Charge Transfer Analysis on the Direct Decomposition of Nitrous Oxide over Fe-BEA Zeolite: An Experimental and Density Functional Study

Abstract

Mulliken population analysis calculated by density functional theory (DFT) has been introduced to investigate the charge transfer (CT) during N2O direct decomposition over Fe-BEA zeolite, associated with a mechanism, involving an O2 formation, being divided into three parts and nine steps. The zeolite framework acting as a charge reservoir played an important role in the decomposition of the first N2O molecule, especially in the adsorption and activation processes (Part 1). However, during the decomposition of the second N2O molecule (Part 2), the roles of active center Fe and α-O became crucial. The high reactivity of α-O was also verified through CT analysis. In both of these two parts, N2O acted as a charge donor with its O end adsorbed on the Fe-BEA zeolite simultaneously with the terminal N and atomic O as the main charge donors. During the decomposition steps of these two parts, the middle N of N2O acting as the main charge acceptor accepted a large amount of charges from the charge donors, which contributed to the bond fracture of O–N2 and N2 formation. The electronic properties of N atoms in the first N2O were found to be the same as those of the corresponding N atoms in the second N2O. In the last part (Part 3), atomic O of Fe–O2–Z acting as the charge donors mainly donated charges to the active center Fe, which induced the formation of O2 and regeneration of Fe–Z, completing the whole catalytic cycle. Additionally, the frontier molecular orbital (FMO) analysis calculated by DFT and the experimental method of diffuse reflectance infrared Fourier transform spectra (DRIFTS) were also employed to investigate the CT, with the results consistent with those obtained through Mulliken population analysis.