Preparation And Properties Of Supported Noble Metal Nanocatalysts Based On MOFs Derivatives

Supported noble metal nanocatalysts have been widely used in the field of catalytic reactions due to their good reactivity and chemical stability,such as reduction of nitro-compounds,selective oxidation of alcohols,selective hydrogenation of unsaturated hydrocarbons and low temperature oxidation of CO,etc.However,the catalytic performance of the catalysts is closely related to the nature of the support,so it is critical to select a suitable support to obtain excellent catalytic performance.In recent years,metal oxides derived from metal-organic frameworks?MOFs?to serve as a support have rich pore structure and high specific surface area,which is beneficial to a series of processes,including the diffusion,adsorption and activation of reactants,thus exhibiting excellent catalytic performance in the catalytic reation.In addition,catalysts with different morphologies and structures exhibit greatly different catalytic performance.In this thesis,two kinds of synthetic methods were used to prepare MOFs with different morphologies and structures,then calcined in air to obtain thermal decomposition-derived porous metal oxides,then loaded with noble metal?Pt,Au?nanoparticles and with a certain modification or structural design,thereby preparing supported noble metal nanocatalysts based on MOFs derivatives.The details are as follows:1?A disk-like Pt/CeO₂-p-TiO₂ catalysts derived from MIL-125?Ti?was prepared by several effective synthetic steps.The morphologies and structures of the catalysts were characterized by XRD,TG,BET,SEM,TEM,EDX and XPS,and its catalytic performance was evaluated by the reduction of 4-NP,which included the discussion of effect of four calcination temperatures?room temperature?300 ^oC?550 ^oC?700 ^oC?on the catalytic performance of the catalysts.The experimental results showed that the Pt/CeO₂-p-TiO₂catalysts calcined at 550 ^oC exhibited the highest catalytic activity with a rate constant of 0.9047 min^-1,and conversion of 94%was achieved after six recycling experiments,showing good reusability and stability.Finally,based on a series of characterization results and related theoretical analyses,a possible reduction reaction mechanism was proposed initially.2?Mesoporous SiO₂/Au/Co₃O₄ hollow spheres?denoted as mSiO₂/Au/Co₃O₄-HS?catalysts with core-shell structure was derived from in situ grown ZIF-67 hollow spheres,which were prepared by a one-step soft template method.The morphologies and structures of the catalysts were characterized by SEM,TEM,EDX,XPS,XRD and BET,and its catalytic performance was evaluated by liquid phase oxidation of benzyl alcohol,which included the discussion of effect of catalyst amount,oxygen flow rate,reaction temperature and reaction time on the catalytic performance of the catalysts.The experimental results showed that the optimum reaction conditions were optimized to be catalyst amount of 40 mg,oxygen flow rate of 50 mL/min,reaction temperature of 140°C and reaction time of 5 h.And benzyl alcohol conversion of 55%and benzaldehyde selectivity of 84%together with the excellent reusability and stability in five recycling experiments were obtained under optimal reaction conditions,which was attributed to the core-shell structure leading to the encapsulation of Au NPs and provision of multiple active reaction interface.Finally,based on the precursor species formed by de-protonation of substrate-benzyl alcohol,a plausible reaction mechanism for liquid phase oxidation of benzyl alcohol to benzaldehyde over mSiO₂/Au/Co₃O₄-HS catalysts was tentatively proposed to investigate the relationship between the structure and the catalytic performance.