Selective Hydrogenation Of Acetylene Research Articles

Semihydrogenation of Alkynes Catalyzed by a Pyridone Borane Complex: Frustrated Lewis Pair Reactivity and Boron–Ligand Cooperation in Concert

The metal‐free cis selective hydrogenation of alkynes catalyzed by a boroxypyridine is reported. A variety of internal alkynes are hydrogenated at 80 °C under 5 bar H2 with good yields and stereoselectivity. Furthermore, the catalyst described herein enables the first metal‐free semihydrogenation of terminal alkynes. Mechanistic investigations, substantiated by DFT computations, reveal that the mode of action by which the boroxypyridine activates H2 is reminiscent of the reactivity of an intramolecular frustrated Lewis pair. However, it is the change in the coordination mode of the boroxypyridine upon H2 activation that allows the dissociation of the formed pyridone borane complex and subsequent hydroboration of an alkyne. This change in the coordination mode upon bond activation is described by the term boron‐ligand cooperation.

Preparation of an Unsupported Copper-Based Catalyst for Selective Hydrogenation of Acetylene from Cu2O Nanocubes

Designing cheap, earth-abundant, and nontoxic metal catalysts for acetylene hydrogenation is of pivotal importance, but challenging. Here, a nonprecious metal catalyst for selective hydrogenation of acetylene in excess ethylene was prepared from Cu2O nanocubes. The preparation includes two steps: (1) thermal treatment in acetylene-containing gas at 160 °C and (2) hydrogen reduction at 180 °C. The resultant catalyst showed outstanding performance at low temperature (80-100 °C) and 0.1-0.5 MPa pressure, completely converting acetylene with a low selectivity to undesired ethane (<20%). The characterization results of high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy corroborated that the formation of an interstitial copper carbide (CuxC) might give rise to significantly enhanced hydrogenation activity. Preliminary density functional theory calculation demonstrated that the lattice spacing of Cu3C was nearly identical to that of the new CuxC crystallite measured in HRTEM and determined by XRD. The calculated dissociation energy of hydrogen on Cu3C(0001) was considerably lower than that on Cu(111), suggesting superior hydrogenation activity of Cu3C(0001). It is experimentally verified that copper(I) acetylide (Cu2C2) might be the precursor of CuxC. Cu2C2 underwent partial hydrogenation to fabricate CuxC crystallites and the thermal decomposition to Cu and carbon materials in parallel.

Regulating Electronic Status of Platinum Nanoparticles by Metal–Organic Frameworks for Selective Catalysis

Selective hydrogenation of alkynes to alkenes remains challenging in the field of catalysis due to the ease of over-hydrogenated of alkynes to alkanes. Favorably, the incorporation of metal nanopar...

Selective Hydrogenation of Acetylene to Ethylene Over Nanosized Gold and Palladium Supported Catalysts.

Ethylene, the main raw material for polyethylene production, is a by-product produced by thermally decomposing naphtha and it contains a small amount of acetylene. The acetylene reacts as a permanent catalyst poison for the ethylene polymerization catalyst. In this study, we wanted to improve the acetylene conversion and the ethylene selectivity by selective hydrogenation of acetylene for removing acetylene contained in ethylene. Catalyst was prepared by loading nanosized gold (Au) and palladium (Pd) particles on support (Al₂O₃, TiO₂). Deposition order Au and Pd particles was changed. The activity of the catalyst was investigated using a flow-typed fixed bed reactor under atmospheric pressure. Au and Pd particles deposited on TiO₂ were oxidized to Au₂O₃ and PdO due to strong metal support interaction (SMSI). It was considered that the Au/Pd/Al₂O₃ catalyst was more active than the Pd/Au/Al₂O₃ catalyst due to the formation of the interface between Au particles and Pd particles (or support). But Pd/Au/Al₂O₃ catalyst is considered to have poor activity because Pd particles cover part of the interface between Au and the support. Au/Pd/Al₂O₃ catalyst showed the best catalytic activity, and acetylene conversion and ethylene selectivity were 100% and about 80% at 40 °C, respectively.

Selective hydrogenation of acetylene catalyzed by nickel and nitrogen-doped C34: A density functional theory study

In this study, the reaction mechanism of selective hydrogenation of acetylene on a series of single Ni-doped fullerene C34 catalysts that are modified with three or four N atoms was investigated. The minimum energy paths for the two hydrogenations of acetylene on each catalyst were obtained via density functional theory calculations and from the effects of the different number of N atoms and doping sites. The four-N atom-doped structures were found to generally exhibit high selectivity, with the best structure demonstrating high ethylene selectivity (ΔE = 58.88) and excellent reactivity (Ea = 21.76 kcal/mol).

