Carbonyl Hydrogenation Research Articles

Chemoselective Hydrogenation of Cinnamaldehyde over Pd/CeO2–ZrO2 Catalysts

Selective hydrogenation of cinnamaldehyde over Pd (2 wt%) supported on CeO2, ZrO2 and CeO2–ZrO2 catalysts is reported for the first time. In general, the olefinic (C=C) group of cinnamaldehyde is preferentially hydrogenated compared to the carbonyl (C=O) group. This selectivity preference could, however, be altered or reversed by adding alkali additives to the catalyst. The influence of additive on the structure and redox properties of the active sites and correlation of that with selective hydrogenation activity is investigated. Selective hydrogenation of cinnamaldehyde over Pd (2 wt%) supported on CeO2, ZrO2 and CeO2–ZrO2 catalysts is reported for the first time. Alkali additives influence the selectivity for hydrogenation of olefinic (C=C) and carbonyl (C=O) groups of cinnamaldehyde. The influences of additive on the structure and redox properties of the active sites and correlation with selective hydrogenation activity are reported.

On the mechanism of carbonyl hydrogenation catalyzed by iron catalyst

Density functional theory calculations have been performed to investigate the detailed mechanism of the carbonyl hydrogenation catalyzed by the first well-defined bifunctional iron catalyst. The catalytic reaction proceeds by hydrogen transfer and dihydrogen activation. The hydrogen transfer reaction occurs via the bifunctional mechanism in which the two hydrogen atoms attached on the Fe and O of the catalyst are transferred to the oxygen and carbon atom of the carbonyl compound concertedly. Both the alcohol-mediated and nonalcohol-mediated dihydrogen activation processes are explored.

Formation and properties of hydrogenation catalysts based on palladium bisacetylacetonate and sodium tetrahydroborate

Properties of the Pd(acac)2-nNaBH4 system in catalysis of the reactions of hydrogenation of alkenes, alkynes, and carbonyl and nitro groups were studied. A number of spectral methods (NMR, UV spectroscopy) and X-ray phase analysis were used to examine the main stages of formation of palladium hydrogenation catalysts produced in the interaction of Pd(acac)2 with sodium tetrahydroborate, and reasons for the bimodal nature of the dependence of the catalytic activity on the B/Pd ratio were considered.

Liquid phase hydrogenation of crotonaldehyde over Au/CeO 2 catalysts

Three Au/CeO 2 catalysts, with different specific surface area (80, 150 and 240 m 2/g) were tested for the hydrogenation of crotonaldehyde in liquid phase. Reactions were carried out with molecular hydrogen as the reductant, in a batch reactor using isopropanol as the solvent, at 80 °C and 1 MPa. The high surface area catalyst (Au/CeO 2, 240 m 2/g) showed a selectivity towards crotyl alcohol of 29%. This value was much lower than the one previously obtained for the same sample under gas phase conditions (73%) [B. Campo, C. Petit, M. Volpe, J. Catal. 242 (2006) 162]. Under liquid phase the promotional effect of high surface area ceria is lost. The low and middle surface area samples (80 and 150 m 2/g respectively) showed meager selectivity to carbonyl hydrogenation due to both the low promotional effect of the support and the relatively large size of gold particles. For the three catalysts the formation of propanol was observed, which decreases catalysts selectivity to crotyl alcohol.

Nature of Asynchronous Hydrogen Transfer in Ketone Hydrogenation Catalyzed by Ru Complex

Three different reaction pathways—concerted hydride transfer, concerted proton transfer, and stepwise hydrogen transfer—in the carbonyl hydrogenation step of the catalytic cycle for ketone hydrogenation catalyzed by Ru complexes are investigated in this work. Our results from this study suggest that hydride and proton asynchronous transfers in the ketone hydrogenation process are stepwise in general. It is the nature of the substrate, electron withdrawing effect, and characteristics of catalytic ligands that make one of two transition states disappear in the concerted mechanism.

Catalytic behavior of supported Pd catalysts in the selective hydrogenation of campholenic aldehyde to naturanol

Selective catalytic reduction of campholenic aldehyde to naturanol was investigated over Sn-and Fe-doped SiO2, and Fe2O3-supported Pd catalysts. On Pd/SiO2 and Pd-Sn/SiO2 only saturated campholenic aldehyde is formed. Addition of Fe increases the C=O hydrogenation rate producing the corresponding unsaturated alcohol with a good selectivity. Also Fe2O3-supported catalysts were found to be more selective towards carbonyl hydrogenation. Addition of tin to Pd/Fe2O3 contributes to a further selectivity enhancement towards naturanol.

