Dw Liao

CO2-reforming of methane on transition metal surfaces

Abstract The mechanisms of CO 2 -reforming of methane on Cu(111), Ni(111), Pd(111), Pt(111), Rh(111), Ru(001), Ir(111) and Fe(110) have been investigated by the the unity bond index-quadratic exponential potential (UBI-QEP) method. This method was named as the bond order conservation Morse potential (BOC-MP) approach before, but it has been generalized and renamed now. The heats of chemisorption ( Q ) for all involved adspecies, activation barriers (Δ E ) and enthalpy changes (Δ H ) for forward and reverse reactions were evaluated. The calculations indicated that both the dissociation of CH 4 and the dissociation of CO 2 are rate-determining steps and that they are promoted by each other. A small amount of OH radical may account for the lower activity for the CO 2 -reforming of methane. The activity sequence of catalysts is Fe>Ni>Rh>Ru>Ir>Pd>Pt>Cu. The most appropriate catalyst for CO 2 -reforming is Ru. The most suitable non-noble catalyst is Ni.

Influence of trivalent metal ions on the surface structure of a copper-based catalyst for methanol synthesis

Abstract The method of doping trivalent metal ions into a copper-based catalyst for methanol synthesis is effective in modifying the surface structure of the catalyst. The promotion effect and its relation to catalytic activity for hydrogenation of CO to methanol after doping with trivalent metal ions such as Al 3+ , Sc 3+ , and Cr 3+ into Cu–ZnO have been investigated by XRD, ESR, XPS, TPR, and the evaluation of catalytic activity. The results show that doping trivalent metal ions into ZnO assists in the formation of monovalent cationic defects on the surface of ZnO. These monovalent cationic defects both enrich and stabilize monovalent copper on the surface of copper-based catalysts for methanol synthesis during reduction and reaction. They increase catalytic activity for methanol synthesis and extend the life of catalysts.

Energetics of chemisorption and conversion of methane on transition metal surfaces

Abstract The chemisorption and conversion of methane on Pt(111), Rh(111), Ru(0001), Ir(111), Cu(111) and Ni(111) were investigated using the unity bond index-quadratic exponential (UBI-QEP) method. Following conclusions were found from the analyses. (1) The main dissociate species of methane on the metal surfaces is CH 3 . The dissociation of CH x species on Ru(0001) is the easiest but the dissociation on Cu(111) is very difficult. (2) Coupling of CH 3 may produce ethane, and then dehydrogenation of ethane may produce ethylene. The coupling of CH 3 is the easiest on Pt(111) and Cu(111), but it is very difficult on Ru(0001). It indicated that copper was favorable to the C 2 selectivity. Non-oxidative reactions of methane coupling may produce ethane but it is difficult to get ethylene. (3) There are two competitive reaction pathways for part oxidation of methane to CO, directly heat-cracking pathway on Ni(111) and burning–reforming pathway on other metal surfaces. The selectivity of CO can be increased at elevated temperatures. (4) Carbon-deposit is the cause of the dissociation of CH. It can easily take place on Ni(111) and Ru(0001), but it is weak on other metal surfaces because that CH can fast produce CO without passing the surface carbon.

EHMO study of the modes of coordination activation and hydrogenation of dinitrogen on α-Fe(111) surface for ammonia synthesis

Abstract The μ7(η2, ω2, ω′2) symmetrical flat-lying mode with double-end-on plus multiple-side-on coordination activation of N2 (mode-A) was compared with other modes, namely, μ7(η2, ω) single-end-on plus multiple-side-on inclined-mounting mode (mode-B), or μ7(η2, ω, ω′) unsymmetrical double-end-on plus multiple-side-on mode (mode-B′), and μ7(η2, ω) single-end-on plus multiple-side-on perpendicular-insertion mode (mode-C), based upon extended Huckel molecular orbital approach together with experimental results of laser Raman and IR spectroscopy of chemisorbed species on ammonia synthesis iron catalysts previously reported. As far as the chemisorption energy is concerned, mode-A appears to be the most favorable to the coordination activation of N2. Preliminary results of EHMO calculations also indicated N2 sufficiently activated with mode-A might react with slightly activated chemisorbed H2 with flat-lying coordination, or with 2H with bridging coordination, to form chemisorbed N2H2, or 2NH.