Hydrogenation Of Unsaturated Hydrocarbons Research Articles

Hydrogenation of C`'5 olefins in vapor phase on the copper oxide catalyst

Hydrogenation of unsaturated hydrocarbons is one of the important processes of the modern petrochemical industry. Quite large amount of C4-5 fractions of hydrocarbons containing paraffins and olefins are formed via pyrolysis of light petroleum products. To increase the production of ethylene and propylene, the separated C4-5 fractions are recycled for pyrolysis. Preliminary hydrogenation of olefin compounds in these fractions is necessary. Preferably, the hydrogenation is carried out in the liquid phase at temperatures of 40 – 80 °C under hydrogen pressure up to 15 bar overhigh-cost palladium-containing catalysts. The aim of this work was to elucidate the possibility of efficient hydrogenation of industrial С5 fraction containing C`5 olefins over some mixed copper-oxide catalysts. Hydrogenation of C`5 fraction of pyrolysis of light petroleum products in the vapor phase over such catalysts as CuO-ZnO-ZrO2-Al2O3 and CuO-ZnOAl2O3 in comparison with commercial Pd/Al2O3 catalyst for C4-5 olefins hydrogenation have been studied. The pyrolysis C`5 fraction containing 51 wt. % of unsaturated hydrocarbons (2-methyl-1-butene, 2-pentene, cis-2-pentene, trans-2-pentene, 2-methyl-2-butene) was used in the work. The catalytic process was carried out in a reactor with a fixed catalyst bed at 170 – 190 oC, and a pressure of 1.1 – 2.5 MPa. Analysis of obtained products was provided by gas-chromatography (Agilent 7820A) and 13C NMR (Bruker Avance 400) methods. It is shown that the hydrogenation of olefins with conversion of the C`5 fraction such high as 98 – 99 % can be carried out in the vapor phase over CuO-ZnO-Al2O3 and CuO-ZnO-Al2O3 catalysts at the temperature of 180 oC and pressure 1.2 – 1.5 MPa. The total C5 olefinsloading can reach 15 – 23 mmol/gcat/h. The residual content of unsaturated hydrocarbons is 1 %. At the pressure of 2.5 MPa, a sharp decrease in conversion is observed, as n-pentane turns into a liquid phase. Catalyst deactivation was not observed for 36 hours. Under the same conditions the drop in activity of industrial catalyst 0.35 % Pd/Al2O3 was observed after 70 minutes from the start of work.

Structural and Electronic Properties of Highly Dispersed Particles of the Active Components of Pd/Al2O3 Catalysts of Butadiene-1,3 Hydrogenation

The effect of the acidic characteristics of an alumina support on the properties of formed palladium particles is studied to improve the activity of catalysts for the hydrogenation of unsaturated hydrocarbons of the pyrogasoline fraction. High catalytic activity is characteristic of highly dispersed palladium particles, but the surfaces of palladium particles are blocked by unsaturated hydrocarbons, due to their electron deficiency. In this work, palladium/alumina catalysts with supports of different acidities due to chemical modification with various reagents are studied via NH3 temperature-programed desorption, transmission electron microscopy, and X-ray photoelectron spectroscopy. The samples are subjected to catalytic tests in the butadiene-1,3 hydrogenation reaction under laboratory conditions. The catalysts on supports with acidic modifiers display low butadiene-1,3 conversion and higher selectivity toward butene-1, relative to an unmodified sample. The catalysts on the supports treated with basic additives displayed high butadiene-1,3 conversion while retaining their selectivities toward butene-1 and butane.

From Palladium Clusters in Solutions to Supported Nanocatalysts for Hydrocarbon Synthesis

