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Confined Single Alkali Metal Ion Platform in a Zeolite Pore for Concerted Benzene C–H Activation to Phenol Catalysis

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journal contribution
posted on 13.11.2018, 00:00 by Shilpi Ghosh, Shankha S. Acharyya, Takuma Kaneko, Kotaro Higashi, Yusuke Yoshida, Takehiko Sasaki, Yasuhiro Iwasawa
The well-known cumene process via an explosive cumene hydroperoxide intermediate in liquid phase currently employed for phenol production is energy-intensive and not environmentally friendly. Therefore, there is a demand for an alternative single-step gas-phase catalysis process. According to the conventional catalysis concept, selective oxidation reactions are promoted by redox catalysts and not by acid–base catalysts. In general, alkali and alkaline earth metal ions cannot activate each of benzene, O2, and N2O when they adsorb separately. However, we observed an unprecedented catalysis of single alkali and alkaline earth metal ion sites incorporated into zeolite pores for the selective oxidation of benzene to phenol with N2O and O2 + NH3, thereby providing a single-site catalytic platform with high selectivity. Among alkali and alkaline earth metal ions, single Cs+ and Rb+ sites with ion diameters of >300 pm in the pores of β-zeolites exhibited remarkable selectivity for benzene C–H activation to phenol catalysis in a concerted reaction pathway.