Controllable Synthesis Of Three Dimensional Mesoporous Mixed Metal Oxides And Bimetallic Nanopartical With Applications

Mesoporous mixed metal oxides (MMMOs), with well-defined organization on the 2-50 nm size scale, have attracted much attention because of their high surface areas, controllable pore sizes, tunable wall compositions and structures, making them potential in advancing vital disciplines such as catalysis, energy conversion and biotechnology. However, most of the MMMOs have pore sizes smaller than 16 nm, which seriously limited their wide applications in many industrial catalytic reactions. It is generally accepted that the catalytic performances of MMMOs-based catalysts are strongly related to the mesoporous networks, which directly determine the mass transfer efficiency during the reaction process.Metal nanoparticles spread on the surface of porous carriers or supports play important role in the industrial catalytic reactions. Additionally, it is already known that bimetallic catalysts usually exhibit significantly enhanced catalytic activity or selectivity compared with the monometallic ones, which is due to the synergistic effects between the two metals. Conventionally, the bimetallic nanocatalysts are synthesized in aqueous solution, which easily aggregate during reactions under high temperature, leading to the significant lost of catalytic activity. Therefore, it is challengeable to develop stable bimetallic nanoparticles avoiding aggregation. Furthermore, it is expected that the obtained stable bimetallic nanocatalysts would exhibit outstanding catalytic performances in the catalytic reactions.This thesis focuses on the development of mesoporous metal oxides and stable bimetallic nanocatalysts. Six chapters are included:Chapter 1 summaries historical background, recent progress and the outlook of my research work. Chapter 2 introduces the main chemicals and equipments used in the experiment, as well as the characterization and catalytic conditions. Chapter 3 is about the general synthetic strategy for ordered extra-large mesoporous mixed metal oxides via uniform sol-gel coating and its catalytic applications. Chapter 4 introduces the solid phase metallurgy strategy to sub-5 nm Au-Pd and Ni-Pd bimetallic nanoparticles with controlled redox properties. Chapter 5 is about the controllable synthesis of Au-Ni composites with different AuNPs initial particle size and its performance in the selective oxidation of benzyl alcohol. The last chapter is the summary and outlook. The conclusions of this thesis are shown in the following.We present a simple and general method for the synthesis of MMMOs with extra-large three-dimensional mesoporous structures, which is based on uniform coating of non-silicate oxide nanoparticles precursors onto the surface of mesoporous silica EP-FDU-12. The successful uniform coating of MOs in the AcHE sol-gel system allows us to synthesize a large variety of EP-MMMOs. The coating thickness can be easily controlled by changing the initial concentration ratio of raw materials.The catalytic performance of the added acid sites in EP-Al2O3 is confirmed by the fact that they can catalyze F-C reaction which is proceeded on strong or moderate Bronsted acid sites. The greatly enhanced activity of EP-Al2O3 is credited not only to the added acid sites but also to the adsorption and mass diffusion of reactants. Moreover, as the support, Pd/EP-Al2O3 also performs a higher activity than others.We report a solid metallurgy process to prepare BMNPs with a tight sub-5 nm particle size distribution. Highly ordered, extra-large mesoporous silica has proven to be an effective support to limit uncontrolled particle growth during the process.One positive feature of the Au-Pd BMNPs is that their redox properties can be tuned by varying the composition, which results in an optimized activity in n-hexane oxidation. O2-TPO suggests that the anti-oxidation property of the Pd composition (from 260℃ to 330℃) in Au-Pd BMNPs has been greatly improved by the alloying.By varying the initial particle size of AuNPs, we synthesize Au-Ni bimetallic composites with different structures. And in the selective oxidation of benzyl alcohol, the activity is dissimilar from each other. This work is still in progress.