Literature data on palladium clusters obtained by the interaction of Pd(II) compounds in solutions with hydrogen are summarized and analyzed. The conclusion is drawn on the influence of ligands and reduction conditions on the polynuclearity of clusters and on the autocatalytic nature of their formation. Palladium clusters become active in the selective hydrogenation of alkynes and dienes only after their treatment with hydrogen containing traces of oxygen or hydrogen peroxide. Clusters containing phosphide ligands are active in the homogeneous hydrogenation of unsaturated hydrocarbons with a high selectivity being of a thermodynamic nature. Most of the distinctive features of nanocluster synthesis in solution are also observed in the synthesis of metal-containing nanoparticles on the support surface from precursors. Catalysts for the liquid-phase selective hydrogenation of phenylacetylene on the Pd supported on coal with a nanoparticle size of 2.8 ± 0.2 nm are obtained. This size is comparable with the size of clusters in solution. The mechanism for the reduction of palladium acetate on carbon is also autocatalytic and is similar to the same process in solutions. A kinetic study of the selective hydrogenation of phenylacetylene to styrene in the presence of Pd supported on coal shows that it is impossible to adequately describe the experimental data in the framework of the Langmuir, Hinshelwood, or Eley–Rideal mechanisms. It is proposed to use this mechanism in the framework of cluster (polynuclear) active sites on the surface of Pd particles capable of adsorbing more than one substrate molecule or its fragments on the same site. This approach makes it possible to describe the mechanisms of other reactions occurring in the presence of nanoscale heterogeneous supported catalysts: deoxygenation of fatty acids obtained from renewable raw materials to paraffins on supported palladium catalysts and olefins on supported nickel sulfide catalysts.

Selective C=C Hydrogenation of Unsaturated Hydrocarbons in Neat Water Over Stabilized Palladium Nanoparticles Via Supported 12-Tungstophosphoric Acid

Stabilized Pd(0) nanoparticles by supported 12-tungstophosphoric acid (Pd(0)-TPA/ZrO2) was explored as a sustainable recyclable catalyst for selective C=C hydrogenation of cyclohexene and crotonaldehyde. The catalyst shows an outstanding performance [catalyst to substrate ratio (1:1.31 × 104)] towards high conversion as well as 100% selectivity of the desired product with high turnover number (> 10,000) and turnover frequency (> 2600 h−1) for both the systems. The use of neat water as a solvent and mild reaction conditions makes the present system environmentally benign and green. Moreover, the catalyst could be recovered and reused up to five cycles without any significant loss in their conversion as well as selectivity. The viability of the catalyst was evaluated towards different aromatic as well as aliphatic arenes and found to be excellent in all the cases. The obtained selectivity, especially butyraldehyde, was correlated with the nature of the catalyst as well as solvent and based on the study, a plausible mechanism for both the reactions was also proposed.

Structural and Electron Properties of High-Disperse Particles of the Active Component of Pd/Al2O3 Catalysts for Hydrogenation of Butadiene-1,3

Studies of the influence of acidity of alumina supports on properties of supported palladium particles were aimed at improving the activity of catalysts for hydrogenation of unsaturated hydrocarbons of pyrolysis gasoline fraction. High-disperse palladium particles demonstrate the high catalytic activity but their electron deficiency make them suffering from blocking with unsaturated hydrocarbons. NH3 TPR, TEM and XPS techniques were used for studying aluminopalladium catalysts; different acidities of the catalyst supports resulted from their chemical modification with various agents. The catalysts were tested for lab-scale hydrogenation of butadiene-1,3. Against the non-modified samples, the catalysts supported on modified alumina provided a lower conversion of butadiene-1,3 but a higher selectivity to butene-1. A higher conversion of butadiene-1,3 at the preserved selectivity to butene-1 and butane was observed in the presence of the catalyst supported on base-modified alumina.

Hydrogenation of Unsaturated Hydrocarbons on Pt and Pd Catalysts Encapsulated in Mesoporous Bakelites

In this work, we sought to find new efficient methods for reducing the sulfur content in crude petroleum coke. The action of reactive dichlorocarbene or chlorocarbene intermediates produced in the reaction of chloroform or methylene chloride and sodium hydroxide under phase transfer catalysis conditions was shown to cause the breakdown of C–S bonds of some individual sulfur compounds to give reaction products identifiable by classical methods. Furthermore, a series of experiments was conducted using crude petroleum coke with high sulfur content (4.3%) under phase transfer catalysis conditions, which showed that, under optimized conditions (by enhancing the mass transfer rate using phase transfer catalysis and/or ultrasound), the sulfur content in the original coke can be reduced to 2%, which comprises a reduction of more than 50% of the initial content.

Hydrogenation of Unsaturated Hydrocarbons on Platinum and Palladium Catalysts Encapsulated in Mesoporous Bakelites

Syntheses are reported for catalysts derived from platinum and palladium nanoparticles supported on a mesoporous phenol formaldehyde polymer modified by an ionic liquid. These catalysts are used for the hydrogenation of unsaturated compounds, specifically, acyclic and cyclic isoprenoids: isoprene, 2,5 – dimethyl–2,4–hexadiene, limonene, α –terpinene, γ –terpinene, as well as phenylacetylene, transstilbene, and 1,4–diphenyl–1,3–butadiene. High activity was found for these catalysts in hydrogenation reactions. The palladium catalysts were more active than their platinum analogs. The products of complete hydrogenation predominate in the hydrogenation of isoprenoids on the palladium catalysts, while monoene products predominate in the reactions on platinum catalysts.

