Theoretical Studies On Dynamics Of CH₃OH Dissociation And H/D Eley-Rideal Reactions On The Cu?111? Surface

Heterogeneous catalysis plays an important role in chemical industries and energy resources.Because of the complexity of these catalytic reactions,our understanding on the reaction mechanisms is still limited.Exploring the mechanisms is beneficial to design of high-efficient and low-cost catalysts.Heterogeneous catalysis involves reactions between gaseous species and surfaces,which occur frequently in industrial processes.Dynamical studies of these reactions could shed valuable light on the interactions between molecules and surfaces.On the other hand,such research helps to optimize reaction conditions and rationalize catalysts.Indeed,it is difficult to understand heterogeneous catalysis,without knowing the dynamics of surface reactions of small molecules.With the development of density functional theory(DFT)and computer power,ab initio molecular dynamics(AIMD)simulations for surface reactions have become widely available.It is straightforward to perform AIMD calculations without constructing a potential energy surface.However,few initial conditions can be simulated due to its high cost.Taking the energies and forces of AIMD trajectories to construct potential energy surfaces can vastly accelerate molecular dynamics simulation so that a large number of trajectories can be run.In Chapter one,I introduce fundamental information of DFT,potential energy surface(PES)and quasi-classical trajectory(QCT)method.I also introduce the basics of Neural networks and the permutation invariant polynomials neural network(PIP-NN)approach which is widely used in constructing PESs of small molecules on rigid surfaces.Finally,I give a brief introduction of a sudden vector projection(SVP)model and an electron friction model.In Chapter two,we have developed the first eighteen-dimensional PES for the methanol dissociative chemisorption on the Cu(111)surface.This globally accurate PES not only includes all molecular degrees of freedom but also describes the multi-channels for O-H,C-H,and C-O dissociation equivalently well.QCT calculations on this PES indicate that the C-O bond breaking is neither kinetically nor dynamically favorable,having a smaller probability than O-H/C-H channels in the ground state.It is also found that the excitation of a stretching mode significantly facilitates the corresponding dissociation process,which represents obvious mode specificity and bond selectivity.Multi-quanta C-O stretching excitations with unprecedented vibrational efficacy are able to invert the C-O/C-H branching ratio.The vibrational control of branching ratio of a multiple-channel reaction is greatly beneficial to enrich our understanding of mode specificity.In Chapter three,we study the electron-hole pair(EHP)effects in a prototypical Eley-Rideal(ER)reaction of an impinging H/D atom and pre-covered D/H atoms on the Cu(111)surface,using the ab initio molecular dynamics simulations with electronic friction.More interestingly,electronic excitation is responsible for the isotopic effect in translational energy distributions,but probably not for that in angular distributions.We find that the product energy in all three channels is distributed with the order of translation>vibration>rotation,in agreement with the experimental findings.The energy loss induced by EHPs plays an important role in the total cross section and the translational energy distribution of products,while affects the rotational and angular distributions weakly.It is found that energy dissipation to EHPs lowers the reaction cross sections by?1/3 leading to quantitative agreement with experimental data.On the other side,we also reproduce well the negligible isotopic effect in total cross section,and strong isotopic effect in translational energy and angular distributions,respectively.Our results highlight the specific role of electronic excitation in detailed dynamic quantities in the ER process.