Mechanochemical synthesis of TiO2/NiFe2O4 magnetic catalysts for operation under RF field

• Novel NiFe2O4–TiO2 composite magnetic catalysts have been prepared by mechanochemical synthesis.
• The synthesis time of 30 min provides the highest specific absorption rate (SAR) in RF heating.
• Formation of NiTiO3 phase during calcination decreases the SAR of the catalysts.
• High stability of the NiFe2O4–TiO2 catalyst was observed in a continuous amide bond synthesis under RF heating.

Composite NiFe2O4–TiO2 magnetic catalysts were prepared by mechanochemical synthesis from a mixture of titania supported nickel ferrite nanoparticles and P25 titania (Evonic). The former provides fast and efficient heating under radiofrequency field, while the latter serves as an active catalyst or catalyst support. The highest heating rate was observed over a catalyst prepared for a milling time of 30 min. The catalytic activity was measured over the sulfated composite catalysts in the condensation of aniline and 3-phenylbutyric acid in a stirred tank reactor and in a continuous RF heated flow reactor in the 140–170 °C range. The product yield of 47% was obtained over the sulfated P25 titania catalyst in the flow reactor.