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 Pd x O y active sites. “Single” and “bridged” PdO x 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 PdO x 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 PdO x species.

Recent Advances in Complete Methane Oxidation using Zeolite‐Supported Metal Nanoparticle Catalysts

“…For zeolite-supported methane oxidation catalysts, metal nanoparticles are significantly more active than single-metal sites. [18,37,73,84,98] Friberg et al explained this by the more facile reduction and reoxidation of metallic nanoparticles over ionexchanged single metal sites. [18] For methane oxidation, Pdbased catalysts follow a Mars-van Krevelen mechanism, in which the active phase is PdO.…”

“…For zeolite‐supported methane oxidation catalysts, metal nanoparticles are significantly more active than single‐metal sites [18,37,73,84,98] . Friberg et al.…”

Feasibility of Methane Oxidation on SSZ-13 Bridged Pd2Ox Sites: A Theoretical Study

“…Methane activation is examined in depth for both |PdO 2 Pd| and |PdOPd|. The free-energy path of methane activation which includes the relative free energies of the initial states (IS) (|PdOPd| and |PdO 2 Pd|), transition states (TS), and final states (FS) (CH 3 |PdOPd|H and |PdO 2 Pd|CH 3 –H) has been previously reported …”

How a quantum computer could accurately solve a hydrogen-air combustion model

“…The chemical reactions in eqn (1a)-(4f) can be used to derive a rst-order ordinary differential equation (ODE) model f ¼ dq dt that relates the change in each species mass fraction (q i ) with the reaction rates (k i ). [28][29][30] All of the species mass fractions can be denoted with a vector q. Previously, a linear approximation of ordinary differential equations employed additional model constraints to remove nonlinearity.…”