Active complexes on engineered crystal facets of MnOx–CeO₂ and scale-up demonstration on an air cleaner for indoor formaldehyde removal

Haiwei LI, Wing Kei HO, Junji CAO, Duckshin PARK, Shun-cheng LEE, Yu HUANG

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Abstract

Crystal facet-dominated surfaces determine the formation of surface-active complexes, and engineering specific facets is desirable for improving the catalytic activity of routine transition-metal oxides that often deactivate at low temperatures. Herein, MnOx–CeO₂ was synthetically administered to tailor the exposure of three major facets, and their distinct surface-active complexes concerning the formation and quantitative effects of oxygen vacancies, catalytically active zones, and active-site behaviors were unraveled. Compared with two other low-index facets {110} and {001}, MnOx–CeO₂ with exposed {111} facet showed higher activity for formaldehyde oxidation and CO₂ selectivity. However, the {110} facet did not increase activity despite generating additional oxygen vacancies. Oxygen vacancies were highly stable on the {111} facet, and its bulk lattice oxygen at high migration rates could replenish the consumption of surface lattice oxygen, which was associated with activity and stability. High catalytically active regions were exposed at the {111}-dominated surfaces, wherein the predominated Lewis acid–base properties facilitated oxygen mobility and activation. The mineralization pathways of formaldehyde were examined by a combination of in situ X-ray photoemission spectroscopy and diffuse reflectance infrared Fourier transform spectrometry. The MnOx–CeO₂-111 catalysts were subsequently scaled up to work as filter substrates in a household air cleaner. In in-field pilot tests, 8 h of exposure to an average concentration of formaldehyde after start-up of the air cleaner attained the Excellent Class of Indoor Air Quality Objectives in Hong Kong. Copyright © 2019 American Chemical Society.
Original languageEnglish
Pages (from-to)10906-10916
JournalEnvironmental Science & Technology
Volume53
Issue number18
Early online dateAug 2019
DOIs
Publication statusPublished - 2019

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Air cleaners
formaldehyde
Formaldehyde
Demonstrations
crystal
Oxygen vacancies
oxygen
Crystals
air
Oxygen
Carbon Monoxide
Photoelectron spectroscopy
X ray spectroscopy
Air quality
Oxides
Spectrometry
transition element
Transition metals
indoor air
Catalyst activity

Bibliographical note

Li, H., Ho, W., Cao, J., Park, D., Lee, S.-C., & Huang, Y. (2019). Active complexes on engineered crystal facets of MnOx–CeO₂ and scale-up demonstration on an air cleaner for indoor formaldehyde removal. Environmental Science & Technology, 53(18), 10906-10916. doi: 10.1021/acs.est.9b03197