Novel Catalyst for the Conversion of Synthesis Gas to Fuel: A Computational Study.

Abstract Novel Catalyst for the Conversion of Synthesis Gas to Fuel: A Computational Study. First-principles density functional theory based calculations with a generalized gradient approximation (GGA) of the PBE exchange correlation functional have been used to study the interaction between noble metal, ruthenium (Ru), and base metal, nickel (Ni), as employed in the making of Ni-Ru bimetallic catalysts. To evaluate the consequences of forming bimetallic materials for catalytic and electronic applications, the electronic structure of nickel-ruthenium interface with low miller index surfaces of nickel have been investigated. The preferred sites and geometry con guration for ruthenium deposition/electroplating is determined and the work of adhesion which characterizes the strength of ruthenium adhesion to the nickel substrate is calculated. It's shown from the calculation of adhesion energies that ruthenium adatom forms the strongest contact with the (110) surface at a 5fold-hollow site, followed by the (111) surface at a 3fold-hcp site and then the (100) surface at a 4fold-site. The bimetallic composite a ords a bifunctional mechanism that thermodynamically favours CO activation on Ni-Ru 0.06 ML coverage and even stronger on 1ML Ni-Ru coverage when both are compared to that of the nickel monometallic system. A systematic study of carbon monoxide hydrogenation on ruthenium-Monolayer-Covered-fcc-Ni-(111), Ru-MLC-fcc-Ni-(111), was undertaken towards the formation of long chain hydrocarbons according to the Fischer-Tropsch Synthesis. The interaction of reactant molecules such as CO and H2 as well as dissociated fragments were investigated. Methanol species and ethylene radical, both of which are precursors to chemical fuel production, CH2-CH2 (Eads = -705.57 kJmol􀀀1) are intermediate species of the FT synthesis on the bimetallic system, Ru- MLC-fcc-Ni-(111). The search for alternative source of energy has also drawn interest in energy production via directly fed fuel cells technology of which there exists di erent kinds of cells which vary in catalytic material for the anode and fuel source. A viable kind of the variations, which mitigates high cost from commonly made platinum-based fuel cells, yet improves fuel cell performance is Direct Hydrazine Fuel Cells with nickel catalyst as the anode. Density functional theory calculations, with a correction for the long-range interactions, of the adsorption of hydrazine (N2H4) on the Ni (110), (100), and (111) surfaces, both defect-free planes and surfaces containing point defects in the form of adatoms and vacancies is undertaken. Several low-energy adsorption structures for hydrazine on the perfect and defective surfaces have been identi ed and compared. The hydrazine molecule is shown to interact with the Ni surfaces mainly through the lone-pair of electrons located on the N atoms, forming either monodentate or bidentate bonds with the surface. The strength of N2H4 adsorption on the perfect surfaces is found to be directly related to their stability, i.e. it adsorbs most strongly onto the least stable (110) surface via both N atoms in a gauche-bridge con guration (Eads = -1.43 eV), followed by adsorption on the (100) where it also binds in gauche-bridge con gurations (Eads = -1.27 eV), and most weakly onto the most stable (111) surface via one N-Ni bond in a trans-atop con guration (Eads = -1.18 eV). The creation of point defects in the form of Ni adatoms and vacancies provides lowercoordinated Ni sites, allowing stronger hydrazine adsorption. Analysis into the bonding nature of N2H4 onto the Ni surfaces reveals that the adsorption is characterized by strong hybridization between the surface Ni d-states and the N p-orbitals, which is corroborated by electron density accumulation within the newly formed N-Ni bonding regions.

Source: KNUST