Titania-Decorated Silicon Carbide-Containing Cobalt Catalyst for Fischer–Tropsch Synthesis

Highly Efficient ZIF-67-Derived PtCo Alloy-CN Interface for Low-Temperature Aqueous-Phase Fischer-Tropsch Synthesis

Designing new materials for selective Fischer-Tropsch synthesis (FTS) is an elegant way to enhance local feedstock utilization like biomass and waste. In this approach, we have designed a thermally and chemically stable bimetallic PtCo/NC hybrid nanocomposite catalyst derived from a zeolitic imidazolate framework (ZIF-67, which contains cobalt as a metal center) through carbonization for low-temperature (413-473 K) aqueous-phase Fischer-Tropsch synthesis (AFTS). The selectivity of the desired range of hydrocarbons is adjusted using a highly dispersed PtCo bimetallic alloy, which facilitates extraordinary reduction of a metal oxide to active species by the synergic effect under the AFTS reaction conditions. The ZIF-derived catalyst tested in this study exhibited the highest activity to date for very low temperatures (433 K) in aqueous-phase Fischer-Tropsch synthesis with CO conversion rates between 0.61 and 1.20 mol_CO·mol_Co^-1·h^-1. Insights of the remarkable catalyst activity were examined by in situ X-ray photoelectron spectroscopy (XPS) studies corroborated by density functional theory (DFT) calculation. The bimetallic Co₃Pt (111) surface was found to be highly active for the C-C coupling reaction between surface-adsorbed C and CO, forming a CCO intermediate with a very low activation barrier (E_a = 0.37 eV), in comparison to the C-C coupling activation barrier obtained over the Co (111) surface (E_a = 0.87 eV). This unique approach and observations create a new path for developing next-generation advanced catalyst systems and processes for selective low-temperature FTS.

SO3 decomposition over silica-modified β-SiC supported CuFe2O4 catalyst: characterization, performance, and atomistic insights

The sulfur-iodine (S-I) thermochemical water-splitting cycle is one of the potential ways to produce hydrogen on a large scale. CuFe₂O₄ was dispersed over modified silica or treated β-SiC and untreated β-SiC using the wet impregnation method for SO₃ decomposition, which is the most endothermic reaction of the S-I cycle. Various state-of-the-art techniques such as XRD, FT-IR, BET, XPS, TEM, HR-TEM, FESEM-EDS and elemental mapping were employed to characterize both the synthesized catalysts. CuFe₂O₄ catalyst supported on silica-modified β-SiC resulted in enhanced catalytic activity and stability due to better metal-support interaction. In order to get a better insight into the reaction mechanism over this bimetallic catalyst, the first principles based simulation under the framework of density functional theory was performed. We have found that the presence of Cu gives rise to an improved charge localization at the O-vacancy site alongside favourable reaction kinetics, which results in an enhanced catalytic activity for the CuFe₂O₄ nano-cluster compared to that of a single metallic catalyst containing Fe₂O₃ nano-cluster.

Surface morphology evolution of cobalt nanoparticles induced by hydrogen adsorption: a theoretical study

Determining the surface structure and morphology under working conditions is essential to obtain facet-dependent catalytic performance.

The effect of the particle size on Fischer-Tropsch synthesis for ZSM-5 zeolite supported cobalt-based catalysts

A series of mesoporous ZSM-5 zeolite supported cobalt-based catalysts with the cobalt crystal sizes in the range of 4.5-18.1 nm were prepared for syngas conversion. The highly selective synthesis of various liquid fuels including gasoline, jet fuel and diesel range hydrocarbons is achieved with different cobalt nanoparticle sizes.

Nanostructured Photothermal Materials for Environmental and Catalytic Applications

Solar energy is a green and sustainable clean energy source. Its rational use can alleviate the energy crisis and environmental pollution. Directly converting solar energy into heat energy is the most efficient method among all solar conversion strategies. Recently, various environmental and energy applications based on nanostructured photothermal materials stimulated the re-examination of the interfacial solar energy conversion process. The design of photothermal nanomaterials is demonstrated to be critical to promote the solar-to-heat energy conversion and the following physical and chemical processes. This review introduces the latest photothermal nanomaterials and their nanostructure modulation strategies for environmental (seawater evaporation) and catalytic (C1 conversion) applications. We present the research progress of photothermal seawater evaporation based on two-dimensional and three-dimensional porous materials. Then, we describe the progress of photothermal catalysis based on layered double hydroxide derived nanostructures, hydroxylated indium oxide nanostructures, and metal plasmonic nanostructures. Finally, we present our insights concerning the future development of this field.

