(732f) Adsorption and Reaction of Furfuryl Alcohol on Pt(111): A Comparison Study to Pd(111)

Biomass-derived compounds are highly functionalized, making them difficult to selectively upgrade into a desired product. This is because the functional groups interact with the surface, resulting in multiple and often uncontrolled adsorption geometries. Previous studies on Pd indicated that adsorption geometry of these oxygenates dictates product selectivity, where flat lying configurations result in higher production of decarbonylation products, which are undesired, and upright conformations favor C—O bond activation, producing the desired hydrodeoxygenation (HDO) products). It was shown that on Pd(111), high surface coverages of furfuryl alcohol lead towards increased selectivity towards the HDO product, methylfuran. However, the mechanism is poorly understood, hampering efforts to design better catalysts. HDO can proceed through two pathways, 1) a low-barrier direct transfer of H atoms between alcohol adsorbates and 2) a high-barrier H transfer via metal-bound H atoms. However, this direct H transfer is poorly understood, hampering efforts towards designing catalyst surfaces or processes that can capitalize on this low-barrier pathway.

In designing effective and efficient catalysts for HDO, both Pt and Pd must be considered due to their ability to activate H₂, which is necessary in HDO. However, little is known if Pt and Pd catalyze the reaction of these oxygenates in the same way. Our recent temperature programmed desorption (TPD) studies show that on Pt(111), furfuryl alcohol undergoes decarbonylation to furan, propylene, carbon monoxide, and hydrogen, as well as undergoes hydrodeoxgyenation to produce methylfuran and water. Furfuryl alcohol also undergoes an unexpected ring decomposition and reformation to produce benzene, which is likely formed via coupling of C₃ surface intermediates. Decarbonylation on Pt(111) occurs through two reaction pathways, surface hydrogen assisted decarbonylation and interadsorbate hydrogen assisted decarbonylation, whereas on Pd(111) furan incorporates only surface hydrogens. Conversely, deoxgyenation of furfuryl alcohol only occurs via a surface hydrogen assisted C—O bond breakage on Pt(111) while Pd(111) catalyzes the C—O bond through both the incorporation of surface hydrogrens and through an interadsorbate hydrogen exchange. The high-resolution electron energy loss spectroscopy (HREELS) studies revealed that furfuryl alcohol bound to the Pt(111) surface through the functional alcohol group, which facilitated increased C—O bond scission, at high surface coverages. These surface science results provide useful mechanistic insights for the reaction of furfuryl alcohol on Pt(111) and how it compares to Pd(111).