Maxim Zabilskiy

Bio: Maxim Zabilskiy is an academic researcher from Paul Scherrer Institute. The author has contributed to research in topics: Catalysis & Copper. The author has an hindex of 8, co-authored 15 publications receiving 437 citations.

Nanoshaped CuO/CeO2 Materials: Effect of the Exposed Ceria Surfaces on Catalytic Activity in N2O Decomposition Reaction

Abstract: This study reports a thorough investigation of nanosized CuO/CeO2 materials as an efficient catalyst for decomposition of N2O, which is a strong greenhouse gas largely produced by chemical industry. Effect of terminating CeO2 crystalline planes ({100}, {110}, and {111}) on the behavior of CuO dispersed over CeO2 nanocubes, nanorods and polyhedral crystallites was examined in detail by using a variety of catalyst characterization techniques. The 4 wt % Cu was found as the most advantageous metal loading, whereas higher Cu content resulted in lower dispersion and formation of significantly less active, segregated bulk CuO phase. It was discovered that CuO/CeO2 solids should enable both excessive oxygen mobility on the catalyst surface as well as formation of highly reducible Cu defect sites, in order to ensure high intrinsic activity. Detailed studies further revealed that CeO2 morphology needs to be tailored to expose {100} and {110} high-energy surface planes, as present in CeO2 nanorods. Oxygen mobility ...

The dynamics of overlayer formation on catalyst nanoparticles and strong metal-support interaction

Abstract: Heterogeneous catalysts play a pivotal role in the chemical industry The strong metal-support interaction (SMSI), which affects the catalytic activity, is a phenomenon researched for decades However, detailed mechanistic understanding on real catalytic systems is lacking Here, this surface phenomenon was studied on an actual platinum-titania catalyst by state-of-the-art in situ electron microscopy, in situ X-ray photoemission spectroscopy and in situ X-ray diffraction, aided by density functional theory calculations, providing a novel real time view on how the phenomenon occurs The migration of reduced titanium oxide, limited in thickness, and the formation of an alloy are competing mechanisms during high temperature reduction Subsequent exposure to oxygen segregates the titanium from the alloy, and a thicker titania overlayer forms This role of oxygen in the formation process and stabilization of the overlayer was not recognized before It provides new application potential in catalysis and materials science Tuning the catalytic activity of metal nanoparticles by encapsulation is a long known process, but mechanistically poorly understood Here, Beck and colleagues reveal the encapsulation mechanism by support material and the outstanding role of oxygen in the encapsulation mechanism by extensive in situ characterization

The unique interplay between copper and zinc during catalytic carbon dioxide hydrogenation to methanol

Abstract: In spite of numerous works in the field of chemical valorization of carbon dioxide into methanol, the nature of high activity of Cu/ZnO catalysts, including the reaction mechanism and the structure of the catalyst active site, remains the subject of intensive debate. By using high-pressure operando techniques: steady-state isotope transient kinetic analysis coupled with infrared spectroscopy, together with time-resolved X-ray absorption spectroscopy and X-ray powder diffraction, and supported by electron microscopy and theoretical modeling, we present direct evidence that zinc formate is the principal observable reactive intermediate, which in the presence of hydrogen converts into methanol. Our results indicate that the copper-zinc alloy undergoes oxidation under reaction conditions into zinc formate, zinc oxide and metallic copper. The intimate contact between zinc and copper phases facilitates zinc formate formation and its hydrogenation by hydrogen to methanol.

Small CuO clusters on CeO2 nanospheres as active species for catalytic N2O decomposition

