Vapor-phase catalytic dehydration of lactic acid to acrylic acid over nano-crystalline cerium phosphate catalysts

Abstract

A series of cerium phosphate (CeP) catalysts were synthesized using precipitation method with varying Ce/P mole ratios ranging from 0.5 to 3.0 followed by calcination. The formation of cerium phosphate was confirmed by X-ray diffraction and FT-IR techniques. The catalysts were further characterized to understand the morphology, surface area by using transmission electron microscopy (TEM) and N2-sorption measurements. The acidic and basic sites were measured by CO2-TPD, NH3-TPD and ex situ pyridine FT-IR methods. These calcined CeP catalysts were employed for the dehydration of lactic acid (LA) to acrylic acid (AA) under vapor-phase reaction conditions. Among the catalysts examined, CeP catalyst with Ce/P mole ratio 2.5 (CeP(2.5)) was found to exhibit better catalytic performance with conversion of lactic acid ~100 and 64 % selectivity towards acrylic acid at optimized conditions. Time-on-stream experiments suggest that CeP(2.5) catalyst exhibited constant activity until 20 h after which a slight drop of conversion of lactic acid was noticed. The characterization studies of the spent catalysts using thermogravimetric (TG), CHNS analysis and FT-IR reveal the presence of carbonaceous species over the catalyst surface causing deactivation of the catalyst.