Hydrogenation Of Isoprene Research Articles

SELECTIVE HYDROGENATION OF ISOPRENE, PIPERYLENE AND THEIR MIXTURES ON SKELETAL NICKEL CATALYSTS

Results of the hydrogenation process of isoprene and piperylene mixtures, as well as their mixtures on multicomponent skeletal nickel catalysts are reported in this article. Hydrogenation of piperylene and isoprene proceeds at a higher rate (W=215-220 cm3/min·g Ni) on Ni-Mo-Cu alloy catalyst than on skeletal nickel (W=112-115 cm3/min·g Ni). The results of chromatographic analysis indicate that the hydrogenation of piperylene proceeds with high selectivity. The selectivity coefficient Кs is 0.95 and 0.98 on skeletal nickel and Ni-Mo-Cu catalyst, respectively. At hydrogenation of the piperylene-isoprene mixture the piperylene conversion rate (P > J) is prevailed. At piperylene conversion degree P=50 % the isoprene J conversion is 35-37 % on Renea Nickel. 34 % on Ni-Mo-Cu catalyst. The selectivity degree of hydrogenation of this mixture is Sp-i = 0.34-0.36 on Renea Nickel, Sp-i = 0.40 on Ni-Mo-Cu. It was found that during hydrogenation of piperylene and isoprene mixtures on Ni-Al-Mo-Cu (42-50-3-5 %) catalysts the mono- and disubstituted acetylenes are saturated with a high degree of conversion compared with isoprene.

Isoprene selective hydrogenation using AgCu-promoted Pd nanoalloys.

Alloying is an effective approach to improve the catalysis performance of Pd-based catalysts for the selective hydrogenation of diolefins towards monoolefines. Herein, PdAgCu ternary nanoalloy catalysts were synthesised by a stepwise impregnation method for isoprene selective hydrogenation. The addition of a moderate amount of Ag and Cu to Pd significantly enhances the isoamylene selectivity in the isoprene hydrogenation, and decreases the non-desired over-hydrogenation. In addition, the loading molar ratio of PdAgCu with 3 : 2 : 3 as the optimal ternary nanoalloy composition maximizes the isoprene conversion (98%) and the monoolefins yield (92%). The surface structure of the catalyst was probed using H2-TPR, TEM, XRD, and XPS characterization methods, and it was confirmed that the surface Pd composition ratio between the metallic and oxidized states shows significant effects on the monoolefines yield. This work demonstrates the advantages of PdAgCu ternary nanoalloy catalysts for isoprene selective hydrogenation, which also provides guidelines for the development of other Pd-based ternary nanoalloys for diolefins selective hydrogenation.

Catalytic cascade upcycling single-use natural rubber glove wastes into fuels via a two-stage pressurized fixed-bed reactor

Chemical upcycling rubber wastes into hydrocarbon fuels offers a promising approach toward achieving carbon neutrality. To generate fuel-range cycloalkanes and isoalkanes from natural rubber glove wastes (NRGWs), the depolymerization of NRGWs was performed by integrating hydropyrolysis with vapor-phase hydrogenation over a bifunctional Ni/Al2O3-SiO2 catalyst. Isoprene and limonene were the primary alkenes obtained from the non-catalytic hydropyrolysis of NRGWs, and these intermediates were vapor-phase hydrotreated over Ni/Al2O3-SiO2 producing C10 cycloalkane as the dominant fuel-range products. Complete hydrogenation of isoprene and limonene was achieved under a catalyst to feedstock mass ratio of 2.0, giving a maximum gasoline yield of 92 wt% under 225 °C hydrogenation temperature at 0.2 MPa H2. A low hydropyrolysis temperature of 450 °C maximized C10 cycloalkane yield at 72.3 wt% with 80.1% selectivity, while a high temperature of 600 °C yielded 76.6 wt% C5 isoalkane. A deconstruction mechanism in the catalytic cascade upcycling of NRGWs was proposed by employing limonene hydrogenation as a probe reaction. The results demonstrate that upcycling polymer wastes by cascade hydropyrolysis‑hydrogenation is a promising approach to produce alternative fuels with improved properties.

