Selective Partial Hydrogenation Research Articles

Unconventional Pd@Sulfonated Silica Monoliths Catalysts for Selective Partial Hydrogenation Reactions under Continuous Flow

AbstractDoubly functionalized, hierarchical‐porosity silica monoliths were synthesized by postgrafting of sulfonic groups and in situ growth of Pd nanoparticles in that order. PdNP of 3.1 nm size located in the mesopores of the material showed to be evenly distributed within 4.6 % wt Pd monoliths. The system was explored in the continuous‐flow, catalytic partial hydrogenation reaction of 3‐halogeno‐nitrobenzenes and 3‐hexyn‐1‐ol in the liquid phase, showing remarkable conversion, selectivity, and resistance under very mild conditions.

Catalysis beyond frontier molecular orbitals: Selectivity in partial hydrogenation of multi-unsaturated hydrocarbons on metal catalysts.

The mechanistic understanding and control over transformations of multi-unsaturated hydrocarbons on transition metal surfaces remains one of the major challenges of hydrogenation catalysis. To reveal the microscopic origins of hydrogenation chemoselectivity, we performed a comprehensive theoretical investigation on the reactivity of two α,β-unsaturated carbonyls-isophorone and acrolein-on seven (111) metal surfaces: Pd, Pt, Rh, Ir, Cu, Ag, and Au. In doing so, we uncover a general mechanism that goes beyond the celebrated frontier molecular orbital theory, rationalizing the C═C bond activation in isophorone and acrolein as a result of significant surface-induced broadening of high-energy inner molecular orbitals. By extending our calculations to hydrogen-precovered surface and higher adsorbate surface coverage, we further confirm the validity of the "inner orbital broadening mechanism" under realistic catalytic conditions. The proposed mechanism is fully supported by our experimental reaction studies for isophorone and acrolein over Pd nanoparticles terminated with (111) facets. Although the position of the frontier molecular orbitals in these molecules, which are commonly considered to be responsible for chemical interactions, suggests preferential hydrogenation of the C═O double bond, experiments show that hydrogenation occurs at the C═C bond on Pd catalysts. The extent of broadening of inner molecular orbitals might be used as a guiding principle to predict the chemoselectivity for a wide class of catalytic reactions at metal surfaces.

An exceptional selectivity for partial hydrogenation on a supported nickel catalyst coated with [BMIM][BF4

Coating supported metal catalysts with ionic liquids (ILs) is a promising approach for controlling performance. Here, we report our results on a commercial supported nickel catalyst coated with 1-n-butyl-3-methylimidazolium tetrafluoroborate, [BMIM][BF4], utilized for partial hydrogenation of 1,3-butadiene. Performance testing on the coated catalyst illustrates a record high selectivity towards partial hydrogenation (over 95% for butenes, irrespective of conversion level) ever reported on a supported nickel catalyst. Characterization provided direct evidence on electron donation from IL to nickel. Density functional theory calculations confirmed these results and showed that electron donation weakens the adsorption behaviour on nickel. Data indicated that binding strengths of butenes decrease more significantly than those of 1,3-butadiene does. This difference leads to increased selectivity towards partial hydrogenation. The filter effect confirmed by Conductor-like Screening Model for Realistic Solvents (COSMO-RS) calculations, on the other hand, helps to maintain this exceptional selectivity at all conversion levels by controlling active concentrations of 1,3-butadiene/butenes on nickel sites.

Low trans-isomers formation in the aqueous-phase Pt/TPPTS-catalyzed partial hydrogenation of methyl esters of linseed oil

