Partial Hydrogenation Of Acetylene Research Articles

Unlocking enhanced selectivity of Pd/Al2O3 in semihydrogenation of alkynes by in situ ligand‐reduction strategy

AbstractThe partial hydrogenation of alkynes into alkenes constitutes a pivotal chemical transformation in the synthesis of fine chemicals, pharmaceuticals, and polymers. Nevertheless, the extant industrial catalyst falls short of achieving a felicitous equilibrium between its catalytic potency and selectivity. Herein, triphenylphosphine (PPh3) modified Pd/Al2O3 catalysts are fabricated through a “one‐pot” process, which achieve highly selective hydrogenation of alkynes at room temperature. PPh3 plays a dual role—as a reducing agent and a ligand. Kinetic and characterization studies reveal PPh3 alters H2 activation from homolytic to heterolytic cleavage, which facilitate the formation of alkene. Moreover, PPh3 can also optimize the reaction microenvironment, achieving the reduced self‐poisoning of alkyne and promoted desorption of alkene. In the realm of alkyne hydrogenation, our philosophy encompasses a global optimization of active sites, ligand systems, and reaction microenvironmental. This method steers the course of catalyst development for other reactions beyond the field of alkyne hydrogenation.

Efficient utilization of glycerol as a hydrogen source for partial hydrogenation of alkynes over a Cu-loaded TiO2 photocatalyst

The utilization of biomass glycerol would contribute to the fight against global warming by reducing greenhouse gas emissions; however, efficient utilization of glycerol in water is still a challenge. In this study, partial hydrogenation of alkynes over a titanium(IV) oxide photocatalyst with a copper cocatalyst (Cu/TiO2) was investigated in the presence of glycerol in an acetonitrile-water solvent. Glycerol worked efficiently as a hydrogen source and alkynes were converted to corresponding alkenes. Glycolic acid and formic acid, which are formed as oxidation products of glycerol, cause a decrease of recyclability due to the partial dissolution of Cu nanoparticles. The stability of the Cu/TiO2 photocatalyst is improved by the addition of NaOH, although the reaction rate decreases. A slight increase in the reaction temperature restores the reaction rate of partial hydrogenation, and preferably, the H2 yield becomes smaller. The results provide a new application of biomass glycerol in water, i.e., a hydrogen source for photocatalytic reactions.

Front Cover: Ruthenium‐Catalyzed E‐Selective Partial Hydrogenation of Alkynes under Transfer‐Hydrogenation Conditions using Paraformaldehyde as Hydrogen Source (5/2021)

Front Cover: Ruthenium‐Catalyzed <i>E</i>‐Selective Partial Hydrogenation of Alkynes under Transfer‐Hydrogenation Conditions using Paraformaldehyde as Hydrogen Source (5/2021)

Ruthenium‐Catalyzed E‐Selective Partial Hydrogenation of Alkynes under Transfer‐Hydrogenation Conditions using Paraformaldehyde as Hydrogen Source

AbstractE‐alkenes were synthesized with up to 100 % E/Z selectivity via ruthenium‐catalyzed partial hydrogenation of different aliphatic and aromatic alkynes under transfer‐hydrogenation conditions. Paraformaldehyde as a safe, cheap and easily available solid hydrogen carrier was used for the first time as hydrogen source in the presence of water for transfer‐hydrogenation of alkynes. Optimization reactions showed the best results for the commercially available binuclear [Ru(p‐cymene)Cl2]2 complex as pre‐catalyst in combination with 2,2‐bis(diphenylphosphino)‐1,1‐binaphthyl (BINAP) as ligand (1 : 1 ratio per Ru monomer to ligand). Mechanistic investigations showed that the origin of E‐selectivity in this reaction is the fast Z to E isomerization of the formed alkenes. Mild reaction conditions plus the use of cheap, easily available and safe materials as well as simple setup and inexpensive catalyst turn this protocol into a feasible and promising stereo complementary procedure to the well‐known Z‐selective Lindlar reduction in late‐stage syntheses. This procedure can also be used for the production of deuterated alkenes simply using d2‐paraformaldehyde and D2O mixtures.

