| AVS 65th International Symposium & Exhibition | |
| Fundamental Discoveries in Heterogeneous Catalysis Focus Topic | Tuesday Sessions |
| Session HC+SS-TuA |
| Session: | A Tale of Two Scales: Catalytic Processes and Surface Science |
| Presenter: | Abinaya Sampath, University of Illinois at Urbana-Champaign |
| Authors: | A. Sampath, University of Illinois at Urbana-Champaign D.W. Flaherty, University of Illinois at Urbana-Champaign |
| Correspondent: | Click to Email |
Aromatic aldehydes constitute a significant weight fraction of bio-oil.Transition metal catalysts can hydrogenate these aldehydes using either gaseous H2 or organic donors to produce valuable chemicals that may replace conventional petroleum derivatives. Here, we study selective decarbonylation of aromatic aldehydes (furfural and benzaldehyde) over Ru(0001) and Px-Ru(0001) to determine how phosphorus introduces new reaction pathways, such as catalytic transfer hydrogenation (CTH) steps between organic reactants. The catalytic properties of Ru(0001) and Px-Ru(0001) were probed with temperature programmed reaction (TPR) of furfural, benzaldehyde, and isotopically labeled forms of furfural under ultra-high vacuum conditions with Ru(0001) single crystal. Px-Ru(0001) is formed by exposing Ru(0001) to 2.5 L of PH3 at 300 K followed by flash annealing to 1400 K. The treatment produces a surface with an atomic ratio of P: Ru of ~0.4, determined by Auger electron spectroscopy.
On P0.4-Ru(0001), ~68% of furfural adsorbed at 100 K decarbonylates to furan and CO, whereas on Ru(0001), furfural decomposes completely to CO, H2, and C-atoms. Similarly, benzaldehyde decarbonylates to benzene with a selectivity that is 12-fold greater over P0.4-Ru(0001) than on Ru(0001). Together, these results suggest that, P-modification of Ru(0001) results in selective decarbonylation of aromatic aldehydes. Charge transfer from Ru to P results in reduced electron back donation from Ru to the adsorbates, and causes adsorbates to interact more weakly with P0.4-Ru(0001) than with Ru(0001). These electronic modifications reduce the extent of dissociative reactions leading to selective decarbonylation of aromatic aldehydes, although ensemble effects may also contribute.
TPR of furfural on P0.4-Ru(0001), pre-covered with D* atoms, yields five times more per-hydrogenated furan (C4H4O) than mono-deuterated furan (C4H3DO), which demonstrates that the CTH does not involve chemisorbed H*-atoms. On P0.4-Ru(0001), TPR of isotopically labeled furfural (C4H3O-CDO) forms two furan isotopologues (C4H4O, and C4H3DO). In addition, C4H3DO formed desorbs at a temperature 20 K higher than C4H4O, which indicates that intermolecular H-transfer determines the rate of furan formation. The comparisons of labeled furan products show that these critical H-atoms originate from the furfural ring and the carbonyl group of furfural. Hence, P0.4-Ru(0001) is more selective for decarbonylation of aromatic aldehydes over Ru(0001), and the addition of phosphorus atoms facilitates CTH steps that do not occur on metallic Ru(0001).