Pedro Castro-Fernández

Bio: Pedro Castro-Fernández is an academic researcher from ETH Zurich. The author has contributed to research in topics: Dehydrogenation & Absorption spectroscopy. The author has an hindex of 2, co-authored 4 publications receiving 19 citations.

Propane Dehydrogenation on Ga2O3-Based Catalysts: Contrasting Performance with Coordination Environment and Acidity of Surface Sites

Abstract: α-Ga2O3, β-Ga2O3, and γ-Ga2O3 as well as the silica-supported catalysts γ-Ga2O3/SiO2, β-Ga2O3/SiO2, and Ga(NO3)3-derived Ga/SiO2 were prepared, characterized, and evaluated for propane dehydrogenat...

Peering into buried interfaces with X-rays and electrons to unveil MgCO3 formation during CO2 capture in molten salt-promoted MgO.

Abstract: The addition of molten alkali metal salts drastically accelerates the kinetics of CO2 capture by MgO through the formation of MgCO3. However, the growth mechanism, the nature of MgCO3 formation, and the exact role of the molten alkali metal salts on the CO2 capture process remain elusive, holding back the development of more-effective MgO-based CO2 sorbents. Here, we unveil the growth mechanism of MgCO3 under practically relevant conditions using a well-defined, yet representative, model system that is a MgO(100) single crystal coated with NaNO3. The model system is interrogated by in situ X-ray reflectometry coupled with grazing incidence X-ray diffraction, scanning electron microscopy, and high-resolution transmission electron microscopy. When bare MgO(100) is exposed to a flow of CO2, a noncrystalline surface carbonate layer of ca. 7-A thickness forms. In contrast, when MgO(100) is coated with NaNO3, MgCO3 crystals nucleate and grow. These crystals have a preferential orientation with respect to the MgO(100) substrate, and form at the interface between MgO(100) and the molten NaNO3. MgCO3 grows epitaxially with respect to MgO(100), and the lattice mismatch between MgCO3 and MgO is relaxed through lattice misfit dislocations. Pyramid-shaped pits on the surface of MgO, in proximity to and below the MgCO3 crystals, point to the etching of surface MgO, providing dissolved [Mg2+…O2–] ionic pairs for MgCO3 growth. Our studies highlight the importance of combining X-rays and electron microscopy techniques to provide atomic to micrometer scale insight into the changes occurring at complex interfaces under reactive conditions.

Atomic-Scale Insight into the Structure of Metastable γ-Ga2O3 Nanocrystals and their Thermally-Driven Transformation to β-Ga2O3

Abstract: Metastable γ-Ga2O3 nanocrystals have gained growing interest for a broad range of technological applications. However, a precise description of their atomic structure and changes thereof during the...

Uncovering selective and active Ga surface sites in gallia–alumina mixed-oxide propane dehydrogenation catalysts by dynamic nuclear polarization surface enhanced NMR spectroscopy

Abstract: Gallia–alumina (Ga,Al)2O3(x : y) spinel-type solid solution nanoparticle catalysts for propane dehydrogenation (PDH) were prepared with four nominal Ga : Al atomic ratios (1 : 6, 1 : 3, 3 : 1, 1 : 0) using a colloidal synthesis approach. The structure, coordination environment and distribution of Ga and Al sites in these materials were investigated by X-ray diffraction, X-ray absorption spectroscopy (Ga K-edge) as well as 27Al and 71Ga solid state nuclear magnetic resonance. The surface acidity (Lewis or Bronsted) was probed using infrared spectroscopy with pyridine and 2,6-dimethylpyridine probe molecules, complemented by element-specific insights (Ga or Al) from dynamic nuclear polarization surface enhanced cross-polarization magic angle spinning 15N{27Al} and 15N{71Ga} J coupling mediated heteronuclear multiple quantum correlation NMR experiments using 15N-labelled pyridine as a probe molecule. The latter approach provides unique insights into the nature and relative strength of the surface acid sites as it allows to distinguish contributions from Al and Ga sites to the overall surface acidity of mixed (Ga,Al)2O3 oxides. Notably, we demonstrate that (Ga,Al)2O3 catalysts with a high Al content show a greater relative abundance of four-coordinated Ga sites and a greater relative fraction of weak/medium Ga-based surface Lewis acid sites, which correlates with superior propene selectivity, Ga-based activity, and stability in PDH (due to lower coking). In contrast, (Ga,Al)2O3 catalysts with a lower Al content feature a higher fraction of six-coordinated Ga sites, as well as more abundant Ga-based strong surface Lewis acid sites, which deactivate through coking. Overall, the results show that the relative abundance and strength of Ga-based surface Lewis acid sites can be tuned by optimizing the bulk Ga : Al atomic ratio, thus providing an effective measure for a rational control of the catalyst performance.

