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

Thermally induced nitrogen oxides (NOx) in Hydrogen Internal Combustion Engine (H2-ICE) are inevitable. Selective catalytic reduction of NOx by H2 (H2-SCR) is a prospective technology for eliminating NOx 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 NOx to nitrate species (NOx-), 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.