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Catalysts
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Surface Design of Metal Oxide Catalysts
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Surface Design of Metal Oxide Catalysts

A special issue of Catalysts (ISSN 2073-4344). This special issue belongs to the section "Catalytic Materials".

Deadline for manuscript submissions: closed (30 September 2021) | Viewed by 7631

Special Issue Editor

Prof. Dr. Simone Mascotto

E-Mail Website
Guest Editor
Institute for Inorganic and Applied Chemistry, Department of Chemistry, University of Hamburg, 20146 Hamburg, Germany
Interests: multimetal oxides; porous materials; defect-induced effects in nanomaterials; small-angle scattering; VOC catalysis

Special Issue Information

Dear Colleagues,

Surface design of oxide-based catalysts has been demonstrated as a promising strategy for the development of numerous renewable energy technologies, from fuel cells and three-way catalytic converters to photocatalytic reactors. In principle, the improvement of the surface properties of metal oxides involves both the maximization of the specific surface area and porosity as well as the optimization of surface chemistry and surface defect structure. Because the crystallization of the oxide lattice is driven by the reduction of excess surface energy, the design of porous architectures is not an easy task. This is particularly true when the synthesis of mesoporous materials, i.e., systems with pores between 2 and 50 nm, is targeted. Applying mesoporous design strategies to metal oxides has been proven to bring novel properties and great efficiency in manifold catalytic applications. In a complementary fashion, strong enhancement of surface reactivity and catalytic performance was observed by tailoring the surface composition of materials. Particularly for ternary oxide systems, changes in the surface chemistry properties, induced by chemical functionalization, cationic segregation phenomena, or by tuning different crystal facets, lead to the formation of unconventional surface defect states with increased functional response. This Special Issue aims to cover recent progress and trends in design, evaluation, and theoretical understanding of metal oxide catalysts for renewable energy applications with advanced physical and chemical surface properties.

Prof. Dr. Simone Mascotto
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Catalysts is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2700 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • surface functionalization
  • oxygen vacancies
  • mesoporosity
  • confinement
  • environmental catalysis

Published Papers (3 papers)

