Synthesis Of Nanosheet Array-like Hybrid-supported Palladium Nanoclusters And Their Reduction Performance For 4-NP

The selective reduction of 4-nitrophenol to 4-aminophenol is of highly environmental and industrial significance.Pd-supported nanocatalysts exhibit superior activity for the 4-NP reduction due to the good capability of hydrogen activation.However,the obtained catalysts by traditional impregnation-reduction methods commonly result in large particle size of Pd nanoparticles,and the studies on the effect of morphologies of the supports on size and dispersion of Pd nanoparticles are limited.Therefore,a new strategy is proposed to prepare a series of novel hierarchical LDH/rGO hybrids supported Pd nanoclussters（NCs）catalysts by using atomically precise Pd NCs（<2 nm）as precursor in the present thesis,and the 4-NP reduction activity and structure-activity relationgship of the prepared catalysts are systematically studied.The thesis focuses on:（1）Atomically precise and water-soluble captopril-capped Pd NCs(Pd₁₇Capt₈ NCs:1.3±0.5 nm),prepared by a chemical reduction method,were supported on hybrid Co₃Al-LDH/rGO（LDH:layered double hydroxide,rGO:reduced graphene oxide）via a p H-adjusted electrostatic adsorption strategy followed proper calcinations giving a series of x-Pd NCs/CoAl（O）/rGO-T catalysts（x（Pd loading）=0.09,0.17,0.43 wt%,T=230,250,280,300,320℃）.The characterization results show that the Pd NCs with the size from～1.3 to 1.8nm are highly distributed at the edge sites of the CoAl（O）nanosheets in as-obtained catalysts with hierarchical nanosheet array-like morphology.The catalysts exhibit superior performance for the reduction of 4-NP,particularly the 0.17-Pd NCs/CoAl（O）/rGO-300 possesses the highest TOF（turnover frequency）of 30042 h^-1,which can be attributed to the ultrafine Pd NCs with clean surface,the strongest Pd NCs-Co²⁺-OH（LDH）-rGO three-phase synergistic effect and enhanced adsorption for substrate viaπ-πstacking upon unique nanosheet array-like morphology.Meanwhile,the catalyst exhibits excellent substrate applicability and reusability.（2）A series of ternary Co₃Ce_yAl_1-y-LDH/rGO hybrid supported Pd NCs catalysts 0.18-Pd NCs/Co₃Al_1-yCe_y-LDO/rGO-300（y=0.05,0.1,0.2）were prepared,which show enhanced catalytic activity for the reduction of 4-NP compared with 0.17-Pd NCs/CoAl（O）/rGO-300,and the TOF value of the optimal 0.18-Pd NCs/Co₃Ce_yAl_1-y-LDO/rGO-300 is 85122 h^-1.The enhanced catalytic activity can be attributed to the promotion effects of more abundant oxygen vacancy and Ce³⁺/Ce⁴⁺and Co²⁺/Co³⁺redox pairs.