Acetylene Conversion Research Articles

Molecular growth paths and dust‐particles nucleation precursors in Ar/C2H2 low pressure discharges

AbstractA numerical model was used to investigate the effect of acetylene concentration in the feed gas on molecular growth and solid particle nucleation in argon‐acetylene CCRF discharges. Results showed that for large acetylene conversion yields and small acetylene concentrations in the discharge, the ionization kinetic is driven by the Penning process and the molecular growth is governed by neutral polyynes. The cluster size distribution predicted shows that nucleation is unlikely in this situation. On the contrary, for limited conversion yields and significant acetylene concentrations in the discharge, the ionization kinetic is driven by the electron‐impact process; the molecular growth is governed by positive ions and leads to significant concentrations of neutral polyynes and enhanced nucleation rate.

Supported ionic liquid-copper catalyst for synergistically catalytic and highly efficient hydration of acetylene

At present, heterogeneous mercury-free catalysts are suffering from rapid deactivation caused by reduction or aggregation/growth of copper particle during preparation and reaction. Here, a high-performance and long-lived catalysts with activated carbon supported copper-ionic liquid system (Cu-xIL/AC, x is the molar ratio of IL and Cu) was prepared by wet impregnation method for the hydration of acetylene to acetaldehyde. Over the optimal Cu-1.5IL/AC catalyst, the acetylene conversion of 96.8% and acetaldehyde selectivity of 87.1% could still be obtained at 20 h (T = 240 °C, GHSVC2H2 = 90 h−1 and VH2O/VC2H2 = 1.15). The experimental results indicated that Cu species were embedded in ionic liquid (IL) and the interaction and synergistic effect between metal ions and IL guaranteed high and stable dispersion of active species on the host and suppress the reduction of active Cu specie, which are mainly responsible for the excellent catalytic property. The findings highlight the contribution of ILs in heterogeneous catalytic reaction and supply a promising industrial application of Cu-1.5IL/AC catalyst in acetylene hydration.

Unveiling the complexity of the dual gold(I) catalyzed intermolecular hydroamination of alkynes leading to vinylazoles

The conversion of alkynes into functionalised alkenes catalyzed by Au(NHC) complexes (NHC = N-heterocyclic carbene) is a fundamental and atom-economical transformation yet its mechanistic understanding is limited. In order to shed light on such catalytic reaction mechanisms, computational tools are utilized to gain insights into the gold catalyzed intermolecular hydroamination of internal alkynes. The combination of alkynes and benzotriazole leads to vinylazoles via a solvent free, gold(I) mediated hydroamination. DFT permits an in-depth discussion of single versus dual metal catalysis in this transformation. The role of the triflate anion is studied, being essential for the protodeauration and it helped to clarify the rate determining step, that consists of the gold-tiazolyl nucleophilic attack to the gold-alkyne π-complex.

π-Adsorption promoted electrocatalytic acetylene semihydrogenation on single-atom Ni dispersed N-doped carbon

As a novel electrocatalyst for acetylene semihydrogenation, single-atom nickel dispersed N-doped carbon exhibits a high acetylene conversion of 97.4%, which are attributed to weak π-adsorption of ethylene on individual Ni sites.

Unraveling high alkene selectivity at full conversion in alkyne hydrogenation over Ni under continuous flow conditions

Carbon dissolution in Ni lattices decreased the interaction of alkenes with the catalyst surface and gave an elusive combination of full phenyl acetylene conversion and high styrene selectivity (92 ± 1%) under continuous flow conditions.

Enabling Semihydrogenation of Alkynes to Alkenes by Using a Calcium Palladium Complex Hydride.

Selective hydrogenation of alkynes to alkenes requires a catalytic site with suitable electronic properties for modulating the adsorption and conversion of alkyne, alkene as well as dihydrogen. Here, we report a complex palladium hydride, CaPdH2, featured by electron-rich [PdH2]δ- sites that are surrounded by Ca cations that interacts with C2H2 and C2H4 via σ-bonding to Pd and unusual cation-π interaction with Ca, resulting in a much weaker chemisorption than those of Pd metal catalysts. Concomitantly, the dissociation of H2 and hydrogenation of C2Hx (x = 2-4) species experience significant energy barriers over CaPdH2, which is fundamentally different from those reported Pd-based catalysts. Such a unique catalytic environment enables CaPdH2, the very first complex transition-metal hydride catalyst, to afford a high alkene selectivity for the semihydrogenation of alkynes.

