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

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 (Pd 1 ), sub-nanometre Pd clusters (Pd c ) and Pd nanoparticles (Pd n )) and presents superb activity for toluene oxidation and water resistance (10.0 vol%). Experiments and theoretical calculations firstly confirm that consecutive H 2 -O 2 and reaction gas treatment (1000 ppm toluene in 20 vol.%O 2 /Ar) induce residual N species from solvent N, N-dimethylformamide to enter UiO-66 skeleton forming Pd 1 -N 1 structures. DFT calculations reveal that the synergistic effect of Pd species (namely, the enhanced activation of O 2 and H 2 O by Pd 1 and the improved adsorption of toluene by Pd c and Pd n ) is the main factor for the excellent activity of Pd-U-H-O-reused catalyst.