Catalysts based on molybdenum and tungsten heteropoly compounds for the hydrotreatment of oil fractions

The results from 15 years of studies performed at the Samara State Technical University in the field of developing highly active sulfide catalysts for the hydrotreatment of straight-run and refractory low-grade oil fractions with the use of molybdenum and tungsten heteropoly compounds (HPCs) as precursors are presented. A wide range of HPCs with Anderson and Keggin structures is studied in the synthesis of sulfide catalysts. The order of activities in the hydrodesulfurization of sulfur compounds and the hydrogenation of unsaturated hydrocarbons are established for the heteroelements incorporated into HPCs. Catalytic activity—HPC heteroatom electronegativity correlations are revealed. Special attention is given to controlling the selectivity of catalysts with respect to parallel hydrogenation and hydrodesulfurization reactions. A wide variety of highly active sulfide catalysts for the hydrotreatment of diesel fuel, catalytic cracking gasoline, vacuum gas oil, and lube feedstocks is developed. The techniques for their synthesis and activation (sulfidation) are substantiated. The developments are patented and are close to being introduced at oil refineries whenever they are ready.

ChemInform Abstract: Metal‐Free Hydrogenation of Unsaturated Hydrocarbons Employing Molecular Hydrogen

AbstractReview: [41 refs.

Subsurface Hydrogen Diffusion into Pd Nanoparticles: Role of Low-Coordinated Surface Sites and Facilitation by Carbon

Hydrogen species absorbed in the volume of Pd nanoparticles play a crucial role in the hydrogenation of unsaturated hydrocarbons. Recent evidence suggests that the rate of diffusion of hydrogen from the surface of Pd nanoparticles to the subsurface region critically affects the hydrogenation rate, as this rate dictates whether or not the nanoparticles can maintain a sufficient concentration of subsurface hydrogen species under operating conditions. Recent theoretical calculations predicted pronounced facilitation of subsurface hydrogen diffusion by coadsorbed carbon and identified the conceptual importance of atomically flexible low-coordinated surface sites on small metal clusters for the diffusion process. In this study, we experimentally probe the kinetics of hydrogen diffusion into the subsurface by performing pulsed molecular beam experiments on carbon-free and carbon-containing Pd nanoparticles and on Pd(111). We provide experimental proof that low-coordinated surface sites on Pd particles play a crucial role in the diffusion process and that their selective modification with carbon results in marked facilitation of subsurface hydrogen diffusion, in line with the theoretical predictions.

Structure sensitivity in the hydrogenation of unsaturated hydrocarbons over Rh nanoparticles

A series of Rh nanoparticles with sizes between 3.5 and 11.4nm were synthesized in the presence of polyvinylpyrrolidone and evaluated for their performance as catalysts in the hydrogenation of phenylacetylene and 1-octene. The reaction is zeroth order in the reactant for phenylacetylene and 1-octene. The catalytic activity increased with Rh particle size in the hydrogenation of phenylacetylene, whereas the activity in 1-octene hydrogenation did not depend on particle size. The possible explanations for this different particle size behavior are discussed.

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.

Ti-Catalyzed Selective Isomerization of Terminal Mono-substituted Olefins

Transition metal complexes have been utilized in the homogeneous catalysis because of selectivity and catalytic activity under mild conditions. The isomerization of olefins catalyzed by transition metal complexes constitutes one of important type of reaction in organometallic chemistry. The isomerization of olefins occurs either by a metal hydride addition-elimination or by a π-allyl metal hydride intermediate. HCo(CO)4, [(C2H4)2RhCl]2, Ni[P(OEt)3]4, and PtCl2(PPh3)2-SnCl2 are effective catalysts for isomerization of olefins via a metal hydride addition-elimination mechanism, and Fe3(CO)12 catalyzed isomerization of 3-ethyl-1pentene and isomerization of 1-heptene catalyzed by (PhCN)2PdCl2 occur via a π-allyl metal hydride mechanism. The cis/trans ratio of 2-butene obtained from isomerization of 1-butene by RhH(CO)(PPh3)3 has also been investigated. The skeletal isomerization of olefins catalyzed by (R3P)2NiCl2 is developed such as conversion of cis-1,4hexadiene to trans-2-methyl-1,3-pentadiene. Titanium complexes serve as an effective catalysts for a variety of reactions such as hydroalumination, hydroboration, and hydrogenation of unsaturated hydrocarbons. We have been interested in the selective reactions of unsaturated hydrocarbons by using titanium and zirconium compounds. The reagent system composed of LiAlH4/Cp2TiCl2 ≤ 2 in the molar ratio promotes the isomerization of 1-octene, but the detailed reaction for isomerization of olefins has not been reported. We report here a selective isomerization of olefins with low valent titanium complex generated from Cp2TiCl2 (Cp=cyclopentadienyl) and LiAlH4.

