Active Sites in Fe-exchanged Zeolites and Catalysis of Benzene Hydroxylation to Phenol
Affiliation: College of Resources and Environment & Chongqing Key Laboratory of Soil Multi-scale Interfacial Process, Southwest University, Chongqing 400715, China.
Keywords: Active site, Activation barrier, Benzene hydroxylation, Reaction mechanism, Zeolite framework.
Fe-exchanged zeolites show great promise for the direct benzene hydroxylation to phenol, one of the most important
industrial chemicals. In this review, the recent achievements on the active sites and benzene hydroxylation have
been summarized and discussed. Firstly, the catalytic results that are assumed in absence of Fe ions are given; secondly,
the indispensible role of Fe ions has been revealed. Four types of Fe-involved active sites reported so far have been elaborated,
and each type may correpond to a variety of active-site structures. Then the catalytic mechanisms of the mono- and
binuclear-Fe sites are sucessively exploited, which are found to be quite similar. The comprising Fe3+ ions are catalytically
unfavorable owing to the formation of specailly stable phenolate intermediates that result in deactivation to the catalysts.
The Fe2+ ions, whether in the mononuclear or binuclear sites, are potentially active for the catalytic reaction. Finally,
a brief concluding remark is presented listing some unresolved problems that may seriously impede this catalytic reaction
on an industrial scale.
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