Tunable Electronic Metal-Support Interactions on Ceria-Supported Noble-Metal Nanocatalysts in Controlling the Low-Temperature CO Oxidation Activity

High-Performance Ir1/CeO2 Single-Atom Catalyst for the Oxidation of Toluene

The elimination of toluene is an obligatory target with increasing VOC emission in recent years. This study successfully prepared a single-atom Ir catalyst (Ir1/CeO2) by a simple incipient wetness impregnation method, confirmed by in situ CO DRIFTS and AC-HAADF-STEM. Compared to the cluster Ir catalyst (Ir/CeO2-C), Ir1/CeO2 exhibited excellent catalytic performance, stability, and water resistance for the oxidation of toluene. By Raman, H2-TPR, O2-TPD, and XPS experiments, abundant oxygen defects and a unique Ir3+-Ov-Ce3+ structure were formed for the Ir1/CeO2 sample because it had a lower oxygen vacancy formation energy. Furthermore, the DFT results revealed that the Ir1/CeO2 sample had a lower ring-opening energy barrier and adsorption energy of the ring-opening products, which was the rate-determining step for the oxidation of toluene. This work provides instructive insights into the construction of Ir/CeO2 catalysts for the highly efficient removal of VOCs.

Boosting Polyethylene Hydrogenolysis Performance of Ru-CeO2 Catalysts by Finely Regulating the Ru Sizes

Hydrogenolysis is an effective method for converting polyolefins into high-value chemicals. For the supported catalysts commonly used, the size of active metals is of great importance. In this study, it is discovered that the activity of CeO2 -supported Ru single atom, nanocluster, and nanoparticle catalysts shows a volcanic trend in low-density polyethylene (LDPE) hydrogenolysis. Compared with CeO2 supported Ru single atoms and nanoparticles, CeO2 -supported Ru nanoclusters possess the highest conversion efficiency, as well as the best selectivity toward liquid alkanes. Through comprehensive investigations, the metal-support interactions (MSI) and hydrogen spillover effect are revealed as the two key factors in the reaction. On the one hand, the MSI is strongly related to the Ru surface states and the more electronegative Ru centers are beneficial to the activation of CH and CC bonds. On the other hand, the hydrogen spillover capability directly affects the affinity of catalysts and active H atoms, and increasing this affinity is advantageous to the hydrogenation of alkane species. Decreasing the Ru sizes can promote the MSI, but it can also reduce the hydrogen spillover effect. Therefore, only when the two effects achieve a balance, as is the case in CeO2 -supported Ru nanoclusters, can the hydrogenolysis activity be promoted to the optimal value.

Tuning Electron Transfer in Atomic-Scale Pt-Supported Catalysts for the Alkaline Hydrogen Oxidation Reaction

Developing efficient atomic-scale metal-supported catalysts is of great significance for energy conversion technologies. However, the precise modulation of electron transfer between the metal and supporter in atomic-scale metal-supported catalysts to further improve the catalytic activity is still a major challenge. Herein, we show tunable electron transfer between atomic-scale Pt and tungsten nitride/oxide supports (namely, Pt/WN and Pt/W₁₈O₄₉). Pt/WN with modest electron exchange and Pt/W₁₈O₄₉ with aggressive electron exchange exhibit notably different catalytic activities for the alkaline hydrogen oxidation reaction (HOR), in which Pt/WN shows a 5.7-fold enhancement in HOR intrinsic catalytic performance in comparison to Pt/W₁₈O₄₉. Additionally, the tunable electronic transfer at the interface of Pt/WN and Pt/W₁₈O₄₉, as proven by the theoretical calculation, resulted in the discrepancy of the adsorption free energy of the reaction intermediates, as well as catalytic activity, for the HOR process. Our work provides new insights into the design of advanced atomic-scale metal-supported catalysts for electrocatalysis.

Regulating the Pt-MnO2 Interaction and Interface for Room Temperature Formaldehyde Oxidation

Formaldehyde (HCHO) is a hazardous pollutant in indoor space for humans because of its carcinogenicity. Removing the pollutant by MnO₂-based catalysts is of great interest because of their high oxidation performance at room temperature. In this work, we regulate the Pt-MnO₂ (MnO₂ = manganese oxide) interaction and interface by embedding Pt in MnO₂ (Pt-in-MnO₂) and by dispersing Pt on MnO₂ (Pt-on-MnO₂) for HCHO oxidation over Pt-MnO₂ catalysts with trace Pt loading of 0.01 wt %. In comparison to the Pt-in-MnO₂ catalyst, the Pt-on-MnO₂ catalyst has a higher Brunauer-Emmett-Teller surface area, a more active lattice oxygen, more oxygen vacancy activating more dioxygen molecules, more exposed Pt atoms, and noninternal diffusion of mass transfer, which contribute to the higher HCHO oxidation performance. The HCHO oxidation performance is stable over the Pt-MnO₂ catalysts under high space velocity and high moisture humidity conditions, showing great potential for practical applications. This work demonstrates a more effective Pt-dispersed MnO₂ catalyst than Pt-embedded MnO₂ catalyst for HCHO oxidation, providing universally important guidance for metal-support interaction and interface regulation for oxidation reactions.

Dry reforming of methane over single-atom Rh/Al2O3 catalysts prepared by exsolution

Single-atom catalysts often show exceptionally high performance per metal loading.