Toward Functionalized Polyolefins from the Hydrogenation of Isoprene–Glycidyl Methacrylate Copolymers Prepared by Reversible Deactivation Radical Polymerization in Heterogeneous Media

Isoprene–glycidyl methacrylate (GMA) copolymers (3%–4% GMA) were prepared by two reversible deactivation radical polymerization (RDRP) techniques (nitroxide-mediated polymerization (NMP) and revers...

Regulating Pd/Al2O3 catalyst by g-C3N4 toward the enhanced selectivity of isoprene hydrogenation

The catalytic performance of Pd NPs in the selective hydrogenation of isoprene is modulated by g-C3N4 deposits on commercial alumina supports.

Highly active and stable Pd/MgAl2O4@MgO catalyst with electronic metal-support interaction for selective hydrogenation of isoprene

Electronic metal-support interaction (EMSI) had attracted increasing attention to tailor the electronic and catalytic properties of supported metal catalysts. In this work, we constructed a hierarchical Pd/MgAl2O4@MgO catalyst with flake-like MgO densely distributed on the surface of MgAl2O4. High specific surface MgAl2O4@MgO contributed to disperse and stabilize Pd particles and induced EMSI that allowing for electron donation from MgO to Pd. This was identified by the increase of the electronic density of Pd and the changes in CO adsorption behavior. Compared with Pd/MgAl2O4, Pd/MgO and Pd/Al2O3 catalysts, the as-prepared Pd/MgAl2O4@MgO catalyst exhibited significantly higher activity and selectivity with excellent stability for selective hydrogenation of isoprene. The improved catalytic activity and stability could be associated with the electronic and geometric interaction between Pd and MgAl2O4@MgO, which promoted the dissociation of H2 and weakened the adsorption of semi-hydrogenation products.

Thioetherification of isoprene and butanethiol on transition metal phosphides

Thioetherification between mercaptan and diolefin is an efficient process to remove mercaptans in FCC gasoline at mild condition, during which the selective hydrogenation of diolefin to monoolefin is also expected. Here, SiO2 supported transition metal (Fe, Co, Ni, Mo and W) phosphides were tested for the thioetherification of isoprene and butanethiol on a fixed-bed reactor at 120 °C and 1.5 MPa H2, and their structure before and after reaction was characterized by means of XRD, HRTEM, N2 sorption, CO chemisorption, NH3-TPD, XPS and TG. It was found that, among different metal phosphides, MoP/SiO2 showed the best performance, and the optimal nominal MoP loading was 25%. Apart from the nature of metal, the density of metal and acid sites determined the catalyst performance. Metal site was mainly responsible for hydrogenation of isoprene, while acid site dominantly contributed to the thioetherification and the polymerization of olefins. Moreover, a balance between metallic and acidic functions is required to arrive at a desired performance. Excessive metal sites or acid sites led to the over-hydrogenation of isoprene or the severe polymerization of olefins, respectively. 25%MoP/SiO2 was tested for 37 h time on stream, and butanethiol conversion maintained at 100%; although isoprene conversion remarkably decreased, the selectivity to isopentenes exceeded 80% after reaction for 11 h. We suggest that the deactivation of MoP/SiO2 is mainly ascribed to the butanethiol poisoning and the carbonaceous deposit, especially the former.

Selective hydrogenation of diene hydrocarbons over palladium catalysts synthesized by modified electric field-assisted laser ablation

Palladium catalysts have been synthesized by electric field-assisted laser ablation at varying orifice voltage. The catalysts have been characterized by XPS and TEM and tested in the hydrogenation of isoprene and 2,5-dimethylhexadiene-2,4. High catalytic activity has been shown (TOFs = 397 and 158 s−1 for isoprene and 2,5-dimethylhexadiene-2.4, respectively).

Hydrogenation of isoprene over gold supported on CeO2, ZrO2, SiO2 and N–SiO2

In gold catalysis, the charge state issue is of particular importance but still under debate. In this work, four categories of active site (anionic Au on ZrO2, cationic Au on SiO2, metallic Au on functionalized SiO2 (N–SiO2) and anionic Au with OH groups on CeO2) were prepared. After evaluation, the charge state effect was observed. Negatively charged Au on irreducible monoclinic ZrO2 benefits the selective hydrogenation of isoprene, meaning “charge sensitive reaction” was observed. However, the selectivity is not dependent on different active site. No isopentane was produced under experimental conditions.

