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), three-dimensional excitation-emission fluorescent matrix (EEFM) spectroscopy, UV-Vis absorption, dynamic light-scattering (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.

Keywords

ammonia (NH₃) / nanosized Pt-Rh/γ-Al₂O₃ catalyst / excitation-emission fluorescent matrix (EEFM) / selective catalytic oxidation (SCO) / tubular fixed-bed reactor (TFBR)

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