Crystal plane effect of copper with different oxides/hydroxides nano-composites on catalytic performance and mechanism towards the reduction of 4-nitrophenol

Here, four copper oxide/hydroxide composites Cu/CuO, Cu-Cu2O/Fe2O3, Cu-CuO/Co(OH)2, and Co(OH)2/CuO with CuO(111) or Cu(111) as the central exposed crystal plane were synthesized and used in the catalytic reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). A study of the dynamic changes of reaction was carried out by real-time HPLC-Q-Orbitrap-HRMS/MS, HPLC, UV–Vis detection, and DFT simulation. It revealed that in copper based catalytic reduction of 4-NP, three different reaction mechanisms are generated over four catalysts. The different adsorption modes and higher adsorption strength of 4-NP on the CuO(111) and Cu(111) plane make it selective and active for both direct hydrogenation and condensation in the reduction of 4-NP. The synergistic effect of different metal crystal faces with CuO(111) can improve the catalytic activity, especially the CuO(111)/Co(OH)(011) crystal planes that have the best synergistic effect on the reduction of 4-NP. This work reports an example where the reaction mechanism was significantly affected by the principal exposed crystal planes of copper oxide/hydroxide composites. It can be very informative for understanding the catalytic processes and providing new ideas for the design of novel catalysts.