Designing a Bifunctional Pt/Cu-SSZ-13 Catalyst for Ammonia-Selective Catalytic Oxidation with Superior Selectivity

Abstract

Ammonia-selective catalytic oxidation (NH3-SCO) is an effective technology to solve the problem of ammonia leakage from diesel vehicles, while ammonia oxidation catalysts (AOC) still suffer from insufficient low-temperature activity and poor nitrogen selectivity. Herein, we prepared a bifunctional Pt/Cu-SSZ-13 catalyst containing an SCO component (Pt) and a selective catalytic reduction (SCR) component (Cu). This bifunctional catalyst exhibited excellent catalytic performance during NH3 oxidation under practical conditions containing water vapor, achieving >85% N2 selectivity over the whole temperature range. Catalysts were systematically characterized by Brunauer–Emmett–Teller, X-ray diffraction, inductively coupled plasma optical emission spectrometry, X-ray photoelectron spectroscopy, H2 temperature-programmed reduction, NH3 temperature-programmed desorption, high-angle annular dark-field scanning transmission electron microscopy, and X-ray absorption fine structure analysis. The results showed that metallic Pt nanoparticles were mainly present on the exterior surface of the Pt/Cu-SSZ-13 zeolite catalyst, while dispersed Cu2+ cations were present in the interior of the zeolite. Based on operando diffuse reflectance infrared Fourier transform spectroscopy with mass spectrometry experiments, it was confirmed that on Pt/SSZ-13, over-oxidation of NH3 produced large amounts of N2O and NOx at low and high temperatures, respectively, resulting in a poor N2 selectivity. With Cu present, in contrast, the byproduct (NO) would further react with adsorbed NH3 on Cu Lewis acid sites to produce N2 by a tandem SCR reaction, thus contributing to the superior N2 selectivity of the Pt/Cu-SSZ-13 bifunctional catalyst.