Efficient and selective conversion of methyl lactate to acrylic acid using Ca3(PO4)2–Ca2(P2O7) composite catalysts

Calcium phosphate Ca3(PO4)2 and calcium pyrophosphate Ca2(P2O7) composite catalysts of different weight ratios were prepared by a slurry-mixing method. These composite catalysts were calcined at 500 °C in air and characterized by N2 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 Ca3(PO4)2–Ca2(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 Ca3(PO4)2–Ca2(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 Ca3(PO4)2–Ca2(P2O7) [50:50 wt%] composite catalyst has been attributed to moderate acid–base strength regulated with surface properties.

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► Ca3(PO4)2–Ca2(P2O7) [50–50 wt%] was an efficient catalyst in methyl lactate (ML) conversion.
► ML conversion (91%) resulted in the highest selectivity (80%) for acrylic acid (AA) and methyl acrylate (MA).
► Catalysts of moderate acid–base strength gave higher conversions and product selectivities.