Rational Design And Catalytic Mechanism Studies For Metal-Oxide Hybrid Nanocatalysts

Heterogeneous catalysis plays a central role in many fields,including energy,environment,and chemical production.Among various heterogeneous catalysts,the hybrid nanocatalysts composed of metal and metal oxide have attracted tremendous attention owing to their unique performance.In detail,the complex interactions between metal and oxide components offer a variety of possibilities for the performance regulation of the hybrid nanocatalysts.Especially in photocatalysis,when the metal component owns obvious plasmon properties,the metal plasmon-induced strong light-matter interactions provide a new strategy for further optimizing the catalytic activities and selectivities.Despite the broad prospect,the complex interactions between metal and oxide have also limited the deep understanding of the reaction mechanisms and structure-performance relationships.In this sense,it is essential to rationally design metal-oxide hybrid nanocatalysts,no matter for deeper mechanistic insight or better performance.In this dissertation,we aim to clarify some critical scientific problems related to catalysts and catalytic reactions by rationally designing and precisely integrating metal-oxide hybrid nanocatalysts.Specifically,by combining the well-designed catalyst structures and advanced characterization techniques,we strive to unveil the catalytic mechanisms and related structure-performance relationships from the molecular/atomic level.Moreover,we intend to obtain a deeper understanding of the metal-oxide interactions and their potential impacts on catalytic processes.The results of this dissertation provide valuable references for the rational design,precise integration,and in-depth mechanistic investigation of high-performance metal-oxide hybrid nanocatalysts.The main results are summarized as follows:1.We design a ZnO supported AuPd core-shell structure to introducing Pd into the ZnO-Au interface,with the aims of tuning the selectivity for photocatalytic methane conversion toward high-value-added unsaturated hydrocarbons(i.e.,ethylene).In the ZnO-AuPd hybrid,Au nanorods are chosen as the plasmonic metal nanostructures to provide the local electric field for promoting the generation of active Zn+-O-pairs on ZnO,while Pd is selected as the modifier to modulate the dehydrogenation capability of the hybrid catalyst for potentially controlling the CH4 conversion pathway and C2H4 selectivity.On the basis of various in situ characterizations,it is revealed that the Pd-induced dehydrogenation capabi lity of the catalyst turns on an alkoxy intermediates-mediated direct photocatalytic methane-to-ethylene conversion pathway.During the reaction,methane molecules are first dissociated into methoxy on the surface of ZnO under the assistance of Pd.Then these methoxy intermediates are further dehydrogenated and coupled with methyl radical into ethoxy,which can be subsequently converted into ethylene through dehydrogenation.This work provides fresh insight into the methane conversion pathway under mild conditions and highlights the significance of dehydrogenation for enhanced photocatalytic activity and unsaturated hydrocarbon product selectivity.2.To further shed light on the energy coupling pathway between Au plasmon and catalytic-active sites and its potential impacts on catalytic performance,we design a Ru-decorated Au@CeO2 catalyst to integrating CeO2-Ru sites onto the Au surface.In the Au@CeO2-Ru hybrid,the CeO2-Ru is chosen as the active site for CO2 hydrogenation,while Au serves as the plasmonic antenna to harvest light energy and drive the surface reaction on CeO2-Ru.Based on this structure design,it is revealed that the Au plasmon can boost CO2 hydrogenation by a combined photothermal and nonthermal effect.The photothermal effect enables Au a nanoheater,providing local high temperatures for the surface reaction on CeO2-Ru.Furthermore,the Au plasmon-induced local electric field can promote the dissociation of H2 on Ru and the subsequent spillover process of H atoms from Ru to CeO2,leading to enhanced CO2-to-CH4 conversion activity and selectivity.This work offers valuable insight into the role of plasmonic nonthermal effect in catalysis and provides a reference for the rational design of highly active and selective plasmonic nanocatalysts.3.Based on the understanding of the importance of metal-oxide interface to catalytic performance,we further unravel the role of the oxide distant from the interface(remote oxide)in catalysis.To this end,we design an Au/oxide core-shell structure with porous oxide shell(viz.offering exposed interface)and controllable shell thickness(viz.adjustable oxide content).In such a structure,the Au is covered by the oxide to form a unique inverse catalyst,which is beneficial for determining the direct contribution of remote oxide to catalysis.It turns out that the remote oxide can make a major contribution in selective alcohol oxidation by working in tandem with Au/oxide interface.In detail,the Au/oxide interface can catalyze alcohol oxidation to produce aldehyde and H2O2 in the presence of O2.Then the accumulated H2O2 byproduct can be further activated on the remote oxide to generate hydroxyl radicals,initiating an additional alcohol oxidation pathway.Impressively,our investigation indicates that the additional pathway can contribute up to 40.8%of the produced aldehyde.This work offers valuable insight into the previously overlooked role of oxide and calls for simultaneous surface and interface structure optimization for designing advanced metal/oxide catalysts.