A DFT Study On The Influences Of Step Structure And Adsorbed Oxygen On Nickel Surface On Dissociation Process Of Methane

The reaction of methane partial oxidation (POM) catalyzed by nickel is anattractive new process for syngas produce recently. The mechanism of POM is stillambiguous because of the restrictions on present experimental apparatuses, however.In this research, Dmol³, a program module based on DFT for quantum-mechanicalcalculation has been utilized to compute and analyze influencing factors onfundamental reaction of POM on the atomic scale. The factors studied in this paperinclude monatomic step and adsorbed oxygen atom on Ni surface. Then the reactionmechanism is improved.Ni (211) slab model has been designed to simulate monatomic step structure.Results of adsorption energy and space configurations of CHx (x=0⁴) on differentactive sites of the surface are discussed. LST/QST method has been carried out onsearching for reaction pathways, transition states and corresponding reaction data ofall dissociation steps of CHx (x=1⁴). Calculation results show that the step structureis more beneficial to CHx adsorption comparing with plan structure. There are activesites on step structure, which can reduce energy barrier of CHx dissociation. Thedecomposition processes of CH4 and CH are key steps of the whole process of CH4dissociation, corresponding active energy can be reduced at special sites on steppedNi surface. Mulliken population analysis results were cited to explain the reactionprocess in this paper.Ni (111) slab model has been used to study the influence of adsorbed oxygenatom on dissociation process of CH₄. Formation and decomposition pathways,transition states and corresponding energy data of CH_xO (x=1³) were also made bycalculations. Simulation results indicate that CH(x (x=0³) adsorption heat decreasegreatly on Ni (111) surface which has absorbed oxygen atom. CHx (x=1³) speciescan be divided into CH_x-1 and H directly, furthermore, they can react with oxygenatom to produce intermediate CH_xO or CH_x-1 and OH. The reactions that CH_xObecome CH_x-1O and H are of great probability in POM process.