Ultra-Fine CeO2 Particles Triggered Strong Interaction with LaFeO3 Framework for Total and Preferential CO Oxidation

Unraveling the formation of oxygen vacancies on the surface of transition metal-doped ceria utilizing artificial intelligence

Ceria has been extensively utilized in different fields, with surface oxygen vacancies playing a central role. However, versatile oxygen vacancy regulation is still in its infancy. In this work, we propose an effective strategy to manipulate the oxygen vacancy formation energy via transition metal doping by combining first-principles calculations and analytical learning. We elucidate the underlying mechanism driving the formation of oxygen vacancies using combined symbolic regression and data analytics techniques. The results show that the Fermi level of the system and the electronegativity of the dopants are the paramount parameters (features) influencing the formation of oxygen vacancies. These insights not only enhance our understanding of the oxygen vacancy formation mechanism in ceria-based materials to improve their functionality but also potentially lay the groundwork for future strategies in the rational design of other transition metal oxide-based catalysts.

Mechanistic Insight into Catalytic Combustion of Ethyl Acetate on Modified CeO2 Nanobelts: Hydrolysis-Oxidation Process and Shielding Effect of Acetates/Alcoholates

In this study, based on the comparison of two counterparts [Mn- and Cr-modified CeO₂ nanobelts (NBs)] with the opposite effects, some novel mechanistic insights into the ethyl acetate (EA) catalytic combustion over CeO₂-based catalysts were proposed. The results demonstrated that EA catalytic combustion consisted of three primary processes: EA hydrolysis (C-O bond breakage), the oxidation of intermediate products, and the removal of surface acetates/alcoholates. Rapid EA hydrolysis typically occurs on surface acid/base sites or hydroxyl groups, and the removal of surface acetates/alcoholates resulting from EA hydrolysis is considered the rate-determining step. The deposited acetates/alcoholates like a shield covered the active sites (such as surface oxygen vacancies), and the enhanced mobility of the surface lattice oxygen as an oxidizing agent played a vital role in breaking through the shield and promoting the further hydrolysis-oxidation process. The Cr modification impeded the release of surface-activated lattice oxygen from the CeO₂ NBs and induced the accumulation of acetates/alcoholates at a higher temperature due to the increased surface acidity/basicity. Conversely, the Mn-substituted CeO₂ NBs with the higher lattice oxygen mobility effectively accelerated the in situ decomposition of acetates/alcoholates and facilitated the re-exposure of surface active sites. This study may contribute to a further mechanistic understanding into the catalytic oxidation of esters or other oxygenated volatile organic compounds over CeO₂-based catalysts.

Keys Unlocking Redispersion of Reactive PdOx Nanoclusters on Ce-Functionalized Perovskite Oxides for Methane Activation

Nowadays, trace CH₄ emitted from vehicle exhausts severely threaten the balance of the ecology system of our earth. Thereby, the development of active and stable catalysts capable of methane conversion under mild conditions is critical. Here, we present a convenient method to redisperse catalytically inert PdO nanoparticles (NPs) (>10 nm) into reactive PdO_x nanoclusters (∼2 nm) anchored on a Ce-doped LaFeO₃ parent. Isothermally activated in an N₂ flow, the redispersed catalyst achieved a CH₄ conversion of 90% at 400 °C, which is significantly higher than the fresh and H₂- and O₂-treated counterparts (625, 616, and 641 °C, respectively), indicating the importance of the gas atmosphere in the redispersion of PdO NPs. In addition, the comprehensive catalyst characterizations demonstrated that the isolated Ce ions in the perovskite lattice play an irreplaceable role in the redispersion of reactive sites and the reduction of the energy barrier for C-H scission. More importantly, the Ce additive helps to stabilize the PdO_x species by reducing overoxidation, resulting in significant lifetime extension. Through a thorough understanding of structural manipulation, this study sheds light on the design of highly performing supported catalysts for methane oxidation.