Very low formation of both undesired products namely trans-C18:1 esters and the fully saturated methyl stearate (MS) with high catalytic activities (TOF=6820h−1) under mild reaction conditions have been achieved by water-dispersible platinum(0) nanoparticle catalysts stabilized by TPPTS ligands and the zwitterionic phospholipid surfactant lecithin in the partial hydrogenation of polyunsaturated methyl esters of linseed oil (MELO) into their monounsaturated counterparts in aqueous/organic micellar reactors. The reaction rate was independent of the stirring rate ensuring that mass transfer was not rate determining. The apparent activation energy of the Pt/TPPTS catalyst was calculated and amounts a low value of 17.8kJ/mol. Employing Pt/TPPTS catalysts the starting material MELO possessing an iodine value (IV) of 202 was reduced to IV=85 and contained only 2.4mol% of trans-C18:1 esters. In contrast, in the traditional industrial partial hydrogenation process of soybean oil possessing an IV of 130 reduced over commercial Ni-based catalyst to IV=80 the trans-fats content was∼30mol% whereas with a further reduction to IV=70 to produce all-purpose shortenings the trans-fats level reached a higher value of∼45mol%. In the aqueous-phase catalysis, in the range of 55–70 IVs for the hydrogenated products of MELO the Pt/TPPTS catalysts gave the least amount of trans-C18:1 esters followed by Rh/TPPTS and then by Pd/TPPTS complexes. Interestingly, with Pt/TPPTS catalysts the formation of MS was very low compared with Pd/TPPTS and Rh/TPPTS systems. Over highly active heterogeneous Pt/Al2O3 (5wt.%) catalysts the formation of trans-C18:1 esters was low whereas the content of MS was high (37.7mol%) compared with the very low formation of MS (2.93mol%) with Pt/TPPTS catalysts. Even at a reduction level of IV=72 a sufficient amount of C18:3 esters (2.9mol%) still remained over Pt/Al2O3 catalysts whereas with Pt/TPPTS at IV=70 the conversion of C18:3 esters was quantitative. A recycling experiment at a higher temperature of 80°C showed that the catalytic activity of water-dispersible platinum(0) nanoparticle catalysts stabilized by TPPTS remained high in a consecutive run and possess the potential to be recycled without any loss of catalytic activity. This partial hydrogenation reaction of MELO employing platinum(0) nanoparticle-TPPTS-lecithin-stabilized catalytic systems is an interesting model of a catalytic reaction for studying the selective partial hydrogenation of edible vegetable oils to foodstuffs with very low or zero amounts of both undesired products namely trans-fats and fully saturated fats employing environmentally attractive aqueous/organic two-phase systems.

Palladium nanoparticles supported onto stereocomplexed poly(lactic acid)-poly(ε-caprolactone) copolymers for selective partial hydrogenation of phenylacetylene

Palladium nanoparticles, generated by hydrogen reduction of Pd acetate, coordinated to a stereocomplexed 2,2′-bipyridine end-functionalized poly(lactic acid)-poly(e-caprolactone) copolymer showed enhanced catalytic activity and chemoselectivity for the partial reduction of phenylacetylene compared to the reference system which did not contain the poly(e-caprolactone). The obtained heterogeneous catalyst proved to be recyclable and suitable for selective phenylacetylene hydrogenation to styrene in solution and under solventless conditions.

Selective Partial Hydrogenation of Methyl Linoleate Using Highly Active Palladium Nanoparticles in Polyethylene Glycol

Partial hydrogenation of carbon–carbon double bonds is among one of the approaches to improve the low oxidative stability of vegetable biodiesel, which is an important drawback in biodiesel technology. In the current work, we developed an efficient two-phase catalytic system utilizing Pd(OAc)2 dissolved in polyethylene glycol (PEG) that in situ generates palladium nanoparticles in order to promote a selective partial hydrogenation reaction of methyl linoleate into mono-hydrogenated compounds while avoiding the generation of saturated compounds. High yield of methyl oleate was also obtained by hydrogenation of sunflower oil biodiesel using the same catalytic system. Through evaluating the palladium nanoparticles by TEM analysis, it is observed that 4 nm palladium nanoparticles generated in situ in PEG4000 showed high selectivity both for the partial hydrogenation of methyl linoleate and sunflower oil biodiesel.

Partial Hydrogenation of Sunflower Oil-derived FAMEs Catalyzed by the Efficient and Recyclable Palladium Nanoparticles in Polyethylene Glycol.

One approach to improve the oxidative stability of biodiesel is the partial hydrogenation of carbon-carbon double bonds. In the current work, an efficient catalytic system using Pd(OAc)2 dissolved in polyethylene glycol (PEG) which in situ generates palladium nanoparticles was developed in order to promote a selective partial hydrogenation reaction of sunflower oil FAMEs into mono-hydrogenated products avoiding the formation of saturated compounds or trans-isomers. High content of methyl oleate (85.0±1.4%) was obtained by hydrogenation of sunflower oil biodiesel with only 7.0±0.2% stearic acid. Through evaluating the palladium nanoparticles by TEM analysis, it is observed that 4 nm palladium nanoparticles generated in situ in PEG4000 are highly selective for the partial hydrogenation of sunflower oil biodiesel. And the Pd-PEG4000 catalyst can be resued for five times without obvious loss of activity or methyl oleate selectivity.

