Understanding morphology-dependent CuO -CeO2 interactions from the very beginning

Rational H2 Partial Pressure over Nickel/Ceria Crystal Enables Efficient and Durable Wide-Temperature-Zone Air-Level CO2 Methanation

On the way to carbon neutrality, directly catalyzing atmospheric CO2 into high-value chemicals might be an effective approach to mitigate the negative impacts of rising airborne CO2 concentrations. Here, we pioneer the investigation of the influence of the H2/CO2 partial pressure ratio (PPR) on air-level CO2 methanation. Using Ni/CeO2 as a case catalyst, increasing H2/CO2 PPR significantly improves low-temperature CO2 conversion and high-temperature CH4 selectivity, i. e., from 10 of H2/CO2 PPR on, CO2 is completely methanized at 250 °C, and nearly 100 % CH4 selectivity is achieved at 400 °C. 100-hour stability tests demonstrate the practical application potential of Ni/CeO2 at 250 °C and 400 °C. In-situ DRIFTS reveal that reinforced formate pathway by increasing H2/CO2 PPR is responsible for the high CH4 yield. In contrast, even though the CO pathway dominated CO2 conversion on Ni is enhanced by rising H2/CO2 PPR, but at a high reaction temperature, the promoted CO desorption still leads to lower CH4 selectivity. This work offers deep insights into the direct air-level CO2 resourceization, contributing to the achievement of airborne CO2 reductions.

Boosting the Photocatalysis of Plasmonic Au-Cu Nanocatalyst by AuCu-TiO2 Interface Derived from O2 Plasma Treatment

Plasmonic gold (Au) and Au-based nanocatalysts have received significant attention over the past few decades due to their unique visible light (VL) photocatalytic features for a wide variety of chemical reactions in the fields of environmental protection. However, improving their VL photocatalytic activity via a rational design is prevalently regarded as a grand challenge. Herein we boosted the VL photocatalysis of the TiO₂-supported Au-Cu nanocatalyst by applying O₂ plasma to treat this bimetallic plasmonic nanocatalyst. We found that O₂ plasma treatment led to a strong interaction between the Au and Cu species compared with conventional calcination treatment. This interaction controlled the size of plasmonic metallic nanoparticles and also contributed to the construction of AuCu-TiO₂ interfacial sites by forming AuCu alloy nanoparticles, which, thus, enabled the plasmonic Au-Cu nanocatalyst to reduce the Schottky barrier height and create numbers of highly active interfacial sites. The catalyst's characterizations and density functional theory (DFT) calculations demonstrated that boosted VL photocatalytic activity over O₂ plasma treated Au-Cu/TiO₂ nanocatalyst arose from the favorable transfer of hot electrons and a low barrier for the reaction between CO and O with the construction of large numbers of AuCu-TiO₂ interfacial sites. This work provides an efficient approach for the rational design and development of highly active plasmonic Au and Au-based nanocatalysts and deepens our understanding of their role in VL photocatalytic reactions.

Stabilizing Cu2+ Ions by Solid Solutions to Promote CO2 Electroreduction to Methane

Copper is the only metal catalyst that can perform the electrocatalytic CO₂ reduction reaction (CRR) to produce hydrocarbons and oxygenates. Its surface oxidation state determines the reaction pathway to various products. However, under the cathodic potential of CRR conditions, the chemical composition of most Cu-based catalysts inevitably undergoes electroreduction from Cu²⁺ to Cu⁰ or Cu¹⁺ species, which is generally coupled with phase reconstruction and the formation of new active sites. Since the initial Cu²⁺ active sites are hard to retain, there have been few studies about Cu²⁺ catalysts for CRR. Herein we propose a solid-solution strategy to stabilize Cu²⁺ ions by incorporating them into a CeO₂ matrix, which works as a self-sacrificing ingredient to protect Cu²⁺ active species. In situ spectroscopic characterization and density functional theory calculations reveal that compared with the conventionally derived Cu catalysts with Cu⁰ or Cu¹⁺ active sites, the Cu²⁺ species in the solid solution (Cu-Ce-O_x) can significantly strengthen adsorption of the *CO intermediate, facilitating its further hydrogenation to produce CH₄ instead of dimerization to give C₂ products. As a result, different from most of the other Cu-based catalysts, Cu-Ce-O_x delivered a high Faradaic efficiency of 67.8% for CH₄ and a low value of 3.6% for C₂H₄.

Effect of CeO2 morphology on the catalytic properties of Au/CeO2 for base-free glucose oxidation

The Au/R-CeO2 catalyst with strong metal–support interaction and abundant oxygen vacancies displays superior glucose oxidation performance, as compared with Au/C-CeO2 and Au/O-CeO2.

