Conformational analysis and comparison between theoretical and experimental vibration spectra for isocyanate species on Ag/Al2O3 catalyst

Density functional theory (DFT) calculations were performed to study the structure and vibrational frequencies of the intermediate for the isocyanate (NCO) surface species on Ag/Al2O3 catalyst using the GAUSSIAN 98 suite of programs. Thermal decomposition of adsorbed CH3NO2 species leads to the formation of two types of NCO species (NCO on Ag and NCO on Al2O3) above 298 K. In order to investigate the reaction mechanism, we have designed the calculated models (a-g) for the NCO intermediate. Through the analysis of the vibration mode and the vibration frequency of the calculated models (a-g), we conclude that there is an excellent agreement between the calculated vibration spectrum of the model (e) containing the -AgNCO group or model (g) containing the -AlNCO group and the experimental vibration spectrum.