Milanesio Marco, Artioli Gilberto, Gualtieri Alessandro F, Palin Luca, Lamberti Carlo
Dipartimento di Scienze e Tecnologie Avanzate, Università del Piemonte Orientale A. Avogadro, Corso T. Borsalino 54, I-15100 Alessandria, Italy.
J Am Chem Soc. 2003 Nov 26;125(47):14549-58. doi: 10.1021/ja037229+.
The high X-ray flux available at the European Synchrotron Radiation Facility (ESRF), combined with the use of a suitably designed area detector setup, allowed us to follow in real time the structural changes occurring during the template burning processes inside TS-1 and Fe-silicalite MFI zeolites with a X-ray powder diffraction technique (XRPD). Rietveld analysis of the XRPD patterns collected in the 350-1000 K interval, integrated each 15 K, yields to the determination of the template overall occupancy factor versus T with an accuracy comparable with that obtained by thermogravimetric measurements, routinely employed for this purpose. The evolution of the structural parameters (V, a, b, c, site occupancy factor of the template molecule) vs T has been obtained. These data allow us to have, for the first time, a complete view of the structural rearrangements induced by the template burning process on the zeolitic framework. The differences caused by the different heteroatom inserted in the MFI lattice (Ti or Fe) are discussed. For both TS-1 and Fe-MFI, the kinetics of the reaction were investigated, to obtain the activation energy of the calcinations process employing the nonisothermal data according to the theory recently proposed by Kennedy and Clark [Thermochim. Acta, 1997, 307, 27-35]. For TS-1 only, the time-resolved template burning experiment has been repeated in isothermal conditions at four different temperatures, to obtain the activation energy from isothermal data, according to the standard procedure. Comparison between Arrhenius plots obtained from isothermal and nonisothermal data demonstrates that the Kennedy and Clark method can be also applied to complex materials such as the MFI zeolites. This approach, when applied to time-resolved XRPD studies, is much less time consuming (requesting, in principle, one single nonisothermal run) with respect to the classic approach, which requests at least three isothermal runs. Moreover, it allows a remarkably lower associated error (151 +/- 11 versus 146 +/- 30 kJ mol(-)(1)) due to the much higher number of experimental points employed to perform the linear fit.
欧洲同步辐射装置（ESRF）所具备的高X射线通量，结合使用经过适当设计的面探测器装置，使我们能够利用X射线粉末衍射技术（XRPD）实时跟踪TS-1和铁硅铝酸盐MFI沸石内部模板燃烧过程中发生的结构变化。对在350 - 1000 K区间内每15 K采集一次的XRPD图谱进行Rietveld分析，可确定模板的总占据因子与温度的关系，其精度与为此目的常规使用的热重测量相当。已获得结构参数（V、a、b、c、模板分子的位点占据因子）随温度的变化情况。这些数据使我们首次全面了解模板燃烧过程对沸石骨架引起的结构重排。讨论了MFI晶格中插入不同杂原子（Ti或Fe）所导致的差异。对于TS-1和铁MFI，均研究了反应动力学，根据Kennedy和Clark最近提出的理论[《热化学学报》，1997，307，27 - 35]，利用非等温数据获得煅烧过程的活化能。仅针对TS-1，已在四个不同温度下于等温条件下重复进行了时间分辨模板燃烧实验，以根据标准程序从等温数据中获得活化能。从等温数据和非等温数据得到的阿累尼乌斯图的比较表明，Kennedy和Clark方法也可应用于诸如MFI沸石之类的复杂材料。与经典方法相比，这种方法应用于时间分辨XRPD研究时耗时少得多（原则上只需一次非等温运行），经典方法至少需要三次等温运行。此外，由于用于进行线性拟合的实验点数量多得多，它所带来的相关误差显著更低（分别为151±11和146±30 kJ mol⁻¹）。
