Engineering a PtCu Alloy to Improve N Selectivity of NH-SCO over the Pt/SSZ-13 Catalyst.

Improving the N selectivity is always a great challenge for the selective catalytic oxidation of ammonia (NH-SCO) over noble-metal-based (especially Pt) catalysts. In this work, Cu as an efficient promoter was introduced into the Pt/SSZ-13 catalyst to significantly improve the N selectivity of the NH-SCO reaction. A PtCu alloy was formed in the PtCu/SSZ-13 catalyst, as confirmed by X-ray diffraction, transmission electron microscopy, energy dispersive spectrometry mapping, and X-ray absorption spectroscopy results. As indicated by the X-ray photoelectron spectroscopy analysis, the Pt species in the alloyed PtCu nanoparticle was mainly present in the electron-rich state on PtCu/SSZ-13, while the electron-deficient Cu and isolated Cu species were both present on the surface of PtCu/SSZ-13. Due to such a unique alloyed structure with an altered oxidation state, the N selectivity of NH-SCO on the PtCu/SSZ-13 catalyst was remarkably improved, while the NH-SCO activity was kept comparable to that on Pt/SSZ-13. The reaction path was changed from the NH mechanism on Pt/SSZ-13 to both NH and internal selective catalytic reduction mechanisms on the PtCu/SSZ-13 catalyst, which was considered the main reason for the enhanced N selectivity. This work provides a new route to synthesize efficient alloy catalysts for optimizing the N selectivity of NH-SCO for NH slip control in diesel exhaust purification.