Heterogeneous Catalytic Transfer Partial-Hydrogenation with Formic Acid as Hydrogen Source Over the Schiff-Base Modified Gold Nano-Catalyst

The catalytic hydrogenation transformation with gaseous hydrogen in liquid phase always refers to a harsh condition and over-hydrogenation, and it is highly desired to develop new methods with partial-hydrogenation at mild condition. Herein, a heterogeneous catalytic transfer partial-hydrogenation strategy with formic acid as hydrogen source was developed over the Schiff-base modified gold nano-catalysts. The Au/Schiff-SiO2 catalyst was successfully prepared by one pot aldimine condensation and NaBH4 reduction of a gold precursor. The characterization results indicated that the gold nanoparticles with an average size below 2 nm were highly dispersed over the Schiff-base modified silica support. Such Schiff-based gold nano-catalysts exhibits excellent activity and partial-hydrogenation selectivity, with a high yield (>99%) for phenylacetylene partial-hydrogenation and achieving a 75% chemoselectivity for imines at a relative low temperature and atmospheric pressure. More importantly, the excess of formic acid can be removed by the direct dissociation of formic acid over Au/Schiff-SiO2 catalyst with CO2 emission into atmosphere, which leads to a hydrogen source as clean as hydrogen gaseous, but with a much more high activity and selectivity under mild reaction process.

IONIC LIQUID ASSISTED ACETYLENE PARTIAL HYDROGENATION OVER SURFACE OF PALLADIUM NANOPARTICLES

The loss of acetylene partial hydrogenation selectivity over bare palladium catalyst is observed by aging. In this study, 1-butyl-3-methyl imidazolinium hydroxide ionic liquid (BMIm[OH]) is loaded on Pd/[Formula: see text]–Al2O3 solid catalyst for enhancing the selectivity and different experimental techniques such as surface area measurements and catalytic performance have been performed to characterize the modified catalyst. Results revealed that the addition of ionic liquid maintains higher selectivity of partial hydrogenation over Pd/[Formula: see text]–Al2O3 catalyst for more than 30[Formula: see text]h especially at the temperature of acetylene complete removal ([Formula: see text]C). The activation energies of partial and complete acetylene hydrogenation on bare and ionic liquid loaded Pd/[Formula: see text]–Al2O3 are also calculated and utilized to clarify the obtained results.

Influence of Mg modifier on cis-trans selectivity in partial hydrogenation of biodiesel using different metal types

The catalytic performance of Pd, Pt, and Ni supported on SiO2 catalysts was investigated for partial hydrogenation of soybean methyl esters, in terms of FAME composition and biodiesel properties, especially oxidative stability and cold flow properties. The effect of Mg modifier over SiO2-supported catalysts on cis-trans selectivity of polyunsaturated FAMEs was also examined. The catalytic testing was performed under reaction conditions of 4bar hydrogen pressure and 80–120°C. Hydrogenation activity was presented by turnover frequency (TOF) of diunsaturated fatty acid (C18:2) within 4h of the reaction time. The highest TOF was obtained over Pd catalysts, while the lowest TOF was obtained from Ni catalysts. At high reaction temperature conditions showed a large amount of cis-monounsaturated fatty acid (cis-C18:1); however, it exhibited a large amount of trans-monounsaturated fatty acid (trans-C18:1) which has a negative impact on biodiesel properties. The XPS revealed that the introduction of Mg leads to a strong metal–support interaction caused by electron transfer from the support to the metal, which decreased trans-C18:1 formation and presented the higher oxidative stability than the catalysts without Mg modifier.

Upgrading of palm biodiesel fuel over supported palladium catalysts

Partial hydrogenation of palm biodiesel fuel (BDF) over 0.5wt%Pd/SBA-15 and 0.5wt%Pd/Zr-SBA-15 catalysts was examined by using a continuous fixed-bed reactor at 100 °C and 0.3 MPa under an atmosphere of H 2 , in comparison to the commercial 0.5wt%Pd/γ-Al 2 O 3 catalyst. The results showed that the 0.5wt%Pd/SBA-15 catalyst with high Pd dispersion and fast molecular diffusion through the short channeling pores gave the highest activity and selectivity in partial hydrogenation of polyunsaturated fatty acid methyl esters (FAME) as unstable components of palm BDF into cis -mono-unsaturated FAME as a target component of upgraded palm BDF with excellent oxidation stability and cold flow properties, which makes the addition of antioxidants unnecessary. By contrast, the 0.5wt%Pd/Zr-SBA-15 catalyst with strongly and moderately acidic sites gave low selectivity toward cis -mono-unsaturated FAME. The commercial 0.5wt%Pd/γ-Al 2 O 3 catalyst displayed much lower polyunsaturated FAME conversion and cis -mono-unsaturated FAME selectivity, associated with poor Pd dispersion and slow molecular diffusion through the disordered pores.

