Cerium dioxide (CeO2, ceria) is becoming an ubiquitous constituent in catalytic systems for a variety of applications. 2016 sees the 40(th) anniversary since ceria was first employed by Ford Motor Company as an oxygen storage component in car converters, to become in the years since its inception an irreplaceable component in three-way catalysts (TWCs). Apart from this well-established use, ceria is looming as a catalyst component for a wide range of catalytic applications. For some of these, such as fuel cells, CeO2-based materials have almost reached the market stage, while for some other catalytic reactions, such as reforming processes, photocatalysis, water-gas shift reaction, thermochemical water splitting, and organic reactions, ceria is emerging as a unique material, holding great promise for future market breakthroughs. While much knowledge about the fundamental characteristics of CeO2-based materials has already been acquired, new characterization techniques and powerful theoretical methods are deepening our understanding of these materials, helping us to predict their behavior and application potential. This review has a wide view on all those aspects related to ceria which promise to produce an important impact on our life, encompassing fundamental knowledge of CeO2 and its properties, characterization toolbox, emerging features, theoretical studies, and all the catalytic applications, organized by their degree of establishment on the market.
Carbon dioxide is a desired feedstock for platform molecules, such as carbon monoxide or higher hydrocarbons, from which we will be able to make many different useful, value-added chemicals. Its catalytic hydrogenation over abundant metals requires the amalgamation of theoretical knowledge with materials design. Here we leverage a theoretical understanding of structure sensitivity, along with a library of different supports, to tune the selectivity of methanation in the Power-to-Gas concept over nickel. For example, we show that carbon dioxide hydrogenation over nickel can and does form propane, and that activity and selectivity can be tuned by supporting different nickel particle sizes on various oxides. This theoretical and experimental toolbox is not only useful for the highly selective production of methane, but also provides new insights for carbon dioxide activation and subsequent carbon–carbon coupling towards value-added products thereby reducing the deleterious effects of this environmentally harmful molecule.
Carbon-supported, Pt and PtCo nanocrystals (NCs) with controlled size and composition were synthesized and examined for hydrodeoxygenation (HDO) of 5-hydroxymethylfurfural (HMF). Experiments in a continuous flow reactor with 1-propanol solvent, at 120 to 160 °C and 33 bar H2, demonstrated that reaction is sequential on both Pt and PtCo alloys, with 2,5-dimethylfuran (DMF) formed as an intermediate product. However, the reaction of DMF is greatly suppressed on the alloys, such that a Pt3Co2 catalyst achieved DMF yields as high as 98%. XRD and XAS data indicate that the Pt3Co2 catalyst consists of a Pt-rich core and a Co oxide surface monolayer whose structure differs substantially from that of bulk Co oxide. Density functional theory (DFT) calculations reveal that the oxide monolayer interacts weakly with the furan ring to prevent side reactions, including overhydrogenation and ring opening, while providing sites for effective HDO to the desired product, DMF. We demonstrate that control over metal nanoparticle size and composition, along with operating conditions, is crucial to achieving good performance and stability. Implications of this mechanism for other reactions and catalysts are discussed
This brief review is focused on recent advancements in methane catalytic oxidation, an important reaction for environmental remediation and clean power generation. Particular attention is given to Pd-based catalysts and novel strategies to gain a fundamental understanding of the reaction mechanism [a] 2885 hindered due to the high stability of the C-H bond (104 kcal mol -1 ). Nonetheless, in the presence of a catalyst, the apparent activation energy can be as low as 7-10 kcal mol -1 . As mentioned previously, Pd-based catalysts are highly active for Eur.
The concept of self-regenerating or "smart" catalysts, developed to mitigate the problem of supported metal particle coarsening in high-temperature applications, involves redispersing large metal particles by incorporating them into a perovskite-structured support under oxidizing conditions and then exsolving them as small metal particles under reducing conditions. Unfortunately, the redispersion process does not appear to work in practice because the surface areas of the perovskite supports are too low and the diffusion lengths for the metal ions within the bulk perovskite too short. Here, we demonstrate reversible activation upon redox cycling for CH oxidation and CO oxidation on Pd supported on high-surface-area LaFeO, prepared as a thin conformal coating on a porous MgAlO support using atomic layer deposition. The LaFeO film, less than 1.5 nm thick, was shown to be initially stable to at least 900 °C. The activated catalysts exhibit stable catalytic performance for methane oxidation after high-temperature treatment.
Combining propane dehydrogenation with propylene metathesis in a single step yields mixtures of propylene, ethylene and butenes, important building blocks for the chemical industry. The open challenges and opportunities in the field are highlighted.
Hydrogen is currently mainly produced via steam reforming of methane (SMR: CH 4 + H 2 O → CO + 3H 2 ). An alternative to this process, utilizing carbon dioxide and thus potentially mitigating its environmentally harmful emissions, is dry methane reforming (DMR: CH 4 + CO 2 → 2CO + 2H 2 ). Both of these reactions are structure sensitive, that is, not all atoms in a catalytic metal nanoparticle have the same activity. Mapping this structure sensitivity and understanding its mechanistic workings provides ways to design better, more efficient, and more stable catalysts. Here, we study a range of SiO 2 -supported Ni nanoparticles with varying particle sizes (1.2−6.0 nm) by operando infrared spectroscopy to determine the active mechanism over Ni (carbide mechanism) and its kinetic dependence on Ni particle size. We establish that Ni particle sizes below 2.5 nm lead to a different structure sensitivity than is expected from and implied in literature. Because of the identification of CH x D x species with isotopically labeled experiments, we show that CH 4 activation is not the only rate-limiting step in SMR and DMR. The recombination of C and O or the activation of CO is likely also an important kinetically limiting factor in the production of synthesis gas in DMR, whereas for SMR the desorption of the formed CO becomes more kinetically limiting. Furthermore, we establish the Ni particle size dependence of carbon whisker formation. The optimal Ni particle size both in terms of activity for SMR and DMR, at 500 and 600 °C, and 5 bar, was found to be approximately 2−3 nm, whereas carbon whisker formation was found to maximally occur at approximately 4.5 nm for SMR and for DMR increased with increasing particle size. These results have direct practical applications for tuning of activity and selectivity of these reactions, while providing fundamental understanding of their working.
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