The promotion of rare earth on Pt-SiO2-Al2O3 catalyst for NO oxidation in diesel exhaust

Abstract

The effective oxidation of NO is the key to the catalytic treatment of diesel vehicle exhaust. Improving the NO oxidation ability is mainly to optimize the chemical state of the active site (Pt), followed by increasing the number of active centers. Considering that the atoms with electronegativity weaker than Pt can provide electrons to change the chemical state of Pt, rare earth elements with weak electronegativity are selected as additives to obtain Pt/M-SiO2-Al2O3 (M = Sc, Y, La, Ce, Pr, Nd, Sm, Eu) catalysts by co-impregnation method. Among them, the Pt/La-SiO2-Al2O3 catalyst has the best NO oxidation performance, compared with the Pt-SiO2-Al2O3, the NO conversion rate increased by 28 %. Due to the special outer electron arrangement of La, its electronegativity is the smallest in rare earth, which makes its outer electrons easy to transfer to Pt atoms, and has the strongest electron interaction. Thus, the highest content of Pt0 was detected in CO diffuse reflectance infrared Fourier transform spectroscopy (CO-DRIFTS) and X-ray photoelectron spectroscopy (XPS). In addition, CO chemisorption and transmission electron microscopy (TEM) confirmed that the introduction of La in the catalyst can significantly improve the dispersion of precious metals. Notably, this simple approach of affecting electron interaction by introducing weakly electronegative elements provides a reference for the design of noble metal catalysts with different valence states to solve complex problems.