Selective partial hydrogenation of alkynes to (Z)-alkenes with ionic liquid-doped nickel nanocatalysts at near ambient conditions.

A selective hydrogenation method for forming (Z)-alkenes from alkynes has been developed using a catalyst system of cheap Ni-NPs in a nitrile functionalised imidazolium based ionic liquid (IL) operating under very mild reaction conditions of 30-50 °C and 1-4 bar H2 pressure.

Rhodium-Catalyzed Selective Partial Hydrogenation of Alkynes

The cationic rhodium complex [Rh(PcPr3)2(η6-PhF)]+[B{3,5-(CF3)2C6H3}4]− (PcPr3 = triscyclopropylphosphine, PhF = fluorobenzene) was used as a catalyst for the hydrogenation of the charge-tagged alkyne [Ph3P(CH2)4C2H]+[PF6]−. Pressurized sample infusion electrospray ionization mass spectrometry (PSI-ESI-MS) was used to monitor reaction progress. Experiments revealed that the reaction is first order in catalyst and first order in hydrogen, so under conditions of excess hydrogen the reaction is pseudo-zero order. Alkyne hydrogenation was 40 times faster than alkene hydrogenation. The turnover-limiting step is proposed to be oxidative addition of hydrogen to the alkyne (or alkene)-bound complex. Addition of triethylamine caused a dramatic reduction in rate, suggesting a deprotonation pathway was not operative.

Toward Pyridine–Heterocycle Patterns through Prins and Aza‐Prins Cyclisations: Application to a Short Synthesis of (±)‐Anabasine

AbstractThe formation of pyridine‐containing bisheterocycles through a Prins‐type cyclisation is described. Pyridine–tetrahydropyran and pyridine–piperidine conjugates could be efficiently obtained using various carbaldehydes including dicarbaldehydes, and either homoallylic alcohols or a homoallylic amine. Selective partial or complete hydrogenation led to new bisheterocycle combinations. A two‐step sequence involving an aza‐Prins cylisation allowed us to prepare the alkaloid anabasine.

Review On Reduction And Partial Oxidation of Organics In Photocatalytic (Membrane) Reactors

Traditional processes for making chemicals are unsustainable in terms of resources and environmental impact. The present pa- per is a review of the most recent advances in the application of selective photocatalytic reactions to organic synthesis, which, in the last years, has attracted the interest of the scientific community addressing on development of environmentally benign synthetic processes. Indeed, selective photocatalysis is operated at ambient temperature and pressure, needs no complex equipments, does not use dangerous chemical reagents and solvents, does not release harmful wastes into the environment and can utilize solar light. Reactions discussed in this paper, as a green approach for valuable fine chemical synthesis, are: i) photocatalytic hydrogenation and/or transfer hydrogenation of ketones and nitrocompounds by using both UV and visible light; ii) photocatalytic hydrogenation and selective partial hydrogenation of unsaturated compounds; iii) selective partial oxidation of alkanes, alkenes, alcohols, aliphatic acids, benzene and other aromatic com- pounds by using both UV and visible light. Use of Photocatalytic Membrane Reactors (PMRs) in reductions (e.g. CO2 to fuels) and in se- lective partial oxidations (e.g. benzene to phenol) is reported, evidencing that opening up of a new avenue is expected in organic synthe- ses, thanks to the synergy of heterogeneous photocatalysis and membrane processes. Nevertheless, these studies are still at nascent stady and much work is needed before taking advantage of PMRs potentiality at industrial level in this interdisciplinary area.

Acrolein Hydrogenation on Ni(111)

Acrolein hydrogenation via allyl alcohol, propanal, and enol into propanol on the Ni(111) surface has been investigated using the spin-polarized periodic density functional theory method. On the basis of the computed adsorption energies and effective hydrogenation barriers, acrolein hydrogenation into propanal and allyl alcohol obeys the Langmuir–Hinshelwood mechanism and propanal formation is more favored kinetically and thermodynamically than allyl alcohol formation. Hydrogenation of propanal and allyl alcohol should follow the Eley–Rideal mechanism. The adsorption energies of acrolein, allyl alcohol, and propanal along with the partial hydrogenation selectivity on Ni, Au, Ag, and Pt catalysts have been compared and discussed.

