Molecular Potential Function For Pd-CO System And The Structure Of Pd Surface Adsorbed By CO

Pd and its alloy membranes have been of interest due to their hydrogen separating capability for a long time. They have been applied in a variety of processes in the chemical industry. In particular, membrane reactors containing Pd membranes have been used for the separation of hydrogen .However, it was reported that CO has poisoning effects on the performance of these materials. Several studies on the CO addition to H₂ during permeation through the Pd membrane revealed a decline in the permeation rate of hydrogen through the Pd membrane. The poisoning becomes more significant with an increasing amount of CO .Therefore, the study of the electronic structure of Pd surface adsorbed by CO and the interaction potential energy between Pd and CO is important for understanding the adsorption mechanism and the adsorption dynamics, which may provide a possible way to inhibit CO adsorption on Pd surface.Density functional(B3LPY) method has been utilized to optimize the possible structures of PdC, PdO and PdCO molecules with contracted valence basis set(LANL2DZ) for Pd atom, the AUG-cc-pVTZ basis set for C and O atoms. The analytical potential energy function for PdCO molecule has been obtained from the many-body expansion theory . The contour of the potential energy surface sheds light on the accurate structure and dissociative energy for PdCO molecule. Furthermore, molecular static reaction pathway based on this potential energy function is investigated.The slab model with periodical boundary condition is used to investigate atomic and molecular adsorption on metal surface. And based on this, two structures of different molecular orientation on Pd(111) surface at 0.75 coverage (ML) have been calculated using density functional theory. It is found that the structure with carbon ended to Pd(111) surface is stable while the structure with oxygen is quite difficult, therefore, controlling the orientation of CO molecule adsorbed on Pd surface may provide an effective way to inhibit CO adsorption on Pd surface.