Advances in the catalysis of Au nanoparticles

Gold catalysts have recently been attracting rapidly growing interests due to their potential applicabilities to many reactions of both industrial and environmental importance. This article reviews the latest advances in the catalysis research on Au. For low-temperature CO oxidation mechanistic arguments are summarized, focusing on Au/TiO 2 together with the effect of preparation conditions and pretreatments. The quantum size effect is also discussed in the adsorption and reaction of CO over Au clusters smaller than 2 nm in diameter. In addition, recent developments are introduced in the epoxidation of propylene, water-gas-shift reaction, hydrogenation of unsaturated hydrocarbons, and liquid-phase selective oxidation. The role of perimeter interface between Au particles and the support is emphasized as a unique reaction site for the reactants adsorbed separately, one on Au and another on the support surfaces.

Characterization and reactivity of Pd–Pt bimetallic supported catalysts obtained by laser vaporization of bulk alloy

Bimetallic Pd–Pt clusters produced by laser vaporization of bulk alloy have been deposited on high surface alumina. Energy dispersive X-ray (EDX) analysis and transmission electron microscopy (TEM) show that they have a perfectly well-defined stoichiometry and a narrow range of size. Therefore, they constitute ideal systems to investigate alloying effects towards reactivity. Pd–Pt alloys are already known for their applications in the hydrogenation of unsaturated hydrocarbons, especially aromatics, because this system is highly resistant to sulfur and nitrogen poisoning. In this context, the catalytic properties of this system have been investigated in the hydrogenation of tetralin in the presence of hydrogen sulfide. Preliminary results show that this model catalyst is more sulfur-resistant than each of the pure supported metals prepared by chemical methods.

The influence of the random sequential adsorption of binary mixtures on the kinetics of hydrocarbon hydrogenation reactions

The hydrogenation of unsaturated hydrocarbons by transition metal catalysts demonstrates complex kinetic behavior that cannot be represented by mean-field kinetic models. In this paper, a Monte Carlo model of the Horiuti-Polanyi hydrogenation mechanism is introduced and is applied to the hydrogenation of a number of alkenes of varying chain length. We demonstrate that the origin of this anomalous kinetic behavior can be explained by assuming that the adsorption of the hydrocarbon on the catalyst surface approximates a random sequential adsorption (RSA) process. The model is shown to reproduce the kinetic discontinuities observed experimentally for the hydrogenation of ethene and ethyne. Monte Carlo simulations conducted on square lattices for a number of hydrocarbons indicate that the transition between the two kinetic regimes occurs at the point where the hydrocarbon surface coverage exceeds the dimer jamming limit.

