Hydroxyalkylation of Phenol with Formaldehyde to Bisphenol F Catalyzed by Keggin Phosphotungstic Acid Encapsulated in Metal–Organic Frameworks MIL-100(Fe or Cr) and MIL-101(Fe or Cr)

Hydroxyalkylation of phenol with formaldehyde to bisphenol F was investigated over the metal–organic frameworks of MIL-100(Fe or Cr) and MIL-101(Fe or Cr) encapsulated with Keggin phosphotungstic acid (PTA). PTA@MIL-100(Fe or Cr)(β) and PTA@MIL-101(Fe or Cr)(β) with different β values (the molar ratio of W/M, where M = Fe or Cr) were prepared and characterized by XRD, BET, FT-IR, TG, SEM, TEM, and ICP. The research results showed that PTA@MIL-100(Fe or Cr)(β) had a higher catalytic activity than PTA@MIL-101(Fe or Cr)(β). PTA@MIL-100(Fe)(0.4) was the most effective among the studied catalysts and had excellent reusability. A 92.12% product yield and 93.01% selectivity for bisphenol F could be obtained over the PTA@MIL-100(Fe)(0.40) catalyst. The effects of the reaction time, reaction temperature, catalyst concentration, and phenol/formaldehyde molar ratio on the reaction performance were also investigated. A plausible mechanism for hydroxyalkylation of phenol with formaldehyde to bisphenol F was proposed.