Pressure and Temperature Effects on the Formation of a Pd/C Surface Carbide: Insights into the Role of Pd/C as a Selective Catalytic State for the Partial Hydrogenation of Acetylene

The stability of the near-surface region of palladium(111) under a pressure of acetylene and hydrogen is studied via a combination of density functional theory calculations and atomistic ab initio thermodynamics. Gibbs free energy maps give insight into the deposition of C in the near surface of Pd(111) due to acetylene fragmentation. Our results indicate that under working conditions Pd is able to incorporate large amounts of C that will be distributed equally among the top metal interlayers. We further explored factors such as the partial hydrogen pressure, temperature, and presence of strain and found that whereas high temperatures and large hydrogen pressures inhibit C accumulation, the presence of tensile strain enhances the dissolution of C. Additional calculations indicated that the accumulation and distribution of C in the near surface of Pd critically weaken the adsorption energy of ethylene, hence favoring its desorption and yielding a high selectivity for partial hydrogenation. We claim that the study of Gibbs free energy maps can be particularly useful in gaining atomic understanding of solute distribution in materials under realistic environmental situations.

Quenched skeletal Ni as the effective catalyst for selective partial hydrogenation of polycyclic aromatic hydrocarbons

Quenched skeletal Ni is an active and selective catalyst for selective partial hydrogenation of polycyclic aromatic hydrocarbons (PAHs). The molecular structure of PAHs significantly dominate the hydrogenation process and furthermore, the distribution of hydrogenated products.

Single step synthesis of metallic nanoparticles using dihydroxyl functionalized ionic liquids as reductive agent

In the last few years, ionic liquids (ILs) have revealed their broad versatility for application towards the synthesis of shape and size controlled nanoscale metal catalysts, respectively metal(0) nanoparticles (M-NPs) in the absence of additive ligand. ILs play the role of solvent and ligand. In our work, we depict the synthesis of M-NPs (M = Cu, Ag, Ni, Ru) using dihydroxyl functionalized imidazolium ILs 1-(2,3-dihydroxypropyl)-2,3-dimethylimidazolium bis(trifluoromethanesulfonimide) [C1C1(EG)Im][NTf2] as solvent, stabilizer and reductive agent simultaneously. In this IL the formation of stable dispersion of NPs from silver and copper salts in the absence of any reducing agent has been observed. The comparison of the 13C-NMR, and IR data of pure IL and IL–NP (Cu and Ag) suspensions proved the oxidation of the hydroxyl group to a carbonyl group, confirming that the dihydroxyl function of the IL acted as the reducing agent. This oxido-reduction depends on the nature of the metal. No reaction occurred with NiII and Ru0 precursors, and with RuII and Ni0 salts the formation of M-NPs is due to the activation of the acidic protons on the imidazolium ring. The Ru-NPs were then further evaluated for selective partial hydrogenation, here we observed good selectivities for α,β-unsaturated compounds such as cyclohexenone and cinnamic aldehyde, which can be converted exclusively into the unsaturated alcohols or saturated alcohols.

Structure–Activity Studies on Highly Active Palladium Hydrogenation Catalysts by X-ray Absorption Spectroscopy

Functionalized carbon nanotubes were used to produce Pd-based hydrogenation catalysts. Pd/CNT with small (1–2 nm) Pd particles showed classical catalytic behavior in propyne hydrogenation, with high propene selectivity at moderate conversion levels and propane formation near full conversion. Pd/CNT with larger (∼15 nm) nanoparticles, however, was selective (88%) toward propene even at practically full propyne conversion. An additionally prepared Pd2Ga/CNT catalyst exhibited even higher propene selectivity at full conversion. All of these materials were studied in situ by X-ray absorption spectroscopy at the Pd K-edge. Pd2Ga/CNT was stable under all conditions examined without variation in XANES or in the derived EXAFS parameters. Both Pd/CNT samples formed β-hydride under hydrogen, as assessed from the calculated lattice expansion and the characteristic red shift of the XANES maxima. The minor spectroscopic difference between the monometallic catalysts observed at high propyne conversion suggests the decisive role of a Pd–C (subsurface C) contribution in the structure of larger Pd particles, being absent with ultrasmall nanoparticles. In general, all factors (intermetallic phase formation, subsurface C, etc.) that reduce the surface H coverage will give rise to enhanced partial hydrogenation selectivity of palladium when secondary alkene hydrogenation at late bed segments or diffusion issues in the pores are avoided.