镧改性的CuHY分子筛中铜离子的分布及其对吸附脱硫性能的影响

在氮气气氛下采用等体积浸渍法制备了载Cu的HY和LaHY分子筛.用x射线衍射(XRD)、N2吸附、氨程序升温脱附和X射线光电子能谱对分子筛进行了表征.通过多晶XRD确定了Cu2+离子在Y型分子筛笼内的结构与分布,并测定了分子筛在含二苯并噻吩(DBT)的模拟柴油中的吸附脱硫性能.结果表明,前驱体CuCl2中的大部分Cu物种与HY和LaHY分子筛进行了离子交换.对于La3+改性的CuHY分子筛(CuLaHY),进入分子筛超笼中的Cu2+离子与骨架氧和水分子配位,牢固地定位于Y型分子筛超笼的SⅡ及SⅢ位;对于CuHY分子筛,超笼中的Cu2+离子只接近于SⅡ及SⅢ位.极少部分CuCl分子高度分散在分子筛笼内,没有定位.处于超笼中SⅡ及SⅢ位的Cu2+离子对模拟柴油中的DBT分子具有吸附作用,是吸附脱硫的活性中心.CuLaHY分子筛的吸附脱硫性能优于CuHY分子筛.当模拟柴油中含有萘时,萘与DBT分子会产生竞争吸附.

Distribution 0f Cu Ions in Lanthanum. Modified CuHY Zeolite and Its Influence on Adsorption Desulfurization Performance

The Cu-loaded CuHY and CuLaHY zeolites were prepared by an incipient wetness method under nitrogen gas atmosphere. The samples were characterized by X-ray diffraction (XRD), N_2 adsorption, NH_3 temperature-programmed desorption, and X-ray photoelectron spectroscopy. The crystalline structure and the distribution of Cu~(2+) cations in the cages of Y zeolite were determined by XRD. The adsorption desulfurization performance of the zeolites was investigated for model diesel containing dibenzothiophene (DBT). The results showed that most of Cu species from the precursor CuCl_2 was ion-exchanged with the HY and LaHY zeolites. For the La3+-modified CuHY zeolite (CuLaHY), the Cu~(2+) cations entering the supercages of the zeolite coordinated with both skeleton-oxygen atoms and water molecules, and thus being firmly situated at the sites Sn and Snr in the supercages. For the CuHY zeolite, however, Cu~(2+) cations entering the supercages were only near the sites Sn and Sm in the supercages. A very small percentage of CuCl molecules was highly scattered in the cages of the Y zeolite, with no definite position. The Cu~(2+) cations at the sites Sn and Snr in the supercages adsorbed DBT molecules in the model diesel were the centers of adsorption desulfurization. The desulfurization capacity of the CuLaHY zeolite was better as compared with the CuHY zeolite. However, naphthalene molecules will result in competitive adsorption with DBT molecules if there are naphthalene molecules in the model diesel.