Sum frequency generation (SFG)-surface vibrational spectroscopy studies ofburied interfaces: catalytic reaction intermediates on transition metal crystal surfaces at high reactant pressures; polymer surface structures at the solid-gas and solid-liquid interfaces
Z. Chen et al., Sum frequency generation (SFG)-surface vibrational spectroscopy studies ofburied interfaces: catalytic reaction intermediates on transition metal crystal surfaces at high reactant pressures; polymer surface structures at the solid-gas and solid-liquid interfaces, APP PHYS B, 68(3), 1999, pp. 549-557
SFG has been utilized to monitor the surface species present on platinum an
d rhodium crystal surfaces during catalytic reactions at atmospheric pressu
res. Ethylene hydrogenation to ethane, cyclohexene hydrogenation to cyclohe
xane and its dehydrogenation to benzene, and carbon monoxide oxidation to c
arbon dioxide have been studied while also measuring the turnover rates and
the gas phase product distribution by gas chromatography. Strongly bound s
pectators, weakly bound reaction intermediates, and pressure-dependent chan
ges in the chemical bonding of surface species have all been observed.
SFG spectra of polyethylene and polypropylene show monolayer sensitivity an
d reveal temperature-dependent changes of surface structure, For polymer bl
ends, the hydrophobic component segregates to the solid-air interface, and
the hydrophilic component segregates at the solid-water interface. Changes
in SFG spectra of polymer blends as a function of bulk concentration correl
ate with changes of contact angle. SFG is an excellent probe of surface-str
ucture and surface-composition changes as the polymer interface is altered.