Preparation Of Mesoporous Materials Supported Metal Catalysts And Their Application In Glucose Catalytic Oxidation

Ordered mesoporous materials have many applications widely in the fields of adsorption, separation, nano-materials synthesis and catalysis for their regular pore structure, uniform pore size distribution and large specific surface area. Template synthesis of mesoporous materials is an effective technique, with good controllability, and template role of space limitation or debugging can prepare inorganic mesoporous materials which are applied to catalytic oxidation or macromolecular transfer reactions. The traditional catalyst of glucose catalytic oxidation reaction used mainly palladium catalysts on activated carbon (Pd/AC), but activated carbon (AC) had complex organic functional groups and high micro-porosity, which not only had a great mass transfer resistance, induced side reactions, and the metal active component in the microporous was difficult to effectively use, reduced catalytic activity of Pd/AC. Therefore, in this paper, a series of ordered mesoporous inorganic materials were synthesized by the template method, and the nano-supported metal catalysts were prepared using these materials as the supports for glucose catalytic oxidation reaction. The influence of the support type, metal loading and reductant type on the catalytic properties was studied by activity evaluation experiments and related characterization results. The conclusions are as follows:1. Synthesis of mesoporous materials SBA-15, CMK-3 and Al₂O₃. Synthesized mesoporous SBA-15 using P123 as the template were hexagonal rods structure, long-range order and stability structure, and the average pore diameter was 6.62nm. Synthesized CMK-3 retained the basic morphology of the original template SBA-15 and the material was much ordered. The average pore size was 3.64nm. Synthesized mesoporous Al₂O₃ had good crystallinity and the emergence of the characteristic diffraction peaks aboutγ-Al₂O₃. The average pore size was 5.45nm.2. Preparation of mesoporous materials supported nano-metal catalysts. The nano-catalysts were preparated by mesoporous material as a carrier and Pd or Au as the active component. The results of characterization showed that: XRD patterns of the catalysts appeared the characteristic diffraction peaks of the metal Pd or Au, and Pd or Au were both nanoparticles. The nano-gold particles for H2 reductant in SBA-15 had a serious reunion and particle size was large. On the contrary, the distribution of nano-gold particles was uniform for KBH4 reductant, and there was a higher dispersion and Au particle size was smaller. XPS analysis showed that the state of reduced Pd and Au played an important role in the catalytic properties, and Pd3d and Au4f peaks were analyzed.3. The reaction properties of glucose catalytic oxidation over mesoporous materials supported nano-metal catalysts. The results of active evaluation showed that: Among Pd-based catalysts, the catalytic property of SBA-15 as the support was better than CMK-3 and Al2O3, and glucose conversion rate was 90.1%. For Au-based catalysts, the catalytic properties of CMK-3 and Al2O3 as the supports were better, and glucose conversion rate could reach 95%. The Au/SBA-15 catalysts were studied the reaction influence of the type and amount of reductant. The results showed that the catalyst reduced by potassium borohydride and sodium citrate had better catalytic properties and glucose conversion rate was up to 88.4%, but formaldehyde and ethylene glycol were less. The influence of the amount of KBH4 was greater for glucose conversion rate, and when molar ratio KBH4/Au was 3 the conversion rate was 87.5%, followed by sodium citrate and its highest conversion rate was 77.1%, formaldehyde and ethylene glycol had little influence and the conversion rate was poor. The addition of protective agents could effectively prevent the reunion of Au particles and improve the dispersion of Au on the support. The catalyst 2%Au/SBA-15 was studied about the catalytic reaction rate, using the catalyst of KBH4 reductant had a higher reaction rate, and after recycling 8 times, the reaction conversion rate was still 70% or so.