Enantioselective Synthesis of Chiral Carboxylic Acids from Alkynes and Formic Acid by Nickel-Catalyzed Cascade Reactions: Facile Synthesis of Profens.

We report a stereoselective conversion of terminal alkynes to α-chiral carboxylic acids using a nickel-catalyzed domino hydrocarboxylation-transfer hydrogenation reaction. A simple nickel/BenzP* catalyst displayed high activity in both steps of regioselective hydrocarboxylation of alkynes and subsequent asymmetric transfer hydrogenation. The reaction was successfully applied in enantioselective preparation of three nonsteroidal anti-inflammatory profens (>90 % ees) and the chiral fragment of AZD2716.

Enantioselective Synthesis of Chiral Carboxylic Acids from Alkynes and Formic Acid by Nickel‐Catalyzed Cascade Reactions: Facile Synthesis of Profens

AbstractWe report a stereoselective conversion of terminal alkynes to α‐chiral carboxylic acids using a nickel‐catalyzed domino hydrocarboxylation‐transfer hydrogenation reaction. A simple nickel/BenzP* catalyst displayed high activity in both steps of regioselective hydrocarboxylation of alkynes and subsequent asymmetric transfer hydrogenation. The reaction was successfully applied in enantioselective preparation of three nonsteroidal anti‐inflammatory profens (>90 % ees) and the chiral fragment of AZD2716.

Divergent Aminocarbonylations of Alkynes Enabled by Photoredox/Nickel Dual Catalysis.

A metallaphotoredox-catalyzed strategy for the selective and divergent aminocarbonylation of alkynes with amines and 1 atm of CO is reported. This synergistic protocol not only enables the Markovnikov-selective hydroaminocarbonylation of alkynes to afford α,β-unsaturated amides, but also facilitates a sequential four-component hydroaminocarbonylation/radical alkylation in the presence of tertiary and secondary alkyl boronate esters, which allows for straightforward conversion of alkynes into corresponding amides. Preliminary mechanistic studies disclose that a photoinduced oxidative insertion of aniline and CO into nickel followed by a migratory insertion of (carbamoyl)nickel species could be involved.

Divergent Aminocarbonylations of Alkynes Enabled by Photoredox/Nickel Dual Catalysis

AbstractA metallaphotoredox‐catalyzed strategy for the selective and divergent aminocarbonylation of alkynes with amines and 1 atm of CO is reported. This synergistic protocol not only enables the Markovnikov‐selective hydroaminocarbonylation of alkynes to afford α,β‐unsaturated amides, but also facilitates a sequential four‐component hydroaminocarbonylation/radical alkylation in the presence of tertiary and secondary alkyl boronate esters, which allows for straightforward conversion of alkynes into corresponding amides. Preliminary mechanistic studies disclose that a photoinduced oxidative insertion of aniline and CO into nickel followed by a migratory insertion of (carbamoyl)nickel species could be involved.

Sn(II)/PN@AC catalysts: synthesis, physical-chemical characterization, and applications.

In this study, the novel tin-based catalysts (Sn(II)/PN@AC) were prepared using the phosphorus and nitrogen dual-modified activated carbon as support and SnCl2 as active compounds, as well as then evaluated in acetylene hydrochlorination. Under the reaction temperature of 180 °C and an acetylene gas hourly space velocity (GHSV-C2H2) of 30 h–1, the 15%Sn(II)/PN@AC-550 showed the initial acetylene conversion of 100% and vinyl chloride selectivity over 98.5%. Additionally, the deactivation rate of 15%Sn(II)/PN@AC-550 reached 0.47% h–1, which was lower than that of 15%Sn(II)/AC-550 (1.02% h–1), suggesting that PN@AC-550 as novel support can retarded the deactivation of Sn(II)/AC-550 catalysts during acetylene hydrochlorination. Based on the catalytic tests and characterization results (XRD, Raman, BET surface area, TEM, C2H2-TPD, H2-TPR, XPS, FT-IR, TGA, and ICP), it demonstrated that PN@AC-550 as support could effectively improve the dispersion of tin species, retard the formation of coke deposition, lessen the oxidation of SnCl2 during the preparation process, as well as relatively inhibit the leach of tin species during the reaction. By combing the FTIR results and Rideal–Eley mechanism, we proposed that that HSnCl3 was transition state of SnCl2 in catalysis acetylene hydrochlorination and then adsorbed the acetylene to produce the vinyl chloride.

