Herein, we report the function of Pd species in the Pd-added La0.7Sr0.3CoO3 perovskite for removal of NOx (NO+NO2) in the lean-burn NOx traps (LNT) process. The addition of Pd significantly improves the De-NOx activity of the perovskite-based catalysts. The Pd-supported catalyst has an excellent NOx removal efficiency of 90.4%, which is higher than the Pd-doped catalyst (74.4%) and pure La0.7Sr0.3CoO3 (51.6%). Our results show that the addition of Pd species enhances both the NOx desorption behaviors to regenerate the NOx storage sites and NOx reduction ability of the catalysts in the fuel-rich period, which induces the improved NOx trapping performance in the followed lean-burn period. These achievements result in the enhanced De-NOx activity of the Pd-added catalyst in the alternative NOx storage and reduction operations. Compared with the Pd-doped catalyst, the Pd-supported catalyst possesses the higher utilization efficiency of the Pd, thus exhibiting a higher catalytic activity.
Xiaodong Zhang,Fukun Bi,Zhenyuan Zhao,Yang Yang,Yintao Li,Liang Song,Ning Liu,Jingcheng Xu,Lifeng Cui
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.
Semi-hydrogenation of acetylene is one of the most promising methods to eliminate acetylene from ethylene / acetylene mixtures to avoid Ziegler−Natta polymerization catalysts being poisoned. Given that acetylene is always over-hydrogenated on conventional palladium-based catalyst, it is of great importance to facilitate the desorption of ethylene to enhance the ethylene selectivity. Herein, we report a simple method to anchor Pd by unsaturated penta-coordinated aluminum (Al 3+ penta ) on Al 2 O 3 (meso-Al 2 O 3 ). Characterized by 27 Al-NMR, XRD, HR-TEM, CO chemisorption and XPS, Pd/meso-Al 2 O 3 catalyst had a highly dispersion and unique electronic property of Pd, thus exhibiting a high ethylene selectivity (~83%) while the acetylene conversion is > 99%. Besides, the agglomeration of Pd is suppressed by the metal-support interaction (MSI) between Pd and meso-Al 2 O 3 support. Therefore, the preparation method of the catalyst is relatively simple and has certain commercial application prospects.
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