Zones Stacey I, Darton Richard J, Morris Russell, Hwang Son-Jong
Chevron Texaco Energy Research and Technology Company, Richmond, California 94802, USA.
J Phys Chem B. 2005 Jan 13;109(1):652-61. doi: 10.1021/jp0402434.
This work is an experimental response to an intriguing paper recently published by Catlow and co-workers, which looked at the computational feasibility of fluorine location in three different all-silica zeotypes (Attfield, M. P.; Catlow, C. R. A.; Sokol, A. A. Chem. Mater. 2001, 13, 4708). The materials were chosen as representative of three unique host locations. Our present work examined the synthesis of zeotypes AST, IFR, and MTT using organo-cations with a strong preference for crystallizing these structures. We studied the effect of reaction time and the H(2)O/SiO(2) reactant ratio. The latter is probably the most important function in these zeolite crystallizations that use HF. As reaction conditions became more dilute, AST gave way to SGT and IFR to MTW as host structures, while the MTT synthesis was invariant. Our reactions were studied in terms of product yield vs time, product organo-cation content, fluorine content, and the representative (29)Si and (19)F NMR spectra for certain samples. A single crystal study was carried out for a sample of MTT. Our results showed that, consistent with other recent studies, low H(2)O/SiO(2) reactant ratios lead to more open framework host structures (i.e., IFR vs MTW), and there is typically a higher uptake of organo-cation and fluorine. The structure may well contain a higher population of 4-rings within the silicate substructure. While MTT that contains no 4-rings was chosen as the best possible candidate to achieve an ion-pair for the organo-cation and fluoride anion within the silicate host, both NMR and single crystal work confirm that fluoride is bonded to a 5-coordinate silica center within the lattice.
这项工作是对卡特洛及其同事最近发表的一篇引人入胜的论文的实验性回应，该论文探讨了氟在三种不同全硅沸石型中的位置的计算可行性（阿特菲尔德，M.P.；卡特洛，C.R.A.；索科尔，A.A.《化学材料》，2001年，13卷，4708页）。这些材料被选为三种独特主体位置的代表。我们目前的工作研究了使用对这些结构结晶有强烈偏好的有机阳离子合成AST、IFR和MTT沸石型。我们研究了反应时间和H₂O/SiO₂反应物比例的影响。在这些使用HF的沸石结晶中，后者可能是最重要的因素。随着反应条件变得更加稀释，AST被SGT取代，IFR被MTW取代作为主体结构，而MTT的合成不变。我们根据产物产率与时间、产物有机阳离子含量、氟含量以及某些样品的代表性²⁹Si和¹⁹F NMR光谱对反应进行了研究。对MTT的一个样品进行了单晶研究。我们的结果表明，与其他近期研究一致，低H₂O/SiO₂反应物比例会导致更开放的骨架主体结构（即IFR与MTW相比），并且通常有机阳离子和氟的吸收量更高。该结构在硅酸盐亚结构中可能含有更多的4元环。虽然选择不含4元环的MTT作为在硅酸盐主体中实现有机阳离子和氟阴离子离子对的最佳候选物，但NMR和单晶研究均证实氟与晶格内的一个五配位硅中心键合。