Discharge dynamics, plasma kinetics and gas flow effect in argon–acetylene discharges

We investigated capacitively coupled Ar/C2H2 RF plasmas with a 1D fluid model that couples a 13.56 MHz discharge module, a long timescale chemical module and a flow transport module. A new solution procedure was developed in order to accurately describe the coupling between the short timescale discharge dynamics and the long characteristic time processes that play a major role in the molecular growth of reactive species. The plasma was simulated for different inlet gas configurations and flowrates. We showed that for a showerhead configuration one may distinguish two situations. For short residence time the plasma was strongly electronegative in the very center of the discharge gap and dominated by large hydrocarbon positive and negative ions. In this situation the acetylene conversion, although moderate, lead to a significant molecular growth. For long residence time, although C2H2 underwent a total conversion, the products of the primary C2H2 dissociation process were consumed by surface deposition which reduced drastically the molecular growth in the short gap discharge considered here. Whatever the conditions, we confirmed the key-role of Ar* in the acetylene conversion, ionization kinetics as well as the subsequent molecular growth for neutral and charged species. We also showed that remote feed gas and showerhead configurations predicted similar results at low flowrate. At larger flowrate the two configurations presented some discrepancy. Especially H2 density was much larger for the remote feed gas configuration, which affected the overall plasma behavior. Our results highlight that realistic gas-flow models are essential for an accurate description of acetylene conversion in Ar/C2H2 plasma.

Grafting nanometer metal/oxide interface towards enhanced low-temperature acetylene semi-hydrogenation

Metal/oxide interface is of fundamental significance to heterogeneous catalysis because the seemingly “inert” oxide support can modulate the morphology, atomic and electronic structures of the metal catalyst through the interface. The interfacial effects are well studied over a bulk oxide support but remain elusive for nanometer-sized systems like clusters, arising from the challenges associated with chemical synthesis and structural elucidation of such hybrid clusters. We hereby demonstrate the essential catalytic roles of a nanometer metal/oxide interface constructed by a hybrid Pd/Bi2O3 cluster ensemble, which is fabricated by a facile stepwise photochemical method. The Pd/Bi2O3 cluster, of which the hybrid structure is elucidated by combined electron microscopy and microanalysis, features a small Pd-Pd coordination number and more importantly a Pd-Bi spatial correlation ascribed to the heterografting between Pd and Bi terminated Bi2O3 clusters. The intra-cluster electron transfer towards Pd across the as-formed nanometer metal/oxide interface significantly weakens the ethylene adsorption without compromising the hydrogen activation. As a result, a 91% selectivity of ethylene and 90% conversion of acetylene can be achieved in a front-end hydrogenation process with a temperature as low as 44 °C.

CH Activation by a Heavy Metal Cation: Production of H2 from the Reaction of Acetylene with C4H4-Os(+) in Gas phase

While first-row transition metal cations, notably Fe(+), catalyze the gas-phase conversion of acetylene to benzene, a distinct path is chosen in systems with Os, Ir, and Rh cations. Rather than losing the metal cation M(+) from the benzene–M(+) complex, as is observed for the Fe(+) system, the heavy metal ions activate CH bonds. The landmark system C4H4-Os(+) reacts with acetylene to produce C6H4-Os(+) and dihydrogen. Following our work on isomers of the form C2nH2n-Fe(+), we show by DFT modeling that the CH bonds of the metalla-7-cycle structure, C6H6-Os(+), are activated and define the gas-phase reaction path by which H2 is produced. The landmark structures on the network of reaction paths can be used as a basis for the discussion of reactions in which a single Os atom on an inert surface can assist reactions of hydrocarbons.

One-Pot Chemoenzymatic Conversion of Alkynes to Chiral Amines

One-Pot Chemoenzymatic Conversion of Alkynes to Chiral Amines

Breaking the inverse relationship between catalytic activity and selectivity in acetylene partial hydrogenation using dynamic metal–polymer interaction

The partial hydrogenation of acetylene impurities in ethylene is industrially important because acetylene acts as a catalyst poison in downstream ethylene polymerization processes. In this reaction, simultaneously achieving high acetylene conversion and partial hydrogenation selectivity is challenging, and most known catalyst systems exhibit an inverse activity–selectivity relationship. Here, an amorphous polyphenylene sulfide (Am-PPS) was synthesized as a promoter for 0.1 wt% Pd/α-Al2O3. The catalyst modification using a trace amount of Am-PPS (0.15 wt%) enabled a remarkable enhancement of ethylene selectivity without an appreciable loss in acetylene hydrogenation activity. This could be attributed to the dynamic change of the Am-PPS–Pd interface, which selectively allows the cooperative adsorption of acetylene and H2, but not ethylene. Besides, the modified catalyst exhibited excellent long-term stability because of the high thermochemical stability of the polymer. These results demonstrate the unique possibility of using dynamic metal–polymer interaction to design partial hydrogenation catalysts that simultaneously exhibit high activity, selectivity, and stability.

