Activity enhancement of Pt/MnOx catalyst by novel β-MnO2 for low-temperature CO oxidation: study of the CO–O2 competitive adsorption and active oxygen species

Abstract

Low-temperature oxidation of carbon monoxide (CO) is one of the most studied reactions because of its scientific and industrial applications. In this study, we discovered that the low-temperature CO oxidation activity over Pt/MnO_x catalyst could be enhanced by a novel β-MnO₂ support material. Nearly complete CO conversion was obtained over the Pt/MnO_x catalyst below 100 °C under our catalysis conditions. TOF (turnover frequency) of Pt/MnO_x was five and nine times that of Pt/MnO_x-COM (COM, commercial) and Pt/Al₂O₃ at 150 °C, respectively. The combined results of X-ray diffraction (XRD) Rietveld refinement of fresh and spent catalysts, CO-temperature-programmed desorption (CO-TPD) and diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy allowed us to conclude that the O₂ molecules exhibited strong adsorption and activation ability on the surface of Pt/MnO_x compared to that on the surface of Pt/MnO_x-COM. From the H₂-TGA (weight loss) and DTGA results, we confirmed that strong metal–support interactions exist between Pt and MnO_xvia formation of Mn–O–Pt bonds for both catalysts. Moreover, by combining the results of Rietveld refinement of XRD, Raman, CO-TPD and O₂-TPD (inlet CO and inlet CO/O₂ mixture gases as adsorbates, respectively) analyses, we inferred that the interfacial lattice oxygen in Pt/MnO_x might be the active oxygen species for low-temperature CO oxidation.