The Quantum Chemistry Studies On The Small Molecules Adsorption On Pd, Au Surfaces And Interactions

The adsorption of molecules on solid surfaces and interactions between molecules have become hot topics in both experimental and theoretical fields. The investigations of molecules adsorption on solid catalyst are very important for the understanding of the catalytic reaction mechanism and the rational design of improved or new catalysts. The investigation of interactions between molecules is of great value for the polymer materials design and the understanding of the metabolic processes. In this thesis, the adsorption of molecules on transition metal surfaces and the interactions between molecules were studied using quantum-chemical methods.In the first part of my thesis, the density functional theory (DFT) was used to study the adsorption of formic acid, formate and carboxyl on the low index surfaces of Pd and Au metals. The bare cluster models were used to describe the (111), (11 0), (100) surfaces of Pd and Au metals. We optimized the geometries of the adsorbed molecules and calculated the energies of the adsorption systems. And then we analyzed the charge population and the vibration properties. We obtained the following results:(1)The adsorption energies of HCOOH on oxygen pre-adsorbed metal surfaces were stronger than those of which on the clean metal surfaces, which agreed well with experiments. The adsorption energies of HCOOH on the clean Pd(111) surface were higher than those on the clean Au(111) surface. However, the adsorption energies of HCOOH on the oxygen pre-adsorbed Au(111) surface were higher than those on the oxygen pre-adsorbed Pd(111) surface. The most stable adsorption of HCOOH on the oxygen pre-adsorbed metal surfaces was viaη2 coordinate, in which the carbonyl oxygen of HCOOH coordinated to a metal atom at top site, meanwhile the hydroxyl hydrogen of HCOOH coordinated to oxygen pre-adsorbed on metal surfaces. (2) The most stable adsorption of HCOO on the clean metal surfaces was viaη2-coordinate, in which the carbonyl oxygen atoms of HCOO were coordinated to two metal atoms at top sites. The most stable adsorption of COOH on the clean metal surfaces was via carbon of COOH coordinated to a metal atom at top site. The adsorption energies of formate or carboxyl species on different surfaces followed the order of (110)>(100)>(111). And the adsorption energies of them on the clean Pd surfaces were stronger than on the clean Au surfaces. The vibration of M—X(M=Pd,Au;X=O,C) were appeared when these species adsorbed on the surfaces.In the second part of my thesis, the theory method was used to study the adsorption of melamine, cyanuric acid on the clean Au(111) surface, and dimolecular hydrogen-bond interactions between selves and each others among melamine, cyanuric acid and water. We optimized the geometries and calculated the energies of these interaction complexes. And then we analyzed the charge population and vibration properties. We obtained the following results:(1) The adsorption of C3N3(NH2)3 and [C(O)NH]3 on clean Au(111) were physical ones. (2) Molecules of C3N3(NH2)3 and [C(O)NH]3 formed a planar conformation via three hydrogen bonds. Bimolecular C3N3(NH2)3 formed a non-planar conformation through two N—H…N hydrogen bonds. Bimolecular [C(O)NH]3 formed a planar conformation via two N—H…O hydrogen bonds. (3) The highest interaction energy of-59.52 kJ·mol-1 was appeared in the system of C3N3(NH2)3-[C(O)NH]3. And the highest E(2)ij was also included in this system. (4) Vibration frequencies apparently changed especial for those hydrogen bonding atoms, the stretching frequency of N8—H9 in C3N3(NH2)3-[C(O)NH]3 gives the most obvious red shift.