用固体核磁方法研究MCM-22分子筛中的Al状态

CHARACTERIZATION OF Al SPECIES IN MCM-22 ZEOLITE BY SOLID STATE NMR

用固体NMR技术研究了新型分子筛MCM 2 2在不同水合状态下的2 7Al谱和1 H谱 .并用新的1 H/2 7Al双共振方法TRAPDOR对MCM 2 2分子筛的各种铝状态进行了研究 ,得到了样品脱水后B酸位 (Bronsted)、L酸位 (Lewis)以及非骨架Al(OH)的四极耦合常数 .

MCM-22 is a new molecular sieve which is expected to be widely used in chemical industry. In this paper we study the {}+{27}Al species of different acid sites in the MCM-22. {}+{27}Al spectra of samples rehydrated in differently extent have been acquired. It is difficult to get high resolution {}+{27}Al spectrum of the dehydration powder sample directly because of the existence of strong quadrupole interaction which comes from asymmetric local chemical environment. In order to overcome the strong quadrupole interaction of {}+{27}Al, the double resonance NMR method {}+1H/{}+{27}Al TRAPDOR is used in this study. Quadrupole coupling constants (QCC) for aluminum species are abtained. By calculation of the second order quandrupole line width of these aluminum species , it can be concluded that 4-, 3-coordinate framework aluminum and extra-framework alumium are all the source of the “NMR invisible aluminum”. ;