One stone four birds: The redox and acid-basic site integral regulation by La in Cu-SAPO-34 for boosting NO reduction

Metal-exchanged CHA-type zeolites, such as SAPO-34 and SSZ-13, are promising catalysts for the NH 3 -selective catalytic reduction (SCR) of NO x . Rare earth modification is a viable method for denitrification performance and stabilization of zeolite framework, a comparative study was conducted to evaluate the NH 3 -SCR activity of Cu-SAPO-34 catalysts before and after modulation with lanthanum (La). Notably, the CuLa 0.05 -SAPO-34 catalyst exhibited over 90 % NO x conversion across a wide temperature range of 160–504 °C. However, Cu-SAPO-34 exhibited a narrower active temperature range, despite having a slightly higher total acid content. Both catalysts contained isolated copper (II) ion (Cu 2 + ) species, but La incorporation led to an increase in the Cu ion and a reduction in the Cu–O bond from 1.53 to 1.51 Å. The addition of La resulted in a slight electron depletion in the Cu species and the aluminum (Al) sites coordinated to La through oxygen bridges at 0.06 |e| and 0.05 |e|, respectively. This electron redistribution enhanced the redox ability of Cu and contributed to the stabilization of the zeolite framework. Furthermore, the inclusion of La introduced additional gas adsorption sites. The de NO x reaction pathway on the CuLa-SAPO-34 surface was elucidated using a combination of density functional theory DFT calculations and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) techniques. The result indicated that the La addition induced a “fast SCR” reaction, which potentially enhanced the performance of de NO x reaction kinetics. The work offered a promising “one stone four birds” approach for enhancing NO x reduction, i.e. , providing additional adsorption sites by La in Cu-CHA alongside the stabilization of the zeolite structure, and the integral regulation of redox properties and acid sites.