摘要
以NH3、吡啶、Et3N、CO2和苯酚为探针，用TPD－MS方法对ZrO2催化剂的酸碱性质进行了表征．ZrO2上碱性探针（NH3、吡啶和Et3N）的脱附温度远低于在强酸性SiO2－Al2O3上；而酸性探针CO2的脱附温度远低于在强碱性MgO上的结果．为ZrO2的弱酸弱碱性质提供了证明．NH3吸附IR结果表明ZrO2表面配位不饱合Zr4＋为酸（Lewis酸）中心．NH3、吡啶和Et3N与这些酸中心作用的方式和能量分布相似．NH3和CO2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ZrO2的酸中心和碱中心具有匹配相当的酸、碱强度，ZrO2为典型的酸－碱双功能催化剂，在苯酚的TPD过程中，ZrO2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NH3和CO2的脱附相联系的表面吸附物种分别进行了讨论．
Acid-base properties of ZrO2 pretreated at 873 K have been studied in relation to a typical acidic SiO2-Al2O3 and a typical basic MgO catalysts by exadring the TPD behavior of NH3,CO2, pyridine, Et3N, and phenol. The weakly acidic property of ZrO2 is evidenced by a much lower desorption temperature of NH3 in comparison with that of SiO2-Al2O3,and its weakly basic property by a much lower desorption temperature of CO2 in comparison with that of MgO. NH3,pyridine and Et3N show similar TPD profiles though decomposition to CH3CN occurs in the TPD process of Et3N. It is shown by the IR of adsorbed NH3 that the acid sites on ZrO2 are Lewis acidic in natare, and some of them can become more acidic in strength at elevated temperatures. Three TPD peaks on the TPD profiles of NH3 and CO2 are observed,respectively.The temperature range of NH3-peaks is very close to that of CO2-peaks. It is concluded from these observations that the strength of the acid and base sites on Zro2 are wen matched, and that ZrO2 is a typical acid-base bifunctional catalyst. A discussion on the relation between the adsorbed surface species and the desorption of NH3 and CO2 is given based on the IR results of adsorbed NH3 and CO2, respectively.In the TPD profile of phenol, the feature of ZrO2 is characterized by a relative difficulty for phenol desorption and an easiness for phenol decomposition.
出处
《物理化学学报》
SCIE
CAS
CSCD
北大核心
1994年第2期107-113,共7页
Acta Physico-Chimica Sinica
基金
国家自然科学基金
青年基金
关键词
氧化锆
酸碱性质
酸碱探针
Zirconium dioxide, Acid-base property, Acid and base probes, TPD,IR