Oxygen vacancy distributions and electron localization in a CeO2(100) nanocube

Oxygen vacancy distributions in a 5 nm CeO2 nanocube were determined using the Reverse Monte Carlo method. The oxygen vacancies tend to be located on the surface of the CeO2 nanocube, with far fewer in subsurface and internal regions.

Insight into the Morphology-Dependent Catalytic Performance of CuO/CeO2 Produced by Tannic Acid for Efficient Hydrogenation of 4-Nitrophenol

The construction of a heterogeneous nanocatalyst with outstanding catalytic performance via an environmentally benign and cost-effective synthetic category has long been one of the challenges in nanotechnology. Herein, we synthesized highly efficient and low-cost mesoporous morphology-dependent CuO/CeO₂ -Rods and CuO/CeO₂ -Cubes catalysts by employing a green and multifunctional polyphenolic compound (tannic acid) as the stabilizer and chelating agent for 4-nitrophenol (4-NP) reduction reaction. The CuO/CeO₂ -Rods exhibited excellent performance, of which the activity was 3.2 times higher than that of CuO/CeO₂ -Cubes. This can be connected with the higher density of oxygen vacancy on CeO₂ -Rods (110) than CeO₂ -Cubes (100), the oxygen vacancy favors anchoring CuO species on the CeO₂ support, which promotes the strong interaction between finely dispersed CuO and CeO₂ -Rods at the interfacial positions and facilitates the electron transfer from BH₄ ^- to 4-NP. The synergistic catalytic mechanism illustrated that 4-NP molecules preferentially adsorbed on the CeO₂ , while H₂ from BH₄ ^- dissociated over CuO to form highly active H* species, contributing to achieving efficient hydrogenation of 4-NP. This study is expected to shed light on designing and synthesizing cost-effective and high-performance nanocatalysts through a greener synthetic method for the areas of catalysis, nanomaterial science and engineering, and chemical synthesis.

In Situ Generation of the Surface Oxygen Vacancies in a Copper-Ceria Catalyst for the Water-Gas Shift Reaction

The dissociation of H₂O is a crucial aspect for the water-gas shift reaction, which often occurs on the vacancies of a reducible oxide support. However, the vacancies sometimes run off, thus inhibiting H₂O dissociation. After high-temperature treatment, the ceria supports were lacking vacancies because of sintering. Unexpectedly, the in situ generation of surface oxygen vacancies was observed, ensuring the efficient dissociation of H₂O. Due to the surface reconstruction of ceria nanorods, the copper species sustained were highly dispersed on the sintered support, on which CO was adsorbed efficiently to react with hydroxyls from H₂O dissociation. In contrast, no surface reconstruction occurred in ceria nanoparticles, leading to the sintering of copper species. The sintered copper species were averse to adsorb CO, so the copper-ceria nanoparticle catalyst had poor reactivity even when surface oxygen vacancies could be generated in situ.

Elucidating the structure, redox properties and active entities of high-temperature thermally aged CuOx-CeO2 catalysts for CO-PROX

CuOx-CeO2 catalysts with different copper contents are synthesized via a coprecipitation method and thermally treated at 700 °C. Various characterization techniques including X-ray diffraction (XRD) Rietveld refinement, N2 adsorption-desorption isotherms, X-ray photoelectron spectra (XPS), UV-Raman, high-resolution transmission electron microscopy (HRTEM), temperature-programmed reduction (TPR) and in situ diffuse reflectance infrared Fourier transform spectra (DRIFTs) were adopted to investigate the structure/texture properties, oxygen vacancies, Cu-Ce interaction and redox properties of the catalysts. After the thermal treatment, the catalysts exhibited outstanding catalytic properties for the preferential oxidation (PROX) of CO (with the T50% of 62 °C and the widest operation temperature window of 85-140 °C), which provided a new strategy for the design of Cu-Ce based catalysts with high catalytic performance. The characterization results indicated that moderately elevating the copper content (below 5%) increases the amount of highly dispersed Cu species in the catalysts, including highly dispersed surface CuOx species and strongly bonded Cu-[Ox]-Ce species, strengthening the Cu-Ce interaction, increasing oxygen vacancies and promoting redox properties, but a further increase in copper content causes the agglomeration of crystalline CuO and decreases the highly dispersed Cu species. This work also provides evidence from the perspective that the catalytic performance of CuOx-CeO2 catalysts for CO-PROX at low and high reaction temperatures is dependent on the redox properties of highly dispersed CuOx species and strongly bonded Cu-[Ox]-Ce species, respectively.