Spatial Confinement as an Effective Strategy for Improving the Catalytic Selectivity in Acetylene Hydrogenation.

While control over chemical reactions is largely achieved by altering the intrinsic properties of catalysts, novel strategies are constantly being proposed to improve the catalytic performance in an extrinsic way. Since the fundamental chemical behavior of molecules can remarkably change when their molecular scale is comparable to the size of the space where they are located, creating spatially confined environments around the active sites offers new means of regulating the catalytic processes. We demonstrate through first-principles calculations that acetylene hydrogenation can exhibit significantly improved selectivity within the confined sub-nanospace between two-dimensional (2D) monolayers and the Pd(111) substrate. Upon intercalation of molecules, the lifting and undulation of a 2D monolayer on Pd(111) influence the adsorption energies of intermediates to varying extents, which, in turn, changes the energy profiles of the hydrogenation reactions. Within the confined sub-nanospace, the formation of ethane is always unfavorable, demonstrating effective suppression of the unwanted overhydrogenation. Moreover, the catalytic properties can be further tuned by altering the coverage of the adsorbates as well as strains within the 2D monolayer. Our results also indicate that for improving the selectivity, the strategy of spatial confinement could not be combined with that of single-atom catalysis, since the reactant molecules cannot enter the sub-nanospace due to the too weak adsorbate-substrate interaction. This work sheds new light on designing novel catalysts with extraordinary performance for the selective hydrogenation of acetylene.

Sharp Increase in Catalytic Selectivity in Acetylene Semihydrogenation on Pd Achieved by a Machine Learning Simulation-Guided Experiment

Pd (metal) is of key value as a heterogeneous hydrogenation catalyst for its high activity and stability. It, however, fails in selective acetylene hydrogenation: at high H2 pressures and 100% conv...

Methanol as the Hydrogen Source in the Selective Transfer Hydrogenation of Alkynes Enabled by a Manganese Pincer Complex.

The first base metal-catalyzed transfer hydrogenation of alkynes with methanol is described. An air and moisture stable manganese pincer complex catalyzes the reduction of a variety of different alkynes to the corresponding (Z)-olefins in high yields. The reaction is stereo- and chemoselective and scalable.

Selective hydrogenation of acetylene over Pd-Sn catalyst: Identification of Pd2Sn intermetallic alloy and crystal plane-dependent performance

In Pd catalyzed acetylene semi-hydrogenation, high selectivity always comes at the expense of activity while improving both selectivity and activity is challenging. In this work, the performance of Pd alloy catalysts was enhanced by inserting Sn phase to modify both surface Pd ensembles and electronic structures. Compared with Pd/C, the optimal Pd2Sn/C catalyst exhibits higher selectivity at the same acetylene conversion level, with its selectivity increased from 10 % to nearly 95 % at ca 100 % acetylene conversion. Both experimental and DFT calculation results reveal that the specific performance is attributed to the redispersion of surface Pd ensembles by Sn insertion and down-shift of d-band center of catalysts, thus changing the adsorption behavior of the reaction gases. This design principle provides an efficient method for tailoring and optimizing durable Pd-based catalysts with desirable reactivity and ethylene selectivity for selective hydrogenation of acetylene.

Selective hydrogenation of acetylene on graphene-supported non-noble metal single-atom catalysts

Large-scale production of polyethylene in industry requires efficient elimination of the trace amount of acetylene impurity. Currently, zeolite adsorption or the conversion of acetylene to ethylene via selective semi-hydrogenation on Pd catalysts is the commonly used method. In this work, we investigate the reaction mechanisms of acetylene hydrogenation on defective graphene (DG) supported single-atom catalysts (SACs), M1/SV-G and M1/DV-G (M=Ni, Pd and Pt) using density functional theory (DFT), where SV-G and DV-G represent DG with single and double vacancies, respectively. It is shown that the metal single-atoms (SAs) as well as their different coordination numbers both affect the activity and selectivity of the hydrogenation process. M1/DV-G provides better H2 dissociation ability than M1/SV-G, which accounts for the poor acetylene hydrogenation activity of M1/SV-G. Based on the reaction barriers, Pt1/DV-G and Ni1/DV-G are better catalysts than other systems considered here, with Ni1/DV-G exhibiting high selectivity for the semi-hydrogenation product of acetylene. These results provide insights for the design of highly selective and noble-metal-free SACs for acetylene hydrogenation on carbon materials.

