Calcium phosphate Ca-3(PO4)(2) and calcium pyrophosphate Ca-2(P2O7) composite catalysts of different weight ratios were prepared by a slurry-mixing method. These composite catalysts were calcined at 500 degrees C in air and characterized by N-2 sorption for specific surface area by XRD for crystal phases and by TPD-NH3 (acidity), TPD-CO2 (basicity) and SEM for morphological features. All the Ca-3(PO4)(2)-Ca-2(P2O7) composite catalysts were found to be active in the vapor phase conversion of methyl lactate (ML) to give mainly acrylic acid (AA) and methyl acrylate (MA) as products. The catalyst Ca-3(PO4)(2)-Ca-2(P2O7) of 50:50 wt% ratio was the most efficient and selective catalyst in the conversion of ML. which gave 91% conversion of ML with selectivity for AA (75%) and MA (5%) together (80%) under optimized reaction conditions. The higher conversion of ML and formation of AA by Ca-3(PO4)(2)-Ca-2(P2O7) [50:50 wt%] composite catalyst has been attributed to moderate acid-base strength regulated with surface properties. (C) 2011 Elsevier B.V. All rights reserved.