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Spectroscopic studies of the mechanistic steps that occur on supported precious metal catalysts used in industrial and automotive applications are hampered by a dearth of suitable experimental methods. We used femtosecond laser excitation followed by nanosecond time-resolved in situ Fourier-transform infrared spectroscopy to initiate a catalytic reaction on alumina-supported silver catalysts, which are of interest in minimizing nitrogen oxide emissions from fuel-efficient lean-burn engines. We found that the key intermediate step in the reaction between carbon monoxide and nitric oxide is the flip of a cyanide group from a silver nanoparticle to the alumina support (with a lifetime of 2 microseconds), which indicates the central role played by the interface between the metal particle and the oxide support.

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Ultrafast laser pulses on Ir{111} cause a highly temperature-dependent redshift of the intramolecular stretch frequency of adsorbed NO. The time-resolved spectral changes are driven by charge transfer of hot electrons to the NO 2pi*d antibonding orbital, which leads to bending of NO and internal bond weakening. The nonadiabatic change in the NO adsorption geometry follows the charge transfer within a time scale of 700 femtoseconds. This geometrical change is the same as the mechanism predicted for thermally induced dissociation.

We investigate the surface-enhanced Raman spectra of 4-mercaptopyridine on gold in a variety of acids. 4-Mercaptopyridine is a known pH sensor which exhibits characteristic spectral changes when the pH is changed. Here we show with the help of experiment and density functional calculations that the ring breathing mode is also highly sensitive to hydrogen bonding. Its spectral signature is a broad band with up to three contributions from free, protonated and hydrogen-bonded 4-mercaptopyridine. Unlike pyridine in solution, where protonation leads to a higher ring breathing frequency than hydrogen-bonding, we find that protonated adsorbed 4-mercaptopyridine possesses a frequency which is lower than the corresponding hydrogen-bonded species. The Raman spectra indicate an orientation change of the aromatic ring in acidic solutions, which could be caused by a cation/π interaction between protonated and deprotonated 4-mercaptopyridine. As the frequencies of the three species are well separated, adsorbed 4-mercaptopyridine can probe more complex changes in the solution environment than just pH.