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Quantum Chemistry Study on Different Isomers for Ptn+/Ptn- (n=3-6) and Reaction of Pt2 with CH4 on Singlet and Triplet Energy Surfaces

Author: GengZongKe
Tutor: MengLingPeng;SunZheng
School: Hebei Normal
Course: Physical and chemical
Keywords: Ptn~+/ Ptn~- Clusters isomers catalysis reaction mechanism quantum chemisty
CLC: O641.1
Type: Master's thesis
Year: 2011
Downloads: 22
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Abstract


The catalytic characteristic of Ptn clusters is of great importance for catalysis. A theoretical study on the influence of charges on electronic structure and catalytic activity of the clusters will give spark on understanding the mechanism of the catalytic reaction involving Ptn clusters.In chapter 1, the basic concept and reserch development on clusters, as well as platinum clusters were summarized basis on a survey of the related literature. The development of quantum chemistry and its application was introduced briefly in Chapter 2, also the Hartree-Fock equation, density functional theory, pseudo basis set and Gaussian program package were introduced in this part.In Chapter 3, 15 kinds of density functional model chemistry were tested for Pt<sup>-C-H system, and PBE1PBE/LANl2DZ was confirmed to be most suitable for the system. Chapter 4 gives the results and discussions on different isomers of Ptn+、Ptn-(n=3-6) at different electronic states. The catalytic mechanisms of the reaction of Pt2 + CH4 on singlet and triplet surfaces were studied at PBE1PBE/LANl2DZ level in chapter 5.The main conclusions are as following:1. A comparison of 15 density functional model chemistry (LSDA, B3LYP, B3P86, B3PW91, PBE1PBE in combination with Los Alamos ECP plus DZ for Pt and D95V for C, H, LANL2TZ for Pt and aug-cc-pVTZ for C, H, Stuttgart RSC 1997 ECP for Pt and aug-cc-pVTZ for C, H respectively) for Pt-C-H system shows PBE1PBE/LANL2DZ is the most suitable for the system.2. Different electronic structures of isomers of Ptn+/Ptn- (n=3-6) studied at PBE1PBE/LANL2DZ show that the ground states of Pt3+ is 4A1, which is a regular triangle structure, 2B2 with equicrural triangle structure is the ground state for Pt3-, 4A1 with regular tetrahedron structure is the ground state for Pt4+, the ground state of Pt4- is sextet with distorted tetrahedron structure, the ground states of Pt5+ and Pt5- are 6B1 with C2V plannar structure and 6A distorted trigonalbiyramid respectively, the ground state of Pt6+ is three dimension structure with C2V point group, it’s electronic state is 4A1, while the ground state of Pt6- is not available in this work.3. The catalytic mechanisms of the reaction of Pt2 + CH4 on singlet and triplet surface were studied at PBE1PBE/LANL2DZ show that there are similar catalytic mechanisms of the reaction at singlet and triplet states: They both have relative low activation energy. The difference of the mechanisms cuased by eletronic states was analysed in spect of eletron transfer. Base on the reaction mechanism, it is speculated that the final products of Pt2 + CH4 on singlet energy surface is CH2=CH2, while it is CH3CH3 on triplet energy surfaces.

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