Catalysis by Gold

Despite occasional references in the older literature to the ability of gold to catalyze certain reactions, the metal has until recently had the reputation of being one of the least catalytically useful. The recent discovery that some supported gold catalysts can affect the oxidation of carbon monoxide at or below ambient temperature has, however, focused attention on the metal's ability in this respect. For oxidation of carbon monoxide at low temperature, catalysts comprising small (<5 nm) gold particles supported preferably on an oxide of the first transition series (e.g., TiO2, α-Fe2O3) are needed. Deposition–precipitation and coprecipitation are better methods than impregnation for this purpose and provide the desired intimacy of contact between metal and support. High activity may well originate at sites at the gold–support interface, with the support making a vital contribution. Stable activity can result by optimizing aging in solution during the preparation, and low calcination temperatures are generally desired. Gold catalysts also have potential for both selective and nonselective oxidation of hydrocarbons, for methanol synthesis by hydrogenation of carbon monoxide or dioxide, for the water–gas shift, and for the reduction of nitric oxide by hydrogen, propene, or carbon monoxide. The hydrogenation of unsaturated hydrocarbons also occurs on highly dispersed gold catalysts. Supported gold chloride is the most active catalyst for the hydrochlorination of ethyne, the activity being correlated with the metal's high standard electrode potential. The remarkable catalytic behavior shown by gold depends on forming it into very small particles. This is because the massive metal and large particles cannot chemisorb typical reactant molecules to any useful extent; this only occurs when an adequate number of low-coordination surface atoms are present, ideally on particles so small that they lack full metallic character. The long neglect of gold as a catalyst is chiefly due to the failure to appreciate the necessity of creating particles that are sufficiently small and, for oxidations, of selecting a helpful support. Other relevant factors may be the likely high mobility of surface atoms on small particles and the electronegative character of gold, both stemming from the relativistic contraction of the s-electron orbitals. Attention is drawn to the uncertainties concerning reaction mechanisms and to areas for possible future development, such as use of promoters and bimetallic compositions and the extension of concepts already revealed to other reactions and metals (e.g., the platinum group metals). The practical application of gold catalysts in oxidations and other processes can be confidently expected.

Hydrogenation of unsaturated hydrocarbons over alkali-metal-modified zinc oxide

Superbasic catalytic systems have been obtained by evaporation of alkali metals onto a ZnO surface. The catalysts were characterized by IR and EPR spectroscopy. Similar to the case of alkali-metal-doped oxide insulators, surface colour centres Fs+, formed by the trapping of an alkali-atom electron in an oxide anionic vacancy, were identified as the source of the extremely strong one-electron donor properties. The studied catalysts exhibited a much higher activity in the hydrogenation of alkenes than the starting ZnO. A mechanism for propene hydrogenation over the superbasic alkali metal/ZnO system was proposed.

Competitive Catalytic Hydrogenation in Unsaturated Hydrocarbon Systems With Sterically Hindered Double Bonds

A competitive hydrogenation of unsaturated hydrocarbons (a-methylstyrene, cyclohexene, 1-methylcyclohex-1-ene, 1-tert-butylcyclohex-1-ene and 3-tert-butylcyclohex-1-ene) in binary and ternary systems with palladium-, platinum- and rhodium-supported catalysts in a semibatch isothermal reactor at 20 °C under atmospheric pressure was studied. It was found that considerable variance in selectivity values of competitive hydrogenation in a series of substrates with increasing substituent bulkiness is caused by differences in adsorption and in reactivity of adsorbed molecules. In the case of ternary systems, a change in selectivity of competitive hydrogenation of two substrates was observed, due to the presence of a third substance, caused by a competitive adsorption of all three substrates and their interaction on a catalytic surface.

Kinetics of the initial stages of CVD diamond growth on non-diamond substrates: surface catalytic effects and homoepitaxy

Abstract Recently, we have reported that the density of chemical vapour deposition (CVD) diamond particles obtained on non-diamond substrates abraded with a diamond slurry can be enhanced by a few orders of magnitude by abrasion with a mixed metal/diamond slurry. In this work, we present growth kinetics studies of isolated diamond crystallites (prior to coalescence into a continuous film), which are formed at the initial stages of deposition on metal/diamond and diamond-pretreated silicon. The metals used were Ti, Fe and Cu. It has been found that the temperature dependence of the diamond growth rates on differently pretreated substrates can be described by an Arrhenius plot. From these plots, it has been concluded that at the initial stages of deposition the activation energy for CVD diamond formation, as observed for diamond-abraded substrates, can be substantially decreased as a result of substrate surface pretreatment with a mixed metal/diamond slurry. However, after coalescence of the crystallites into a continuous film, the activation energies for metal/diamond and diamond-pretreated substrates were found to be similar. Based on micro-Raman measurements it has been found that at the initial stages of deposition, the quality of diamond that was grown on the metal/diamond abraded substrates is higher than that deposited on the diamond-abraded ones. In contrast, after a long deposition time, the quality of diamond grown on the differently pretreated substrates was found to be similar. It is suggested that the observed effects are associated with the metal's catalytic activity towards the hydrogenation of unsaturated hydrocarbons, namely enhancing the concentration of sp 3 -bonded hydrocarbon fragments. At the initial stage of deposition, before a stable substrate is formed, this enhancement leads to an increase in the diamond growth rate, lowering of the activation energy for its homoepitaxial growth on diamond residues left by pretreatment, and improvement of its quality.