The flow cell system probes
the dynamics of a catalytic oxidation reaction over a polycrystalline
platinum gauze. In addition to using mass spectroscopy to determine the
ratios of reaction products, the flow system also uses diode laser
absorption spectroscopy. to measure the internal energy distribution of
the nascent carbon dioxide product of the reaction. This distribution
will favor vibrational modes indicative of the transition state since
any carbon dioxide formed on the platinum surface is weakly bound and
desorbs before equilibrating with the surface. Previous studies on the
combustion of CO(g)+O2(g), CO(g)+NO(g), and C2H2(g)+O2(g) have found that the
carbon dioxide produced in each reaction has similar energy
distributions over CO2(g)’s four
vibrational modes suggesting that the CO2(g) formed in these reactions
follows the same pathway. For these reactions, all the vibrational
modes were excited relative to what is expected from CO2(g) in energetic equilibrium
with the platinum surface. Moreover, the energy
distribution favors the asymmetric mode over the similarly distributed
bending and symmetric modes. The laser is a tunable diode laser and has
a frequency range of 2250-2350 cm-1, appropriate for probing the
asymmetric stretch of the CO2 molecule. In a typical
spectrum at room temperature there are about 15 lines in one mode. This
trend does not continue for the CH3OH(g)+O2(g) reaction. In this case the internal state distribution data suggests
the presence of a formaldehyde intermediate in the oxidation of methanol. Currently, we are
using this apparatus to investigate the catalytic oxidation of CO occuring on Pt nanoparticles
deposited on bundles of carbon nanotubes.