Electronic Metal–Support Interactions in the Activation of CO Oxidation over a Cu/TiO₂ Aerogel Catalyst

Abstract

Carbon monoxide (CO) oxidation is not only an important industrial reaction but also a useful model system for investigations into reaction dynamics involving new catalyst designs. In this work, we use CO oxidation to probe the metal−support interactions between Cu nanoparticles and a TiO2 aerogel support. We utilized a packed-bed reactor to demonstrate the activity of a Cu/TiO2 aerogel catalyst for CO oxidation at temperatures above 463 K. In situ infrared spectroscopic methods revealed that the reaction proceeds primarily by a Cu-assisted Mars-van-Krevelen type mechanism. Results indicate that Ti4+ sites are reduced by CO to generate Ti3+ sites adjacent to oxygen vacancies. Lattice oxygen extraction appears to be accompanied by interfacial charge transfer from lower work function copper nanoparticles to the TiO2 support, as evidenced by variable-temperature infrared spectroscopic studies of adsorbed CO. The charge transfer is evidenced by differences in the nature of CO bound to Ti4+ sites within aerogels in the presence and absence of Cu. The Cu particles on the TiO2 support lower the vibrational frequency for CO bound to Ti4+ sites by 3 cm–1 and increase the binding enthalpy by 7 kJ/mol. Infrared spectroscopic probes of oxidation state cycling during catalysis contribute toward the development of an overall CO oxidation reaction mechanism on the Cu/TiO2 aerogel.

CO Oxidation at Near-Ambient Temperatures over TiO2-Supported Pd-Cu Catalysts: Promoting Effect of Pd-Cu Nanointerface and TiO2 Morphology

“…It is well-known that Ti 3+ formation on the reducible TiO 2 contributes to the formation of the oxygen vacant sites [ 8 , 69 ]. We suggest in our study that CO-oxidation proceeds on Pd-Cu/TiO 2 catalyst by Mars-van Krevelen mechanism.…”

Designing Oxide Aerogels With Enhanced Sorptive and Degradative Activity for Acute Chemical Threats

“…Figure 9A illustrates the synthesis of Cu/TiO 2 aerogels through photodeposition, with inset transmission electron micrographs showing the highly porous network structure. The TiO 2 aerogel provides a high surface area for CW agent adsorption, facilitates mass transport via the mesoporous network, and serves as a promoting support for catalytic/ plasmonic nanoparticles of Cu (DeSario et al, 2017;DeSario et al, 2019;Maynes et al, 2020;McEntee et al, 2020;DeSario et al, 2021) or Au (DeSario et al, 2013;Panayotov et al, 2013;Pennington et al, 2020;Rolison et al, 2020). Coupling TiO 2 to supported metal nanoparticles provides the dual benefits of enhancing dark and photo-driven degradation pathways.…”

“…McEntee et al characterized the hydrolytic degradation of DMMP on composite Cu/TiO 2 aerogels and Au/TiO 2 aerogels under aerobic and anaerobic conditions (McEntee et al, 2020). The Cu/TiO 2 aerogels prepared by photodepositing ∼3-5 nm diameter Cu nanoparticles (DeSario et al, 2017;DeSario et al, 2019;Maynes et al, 2020) exhibit significantly faster and more complete hydrolytic degradation of DMMP compared to Au/ TiO 2 or TiO 2 aerogels. After 1 h of exposure to DMMP vapor, only hydrolysis products are observed on the Cu/TiO 2 aerogel surface (McEntee et al, 2020).…”

“…In contrast, plasmonic applications for nonprecious and more abundant Cu are limited by its propensity to oxidize at the expense of its plasmon resonance. The intimate interfacial contact between photodeposited Cu nanoparticles and the TiO 2 aerogel stabilizes a high fraction of catalytically active Cu(0/I) and a sufficient amount of Cu(0) to maintain its plasmon resonance, unlike Cu nanoparticles photodeposited on larger, nanoparticulate TiO 2 supports (DeSario et al, 2017;DeSario et al, 2019;Maynes et al, 2020). Recent work with photodepositing Cu nanoparticles on ceria (CeO 2 ) aerogels finds retention of Cu plasmonic function and even higher catalytic activity for thermal oxidation of the model probe CO as compared to Cu/TiO 2 aerogel (Pitman, et al, 2020), pointing the way to another pore-solid oxide architecture with promise for the more challenging reactions necessary to remediate CW agents and TICs.…”

Reactivity of Pd–MO2 encapsulated catalytic systems for CO oxidation

“…One of the most studied reactions is CO oxidation, which has important practical application for pollution abatement and is a useful model reaction system for investigations of new catalyst designs. 1–10 Vast literature exists on different catalytic systems that have been explored to increase conversion of CO oxidation at lower temperatures for energy optimization. One strategy involves generating a bifunctional interface between precious metals (for example, Pt, Au, and Pd) and metal oxide supports (for example, TiO 2 , CeO 2 , Co 3 O 4 , NiO, Al 2 O 3 , SiO 2 , and ZrO 2 ).…”