Molecular surface chemistry by metal single crystals and nanoparticles from vacuum to high pressure

Abstract

Model systems for studying molecular surface chemistry have evolved from single crystal surfaces at low pressure to colloidal nanoparticles at high pressure. Low pressure surface structure studies of platinum single crystals using molecular beam surface scattering and low energy electron diffraction techniques probe the unique activity of defects, steps and kinks at the surface for dissociation reactions (H-H, C-H, C-C, O=O bonds). High-pressure investigations of platinum single crystals using sum frequency generation vibrational spectroscopy have revealed the presence and the nature of reaction intermediates. High pressure scanning tunneling microscopy of platinum single crystal surfaces showed adsorbate mobility during a catalytic reaction. Nanoparticle systems are used to determine the role of metal-oxide interfaces, site blocking and the role of surface structures in reactive surface chemistry. The size, shape and composition of nanoparticles play important roles in determining reaction activity and selectivity.

Janus Nanostructures Based on Au−TiO2 Heterodimers and Their Photocatalytic Activity in the Oxidation of Methanol

“…Figure 4 shows the UV-vis absorption profile of TiO 2 nanoparticles in the presence of acac, NH 4 Ac, and methanol. Because the particles are not soluble in the reaction media, the optical profiles are mostly due to the scattering of light by TiO 2 nanoparticles (the diminishment of the absorbance, as indicated by the dotted arrow, is due to the gradual settling down of the particles from the reaction solution).…”

“…In a typical experiment, 1.0 mg of the Au-TiO 2 heterodimer nanoparticles was dissolved in a mixture of THF and water (1:1 by volume; total volume 20 mL). To this were added 0.01 M acac, 0.33 M NH 4 Ac, and 0.62 mM of methanol, and the solution was mixed by vigorous magnetic stirring. The resulting solution was saturated with oxygen by bubbling ultrapure oxygen into the solution for 5 min.…”

“…N anosized metal oxide particles have been used extensively as active components in photocatalysis, photovoltaics, and electrochromic devices, as well as chemical and biological sensors, largely because of their large band-gap energy, corrosion resistance, mechanical durability, and abundant availability (and, hence, low costs) (1)(2)(3)(4)(5)(6). Of these, titanium dioxide (TiO 2 ) has attracted particular attention.…”

The electronic structure and geometric structure of nanoclusters as catalytic active sites

“…The progresses of experimental methods and theoretical simulations facilitated the catalysis [6] researches at the molecular level [7][8][9][10][11][12][13]. Researchers now design the catalysts through reaction mechanisms and in situ characterizations [10,[13][14][15][16][17][18][19]. Catalysis is a complex multidisciplinary science.…”

Design of a new reactor-like high temperature near ambient pressure scanning tunneling microscope for catalysis studies

“…[25][26][27][28] scanning tunneling microscope (STM) is complimentary for vibrational spectroscopy since microscopy provides structural signature of the catalyst surface at atomic scale. However, operando study of surface structures of catalysts (surface coordination, atomic arrangement) at high temperature at atomic level has been an extremely challenging issue for many years.…”