Morphology‐Dependent Catalysis of CeO₂‐Based Nanocrystal Model Catalysts

Abstract

Comprehensive Summary Recent progress in colloidal synthesis has realized the preparations of uniform nanocrystal (NC) model catalysts with rich and well‐controlled morphologies that were employed to explore structure‐activity relationships of powder catalysts, similar to single‐crystal‐based model catalysts under ultrahigh vacuum conditions but can work at the same conditions as powder catalysts without the “materials gap” and “pressure gap”. In this perspective, the CeO2‐based NC model catalysts with various morphologies are included and their relevant progresses are critically reviewed. The detailed descriptions of morphology‐controlled synthesis and characterizations of uniform CeO2 NCs, and morphology‐dependent catalysis of CeO2‐based NC model catalysts containing pure CeO2 NCs, CeO2‐supported oxide catalysts, and CeO2‐supported metal catalysts, provide us a comprehensive cognition in CeO2‐involved catalytic reactions and also open up a new approach for the fundamental studies of complex heterogeneous catalysis. Finally, a concept of oxide‐based NC model catalysts and outlook of oxide NCs acting not only as model catalysts for the fundamental study but also as the support in tailoring structures and optimizing performance of oxide‐involved catalysts are discussed.

Decoupling the Interfacial Catalysis of CeO2-Supported Rh Catalysts Tuned by CeO2 Morphology and Rh Particle Size in CO2 Hydrogenation

“…According to Wulff’s rule, c-CeO 2 NCs with highly symmetric cubic morphologies are enclosed with {100} crystal planes. However, the {111} crystal planes are predominantly exposed on p-CeO 2 with irregular shapes, as evidenced by previous literature. − It could be controversial on the exposed crystal planes of r-CeO 2 NCs with less symmetric morphologies that depend on the preparation parameters such as the calcination temperature. , Based on previous detailed characterizations, it could be concluded that r-CeO 2 NCs calcined at 500 °C are mainly enclosed with both the {110} facets (top, bottom, and side) and the {100} facets (side). The Ce 3d XPS spectra together with vis- and UV-Raman spectra (Figure S2) clearly demonstrate both the total and the surface oxygen vacancy concentrations following the order r-CeO 2 > c-CeO 2 > p-CeO 2 , consistent with previous results. ,− …”

“…Second, the oxygen vacancy concentrations were qualitatively compared on the basis of the Raman and Ce 3d XPS spectra. In the Raman spectra (Figure C,D), two vibrational bands at around 465 and 593 cm –1 were observed, typically assignable to the F 2g and defect-induced mode (D) of the cubic fluorite CeO 2 phase, respectively. , It is noteworthy that the I D / I F2g values in both the vis-Raman (Figure C) and the UV-Raman (Figure D) spectra, respectively, used to evaluate the total and surface oxygen vacancy concentrations, − follow the order 2%Rh/r-CeO 2 > 2%Rh/c-CeO 2 ≫ 2%Rh/p-CeO 2 . This indicates that the oxygen vacancy concentrations over the 2%Rh/r-CeO 2 catalyst are always higher than those over 2%Rh/c-CeO 2 and 2%Rh/p-CeO 2 catalysts, consistent with the orders of pristine CeO 2 supports (Figure S2).…”

“…The relatively finer Rh NPs emerging on the 2%Rh/r-CeO 2 catalyst could arise from either larger surface areas (Table S1) or higher surface oxygen vacancy concentrations over the r-CeO 2 support (Figure S2) that is beneficial for the dispersion of supported Rh species, as per previously reported results. 27,41,47 It was found that the supported Rh NPs are randomly dispersed on three CeO 2 supports without preferentially enriched on one or two facets (Figures S3 and S4). Therefore, the CeO 2 morphologies with predominantly exposed one and/or two crystal planes determine the nature of Rh−CeO 2 interfaces.…”

“…Following previously established procedures, ,,− CeO 2 nanorods (r-CeO 2 ) and nanocubes (c-CeO 2 ) with well-controlled morphologies were prepared; nevertheless, CeO 2 nanopolydra (p-CeO 2 ) were purchased commercially and used without further purification. Both ICP-AES (Table S1) and Na 1s X-ray photoelectron spectroscopy (XPS) (Figure S1) results confirm the absence of Na in these CeO 2 NCs.…”

Adsorption of Molecules on Defective CeO2 for Advanced Catalysis

“…Among various metal oxides, the regulation of surface properties of CeO 2 has been widely explored for many important heterogeneous catalysts due to its reversible Ce 3+ /Ce 4+ redox pair associated with the tailorable structural defects of oxygen vacancy. − The rich surface chemistry of CeO 2 including Lewis acidic site, Lewis basic site, Bronsted acidic site, and oxygen vacancy provides an ideal platform to understand the significant influence of adsorption behavior on catalytic performance of CeO 2 -based heterogeneous catalysts. The regulation of surface properties of CeO 2 -based catalysts and their catalytic applications have been well summarized and illustrated in previous reviews. ,,,− …”