CeO₂ Facet-Dependent Surface Reactive Intermediates and Activity during Ketonization of Propionic Acid

Abstract

CeO2 rods, octahedrons, and cubes exposing well-defined (110), (111), and (100) surfaces, respectively, were synthesized and investigated for the catalytic ketonization of propionic acid. The intrinsic ketonization rates at 350 °C on the rods, octahedrons, and cubes are 54.3, 40.4, and 25.1 mmol·m–2·h–1, respectively, indicating that the (110) facet is the most active surface for ketonization. The reaction was tracked by both in situ infrared and mass spectroscopies under transient conditions, and the results showed that monodentate propionate, a minority surface species, is responsible for the formation of 3-pentanone. In contrast, bidentate propionate, a dominant species on all three surfaces, appears to a spectator for ketonization. Moreover, the ketonization activity can be correlated with relative concentration of monodentate propionate. A density functional theory study showed that the relative concentration of monodentate propionate (or the adsorption energy difference between monodentate and bidentate configurations) at high coverages is strongly dependent on the surface geometry. The stability of monodentate propionate on the (110) surface exposing both the O and Ce sites in the outermost layer with the well-separated Ce sites exhibits little dependence on the propionate coverage. In contrast, strong steric hindrance due to the top layer O atom and the closely packed Ce atoms in (111) destabilizes monodentate propionate significantly at high coverages. This study demonstrates that the surface geometrical structure of CeO2 can determine the abundance of the active monodentate propionate, which, in turn, will determine the catalytic activity of CeO2 for ketonization.

Atomically Dispersed Palladium to Enhance the Propyne Semihydrogenation over CeO2 Catalysts

“…The O 1s XPS spectra show three peaks at 529.4, 531.3, and 532.0 eV (Figure b), which are assigned to lattice oxygen (O α : O – ), surface oxygen (O β : O 2– , O 2 2– /O – ), and weakly bound oxygen species (O γ ) such as CO 3 2– species, respectively. – The presence of O β species is indicative of the oxygen vacancies, and thus, the proportion of oxygen vacancies could be estimated by the ratio of O β /(O α + O β + O γ ) . The fraction of oxygen vacancies estimated for the Pd 0.025 /r-CeO 2 and Pd 0.1 /r-CeO 2 catalysts are 29.7 and 30.1%, respectively (Table S4), which are higher than those of Pd 2.0 /r-CeO 2 and r-CeO 2 .…”

Structure engineering of CeO2for boosting the Au/CeO2nanocatalyst in the green and selective hydrogenation of nitrobenzene

“…[20][21][22][23][24][25][26][27][28][29][30] CeO 2 has different morphologies with the exposure of different crystal planes. The crystal plane effect is an influential factor in many reactions; 31,32 for example, CO oxidation, [33][34][35][36][37] and the water-gas shift reaction, [38][39][40] and so on. Generally speaking, CeO 2 exposure to different crystal planes affects the formation energy of O vacancies, which can further regulate the interaction between the active metal and the CeO 2 support, as well as the electronic properties of the active metal centers.…”

Efficient Cu/CeO2 for Ketonization of Carboxylic Acids with Synergistic Interactions

“…Compared with other deoxygenation strategies, this reaction lengthens the carbon chain and promotes the combustibility of fuels without requiring H-donor molecules such as hydrodeoxygenation. Besides, platform chemicals like alkane and alkene can be produced from biofuels that contain oxygenated compounds, including carboxylic acids, phenols, and furans. − Moreover, the ketonization reaction is essential for reducing the side effects of carboxylic acids in biofuels, whose products can be further upgraded to increase the proportion of gasoline or diesel by aldol condensation, hydrogenation, etc. , 2 normalR normalC normalO normalO normalH → R 2 normalC normalO + normalC normalO 2 + H 2 normalO …”