Sub-Nano Copper Sites on SiO<sub>2</sub> with Downshifted <i>d</i>-Band Centers Dominate Non-Radical Selective Oxidation of Benzene to Phenol.
basic_science · Level V
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- Record sourced from PubMed, PMID 40558066.
- Also identified by DOI 10.1021/acs.nanolett.5c02838.
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Abstract
The identification of dominant reactive oxygen species (ROS) in the direct oxidation of benzene with H<sub>2</sub>O<sub>2</sub> holds crucial significance for understanding catalytic mechanisms and guiding catalyst design. Herein, we developed a sub-nanoscale Cu cluster supported on SiO<sub>2</sub> (Cu<sub><i>n</i></sub>/SiO<sub>2</sub>) catalyst, which achieved comparable benzene conversion to its nanoparticle counterpart (46.6% vs 55.4%) while exhibiting significantly enhanced phenol selectivity (96.8% vs 88.1%). Systematic studies reveal distinct reaction pathways between the two catalytic systems. In the Cu<sub><i>n</i></sub>/SiO<sub>2</sub>-catalyzed system, benzene oxidation predominantly proceeds through a nonradical pathway mediated by Cu=O* species, while the nanoparticle Cu<sub>p</sub>/SiO<sub>2</sub> catalyst follows a free radical mechanism dominated by <sup>•</sup>OH radicals. Density functional theory (DFT) calculations elucidate the sub-nanoscale Cu<sub><i>n</i></sub> sites in Cu<sub><i>n</i></sub>/SiO<sub>2</sub> exhibit a downshifted <i>d</i>-band center relative to CuO nanoparticles in Cu<sub>p</sub>/SiO<sub>2</sub>, which weakens substrate adsorption strength and redirects H<sub>2</sub>O<sub>2</sub> dissociation pathways. The fundamental insights gained from this comparative study elucidate structure-activity relationships in copper-based catalytic systems.