钙改性的Pd/CeO_2-ZrO_2-Al_2O_3催化剂催化甲醇裂解反应

Ca-Modified Pd/CeO_2-ZrO_2-Al_2O_3 Catalysts for Methanol Decomposition

采用共沉淀法制备了未改性的和Ca掺杂的CeO2-ZrO2-Al2O3样品,进一步用浸渍法制备了Pd/CeO2-ZrO2-Al2O3(Pd/CZA)和Pd/CeO2-ZrO2-Al2O3-CaO(Pd/CZACa)催化剂.运用X射线衍射、N2吸附-脱附、储氧量测定、CO化学吸附、NH3程序升温脱附、CO2程序升温脱附、H2程序升温还原和X射线光电子能谱对催化剂进行了表征,并考察了其催化甲醇裂解反应活性.结果表明,Ca的添加使载体酸性位中毒,弱碱中心数目增加,从而影响了催化剂上吸附物种的吸附-脱附平衡过程;同时,使得金属和载体间相互作用增强,增加了Pd周围的电子密度,使Pd保持在部分氧化状态Pdδ+(0<δ<2),进而提高了甲醇催化裂解反应的活性,使甲醇完全裂解温度降低了34°C.

CeO2-ZrO2-Al2O3 and CeO2-ZrO2-Al2O3-CaO supports were prepared by the coprecipitation method and were loaded with Pd by impregnation to form Pd/CeO2-ZrO2-Al2O3 （Pd/CZA） and Pd/CeO2-ZrO2-Al2O3-CaO （Pd/CZACa） catalysts. The catalysts were characterized by X-ray diffraction, low temperature N2 adsorption-desorption, oxygen storage capacity, CO chemisorption, NH3 temperature-programmed desorption （NH3-TPD）, CO2 temperature-programmed desorption （CO2-TPD）, H2 temperature-programmed reduction （H2-TPR）, and X-ray photoelectron spectroscopy （XPS）. The catalyst activity for methanol decomposition showed that the Ca modification improved the low-temperature activity of the catalyst, which lowered the complete conversion temperature on 34 oC. NH3-TPD and CO2-TPD showed that the addition of Ca poisoned the acid sites of the support or increased the number of weak basic sites and therefore changed the adsorption-desorption equilibria of the adsorbed species. It also enhanced the metal-support interaction and increased the electronic surroundings of Pd sites, which maintained Pd in a partly oxidized （Pdδ＋） state and consequently increased the activity for methanol decomposition according to H2-TPR and XPS measurements.