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, P-31 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 Bronsted 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 C-H bond activation of toluene to benzaldehyde. The catalyst was easily recovered and reused for five cycles with stable activity. (C) 2016 Elsevier B.V. All rights reserved.