Selective Hydrogenation of Acetylene to Ethylene over the Surface of Sub-2 nm Pd Nanoparticles in Miscanthus sinensis-Derived Microporous Carbon Tubes

As one of the organic carbon-rich feedstocks, Miscanthus sinensis is an interesting candidate for producing many high-value materials and chemicals. In this study, M. sinensis-derived activated carbon (msAC) particles with ca. 3.4 nm average pore size have been prepared by a simple carbonation method for supporting Pd nanoparticles (NPs) to hydrogenate acetylene. Catalytic test results showed that the 0.25% Pd/msAC catalyst could convert ∼99.9% of acetylene with ∼99.9% of ethylene selectivity. The life test result strongly demonstrated that the catalyst had a good durability for long-term (>100 h) acetylene hydrogenation with high conversion (∼99.9%) and ethylene selectivity (∼93.1%) at 260 °C with a space velocity of 80,000 h–¹. The characterization results indicated that the msAC with the micro- and nanoscale pore structure and uniformly distributed oxygen-containing functional groups could efficiently disperse Pd nanoparticles and promote their Pd (111) crystal plane exposure. The above structure nature was co-contributing to the catalyst to choose the energetically favorable path for efficient acetylene hydrogenation and ethylene desorption. This work opens up valuable insights into the high-value utilization of M. sinensis biomass to design an efficient isolated Pd NP catalyst.

AgPd and CuPd Catalysts for Selective Hydrogenation of Acetylene

The selective hydrogenation of acetylene has been studied over AgPd and CuPd catalysts. Controlled surface reactions were used to synthesize these bimetallic nanoparticles on both TiO2 and SiO2 sup...

Dynamic metal-polymer interaction for the design of chemoselective and long-lived hydrogenation catalysts.

Metal catalysts are generally supported on hard inorganic materials because of their high thermochemical stabilities. Here, we support Pd catalysts on a thermochemically stable but "soft" engineering plastic, polyphenylene sulfide (PPS), for acetylene partial hydrogenation. Near the glass transition temperature (~353 K), the mobile PPS chains cover the entire surface of Pd particles via strong metal-polymer interactions. The Pd-PPS interface enables H2 activation only in the presence of acetylene that has a strong binding affinity to Pd and thus can disturb the Pd-PPS interface. Once acetylene is hydrogenated to weakly binding ethylene, re-adsorption of PPS on the Pd surface repels ethylene before it is further hydrogenated to ethane. The Pd-PPS interaction enables selective partial hydrogenation of acetylene to ethylene even in an ethylene-rich stream and suppresses catalyst deactivation due to coke formation. The results manifest the unique possibility of harnessing dynamic metal-polymer interaction for designing chemoselective and long-lived catalysts.

Chemoselective Hydrogenation of Alkynes to (Z)-Alkenes Using an Air-Stable Base Metal Catalyst.

A highly selective hydrogenation of alkynes using an air-stable and readily available manganese catalyst has been achieved. The reaction proceeds under mild reaction conditions and tolerates various functional groups, resulting in (Z)-alkenes and allylic alcohols in high yields. Mechanistic experiments suggest that the reaction proceeds via a bifunctional activation involving metal-ligand cooperativity.

Selective Hydrogenation of Acetylene over Pd-Mn/Al2O3 Catalysts

Novel bimetallic Pd-Mn/Al2O3 catalysts are designed by the decomposition of cyclopentadienylmanganese tricarbonyl (cymantrene) on reduced Pd/Al2O3 in an H2 atmosphere. The peculiarities of cymantrene decomposition on palladium and, thus, the formation of bimetallic Pd-Mn catalysts are studied. The catalysts are characterized by N2 adsorption, H2 pulse chemisorption, temperature-programmed desorption of hydrogen (TPD-H2), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The modified catalysts show the changed hydrogen chemisorption properties and the absence of weakly bonded hydrogen. Using an organomanganese precursor provides an uniform Mn distribution on the catalyst surface. Tested in hydrogenation of acetylene, the catalysts show both higher activity and selectivity to ethylene (20% higher) compared to the non-modified Pd/Al2O3 catalyst. The influence of the addition of Mn and temperature treatment on catalyst performance is studied. The optimal Mn content and treatment temperature are found. It is established that modification with Mn changes the route of acetylene hydrogenation from a consecutive scheme for Pd/Al2O3 to parallel one for the Pd-Mn samples. The reaction rate shows zero overall order by reagents for all tested catalysts.

Gas-Phase and Liquid-Phase Hydrogenation of Acetylene in Lean and Enriched Mixtures over Supported Modified Palladium Catalysts

The results of studies on selective hydrogenation of acetylene to ethylene over bimetallic palladium-containing catalysts were summarized. Regular and specific features of the catalyst action in gas-phase hydrogenation of traces of acetylene in the acetylene-ethylene mixture produced by pyrolysis of petroleum feedstock, as well as in liquid-phase hydrogenation of mixtures enriched in acetylene and hydrogen were analyzed. The advantages of ethylene production by liquid-phase hydrogenation of acetylene were shown, and ways of increasing the selectivity to ethylene in this process were considered.

