Evolution of the surface science of catalysis from single crystals to metal nanoparticles under pressure

Abstract

Vacuum studies of metal single crystal surfaces using electron and molecular beam scattering revealed that the surface atoms relocate when the surface is clean (reconstruction) and when it is covered by adsorbates (adsorbate induced restructuring).It was also discovered that atomic steps and other low coordination surface sites are active for breaking chemical bonds (H-H, O=O, C-H, C=O and C-C) with high reaction probability. Investigations at high reactant pressures using sum frequency generation (SFG) -vibrational spectroscopy and high pressure scanning tunneling microscopy (HPSTM) revealed bond breaking at low reaction probability sites on the adsorbatecovered metal surface, and the need for adsorbate mobility for continued turnover. Since most catalysts (heterogeneous, enzyme and homogeneous) are nanoparticles, colloid synthesis methods were developed to produce monodispersed metal nanoparticles in the 1-10 nm range and controlled shapes to use them as new model catalyst systems in twodimensional thin film form or deposited in mesoporous three-dimensional oxides. Studies of reaction selectivity in multipath reactions (hydrogenation of benzene, cyclohexene and crotonaldehyde) showed that reaction selectivity depends on both nanoparticle size and shape. The oxide-metal nanoparticle interface was found to be an important catalytic site because of the hot electron flow induced by exothermic reactions like carbon monoxide oxidation.

Synergetic Effect of Surface and Subsurface Ni Species at Pt−Ni Bimetallic Catalysts for CO Oxidation

“…Although the surface structure of the supported catalyst NPs is complex, in particular for the multicomponent catalysts, a bridge between model systems and practical catalysts made in this work helps to understand the reaction mechanism at the microscopic scale and to construct highly efficient practical nanocatalysts. 84 Furthermore, our work demonstrates that activation in H 2 is a simple but effective route to manipulate the surface architecture of multicomponent catalysts and produce the active sandwich Pt-Ni catalysts. Considering that activation of powdered catalysts in H 2 is the most frequently used pretreatment, the sandwich Pt-TM catalysts produced by the reduction process should be generally present in many Pt-TM systems but are often ignored.…”

Advancing the Frontiers in Nanocatalysis, Biointerfaces, and Renewable Energy Conversion by Innovations of Surface Techniques

“…Using model surfaces, single crystals at first, the evolution of electron, ion and molecular scattering techniques provided atomic and molecular structures, composition and oxidation states and energy transfer information upon adsorption, desorption and scattering of molecules from surfaces [1][2][3][4] . Figure 1 shows the timeline of this development and evolution of surface science.…”

Nanocatalysis: hypothesis on the action mechanism of gold

“…At the same time, nanoparticles have a characteristic that describes the above properties in an integrated manner; we are speaking of confinement of elementary excitations in a nanoparticle. The most important property determined by the confinement of electrons is the discretization of their electronic spectra, which accompanies the increase in the spectral gap width; the broadening of the gap increases when the characteristic size of a nanoparticle decreases [4]. Therefore, it is reasonable to consider the features introduced into the Tamm surface states of nanoparticles by a fundamental property like the electron confinement.…”

“…Although the catalytic properties of Au (hydrogen-deuterium exchange, the reduction of NO x by using of H 2 , isomerization of paraffins, partial oxidation) had been quite widely studied until the end of the 1980's [1][2][3][4][5][6], it was found that Au is a much less efficient catalyst than the group VIII elements of Mendeleev's table and other transition metals. However, in 1987, it was found by Haruta et al [7][8][9] that small size Au particles increased the activity of CO oxidation dramatically, performing the reaction at temperatures below those of such classical catalysts as Pt [7][8][9][10].…”