Theoretical Studies of the Following Reaction Mechanisms:I.The C-N Coupling Reaction on Pt(111) and Ni(111) Surface II.the HCN Formation from CHxNO on Pt(111) surface

• Main Author: 陳維家
• Other Authors: 何嘉仁
• Format: Others
• Language: zh-TW
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/52966892223090960757

碩士 === 國立臺灣師範大學 === 化學系 === 99 === I: The C-N Coupling Reaction on Pt(111) and Ni(111) Surface. We used the density functional theory (DFT) with the projector-augmented-wave method (PAW) to systematically investigate the C-N coupling reaction, an important catalytic process in industrial synthesis to form hydrogen cyanide (HCN), on Pt(111) and Ni(111)surface. This reaction includes several steps, such as the adsorption of reactants and products (CHx, NHy and CHxNHy x=0-3 y=0-2), dehydrogenation of methane and ammonia, movement of molecular fragments on the surface, and C-N coupling processes. From our calculation, the adsorption energy of CHx and NHy on Pt(111)/Ni(111) surfaces in the decreasing order are: C > CH > CH2> CH3,and N > NH > NH2 with the values of 7.41/6.91, 6.97/6.52, 4.58/4.39, 2.19/2.01 eV, and 5.10/5.49, 4.12/4.79, 2.75/2.87 eV, respectively. For the adsorption energy of CHxNHy, the CNH2 species is the largest on Pt(111) surface, but on Ni(111) surface, CH3N is the most stable. The C-N coupling barriers are different on the two metal surfaces while the initial, transition state and finial structures are very similar. On Pt(111) surface, the coupling reaction of CH2+NH2 has the lowest barrier, but CH+NH2 is the most favorable on Ni(111) surface. The detail local density of states (LDOS), electron localization function (ELF), and Bader-charge analysis have also been investigated to rationalize the calculated outcomes. II: The HCN formation from CHxNO on Pt(111) surface. We applied density functional theory (DFT) with the projector-augmented-wave method (PAW) to investigate the hydrogen cyanide synthesis in the presence of oxygen, a simulation of Andrussow process. The CHxNO (x=0-3), produced by the coupling of NO (oxidation of NH3) and CHx (dehydrogenation of CH4), which is used as the reactant in our caculatation, with adsorption energies 4.11, 1.91, 2.04 and 2.12 eV on Pt(111) surface, respectively. The most possible synthesis pathway from CH3NO to HCN is: (i) the continuous dehydrogenation of CH3NO to CHNO, (ii) the hydrogenation of CHNO to CHNOH, and (iii) the bond scission of N-OH to form the finally product, HCN. The rate determing state is CH3NO (a)→CH2NO(a) +H(a)，Ea = 1.22 eV.