固载型杂多酸的合成与表征及催化异丙醇气相脱水反应的活性

STUDIES ON SYNTHESIS, CHARACTERIZATION AND CATALYTIC ACTIVITY OF SUPPORTED HETEROPOLY ACIDS FOR DEHYDRATION OF ISOPROPANOL IN VAPOR-PHASE

采用浸渍法和吸附法分别制备固载型杂多酸 ( HPA)催化剂 HPA/MCM-4 1 ( Si O2 ,γ-Al2 O3 )及 PW1 2 /C,用 FT-IR,XRD表征了催化剂的骨架及晶体结构。除 HPA/γ-Al2 O3 外 ,其他固载型 HPA均能保持 Keggin结构 ,对题述反应的活性较未固载前均有所提高。其原因为 HPA在载体表面得到高度分散 ,提高了 HPA的比表面积 ;而 γ-Al2 O3 相对碱性较强 ,用浸渍法固载 HPA时 ,HPA可能发生了分解 ,Keggin结构遭到破坏 ,致使催化剂活性下降。PW1 2 固载于 Si O2 上以后 ,使杂多阴离子负电荷有所增加。焙烧后的 HPA/MCM-4 1酸性得到了提高 ,催化活性显著升高 ;适量固载 HPA对 MCM-4 1的中孔性质无影响。不同载体与 HPA之间的作用不尽相同 ,其结果直接影响异丙醇气相脱水反应的活性及产物的选择性。

The solid acid catalysts which consist of heteropoly acids (HPAs) H 3PW 12 O 40 (PW 12 ), H 4SiW 12 O 40 (SiW 12 ) and H 3PMo 12 O 40 (PMo 12 ) supported on mesoporous molecular sieve MCM 41, SiO 2, γ Al 2O 3 and active carbon were prepared by dipping and adsorbing methods respectively. The structures and properties of supported HPAs were investigated by FT IR and XRD. The results showed that the supported HPAs still remain their Keggin structure and the catalytic activities for title reaction were improved except HPA/ γ Al 2O 3. That was conceived that the high dispersibility of HPAs on the surface of supporter comparatively improved available surface area of HPAs, but the Keggin structure of HPAs were destroyed while using dipping methods to prepare HPA/ γ Al 2O 3. The negative electric charge of HPAs' anion increased while PW 12 were supported on SiO 2. Acidities and catalytic activities of baked HPA/MCM 41 were improved and the Keggin structure of HPAs still remained. Proper supporting amounts of HPAs were confirmed to be not destructive to the crystalline structure of MCM 41. The actions of HPAs with supporters were not the same, and they directly affect the activity and selectivity of dehydration of isopropanol in vapor phase.