First-Principles Study On The Catalytic Mechanism Of Iron-Based Catalyst In Water Gas Shift Reaction

Since the energy crisis, energy shortage, and the serious pollution to the environment caused by the original carbon energy, looking for clean and renewable energy is one of the big challenges which the human beings face now. Among the new energies, hydrogen as a kind of renewably clean energy has become a hotspot of researches. Hydrogen with high efficiency, low pollution and wide application has attracted attention. The successful application of hydrogen can solve our current energy crisis and environmental pollution problems.Water gas shift(WGS) reaction is the main way for hydrogen production in industry. In the last decade,with the increase of demand for pure hydrogen gas, and the development of the hydrogen fuel cells, and the researches on the catalyst for WGS reaction aroused the interest of scientists. Nowadays, the commercially high temperature catalyst is copper doped iron oxide catalyst, and magnetite(Fe3O4) is the active ingredient in iron-based catalyst. In this paper, the iron-based catalysts used in the high temperature WGS reaction are studied. Our goal is to find out the catalytic mechanism of iron oxide catalyst, to make theoretical guidance for the design and development the more excellent catalysts. The main research work and results are as follows:1. The adsorption of carbon monoxide and water on the small Cux(x =1–4) clusters modified Fe3O4(111) surface is investigated. It is found that the addition of Cu to the Fe3O4(111) plays a critical role in activating the surface for CO adsorption. The presence of Cux clusters on the surface enhances the adsorption of CO, which would provide the CO with more stable adsorption sites and harmonize the coadsorption of CO and H2 O on the Cux/Fe3O4 surface. The results shed light on the promoting effect of the Cu-modified Fe3O4 catalysts.2. The adsorption properties of CO on the nondefective and defective(with an oxygen vacancy)B-layer Fe3O4(0 0 1) surfaces(an octahedral environment of iron ions) at different coverages are studied using the spin-polarized density functional theory with the inclusion of on-site Coulomb interaction by introducing Hubbard U parameter(DFT + U) method. It is found that the CO adsorption energy in general increases with the CO coverage. Both types of B-layer Fe3O4(0 0 1) surfaces have the excellent ability forCO oxidation. Comparatively, the defective B-layer Fe3O4(0 0 1) surface has a much stronger CO adsorption ability and a lower CO oxidation ability than the nondefective B-layer Fe3O4(0 0 1) surface. The density of state reveals the bonding mechanism of CO on the two surfaces. The effects of the ambient conditions on the CO adsorption processes are analyzed.