Selectivity patterns in heterogeneously catalyzed hydrogenation of conjugated ene-yne and diene compounds

Selectivity control in heterogeneously catalyzed hydrogenation of conjugated hydrocarbons (ene-yne and diene compounds) is a challenging task. Available studies on the topic mainly encircle 1,3-butadiene as the substrate and palladium as the catalyst, while more elaborated playground molecules and other metals remain largely unexplored. This study investigates the gas-phase hydrogenation of valylene (2-methyl-1-butene-3-yne) and isoprene (2-methyl-1,3-butadiene) over Pd, Pb-poisoned Pd, CO-modified Pd, Cu, Ni, and bimetallic Cu Ni catalysts. Chemoselectivity, regioselectivity, full hydrogenation, and C C bond formation/scission footprints of the catalytic systems at different inlet hydrogen-to-hydrocarbon ratios and conversion degrees have been rationalized. Complementary studies of 3-methylbutyne and 1-penten-4-yne hydrogenation were carried out in order to analyze (i) the impact of isomerization on the observed mono-olefin distribution in valylene/isoprene hydrogenation and (ii) the conjugation issue in partial ene-yne hydrogenation. Our results lead to an improved understanding of hydrogenation of polyunsaturated hydrocarbons and open doors to design more selective heterogeneous catalysts and related processes for this practically important class of reactions.

Effect of metal–support interaction on the catalytic performance of Ni/Al 2O 3 for selective hydrogenation of isoprene

The effect of the interaction between metal and support on the performance of different phases alumina supported nickel catalysts was demonstrated in liquid phase selective hydrogenation of isoprene in simulated gasoline. Catalysts supported on γ-Al 2O 3 and κ-Al 2O 3 were characterized by BET, XRD, TPR, and XPS techniques. The results showed that a “surface spinel”, NiAl 2O 4 was formed. The supported nickel ions preferentially incorporate into the tetrahedral vacancies of γ-Al 2O 3 support to form SMSI (strong metal–support interaction), while WMSI (weak metal–support interaction) was formed on κ-Al 2O 3 support with little tetrahedral vacancy. When there were enough hydrogenation sites, the Ni/γ-Al 2O 3 catalysts with SMSI which can resist carbon deposition, performed higher isoprene conversion, higher stability and lower selectivity than the same nickel loading Ni/κ-Al 2O 3 samples with WMSI. The weak interaction had a positive effect on the formation of coke, which was mainly related to the hydrogenolytic sites, leading to main reaction with high mono-olefins selectivity with isoprene conversion decrease evidently.

Polymers as novel modifiers for supported metal catalyst in hydrogenation of benzaldehydes

Polyethylene glycol (PEG) was impregnated on a palladium metal supported on silica gel and used in a catalyst for hydrogenation of benzaldehydes. In the vapor-phase flow reaction, the PEG modification improved catalytic activity and selectivity for a partially hydrogenated product, benzyl alcohol. In isoprene hydrogenation, selectivity for partially hydrogenated products, monoenes, was also enhanced. X-ray photoelectron spectroscopy (XPS) analysis of the modified catalysts revealed that the modification with PEG makes the palladium surface negatively charged, possibly leading to an increase in the selectivity for the partially hydrogenated product caused by enhancement of its desorption from the surface. In the liquid-phase hydrogenation of benzaldehyde, the PEG modification also increased the selectivity for benzyl alcohol.

Hydrogenation of unsaturated hydrocarbons catalyzed by homogeneous and supported Rh, Rh-Co, and Pd, Pd-Ni complexes with oligomeric allene ligands

Mono- and bimetallic Rh and Rh-Co complexes containing oligoallene ligands were synthesized. Their catalytic activity was examined in the hydrogenation of unsaturated compounds, such as isoprene, hexene-1, and toluene. The catalytic activity of Rh(DMA)ol and Rh-Co(DMA)ol was shown to be 16 800 and 23000 mol/(mol h) in the hydrogenation of hexene-1 and 72 and 90 mol/(mol h) in the hydrogenation of toluene, respectively. Isoprene is hydrogenated completely: the rate curves exhibit two portions corresponding to hydrogenation of both double bonds. The catalytic activity of palladium oligodimethylallene complexes deposited on an inorganic support (γ-Al2O3) in isoprene hydrogenation depends on the support preparation procedure, the particle size, and the metal loading on the surface. Heterogenization of the homogeneous mono- and bimetallic Rh and Pd complexes somewhat enhances the catalytic activity in hydrogenation of the given substrates.