Exsolution of Iron Oxide on LaFeO3 Perovskite: A Robust Heterostructured Support for Constructing Self-Adjustable Pt-Based Room-Temperature CO Oxidation Catalysts

Constructing highly active and stable surface sites for O₂ activation is essential to lower the barrier of Pt-based catalysts for CO oxidation. Although a few active Pt-metal oxide interfaces have been reported, questions about the stability of these sites under the long-term storage and operation remain unresolved. Here, based on developing a robust FeO_x/LaFeO₃ heterostructure as a support, we constructed stable Pt-support interfaces to achieve highly active CO oxidation at room temperature. Even after it is kept in the air for more than 6 months, the catalyst (without pretreatment) still maintains the high activity like a fresh one, which is superior to metal hydroxide-Pt interfaces, and meets the requirements of long-term storage for emergency use. In situ characterizations and systematic reaction results showed that CO oxidation occurs through an alternative mechanism, which is triggered by intrinsic reactants and self-adjusted to a more active interface in the reaction process. Theoretical calculations and ⁵⁷Fe Mössbauer spectra revealed that abundant cation vacancies significantly increase the activity of surface oxygen species and should be responsible for this unique process. This work demonstrates an alternative concept to fabricate robust and highly active Pt-based catalysts for catalytic oxidation.

Facet-Dependent Reactivity of Ceria Nanoparticles Exemplified by CeO2-Based Transition Metal Catalysts: A Critical Review

The rational design and fabrication of highly-active and cost-efficient catalytic materials constitutes the main research pillar in catalysis field. In this context, the fine-tuning of size and shape at the nanometer scale can exert an intense impact not only on the inherent reactivity of catalyst’s counterparts but also on their interfacial interactions; it can also opening up new horizons for the development of highly active and robust materials. The present critical review, focusing mainly on our recent advances on the topic, aims to highlight the pivotal role of shape engineering in catalysis, exemplified by noble metal-free, CeO2-based transition metal catalysts (TMs/CeO2). The underlying mechanism of facet-dependent reactivity is initially discussed. The main implications of ceria nanoparticles’ shape engineering (rods, cubes, and polyhedra) in catalysis are next discussed, on the ground of some of the most pertinent heterogeneous reactions, such as CO2 hydrogenation, CO oxidation, and N2O decomposition. It is clearly revealed that shape functionalization can remarkably affect the intrinsic features and in turn the reactivity of ceria nanoparticles. More importantly, by combining ceria nanoparticles (CeO2 NPs) of specific architecture with various transition metals (e.g., Cu, Fe, Co, and Ni) remarkably active multifunctional composites can be obtained due mainly to the synergistic metalceria interactions. From the practical point of view, novel catalyst formulations with similar or even superior reactivity to that of noble metals can be obtained by co-adjusting the shape and composition of mixed oxides, such as Cu/ceria nanorods for CO oxidation and Ni/ceria nanorods for CO2 hydrogenation. The conclusions derived could provide the design principles of earth-abundant metal oxide catalysts for various real-life environmental and energy applications.

Crystal plane effect of ceria on supported copper catalyst for liquid-phase hydrogenation of unsaturated aldehyde

Ceria has been widely used as catalyst support displaying a size- or shape-dependent catalytic performance due to the strong metal-support interaction (SMSI) effect with active metal. Almost all the studies on the SMSI effect of ceria-supported metal catalysts are involved generally in gas-phase reaction, but rarely in the liquid-phase reaction system. In this work, Cu/CeO₂-P (copper loaded on nano-polyhedral CeO₂ with (111) terminated surface) was investigated its catalytic performance on liquid-phase hydrogenation and studied the SMSI effect by comparing with the catalysts supported on nano-rod and nano-cube CeO₂. It was found that Cu was highly dispersed on the external surface of ceria in the Cu/CeO₂-P catalyst via a moderate SMSI effect. Furthermore, the degree of the interaction showed great influence on the chemical state of Cu species, and the ratio of (Cu⁺+Cu⁰)/Cu²⁺ in Cu/CeO₂-P was higher than Cu/CeO₂-R (Cu loaded on nano-rod CeO₂ with (110) plane) and Cu/CeO₂-C (Cu loaded on nano-cube CeO₂ with (100) facet). As a result, the Cu/CeO₂-P catalyst showed the best catalytic performance among three types of catalysts. Based on series of catalytic investigations, the catalytic performance in liquid-phase hydrogenation was intrinsically relevant to the crystal plane effect and reduced Cu proportion induced by an appropriate SMSI effect, which was completely different from gas-phase hydrogenation.

High-heat treatment enhanced catalytic activity of CuO/CeO2 catalysts with low CuO content for CO oxidation

CuO/CeO₂ catalysts with low CuO content and calcined at 800 °C exhibited better catalytic performance than those calcined at 500 °C. The coordinatively unsaturated copper atoms were proved to be the main active sites in the CuO/CeO₂ catalysts.