Single-Atom Ni Catalysts Enable a Cl-Shift Pathway for Low-Temperature Chlorobenzene Decomposition

In municipal solid waste incineration, flue gas temperatures in the air pollution control (APC) segment typically range from 120 to 180 °C, making low-temperature catalytic decomposition of chlorobenzenes (CBzs) crucial for emission control. Despite their widespread use, the decomposition mechanisms of transition metal catalysts under these conditions remain unclear. Here, using a Ni single-atom catalyst (Ni@rGO) as a model system, we reveal that CBz degradation at 150 °C proceeds predominantly via hydrodechlorination, accompanied by an extensive Cl-shift process in the CBz skeleton. This rearrangement optimizes adsorption geometry at the active sites, increases surface coverage, and stabilizes adsorption without disrupting the aromatic ring. Density functional theory (DFT) calculations show that the Cl-shift originates from the unique η²-C coordination between Ni and CBzs, with a directional preference for chlorine-substituted carbon atoms. The Ni-CBz complexes undergo continuous coordination-isomerization cycles, reducing C-Cl bond energy, alleviating steric hindrance, and thereby accelerating low-temperature decomposition. Leveraging these synergistic effects, Ni@rGO achieves a CBz decomposition efficiency of 98.6% at 150 °C with ultralow Ni loading. To our knowledge, this represents the first report of a Ni single-atom-driven Cl-shift mechanism in halogenated aromatic degradation.