Characterization of Catalytically Active Octahedral Metal Halide Cluster Complexes

Metals

Sayoko Nagashima¹  Teiji Chihara¹  Satoshi Kamiguchi² 

[1] Graduate School of Science and Engineering, Saitama University, Shimo-Okubo, Sakura-Ku, Saitama City, Saitama 338-8570, Japan;Organometallic Chemistry Laboratory, RIKEN, 2-1 Hirosawa, Wako City,Saitama 351-0198, Japan;

关键词: niobium and tantalum;    molybdenum and tungsten;    rhenium;    chloride and bromide;    inorganic cluster complex;    Brønsted acid;    coordinatively unsaturated site;    bi-functional catalyst;   

DOI  :  10.3390/met4020084

来源: DOAJ

【 摘 要 】

Halide clusters have not been used as catalysts. Hexanuclear molecular halide clusters of niobium, tantalum, molybdenum, and tungsten possessing an octahedral metal framework are chosen as catalyst precursors. The prepared clusters have no metal–metal multiple bonds or coordinatively unsaturated sites and therefore required activation. In a hydrogen or helium stream, the clusters are treated at increasingly higher temperatures. Above 150–250 °C, catalytically active sites develop, and the cluster framework is retained up to 350–450 °C. One of the active sites is a Brønsted acid resulting from a hydroxo ligand that is produced by the elimination of hydrogen halide from the halogen and aqua ligands. The other active site is a coordinatively unsaturated metal, which can be isoelectronic with the platinum group metals by taking two or more electrons from the halogen ligands. In the case of the rhenium chloride cluster Re3Cl9, the cluster framework is stable at least up to300 °C under inert atmosphere; however, it is reduced to metallic rhenium at 250–300 °C under hydrogen. The activated clusters are characterized by X-ray diffraction analyses, Raman spectrometry, extended X-ray absorption fine structure analysis, thermogravimetry–differential thermal analysis, infrared spectrometry, acid titration with Hammett indicators, and elemental analyses.

【 授权许可】

Unknown