Effects of Au–Ce strong interactions on catalytic activity of Au/CeO2/3DOM Al2O3 catalyst for soot combustion under loose contact conditions

Ru-Ce0.7Zr0.3O2-δ as an Anode Catalyst for the Internal Reforming of Dimethyl Ether in Solid Oxide Fuel Cells

The development of direct dimethyl ether (DME) solid oxide fuel cells (SOFCs) has several drawbacks, due to the low catalytic activity and carbon deposition of conventional Ni-zirconia-based anodes. In the present study, the insertion of 2.0 wt.% Ru-Ce0.7Zr0.3O2-δ (ruthenium-zirconium-doped ceria, Ru-CZO) as an anode catalyst layer (ACL) is proposed to be a promising solution. For this purpose, the CZO powder was prepared by the sol-gel synthesis method, and subsequently, nanoparticles of Ru (1.0-2.0 wt.%) were synthesized by the impregnation method and calcination. The catalyst powder was characterized by BET-specific surface area, X-ray diffraction (XRD), field emission scanning electron microscopy with an energy-dispersive spectroscopy detector (FESEM-EDS), and transmission electron microscopy (TEM) techniques. Afterward, the catalytic activity of Ru-CZO catalyst was studied using DME partial oxidation. Finally, button anode-supported SOFCs with Ru-CZO ACL were prepared, depositing Ru-CZO onto the anode support and using an annealing process. The effect of ACL on the electrochemical performance of cells was investigated under a DME and air mixture at 750 °C. The results showed a high dispersion of Ru in the CZO solid solution, which provided a complete DME conversion and high yields of H2 and CO at 750 °C. As a result, 2.0 wt.% Ru-CZO ACL enhanced the cell performance by more than 20% at 750 °C. The post-test analysis of cells with ACL proved a remarkable resistance of Ru-CZO ACL to carbon deposition compared to the reference cell, evidencing the potential application of Ru-CZO as a catalyst as well as an ACL for direct DME SOFCs.

Three-dimensional porous CuO-modified CeO2-Al2O3 catalysts with chlorine resistance for simultaneous catalytic oxidation of chlorobenzene and mercury: Cu-Ce interaction and structure

Chlorine poisoning effects are still challenging to develop efficient catalysts for applications in chlorobenzene (CB) and mercury (Hg⁰) oxidation. Herein, three-dimensional porous CuO-modified CeO₂-Al₂O₃ catalysts with macroporous framework and mesoporous walls prepared via a dual template method were employed to study simultaneous oxidation of CB and Hg⁰. CuO-modified CeO₂-Al₂O₃ catalysts with three-dimensional porous structure exhibited outstanding activity and stability for simultaneous catalytic oxidation of CB and Hg⁰. The results demonstrated that the addition of CuO into CeO₂-Al₂O₃ can simultaneously enhance the acid sites and redox properties through the electronic inductive effect between CuO and CeO₂ (Cu²⁺+Ce³⁺↔Cu⁺+Ce⁴⁺). Importantly, the synergistic effect between Cu and Ce species can induce abundant oxygen vacancies formation, produce more reactive oxygen species and facilitate oxygen migration, which is beneficial for the deep oxidation of chlorinated intermediates. Moreover, macroporous framework and mesoporous nanostructure dramatically improved the specific surface area for enhancing the contact efficiency between reactants and active sites, leading to a remarkable decrease of byproducts deposition. CB and Hg⁰ had function of mutual promotion in this reaction system. In tune with the experimental results, the possible mechanistic pathways for simultaneous catalytic oxidation of CB and Hg⁰ were proposed.