Deep Insight into the Mechanism of Catalytic Combustion of CO and CH4 over SrTi1-xBxO3 (B = Co, Fe, Mn, Ni, and Cu) Perovskite via Flame Spray Pyrolysis

Perovskites have been recognized as affordable substitutes for noble-metal catalysts for their tunable catalytic activity and thermal stability. Nevertheless, the highly demanding synthesis procedure still hinders the application of perovskites in catalytic combustion. In this work, a series of nanostructured SiTiO3 perovskites with B-site partial substitution by Co, Fe, Mn, Ni, and Cu are synthesized via flame spray pyrolysis in one step. The comprehensive characterizations on textural properties of nanostructured perovskites reveal that the flame-made perovskite nanoparticles all exhibit high crystal purity and large specific surface area (∼40 m2/g). Furthermore, the highest catalytic activity is achieved by SrTi0.5Co0.5O3 due to the formation of favorable oxygen vacancies, outstanding reducibility, and oxygen desorption capability. Additionally, the presence of 10 vol % water vapor during long-term testing indicates remarkable durability and water resistance. Finally, the CO oxidation and CH4 dehydrogenation on SrTiO3 incorporating Co atoms are more thermodynamically and kinetically favorable than those on other doped surfaces.

Enhanced Catalytic Activity Induced by the Nanostructuring Effect in Pd Decoration onto Doped Ceria Enabling an Origami Paper Analytical Device for High Performance of Amyloid-β Bioassay

In this work, we fabricated a novel origami paper-based analytical device (oPAD) assisted by the nanostructuring effect of in situ Pd decoration of Cu/Co-doped CeO₂ (CuCo-CeO₂-Pd) nanospheres, functionalized with their strongly enhanced electrocatalytic properties to realize an electrochemical and visual signal readout system in oPAD, for highly sensitive detection of amyloid-β (Aβ). The CuCo-CeO₂-Pd nanospheres were introduced as an enhanced "signal transducer layer" on account of the electron transfer acceleration caused by catalyzing glucose to produce H₂O₂ for differential pulse voltammetry signal readout and further 3,3'5,5'-tetramethylbenzidine (TMB) oxidation for colorimetric analysis. Meanwhile, for achieving superior performance of the proposed oPAD, in situ growth of urchin-like gold nanoparticles (Au NPs) onto cellulose fibers was adopted to improve "the recognition layer" in favor of immobilizing antibodies for targeting Aβ through specific antigen-antibody interactions. Combined with the delicate design of oPAD, exhibiting actuation of the conversion procedure between hydrophobicity and hydrophilicity on paper tabs in the assay process, the oPAD successfully enabled sensitive diagnosis of Aβ in a linear range from 1.0 pM to 100 nM with a limit of detection of 0.05 pM (S/N = 3) for electrochemical detection, providing a reliable strategy for quantifying the Aβ protein in clinical applications.

Gold Nanoparticles on Nanosheets Derived from Layered Rare-Earth Hydroxides for Catalytic Glycerol-to-Lactic Acid Conversion

Layered rare-earth hydroxides (LREHs), as a series of special lamellar compounds having a similar structure to layered double hydroxides (LDHs), are becoming a new type of catalyst materials. In this study, we have prepared a series of uniform LREH (RE = Y, La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, and Tm) nanosheets through a reverse-microemulsion method. After deposition-precipitation of HAuCl₄ and calcination, supported Au catalysts (denoted as Au/LREO) were subsequently obtained. The catalytic properties of all the derived Au/LREO catalysts were evaluated by aerobic conversion of glycerol to lactic acid under mild conditions (90 °C, 1 atm). Among these catalysts, Au/LPrO displays the best performances, including the highest glycerol conversion, lactic acid, and C₃ product selectivity. Both the catalytic activities and the characterizations of the structure of Au/LREO indicate that the kind of rare-earth ions plays a key role in determining the Au particle size and its valence state and reducibility, which are the important factors correlated with the catalytic activities in glycerol conversion. In fact, the three features of gold particles, the extra-small size (∼3 nm), high content of Au⁰ species, and high reducibility, are the essential prerequisites for achieving the superior catalytic performance of Au/LPrO.