Investigation of Potential Catalytic Active Sites of Pd/SSZ-13: A DFT Perspective

Abstract

In this theoretical work, potential active sites on Pd/SSZ-13 were identified and investigated for the application of methane oxidation using density functional theory. Unique zeolite structures were automatically generated, and their ground state energies were used to find stable structures to serve as frameworks for various PdxOy active sites. “Single” and “bridged” PdOx active site structures were evaluated on the basis of their stability and thermodynamic capability to dissociatively adsorb methane. Results indicate that less stable active site structures tend to yield more favorable methane adsorption energies. A Langmuir adsorption model used to predict active site coverages found that single PdOx sites are unlikely to form at temperatures above 200 °C while bridged active sites maintain significant coverage (>30%) up to 300 °C. Temperatures above 300 °C will predominantly result in vacant ZPd2+ sites (not including Pd/PdO nanoparticles). Bridged active sites show more promising methane activity based on better stability coupled with more thermodynamically favorable methane adsorption compared to single site PdOx species.