Wang Miao-Miao, Yu Jing, Wang Dao-Lei, Si Rui
Shanghai Institute of Applied Physics, Chinese Academy of Sciences Shanghai 201204 Shanghai China
University of Chinese Academy of Science Beijing 100049 China.
RSC Adv. 2020 Mar 26;10(21):12326-12333. doi: 10.1039/d0ra01252a. eCollection 2020 Mar 24.
Platinum oxide supported on a Lewis acid niobium oxide (NbO) support has been used for various heterogeneous and homogeneous catalysts. In this work, we used urea as a precipitating agent to obtain crystallized NbO with high surface area a hydrothermal route. NbO-supported Pt catalysts were subsequently synthesized an incipient wetness impregnation approach. Multiple characterizations including X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and nitrogen adsorption/desorption confirmed the identical structural and textural properties of the NbO support before and after the impregnation process. Furthermore, the X-ray absorption fine structure technique (XAFS) results with related data analysis indicate that the platinum species in the fresh and H-pretreated samples were in the form of single atoms or ultrafine clusters. In addition, the decrease in coordination number (CN) of the first-shell Pt-O bond, as well as the formation of Pt-Pt contribution with very low CN, after H-pretreatment was verified, which corresponds to the decrease of oxidation state for Pt species on the surface of supports. Thus, the ultrafine-clustered metallic Pt species are considered to be more active than the oxidized Pt single ions. The current results will be of great significance in controllable synthesis of active Pt-based catalysts for other catalytic oxidation reactions.
负载在路易斯酸铌氧化物（NbO）载体上的氧化铂已被用于各种多相和均相催化剂。在这项工作中，我们使用尿素作为沉淀剂，通过水热法获得具有高比表面积的结晶NbO。随后采用初湿浸渍法合成了负载在NbO上的铂催化剂。包括X射线衍射（XRD）、高分辨率透射电子显微镜（HRTEM）和氮吸附/脱附在内的多种表征证实了浸渍前后NbO载体相同的结构和织构性质。此外，X射线吸收精细结构技术（XAFS）结果及相关数据分析表明，新鲜样品和H预处理样品中的铂物种为单原子或超细团簇形式。另外，经H预处理后，第一壳层Pt - O键的配位数（CN）降低，以及形成了极低CN的Pt - Pt贡献，这对应于载体表面铂物种氧化态的降低。因此，超细团簇金属铂物种被认为比氧化态的铂单离子更具活性。目前的结果对于可控合成用于其他催化氧化反应的活性铂基催化剂具有重要意义。
