Density functional study of H2O adsorption and dissociation on WC(0001)

Syngas Conversion to C2 Species over WC and M/WC (M = Cu or Rh) Catalysts: Identifying the Function of Surface Termination and Supported Metal Type

Improving the selectivity and activity of C₂ species from syngas is still a challenge. In this work, catalysts with monolayer Cu or Rh supported over WC with different surface terminations (M/WC (M = Cu or Rh)) are rationally designed to facilitate C₂ species generation. The complete reaction network is analyzed by DFT calculations. Microkinetics modeling is utilized to consider the experimental reaction temperature, pressure, and the coverage of the species. The thermal stabilities of the M/WC (M = Cu or Rh) catalysts are confirmed by AIMD simulations. The results show that the surface termination and supported metal types in the M/WC (M = Cu or Rh) catalysts can alter the existence form of abundant CH_x (x = 1-3) monomer, as well as the activity and selectivity of CH_x monomer and C₂ species. Among these, only the Cu/WC-C catalyst is screened out to achieve outstanding activity and selectivity for C₂H₂ generation, attributing to that the synergistic effect of the subsurface C atoms and the surface monolayer Cu atoms presents the noble-metal-like character to promote the generation of CH_x and C₂ species. This work demonstrates a new possibility for rational construction of other catalysts with the non-noble metal supported by the metal carbide, adjusting the surface termination of metal carbide and the supported metal types can present the noble-metal-like character to tune catalytic performance of C₂ species from syngas.

Strategies for Perfect Confinement of POM@MOF and Its Applications in Producing Defect-Rich Electrocatalyst

Polyoxometalate encapsulated by metal-organic framework (POM@MOF) hybrid is an ideal precursor for electrocatalysts because it provides a homogeneous catalyst system with a flexible synergistic effect. However, controlling its fine structures to activate the derived catalyst after pyrolysis remains a challenge. The uniformly distributed carbon-defect tungsten oxides on the 3D carbon matrix were synthesized by using phospho-tungstic acid confined in HKUST-1 (PA@HKUST-1) as the precursor. By choosing ethanol as the solvent, the framework of PA@HKUST-1 was retained integrally and each pore of HKUST-1 kept intact even with holding the PA molecule inside. The well-organized structure of PA@HKUST-1 facilitated to offer a highly distributed metal source, and further transform into defect-rich catalyst. The average size of the resulting WO_xC_y/C catalysts was 1.5 nm, which was similar to a single molecule of PA. The WO_xC_y/C catalysts exhibited superior activity in the methanol oxidation reaction after being platinized due to the enhanced resistance to CO poisoning, which is also confirmed by DFT. This finding suggests a new route to design and achieve the defect-rich catalyst with controllable size.

Binding and activation of ethylene on tungsten carbide and platinum surfaces

Density functional theory calculations were used to evaluate the ability of surfaces of cubic and hexagonal phases of tungsten carbide to bind ethylene.

A Au monolayer on WC(0001) with unexpected high activity towards CO oxidation

Catalysts with weak adsorption yet high reactivity towards CO are urgently required to solve the serious problem of CO poisoning that occurs in many important reactions, e.g., in fuel cells. Using the combination of density functional calculations and ab initio molecular dynamic simulations, we found a promising electrocatalyst for this purpose: a Au monolayer on WC(0001) (Au_ML/WC), which has both high oxygen reduction activity and high tolerance to CO poisoning. The advantages of using Au_ML/WC as an electrocatalyst in fuel cells are demonstrated through analyses of energetics of different reaction steps as well as interaction properties of reactants and products. We anticipate that the present results are useful to advance the development of efficient catalysts with high tolerance to CO poisoning.

A theoretical study of formaldehyde adsorption and decomposition on a WC (0001) surface

A lot of research attention has been paid to designing and exploring efficient adsorbents for HCHO adsorption and decomposition. Herein, we have demonstrated a highly active material, WC, for HCHO adsorption through first-principles calculations. Due to the exposed three-coordinated W atoms (W_3c) of the WC (0001) surface, HCHO molecules can be settled on the WC (0001) surface through newly formed O_F–W_3c and/or C_F–W_3c bonds, forming different adsorption configurations. When settled on the WC (0001) surface, the molecular configuration of the HCHO molecule and the corresponding C_F–H_F and C_F–O_F bond lengths would be greatly changed. Due to the enlarged C_F–H_F and C_F–O_F bond lengths, the adsorbed HCHO molecules tend to dissociate through two possible pathways; these are the two-step C_F–H_F bond scission or the one-step C_F–O_F bond scission. The former results in two H adatoms and a CO molecule chemisorbed to the surface and the latter produces an O adatom and a CH₂ group on the surface. Further Cl-NEB calculations demonstrate that the pre-adsorbed O atom has little influence on the first C_F–H_F bond scission and the C_F–O_F bond scission, while promoting the second C_F–H_F bond scission. Considering the dissociative products, H and CH₂ have the potential to couple into a CH₃ group (or even a CH₄ molecule) and two CH₂ groups may couple into a C₂H₄ molecule. In the end, we propose that OH ions may couple with the dissociative products of HCHO, so an alkali solution could be used to post-process the WC (0001) surface to restore its surface active sites. These results demonstrated the potential of WC in HCHO sensing and abatement.

WC is a material capable of HCHO adsorption and dissociation, indicating its potential application in HCHO sensing and elimination.