Journal: ACS Catalysis

Abbreviation

ACS Catal.

Publisher

American Chemical Society

Journal Volumes

ISSN

2155-5435

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2011 - 20191112020 - 202693
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Publications 1 - 10 of 204
  • Origins of N₂O Selectivity Limits in Catalyzed Ammonia Oxidation
    Item type: Journal Article
    Surin, Ivan; Kondratenko, Evgenii V.; Pérez-Ramírez, Javier (2026)
    ACS Catalysis
    Ammonia (NH₃) oxidation to nitrous oxide (N₂O) is a promising route to obtain this selective oxidant, but controlling product distribution is inherently challenging because N₂O occupies an intermediate nitrogen oxidation state between N₂ and NO. Despite recent advances, leading CeO₂-based catalytic systems have consistently encountered a selectivity limit in the range of 80-85%. Herein, CeO₂-supported Mn single atoms are employed as a stable, selective benchmark to investigate the origins of the N₂O selectivity losses. Thorough kinetic analysis revealed that direct oxidation of NH₃ to N₂ is the main reason for incomplete N₂O selectivity. This reaction dominates in a thin upstream catalyst bed layer, driven by its strong dependence on the NH₃ partial pressure that ensures dense surface coverage by N-containing intermediates and promotes their irreversible coupling to N₂. However, due to the inhibiting effect of H₂O, this reaction is increasingly hindered along the catalyst bed, with N₂O becoming the dominant product. Based on these insights, N₂O selectivity could be increased from 81% to 90% while N₂ selectivity decreased to 6% by water cofeeding and adjusting reactant partial pressures to tune surface coverage by N-containing intermediates. Evaluation of side reactions revealed a negligible impact of N₂O decomposition or N₂O reduction on product distribution. Conversely, employing isotopic tracing, reduction of in situ-formed NO by NH₃ was established as a significant route to secondary N₂O, and to a lesser extent, N₂. This was shown to be a general feature of CeO₂-based catalysts, including Mn, Au, and Cr systems, providing a lever for selectivity control. This work demonstrates how kinetic analysis can disentangle complex reaction pathways and identify both catalyst- and process-level strategies to advance NH₃ oxidation to N₂O beyond current limits.
  • Efficient polymerization of the aniline dimer p-Aminodiphenylamine (PADPA) with Trametes versicolor laccase/O2 as catalyst and oxidant and AOT vesicles as templates
    Item type: Journal Article
    Junker, Katja; Luginbühl, Sandra; Schüttel, Mischa; et al. (2014)
    ACS Catalysis
  • Role of Carbonaceous Supports and Potassium Promoter on Higher Alcohols Synthesis over Copper-Iron Catalysts
    Item type: Journal Article
    Luk, Ho Ting; Mondelli, Cecilia; Mitchell, Sharon; et al. (2018)
    ACS Catalysis
  • Isostructural Molecular and Surface Mimics of the Active Sites of the Industrial WO3/SiO2 Metathesis Catalysts
    Item type: Journal Article
    Mougel, Victor; Copéret, Christophe (2015)
    ACS Catalysis
  • The Critical Role of Tilted Cinchona Surface Species for Enantioselective Hydrogenation
    Item type: Journal Article
    Rodriguez-Garcia, Laura; Hungerbühler, Konrad; Baiker, Alfons; et al. (2017)
    ACS Catalysis
  • Enhanced Two-Dimensional Dispersion of Group v Metal Oxides on Silica
    Item type: Journal Article
    Grant, Joseph T.; Carrero, Carlos A.; Love, Alyssa M.; et al. (2015)
    ACS Catalysis
    The catalytic performance of supported metal oxides is often controlled by their two- or three-dimensional dispersion. Silica, one of the popular inert supports, triggers the undesired formation of three-dimensional nanoparticles at significantly lower loadings than other conventional supports like Al2O3, TiO2, Nb2O5, or ZrO2. This observation has been ascribed to the lower reactivity of surface SiOH groups toward the precursor, compared to other metal hydroxyl groups on different supports. In this contribution, we show that by promoting amorphous silica with low amounts of sodium, the surface density of two-dimensional metal oxide species can be significantly enhanced to the same level as all other oxide supports previously reported in the literature. This effect is demonstrated for the case of supported vanadia using a variety of spectroscopic techniques (i.e., Raman, diffuse reflectance UV–vis, and 51V-MAS NMR), as well as a catalytic activity study for the oxidative dehydrogenation of propane (ODHP), a structure-sensitive probe reaction. The propane consumption rate was found to increase linearly with the vanadium surface density while the propylene selectivity was not affected until a monolayer coverage of ca. 9 vanadia per nm2 was surpassed. The method is also applicable to other group V metals (i.e., Nb- and Ta-oxide), opening new perspectives for supported metal oxides.
  • Surface Noble Metal Concentration on Ceria as a Key Descriptor for Efficient Catalytic CO Oxidation
    Item type: Journal Article
    Maurer, Florian; Beck, Arik; Jelic, Jelena; et al. (2022)
    ACS Catalysis