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Research

17 pages, 2597 KiB  
Article
Dynamics of Reactive Oxygen Species on Cobalt-Containing Spinel Oxides in Cyclic CO Oxidation
by Maik Dreyer, Anna Rabe, Eko Budiyanto, Klaus Friedel Ortega, Sharif Najafishirtari, Harun Tüysüz and Malte Behrens
Catalysts 2021, 11(11), 1312; https://doi.org/10.3390/catal11111312 - 29 Oct 2021
Cited by 7 | Viewed by 1916
Abstract
Reactive oxygen species (ROS) are considered to be responsible for the high catalytic activity of transition metal oxides like Co3-xFexO4 in oxidation reactions, but the detailed influences of catalyst composition and morphology on the formation of these reactive [...] Read more.
Reactive oxygen species (ROS) are considered to be responsible for the high catalytic activity of transition metal oxides like Co3-xFexO4 in oxidation reactions, but the detailed influences of catalyst composition and morphology on the formation of these reactive oxygen species are not fully understood. In the presented study, Co3O4 spinels of different mesostructures, i.e., particle size, crystallinity, and specific surface area, are characterized by powder X-ray diffraction, scanning electron microscopy, and physisorption. The materials were tested in CO oxidation performed in consecutive runs and compared to a Co3-xFexO4 composition series with a similar mesostructure to study the effects of catalyst morphology and composition on ROS formation. In the first run, the CO conversion was observed to be dominated by the exposed surface area for the pure Co-spinels, while a negative effect of Fe content in the spinels was seen. In the following oxidation run, a U-shaped conversion curve was observed for materials with high surface area, which indicated the in situ formation of ROS on those materials that were responsible for the new activity at low temperature. This activation was not stable at the higher reaction temperature but was confirmed after temperature-programmed oxidation (TPO). However, no activation after the first run was observed for low-surface-area and highly crystalline materials, and the lowest surface-area material was not even activated after TPO. Among the catalyst series studied here, a correlation of small particle size and large surface area with the ability for ROS formation is presented, and the benefit of a nanoscaled catalyst is discussed. Despite the generally negative effect of Fe, the highest relative activation was observed at intermediate Fe contents suggesting that Fe may be involved in ROS formation. Full article
(This article belongs to the Special Issue Surface Design of Metal Oxide Catalysts)
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11 pages, 2310 KiB  
Communication
Influence of Phase Composition and Pretreatment on the Conversion of Iron Oxides into Iron Carbides in Syngas Atmospheres
by Aleks Arinchtein, Meng-Yang Ye, Michael Geske, Marvin Frisch and Ralph Kraehnert
Catalysts 2021, 11(7), 773; https://doi.org/10.3390/catal11070773 - 25 Jun 2021
Cited by 4 | Viewed by 1905
Abstract
CO2 Fischer–Tropsch synthesis (CO2–FTS) is a promising technology enabling conversion of CO2 into valuable chemical feedstocks via hydrogenation. Iron–based CO2–FTS catalysts are known for their high activities and selectivities towards the formation of higher hydrocarbons. Importantly, iron [...] Read more.
CO2 Fischer–Tropsch synthesis (CO2–FTS) is a promising technology enabling conversion of CO2 into valuable chemical feedstocks via hydrogenation. Iron–based CO2–FTS catalysts are known for their high activities and selectivities towards the formation of higher hydrocarbons. Importantly, iron carbides are the presumed active phase strongly associated with the formation of higher hydrocarbons. Yet, many factors such as reaction temperature, atmosphere, and pressure can lead to complex transformations between different oxide and/or carbide phases, which, in turn, alter selectivity. Thus, understanding the mechanism and kinetics of carbide formation remains challenging. We propose model–type iron oxide films of controlled nanostructure and phase composition as model materials to study carbide formation in syngas atmospheres. In the present work, different iron oxide precursor films with controlled phase composition (hematite, ferrihydrite, maghemite, maghemite/magnetite) and ordered mesoporosity are synthesized using the evaporation–induced self–assembly (EISA) approach. The model materials are then exposed to a controlled atmosphere of CO/H2 at 300 °C. Physicochemical analysis of the treated materials indicates that all oxides convert into carbides with a core–shell structure. The structure appears to consist of crystalline carbide cores surrounded by a partially oxidized carbide shell of low crystallinity. Larger crystallites in the original iron oxide result in larger carbide cores. The presented simple route for the synthesis and analysis of soft–templated iron carbide films will enable the elucidation of the dynamics of the oxide to carbide transformation in future work. Full article
(This article belongs to the Special Issue Surface Design of Metal Oxide Catalysts)
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19 pages, 5354 KiB  
Article
The Effect of Co Incorporation on the CO Oxidation Activity of LaFe1−xCoxO3 Perovskites
by Maik Dreyer, Moritz Krebs, Sharif Najafishirtari, Anna Rabe, Klaus Friedel Ortega and Malte Behrens
Catalysts 2021, 11(5), 550; https://doi.org/10.3390/catal11050550 - 27 Apr 2021
Cited by 15 | Viewed by 3045
Abstract
Perovskite oxides are versatile materials due to their wide variety of compositions offering promising catalytic properties, especially in oxidation reactions. In the presented study, LaFe1−xCoxO3 perovskites were synthesized by hydroxycarbonate precursor co-precipitation and thermal decomposition thereof. Precursor and [...] Read more.
Perovskite oxides are versatile materials due to their wide variety of compositions offering promising catalytic properties, especially in oxidation reactions. In the presented study, LaFe1−xCoxO3 perovskites were synthesized by hydroxycarbonate precursor co-precipitation and thermal decomposition thereof. Precursor and calcined materials were studied by scanning electron microscopy (SEM), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), thermogravimetric analysis (TG), and X-ray powder diffraction (XRD). The calcined catalysts were in addition studied by transmission electron microscopy (TEM) and N2 physisorption. The obtained perovskites were applied as catalysts in transient CO oxidation, and in operando studies of CO oxidation in diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). A pronounced increase in activity was already observed by incorporating 5% cobalt into the structure, which continued, though not linearly, at higher loadings. This could be most likely due to the enhanced redox properties as inferred by H2-temperature programmed reduction (H2-TPR). Catalysts with higher Co contents showing higher activities suffered less from surface deactivation related to carbonate poisoning. Despite the similarity in the crystalline structures upon Co incorporation, we observed a different promotion or suppression of various carbonate-related bands, which could indicate different surface properties of the catalysts, subsequently resulting in the observed non-linear CO oxidation activity trend at higher Co contents. Full article
(This article belongs to the Special Issue Surface Design of Metal Oxide Catalysts)
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