Selective Hydrogenation Of Acetylene Research Articles

Magnesium oxide-supported potassium hydride as a transition-metal-free catalyst for the selective hydrogenation of alkynes

Catalytic hydrogenation of alkynes to alkenes is pivotal in both petrochemical and fine chemical industries. Its implementation relies on the use of transition metals, especially those precious Pd-based catalysts. In this work, we utilize a melt infiltration method to prepare magnesium oxide-supported potassium hydride (KH/MgO), which is illustrated as a transition-metal-free catalyst for selective hydrogenation of alkynes. H2-D2 exchange experiment proves that dihydrogen activation and dissociation on KH/MgO is plausible at room temperature and ambient pressure. KH/MgO catalyzes hydrogenation of diphenylacetylene (DPA) already at 40 ℃, implying its high intrinsic activity at very mild conditions. Under an optimized condition of 80°C, 2 bar H2, and 40 h, 75 % conversion of DPA is achieved, affording 82 % selectivity to stilbenes. Mechanistic study suggests that surface hydride on KH/MgO plays an important role toward dihydrogen activation, and involved in the hydrogenation step to form stilbenes. This work shows the promise for using light metal hydrides consisting of earth-abundant elements as alternative hydrogenation catalysts.

Co-infiltration and dynamic formation of Pd3ZnCx intermetallic carbide by syngas boosting selective hydrogenation of acetylene

Transition metal carbide shows excellent performance in selective hydrogenation of acetylene, however, the carburization of Pd-based intermetallic compounds remains infeasible. Here we report the successful synthesis of an unprecedented Pd3ZnCx intermetallic carbide, via co-infiltration of zinc and carbon in one-step carburization by syngas. Utilizing state-of-the-art in situ characterizations and theoretical calculation, we unveil the dynamic evolution of Pd3ZnCx during carburization, forming a Pd3Zn like cubic phase carbide structure. A unique transitional state (Pdt) with low content of Zn/C co-infiltration is clearly identified facilitating phase transition and sustain incorporation of carbon and zinc at elevated temperatures. The Pd3ZnCx carbide shows by far the best catalytic performance in the selective hydrogenation of acetylene with a high selectivity (>90%) even at a high H2/C2H2 ratio. Our results therefore provide a co-infiltration strategy and dynamic insights for the one-step synthesis of Pd based intermetallic carbides, towards high-performance intermetallic compound for selective hydrogenation of acetylene.

Embedding Single Pd Atoms on NiGa Intermetallic Surfaces for Efficient and Selective Alkyne Hydrogenation.

Catalytic removal of alkynes is essential in industry for producing polymer-grade alkenes from steam cracking processes. Non-noble Ni-based catalysts hold promise as effective alternatives to industrial Pd-based catalysts but suffer from low activity. Here we report embedding of single-atom Pd onto the NiGa intermetallic surface with replacing Ga atoms via a well-defined synthesis strategy to design Pd1-NiGa catalyst for alkyne semi-hydrogenation. The fabricated Pd1Ni2Ga1 ensemble sites deliver remarkably higher specific mass activity under superb alkene selectivity of >96 % than the state-of-the-art catalysts under industry-relevant conditions. Integrated experimental and computational studies reveal that the single-atom Pd synergizes with the neighbouring Ni sites to facilitate the σ-adsorption of alkyne and dissociation of hydrogen while suppress the alkene adsorption. Such synergistic effects confer the single-atom Pd on the NiGa intermetallic with a Midas touch for alkyne semi-hydrogenation, providing an effective strategy for stimulating low active Ni-based catalysts for other selective hydrogenations in industry.

Catalytic performance of a single atom Pd1Ag10/Al2O3 catalyst for the selective hydrogenation of acetylene: The role of CO-induced segregation

The single-atom Pd catalysts based on silver-rich bimetallic compositions are known for their extremely high ethylene selectivity in the acetylene hydrogenation reaction; however, their activity is noticeably lower than that of traditional monometallic Pd catalysts. The aim of the work was to apply a method of CO-induced segregation to increase the concentration of single atom Pd1 sites on the surface of Pd1Ag10/Al2O3 catalyst without noticeable formation of multiatomic Pdn (n ≥ 2) ensembles. It has been experimentally established by DRIFTS-CO and XPS methods that the effect of 30 vol% CO exposure temperature on the increase of surface Pd1 sites concentration in the range of 50 to 350 °C has a volcano-like dependence with a maximum at ∼ 200–250 °C. The catalytic tests show a considerable enhancement in activity for samples treated in CO at 200–250 °C (the temperature of 100 % acetylene conversion is reduced by ∼ 30 °C), while the C2H4 selectivity was similar for both freshly reduced and CO-treated catalysts. These results demonstrate the use of CO-induced segregation as a promising method for the controlled increase in the concentration of isolated Pd1 sites to improve the activity of silver-rich palladium catalyst without compromising its selectivity.

