The conversion of methyl lactate (ML) over sodium tripolyphosphate, a model catalyst derived from silica supported sodium polyphosphate, was studied systematically by quantum mechanical calculations using MP2 and B3LYP methods. The reaction profiles of ML and its reaction products, acrylic acid (AA), methyl acrylate (MA) and lactic acid (LA) via various reactions such as dehydration, decomposition, decarbonylation, hydrolysis and esterification has been determined with the catalyst. For each reaction, the intermediate and transition state as well as their energetics were calculated. Over the catalyst, the main consumption routes for ML were identified to be the direct decomposition to AA and methanol and decarbonylation to acetaldehyde (AD), methanol and carbon monoxide. Both of the above reactions start from the same reaction intermediate. The main route for the formation of MA was supposed to be via esterification of AA with methanol. The values of activation barriers also indicate that over the sodium polyphosphate catalyst conversion of ML to AA has a higher selectivity than that from LA to AA. (C) 2010 Elsevier B.V. All rights reserved.