Spectroscopic Determination of Hydrogenation Rates and Intermediates during Carbonyl Hydrogenation Catalyzed by Shvo's Hydroxycyclopentadienyl Diruthenium Hydride Agrees with Kinetic Modeling Based on Independently Measured Rates of Elementary Reactions

The catalytic hydrogenation of benzaldehyde and acetophenone with the Shvo hydrogenation catalysts were monitored by in situ IR spectroscopy in both toluene and THF. The disappearance of organic carbonyl compound and the concentrations of the ruthenium species present throughout the hydrogenation reaction were observed. The dependence of the hydrogenation rate on substrate, H2 pressure, total ruthenium concentration, and solvent were measured. In toluene, bridging diruthenium hydride 1 was the only observable ruthenium species until nearly all of the substrate was consumed. In THF, both 1 and some monoruthenium hydride 2 were observed during the course of the hydrogenation. A full kinetic model of the hydrogenation based on rate constants for individual steps in the catalysis was developed. This kinetic model simulates the rate of carbonyl compound hydrogenation and of the amounts of ruthenium species 1 and 2 present during hydrogenations.

Hydrogen Transfer to Ketones Catalyzed by Shvo's Ruthenium Hydride Complex: A Mechanistic Insight

The Shvo catalyst is one of the most prominent examples of a hydrogen-transfer catalyst successfully applied in a broad scope of hydrogen-transfer processes. The reaction takes place by transferring a hydride (bonded to the metal center) and a proton (bonded to a ligand) to a double bond. The reaction mechanism for the hydrogen-transfer process, however, is a matter of controversy. Experimental studies by means of primary deuterium isotope effects on the hydrogenation of ketones via the active reducing form of the Shvo catalyst by the Casey and Bäckvall groups concluded that carbonyl hydrogenation is concerted. Nevertheless, it is not clear whether the reaction goes through an outer-sphere mechanism (without substrate coordination) or through an inner-sphere mechanism (with substrate coordination). In the present work several inner- and outer-sphere mechanisms are explored by means of theoretical methods. Energy reaction profiles clearly support the outer-sphere mechanism. Theoretically combined KIEs also suggests the concerted outer-sphere mechanism for this reaction. Some interesting features on the behavior of the Ru complex were found during the mechanistic investigations.

Preparation of NiB nanoparticles in water-in-oil microemulsions and their catalysis during hydrogenation of carbonyl and olefinic groups

Abstract Surfactant-stabilized NiB catalysts (ME-NiB) were prepared using the chemical reduction method in the ternary microemulsion system of water/cetyl-trimethyl-ammonium bromide (CTAB)/ n -hexanol. The surfactant molecules could adsorb onto the surface of the formed particles, and acted as a protective agent to stabilize and restrict the growth of particles. The size of the nanoparticles was not fully determined by the size of the microemulsion droplets, which depended on the composition of the microemulsion system. Additionally, the particle sizes and the reactivities of the ME-NiB nanoparticles depended on the concentration of nickel salt, the amount and speed of addition of NaBH 4 and the temperature. The ME-NiB samples were characterized by X-ray diffraction (XRD) as an amorphous structure and by transmission electron microscopy (TEM) as having particle size distributions in the range 3–8 nm, which was much smaller than that of NiB (20–50 nm) prepared by the typical chemical reduction method. The ultrafine catalyst of ME-NiB was markedly more active than NiB in the hydrogenation of carbonyl and olefinic groups. A good yield of citronellal/citronellol was obtained from the selective hydrogenation of citral at a low temperature of 30 °C over the ME-NiB catalyst.

Preparation and catalysis of polymer-stabilized NiB catalysts on hydrogenation of carbonyl and olefinic groups

PVP-stabilized NiB catalysts were prepared using the chemical reduction method with NaBH 4, dissolving the water-soluble polymer of polyvinylpyrrolidone (PVP) in the precursor salt solution as a protective reagent. The PVP-NiB catalysts were characterized and examined for their catalysis on the hydrogenation of furfural, crotonaldehyde and citral. PVP polymer could adsorb on the nano-particles of NiB via a weak coordination bonding and stabilize it; a molecular weight of PVP of about 10,000 was suitable, and the optimal quantity of PVP (PVP/Ni) in the salt solution for preparing catalysts was around 20. The PVP-NiB samples were characterized by XRD as an amorphous structure and by TEM with a particle size distribution in the range of 3–5 nm. On catalysis, the PVP-NiB catalyst was significantly more active and slightly more selective than NiB for hydrogenating furfural to furfuryl alcohol and crotonaldehyde to butyraldehyde. A good yield of citronellal, about 90%, could be obtained by reducing citral in cyclohexane at a low reaction temperature of 50 °C over the PVP-NiB catalyst.