Heteroatoms‐Stabilized Single Palladium Atoms on Amorphous Zeolites: Breaking the Tradeoff between Catalytic Activity and Selectivity for Alkyne Semihydrogenation

AbstractAs a fundamental industrial catalytic process, the semihydrogenation of alkynes presents a challenge in striking a balance between activity and selectivity due to the issue of over‐hydrogenation. Herein, we develop an efficient catalytic system based on single‐atom Pd catalysts supported on boron‐containing amorphous zeolites (Pd/AZ−B), achieving the tradeoff breaking between the activity and selectivity for the selective hydrogenation of alkynes. Advanced characterizations and theoretical density functional theory calculations confirm that the incorporated B atoms in the Pd/AZ−B can not only alter the geometric and electronic properties of Pd atoms by controlling the electron migration from Pd but also mitigate the interaction between alkene and the catalyst supports. This boosts the exceptional catalytic efficacy in the semihydrogenation of phenylacetylene to styrene under mild conditions (298 K, 2 bar H2), achieving a recorded turnover frequency (TOF) value of 24198 h−1 and demonstrating 95 % selectivity to styrene at full conversion of phenylacetylene. By comparison, the heteroatom‐free amorphous zeolite‐anchored Pd nanoparticles and the commercial Lindlar catalyst have styrene selectivities of 73 % and 15 %, respectively, under identical reaction conditions. This work establishes a solid foundation for developing highly active and selective hydrogenation catalysts by controllably optimizing their electronic and steric properties.

Heteroatoms-Stabilized Single Palladium Atoms on Amorphous Zeolites: Breaking the Tradeoff between Catalytic Activity and Selectivity for Alkyne Semihydrogenation.

As a fundamental industrial catalytic process, the semihydrogenation of alkynes presents a challenge in striking a balance between activity and selectivity due to the issue of over-hydrogenation. Herein, we develop an efficient catalytic system based on single-atom Pd catalysts supported on boron-containing amorphous zeolites (Pd/AZ-B), achieving the tradeoff breaking between the activity and selectivity for the selective hydrogenation of alkynes. Advanced characterizations and theoretical density functional theory calculations confirm that the incorporated B atoms in the Pd/AZ-B can not only alter the geometric and electronic properties of Pd atoms by controlling the electron migration from Pd but also mitigate the interaction between alkene and the catalyst supports. This boosts the exceptional catalytic efficacy in the semihydrogenation of phenylacetylene to styrene under mild conditions (298 K, 2 bar H2), achieving a recorded turnover frequency (TOF) value of 24198 h-1 and demonstrating 95 % selectivity to styrene at full conversion of phenylacetylene. By comparison, the heteroatom-free amorphous zeolite-anchored Pd nanoparticles and the commercial Lindlar catalyst have styrene selectivities of 73 % and 15 %, respectively, under identical reaction conditions. This work establishes a solid foundation for developing highly active and selective hydrogenation catalysts by controllably optimizing their electronic and steric properties.

Selective hydrogenation of acetylene over Pd/β-Mo2C catalyst: Experimental and theoretical studies

Molybdenum carbide is a promising support to tune the metal reactivity, which originates from the interaction between metal and support. In this work, Pd/β-Mo2C was prepared using a deposition-precipitation method for selective hydrogenation of acetylene. The high temperature calcination is employed to modulate the interaction between Pd and β-Mo2C. The Pd/β-Mo2C catalyst calcined at 600 °C exhibits significant promotion in selective hydrogenation, which shows 100 % acetylene conversion and 81.4 % ethylene selectivity at 160 °C. The activity promotion originates from the enhanced electronic metal-support interaction, which induces a shift of Pd 3d to higher binding energy. Besides, the Pd species become atomically dispersed after calcination. The changes in geometric and electronic structure suppress the formation of Pd hydrides, which consequently inhibits the excessive hydrogenation capacity of Pd. The structure variation also affects the adsorption of ethylene. No strong adsorbed ethylene (di-σ bonded ethylene) can be identified, which is conducive to the improvement of ethylene selectivity. Density functional theoretical (DFT) calculations confirm that Pd on β-Mo2C is positively charged. The desorption energy of C2H4* (0.78 eV) is significantly lower than that of further hydrogenation (1.45 eV), which explains the improved ethylene selectivity of the calcinated catalyst. The present study indicates calcination is an effective method to tune the activity of Pd/β-Mo2C for reactions beyond selective hydrogenation of acetylene.

