A General Method For The Synthesis Of Porous Tetravalent Metal Oxide Nanomaterials And Their Structures’ Study

Tetravalent oxide nanomaterials as a kind of important inorganic functional materials are widely used as catalysts or catalyst supports (photocatalytic, hydrogenation, oxidation, etc.) due to their unique physical and chemical properties, especially with a reducible of oxide nanomaterials such as zirconium dioxide (ZrO2), ceria (CeO2), titania (TiO2) and so on.However, these metal oxides are generally still prepared conventional method such as sol-gel method and/or co-precipitation method, which often suffers drawbacks such as low thermal and mechanical instability, poorly crystalline, broad particle size distributions, low surface area, and restriction on scale-up synthesis. In order to overcome the shortcomings of these traditional preparation methods and technologies, it is highly necessary to make or create a new preparation method to synthesize propus metal oxides with consistent structure, high specific surface area, developed pore structure, special crystal orientations and surface defects, which can ensure its greatest play in the actual catalytic reactions and develop their potential value.We present a new method of hydrothermal synthesis of dynamic controlled. It is a direct one-step method to synthesis of required tetravalent metal oxide using sodium borohydride (NaBH4) as a precipitating agent firstly without any surfactant or template and does not need high-temperature calcination. We confirmed the feasibility and universality of the new method and the new method is explained by the kinetically controlled synthesis mechanism, and finally its performance was also studied.1. We use the proposed of kinetically controlled hydrothermal method and NaBH4 as the precipitating agent to synthesize tetragonal ZrO2 metal oxide of which specific surface area is up to 274.8 m2 g-1. In order to investigate its stability, we calcined ZrO2 at 200℃,400℃ and 600℃ respectively. We found the prepared Z1O2 with high surface area, good stability and developed pore structure by XRD, TEM, BET and so on, which demonstrated the feasibility of the new approach. Meanwhile, in order to explore the mechanism of hydrothermal synthesis method of thermodynamic controlled, we also investigated the effect of precipitant concentration, reaction temperature, kind of precipitating agent on the morphology, crystal phase and texture properties of prepared-ZrO2. We found that NaBH4 not only acts as a precipitating agent, but also prdvides a continuous disturbance of the environment for this reaction. High surface energy of initially formed ZrO2 nuclei and kinetic disturbance generated from the H2 bubbles are believed to be the driving forces for the growth and assembly of ZrrO2 particles and directly affects the morphology, the crystalline phase and texture performance of ZrO2. In other words, when the colloid mill slit width and speed is constant, the morphology, crystal phase and texture properties of ZrO2 can be controlled by the concentration of NaBH4. However, our purpose is to to find a new facile scale-up method for the synthesis of Micro/meso-porous morphology-controlled tetravalent metal oxide nano materials. In the basis of feasibility, we need to prove the universality. After that, we take advantage of this new method to synthesize CeO2 (291.2 m2 g-1 specific surface area) and TiO2 (186.1 m2 g-1 specific surface area) successfully, of which specific surface area are much higher than the conventional method preparation. Although other tetravalent metal oxide preparations are ongoing, the universality of this approach has been preliminarily verified.2. This method is not only suitable for preparation of single metal oxide, but also for preparation of multiple metal and metal oxide. The new ZrO2-Ni(OH)2 composite oxide with high specific surface area of 263.5 m2 g-1 was synthesized by hydrothermal method of dynamic controlled. And we prepared the Au/ZrO2-Ni(OH)2 catalyst by NaBH4 direct reduction method and it was applied to the catalytic oxidation of benzyl alcohol. The catalytic activity was significantly higher than that of Au/ZrO2. Through the analysis of TPD and XPS spectra, synergistic effect was found between the doped Ni(OH)2 and ZrO2 which enhanced the basic sites on the catalyst surface.The stronger basic sites, the more favorable oxidation of benzaldehyde, and thus improving catalytic activity.