Effect of the Transforming Ag into an Active Species (Silver Chloride) for the Acetylene Hydrochlorination

AbstractEffective approaches are desired to improve catalytic performances for the hydrochlorination of acetylene. Crucially, the systematic explorations of catalytic and deactivation mechanisms are prerequisites to the implementation of such approaches. Ag has been scarcely researched for acetylene hydrochlorination reaction because it is easily poisoned by Cl, which inactivates it. However, this challenge must be further verified. Here, the active species and causes of the deactivation of Ag/activated carbon (AC) were discussed in detail. The results indicated that Ag/AC exhibited excellent catalytic performance in the acetylene hydrochlorination. Specifically, X‐ray photoelectron spectroscopy (XPS) analysis revealed that AgCl was the main active site, which was almost transformed from Ag0 after the activation with HCl for 0.5 h. Moreover, inductively coupled plasma optical emission spectrometer (ICP‐OES) and transmission electron microscopy (TEM) results confirmed that the deactivation of the catalyst was justified by the loss of Ag and particle aggregation. Thus, the conversion of acetylene of the small‐sized AgCl nanoparticles were significantly enhanced, and these inhibited the agglomeration of the particles, thereby further verifying that AgCl was the active site. This perspective offered a suitable insight for the subsequent research on Ag‐based catalysts.

Confinement of ultrasmall Pd nanoparticles by layered covalent triazine frameworks for semihydrogenation of acetylene

Acetylene hydrogenation is an important reaction in the petrochemical industry, the key is to develop efficient and selective catalyst. In this work, a highly crystalline layered covalent triazine frameworks (CTFs) with excellent thermal stability was used as carbon support to immobilize ultrasmall Pd nanoparticle for semihydrogenation of acetylene. Downsizing the particle sizes were realized by dual-solution assisted precursor mixture and using H2 instead of NaBH4 as reducing agent.The pore confinement effect of CTFs and the electronic intercalation from N atoms play key roles in improving the catalytic activity and stabilizing the Pd nanoparticles. The Pd/CTFs-H2 catalyst exhibits 100% acetylene conversion and 99.9% ethylene selectivity at 250 °C and space velocity of 110,000 h−1. The life test (>150 h), cycle test and chemical stability test demonstrated the long-term stability of the Pd/CTFs-H2. The process mechanism of selective hydrogenation of acetylene in this catalyst is investigated by the in-situ infrared spectra.

Single-Atom Ruthenium Catalytic Sites for Acetylene Hydrochlorination.

The high cost of noble metal catalysts has been a major factor limiting their industrial applications. It is thus of strong interest to develop catalysts with minimum metal loading. Here, we designed and prepared a single-atom ruthenium catalyst through a cascade anchoring strategy to maximize the efficiency of Ru atoms for acetylene hydrochlorination. The single-atom catalyst supported on commercial activated carbon (AC) exhibits excellent catalytic activity with acetylene conversion of 95.4% at an acetylene gas hourly space velocity (GHSV) of 720 h-1 and almost no deactivation during a 600 h catalyst lifetime test. In conjunction with a series of experimental characterizations of the catalyst, including aberration-corrected scanning transmission electron microscopy (Ac-STEM), X-ray photoelectron spectroscopy (XPS), and extended X-ray absorption fine spectroscopy (EXAFS), density functional theory (DFT) study shows that RuN4 sites are likely responsible for acetylene hydrochlorination catalytic activity. This work provides a strategy to design efficient single-atom catalysts for acetylene hydrochlorination and helps us to gain deeper understanding of single-atom catalytic mechanisms.

Highly selective hydrogenation of acetylene over reduced graphene oxide carbocatalyst

Nitrogen-doped reduced graphene oxide (N-RGO) was synthesized by the treatment of graphene oxide with hydrazine. The obtained material was characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectoscopy, nitrogen adsorption-desorption isotherm, and XPS. The catalytic activity of N-RGO in acetylene, ethylene hydrogenation, and preferential acetylene hydrogenation in the ethylene excess was determined. In the acetylene hydrogenation, the selectivity of 97% for ethylene is achieved. A possibility of a complete conversion of acetylene to ethylene in the acetylene-ethylene mixture with ratio 1:9 is shown.