Abstract: High surface area CeO 2 nanospheres as an active catalyst support were synthesized using glycothermal approach. Different loadings of copper (4, 6, 10 and 15 wt.%) were supported by wet impregnation method. Prepared materials were characterized by means of TEM, SEM-EDX, XRD, UV-Vis diffuse reflectance, N 2 adsorption/desorption, DRIFT and H 2 -TPR techniques, and tested for the catalytic reaction of nitrous oxide decomposition. The best activity in the N 2 O degradation was found for the sample containing 10 wt.% of Cu that can be attributed to the highest number of small CuO clusters on the catalyst surface. Further increase of copper content strongly affects the dispersion and leads to the formation of less active segregated CuO phase, which was confirmed by XRD, UV-Vis and H 2 -TPR results. Accordingly to UV–Vis examination and DRIFT analysis using CO as a probe molecule, all solids contain Cu +1 ions which play a crucial role in the N 2 O decomposition mechanism. The synthesized catalysts were also tested in wet or NO containing atmospheres, where an inhibiting effect takes place and leads to shifting of conversion profiles to higher temperature by 65 and 10 °C, correspondingly. It was found out that the formation of a new, crystalline CuO·3H 2 O phase occurs in water vapour containing atmosphere, which can result in catalyst deactivation. However, this effect is fully reversible and the catalyst is able to replenish initial activity in dry atmosphere. Potentiality of CuO/CeO 2 materials in catalytic N 2 O decomposition in industrial processes was confirmed by long-term stability tests performed in the period of 50 h in the presence of inhibiting gas components.

Following the structure of copper-zinc-alumina across the pressure gap in carbon dioxide hydrogenation

Abstract: Copper-zinc-alumina catalysts are used industrially for methanol synthesis from feedstock containing carbon monoxide and carbon dioxide. The high performance of the catalyst stems from synergies that develop between its components. This important catalytic system has been investigated with a myriad of approaches, however, no comprehensive agreement on the fundamental source of its high activity has been reached. One potential source of disagreement is the considerable variation in pressure used in studies to understand a process that is performed industrially at pressures above 20 bar. Here, by systematically studying the catalyst state during temperature-programmed reduction and under carbon dioxide hydrogenation with in situ and operando X-ray absorption spectroscopy over four orders of magnitude in pressure, we show how the state and evolution of the catalyst is defined by its environment. The structure of the catalyst shows a strong pressure dependence, especially below 1 bar. As pressure gaps are a general problem in catalysis, these observations have wide-ranging ramifications. Copper-zinc-alumina is used in industry to catalyse the synthesis of methanol from CO2, but many aspects of its high performance remain elusive. Now, by using in situ and operando techniques over four orders of magnitude in pressure, the authors show how the catalyst structure and kinetics change with the applied conditions.

Fundamentals and Catalytic Applications of CeO2-Based Materials

Abstract: Cerium dioxide (CeO2, ceria) is becoming an ubiquitous constituent in catalytic systems for a variety of applications. 2016 sees the 40th 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 dee...

Ceria Catalysts at Nanoscale: How Do Crystal Shapes Shape Catalysis?

Abstract: Engineering the shape and size of catalyst particles and the interface between different components of heterogeneous catalysts at the nanometer level can radically alter their performances. This is particularly true with CeO2-based catalysts, where the precise control of surface atomic arrangements can modify the reactivity of Ce4+/Ce3+ ions, changing the oxygen release/uptake characteristics of ceria, which, in turn, strongly affects catalytic performance in several reactions like CO, soot, and VOC oxidation, WGS, hydrogenation, acid–base reactions, and so on. Despite the fact that many of these catalysts are polycrystalline with rather ill-defined morphologies, experimental and theoretical studies on well-defined nanocrystals have clearly established that the exposure of specific facets can increase/decrease surface oxygen reactivity and metal–support interaction (for supported metal nanoparticles), consequently affecting catalytic reactions. Here, we want to address the most recent developments in this...

Effect of Ceria Crystal Plane on the Physicochemical and Catalytic Properties of Pd/Ceria for CO and Propane Oxidation

Abstract: Ceria nanocrystallites with different morphologies and crystal planes were hydrothermally prepared, and the effects of ceria supports on the physicochemical and catalytic properties of Pd/CeO2 for the CO and propane oxidation were examined. The results showed that the structure and chemical state of Pd on ceria were affected by ceria crystal planes. The Pd species on CeO2-R (rods) and CeO2-C (cubes) mainly formed PdxCe1–xO2−σ solid solution with −Pd2+–O2––Ce4+– linkage. In addition, the PdOx nanoparticles were dominated on the surface of Pd/CeO2-O (octahedrons). For the CO oxidation, the Pd/CeO2-R catalyst showed the highest catalytic activity among three catalysts, its reaction rate reached 2.07 × 10–4 mol gPd–1 s–1 at 50 °C, in which CeO2-R mainly exposed the (110) and (100) facets with low oxygen vacancy formation energy, strong reducibility, and high surface oxygen mobility. TOF of Pd/CeO2-R (3.78 × 10–2 s–1) was much higher than that of Pd/CeO2-C (6.40 × 10–3 s–1) and Pd/CeO2-O (1.24 × 10–3 s–1) at 5...