Comparison of Pd and Pd4S based catalysts for partial hydrogenation of external and internal butynes

The partial hydrogenation of but-1-yne and but-2-yne was studied with a view to probing the difference between external and internal alkynes. Catalysts with Pd and Pd4S active phases were prepared on a carbon nanofiber support. Over the simple Pd catalyst over-hydrogenation was common which restricted alkene selectivity greatly – 25–35% depending on temperature. In contrast, the Pd4S active phase offered exceptional alkene selectivity (maximum of 92–93% alkene selectivity for both the external and internal alkyne). DFT calculations were subsequently used to rationalise this difference in product selectivity – sulfur appears to change the geometry of the active site in Pd4S and create a surface which favours alkene desorption relative to over-hydrogenation. This work further emphases the potential of palladium sulfide phases as an alternative to purely metallic palladium catalysts for partial alkyne hydrogenation.

On the Limited Role of Electronic Support Effects in Selective Alkyne Hydrogenation: A Kinetic Study of Au/MOx Catalysts Prepared from Oleylamine‐Capped Colloidal Nanoparticles

AbstractWe report a quantitative kinetic evaluation and study of support effects for partial alkyne hydrogenation using oleylamine‐capped Au colloids as catalyst precursors. The amine capping agents can be removed under reducing conditions, generating supported Au nanoparticles of ∼2.5 nm in diameter. The catalysts showed high alkene selectivity (&gt;90 %) at all conversions during alkyne partial hydrogenation. Catalytic activity, observed rate constants, and apparent activation energies (25–40 kJ/mol) were similar for all Au catalysts, indicating support effects are relatively small. Alkyne adsorption, probed with FTIR and DFT, showed adsorption on the support was associated with hydrogen‐bonding interactions. DFT calculations indicate strong alkyne adsorption on Au sites, with the strongest adsorption sites at the metal‐support interface (MSI). The catalysts had similar hydrogen reaction orders (0.7–0.9), and 1‐octyne reaction orders (∼−0.2), suggesting a common mechanism. The reaction kinetics are most consistent with a mechanism involving the non‐competitive activated adsorption of H2 on an alkyne‐covered Au surface.

A facile synthesis of Ag@PdAg core-shell architecture for efficient purification of ethene feedstock

Precise control of elemental configurations within multimetallic nanoparticles could enable access to functional nanomaterials with significant performance benefits. Here, we present a one-pot synthesis of supported Ag@PdAg core-shell catalyst with an ordered PdAg alloy shell and an Ag core. Both the relative reduction potential and ratio of metal precursors are essential for this synthesis strategy. The distinguished properties of Ag@PdAg, particularly the electronic structure, indicates the existence of electron modification not only between Pd and Ag on PdAg shell, but between Ag core and alloy shell. The Ag@PdAg catalyst displays 97% ethene yield in the partial hydrogenation of acetylene, which is 2.0 and 8.1 times that of over PdAg alloy and pure Pd catalysts, and this is the most selective catalyst reported to data under industrial evaluation conditions. Moreover, this core-shell structure exhibits preferable stability with comparison to PdAg alloy catalyst. The facile synthesis of core-shell architecture with alloy shell structure provides a new platform for efficient catalytic transfer of chemical resource.

Selective ensembles in supported palladium sulfide nanoparticles for alkyne semi-hydrogenation

Ensemble control has been intensively pursued for decades to identify sustainable alternatives to the Lindlar catalyst (PdPb/CaCO3) applied for the partial hydrogenation of alkynes in industrial organic synthesis. Although the geometric and electronic requirements are known, a literature survey illustrates the difficulty of transferring this knowledge into an efficient and robust catalyst. Here, we report a simple treatment of palladium nanoparticles supported on graphitic carbon nitride with aqueous sodium sulfide, which directs the formation of a nanostructured Pd3S phase with controlled crystallographic orientation, exhibiting unparalleled performance in the semi-hydrogenation of alkynes in the liquid phase. The exceptional behavior is linked to the multifunctional role of sulfur. Apart from defining a structure integrating spatially-isolated palladium trimers, the active ensembles, the modifier imparts a bifunctional mechanism and weak binding of the organic intermediates. Similar metal trimers are also identified in Pd4S, evidencing the pervasiveness of these selective ensembles in supported palladium sulfides.

