ZrO_2酸碱性质的TPD表征Ⅱ.NH_3和CO_2共吸附研究

Characterization of Acid-Base Property of ZrO_2 by Thermal Desorption: Ⅱ.Dual Adsorption of NH_3 and CO_2

用NH3和CO2双组分并吸附TPD－MS和IR技术对ZrO2催化剂表面酸中心和碱中心的相互关系进行了表征·先吸附NH3（或CO2）对在其后吸附的CO2（或NH3）不仅无阻碍，反而导致后吸附CO2（或NH3）在最高程脱峰温区（＞510K）的脱附量增加．这种双组分并吸附效应在IR谱图上表现为NH3共吸附诱发生成了一种新的CO2吸附态，即在碱中心上形成单齿碳酸根物种．同时CO2共吸附又强化NH3与Zr4＋（Lewis酸中心）的配位键合．这表明ZrO2表面存在相互邻接的酸中心和碱中心，它们通过表面键诱导极化而令酸－碱相互作用加强．这类双组分共吸附效应可归结为表面键诱导酸－碱相互作用．

Dual adsorption of NH3 and CO2 has been used to study the acid property of ZrO2 in relation to its base property by TPD and IR spectroscopy. It is found that preadsorbed NH3 (or CO2) has no inhibitory but a promotive effect to a postadsorption of CO2 (or NH3). The increased adsorption of the postadsorbed moecules is most pronounced in the TPD curves at above 510 K. In the IR observation, the dual adsorption effect is characterized by a formation, on one hand, of a monodentate carbonate species which can not be formed in the single adsorption of CO2, and by a strengthened bonding of NH3 to surface acid site (Zr4+) on the other hand. These results suggest that there ekists not only independently located acid and base sites, responsible for the adsorption of NH3 and CO2, but some sites located closely(i.e acid-base pair sites). A surface induced through-bond acid-base interaction seems to be the nature of the dual adsorption effect.