Ni-Cu Alloy Nanoparticles Confined by Physical Encapsulation with SiO2 and Chemical Metal-Support Interaction with CeO2 for Methane Dry Reforming

Fabrication of sintering- and carbon-free Ni catalysts for methane dry reforming (MDR), which is attractive to upgrade greenhouse gases CH₄ and CO₂, is challenging. In this work, we innovatively synthesized Ni-Cu alloy nanoparticles confined by physical encapsulation and chemical metal-support interaction (MSI); the synergism of alloy effect, size effect, MSI, and confinement effect in the catalysts gave high rates of CH₄ and CO₂ of 6.98 and 7.16 mmol/(g_Nis), respectively, at 1023 K for 50 h. The rates were 2-3 times enhanced compared to those in the literature. XRD, TEM, H₂-TPR, and so forth revealed that the alloy effect, size effect, and MSI of Ni-Cu and CeO₂ enhanced the MDR activity; MSI promoted the ceria surface lattice oxygen mobility and generated more oxygen vacancies, almost completely gasifying carbon deposits; chemical confinement from MSI and physical confinement from SiO₂ nanospheres realized sintering-free alloys and CeO₂ nanoparticles. The synergistic approach provides a universal strategy for sintering- and carbon-free Ni catalyst design for MDR reaction.

Effects of Subsurface Oxide on Cu1/CeO2 Single-Atom Catalysts for CO Oxidation: A Theoretical Investigation

Supported atomic dispersion metals are of great interest, and the interfacial effect between isolated metal atoms and supports is crucial in heterogeneous catalysis. Herein, the behavior of single-atom Cu catalysts dispersed on CeO₂ (100), (110), and (111) surfaces has been studied by DFT + U calculations. The interactions between ceria crystal planes and isolated Cu atoms together with their corresponding catalytic activities for CO oxidation are investigated. The CeO₂ (100) and (111) surfaces can stabilize active Cu⁺ species, while Cu exists as Cu²⁺ on the (110) surface. Cu⁺ is certified as the most active site for CO adsorption, which can promote the formation of the reaction intermediates and reduce reaction energy barriers. For the CeO₂ (100) surface, the interaction between CO and Cu is weak and the CO adsorbate is more likely to activate the subsurface oxygen. The catalytic performance is closely related to the binding strength of CO to the active Cu single atoms on the different subsurfaces. These results bring a significant insight into the rational design of single metal atoms on ceria and other reducible oxides.

Enhanced catalytic performance of atomically dispersed Pd on Pr-doped CeO2 nanorod in CO oxidation

Single-atom noble metal catalysts have been widely studied for catalytic oxidation of CO. Regulating the coordination environment of single metal atom site is an effective strategy to improve the intrinsic catalytic activity of single atom catalyst. In this work, single atom Pd catalyst supported on Pr-doped CeO₂ nanorods was prepared, and the performance and nature of Pr-coordinated atomic Pd site in CO catalytic oxidation are systematically investigated. The structure characterization using AC-HAADF-STEM, EXAFS, XRD and Raman spectroscopy demonstrate the formation of single atom Pd site and abundant surface oxygen vacancies on the surface of Pr-doped CeO₂ nanorod. With the combination of the XPS characterization and DFT calculations, the oxidation state of Pd on Pr-doped CeO₂ nanorod is determined lower than that on CeO₂ nanorod. The turnover frequency of CO oxidation is markedly increased from 8.4 × 10^-3 to 31.9 × 10^-3 s with Pr-doping at 130 ºC and GHSV of 70,000 h^-1. Combined with kinetic studies, DRIFT and DFT calculations, the doped-Pr atoms reduced the formation energy of oxygen vacancies and generate more oxygen vacancies around the atomically dispersed Pd sites on the surface of cerium oxide, which reduces the dissociation energy of oxygen, thereby accelerating the reaction rate of CO oxidation.

Insight into the Crystal Structures and Surface Property of Manganese Oxide on CO Catalytic Oxidation Performance

α-MnO₂ nanorods and flower-like γ-MnO₂ microspheres were synthesized by facile and mild methods to illustrate the effect of crystal structures and surface features on catalytic performance with the help of carbon monoxide (CO) oxidation. It is revealed that the flower-like γ-MnO₂ microspheres possess better catalytic oxidation performance (CO complete conversion temperature at 120 °C and long-time stability for 50 h) than α-MnO₂ nanorods, which can be attributed to the obvious differences in the chemical bonds and linking modes of [MnO₆] octahedra due to the different crystal structures. γ-MnO₂ possesses lower Mn-O bond strength that enables γ-MnO₂ to present a large amount of surface lattice oxygen and superior oxygen mobility. The disordered random intergrowth tunnel structure can adsorb effectively CO molecules, resulting in excellent catalytic performance for CO catalytic oxidation. In addition, the MnO₂ catalyst probably occurred via a Mars-van Krevelen mechanism for CO oxidation. This work provides an insight into the effect of crystal structures and surface property of manganese oxide on catalytic oxidation performance, which presents help for the future design of promising catalysts with excellent catalytic performance.

Facile Fabrication of CeO2-Al2O3 Hollow Sphere with Atomically Dispersed Fe via Spray Pyrolysis

A facile spray pyrolysis method is introduced to construct the hollow CeO₂-Al₂O₃ spheres with atomically dispersed Fe. Only nitrates and ethanol were involved during the one-step preparation process using the ultrasound spray pyrolysis approach. Detailed explorations demonstrated that differences in the pyrolysis temperature of the precursors and heat transfer are crucial to the formation of the hollow nanostructure. In addition, iron species were in situ atomically dispersed on the as-formed CeO₂-Al₂O₃ hollow spheres via this strategy, which demonstrated promising potential in transferring syn-gas to valuable gasoline products.