Efficient Catalysts Based on Substitutional Solid Solutions and Palladium Intermetallic Compounds for the Selective Hydrogenation of Acetylene to Ethylene

Efficient Catalysts Based on Substitutional Solid Solutions and Palladium Intermetallic Compounds for the Selective Hydrogenation of Acetylene to Ethylene

Performance of PdAu/Al2O3 egg-shell catalyst with isolated Pd1 sites for selective hydrogenation of acetylene

A herein proposed PdAu/Al2O3 egg-shell catalyst for selective acetylene hydrogenation combines two factors to provide perfect performance: isolation of Pd1 active sites by Au and an egg-shell distribution of the active phase across the catalyst pellets. The PdAu/Al2O3 catalyst exhibits high acetylene hydrogenation activity at the level of Pd-catalysts and high intrinsic ethylene selectivity of Au-catalysts.

Hydroxyl group modification improves the selectivity of metal single atom on poly(heptazine imide) for electrocatalytic acetylene semi-hydrogenation

Electrocatalytic semi-hydrogenation of acetylene to ethylene has recently attracted attention as a process for removing acetylene from ethylene-rich gas streams due to its mild conditions and energy-saving advantages. However, developing catalysts with low cost and high selectivity for acetylene semi-hydrogenation remains a huge challenge. Here, we investigated the effect of hydroxyl group modification on the acetylene semi-hydrogenation selectivity of poly(heptazine imide) (PHI) supported metal single atom catalyst under alkaline conditions by density functional theory calculations. The results show that hydroxyl group as ligand not only increases the steric resistance of acetylene adsorption, but also acts as electron-withdrawing group to delocalize the electrons of metal atoms, weaken the interaction with acetylene and subsequent intermediates, and make the adsorption moderate, which is beneficial to the desorption of ethylene and avoid over-hydrogenation. The Ni-OH/PHI and Fe-2OH/PHI are capable of achieving the selective hydrogenation of acetylene to ethylene and have good thermodynamic stability, which can be used as ideal catalysts for the electrocatalytic semi-hydrogenation of acetylene to selectively generate ethylene. This study provides theoretical guidance for the rational design of electrocatalysts for the selective semi-hydrogenation of acetylene.

(Semi)hydrogenation of enoates and alkynes effected by a versatile, particulate copper catalyst

We communicate a versatile and user-friendly Cu-based catalytic method that allows for the selective hydrogenation of enoates and alkynes. The introduced protocol is free from any ex ante modifications of the used Cu(I) precursors by air-sensitive phosphines or elaborate N-heterocyclic carbene ligands. The conjugate hydrogenation of enoates and the (selective) reduction of CC bonds is achieved through a [Cu(CH3CN)4]+/tert-butoxide pair whereby we describe a delicate influence of the base cation on the chemoselectivity of the respective transformation. In case of the ester-to-alcohol reduction, a combination of simple CuI and NaOtBu proved to be successful. Deuteration experiments are included to address certain mechanistic aspects of the introduced catalytic system. All requisite chemicals are readily obtainable through commercial channels and the catalyst assembly is set up on the bench without the need for special lab-technical precautions.

CFD modeling using reactions kinetics for selective hydrogenation for acetylene in a fixed-bed reactor

Selective hydrogenation of acetylene (SHA) reactions is usually performed in fixed-bed reactors (FBR). The traditional SHA kinetics, when coupled with a three-dimensional computational fluid dynamics (CFD) model, requires improvement to accurately predict SHA reaction outcomes. The SHA microdynamics, when integrated with a three-dimensional CFD model, have not been comprehensively examined. In this paper, a mathematical model based on CFD was developed to simulate the reactive flow behavior of SHA in FBR using a novel OleMax100 catalyst. In this study, a 3D catalyst bed numerical simulation of FBR with coupled microdynamics description of conjugate heat transfer and surface catalytic reaction was carried out, and the accuracy of CFD at different Reynolds numbers (Re) was verified by experimental results, which showed a high degree of agreement between the model and experimental results. The effect of the ratio of tube to pellet diameter (D/d=N) on the fluid flow characteristics and SHA reaction in the bed was investigated, and the catalyst shape was considered. The simulation results show that an increase in N significantly improves the homogeneity of the flow field and the heat and mass transfer between the phases in the FBR, which leads to an increase in the conversion efficiency of acetylene. When N was increased from 4.00 to 6.67, the conversion was enhanced by 6.7 %. Increasing the Re value affects the reactivity, and the SHA reaction exists in a reaction zone where excessive residence time exacerbates the decrease in selectivity. The adopted and novel catalyst microkinetic models can provide some theoretical guidance for the optimal design of the SHA reaction and process improvement in FBR.

