光活性化酸化ニオブ触媒によるオレフィンの転換反応

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  • Olefin Conversion Reactions on Photoactivated Niobium Oxide Catalys
  • ヒカリ カッセイカ サンカ ニオブ ショクバイ ニ ヨル オレフィン ノ テン

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It has been found that niobium oxide is an effective catalyst under UV irradiation for converting olefin into other olefins. The niobium oxide catalyst supported on porous Vycor glass catalyzed propene metathesis under UV irradiation (Fig.1). The catalyst was also active for ethene dimerization, in which very high selectivity to 1-butene formation was observed (Fig.3). The catalyst was activated by UV irradiation in the presence of ethene, but not without ethene (Fig.2). When the catalyst was reduced in the presence of hydrogen either under UV irradiation or at high temperature, it was activated to catalyze ethene dimerization (Fig.4). Both metathesis and dimerization on the catalyst were poisoned when a little amount of oxygen gas was mixed in the reactant gas. The wavelength of UV light effective for the activation of the catalyst corresponded to the UV absorption spectrum of niobium(V) oxide (Table 1). It is therefore suggested that a certain reduced state produced from niobium (V) oxide by the photoreduction is active for both of the reactions. It was observed that the catalytic activity for propene metathesis and ethene dimerization individually depends in a different manner upon the amount of niobium loaded on the support (Fig.7). Therefore, the type of the active site for dimerization is different from that for metathesis. It has been suggested that metathesis proceeds in the same reaction mechanism as proposed for the propene photometathesis by molybdenum oxide, and dimerization was catalyzed by niobium(IV) species produced by the photoreduction of niobium(V) oxide in the presence of ethene. It was found that on the activated catalyst oligomerization of ethene proceeded as well as its dimerization, and also 1-butene was isomerized to 2-butenes (Figs.6, 8). It became clear that ethene dimerization and oligomerization proceeded on the niobium oxide supported on various supports (Figs.9, 10).

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