IR. MAS NMR法研究富硅超稳镨氢Y沸石

制备了NH_4Y、USY、PrHY、USPrHY、F8Y及FSPrHY催化剂, 测定其组成和物性. 于红外光谱装置上比较了上述催化剂羟基峰的异同, 通过对吡啶的吸脱附测定了诸催化剂的酸强度. B 酸强度顺序为: FSPrHY>FSY>USPrHY>USY>PrHY>NH_4Y. ~(29)Sit MAS NMR谱表明, 在USPrHY 及FSPrHY 的Si(0Al)%甚多于PrHY 和NH_4Y中的Si(0Al)%. IR、~(29)Si MAS NMR及活性测试等结果说明: 沸石中0NNN铝位的存在, 是达到强酸性的必要条件. 高价稀土阳离子形成(?)及Pr(OH)~(2+)抵消了方钠石笼中AlO_4~-上的电荷, 增强了剩余铝位上羟基酸强度; 且从骨架羟基上吸引电子, 因而使质子酸性更强, 从而提高了裂解、岐化、脱烷基活性.

STUDIES ON SILICON-RICH PrHY ZEOLITES OF ULTRASTABILITY BY IR AND ~(29)Si MAS NMR

NH_4Y, USY, PrHY, USPrHY and FSPrHY were prepared. Their compositions and physical properties were determined. The difference among their hydroxyl group has been compared on the IR system. The acid strength of every sample was deter-mined by IR-Pyridine method. The order of Bronsted acid strength are FSPrHY>FSY>USPrHY>USY>PrHY>NH_4Y. ~(29)Si MAS NMR spectra,showed that Si(0Al) content in USPrHY and FSPrHY is more than in PrHY and NH_4Y. These results show that the 0-NNN and 1-NNN strong acidity site is more than 2-NNN and 3-NNN weak acidity site on USPrHY and FSPrHY Zeolites. All the results of IR ~(39)Si MAS NMR and activity test are consistent with a model of strong acidity in which both the presence of 0-NNN strong acidity site and polyvalent cations in the β-cages are important. Praseodymium ions in the form of (?) and Pr(OH)~(2+) species are believed to be responsible for the withdrawal of electrons from the framework hydroxyl groups, thus making the protons more acidic, the cracking disproportionation and dealkylation activity were heightened.