Engineering a PtCu Alloy to Improve N₂ Selectivity of NH₃–SCO over the Pt/SSZ-13 Catalyst

Improving the N2 selectivity is always a great challenge for the selective catalytic oxidation of ammonia (NH3–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 N2 selectivity of the NH3–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 Cu2+ species were both present on the surface of PtCu/SSZ-13. Due to such a unique alloyed structure with an altered oxidation state, the N2 selectivity of NH3–SCO on the PtCu/SSZ-13 catalyst was remarkably improved, while the NH3–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 N2 selectivity. This work provides a new route to synthesize efficient alloy catalysts for optimizing the N2 selectivity of NH3–SCO for NH3 slip control in diesel exhaust purification

Advanced Insight into the Size Effect of PtPd Nanoparticles on NO Oxidation by <i>in Situ</i> FTIR Spectra

It is a recognized view that particle size could play a significant role in catalytic performance. To obtain the nanoparticles with the different size, a series of bimetallic PtPd/SiO₂–Al₂O₃ catalysts subjected to hydrothermal treatment in different time were prepared and applied for NO oxidation under diesel exhaust. The experimental results confirmed that the average noble particle size was gradually increased at a different variation rate, along with aging time. An increasing of average particle size resulted in the reduction of the corresponding NO turnover frequencies (TOFs) by different degrees. Thus, a new sight on the relationship between particle size and NO catalytic activity is obtained. In the aging process, the overall trend of noble metal particles got larger along with receding NO catalytic performance, yet in a period, a few small particles presented more bridged/chelating nitrate and ionic nitrate species, further retarding its rate of loss activity