Widening Temperature Window for CO Preferential Oxidation in H₂ by Ir Nanoparticles Interaction with Framework Fe of Hexaaluminate

Abstract

It is important to develop an efficient noble-metal-based catalyst that has a wide work temperature window and good stability for CO preferential oxidation in H 2 (CO-PROX), a key step to purify industrial hydrogen resource. Herein, a catalyst of Fe-substituted hexaaluminatesupported Ir nanoparticles with a mean size of ∼1.4 nm (Ir/BaFeAl 11 O 19 ) is synthesized. It can exhibit total CO conversion for the CO-PROX reaction in an unprecedented temperature range from 20 to 200 °C, high stability, and good resistance to CO 2 and H 2 O in a simulated practical atmosphere. Detailed characterizations coupled with density functional theory (DFT) calculations show that the interaction between Ir species and framework Fe cations in mirror planes of hexaaluminate promotes the formation of a certain amount (8%) of Fe 2+ species for low-temperature CO oxidation, while the Ir species interacting with these Fe 2+ provide moderate CO bond strength that is critical to maintaining the preferential oxidation of CO rather than H 2 at high temperatures.

Enhanced Catalytic Performance of an Fe-Substituted La-Hexaaluminate Supported Ir Catalyst for N2O Decomposition

“…42,48 With the loading of Ir particles, the increase of lattice oxygen mobility can promote the generation of oxygen vacancies due to the MSI, and the reduction process in H 2 further promotes the formation of oxygen vacancies. 24,28,39 This has been proved by XRD, Raman spectroscopy, XPS, and 57 Fe Mossbauer spectroscopy in this paper, and the results of H 2 -TPR and O 2 -TPD in our previous work studied that as well. 24 Comparatively, the lattice oxygen is stable in Mgsubstituted hexaaluminates due to the substitution of Mg ions in Al(2) sites in the spinel planes of hexaaluminates.…”

“…The alterations in lattice oxygen typically facilitate the valence shift of the transition metal within the structure of hexaaluminate . The XPS spectra of Fe 2p are presented in Figure b, which could be divided into the peaks for Fe 3+ and Fe 2+ according to the literature. ,, The fresh sample contained part of Fe 2+ due to the formation of oxygen vacancies, as confirmed by 57 Fe Mössbauer spectroscopy. Fe 2+ decreased at 250 °C, accompanied by the increase of Fe 3+ at the same time.…”

“…The shift of binding energy in O 1s mainly occurred at 250 and 300 °C. Furthermore, these O 1s spectra were divided into different oxygen species: the lattice oxygen (O I ) in hexaaluminate (530.5–531.0 eV) and oxygen species (O II ) absorbed by oxygen vacancies (∼532 eV). − It could be found that O II species slightly decreased at 250 °C and a significant decrease was shown at 300 °C. There was no obvious variation for O II species at 350 °C.…”

Lattice Oxygen Lability of La-Hexaaluminates Substituted by Different Metals and Their Effects on the Thermal Stability of Supported Nano-Ir Particles

“…Furthermore, Figure shows the O1s and Fe2p spectra of LFA, Ir@LFA-br, and Ir@LFA-ar. According to the literature, − the spectra of O 1s and Fe 2p were divided into different species There was only lattice oxygen on LFA, and the oxygen species on Ir@LFA-br and Ir@LFA-ar can be divided into the lattice oxygen and oxygen vacancies. With the loading of Ir species and reduction, the ratio of the oxygen vacancies increased (Table ).…”

Dual Active Sites of CO Adsorption and Activation over PtCu Alloy Nanocages for Preferential Oxidation of Carbon Monoxide

“…Seeking catalysts that can fulfill activity, selectivity, and durability requirements in the CO-PROX reaction remains a significant challenge. Transition-metal catalysts exhibit poor stability despite excellent activity and selectivity. − Au-based catalysts are highly active at low temperatures but suffer from low selectivity due to the occurrence of competitive H 2 oxidation. − Pure Pt exhibits a lower activity than the above two types of catalysts below 100 °C, following the Langmuir–Hinshelwood (L–H) mechanism. The reason originates from the strong adsorption of CO on Pt sites, preventing the activation of O 2 at low temperatures .…”