Study on the reaction mechanism of acetylene selective hydrogenation catalysts Pd-Ag/Al2O3

Taking active component Pd-Ag alloy and catalyst carrier Al2O3 as the research object, the catalytic mechanism of acetylene hydrogenation reaction was explored by quantum mechanics theory and Monte Carlo method. In this paper, the activation energy on the catalyst surface, H2 dissociation process, acetylene and ethylene hydrogenation reaction were calculated. From the thermodynamic point of view, the increase of the co-catalyst Ag content enhances the desorption of ethylene on the catalyst surface, reduces the probability of ethane formation, and thus enhances the selectivity of acetylene hydrogenation. Through further process simulation studies, the quantum chemistry method and Monte Carlo method can be used to obtain the mechanism and optimal conditions for the selective catalytic hydrogenation of acetylene, with saving a lot of manpower and material resources.

Modeling the Process of Purifying Ethylene from Acetylene Hydrocarbons over Palladium Nanocatalysts

An analysis of the process of selective hydrogenation of acetylene in the ethane–ethylene fraction of pyrolysis gas over a palladium-containing catalyst of the KPNM-45M brand promoted by the elements from Groups I, II, and VI of the Periodic Table is performed. Spherical granules of α-Al2O3 with a diameter of 0.4 cm are used as the support. The concentration of palladium on the support is less than 0.05 wt %. The activation of a KPNM-45M catalyst and kinetic experiments are performed in a plug flow laboratory-scale reactor with a diameter of 2 cm with a length of the catalytic zone of 35 cm. When performing the experiments, the space velocity of the feedstock is varied from 2000 to 4000 h−1, the pressure is varied from 20 to 30 atm, the temperature of the reaction medium is varied from 333 to 393 K, and the hydrogen/acetylene molar ratio is varied from 1.5 to 3. A stage mechanism of the hydrogenation reactions of acetylene and ethylene is proposed and a kinetic model corresponding to it is constructed. Overall, 80 kinetic experiments are carried out. The kinetic model parameters are estimated based on the results of the experiment by the least squares method. The region of selective hydrogenation of acetylene in the acetylene–ethylene–ethane mixtures is determined in which a gain in ethylene in the output stream of the reagents is observed during the hydrogenation reaction of acetylene. The results of the laboratory-scale kinetic experiment are confirmed on bench-scale and prototype industrial reactors.

Selective acetylene hydrogenation over single metal atoms supported on Fe3O4(001): A first-principle study

Supported single-atom catalysts (SACs) have gained increasing attention for improved catalytic activity and selectivity for industrially relevant reactions. In this study, we explore the hydrogenation of acetylene over single Pt, Ru, Rh, Pd, and Ir atoms supported on the Fe3O4(001) surface using density functional theory calculations. The thermodynamic profile of H diffusion is significantly modified by the type of single metal atoms used, suggesting that H spillover from the single atom dopant to the Fe3O4(001) surface is favored and will likely lead to high H coverages of the functioning catalyst. Correspondingly, as the surface H coverage increases, the important desorption step of ethylene becomes energetically competitive against the detrimental hydrogenation steps of ethylene to ethane. A kinetic model is employed to explore how the activity and selectivity of SACs toward ethylene production change as a function of mass of the catalyst loaded into a flow reactor. Overall, we show that the selectivity of SACs toward ethylene production can be tuned by considering the proper type of metal and controlling the redox state of the support.

Sub‐5 nm Intermetallic Nanoparticles Confined in Mesoporous Silica Wells for Selective Hydrogenation of Acetylene to Ethylene

AbstractWe report the synthesis and catalytic application of intermetallic PtSn nanoparticles confined in MSWs (Mesoporous Silica Wells) in the semi‐hydrogenation of acetylene. Platinum nanoparticles with a size of 2.9 nm supported on amine‐functionalized ∼180 nm silica spheres were enmeshed in a mesoporous silica shell. After the addition of tin via a polyol synthesis method, we obtained the final PtSnx@MSW (x=0.30, 0.50, 0.70, 1.0 and 2.0). Owing to the mesoporous encapsulation the sub‐5 nm bimetallic particles are shown to be monodisperse and well protected against aggregation on the silica sphere even under high‐temperature treatment conditions. In the gas phase semi‐hydrogenation of acetylene, the PtSn@MSW with Sn/Pt molar ratios equal to or greater than one displayed higher selectivity to ethylene. Meanwhile, increasing Sn content decreases acetylene conversion. The intermetallic PtSn@MSW catalysts also displayed long‐term stability and regenerability due to the confined environment provided by MSW.