Deoxygenation of propionic acid on heteropoly acid and bifunctional metal-loaded heteropoly acid catalysts: Reaction pathways and turnover rates

Abstract

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°C in flowing H2 or N2. Silica-supported H3PW12O40 (HPW) and bulk acidic salt Cs2.5H0.5PW12O40 (CsPW), both in H2 and in N2, exhibited ketonisation activity between 250 and 300°C to yield 3-pentanone, CsPW being more selective than HPW. At 400°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 H2 but had little effect in N2. Similar performance exhibited Pd/SiO2 and Pt/SiO2, giving almost 100% selectivity to ethene in H2. These results are consistent with hydrodeoxygenation of propionic acid on Pd and Pt, suggesting that hydrogenolysis of CC 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 CO 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.