In the present endeavor, amorphous cerium phosphate (CP) and thorium phosphate (TP) have been synthesized by the sol-gel method. Further, CP and TP also have been synthesized under microwave irradiation to yield CPM and TPM. The materials have been characterized for elemental analysis (inductively coupled plasma-atomic emission spectrometry, ICP-AES), spectral analysis (Fourier transform infrared spectroscopy, FTIR), thermal analysis (TGA), X-ray diffraction studies, scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis, Brunauer-Emmett-Teller (BET) surface area analysis, and surface acidity (NH3-temperature programmed desorption (TPD)). Chemical stability of the materials in various acids, bases, and organic solvent media has been studied, and their potential use as solid acid catalysts has been explored by studying acetal formation. A simple, efficient, and highly eco-friendly protocol is described for the acetalization of benzaldehyde, cyclohexanone, acetophenone and benzophenone with pentaerythritol by varying parameters such as reaction time, catalyst amount, and mole ratio of the reactants. The catalytic activity of CP, TP, CPM, and TPM has been compared and correlated with surface properties of the materials.