Hierarchical N‐doped Carbon Nanosheets Anchored Bimetallic Oxides for Selective Hydrogenation of Phenylacetylene

AbstractSelective hydrogenation of alkynes to alkenes using a low‐cost non‐noble metal catalyst is urgently desirable but challenging because of their over‐hydrogenation to undesired alkanes. Herein, a series of hierarchical N‐doped carbon nanosheets anchored bimetallic oxides were successfully fabricated. The resultant composite catalysts had advantages associated with not only two‐dimensionality (2D) nanosheets with highly active sites and fast mass transfer, but also bimetallic oxides that dissociate and transfer hydrogen with the assistance of the oxygen vacancies. Furthermore, the bimetallic oxides combined with the advantages of high activity of Ni and the selectivity regulation of Co. Benefiting from these advantages, the catalytic performance of CoNiO2−ZnCo2O4/NC NSs can reach nearly full conversion with 92 % selectivity at moderate reaction conditions and can keep excellent selectivity even prolonging the reaction time to 12 h, outperforming CoNiO2−ZnCo2O4/NC NPs, CoO−ZnCo2O4/NC NSs, and the commercial Lindlar catalysts, which demonstrate the huge potential for selective hydrogenation applications.

Carburization in the Crystalline Structure of the Metal Ag for Efficient Selective Hydrogenation of Acetylene

Carburization in the Crystalline Structure of the Metal Ag for Efficient Selective Hydrogenation of Acetylene

Sn-doped PdAg/Al2O3 catalysts: Efficient catalysts for the selective hydrogenation of acetylene to ethylene under industrial conditions

PdAg/Al2O3 catalysts were prepared using a simple and scalable preparation method. A systematic approach established a preparation-performance relationship which revealed that the Pd:Ag ratio and Pd reduction method affects the overall performance for the selective hydrogenation of acetylene to ethylene under industrially relevant tail-end reaction conditions. The addition of Sn improved selectivity with the optimum system achieving 97% selectivity towards ethylene, outperforming two industrial references. Density functional theory (DFT) simulations and electron microscopy analysis revealed that Sn integrates into the Pd lattice and increases the energy barrier for ethylene adsorption. This work demonstrates that Sn can be used to tailor catalyst performance for industrially relevant PdAg/Al2O3 catalysts.

Promotion of Mg(OH)2 in Cu-Based Catalysts for Selective Hydrogenation of Acetylene

Promotion of Mg(OH)2 in Cu-Based Catalysts for Selective Hydrogenation of Acetylene

Surface Engineering of Noble Metal Nanocrystals for Selective Hydrogenation

The selective hydrogenation has attracted increasing attention to chemists for the production of value‐added products in chemical industry. Over the past several decades, substantial effort has been devoted to the design of catalyst for the selective hydrogenation of light alkynes and α, β‐unsaturated aldehydes, two classic cases for selective hydrogenation in chemical industry. Despite the great progress, it remains great challenges to achieve the selective hydrogenation because the desired products are generally thermodynamically unfavored. Here, we summarize the recent advances on selective hydrogenation using noble metal nanocrystals, with an emphasis on the surface engineering of noble metal nanocrystals for the selective hydrogenation of light alkynes and α, β‐unsaturated aldehydes. We will highlight the strategies for surface engineering, the advanced techniques for characterizations, as well as mechanism studies. We hope this review will promote chemists to develop efficient and robust catalysts for selective hydrogenation.

