Kim Sungmin, Lee Mal-Soon, Camaioni Donald M, Gutiérrez Oliver Y, Glezakou Vassiliki-Alexandra, Govind Niranjan, Huthwelker Thomas, Zhao Ruixue, Rousseau Roger, Fulton John L, Lercher Johannes A
Institute for Integrated Catalysis and Physical Science Division, Pacific Northwest National Laboratory, Richland, Washington 99354, United States.
Swiss Light Source, Paul Scherrer Institut (PSI), 5232 Villigen, Switzerland.
JACS Au. 2023 Aug 30;3(9):2487-2497. doi: 10.1021/jacsau.3c00259. eCollection 2023 Sep 25.
In situ Al K-edge X-ray absorption near edge structure (XANES) and Extended X-ray absorption fine structure (EXAFS) spectroscopy in conjunction with ab initio molecular dynamics (AIMD) simulations show that adsorption of 1-propanol alters the structure of the Brønsted acid site through changes in the associated aluminum-oxygen tetrahedron in zeolite H-MFI. The decreasing intensity of the pre-edge signal of the in situ Al K-edge XANES spectra with increasing 1-propanol coverage shows that Al T-sites become more symmetric as the sorbed alcohol molecules form monomers, dimers, and trimers. The adsorption of monomeric 1-propanol on Brønsted acid sites reduces the distortion of the associated Al T-site, shortens the Al-O distance, and causes the formation of a Zundel-like structure. With dimeric and trimeric alcohol clusters, the zeolite proton is fully transferred to the alcohols and the aluminum-oxygen tetrahedron becomes fully symmetric. The subtle changes in Al-K-edge XANES in the presence of sorbate structures, with the use of theory, are used to probe the local zeolite structures and provide a basis to predict the population and chemical state of the sorbed species.
原位铝 K 边 X 射线吸收近边结构（XANES）和扩展 X 射线吸收精细结构（EXAFS）光谱结合从头算分子动力学（AIMD）模拟表明，1-丙醇的吸附通过改变沸石 H-MFI 中相关铝氧四面体的结构来改变布朗斯特酸位点的结构。随着 1-丙醇覆盖度增加，原位铝 K 边 XANES 光谱的边前信号强度降低，这表明随着吸附的醇分子形成单体、二聚体和三聚体，铝 T 位点变得更加对称。单体 1-丙醇在布朗斯特酸位点上的吸附减少了相关铝 T 位点的畸变，缩短了铝-氧距离，并导致形成类似津德尔的结构。对于二聚体和三聚体醇簇，沸石质子完全转移到醇上，铝氧四面体变得完全对称。利用理论，在存在吸附质结构的情况下铝 K 边 XANES 的细微变化用于探测局部沸石结构，并为预测吸附物种的数量和化学状态提供依据。
