The Reaction of Alkynes with Model Gold Catalysts: Generation of Acetylides,Self-coupling and Surface Decomposition

Catalysis Letters - Alkynes are one of the most important groups of building blocks in organic chemistry as they work as nucleophiles upon deprotonation of its acidic hydrogen. On the surface of a...     

Real-time observation of surface reactivity and mobility with scanning tunneling microscopy

Scanning tunneling microscopy allows the direct observation of reactions on surfaces on the atomic scale that otherwise must be inferred from the statistical behavior of hundred of trillions of molecules or atoms. Since the study of the details of reactions on this length scale began, our conception of surface reactivity has changed profoundly. In this Account we focus attention on our real-time observations of reactions for a number of systems, including the island growth of surface oxide on Cu(110), the anisotropic and site-specific reactivity of this oxide with carbon monoxide and ammonia, the collective motion of laterally interacting O(a) and SO(3)(a), and the incorporation of metal atoms into the structures of molecular intermediates formed in the reaction of ammonia with O(a) on Ag(110). These nanoscale, time-resolved movies capture the events as they occur, providing a dynamic picture of the distribution of reactants and products on the surface, thus providing a better understanding of the roles of reactant distribution and site specificity in surface reactivity.     

Thermal desorption study of the acetic acid decomposition on clean Ni/Cu(110) alloy surfaces

The decomposition of acetic acid was studied on a clean Ni/Cu(110) alloy single crystal by means of thermal desorption spectroscopy. The primary alloy surface composition employed in this work was 37% Ni and 63% Cu as measured by Auger electron spectroscopy. Acetate was the predominant surface intermediate observed, giving rise to the CO₂ and H₂ decomposition products observed, in analogous fashion to the decomposition of formic acid. Surface carbon residue was also detected and could be driven into the bulk by annealing the sample above 900 °K. The rate constant for the decomposition of the acetate intermediate on the alloy was found to be 10^13.5 exp(?33(kcal/mol)/RT)sec^?1. The autocatalytic decomposition of both carboxylic acids previously observed on a clean Ni(110) surface was totally suppressed. The product distribution from acetic acid observed on both the 37% Ni/65% Cu alloy and the carburized Ni(110) surfaces were very similar, indicating chemical similarities between these two surfaces. At high coverages of the acetate intermediate the activation energy for CO₂ formation increased by 14 kcal/gmol. This effect was attributed to strong attractive interactions in the adsorbate layer.     

Reaction Kinetics and Mechanism: Model Studies on Metal Single Crystals [P.H. Emmett Award Address, 1983]

In the past decade remarkable progress has been made in the surface science of catalysis. Studies on both small single crystal metal particles on supporting materials and on large (bulk) single crystals point toward a more refined understanding of the fundamental processes underlying catalytic chemistry and, hopefully, toward a rational design of catalytic materials. It seems clear that concepts gleaned from studies on single crystal surfaces will strongly influence the research with supported metal catalysts and ultimately affect the nature of the materials used as practical catalysts.     

Molecular ethane adsorption dynamics on oxygen-covered Pt(111)

The dynamics of ethane trapping on Pt(111)-p(2×2)-O were investigated by supersonic molecular beam techniques at a surface temperature of 100 K. The initial trapping probability was measured in the range of incident energy from 10 to 45 kJ/mol and incident angles from 0^° to 60^°. A broad angular distribution of scattered ethane and total energy scaling (E_T cos^0.2) for ethane trapping indicated a corrugated gas–surface potential. Stochastic trajectory simulations employing a potential developed from the trapping of ethane on Pt(111) gives quantitative agreement of the measured initial trapping probabilities over entire ranges of incident energies and angles. Calculations of energy transfer for ethane after the first bounce on Pt(111) and Pt(111)-p(2×2)-O clearly indicate that interconversion of parallel and perpendicular momentum and energy transfer to lattice vibrations account primarily for the differences in trapping probabilities between ethane on the two surfaces. At glancing incidence trapping is not significantly reduced on the oxygen-covered Pt(111) because the parallel momentum appears to be transferred partially to phonons.     

Reaction Kinetics and Mechanism: Model Studies on Metal Single Crystals [P.H. Emmett Award Address, 1983]

In the past decade remarkable progress has been made in the surface science of catalysis. Studies on both small single crystal metal particles on supporting materials and on large (bulk) single crystals point toward a more refined understanding of the fundamental processes underlying catalytic chemistry and, hopefully, toward a rational design of catalytic materials. It seems clear that concepts gleaned from studies on single crystal surfaces will strongly influence the research with supported metal catalysts and ultimately affect the nature of the materials used as practical catalysts.