Selectivity issues in the catalytic multiphase reduction of functionalized halogenated aromatics over Pd/C, Pt/C, and Raney-Ni

The multiphase system, consisting of a biphasic isooctane-aqueous medium, a heterogeneous catalyst, and a quaternary ammonium salt (Aliquat 336)—a supported ionic liquid catalyst surface modifier—allows efficient hydrodehalogenation under mild conditions (50°C and 1atm H2). In the reactions of various halogenated benzenes, nitrobenzene, benzonitrile, benzaldehyde in the multiphase catalytic system, the selectivity of reduction of certain groups (hydrodehalogenation, carbonyl hydrogenation, hydroxyl hydrogenolysis, aromatic reduction) is a function of the presence of a phase-transfer agent, pH of the aqueous phase, catalyst choice (5% Pd/C, 5% Pt/C or Raney-Ni). The suggested mode of action of the quaternary salt involves the formation of a distinct ionic liquid layer at the catalyst–solution interface, where the reaction proceeds with alternative selectivity.

Study of selective hydrogenation of acetophenone on Pt/SiO 2

The competitive hydrogenation between phenyl and carbonyl groups of acetophenone (AP) and the reaction pathway were investigated by gas phase hydrogenation, infrared (IR) spectra and TPD experiments on reduced and oxidized Pt/SiO 2. The reduced Pt/SiO 2 offers good catalytic activity for carbonyl and phenyl hydrogenation to produce 1-phenylethanol (PE) and cyclohexylethanol at room temperature, but the formation rate and reaction selectivity of 1-phenylethanol are gradually boosted with decreasing formation rate of cyclohexylethanol. The catalytic selectivity of acetophenone hydrogenation is proposed to be dominated by some fragments from acetophenone dissociation and by 1-phenylethanol product strongly adsorbed on the surface. The fragments formed from acetophenone dissociation during reaction will inhibit the bonding between phenyl group and Pt surface leading to a decrease in the rate of cyclohexylethanol formation. On the other hand, the large amount of 1-phenylethanol product with strong adsorption ability remaining on the surface without desorption also leads to suppressing hydrogenation of phenyl group. Oxidized Pt catalyst can provide lower catalytic activity than reduced Pt, but reaction selectivity shifts to formation of 1-phenylethanol and ethylbenzene (EB). The hydrogenation of aromatic ring was almost suppressed by oxygen. The oxidized Pt surface induces the activation of CO; this is more advantageous for CO hydrogenation than for CC hydrogenation. Formation of both main products is proposed to follow the route: acetophenone → 1-phenylethanol → cyclohexylethanol.

Regio‐ and Chemoselective Catalytic Transfer Hydrogenation of Aromatic Nitro and Carbonyl as Well as Reductive Cleavage of Azo Compounds over Novel Mesoporous NiMCM‐41 Molecular Sieves.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Regio- and Chemoselective Catalytic Transfer Hydrogenation of Aromatic Nitro and Carbonyl as Well as Reductive Cleavage of Azo Compounds over Novel Mesoporous NiMCM-41 Molecular Sieves

Regio- and Chemoselective Catalytic Transfer Hydrogenation of Aromatic Nitro and Carbonyl as Well as Reductive Cleavage of Azo Compounds over Novel Mesoporous NiMCM-41 Molecular Sieves

Regio- and chemoselective catalytic transfer hydrogenation of aromatic nitro and carbonyl as well as reductive cleavage of azo compounds over novel mesoporous NiMCM-41 molecular sieves.

[reaction: see text] [corrected] Regio- and chemoselective reduction of nitroarenes and carbonyl compounds and reductive cleavage of azo compounds, including bulkier molecules, was achieved by the catalytic transfer hydrogenation method (CTH) using a novel nickel-containing mesoporous silicate (NiMCM-41) molecular sieve catalyst. In addition, the catalyst was also found to behave as a truly heterogeneous catalyst as the yield was practically unaffected.