Rejuvenation of Moisture-Exposed Pd/δ-Al2O3 Catalysts for Isoprene-Selective Hydrogenation: Correlation between Pd Dispersion and Catalytic Properties

Exposure of commercial δ-alumina-supported Pd catalysts to moisture is unavoidable. Besides handling the catalysts with care, development of rejuvenation procedure for moisture-exposed catalyst is also necessary to minimize the economical loss. By use of in situ EXAFS (extended X-ray absorption fine structure) spectroscopy and CO chemisorption, we observed (1) moisture adsorbed on the catalyst facilitates the mobility of palladium oxides, leading to formation of bigger Pd clusters, and (2) moisture adsorbed on PdO could not be removed at temperatures of 200 °C or below, whereas it can be removed significantly in flowing air at 550 °C without growth in PdO clusters. In contrast, in the flow on nitrogen at 550 °C, the PdO is decomposed to Pd metal, which aggregates to large clusters. The impact of water exposure and the efficiency of rejuvenation were further examined by isoprene hydrogenation at a weight hourly space velocity (WHSV) of 36 h-1 (g of feed/(h g of catalyst)), 40 °C, and 30 atm total pressures. The results indicate that moisture saturation caused the decrease in isoprene conversion and selectivity to 2-methyl-2-butene (2M2B) by at least 20%. The losses of selectivity and activity can be recovered to about 60% by flowing air at 550 °C to remove the adsorbed moisture. Moreover, the test results show that isoprene conversion increases with Pd dispersion both at start of run and at nearly steady state, whereas the selectivity to 2-methyl-2-butene decreases with Pd dispersion at start of run and reaches a steady state as the time on stream is increased. The change of selectivity to 2-methyl-2-butene can be explained on the basis of FT-IR characterizing CO adsorbed on the Pd catalysts; Pd sites for CO chemisorption can be distinguished as bridging and terminal sites, and the terminal site has a higher tendency to convert isopentene to isopentane and is more vulnerable to be poisoned by coke deposition.

Synergism in the Activity of the Mixed Oligoallene Complexes of Palladium and Group VIII Nonnoble Metals in the Hydrogenation of Dienes to Alkenes

The superadditivity of the catalytic properties of various bimetallic Pd–Ni, Pd–Co, and Pd–Fe complexes with oligodimethylallene ligands was studied. Palladium–nickel catalysts of an equimolar composition exhibited the highest activity. The complexes were studied by IR spectroscopy. Conceivable structures were proposed for the complexes. The main kinetic features of the isoprene hydrogenation reaction under the action of palladium and palladium–nickel systems were studied. A two-center mechanism, which takes into account the presence of properly arranged palladium and nickel atoms in the active center of the catalyst, was considered as a probable reason for the appearance of a synergistic effect.

Selective isoprene hydrogenation over LnNi (Ln=Pr, Gd, Tm) intermetallic compounds

Isoprene hydrogenation on LnNi (Ln=Pr, Gd, Tm) rare earth intermetallic compounds has been studied. The effect of rare earth elements on nickel catalytic behaviour was investigated. The results at steady state indicate that the compounds are all more active than pure nickel. The main reaction products are 2M2B (2-methyl-2-butene) and 2M1B (2-methyl-1-butene) with a selectivity greater than 90%. The activity at t o (initial time reaction) and the selectivity at isoprene isoactivity clearly indicate the promotion of nickel’s catalytic behaviour by the rare earth element.

