Complete CO Oxidation by O₂ and H₂O over Pt–CeO_2−δ/MgO Following Langmuir–Hinshelwood and Mars–van Krevelen Mechanisms, Respectively

Abstract

CO oxidation has attracted great attention in the automobile exhaust treatment and fuel cell industrial process, with Pt as one of the most promising catalysts. The efficiency of the catalyst is still below the requirement of the industry due to limited understanding about the reaction mechanism of CO oxidation by O2 or H2O, which were proposed to be following the similar/same reaction mechanism (the Mars–van Krevelen reaction mechanism). Our recent results indicate that this assumption might not be correct. Here, we design a catalyst with a combination of isolated platinum atoms (Pt1) and nanoparticles (Ptn) supported on MgO-dispersed CeO2−δ (CeO2−δ/MgO), named as 0.5Pt–xCeO2−δ/MgO (x = 0, 1, 2, 5, 10, 20) to establish two types of active sites, one is solely over Pt NPs (type-I) and the other is at the interface between Pt atoms and the reducible metal oxide support CeO2−δ (type-II), and we perform kinetic, thermodynamic, and in situ spectroscopy analysis on this catalyst to prove that CO oxidation by O2 undergoes the Langmuir–Hinshelwood reaction mechanism on type-I sites (Pt NPs), while water–gas shift (WGS) reaction undergoes the Mars–van Krevelen reaction mechanism at the interface between Pt atoms and the reducible support CeO2−δ (type-II) verified by activation energy assessment and the reactant and product pressure dependency studies applied, in which a systematic reduction of the reaction barrier of CO oxidation (by O2) was obtained once the size of Pt NPs increased and was independent of the changes in the size of CeO2−δ, while the reaction barrier of the WGS was very sensitive to the size of CeO2−δ and slightly inert against the size of Pt NPs. Additionally, there is competitive adsorption between CO and O2 over Pt–CeO2−δ/MgO, while there is no competitive adsorption between CO and H2O based on our pressure dependency studies. Collectively, our current work provides convincing evidence that the promotion of H2O on CO oxidation is the change of the reaction mechanism rather than the simple effect of hydroxyl dissociated by H2O dosing.

Weakening the Metal–Support Interactions of M/CeO2 (M = Co, Fe, Ni) Using a NH3-Treated CeO2 Support for an Enhanced Water–Gas Shift Reaction

“…The intensity of the oxygen defect peak gradually declined with an increase of temperature, also meaning that oxygen vacancies decreased. The decrease of oxygen vacancies might weaken the interaction between the Co species and CeO 2 support. − Figure d shows the XPS results of Co 2p in four catalysts. The Co 2p binding energy increased by 0.62 eV from Co/CeO 2 to Co/800N-CeO 2 .…”

Metal Oxide-Stabilized Hetero-Single-Atoms for Oxidative Cleavage of Biomass-Derived Isoeugenol to Vanillin

“…Single-atom (SA) catalysts draw intense research interest in heterogeneous catalysis due to their fascinating properties including high atom utilization, well-defined active centers, and designable electronic structures. − Uniform SA sites featuring homogeneous electronic properties endow the entire SA catalysts with fantastic performances in a variety of reactions. According to the previous reports, some noble metal SA catalysts (e.g., Ir, Pd, and Ru) exhibit attractive performances in both hydrogenation and oxidation reactions. − Also, metal oxides have been widely utilized as supports for the immobilization of SAs due to their strong metal–oxygen bonds and high electronic conductivity that could facilitate the modulations of the electronic properties of SA sites. − …”

Who Does the Job? How Copper Can Replace Noble Metals in Sustainable Catalysis by the Formation of Copper–Mixed Oxide Interfaces

“…Controlling this exsolution by exploiting the properties of the entire perovskite entity and the individual building blocks allows for direct steering of the interfacial properties of the resulting metal–oxide or metal–mixed-oxide material. The so-formed interfaces derived from perovskites usually combine two beneficial mechanistic aspects: the oxygen-vacancy chemistry of the oxide promoting dissociation of O-containing gas-phase molecules − and the metal–d-band structure fulfilling proper adsorption chemistry for the activation or release of selected gas-phase species. ,, Thereby, both the oxide and metallic constituents can be tuned by dopants to change the oxygen-vacancy reactivity ,, or to alter the d-band structure , and thus the adsorption properties.…”