Differentiating Surface Ce Species among CeO₂ Facets by Solid-State NMR for Catalytic Correlation

Abstract

Altering the exposed facet of CeO2 nanocrystallites and hence the control of surface chemistry on the nano level have been shown to significantly change their performances in various catalytic reactions. The chemical state of surface Ce, which is associated with Lewis acidity and hence the adsorption/activation energy of reactants on the surface, is expected to vary with their hosted facets. Unfortunately, traditional surface tools fail to differentiate/quantify them among hosted facets and thus have led to different interpretations among researchers in the past decades. Herein, probe-assisted nuclear magnetic resonance is employed for the surface investigation of different CeO2 facets. They not only allow differentiation of the surface Ce atoms between hosted facets at high resolution but can also provide their corresponding concentrations. The as-established facet fingerprint of CeO2 can thus report on the facet distribution/concentration of a given CeO2 sample. Dephosphorylation and H2O2 reduction were tested as probe reactions to demonstrate the importance of obtaining comprehensive surface Ce information for the active site identification and the rational design of CeO2-based catalysts. Around 1000 and 4500% increase in activity of those reactions can be easily achieved on pristine CeO2 without further surface engineering when its terminal facet is wisely chosen. Our results thus imply that the basic surface knowledge of even a simple catalyst can be more important than the continuous development of their fancy derivatives without clear guidance.

Electronic‐State Manipulation of Surface Titanium Activates Dephosphorylation Over TiO2 Near Room Temperature

“…The use of 31 P NMR with trimethylphosphine (TMP) as the probe molecule has been demonstrated by our group a promising method for the surface study of various metal oxides [30–33] . In general, the 31 P signal with chemical shift (δ 31 P) between 0 and −5 ppm can be attributed to the formation of TMPH + species due to the surface BA site, while the coordination of TMP to a surface cation can generate δ 31 P in a wider range from −20 to −60 ppm depending on its LA strength (or electron density) [34] .…”

Hot Electrons, Hot Holes, or Both? Tandem Synthesis of Imines Driven by the Plasmonic Excitation in Au/CeO2 Nanorods

“…We also studied the Au/CeO 2 and CeO 2 nanorods by 31 P-ssNMR analysis employing trimethylphosphine (TMP) as a surface probe. TMP is an electron donor molecule that can specifically form an adduct with surface Ce cation (i.e., TMP-Ce) [29]. In this case, the chemical shift of 31 P is expected to differentiate the strength of the adduct bond formed with various Ce acidities (or electron density) as the stronger surface Lewis acid site pushes δ 31 P to positive ppm [30].…”

“…Based on these results we would like to propose that the unique structure of the (110) surface facets in the CeO 2 nanorods ( Figure 3 A) allow first the adsorption of benzyl alcohol (via a deprotonation pathway) ( Figure 3 B). As Tamura and collaborators demonstrated, this deprotonation step does not depend on O 2 [ 6 ] and is easily accomplished by the Lewis acid (LA) sites on the CeO 2 (110) surface facet (i.e., Ce 4+ surficial species) [ 29 , 33 , 34 ]. Even under dark conditions some synergistic effect is observed for the Au/CeO 2 , the Au NPs promotes an increment from 62.5% (Entry 3) to 69.5% (Entry 5) for the imine formation.…”

Nanoisozymes: The Origin behind Pristine CeO2 as Enzyme Mimetics

“…The use of 31 PNMR spectroscopy with 31 P-containing molecules as surface probesh as been shown to be ap romising methodf or the surfaces tudy of metal oxides. [21][22][23][24][25][26][27] TMPO was selected herein, not only for the above purpose, but also to investigate the interaction between surface Ce and P=Oo fp-NPP by meanso f 31 PNMR spectroscopy (Figure 3d). The P=O group of TMPO can specifically bind to surfaceC ec ations (Lewis acid) throughL ewis acid-base interactions (i.e.,P =O!…”