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

氨的程序升温脱附（TPD）法是一种快速测定沸石酸性的简便方法。然而，它通常被氨的再吸附所混淆，这使解释复杂化。在本研究中，对各种沸石上的TPD的各种条件进行了检查，并且这些实验阐明了TPD由气态氨和吸附氨之间的平衡控制。根据此平衡关系，推导出了理论方程。熵变假定由相变项和气体混合项组成，由各种条件下的实验确定。前者在不同晶体结构和组成的沸石上几乎是常数，符合Trouton热力学规则。这些都支持了理论的正确性。该理论方程给出了由一点实验确定酸量和酸强度的方法，并给出了确定酸量和酸强度的方法 关于我们 提出了一种用实测曲线与理论方程拟合曲线的方法，从一次实验中得到酸量、酸强度及其分布。该方法还可将酸性位脱附的氨峰与弱吸附的氨峰分开。用该方法分析了Y型和β型弱酸性沸石的酸性质，确定了酸量，证实了一个铝原子同晶取代产生一个Brphinsted酸中心，一个钠原子封闭一个酸中心的简单原理。测定的酸强度在每种沸石上具有窄的分布，并且主要由丝光沸石>ZSM-5> β>Y的晶体结构控制。通过脱铝或改变离子交换比改变组成，强度不变。提出了一个非常简单的原理，即沸石的酸强度由晶体结构控制，因此在一个沸石上是均匀的。本研究建立了准确和快速测定沸石酸性质的实验和分析方法，沸石的酸量、强度及其分布。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