SCATTERING OF GROUND STATE AND VIBRATIONALLY EXCITED NO MOLECULES FROM VANADIUM DIOXIDE FILMS: BRIDGING THE GAP BETWEEN SINGLE CRYSTALS AND COMPLEX MODEL CATALYSTS

The current state-of-the-art in the field of gas-surface scattering dynamics, presently dominated by simple crystalline surfaces, calls for expanding its unique experimental approaches to the investigation of fundamental molecular interactions at complex catalytic materials.

Vanadia-based catalysts are being widely used for selective catalytic reduction of NOx emissions. Vanadium dioxide (VO₂) provides a unique testing ground for molecular interactions at surfaces as it can morph itself from insulator to metal in only a few degrees temperature range (Mott transition). The dependence of the metallic properties of VO₂ films on their temperature is expected to bear on their propensity to interact with molecular vibrational coordinate and hence, possibly influence the chemistry of heterogeneous catalysis.

Here we report our first experiments, where model catalyst films of VO₂ fabricated by chemical vapor deposition (CVD) in Tel Aviv were subjected to scattering experiments in Goettingen where NO(v=0) and NO(v=11) molecules were scattered from the catalyst samples and translational and rotational energy transfer was studied. Remarkably, our results indicate that even for scattering from rough CVD deposited surfaces the rotational temperature of the scattered NO molecules is substantially higher the surface temperature and depends on the incident energy of the impinging NO molecules. The translational energy of the scattered NO molecules is also sensitive to the incident kinetic energy. These findings indicate that the direct single bounce scattering channel, retaining the memory of the incident beam, plays an important role, suggesting that catalytically relevant dynamical fingerprints can be inferred from these experiments.