Amino-acid modulated hierarchical In/H-Beta zeolites for selective catalytic reduction of NO with CH4 in the presence of H2O and SO2.

Abstract

Selective catalytic reduction of NO with CH4 (CH4-SCR) has been studied over a series of amino-acid mediated hierarchical beta zeolites with indium exchange. Amino acid mesoporogens greatly affect the NO reduction (DeNOx) efficiency of In/H-Beta catalysts. Mesoporous In/H-Beta-P synthesized using proline exhibits the highest NOx removal efficiency of 40% in excess oxygen and poisonous SO2 and H2O, 10% higher than our previously optimized In/H-Beta catalyst using commercial beta zeolites with a similar Si/Al ratio. Analyses using XRD, N2 adsorption-desorption, EPR, SEM, TEM, EDX, ICP, 27Al and 29Si MAS NMR, XPS, H2-TPR, NH3-TPD, and Py-IR reveal that amino acids promote beta crystallization, modulate zeolite acid sites and surface oxygen species, and generate hierarchical pore architectures without affecting the Si/Al ratio, indium content, and percentage of the active InO+ species. The mosaic-structured In/H-Beta-P exhibits the strongest Brønsted acidity and surface labile oxygen which enhance the oxyindium interaction with the zeolite framework, promoting CH4-SCR activity. The strong acidity, surface active oxygen species, and mesopores lead to excellent stability of the In/H-Beta-P catalyst in the presence of SO2 and H2O, withstanding several catalytic DeNOx cycles under harsh reaction conditions.