二氧化硅负载偏钨酸铵催化剂上邻苯二酚和甲醇气相单醚化反应

考察了SiO2负载的偏钨酸铵催化剂(AMT/SiO2)上邻苯二酚和甲醇气相单醚化反应的性能.结果表明,经533和573K焙烧的AMT/SiO2催化剂表现出较高的邻苯二酚转化率(97%)和主产物邻羟基苯甲醚的选择性(91%).程序升温脱附和吡啶吸附红外光谱结果表明,催化剂表面存在的弱酸-弱碱位是反应的活性中心.经533K焙烧制备的催化剂在反应最初46h内保持较高的稳定性,随着反应时间延长,邻苯二酚的转化率逐渐降低,但主产物的选择性基本保持不变.扫描电镜和差热热重分析结果表明,催化剂表面积炭是其活性下降的主要原因,采用适当的焙烧处理可以消除大部分积炭,从而部分恢复催化剂活性.

Vapour-Phase o-Methylation of Catechol with Methanol on SiO2 -Supported Ammonium Metatungstate Catalysts

Catalytic properties of SiO2-supported ammonium metatungstate (AMT) catalysts calcined at different temperatures were investigated for the vapour-phase o-methylation of catechol with methanol. The catalysts calcined at 533 and 573 K showed relatively high catechol conversion (97%) and guaiacol selectivity (91%). The results of temperature-programmed desorption and infrared spectroscopy of adsorbed pyridine revealed that all the tested catalysts possessed weak acid-base sites, which might be the main active sites of the reaction. The stability of AMT/SiO2 calcined at 533 K was studied, and no obvious activity loss occurred within 46 h. With further increase of reaction time, the catalyst activity decreased gradually, but the selectivity for the main product remained almost steady. According to the results of scanning electron microscopy and TGA-DTA thermal analysis, it can be deduced that the coke deposited on the surface of AMT/SiO2 was the main reason for the catalyst deactivation. The catalytic properties of the catalyst could be partially recovered by calcining the used catalyst at a suitable temperature in air.