ISSN:
1572-879X
Keywords:
cubane-type molybdenum oxide clusters
;
CO-photoreduction
;
propene metathesis reaction
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
Notes:
Abstract SiO2-impregnated complete and incomplete cubane-type molybdenum oxide clusters such as [(RhCp*)4Mo4O16] (I) and [(RhCp*)2Mo3O9(OMe)4] (II) were photoreduced with a UHP-Hg lamp (〉 365 nm) in CO, resulting in the formation of catalytically active species for propene metathesis at 300 K. The CO-photoreduced Mo oxide clusters were characterized by EXAFS, IR, XPS and TPD technique. The results suggest that the Mo-O4c (four-centered bridging oxygens) in I were specifically reduced with CO under the illumination to produce two sets of subcarbonyl species, e.g., those characteristic of the IR bands at 2061 and 2021 cm−1, which were thermally inactive for the13CO exchange reaction but very active under illumination at 300 K, possibly assignable to Mo(CO)x (x = 2, 3), whereas those at 2092 and 2035 cm−1 due to Rh(CO)2, which were readily exchangeable with13CO at 300 K in dark. Removal of both carbonyls attached on Rh and Mo in photoreduced I and II by evacuation at 375–440 K led to the formation of oxygen-deficient Mo4+/Mo5+ sites, which exhibited high catalytic activities in propene metathesis at 300 K to produce an equimolar mixture of ethene and 2-butenes. The CO-photoreduced incomplete cubane Mo oxide cluster (II) exhibited higher activities and higher trans/cis ratios of 2-butenes in the reaction, compared with those on the photoreduced I.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00806907
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