Isoprene hydrogenation on supported Pd [sbnd]Fe catalysts. Influence of the catalyst preparation procedure

Isoprene hydrogenation was investigated on Pd Fe/alumina catalysts in the liquid phase. Iron added by a controlled surface reaction (CSR) promotes the activity of small palladium particles while the opposite effect is generally observed on catalysts prepared by coimpregnation or successive impregnations of the metal precursor salts. Iron introduced by CSR would be deposited on the surface of palladium particles while the other preparation techniques would lead to alloy formation.

Catalytic Properties of Eggshell Pd/δ-Al2O3 Catalysts for Isoprene-Selective Hydrogenation: Effects of Water Poisoning

The influences of water poisoning on isoprene-selective hydrogenation over δ-alumina-supported eggshell Pd catalysts were investigated by test reactions at 40 °C and 420 psig of total pressure. Both fresh and water-poisoned catalysts were characterized by fast Fourier transform infrared (FFT-IR) spectroscopy and temperature-programmed desorption (TPD) of hydrogen. The catalytic performance tests showed that water poisoning suppresses the hydrogenation of isoprene and the double-bond migration of 2-methyl-1-butene and 3-methyl-1-butene to 2-methyl-2-butene, whereas it slightly facilitates the selectivity to the formation of isopentenes. FFT-IR spectroscopy characterizing CO adsorbed on the fresh and water-poisoned catalysts indicated that the bond strength between CO and palladium was weakened by the adsorption of H2O on Pd, suggesting that the adsorbed water abstracts electrons from Pd clusters. The TPD results further indicated that the formation of β-hydride was inhibited by this water adsorption. Toget...

Selective hydrogenation of isoprene over δ-alumina-supported eggshell Pd catalysts: Particle size effects

The effects of calcination temperature on the metal dispersion of δ-alumina-supported eggshell profile Pd catalyst and its catalytic performance in isoprene selective hydrogenation were investigated. The CO chemisorption results indicated that Pd particles grew with the elevation of calcination temperature. Catalytic tests showed that isoprene conversion increased with increasing Pd dispersion, while the selectivity to isopentenes decreased. Based on the results of CO chemisorption and isoprene temperature programmed desorption (TPD), the lower isoprene conversion of catalyst with lower Pd dispersion was attributed to fewer Pd sites for isoprene adsorption. The higher selectivity to isopentenes, however, was regarded as a consequence of both insufficient active sites for further hydrogenation of isopentenes to isopentane and lower electronic interaction between Pd and the alumina surface. Microscopic photo, electron probe microanalysis (EPMA), isoprene TPD, and catalysts test showed that coke was formed on both the Pd and on the alumina surface. The results also showed that, the higher the Pd dispersion the less is the coke formation on alumina.

Product selectivities in isoprene hydrogenation: diagnosis of π-allylic intermediates

Hydrogenation of isoprene (2-methyl-1,3-butadiene) on heterogeneous Pd catalysts affords the three methylbutene isomers in high selectivity and in the ratio: 2-methyl-1-butene:3-methyl-1-butene:2-methyl-2-butene ⋍ 1:1:2. Small variations from this ratio are accounted for by changes in the probabilities of adding the second H atom to different ends of the two distinguishable π-allylic intermediates, which are the half-hydrogenated states. These changes originate in the effects of the methyl substituents on electron distribution within the π-allylic radicals, the preferred position of addition depending on the charge carried by the H atom. Literature results for isoprene hydrogenation on various heterogeneous Pd catalysts and by various metal complexes in solution are examined to see whether the methylbutene isomer distributions are compatible with the π-allylic mechanism, and what kind of charge the second H atom carries. When a Pd C catalyst is selectively poisoned by the triphenyl compounds of the Group 15 elements, the charge on the second H atom appears to decrease with increasing atomic mass of the element. A variety of homogeneous complex catalysts also seem to operate through π-allylic intermediates, the second H atom apparently carrying some degree of positive charge. In both homogeneous and heterogeneous systems, mass-transport limitation may allow the methylbutenes to isomerize, and hence their concentrations will move towards their equilibrium values. This problem is signalled by the occurrence of a low total alkene selectivity. Providing this possible complication is borne in mind, obedience of the isomer distribution to the predictions of the π-allylic mechanism can be used as a diagnostic test for its operation, and can indicate qualitatively what charge the second H atom bears as it adds to the π-allylic radical.