TiO2–ZrO2的表征及其异丙醇催化转化性能

用共沉淀法制备了TiO2-ZrO2复合氧化物. 采用N2吸附、XRD、TEM、NH3和CO2吸附量热、NH3吸附红外对TiO2-ZrO2体系的结构及酸碱性等进行了表征. 结果表明: 与单纯的氧化物相比, 形成的复合氧化物为无定形物相, 有介孔结构, 表面积明显提高, 可达218 m2·g-1; 初始吸附热差别不大, 但具有更多的表面B酸位; 随着TiO2掺入量的增大, 复合氧化物表面碱位减少. 异丙醇催化转化, 在无氧条件下, ZrO2、TiO2和TiO2-ZrO2复合氧化物上丙烯的选择性大于90%, 说明这些氧化物具有强的表面酸性; 在有氧条件下, ZrO2和TiO2丙酮的选择性达到70%～85%, 主要体现为氧化还原性; 而在复合氧化物上丙烯选择性增大到70％左右, 丙酮的选择性下降为30%左右, 表明生成的复合氧化物表面上的氧化还原性削弱, 酸性增强.

Characterization of TiO2-ZrO2 and Isopropanol Catalytic Conversion

A series of TiO2-ZrO2 composite oxides were prepared by a coprecipitation method. They were characterized by N2 adsorption, XRD, TEM, microcalorimetric adsorption of NH3 and CO2, infrared spectra of ammonia adsorption. In comparison with single metal oxide, amorphous composite oxides could be observed with mesoporous structure and higher BET surface area(SBET=218 m2·g-1). Although the initial adsorption heat for all these samples did not vary significantly, composite oxides possessed more Bronsted acid sites than single oxide. With an increase in the incorporated amount of titania, the number of basic sites on the surface of composite oxides was decreased. In the absence of O2, the values of selectivity for propene exceeded 90% for all these catalysts via isopropanol catalytic conversion, revealing that each of the samples had a strong surface acidity. However, in the presence of O2, 70%～85% selectivity for acetone was obtained for TiO2 and ZrO2, suggesting that redox properties were predominant over acidity. Due to the formation of composite oxide, selectivity for propene increased to about 70%, whereas selectivity for acetone decreased to about 30%, indicating that the acidity was enhanced and the redox property was weakened.