Visible light assisted thermocatalytic reaction of CO + NO over Pd/LaFeO3

Abstract

A LaFeO3 supported Pd nanoparticle catalyst Pd/LaFeO3 was prepared by a two-step precipitation–deposition method. Its catalytic performance for the reduction of NO by CO was subsequently evaluated in the lower temperature under visible light irradiation or not. It was found that visible light could boost the progress of the reaction and the selectivity of forming N2. The results of temperature-programmed desorption (TPD) of CO and in-situ diffuse reflectance infrared Fourier transform spectra (in-situ DRIFTS) showed that visible light could enhance the adsorption of NO and its activation at Pd or LaFeO3 site and that of CO at Pd site, respectively. Co-adsorption results of NO + CO suggested that the activated intermediates of CO and NO would further interact to form the isocyanate (–NCO) and N2O species, which finally transformed to N2 and CO2. Based on the results of Raman spectrum, H2-temperature programmed reduction (TPR), the X-ray photoelectron spectroscopy (XPS), photoluminescence spectra (PL) and photocurrent testing, it was proposed that visible light irradiation could cause the increase in surface electron density of Pd nanoparticles by the photo-induced electron (from O2p to Fe3d orbit) transfer from LaFeO3 to Pd. Moreover, the valence exchange of Fe4+ and Fe3+ induced by visible light could promote the formation of oxygen vacancies and then the adsorption and activation of CO and NO. This result also indicated that the photo-excitation of supports could strengthen the strong interaction between support and metal nanoparticles, and then promote the thermo-catalytic reactivity of catalysts.