Transformation of Bulk Pd to Pd Cations in Small-Pore CHA Zeolites Facilitated by NO

Atomic dispersion of metal species has attracted attention as a unique phenomenon that affects adsorption properties and catalytic activities and that can be used to design so-called single atom materials. In this work, we describe atomic dispersion of bulk Pd into small pores of CHA zeolites. Under 4% NO flow at 600 degrees C, bulk Pd metal on the outside of CHA zeolites effectively disperses, affording Pd2+ cations on Al sites with concomitant formation of N2O, as revealed by microscopic and spectroscopic characterizations combined with mass spectroscopy. In the present method, even commercially available submicrosized Pd black can be used as a Pd source, and importantly, 4.1 wt % of atomic Pd2+ cations, which is the highest loading amount reported so far, can be introduced into CHA zeolites. The structural evolution of bulk Pd metal is also investigated by in situ X-ray absorption spectroscopy (XAS) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), as well as ab initio thermodynamic analysis using density functional theory (DFT) calculations.

Automated summary

This study describes the atomic dispersion of Pd metal into small pores of CHA zeolites, achieving the introduction of Pd2+ cations into the zeolites. The research utilized various characterization techniques to investigate the structural evolution of Pd metal and successfully achieved the highest loading amount of atomic Pd2+ cations into CHA zeolites reported thus far.