Infrared study of competitive crotonaldehyde and CO adsorption on Cu/TiO2

Infrared spectra of adsorbed CO have been used to monitor the surface of Cu/TiO2 which had been reduced in H2 at 523, 623 or 723 K and was also exposed to propene, butanal or crotonaldehyde. For CO alone infrared bands at 2118–2133 cm−1 dominated the spectra and are ascribed to CO interacting with Cu(I) sites in chains or two-dimensional rafts of Cu atoms distributed at lattice points determined by the geometric and electronic character of the underlying TiO2 surface. Three effects of crotonaldehyde on co-adsorbed CO are a geometric site blocking effect which reduces the surface concentration of sites available for CO adsorption, an electronic effect due to the electron-donating character of crotonaldehyde acting as a Lewis base and a redox effect which leads to the oxidation of crotonaldehyde to adsorbed crotonate ions and the reduction of Cu(I) to Cu(0). The enhanced selectivity, induced by TiO2 as support, towards crotyl alcohol rather than butanal formation from crotonaldehyde hydrogenation over Cu is attributed to the promotion by TiO2 of Cu(I) sites and the co-existence on catalyst surfaces of Cu(0) and Cu(I) sites which are particularly active for hydrogenation of carbonyl (CO) bonds.

The Development and Use of New Hydrogenation Catalysts1

Advantages and drawbacks of commercial catalysts for gas-phase hydrogenation are considered. The use of modified catalysts, including nickel catalysts modified with heteropoly compounds, is promising. Data on the selective reduction of carbonyl compounds and hydrogenation of aromatic hydrocarbons over these catalysts are presented. Palladium films are shown to be the best catalysts for the selective reduction of acetylene compounds to olefins.

Redox behaviour of ceria–titania mixed oxides

The reducibility of the supports is one of the properties influencing the catalytic behaviour of platinum catalysts in the selective hydrogenation of α,β-unsaturated aldehydes. Platinum on reducible supports has shown higher selectivities in carbonyl hydrogenation compared to Pt/Al 2O 3 and Pt/SiO 2 catalysts. We report here a study on the redox properties of mixtures of titania and ceria, precursors of Pt/TiO 2–CeO 2 catalysts. Two samples, with atomic compositions Ti/Ce 8/2 and 5/5, were prepared using a sol–gel process. They were treated under hydrogen and air in a wide range of temperatures. Surface compositions and the percentage of reduced ceria were determined by X-ray photoelectron spectroscopy. Temperature programmed reduction (TPR) profiles, and X-ray diffraction patterns were interpreted in terms of the formation and stability of several mixed compounds.

Hydrodehalogenation of Halogenated Aryl Ketones under Multiphase Conditions. 6. pH Effect on the Chemoselectivity and Preliminary Mechanistic Investigation

A model halogenated aryl ketone (4-chloropropiophenone 1) was subjected to mild catalytic hydrodehalogenation (p[H2] = 1 atm, T = 50 °C) in a multiphase system consisting of isooctane and an alkaline aqueous phase, in the presence of onium salts as phase-transfer agents. The chemoselectivity of the reaction was sharply influenced by the KOH concentration of the aqueous phase: thus, the formation of 1-phenyl-1-propanol 4 was favored in a highly alkaline pH range (>13.5 by 50% to 5% KOHaq). Instead, up to 95% selectivity toward phenyl ethyl ketone 2 was observed if the pH was controlled (8 < pH < 13) by adjusting the KOHaq concentration in the range between 5 and 1%. Further investigation of the pH effect indicated that an acidic aqueous phase directed the reaction chemoselectivity toward the formation of products arising from aromatic ring reduction (i.e., cyclohexyl ethyl ketone 7 and 1-cyclohexyl-1-propanol 8) rather than from carbonyl hydrogenation or hydrogenolysis. Also aliphatic amines, used in place of the PT onium salt, afforded good selectivities toward 2, although not as high as the ones obtained with Aliquat 336.

Easy and partial hydrogenation of aromatic carbonyls to benzyl alcohols using Pd/C(en)-catalyst

Although 10% Pd/C catalyzed hydrogenolysis of aromatic ketones and aldehydes readily affords methylene compounds via intermediary benzyl alcohols, the employment of 10% Pd/C–ethylenediamine complex [Pd/C(en)] as a catalyst eased the formation of benzyl alcohols.