Guaiacol Adsorption and Decomposition on Platinum

Guaiacol (2-methoxyphenol, C₆H₄(OH)(OCH₃)) adsorption and reactions on a Pt(100) surface were studied with infrared reflection-absorption spectroscopy (IRAS) and temperature programmed desorption (TPD) measurements at different surface coverage values from 100 to 800 K. In addition, density functional theory (DFT) calculations were used to determine geometries, adsorption energies, and vibrational frequencies for adsorption structures. Depending on surface coverage, guaiacol formed one or two physisorbed states. At low coverage, a single state with a desorption peak at 225 K was observed. At high coverage, two physisorbed states were observed with desorption peaks at 195 and 225 K. At temperatures above 225 K, after the desorption of physisorbed layers, a dissociatively adsorbed structure, C₆H₄O(OCH₃) + H, was observed. Recombinative molecular guaiacol desorption was detected at 320 K. The dissociatively adsorbed structure was stable up to 337 K when C-O bonds began to break. Molecularly adsorbed guaiacol in horizontal (flat-lying) configurations bound through its benzene ring was not observed under all tested conditions. Similarities of vibrational spectra and desorption measurements for a Pt(100) surface in this study and a Pt(111) surface reported previously demonstrate that the obtained results are generally valid for low-index Pt crystal planes and, more importantly, for catalytic Pt nanoparticles.