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

Abstract

Platinum-tungsten oxides are among the most studied metal−metal oxide pair catalysts for C−O hydrogenolysis reactions. The Brønsted acid density and synergy between Pt and WO x , especially in the inverse structure, are critical to reactivity and selectivity. However, a clear molecular-level understanding of the formation and dynamics of Brønsted acid sites (BAS) is lacking. Here, using in situ spectroscopic characterizations (Raman and FTIR), chemical probing (CO chemisorption and pyridine titration), density functional theory (DFT) calculations, and a model reaction (tert-butanol dehydration), we demonstrate the structural evolution of WO x species and associated BAS dynamics in various environments. In situ Raman and DFT calculations show that below monolayer coverage, the WO x species stay as isolated monomers on the SiO 2 support and W 3 O x trimers on Pt. The W 3 O x trimers on Pt are dynamic and 10× more active toward dehydration than the WO x species on the SiO 2 support. H 2 plays a complex role: at low temperatures (<473 K), it creates more BAS in the form of W 3 O 7 H on Pt by reversible hydrogen spillover, and at higher temperatures (>573 K), it partially reduces the W 3 O x . We further show that the inverse configuration allows changes in the BAS density via catalyst pretreatments. This study provides a strategy for tuning Brønsted acid density and regenerating sites by pretreatment and catalyst composition.

Tuning Interfacial Sites of WOx/Pt for Enhancing Reverse Water Gas Shift Reaction

“…As shown in Figure 1B, bare SiO 2 exhibited weak bands at ∼477, 594, and 800 cm −1 , assignable to D1 and D2 defect modes of tri-and tetra-cyclotrisiloxane as well as bridging Si−O−Si symmetrical stretching, respectively. 50,55 at 716 and 800 cm −1 corresponding to W−O−W stretching vibration were present for 2W/SiO 2 , indicating the formation of bulk WO 3 nanoparticles. 55 In contrast, these two bands were barely observable for 1W/SiO 2 , indicating the WO x species were dispersed completely at low W loadings.…”

“…50,55 at 716 and 800 cm −1 corresponding to W−O−W stretching vibration were present for 2W/SiO 2 , indicating the formation of bulk WO 3 nanoparticles. 55 In contrast, these two bands were barely observable for 1W/SiO 2 , indicating the WO x species were dispersed completely at low W loadings. A W density of 0.16 atoms•nm −2 on 1W/SiO 2 is significantly lower than 0.5 atoms• nm −2 for a monolayer coverage of WO 3 on SiO 2 .…”

Effect of Dynamic and Preferential Decoration of Pt Catalyst Surfaces by WOx on Hydrodeoxygenation Reactions

“…Two different step models, Pt(221) and Pt(553), were chosen to understand the effect of terrace width on WO x stability. Based on a recent phase diagram analysis of WO x domains on Pt(111), W 3 O 7 is considered a representative model structure for reduced WO x growth on metal surfaces. , Additional WO x models, including domains containing Brønsted acid sites ( e.g. , W 3 O x H), higher W-oxidation states, and select W 4 O x structures, were considered.…”

“…Based on a recent phase diagram analysis of WO x domains on Pt(111), 28 W 3 O 7 is considered a representative model structure for reduced WO x growth on metal surfaces. 15,29 Additional WO x models, including domains containing Brønsted acid sites (e.g., S4). The framework utilized to generate structures is discussed elsewhere, 32,33 and its adaptation is detailed in the Methods and Materials Section.…”

Rebalancing Hydrogenation and Dehydration Performances for Efficient Hydrodeoxygenation of Biomass Derivatives to Match Reaction Temperature-Induced Rate-Determining Step Switch

“…Being aware of this, we tend to unfold the catalyst design requirement for efficient HDO of biomass-derived oxygenated monomers which involves weak adsorption situations, rather than simply report an efficient HDO catalyst. As reported, W–OH–W present on tungsten oxide acts as BAS to facilitate the dehydration process, and its BAS can be generated in the following two ways: , (i) dissociated hydrogen species on the metal surface spill to adjacent WO x sites; (ii) heterolytic cleavage of H 2 on WO x forms W–OH and hydride. Here, we choose WO 3 as the target support to develop an oxophilic Fe-doped Pt/WO x multifunctional catalyst to elucidate the effect of different active sites on the main subreaction process during the HDO process.…”