IR.MAS NMR法研究富硅超稳镨氢Y沸石

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

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)Sj 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.

NH_4Y,USY,PrHY,USPrHY and FSPrHY were prepared.Their compositionsand physical properties were determined.The difference among their hydroxyl grouphas 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 resultsshow 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 ^(29)SiMAS NMR and activity test are consistent with a model of strong acidity in whichboth the presence of 0-NNN strong acidity site and polyvalent cations in the β-cages areimportant.Praseodymiumions in the form of(?)^(4+) and Pr(OH)^(2+)species are believed to be responsible for the withdrawal of electrons from theframework hydroxyl groups,thus making the protons more acidic,the crackingdisproportionation and dealkylation activity were heightened.