氢氟酸处理对β沸石催化剂烷基化反应的影响

Effect of Fluorination on β Zeolite and Alkylation of Benzene with Long-Chain Olefins

用不同浓度的HF溶液对β沸石催化剂进行处理,当HF浓度较低时,催化剂的晶格外物种和不稳定的骨架铝被溶解,桥形羟基被F取代,孔体积和比表面积增加,总酸量减少。随着HF浓度的继续增加,强B酸变化不明显,强L酸量增加,这是因为强B酸主要来源于缺陷处硅羟基,强L酸是由AlF3或其它铝物种的形成。深度氟化的催化剂孔体积和比表面积均减少,此时β沸石被溶解。催化剂寿命主要取决于催化剂的比表面积和孔体积,而不是酸量。当氟质量分数为0 5%时,催化剂的孔体积和比表面积最大,此时催化剂寿命提高约30%。

The effects of fluorination on β zeolite and alkylation of benzene with long-chain olefins were investigated by means of XRD, BET measurements,FTIR,TPD,elemental analysis and catalyst testing.When β zeolite was impregnated with low concentration HF solutions,the extra-lattice species were dissolved,bridging hydroxyl groups (3605 cm -1 ) were substituted by fluorine and unstable lattice aluminum (3782 cm -1 ) was removed, so the specific area and pore volume increased and total amount of acid decreased gradually.With increasing HF concentration,decrease in strong Brnsted acid sites was less than that in weak Brnsted acid sites because the hydroxyl groups bonded to Si (3730 cm -1 and 3745 cm -1 ) were more stable and strong.Lewis acid sites increased owing to the formation of AlF 3 or other fluorinated compounds.When both β zeolite and the extra-lattice species dissolved,the specific area and pore volume decreased.The lifetime of the catalysts depended on the surface area and pore volume instead of acidity.When the fluorine content was 0 5%,keeping the catalyst at maximum specific surface area and pore volume the lifetime could be improved by 30%.