Reaction pathways of the gas-phase deoxygenation of propionic acid in the presence of heteropoly acid and bifunctional metal-loaded heteropoly acid catalysts were investigated in a fixed-bed reactor at 250-400 degrees C in flowing H-2 or N-2. Silica-supported H3PW12O40 (HPW) and bulk acidic salt Cs2.5H0.5PW12O40 (CsPW), both in H-2 and in N-2, exhibited ketonisation activity between 250 and 300 degrees C to yield 3-pentanone. CsPW being more selective than HPW. At 400 degrees C, HPW and CsPW were active for decarbonylation and decarboxylation of propionic acid to yield ethene and ethane, respectively. Loading Pd or Pt onto CsPW greatly enhanced decarbonylation in flowing H-2 but had little effect in N-2. Similar performance exhibited Pd/SiO2 and Pt/SiO2, giving almost 100% selectivity to ethene in H-2. These results are consistent with hydrodeoxygenation of propionic acid on Pd and Pt, suggesting that hydrogenolysis of C C bond plays essential role. In contrast to the Pd and Pt catalysts, Cu catalysts, Cu/CsPW and Cu/SiO2, were both active in hydrogenation of C=O bond to yield propanal and 1-propanol. Turnover rates of propionic acid conversion on metal catalysts followed the order Pd > Pt > Cu for both CsPW-supported and silica-supported metal catalysts. (c) 2012 Elsevier B.V. All rights reserved.