Coke Deposition on Pt-Based Catalysts in Propane Direct Dehydrogenation: Kinetics, Suppression, and Elimination

Abstract: Pt-based catalysts are widely used in propane dehydrogenation to meet the dramatically increased demand of propylene from an on-purpose catalytic process. Although the process has been commercializ...

Propane Dehydrogenation on Ga2O3-Based Catalysts: Contrasting Performance with Coordination Environment and Acidity of Surface Sites

Abstract: α-Ga2O3, β-Ga2O3, and γ-Ga2O3 as well as the silica-supported catalysts γ-Ga2O3/SiO2, β-Ga2O3/SiO2, and Ga(NO3)3-derived Ga/SiO2 were prepared, characterized, and evaluated for propane dehydrogenat...

Heterogeneous alkane dehydrogenation catalysts investigated via a surface organometallic chemistry approach

Abstract: The selective conversion of light alkanes (C2-C6 saturated hydrocarbons) to the corresponding alkene is an appealing strategy for the petrochemical industry in view of the availability of these feedstocks, in particular with the emergence of Shale gas. Here, we present a review of model dehydrogenation catalysts of light alkanes prepared via surface organometallic chemistry (SOMC). A specific focus of this review is the use of molecular strategies for the deconvolution of complex heterogeneous materials that are proficient in enabling dehydrogenation reactions. The challenges associated with the proposed reactions are highlighted, as well as overriding themes that can be ascertained from the systematic study of these challenging reactions using model SOMC catalysts.

Single Co Sites in Ordered SiO₂ Channels for Boosting Nonoxidative Propane Dehydrogenation

Abstract: Searching for low-cost, environmentally friendly, and highly active catalysts for C–H bond activation in propane dehydrogenation (PDH) reaction remains a great challenge. Herein, SiO2 nanomeshes (NMs) with ultrashort three-dimensional (3D) channels were constructed to effectively confine the Co single atoms (Co SAs/SiO2 NMs). The ultrashort 3D channels were formed by gasifying carbon in the self-assembled SiO2@polymer composites under the air atmosphere. The carbon removal process resulted in abundant oxygen (O*) defects in the channel windowsill that immobilized the dissociative Co1 species to afford the sintering-resistant Co SAs/SiO2 NMs catalyst. The as-obtained Co SAs/SiO2 NMs with unsaturated Co–O3 sites exhibited an outstanding PDH catalytic behavior (95% selectivity and 196 h–1 turnover frequency), superior to Co SAs/SiO2 commerce (83%, 49 h–1), Co NPs/SiO2 NMs (87%, 13 h–1), and most non-noble metal-based catalysts. Furthermore, Co SAs/SiO2 NMs showed high long-term stability with no significant deactivation during 24 h of reaction. Theoretical and experimental analysis indicated that these unsaturated Co–O3 sites could selectively activate the first and second C–H bonds and limit the further splitting of C–H (C) bonds during PDH. This work paves a way for designing high-efficiency single-atom catalysts for PDH.

Synthetic solid oxide sorbents for CO₂ capture: state-of-the art and future perspectives

Abstract: Solid oxides have been extensively investigated as possible high-temperature CO 2 sorbents by a number of research groups. We summarised the different strategies to develop synthetic solid oxide sorbents.