Tuning surface composition of Cs exchanged phosphomolybdic acid catalysts in C[sbnd]H bond activation of toluene to benzaldehyde at room temperature

Abstract

A series of Cs exchanged phosphomolybdic (PMA) catalysts were synthesised by the ion exchange method. The prepared materials were characterized by various physico-chemical techniques such as X-ray diffraction, FT-IR, Raman spectroscopy, pyridine adsorbed FT-IR spectroscopy, 31P NMR, BET surface area, nitrogen isotherms, TEM and STEM analysis. XRD results show crystallites of the Keggin ion of heteropolyacid catalysts. FT-IR and Raman spectra data reveal that the Keggin structure of PMA catalyst is maintained even after the exchange of the protons with Cs ions. Pyridine adsorbed FT-IR spectra show that available Brønsted acidic sites increases after Cs is incorporated in PMA. TEM analysis shows that the spherical shape remains intact after Cs exchange and STEM analysis shows a uniform distribution of elements in the Cs exchanged PMA catalyst. Nitrogen isotherms studies reveal a type IV isotherms for the Cs exchanged catalyst. The Cs exchanged phosphomolybdic acid (CsPMA) showed better catalytic performance than the phosphomolybdic acid (PMA) catalyst when evaluated for the CH bond activation of toluene to benzaldehyde. The catalyst was easily recovered and reused for five cycles with stable activity.