Preparation of K Modified Three-Dimensionally Ordered Macroporous MnCeOx/Ti0.7Si0.3O2 Catalysts and Their Catalytic Performance for Soot Combustion

Soot particles in diesel engine exhaust is one of the main reasons for hazy weather and elimination of them is urgent for environmental protection. At present, it is still a challenge to develop new catalysts with high efficiency and low cost. In this paper, a kind of K modified three-dimensionally ordered macroporous (3DOM) MnCeOx/Ti0.7Si0.3O2 catalysts are designed and synthesized by a sample method. Due to the macroporous structure and synergistic effect of K, Mn, and Ce, the KnMnCeOx/Ti0.7Si0.3O2 (KnMnCeOx/M-TSO) catalysts exhibit good catalytic performance for soot combustion. The catalytic activity of K0.5MnCeOx/M-TSO was the best, and the T10, T50, and T90 are 287, 336, and 367 °C, respectively. After the prepared catalyst was doped with K, the physicochemical properties and catalytic performance changed significantly. In addition, the K0.5MnCeOx/M-TSO catalyst also somewhat exhibits sulfur tolerance owing to it containing Ti. Because of its simple synthesis, high activity, and low cost, the prepared KnMnCeOx/M-TSO catalysts are regarded as a promising candidate for application.

Roles of noble metals (M = Ag, Au, Pd, Pt and Rh) on CeO2 in enhancing activity toward soot oxidation: Active oxygen species and DFT calculations

The effects of noble metal (M = Ag, Au, Pd, Pt, and Rh) on CeO₂ in enhancing the activity toward soot oxidation were studied through experimental methods and density functional theory (DFT) calculations. Each noble metal (3 mol.%) was supported on CeO₂ (M/CeO₂) and the properties of the catalysts were verified by XRD, HRTEM, N₂ physisorption, CO chemisorption, XPS, and H₂-TPR results. The noble metal was highly dispersed over CeO₂, except for Au due to the sintering of Au, and the reducibility of the catalysts was greatly improved according to degree of the interaction between each noble metal and CeO₂. The activities of M/CeO₂ catalysts for soot oxidation were better than that of CeO₂, and followed the order Rh/CeO₂ > Ag/CeO₂ > Pt/CeO₂ > Au/CeO₂ > Pd/CeO₂ > CeO₂. Moreover, our DFT calculations showed that vacancy formation energy was gradually lowered in the following order: CeO₂ > Pd₄/CeO₂ > Pt₄/CeO₂ > Au₄/CeO₂ = Ag₄/CeO₂ > Rh₄/CeO₂, which was similar order with experimental activity. In addition, the electronic states of the p and f orbitals of CeO₂ were studied to compare with the occupied Ce 4f electrons, which affect the redox property. Rh/CeO₂ and Ag/CeO₂ showed the improved soot oxidation activity, with an enhanced ability to generate oxygen vacancy formation and oxygen adsorption and increased electron transfer. Consequently, the experimental and DFT calculation results revealed the roles of noble metals on ceria with respect to catalytic activity.

Enhancement of the Generation and Transfer of Active Oxygen in Ni/CeO2 Catalysts for Soot Combustion by Controlling the Ni-Ceria Contact and the Three-Dimensional Structure

The effect of the three-dimensionally ordered macroporous (3DOM) structure and the Ni doping of CeO₂ on the physicochemical properties and catalytic activity for soot combustion was studied. Moreover, the way in which Ni is introduced to the ceria support was also investigated. For this, CeO₂ supports were synthesized with uncontrolled (Ref) and 3DOM-structured morphology, and their respective Ni/CeO₂ catalysts were prepared by impregnation of the previously synthesized supports or by successive impregnation of both precursors (Ni and Ce) on the 3DOM template. Conclusions reached in this study are: (1) the 3DOM structure increases the surface area of the catalysts and improves the catalyst-soot contact. (2) The doping of CeO₂ with Ni improves the catalytic activity because the NiO participates in the catalytic oxidation of NO to NO₂, and also favors the production of active oxygen and the catalyst oxygen storage capacity. (3) Ni incorporation method affects its physicochemical and catalytic properties. By introducing Ni by successive infiltration in the solid template, the CeO₂ crystal size is reduced, Ni dispersion is improved, and the catalyst reducibility is increased. All of these characteristics make the catalyst synthesized by successive infiltration to have higher catalytic activity for soot combustion than the Ni-impregnated CeO₂ catalyst.