Application Of Carbon-based Hybrid Materials In The Benzyl Alcohol And Water Oxidation Reactions

Oxidation of alcohols to the corresponding carbonyl species plays an important role in organic synthesis.The traditional way of performing this conversion is to use stoichiometric inorganic oxidants,such as chromium or manganese reagents.However,the use of clean oxidants such as O₂ and H₂O₂ for the synthesis of fine chemicals is a more clean way.From the economic and environmental point of view,improving the atom utilization rate is advocated by chemical production.Therefore,it is imperative to study an efficient and green catalytic oxidation system in the benzyl alcohol oxidation reaction.The electrocatalytic or photoelectrocatalytic of water splitting to produce H₂provides abundant renewable fuel resources for economic sustainable development.Compared with fossil fuels,hydrogen fuels have extremely high energy density and minimal environmental hazards and have become important raw materials for the chemical industry.In the process of electrolysis of water,water oxidation plays a key role by providing the required protons and electrons.The main efficiency loss occurs when driving the water oxidation reaction,which is one of the major bottlenecks impeding the implementation of solar fuel-based global economy.Increasing the efficiency and durability of water oxidation catalysts has a direct impact on device efficiency and cost effectiveness.Therefore,in this thesis,starting from the preparation of catalysts,the active metal centers were loaded onto carbon materials by different methods for the benzyl alcohol oxidation and water oxidation reactions.The details are as follows:1.Preparation of single-site cobalt-based catalysts for selective oxidation of be nzyl alcoholCatalysts with atomically dispersed active sites are highly desirable to maximize atom efficiency.Herein,we reported atomically cobalt dispersed onto nitrogen-doped graphene?denoted as Co-NG?by heat-treating cobalt salts and graphene oxide in ammonia atmosphere.The Co-NG catalyst was characterized by multiple characterization techniques,such as XPS,XRD,Raman,TEM,SEM,HAADF-STEM and N₂ adsorption-desorption.Characterization results showed that the surface O content decreased as the doping temperature increased,while the surface N content kept increasing up to 7.94 at%at the doping temperature of 750°C.The coordination of N with Co should improve the catalytic behavior of Co-NG.The Co-NG catalyst has extremely high atom efficiency and shows high activity and excellent stability for the selective oxidation of various alcohol compounds?e.g.benzyl alcohol,4-chloro-benzyl alcohol,4-methyl-benzyl alcohol,4-methoxy-benzyl alcohol,4-hydroxy-benzyl alcohol,phenethyl alcohol,2-methyl heptanol,etc?by using oxygen molecule as the oxidant.For example,94.8%benzyl alcohol conversion and 97.5%benzaldehyde selectivity can be achieved over Co-NG after reaction for 5 h,and the catalyst yields an average TOF of over 500 h^-1.2.Preparation of Co-based catalysts derived from MOF and their catalytic pe rformance in water oxidation and o xygen reduction reactionsOxygen e volution reaction is the key reaction in electrochemical water splitting processes.Herein,we prepared a hybrid electrocatalyst consisting of cobalt oxide embedded amorphous carbon through simple pyrolysis of cobalt-based metal organic framework for water oxidation.The catalyst was characterized by various analysis techniques,such as XPS,XRD,Raman,TEM,SEM,HAADF-STEM and N2adsorption-desorption.The influence of pyrolysis temperature on the morphology and catalytic behavior of the catalytic materials was investigated.Good contact between Co/Co O_x and amorphous carbon resulted in a high catalytic efficiency.The hybrid obtained under pyrolysis temperature of 600 ^o C exhibited superior performance for oxygen evolution reaction?OER?,offering a low a stable current density of 10 mA·cm^-2 at 277 mV in base media.Besides good OER behavior,it also showed good oxygen reduction reaction?ORR?performance?onset potential:?0.87V vs RHE,diffusion-limiting current density:?4.9 mA·cm²?.This work provides a novel and efficient catalyst that greatly expands the scope of low-cost Co-based water oxidation electrocatalytic materials.