Experimental and Theoretical Insights into the Active Sites on WO_x/Pt(111) Surfaces for Dehydrogenation and Dehydration Reactions

Abstract

The catalytic upgrading of biomass is an important step toward realizing renewable chemical production. Pt/WO x and the inverse catalyst, WO x /Pt, have been shown to be highly active and selective for the C−O bond scission of various biomassderived oxygenates. Yet, the nature of the active sites and detailed reaction mechanisms have not been well understood. In this study, carbon monoxide and isopropyl alcohol (IPA) have been used as probe molecules to study the active sites of WO x /Pt(111) model surfaces. Temperature-programmed desorption experiments identified two distinct active sites responsible for different reaction pathways: dehydrogenation over Pt sites and dehydration over WO x sites. High-resolution electron energy loss spectroscopy (HREELS) identified the surface reaction intermediates. In situ infrared reflection absorption spectroscopy and HREELS measurements confirmed the presence of hydroxyl groups on WO x , which were consumed upon the adsorption of IPA, suggesting that the hydroxyl groups were the active sites for IPA dehydration. Density functional theory (DFT) calculations further revealed the reaction mechanisms and activation barriers of the IPA dehydrogenation and dehydration reactions. The comparison of different in situ-generated hydroxyl groups on WO x by DFT calculations suggested that the most active sites for dehydration should be those with protons least strongly bound (site formation energy of −0.3 eV), with a dehydration activation barrier of 1.23 eV. The understanding from this study provides insights into the design of relevant metal/metal oxide catalysts for the upgrading of biomassderived oxygenates.

Full-spectrum nonmetallic plasmonic carriers for efficient isopropanol dehydration

“…5. Surface oxygen vacancies of plasmonic W 18 O 49 -NWs can absorb H 2 O molecules to form OH moieties as Brønsted acid sites which are active in catalyzing isopropanol dehydration for propylene 12,28 . When isopropanol molecules diffuse to the surface of W 18 O 49 -NWs, they are coordinated to OH groups by hydroxyl accepted a proton.…”

“…Gallium borates with Brønsted acid sites were reported to show 98.3% conversion of isopropanol to 100% propylene at 573 K 11 . Chen et al studied the active sites on the WO x /Pt (111) surface for the dehydration and dehydrogenation of isopropanol, demonstrating dominant dehydration reaction on W 3 O 9 clusters with an activation barrier of 1.23 eV 12 . However, all these reports showed that a high temperature was required to active the catalysts and that the reactions were associated with high activation barriers.…”

Highly basic and active ZnO–x% K2O nanocomposite catalysts for the production of methyl ethyl ketone biofuel

“…Another research team 68 postulated that there was a strong correlation between the selectivity of dehydrogenation of IPA and the redox couple species evaluated on LaCoO 3 catalyst. To support their proposed mechanism, Lin et al 69 employed density functional theory (DFT) to calculate the activation barrier of dehydrogenation and dehydration reactions of IPA over WO x /Pt (111) surfaces. In the case of 2B, we had previously attributed the dehydrogenation activity of NiO, whether pure or modified with K 2 O or F‐ions, during dehydrogenation of 2B to MEK to the presence of basic sites of varying strengths 33,34 .…”

Dynamic Formation of Brønsted Acid Sites over Supported WOx/Pt on SiO2 Inverse Catalysts─Spectroscopy, Probe Chemistry, and Calculations

“…The WO x /Pt catalysts were represented by W 3 O x trimers on a 5 × 4 Pt(111) slab following prior work by Lin et al DFT calculations were performed using the Perdew–Burke–Erzenhof exchange-correlation function as implemented in version 5.4 of the Vienna Ab initio Simulation Package (VASP) − with the projector augmented wave method (PAWs) used to describe core electrons. The plane-wave energy cutoff was set to 520 eV.…”