Study of CO and Hydrogen Interactions on Carbon-Supported Pt Nanoparticles by Quadrupole Mass Spectrometry and Operando Diffuse Reflectance FTIR Spectroscopy

Abstract

CO adsorption on carbon-supported Pt nanoparticles under operando conditions was studied by quadrupole mass spectrometry and diffuse reflectance infrared fourier transform spectroscopy (DRIFTS). The Pt catalyst was also studied by high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). It was shown by HRTEM and XPS that Pt nanoparticles can be fully reduced by H2 at room temperature instead of by conventional high-temperature treatment. The Pt dispersion was determined by XRD, HRTEM, and CO chemisorption techniques with an excellent agreement among them. The room-temperature H2/O2 titration method was also used, but if assuming H/PtS = O/PtS = 1, it led to the underestimation of the dispersion compared to the other techniques. The existence of adsorption sites inaccessible to H2 (or O2) but accessible to CO because of a stronger interaction with Pt was proposed to explain the results. It was also concluded that H/Pts was lower than unity (H/Pts = 0.72) and, as a major consequence, that Pt nanoparticles with 2.7 nm diameter still have a bulk-like behavior in contrast with what was reported in the literature for 1 nm Pt particles. CO adsorption on Pt/C at 298 K after H2 treatment was studied by operando DRIFTS. The C–O stretching vibration (νCO) bands were ascribed to CO adsorbed on Pt surface at (111)-terrace, (100)-terrace, edge, and kink sites in linear and bridge forms. An unexpected νCO band at 1703 cm–1 was observed upon CO adsorption and tentatively attributed to CO on surface Pt sites interacting through its oxygen end with the carbon support. It was also shown that the adsorption of CO and H2 in successive repeated steps was necessary to reach a stable state of the adsorbed CO phase. Possible reconstruction of Pt nanoparticles at room temperature during this process is discussed.