Investigation of fluorescence characterization and electrochemical behavior on the catalysts of nanosized Pt-Rh/γ-Al2O3 to oxidize gaseous ammonia

Abstract

This work describes the environmentally friendly technology for oxidation of ammonia (NH3) to form nitrogen at temperatures range from 423K to 673K by selective catalytic oxidation (SCO) over a nanosized Pt-Rh/γ-Al2O3 catalyst prepared by the incipient wetness impregnation method of hexachloroplatinic acid (H2PtCl6) and rhodium (III) nitrate (Rh(NO3)3) with γ-Al2O3 in a tubular fixed-bed flow quartz reactor (TFBR). The characterization of catalysts were thoroughly measured using transmission electron microscopy (TEM), threedimensional excitation-emission fluorescent matrix (EEFM) spectroscopy, UV-Vis absorption, dynamic lightscattering (DLS), zeta potential meter, and cyclic voltammetry (CV). The results demonstrated that at a temperature of 673K and an oxygen content of 4%, approximately 99% of the NH3 was removed by catalytic oxidation over the nanosized Pt-Rh/γ-Al2O3 catalyst. N2 was the main product in NH3-SCO process. Further, it reveals that the oxidation of NH3 was proceeds by the over-oxidation of NH3 into NO, which was conversely reacted with the NH3 to yield N2. Therefore, the application of nanosized Pt-Rh/γ-Al2O3 catalyst can significantly enhance the catalytic activity toward NH3 oxidation. One fluorescent peak for fresh catalyst was different with that of exhausted catalyst. It indicates that EEFM spectroscopy was proven to be an appropriate and effective method to characterize the Pt clusters in intrinsic emission from nanosized Pt-Rh/γ-Al2O3 catalyst. Results obtained from the CV may explain the significant catalytic activity of the catalysts.