High-selectivity palladium catalysts for the partial hydrogenation of alkynes by gas-phase cluster deposition onto oxide powders

The selective hydrogenation of alkynes is an important reaction in the synthesis of fine and bulk chemicals. We show that the synthesis of metal nanoparticles in the gas phase, followed by depositi...

Molybdenum nitrides: a study of synthesis variables and catalytic performance in acetylene hydrogenation

We have examined the catalytic action of β- and γ-Mo2N in the partial hydrogenation of acetylene. The influence of variations in GHSV (230–1600 min−1), feed composition (5–30% v/v N2/H2), heating rate (0.1–5 K min−1) and isothermal hold (1–7 h at 933 K) on nitride structural properties has been assessed. At ≥ 2 K min−1, β-Mo2N (≤ 15 m2 g−1) consisting of small crystallites (< 5 μm) was generated. At ≤ 0.5 K min−1, γ-Mo2N with a platelet morphology and surface area ≥ 45 m2 g−1 was formed. High GHSV, low N2 feed content and a prolonged isothermal hold served to increase γ-Mo2N area (to 135 m2 g−1). Lower alkene selectivity and a twofold higher specific (per m2) acetylene hydrogenation rate were recorded for β-Mo2N and linked to higher surface Mo/N ratio (from XPS). Olefin selectivity for both nitrides was greater than that reported for Pd catalysts. Moreover, we recorded negligible green oil formation in reactions over γ-Mo2N.

Correlation between Microstructure Evolution of a Well‐Defined Cubic Palladium Catalyst and Selectivity during Acetylene Hydrogenation

AbstractThe varied surface structures of a Pd catalyst showed different catalytic performances in the partial hydrogenation of acetylene. The exposed Pd (1 0 0) facet is considered to be the most selective of all other facets for the formation of ethylene, but it is unstable and the fine structure needs to be revealed during the reaction. Herein, the evolution of the surface structure of cubic Pd nanoparticles, which are all bound with (1 0 0) facets, was studied by transmission electron microscopy in the partial hydrogenation of acetylene. Furthermore, the relation between the varying surface structure and the activity/selectivity was correlated. The (1 0 0) facets of Pd were transformed into stepped facets during the reaction, derived by adsorption/desorption of the reactants and energy compensation, which was the main reason for the decrease in the selectivity towards ethylene.

Intermetallic Compounds as Potential Alternatives to Noble Metals in Heterogeneous Catalysis: The Partial Hydrogenation of Butadiene on γ‐Al4Cu9(1 1 0)

AbstractRecently, non‐noble intermetallic compounds have shown promising catalytic performances in the partial hydrogenation of alkynes and alkenes. In this work, the properties of γ‐Al4Cu9(1 1 0) toward the gas‐phase hydrogenation of butadiene were investigated at total pressures of 2–20 mbar and temperatures of 110–180 °C. The model catalyst is active and 100 % selective to butenes. Moreover, although less active than Al13Fe4(0 1 0), which was evaluated previously for the same reaction, it is more selective and more stable. The combination of catalytic tests with pre‐ and postreaction Auger electron spectroscopy measurements and comparative tests with Cu(1 1 0) shows that Cu governs the reaction on γ‐Al4Cu9(1 1 0). However, the lower activity of the (more Cu‐rich) sputtered Al4Cu9 surface with respect to the annealed one and the differences between Al4Cu9 and Cu surfaces in terms of butene isomer distribution, butene conversion kinetics, and sensitivity to poisons, demonstrate the unique character of the intermetallic compound.

