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.

Effect of surface modification with silica on the structure and activity of Pt/ZSM-22@SiO2 catalysts in hydrodeoxygenation of methyl palmitate

“…It seems plausible that the existence of Pt surface sites at the interface between the support and the Pt particles (close contact between silica and platinum as shown in Fig. S5) are accessible to CO. A similar particle-support interface effect on CO adsorption has been reported in other literature [57]. Based on these results, it could be suggested that silica coating would influence not only the amount but also the nature of exposed Pt particles.…”

Pt–Zn nanoparticles supported on porous polymeric matrix for selective 3-nitrostyrene hydrogenation

“…planes, edges, corners) that can have different reactivity [52]. The studies of CO adsorption on Pt showed the strongest bonding on low-coordination atoms located on the edges of NP [32]. Indeed, strong adsorption of electron-rich unsaturated carbon-carbon bonds on low-coordination edge atoms led to a decrease in selectivity toward the olefin product [53].…”

“…bridged/triple mode of CO adsorption on Pt planes and edges), while Pt-Zn/HPS sample shows only a small shoulder at 1980 cm À1 after CO evacuation ascribed to bridged CO species on Pt planes [32,36,37]. Such deviations in the spectra bring to a conclusion about different surface structures of metal NPs in two catalysts, i.e., the NP surface in Pt/HPS is composed of atoms ensembles that are absent on the NP surface of Pt-Zn/HPS.…”

“…2(I)) exhibit a high intensity peak at 2061 cm À1 attributed to linearly adsorbed CO [32][33][34]. The broad peak between 1980 and 1810 cm À1 reportedly corresponds to the multiple-coordinated CO adsorption on the Pt surface [32,[34][35][36], while two branches at 2143 cm À1 are associated with CO rotational bands in the gas phase [36]. The increase of CO pressure above 8 mbar did not significantly change the peak intensity indicating a saturation of the Pt surface by adsorbed CO.…”

Influence of structural parameters on the reaction of low temperature ethanol steam reforming over Pt/Al2O3 catalysts

“…The band located at 2178 cm −1 , has been previously attributed to CO adsorbed on weak Lewis acid sites of the Al 2 O 3 support [35][36][37][38]. The band at 2038 cm −1 appears at wavenumbers corresponding to CO linearly adsorbed on Pt step sites [39][40][41][42][43][44][45][46], whereas the weak band at 1787 cm −1 has been assigned to CO adsorbed in bridge form on Pt step sites [25,27,28,31]. However, the low frequency of the latter band could be also related to 3-fold bridged CO species [42,45].…”