Improved low-temperature CO oxidation using heterogeneous nanofibrous structures decorated with Pd atoms and nanocrystals

Abstract

Amorphous alumina shaped as nanofibers forming a non-woven network, functioning as a heterogeneous dispersion for palladium (Pd) atoms and nanocrystals, is unique yet unstudied for low-temperature CO oxidation. This work demonstrates that nanometric-size alumina fibers (ANFs) with a surface area of ⁓230 m2/g can host Pd species that remain nearly intact after CO oxidation. The ANFs contain various Pd (Pd-ANFs) loadings, ranging from 1 %wt. (Pd1-ANFs), 3 %wt. (Pd3-ANFs), to 5 %wt. (Pd5-ANFs). Among them, Pd3-ANFs show the highest CO chemisorption. Hence, the chemical environment of the Pd3-ANFs is assessed using NAP-XPS under various CO and O2 mixtures. NAP-XPS shows the presence of metallic and oxidized Pd species. The results are correlated with DRIFT spectroscopy, which unveils the CO species adsorbed over Pd. Furthermore, a computational-based kinetic model for CO oxidation shows that Pd single atoms start the CO-oxidation, followed by larger Pd crystals during light-off. Our results demonstrate that the Pd-ANFs have higher activity when compared with the Pd alumina nanoparticles (Pd-ANP) counterpart that lacks a fibrous structure, highlighting the benefits of the ANF´s structural network in stabilizing atomic and nanometric scale metal catalysts for low-temperature CO oxidation.