Ceria nanoparticles shape effects on the structural defects and surface chemistry: Implications in CO oxidation by Cu/CeO2 catalysts

Abstract: Copper-ceria binary oxides have been extensively used in a wide variety of catalytic processes due to their unique catalytic features in conjunction to their lower cost as compared to noble metal-based systems. However, various parameters related to different counterparts characteristics, such as particle size and morphology, can exert a profound influence on the structural/redox properties of binary oxides and, consequently, on their catalytic performance. Here, we report on ceria nanoparticles shape effects: nanorods (NR), nanopolyhedra (NP) and nanocubes (NC) on the solid state properties of copper-ceria binary oxides. A thorough characterization study by both ex situ (surface area determination, X-ray diffraction, X-ray fluorescence, H2-temperature programmed reduction, transmission electron microscopy, X-ray photoelectron spectroscopy) and in situ (Raman spectroscopy) techniques was undertaken to gain insight into the impact of the support morphology on the surface, structural and redox properties. A novel approach based on sequential in situ Raman spectra obtained under alternating oxidizing and reducing atmospheres was employed to reveal the impact of ceria exposed facets on the structural defects. CO oxidation was employed as a probe reaction to disclose structure-property relationships. The results clearly revealed the key role of ceria morphology rather than structural/textural characteristics on the reducibility and oxygen mobility, following the sequence: NR > NP > NC. The latter seems to have a profound influence on copper-ceria interactions towards the stabilization of Cu+ species, via Ce4+/Ce3+ and Cu2+/Cu+ redox equilibrium. Interestingly, CuO incorporation in different ceria carriers boosts the catalytic activity without, however, affecting the order observed for bare ceria, i.e., CeO2-NR > CeO2-NP > CeO2-NC, implying the key role of support. The Cu/CeO2 sample with the rod-like morphology exhibited the highest catalytic performance, offering almost complete CO elimination at temperatures as low as 100 °C. A perfect relationship between the catalytic performance and the following parameters was disclosed, on the basis of a Mars-van Krevelen mechanism: i) abundance of weakly bound oxygen species, ii) relative population of Cu+/Ce3+ redox pairs, iii) relative abundance of defects and oxygen vacancies.

Tuning of Persulfate Activation from a Free Radical to a Nonradical Pathway through the Incorporation of Non-Redox Magnesium Oxide

Abstract: Nonradical-based advanced oxidation processes for pollutant removal have attracted much attention due to their inherent advantages. Herein we report that magnesium oxides (MgO) in CuOMgO/Fe3O4 not only enhanced the catalytic properties but also switched the free radical peroxymonosulfate (PMS)-activated process into the 1O2 based nonradical process. CuOMgO/Fe3O4 catalyst exhibited consistent performance in a wide pH range from 5.0 to 10.0, and the degradation kinetics were not inhibited by the common free radical scavengers, anions, or natural organic matter. Quantitative structure-activity relationships (QSARs) revealed the relationship between the degradation rate constant of 14 substituted phenols and their conventional descriptor variables (i.e., Hammett constants σ, σ-, σ+), half-wave oxidation potential (E1/2), and pKa values. QSARs together with the kinetic isotopic effect (KIE) recognized the electron transfer as the dominant oxidation process. Characterizations and DFT calculation indicated that the incorporated MgO alters the copper sites to highly oxidized metal centers, offering a more suitable platform for PMS to generate metastable copper intermediates. These highly oxidized metals centers of copper played the key role in producing O2•- after accepting an electron from another PMS molecule, and finally 1O2 as sole reactive species was generated from the direct oxidation of O2•- through thermodynamically feasible reactions.