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 C₃H_x 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 ∼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.