采用离子交换法,分别在微波加热和常规加热的条件下,制备了La/β分子筛催化剂,并采用红外光谱、扫描电子显微镜、X射线衍射与能量色散谱进行了表征.考察了不同加热条件下所得的改性β分子筛上La的负载量,La在分子筛表面的分散度以及催化剂对乙醇-水-异丁烯体系水合醚化复合反应的催化性能,并分析了反应机理.与传统加热法相比,微波加热法制得的催化剂上La离子的一次交换度和负载量高,且交换时间大大缩短.La离子的引入使得β分子筛上乙醇与水的转化率提高了10%~20%,而且随着La负载量的增加,催化剂的活性呈明显的上升趋势.反应机理的分析表明,上述水合醚化反应主要发生在β分子筛的表面上,B酸位桥接Al-OH-Si酸性点可能是主要的反应活性点,并且反应过程经历碳正离子中间体的形成步骤.
The La/β molecular sieve catalyst was prepared by the ion-exchange method using microwave heating and conventional heating. The catalyst was characterized by infrared spectroscopy, scanning electron microscopy, X-ray diffraction, and energy dispersive spectroscopy. Hydration and etherification reactions of isobutylene with an ethanol-water mixture to produce a fuel mixture were carried out over these catalysts. The effects of the preparation method and La loading on the catalytic performance of La/β catalysts were studied, and the reaction mechanism was proposed. The results indicated that the ion-exchange degree and La loading of the La/β catalyst prepared by the microwave heating method were higher than the one prepared by the conventional heating method, and the ion-exchange time was shorter. The conversion of water and ethanol over the modified La/β molecular sieve catalyst was increased by 10 % -20 % compared with the unmodified Hβ molecular sieve, and the catalyst activity increased with the La loading. The hydration and the etherification mainly occurred on the external surface of the β molecular sieve catalyst. Bridging Al-OH-Si acid sites, i.e. , Broensted acid sites, were the main active sites, and the carbonium ion was formed during the reaction.