ZrO2酸碱性质的TPD表征 I. 单组分吸附研究

以NH_3、吡啶、Et_3N、CO_2和苯酚为探针，用TPD-MS方法对ZrO_2催化剂的酸碱性质进行了表征．ZrO_2上碱性探针（NH_3、吡啶和Et_3N）的脱附温度远低于在强酸性SiO_2－Al_2O_3上；而酸性探针CO_2的脱附温度远低于在强碱性MgO上的结果．为ZrO_2的弱酸弱碱性质提供了证明．NH_3吸附IR结果表明ZrO_2表面配位不饱合Zr~(4＋)为酸（Lewis酸）中心．NH_3、吡啶和Et_3N与这些酸中心作用的方式和能量分布相似．NH_3和CO_2的TPD谱图均存在三个脱附峰，且相应脱附峰的温度范围相近．表明ZrO_2的酸中心和碱中心具有匹配相当的酸、碱强度，ZrO_2为典型的酸－碱双功能催化剂，在苯酚的TPD过程中，ZrO_2的特征表现为对苯酚的强吸附和对苯酚分解的高活性．文中结合IR结果，对与NH_3和CO_2的脱附相联系的表面吸附物种分别进行了讨论.

Characterization of Acid-base Property of ZrO2 by Thermal Desorption: I. TPD Studies of Acid and Base Probes

Acid-base properties of ZrO_2 pretreated at 873 K have been studied in relation to a typical acidic SiO_2-Al_2O_3 and a typical basic MgO catalysts by exadring the TPD behavior of NH_3, CO_2, pyridine, Et_3N, and phenol. The weakly acidic property of ZrO_2 is evidenced by a much lower desorption temperature of NH_3 in comparison with that of SiO_2-Al_2O_3, and its weakly basic property by a much lower desorption temperature of CO_2 in comparison with that of MgO. NH_3, pyridine and Et_3N show similar TPD profiles though decomposition of CH_3CN occurs in the TPD process of Et_3N. It is shown by the IR of adsorbed NH_3 that the acid sites on ZrO_2 are Lewis acidic in nature, and some of them can become more acidic in strength at elevated temperature. Three TPD peaks on the TPD profiles of NH_3 and CO_2-peaks. It is concluded from these observations that the strength of the acid and base sites on ZrO_2 are well matched, and that ZrO_2 is a typical acid-base bifunctional catalyst. A discussion on the relation between the adsorbed surface species and the desorption of NH_3 and CO_2 is given based on the IR results of adsorbed NH_3 and CO_2, respectively.
In the TPD profile of phenol, the feature of ZrO_2 is characterized by a relative difficulty for phenol desorption and an easiness for phenol decomposition.