Chemical synthesis and biological evaluation of ω-hydroxy polyunsaturated fatty acids

ω-Hydroxy polyunsaturated fatty acids (PUFAs), natural metabolites from arachidonic acid (ARA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) were prepared via convergent synthesis approach using two key steps: Cu-mediated CC bond formation to construct methylene skipped poly-ynes and a partial alkyne hydrogenation where the presence of excess 2-methyl-2-butene as an additive that is proven to be critical for the success of partial reduction of the poly-ynes to the corresponding cis-alkenes without over-hydrogenation. The potential biological function of ω-hydroxy PUFAs in pain was evaluated in naive rats. Following intraplantar injection, 20-hydroxyeicosatetraenoic acid (20-HETE, ω-hydroxy ARA) generated an acute decrease in paw withdrawal thresholds in a mechanical nociceptive assay indicating pain, but no change was observed from rats which received either 20-hydroxyeicosapentaenoic acid (20-HEPE, ω-hydroxy EPA) or 22-hydroxydocosahexaenoic acid (22-HDoHE, ω-hydroxy DHA). We also found that both 20-HEPE and 22-HDoHE are more potent than 20-HETE to activate murine transient receptor potential vanilloid receptor1 (mTRPV1).

Catalytic performance of Pd-promoted Cu hydrotalcite-derived catalysts in partial hydrogenation of acetylene: effect of Pd–Cu alloy formation

A highly dispersed PdCu nanoalloy catalyst derived from a CuMgAl-hydrotalcite precursor exhibited superior catalytic performance in partial hydrogenation of acetylene.

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.

ChemInform Abstract: Supported Catalysts Based on Layered Double Hydroxides for Catalytic Oxidation and Hydrogenation: General Functionality and Promising Application Prospects

AbstractReview: 220 refs.

ChemInform Abstract: The Non‐innocent Role of Cerium Oxide in Heterogeneous Catalysis: A Theoretical Perspective

AbstractReview: 125 refs.

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.

The non-innocent role of cerium oxide in heterogeneous catalysis: A theoretical perspective

Ceria (CeO2) is the most significant of the oxides of rare-earth elements in industrial catalysis with its reducibility being essential to its functionality in catalytic applications. The complexity of real (powder) catalysts hinders the fundamental understanding of how they work. Specifically, the role of ceria in the catalytic activity of ceria-based systems is still not fully understood. To elucidate it, well-defined ceria-based model catalysts are prepared experimentally or created theoretically and studied. The purpose of this brief review is to discuss recent results on model ceria-based catalysts using CeO2(111), VOx/CeO2(111), and Ni/CeO2(111) as examples of catalysts for partial alkyne hydrogenation, oxidative dehydrogenation, and hydrogen production, respectively. The emphasis is here put on theoretical studies and special attention is given to the effects of ceria as catalyst support.

Promoted ceria catalysts for alkyne semi-hydrogenation

CeO2 is a highly selective catalyst for the partial hydrogenation of alkynes. However, due to its limited H2 splitting ability, a high operating temperature is required for the reaction, hampering the practical exploitation of this abundant oxide. In this work, we demonstrate that gallium promotes the activity of CeO2 for the semi-hydrogenation of acetylene and methylacetylene, enabling a reduction of the operating temperature to 373K, while maintaining an outstanding ethylene and propylene selectivity (80–97%), even in the presence of excess alkene in the feed. Oligomers comprised the main secondary product, while the selectivity to the corresponding alkane did not exceed 2%. The characterization of mixed Ce-Ga oxides reveals that the progressive incorporation of gallium into the ceria structure, forming a solid solution, boosts the oxygen storage capacity and the reducibility of the material. This is ascribed to the facilitated H2 activation on the Ga-promoted samples, as confirmed by in situ infrared spectroscopy and density functional theory simulations. The interplay between the advantage brought by the decreased barrier for H2 cleavage and the disadvantage due to the increased number of oxygen vacancies governs the reactivity of the CeGaOx catalysts in alkyne hydrogenation. The composition in the optimal catalyst, containing a molar Ce:Ga ratio of 95:5, was extrapolated to other trivalent cations. Indium incorporated in the ceria lattice favored the low-temperature H2 activation and led to an activity enhancement that surpassed that of gallium. However, aluminum did not form a solid solution with ceria and caused no effect. This work comprises the first application of promoted cerias in hydrogenation catalysis and may prompt further developments in olefin purification.