    During the CO oxidation over metallic Pt clusters and Pt nanoparticles in Pt/CeO$_2$ catalysts, we found that the Pt surface concentration is a key descriptor for the reaction rate. By increasing the surface noble metal concentration (SNMC) of a Pt/CeO$_2$ catalyst by a factor of ~4, while keeping the weight hourly space velocity constant, the ignition temperature of CO oxidation was decreased by ~200 °C in the as-prepared state. Moreover, the stability was enhanced at higher SNMC. Complementary characterization and theoretical calculations unraveled that the origin of this improved reaction rate at higher Pt surface concentrations can be traced back to the formation of larger oxidized Pt-clusters and the SNMC-dependent aggregation rate of highly dispersed Pt species. The Pt diffusion barriers for cluster formation were found to decrease with increasing SNMC, promoting more facile agglomeration of active, metallic Pt particles. In contrast, when Pt particle formation was forced with a reductive pretreatment, the influence of the SNMC was temporarily diminished, and all catalysts showed a similar CO oxidation activity. The work shows the general relevance of the proximity influence in the formation and stabilization of active centers in heterogeneous catalysis.
  • Design of Base Zeolite Catalysts by Alkali-Metal Grafting in Alcoholic Media
    Item type: Journal Article
    Keller, Tobias C.; Desai, Kartikeya; Mitchell, Sharon; et al. (2015)
    ACS Catalysis
  • Remote, Diastereoselective Cobalt-Catalyzed Alkene Isomerization-Hydroboration: Access to Stereodefined 1,3-Difunctionalized Indanes
    Item type: Journal Article
    Léonard, Nadia G.; Palmer, W. Neil; Friedfeld, Max R.; et al. (2019)
    ACS Catalysis
    The remote, diastereoselective hydroboration of 2- and 3-substituted indenes with a 2,2′:6′,2″-terpyridine cobalt alkyl precatalyst is described that maintains high regio- and stereoselectivity independent of the starting position of the alkene. Several 1,2- and 1,3-disubstituted indanyl boronate esters were obtained with exclusive (>20:1 dr) selectivity for the trans diastereomer including synthetically versatile, stereodefined diboron derivatives. Alkene isomerization by a putative cobalt hydride intermediate precedes carbon–boron bond formation, leading to the observed regioselectivity for boron incorporation at the unsubstituted C(sp3)–H benzylic site. The regio- and diastereoselectivity of the transformation were maintained independent of the starting position of the alkene, as demonstrated by hydroboration of three isomers of methyl-substituted indene. Deuterium-labeling experiments support rapid and reversible insertion and β-hydride elimination to isomerize 3-methylindene and 1-exo-methylene-indane, accounting for the isotopic distribution observed in the products. Mechanistic studies, including stoichiometric experiments, density functional theory calculations, and kinetic analysis, support a mechanism in which 2,3-alkene insertion into a cobalt hydride intermediate determines both the regio- and diastereoselectivity of the catalytic reaction. Synthetic applications of the indanyl boronate esters were demonstrated through the elaboration of the products to several examples of 1,3-disubstituted indanes, important carbocyclic structural motifs in both pharmacological and bioactive molecules. Copyright © 2019 American Chemical Society
  • Co1–xFexOy Oxygen Evolution Nanocatalysts: On the Way To Resolve (Electro)Chemically Triggered Surface-Bulk Discrepancy
    Item type: Journal Article
    Aegerter, Dino; Fabbri, Emiliana; Yüzbasi, Nur Sena; et al. (2023)
    ACS Catalysis
    Unveiling relevant properties of the electrocatalyst’s active phase for the oxygen evolution reaction (OER) is crucial to rationally improve the efficiency of water electrolyzers. This is particularly challenging for materials with a nonuniform pristine phase, which further changes during the OER process. Here, combining surface- and bulk-sensitive analysis techniques unraveled the presence of a gradually changing surface-bulk discrepancy in flame-spray synthesized Co1-xFexOy nanoparticles as a function of the Fe-content. The bulk of the as-synthesized low Fe-content material (x = 0.01) consists of rock salt CoO and is covered on the surface by the thermodynamically more favorable Co3O4 phase. This surface Co3O4 limits the electrocatalytic performance and explains its highly reversible behavior in Co redox processes, as evidenced by cyclic voltammetry and soft X-ray absorption spectroscopy in total-electron-yield. In contrast, the high Fe-content material (x = 0.70), initially with a uniform CoFe2O4 spinel structure, undergoes irreversible surface modifications during OER, driven mainly by Co2+ oxidation in octahedral sites, boosting activity and stability. These insights demonstrate the necessity to resolve (electro)chemically triggered surface-bulk discrepancy on unsupported Co(−Fe)-based nanocatalysts for a better understanding of their electrochemical behavior and to further improve their electrocatalytic performance.
Publications 1 - 10 of 204