Decoupling the Chemical and Mechanical Strain Effect on Steering the CO₂ Activation over CeO₂-Based Oxides: An Experimental and DFT Approach.

Content Provider	Europe PMC
Author	Polychronopoulou, Kyriaki AlKhoori, Sara AlBedwawi, Shaima Alareeqi, Seba Hussien, Aseel G. S. Vasiliades, Michalis A. Efstathiou, Angelos M. Petallidou, Klito C. Singh, Nirpendra Anjum, Dalaver H. Vega, Lourdes F. Baker, Mark A.
Copyright Year	2022
Abstract	Doped ceria-based metal oxides are widely used as supportsandstand-alone catalysts in reactions where CO2 is involved.Thus, it is important to understand how to tailor their CO2 adsorption behavior. In this work, steering the CO2 activationbehavior of Ce–La–Cu–O ternary oxide surfacesthrough the combined effect of chemical and mechanical strain wasthoroughly examined using both experimental and ab initio modelingapproaches. Doping with aliovalent metal cations (La3+ orLa3+/Cu2+) and post-synthetic ball milling wereconsidered as the origin of the chemical and mechanical strain ofCeO2, respectively. Experimentally, microwave-assistedreflux-prepared Ce–La–Cu–O ternary oxides wereimposed into mechanical forces to tune the structure, redox ability,defects, and CO2 surface adsorption properties; the latterwere used as key descriptors. The purpose was to decouple the combinedeffect of the chemical strain (εC) and mechanicalstrain (εM) on the modification of the Ce–La–Cu–Osurface reactivity toward CO2 activation. During the abinitio calculations, the stability (energy of formation, EOvf) of different configurationsof oxygen vacant sites (Ov) was assessed under biaxialtensile strain (ε > 0) and compressive strain (ε <0), whereas the CO2-philicity of the surface was assessedat different levels of the imposed mechanical strain. The EOvf values were foundto decrease with increasing tensile strain. The Ce–La–Cu–O(111)surface exhibited the lowest EOvf values for the single subsurface sites, implying thatOv may occur spontaneously upon Cu addition. The mobilityof the surface and bulk oxygen anions in the lattice contributingto the Ov population was measured using 16O/18O transient isothermal isotopic exchange experiments; themaximum in the dynamic rate of 16O18O formation, Rmax(16O18O), was 13.1and 8.5 μmol g–1 s–1 forpristine (chemically strained) and dry ball-milled (chemically andmechanically strained) oxides, respectively. The CO2 activationpathway (redox vs associative) was experimentally probed using insitu diffuse reflectance infrared Fourier transform spectroscopy.It was demonstrated that the mechanical strain increased up to 6 timesthe CO2 adsorption sites, though reducing their thermalstability. This result supports the mechanical actuation of the “carbonate”-boundspecies; the latter was in agreement with the density functional theory(DFT)-calculated C–O bond lengths and O–C–O angles.Ab initio studies shed light on the CO2 adsorption energy(Eads), suggesting a covalent bondingwhich is enhanced in the presence of doping and under tensile strain.Bader charge analysis probed the adsorbate/surface charge distributionand illustrated that CO2 interacts with the dual sites(acidic and basic ones) on the surface, leading to the formation ofbidentate carbonate species. Density of states (DOS) studies revealeda significant Eg drop in the presenceof double Ov and compressive strain, a finding with designimplications in covalent type of interactions. To bridge this studywith industrially important catalytic applications, Ni-supported catalystswere prepared using pristine and ball-milled oxides and evaluatedfor the dry reforming of methane reaction. Ball milling was foundto induce modification of the metal–support interface and Nicatalyst reducibility, thus leading to an increase in the CH4 and CO2 conversions. This study opens new possibilitiesto manipulate the CO2 activation for a portfolio of heterogeneousreactions.
ISSN	19448244
Journal	ACS Applied Materials & Interfaces
PubMed Central reference number	PMC9335529
Issue Number	29
PubMed reference number	35820019
e-ISSN	19448252
DOI	10.1021/acsami.2c05714
Language	English
Publisher	American Chemical Society
Publisher Date	2022-07-12
Access Restriction	Open
Rights License	Permits the broadest form of re-use including for commercial purposes, provided that author attribution and integrity are maintained (https://creativecommons.org/licenses/by/4.0/). © 2022 The Authors. Published by American Chemical Society
Subject Keyword	mechanochemistry ball milling surface tuning strain engineering CO2 activation ceria oxygen vacancies ternary oxides DFT DRM DRIFTS
Content Type	Text
Resource Type	Article
Subject	Nanoscience and Nanotechnology Medicine Materials Science