X分子筛的热稳定性研究

STUDY ON THE THERMAL STABILITY OF X ZEOLITE

为了研究X分子筛的热稳定性,采用水热晶化法合成了纯相X分子筛,在氮气气氛中分别于500,600,700,800,900℃对X分子筛进行高温焙烧处理。采用X射线衍射、N_(2)吸附-脱附、扫描电镜、热重分析、差示扫描量热、固体核磁共振和傅里叶变换红外光谱对X分子筛及其热处理产物进行表征。结果表明,热处理温度不超过800℃时,X分子筛晶体结构和微孔孔道均没有被破坏,热处理产物仍然保持了八面体形貌,晶体结构中的Si-O-Al连接保持稳定,且没有形成非骨架铝物种。当热处理温度达到900℃时,X分子筛的晶体结构发生熔融破坏,转变为边缘圆滑的无定形物种,微孔孔体积降至0,但是热处理产物中并没有形成明显的独立无定形铝物种,而是仍然存在大量Si-O-Al和Si-O-Si连接。

In order to study the thermal stability of X zeolite,X zeolite was synthesized by using hydrothermal crystallization method,and then was calcined at 500,600,700,800 and 900℃in nitrogen atmosphere.X zeolite and its calcination products were thoroughly characterized by X-ray diffraction,N_(2) adsorption-desorption,scanning electron microscope,thermogravimetry,differential scanning calorimetry,magic angle spinning solid nuclear magnetic resonance and Fourier transform infrared spectroscopy.The results showed that when the calcination temperature was lower than 800℃,the crystalline structure and micropores of X zeolite were not destroyed,the calcination products still maintained the same octahedral morphology as the original X zeolite,the Si-O-Al connection in the crystalline structure was stable,and no non-framework aluminum species were formed.When the calcination temperature reached 900℃,the crystalline structure of X zeolite was completely destroyed after melting,leading to the formation of the amorphous species with smooth edge and the micropore volume of 0.There were still a lot of Si-O-Al and Si-O-Si connections,and no obvious independent amorphous aluminum species was observed in the calcination products.