Boosting toluene oxidation by the regulation of Pd species on UiO-66: Synergistic effect of Pd species

Abstract

Supported single-atoms and sub-nanometre clusters have exhibited superb catalytic performance toward many reactions. However, inactivation of single-atom or cluster catalysts in complex reactive conditions poses major challenge for their practical application. Herein, we demonstrate that the prepared Pd-UiO-66 with ultra-low Pd loading (0.05 wt%) contains three robust active Pd species, (isolated Pd atom (Pd1), sub-nanometre Pd clusters (Pdc) and Pd nanoparticles (Pdn)) and presents superb activity for toluene oxidation and water resistance (10.0 vol%). Experiments and theoretical calculations firstly confirm that consecutive H2-O2 and reaction gas treatment (1000 ppm toluene in 20 vol.%O2/Ar) induce residual N species from solvent N, N-dimethylformamide to enter UiO-66 skeleton forming Pd1-N1 structures. DFT calculations reveal that the synergistic effect of Pd species (namely, the enhanced activation of O2 and H2O by Pd1 and the improved adsorption of toluene by Pdc and Pdn) is the main factor for the excellent activity of Pd-U-H-O-reused catalyst.