Interface Reactions Dominate Low-Temperature CO Oxidation Activity over Pt/CeO₂

Abstract

First-principles-based kinetic Monte Carlo simulations and kinetic experiments are used to explore CO oxidation over Pt/CeO2. The simulations compare CO oxidation over a ceria-supported ∼1 nm particle with simulations of a free-standing particle and Pt(111). The onset of the CO oxidation over ceria supported Pt is shifted to lower temperatures compared to the unsupported systems thanks to a Mars–van Krevelen mechanism at the Pt/CeO2 interface perimeter, which is not sensitive to CO poisoning. Both the Mars–van Krevelen mechanism and the conventional Langmuir–Hinshelwood mechanism over the Pt nanoparticle are contributing to the conversion after the reaction onset. The reaction orders in CO and O2 are compared experimentally for Pt/CeO2 and Pt/Al2O3. The reaction orders over Pt/CeO2 are close to zero for both CO and O2, whereas the corresponding reaction orders are −0.75 and 0.68 over Pt/Al2O3. The measured zero orders for Pt/CeO2 show the absence of CO/O2 site competition and underline the relevance of interface reactions. The measurements for Pt/Al2O3 indicate that the main reaction path for CO oxidation over Pt is a conventional Langmuir–Hinshelwood reaction. The results elucidate the interplay between condition-dependent reaction mechanisms for CO oxidation over Pt supported on reducible oxides.

Pt Atomic Single-Layer Catalyst Embedded in Defect-Enriched Ceria for Efficient CO Oxidation

“…The CO oxidation rates on both Pt ASL /CA and Pt ASL /CA-e catalysts depended on the partial pressures of neither CO nor O 2 , indicating that there was no competitive adsorption between CO and O 2 because they should have different adsorption sites. Similar to previous reports on Pt–CeO 2 -based catalysts, ,, the CO oxidation on Pt ASL /CA and Pt ASL /CA-e followed the Mars-van Krevelen (MvK) mechanism, in which the CO adsorbed on Pt ASL sites could react with lattice oxygen from CeO 2 or Pt–O–Pt. In addition, compared to the positive reaction order for CO on Pt 1 sites, the zero-reaction order for CO on Pt ASL sites indicated again that the Pt ASL sites were more beneficial for CO adsorption.…”

Critical Step in the HCl Oxidation Reaction over Single-Crystalline CeO2–x(111): Peroxo-Induced Site Change of Strongly Adsorbed Surface Chlorine

“…These experiments are fully explained by this DFT study. The most important reaction intermediate for the reoxidation and dechlorination of Cl vac -CeO 2– x (111) turns out to be the peroxo species (O 2 2– ) that is stabilized in surface oxygen vacancies by ∼2 eV, in agreement with the previous theoretical works. ,,− Whenever an additional vacancy appears in the subsurface region directly below the peroxo species, the peroxo species dissociates and replenishes two oxygen vacancies. From the calculated activation energies, bulk reoxidation (0.80 eV) precedes the Cl vac → Cl top displacement step (1.04 eV).…”

“…Whenever an O 2 molecule from the gas phase strikes a surface oxygen vacancy (V O,S ), O 2 is strongly adsorbed by about 2 eV in the form of a peroxo-species (O 2 2– ) and pins the vacancy to the surface. The O–O bond length is 144 pm, which agrees well with a typical bond length of peroxide groups. , The oxidation state of oxygen in chemisorbed O 2 species is determined through several factors, including the count of the remaining Ce 3+ sites in the system after the formation of the O 2 species, the O–O bond length, magnetization, and Bader charges. Upon O 2 adsorption, the number of Ce 3+ is reduced by two per (3 × 3) cell, providing clear evidence of the formation of a peroxo species O 2 2– , with O in the oxidation state −1.…”

“…Superoxide (O 2 – ) and peroxide (peroxo: O 2 2– ) are known to be important oxygen species in catalytic oxidation reactions on ceria-based catalysts that were studied both experimentally and theoretically (see, e.g., ref. ,,,− ). In this work, we unveiled the crucial role of the peroxo species in the HCl oxidation reaction during the dechlorination process.…”

Unravelling the correlation of dielectric barrier discharge power and performance of Pt/CeO2catalysts for toluene oxidation

“…2,3 For catalytic oxidation of VOCs, most researchers recognized that they follow the Mars-van Krevelen (MvK) mechanism because oxygen vacancies participated in the activation of oxygen molecules and migration of active oxygen. 4,5 However, not all the oxygen vacancies and Pt atom active sites in the Pt/CeO 2 catalyst can be used effectively. In order to improve the performance of catalytic oxidation, the investigation of the Pt/CeO 2 catalyst's activity concentrated on increasing the number of oxygen vacancies and effective Pt atoms on the surface of CeO 2 .…”