Deoxygenation of Ethers and Esters over Bifunctional Pt-Heteropoly Acid Catalyst in the Gas Phase

Deoxygenation and decomposition of ethers and esters, including anisole, diisopropyl ether (DPE), and ethyl propanoate (EP), was investigated using bifunctional metal–acid catalysis at a gas–solid interface in the presence and absence of hydrogen. The bifunctional catalysts studied comprised Pt, Ru, Ni, and Cu as the metal components and Cs2.5H0.5PW12O40 (CsPW), an acidic Cs salt of Keggin-type heteropoly acid (HPA) H3PW12O40, as the acid component, with the main focus on Pt–CsPW catalyst. It was found that bifunctional metal–acid catalysis in the presence of H2 is more efficient for ether and ester deoxygenation than the corresponding monofunctional metal and acid catalysis and that metal- and acid-catalyzed pathways play different roles in these reactions. With Pt-CsPW, hydrodeoxygenation of anisole, a model for the deoxygenation of lignin, occurred with 100% yield of cyclohexane under very mild conditions (60–100 °C and 1 bar of H2). This catalyst had the highest activity in anisole deoxygenation for a gas-phase catalyst system reported so far. The catalyst activity decreased in the order of metals: Pt ≫ Ru > Ni > Cu. For HPA-catalyzed DPE and EP decomposition, relationships between the turnover reaction rate (turnover frequency) and the HPA acid strength were found, which can be used to predict the activity of acid catalysts in these reactions