改性Beta/Al2O3无水环境催化合成聚甲氧基二甲醚

分别采用硝酸镧、柠檬酸和磷酸改性Beta/Al2O3，对改性后的分子筛材料进行XRD、TEM、N2吸附-脱附、NH3-TPD和Py-IR表征，并将改性后的Beta/Al2O3用于催化甲缩醛(DMM)和三聚甲醛(TOX)合成聚甲氧基二甲醚(PODEn)的反应中，考察其孔结构和酸性质对反应活性的影响。结果表明：3种形式的改性并未改变原有Beta分子筛的晶相结构，镧改性对孔结构影响不大，而2种酸改性都出现多级孔道结构；所有改性后Beta/Al2O3的B酸含量均有所提高，酸处理还会导致Beta/Al2O3的L酸量明显下降，有效地改善了其酸分布；B酸量的增加会提高Beta/Al2O3催化剂的催化反应活性，其孔径的大小直接影响传质效率，进而影响其催化反应活性；柠檬酸处理的Beta/Al2O3具有最优的孔道结构，与未改性前相比，三聚甲醛的转化率提高了80%。

Catalytic Synthesis of Polyoxymethylene Dimethyl Ethers by Modified Beta/Al2O3 Under Anhydrous Conditions

Beta/Al2O3 material was modified by lanthanum nitrate, citric acid and phosphoric acid, and characterized by XRD, TEM, N2 adsorption-desorption, NH3-TPD and Py-IR. These modified catalysts were used to catalyze the reaction of dimethoxymethane with trioxane, to investigate the effects of its pore structure and acid properties on reactivity. Results show that three kinds of modifications do not change the crystal structure of Beta zeolite, while the lanthanum nitrate modification has little effect on pore structure, with appearing of hierarchical structure in both acid modifications. However, all modified materials have increased amount of Brnsted acid sites, and acid treatment causes significant drop of the amount of Lewis acid sites. These modifications effectively improve the acid distribution of catalysts. These results demonstrate the reactive activity is increasing along with the amount enhancement of Br?nsted acid sites, and the pore size of these catalysts affects mass transfer efficiency, and then changes reactivity. The catalyst treated with citric acid has good pore structure, with the conversion of trioxane increased by 80% compared with unmodified material.