Trends of Water Gas Shift Reaction on Transition Metal Surfaces from First Principles calculation

• Main Authors: Huang Shih-Chang, 黃世昌
• Other Authors: Wang Jeng-han
• Format: Others
• Language: zh-TW
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/94731086812772503650

碩士 === 國立臺灣師範大學 === 化學系 === 98 === The mechanism of water gas shift reaction (WGSR) on the close-packed transition metal surfaces of Co, Ni Cu (from the 3d row) Rh, Pd, Ag (from the 4d row) and Ir, Pt, Au (from the 5d row) has been systematically examined by periodic density functional theory (DFT) calculations. The computed potential energy surface (PES) shows that the activity of WGSR is influenced by two kinds of elementary steps: O-H bond dissociation and C-O bond formation. Activation barriers (Ea) and reaction energies (H) on a series of metal surfaces show good BEP relationship; the energetic trends in periodic table are opposite in these two kinds of steps. In O-H bond dissociation steps, trends of Ea and H are groups 9 < 10 < 11 and 3d < 4d < 5d. On the other hand, the lower-right metal surfaces in the Periodic Table, Cu(111), Ag(111), Pt(111) and Au(111), have relatively lower Ea and H in C-O bond formation steps, which is responsible for their highly WGSR activity of metal/oxide catalysts. In addition, the fundamental of energetic trends has been examined from the analyses of adsorption energy, density of state (DOS) and charge density. The result shows that the surfaces of upper-left metals in the Periodic Table with higher energy and narrower delocalization of their d orbitals yield a stronger adsorption energy that will stabilize dissociating fragments and lower Ea and H in O-H bond dissociation steps. The prediction of energetic trends in the present work is also appropriate for other catalytic reactions, such as ethanol decomposition and CO oxidation, and can help us scientifically design a better catalyst for the desired reaction.