Adsorption and Reactivity of 2,3-Dihydrofuran and 2,5-Dihydrofuran on Pd(111): Influence of the C=C Position on the Reactivity of Cyclic Ethers

High-resolution electron energy loss spectroscopy (HREELS) and temperature-programmed desorption (TPD) were used to study the adsorption and thermal chemistry of 2,3-dihydrofuran (2,3-DHF) and 2,5-dihydrofuran (2,5-DHF) on Pd(111). The results, paired with earlier computational results, indicate that 2,3-DHF and 2,5-DHF both adsorb on Pd(111) primarily via their respective olefin functional groups at low temperature (<170 K). Both molecules undergo dehydrogenation by 248 K to form species that produce furan in a reaction limited process above 300 K. The furan-producing intermediate intermediate can also undergo decomposition to form C3Hx and CO. In addition, benzene resulting from C-C coupling reactions is detected on the surface and as a desorption product from both species, at about 520 K. A key difference between the two species is that 2,3-DHF can be hydrogenated to produce tetrahydrofuran at about 330 K, whereas 2,5-DHF is more likely to dehydrogenate, producing furan in an additional low-temperature channel at similar to 320 K. The results point to the importance of the position of the olefin functional group in relation to the ether function in determining the reactivity of cyclic oxygenates.