高温下碳对SBA-15结构的影响研究

Phase Compositions and Structural Properities of C/SBA-15 under Different Annealing Temperatures

以介孔分子筛SBA-15为考察对象,蔗糖为碳源,浓硫酸为碳化剂,制备了C/SBA-15复合材料。在氩气氛下进行热处理,考察了在碳存在的情况下,热处理温度对SBA-15物相、组成和结构的影响规律。采用X射线衍射分析（XRD）、N2吸附-脱附等温线、扫描电镜（SEM）等测试手段对产物的晶相、化学组成和形貌进行分析。结果表明,经800-1200℃高温处理,SBA-15主要以无定型氧化硅存在,有序介孔孔道均有部分保持,同时,随着热处理温度升高,SBA-15孔道的有序度降低,比表面、孔容和孔径逐渐减小。当温度升高到1300℃时,碳不仅起到支撑孔道的作用,也作为反应物与氧化硅反应生成碳化硅。而没有碳支撑的SBA-15在1000℃介孔结构完全消失,在1200℃即开始生成方石英相,1300℃完全转为方石英。碳在SBA-15热处理的过程中不仅起到对介孔结构的支撑作用,且能抑制无定形二氧化硅向晶体方石英的转变。

The structures and phase as well as compositions of carbon-filled SBA-15 under different temperatures between 800 ℃ and 1300 ℃ were investigated in the present work. Sucrose and mesoporous SBA-15 were used as carbon and silica source,respectively. Concentrated sulfuric acid,as carbonizer,was added into the system as catalyst to synthesize carbon-filled SBA-15. The influence of annealing temperature on the structures of silica were studied in detail by means of X-ray diffraction（ XRD）,nitrogen adsorption-desorption and scanning electron microscope（ SEM）. Results showed that the carbon could prevent the collapse of mesopores to some extent,SBA-15 mainly existed in the amorphous state at800、1000、1200 ℃,the mesoporous channels maintained well and the regularities decreased with the increasing temperatures. The specific surface areas,pore volumes and pore diameters decreased when the annealing temperature increased from 800 ℃ to 1200 ℃. When the temperature was up to 1300 ℃,silicon carbide began to form. For SBA-15 without carbon support,mesoporous structure completely disappeared at 1000 ℃,the cristobalite phase begin to generate at 1200 ℃ and completely into the cristobalite phase when the temperature is up to 1300 ℃. Carbon not only plays the supporting role ofmesoporous structure,but also can restrain the transition of the amorphous silica to crystal cristobalite in the process of heat treatment.