Development of quickly measurement method for acid amount and strength of zeolite

氨的程序升温脱附(TPD)是一种快速测定沸石酸性的简便方法。然而，它通常被氨的重新吸附所混淆，这使得解释变得复杂。本研究考察了不同沸石上TPD的各种条件，这些实验表明，TPD是由气态和吸附氨气之间的平衡控制的。在此基础上推导出了理论方程。在不同条件下的实验中，确定了由相变项和气体混合项组成的熵变。前一项在不同晶体结构和组成的沸石上几乎是恒定的，符合Trouton热力学定律。这些都支持了该理论的正确性。该理论方程给出了由单点实验确定酸量和酸强度的方法，并给出了确定…的方法通过一次实验，对观测曲线和基于理论方程模拟的曲线进行了曲线拟合，得到了更多的酸量、酸强度及其分布。该方法还可以将氨解吸峰与弱吸附氨峰分离。测定的酸量证实了一个简单的原理，即一个铝原子的类质同象取代生成一个Brphinsted酸性中心，一个Na原子可以封闭一个酸性中心。测定的酸强度在各沸石上的分布很窄，主要受丝光沸石&GT；ZSM-5&GT；β&GT；Y的晶体结构控制。通过脱铝改变组成或改变离子交换比，酸强度不变。这提出了一个非常简单的原理，即沸石的酸强度是由晶体结构控制的，因此在一个沸石上是均匀的。因此，本研究建立了准确、快速地测定沸石的酸性质，即酸的量、强度及其分布的实验和分析方法。较少

Temperature-Programd Desorption (TPD) of ammonia is a convenient method to quickly measurement of acidic property of zeolite. However, it is usually confused by readsorption of ammonia, and this complicates the interpretation. Various conditions were examined for the TPD on various zeolites in the present study, and these experiments clarified that the TPD was controlled by an equilibrium between gaseous and adsorbed ammonia. A theoretical equation was derived based on this equilibrium. The entropy change, which was assumed to consist of the phase-transformation and gaseous mixing terms, was determined from the experiments under various conditions. The former term was almost constant on the zeolites with various crystal structures and compositions, and consistent with Trouton's rule of thermodynamics. These support the validity of the theory. This theoretical equation gave the method to determine the acid amount and strength from one-point experiment.Moreover, a method to determine the … More acid amount, strength and its distribution from one experiment with curve-fitting of the observed curve and the curve simulated based on the theoretical equation is proposed. This method also could separate the peaks due to ammonia desorbed from acid site from that due to the weakly adsorbed ammonia. Analysis of acidic property on weakly acidic zeolites such as Y and beta types became possible by this method.The determined acid amount confirms a simple principle that isomorphous substitution of one aluminum atom generates one Brphinsted acid site, and one sodium atom can block one acid site. The determined acid strength had a narrow distribution on each zeolite, and was mainly controlled by the crystal structure as mordenite>ZSM-5>beta>Y.The strength was unchanged by varying the composition by dealumination or varying the ion-exchange ratio. This proposes a very simple principle that the acid strength of zeolite is controlled by the crystal structure, and hence homogeneous on one zeolite.The present study thus establishes the experimental and analytical methods to exactly and quickly determine the acidic property, i.e., acid amount, strength and its distribution, of zeolite. Less