. Pseudo-contact shifts have been observed with the intermediate complexes in the en system, and broadening without shift in the bipy and phen systems. These behaviours are explained in terms of the formation of cyanide-bridged paramagnetic dimeric complexes. Catalytic activity is controlled by the lability of the Co–H bond of hydrido-complexes [Co(CN)3(am)H]– rather than the stability of the intermediate complexes.

THE DISTRIBUTION OF SULFER COMPOUND ON PALLADIUM BLACK AND ITS CATALYTIC POISONING EFFECT

Abstract The difference of the selectivity between poisoned by ethylsulfide and non-poisoned Pd-black was observed in the catalytic hydrogenation of isoprene. To obtain the information of the poisoning state, electron microprobe X-ray analysis method was applied. According to the S-Kα radiation profile, ethylsulfide was distributed uniformly on the surface.

Hydrogenation by Cyanocobaltate. II. Mechanisms of the Hydrogenations of 1,3-Butadiene and Isoprene Catalyzed by Pentacyanocobaltate(II) in Aqueous Solution

Abstract Hydrogenations of 1,3-Butadiene and isoprene catalyzed by pentacyanocobaltate(II) have been studied by the measurements of infrared and nuclear magnetic resonance spectra on the reaction solutions and by following the time-courses of the reactions. Infrared spectroscopy has revealed: (1) The aging reaction is promoted by CN- ion and it hardly occurs at a low CN/Co ratio. (2) In the hydrogenation of butadiene the formation of a σ-but-2-enyl complex at a high CN/Co ratio is very rapid, but that of a syn-π-(1-methylallyl) complex at a low CN/Co ratio is generally slow. The rate of the formation of these complexes is affected by the relative concentration of butadiene to Co(CN)5H3−. (3) In the hydrogenation of isoprene a σ-3-methylbut-2-enyl complex is formed regardless of the CN/Co ratio. Nuclear magnetic resonance spectroscopy has confirmed the structures of these complexes and it also showed that the σ-but-2-enyl complex consists of simliar amounts of the cis- and trans-isomers. The reactions are explained by the mechanisms, in which intermediate complexes in the formation of alk-1-enes and alk-2-enes are the cis- and trans σ-but-2-enyl and the syn-π- (1-methylallyl) complexes in the case of butadiene, and the σ-2- and -3-methylbut-2-enyl and the π-(1,2-dimethylallyl) complexes in the case of isoprene. It is described that the reactivity and the selectivity in the hydrogenation of conjugated dienes are strongly controlled by the steric factor in the transition state.

Hydrogenation of benzene and isoprene on aluminoplatinum catalysts modified with manganese and chromium

1. Modification of an aluminoplatinum catalyst with manganese in a ratio Pt∶Mn=10∶1 promotes an increase in the activity of this catalyst in the reaction of hydrogenation of benzene and a decrease in the effect of poisoning by thiophene. The addition of chromium in the same amount reduces the activity and stability of the catalyst with respect to poisoning by thiophene. 2. In the case of modification of an aluminoplatinum catalyst with additions of manganese and chromium, the activity of the catalysts obtained in the liquid phase low-temperature hydrogenation of isoprene is increased.

Hydrogenation of isoprene and 2,3-dimethylbuta-1,3-diene on a skeletal cobalt catalyst

1. 1. Skeletal cobalt catalyst has a considerable activity and high selectivity of action in hydrogenation of isoprene and 2,3-dimethylbuta-1,3-diene. 2. 2. The α-olefins forming do not hydrogenate in the presence of dienes as a consequence of adsorption displacement. 3. 3. The cobalt catalyst, with a higher selectivity than that of a nickel catalyst, directs the hydrogenation of dienes into the 1,2- and 3,4-positions with the formation of thermodynamically less stable 2-methylbut-1-ene and 2,3-dimethylbut-1-ene. 4. 4. Cobalt catalyses the transfer of the double bond in isopentene and isohexene to a small extent.

Hydrogenation of isoprene and binary mixtures of isopentenes on a skeletal nickel catalyst

Hydrogenation of isoprene and binary mixtures of isopentenes on a skeletal nickel catalyst

Selectivity of catalysts Communication 3. Hydrogenation of isoprene over Raney nickel

1. A study was made of stepwise character of reaction and selectivity in the hydrogenation of the conjugated double bonds of isoprene in presence of Raney nickel. 2. At 20° and atmospheric pressure the double bonds of isoprene are hydrogenated successively. 3. Over a catalyst whose surface has been blocked with pyridine or quinoline, under normal conditions isoprene is hydrogenated to a mixture of isopentenes, after which reaction stops completely. 4. In presence of pyridine the selectivity of the process is maintained also in the hydrogenation of isoprene under pressures of up to 88 atm.

Catalytic hydrogenation of doubly unsaturated compounds having a conjugated system of double bonds Communication 2. Hydrogenation of isoprene in presence of platinum, palladium and nickel

1. Hydrogenation of isoprene in presence of palladium and nickel proceeds, as in the case of hydrogenation in presence of platinum studied previously by Lebedev, as a diene hydrogenation of the second type. 2. For addition of hydrogen in presence of platinum, lower selectivity is observed than in presence of palladium and nickel, which are very similar to one another in this respect. 3. The forms of the hydrogenation rate curves are in no case characteristic of the actual course of the reaction.