Insights into the roles of Al in improving the H2-SCR performance of Pt/ZrTiO2 catalyst

Abstract

Thermally induced nitrogen oxides (NO_x) in Hydrogen Internal Combustion Engine (H₂-ICE) are inevitable. Selective catalytic reduction of NO_x by H₂ (H₂-SCR) is a prospective technology for eliminating NO_x in H₂-ICE, thanks to the availability of H₂ in exhaust. Herein, we report an Al-modified Pt/ZrTiO₂ catalyst that significantly enhances the H₂-SCR activity of Pt/ZrTiO₂ (Pt/ZT) at low-temperature and its stability. With part of Al incorporates the lattice of ZT to generate more Lewis acid sites and oxygen defects that facilitate the activation of NO_x to nitrate species (NO_x⁻), and the rest of Al exists in the form of isolated Al₂O₃ that inhibits the agglomeration of ZT particles after thermal treatment. Ultimately, the optimal H₂-SCR activity and stability is achieved on Pt/ZT catalyst with 30 % Al addition (Pt/ZTA₃). In situ diffuse reflectance infrared Fourier transform spectroscopy (In situ DRIFTs) demonstrates that monodentate nitrate species are critical intermediate for H₂-SCR reaction at low temperatures, whereas bridged nitrate species are the ones with higher H₂ reactivity in the mid-temperatures. This study provides a feasible strategy to develop a stable H₂-SCR catalyst that operates in a wide window at low temperatures.