Cost-Effective Palladium-Doped Cu Bimetallic Materials to Tune Selectivity and Activity by using Doped Atom Ensembles as Active Sites for Efficient Removal of Acetylene from Ethylene

Selective hydrogenation of acetylene on Cu-Pd intermetallic compounds and Pd atoms substituted Cu(111) surfaces

The selective hydrogenation of acetylene was studied on the ordered Cu-Pd intermetallic compounds (L1₀-type CuPd, L1₂-type Cu₃Pd, and L1₂-type CuPd₃) and Pd-modified Cu(111) surfaces through first-principles calculations. The catalytic selectivity and activity of Cu-Pd alloy catalysts are closely related to the crystal structure and composition of Cu-Pd intermetallic compounds and the size of Pd ensembles of Cu-based dilute alloy surface for the selective hydrogenation of acetylene to ethylene. Significantly, we found that the ordered Cu-Pd alloy surface containing isolated Pd atoms (i.e., L1₂-type Cu₃Pd(111) surface) is highly efficient for the selective hydrogenation reaction of C₂H₂ + H₂→ C₂H₄. The contiguous Pd atom ensembles (Pd dimer and trimer) are catalytically active towards C₂H₂ + H → C₂H₃ and C₂H₃ + H → C₂H₄ reactions than the single Pd atom on a Pd-decorated Cu(111) surface. However, the small Pd ensembles on Cu(111) present a low chemical activity for H₂ dissociation compared with the ordered Cu-Pd intermetallic compounds. Our theoretical results provide a strategy of crystal phase and composition control for enhancing the selectivity and activity of Cu-Pd catalysts towards acetylene selective hydrogenation.

Copper-Based Catalysts for Selective Hydrogenation of Acetylene Derived from Cu(OH)2

Replacing precious metals with cheap metals in catalysts is a topic of interest in both industry and academia but challenging. Here, a selective hydrogenation catalyst was prepared by thermal treatment of Cu(OH)₂ nanowires with acetylene-containing gas at 120 °C followed by hydrogen reduction at 150 °C. The characterization by means of transmission electron microscopy observation, X-ray diffraction, and X-ray photoelectron spectroscopy revealed that two crystallites were present in the resultant catalyst. One of the crystal phases was metal Cu, whereas the other crystal phase was ascribed to an interstitial copper carbide (Cu _x C) phase. The reduction of freshly prepared copper (II) acetylide (CuC₂) at 150 °C also afforded the formation of Cu and Cu _x C crystallites, indicating that CuC₂ was the precursor or an intermediate in the formation of Cu _x C. The prepared catalysts consisting of Cu and Cu _x C exhibited a considerably high hydrogenation activity at low temperatures in the selective hydrogenation of acetylene in the ethylene stream. In the presence of a large excess of ethylene, acetylene was completely converted at 110 °C and atmospheric pressure with an ethane selectivity of <15%, and the conversion and selectivity were constant in a 260 h run.

Applications of bimetallic PdCu catalysts

Bimetallic PdCu nanoparticles can be applied as catalysts in a wide range of chemical and electrochemical reactions.

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 (Cu_xC) 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 Cu_xC 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 Cu_xC. Cu₂C₂ underwent partial hydrogenation to fabricate Cu_xC crystallites and the thermal decomposition to Cu and carbon materials in parallel.

A new and different insight into the promotion mechanisms of Ga for the hydrogenation of carbon dioxide to methanol over a Ga-doped Ni(211) bimetallic catalyst

The hydrogenation of CO₂ to CH₃OH is one of the most promising technologies for the utilization of captured CO₂ in the future. Nano Ni-Ga bimetallic catalysts have been proven to be excellent catalysts in the hydrogenation of CO₂ to CH₃OH. To investigate the promotion mechanisms of Ga for the hydrogenation of CO₂ to CH₃OH over Ga-doped Ni catalysts and the wide application of these promotion mechanisms in other catalysts and reactions, herein, density functional theory (DFT) was employed. The reaction mechanisms and the properties of Ni(211) and Ga-Ni(211) surfaces were comparatively studied. The results show that the Ni sites on both the Ni(211) and the Ga-Ni(211) surfaces are active sites, and the most stable structures of the intermediates are similar. Moreover, the Ga-Ni(211) surface is more favorable for the hydrogenation of CO₂, whereas Ni(211) is more favorable for the dissociation of CO₂. The activation barrier of the rate-limiting step in the CH₃OH formation pathway on Ni(211) is 0.54 eV higher than that on Ga-Ni(211). According to the analyses of the projected density of states (PDOS) and Hirshfeld charge transfer, the addition of Ga atoms demonstrates the reactivity of the Ga-doped Ni(211) surfaces. Most importantly, the replacement of some secondary active sites of Ni atoms with the non-active Ga atoms may lower the activities of the secondary active sites and strengthen the activities of the active sites at the step edge. These results provide a new perspective for the reaction mechanism of the hydrogenation of CO₂ to CH₃OH over the state-of-the-art Ga-doped catalysts.

Enhancing C2H2/C2H4 separation by incorporating low-content sodium in covalent organic frameworks

A simple and general method by means of doping low-content Na⁺ ions into COFs to enhance C₂H₂/C₂H₄ separation potential is proposed herein.