Au Nanoparticles Supported on Hydrotalcite-Based MMgAlOx (M=Cu, Ni, and Co) Composite: Influence of Dopants on the Catalytic Activity for Semi-Hydrogenation of C2H2

Semi-hydrogenation of acetylene to ethylene over metal oxide-supported Au nanoparticles is an interesting topic. Here, a hydrotalcite-based MMgAlOx (M=Cu, Ni, and Co) composite oxide was exploited by introducing different Cu, Ni, and Co dopants with unique properties, and then used as support to obtain Au/MMgAlOx catalysts via a modified deposition–precipitation method. XRD, BET, ICP-OES, TEM, Raman, XPS, and TPD were employed to investigate their physic-chemical properties and catalytic performances for the semi-hydrogenation of acetylene to ethylene. Generally, the catalytic activity of the Cu-modified Au/CuMgAlOx catalyst was higher than that of the other modified catalysts. The TOR for Au/CuMgAlOx was 0.0598 h−1, which was 30 times higher than that of Au/MgAl2O4. The SEM and XRD results showed no significant difference in structure or morphology after introducing the dopants. These dopants had an unfavorable effect on the Au particle size, as confirmed by the TEM studies. Accordingly, the effects on catalytic performance of the M dopant of the obtained Au/MMgAlOx catalyst were improved. Results of Raman, NH3-TPD, and CO2-TPD confirmed that the Au/CuMgAlOx catalyst had more basic sites, which is beneficial for less coking on the catalyst surface after the reaction. XPS analysis showed that gold nanoparticles exhibited a partially oxidized state at the edges and surfaces of CuMgAlOx. Besides an increased proportion of basic sites on Au/CuMgAlOx catalysts, the charge transfer from nanogold to the Cu-doped matrix support probably played a positive role in the selective hydrogenation of acetylene. The stability and deactivation of Au/CuMgAlOx catalysts were also discussed and a possible reaction mechanism was proposed.

Lattice Strain and Mott-Schottky Effect of the Charge-Asymmetry Pd1Fe Single-Atom Alloy Catalyst for Semi-Hydrogenation of Alkynes with High Efficiency.

The ideal interface design between the metal and substrate is crucial in determining the overall performance of the alkyne semihydrogenation reaction. Single-atom alloys (SAAs) with isolated dispersed active centers are ideal media for the study of reaction effects. Herein, a charge-asymmetry "armor" SAA (named Pd1Fe SAA@PC), which consists of a Pd1Fe alloy core and a semiconducting P-doped C (PC) shell, is rationally designed as an ideal catalyst for the selective hydrogenation of alkynes with high efficiency. Multiple spectroscopic analyses and density functional theory calculations have demonstrated that Pd1Fe SAA@PC is dual-regulated by lattice tensile and Schottky effects, which govern the selectivity and activity of hydrogenation, respectively. (1) The PC shell layer applied an external traction force causing a 1.2% tensile strain inside the Pd1Fe alloy to increase the reaction selectivity. (2) P doping into the C-shell layer realized a transition from a p-type semiconductor to an n-type semiconductor, thereby forming a unique Schottky junction for advancing alkyne semihydrogenation activity. The dual regulation of lattice strain and the Schottky effect ensures the excellent performance of Pd1Fe SAA@PC in the semihydrogenation reaction of phenylethylene, achieving a conversion rate of 99.9% and a selectivity of 98.9% at 4 min. These well-defined interface modulation strategies offer a practical approach for the rational design and performance optimization of semihydrogenation catalysts.

Efficient catalysis of acetylene semi-hydrogenation through synergistic action of supported ionic liquid-nickel catalyst

In the semi-hydrogenation of acetylene, nickel-based catalysts offer a promising alternative to precious metal palladium catalysts. Despite the positive hydrogenation activity of nickel-based catalysts, there is still room for improvement in terms of their selectivity and stability. In this study, a simple incipient wetness impregnation method was employed to prepare Ni(OAC)2-IL/Al2O3 catalyst and its performance in the selective hydrogenation of acetylene was investigated. It was found that under the conditions of 170 °C and a space velocity of 600 h−1, the 3 % Ni(OAC)2-IL/Al2O3 catalyst achieved a 95.3 % acetylene conversion with an 85.6 % ethylene selectivity. Furthermore, the catalyst exhibited outstanding stability over a 100 hour test. TEM, XPS and C2H4-TPD experiments showed that the Ni species were encapsulated in the ionic liquids (ILs), and the interaction between the metal ions, nickel, and the ILs ensured a high dispersion and stability of the actives on the carriers, and the electronic effect between the ionic nickel and the ionic liquids increased the electron cloud density of the Ni, which improved the catalyst selectivity, which is the main reason for its excellent catalytic performance.