Porous Silicon Carbide (SiC): A Chance for Improving Catalysts or Just Another Active-Phase Carrier?

There is an obvious gap between efforts dedicated to the control of chemicophysical and morphological properties of catalyst active phases and the attention paid to the search of new materials to be employed as functional carriers in the upgrading of heterogeneous catalysts. Economic constraints and common habits in preparing heterogeneous catalysts have narrowed the selection of active-phase carriers to a handful of materials: oxide-based ceramics (e.g. Al₂O₃, SiO₂, TiO₂, and aluminosilicates-zeolites) and carbon. However, these carriers occasionally face chemicophysical constraints that limit their application in catalysis. For instance, oxides are easily corroded by acids or bases, and carbon is not resistant to oxidation. Therefore, these carriers cannot be recycled. Moreover, the poor thermal conductivity of metal oxide carriers often translates into permanent alterations of the catalyst active sites (i.e. metal active-phase sintering) that compromise the catalyst performance and its lifetime on run. Therefore, the development of new carriers for the design and synthesis of advanced functional catalytic materials and processes is an urgent priority for the heterogeneous catalysis of the future. Silicon carbide (SiC) is a non-oxide semiconductor with unique chemicophysical properties that make it highly attractive in several branches of catalysis. Accordingly, the past decade has witnessed a large increase of reports dedicated to the design of SiC-based catalysts, also in light of a steadily growing portfolio of porous SiC materials covering a wide range of well-controlled pore structure and surface properties. This review article provides a comprehensive overview on the synthesis and use of macro/mesoporous SiC materials in catalysis, stressing their unique features for the design of efficient, cost-effective, and easy to scale-up heterogeneous catalysts, outlining their success where other and more classical oxide-based supports failed. All applications of SiC in catalysis will be reviewed from the perspective of a given chemical reaction, highlighting all improvements rising from the use of SiC in terms of activity, selectivity, and process sustainability. We feel that the experienced viewpoint of SiC-based catalyst producers and end users (these authors) and their critical presentation of a comprehensive overview on the applications of SiC in catalysis will help the readership to create its own opinion on the central role of SiC for the future of heterogeneous catalysis.

Tuning the Chemical Properties of Co-Ti3 C2 Tx MXene Materials for Catalytic CO2 Reduction

MXenes, a novel family of 2D materials, are energy materials that have gained considerable attention, particularly for their catalytic applications in emerging areas such as CO₂ and N₂ hydrogenation. Herein, for the first time, it is shown that the surface reducibility of Ti₃ C₂ T_x MXene can be tuned by N doping, which induces a change in the catalytic properties of supported Co nanoparticles. Pristine Co-Ti₃ C₂ T_x MXene favors CO production during CO₂ hydrogenation, whereas CH₄ production is favored when the MXene is subjected to simple N doping. X-ray photoelectron spectroscopy and transmission electron microscopy (TEM) reveal that surface rutile TiO₂ nanoparticles appear on the Ti₃ C₂ T_x support upon N doping, which interact strongly with the supported Co nanoparticles. This interaction alters the reducibility of the supported Co nanoparticles at the interface with the TiO₂ nanoparticles, shifting the product selectivity from CO to CH₄ . This study successfully showcases a practical strategy, based on surface chemistry modulation of 2D MXenes, for regulating product distribution in CO₂ hydrogenation.

The effect of microwave irradiation on heterogeneous catalysts for Fischer–Tropsch synthesis

The work that has been carried out on microwave irradiation applied in catalyst preparation for drying, calcination or postsynthesis methods, and as a heating source for the Fischer–Tropsch reaction has been reviewed. It has been found that microwave irradiation can, in some cases, greatly enhance the performance of heterogeneous catalyst systems for Fischer–Tropsch synthesis. We have also summarized the advantages and drawbacks of using microwave irradiation in Fischer–Tropsch catalyst preparation and postsynthesis, and identified opportunities for future investigation.

Superparamagnetic behaviour of metallic Co nanoparticles according to variable temperature magnetic resonance

Investigating the size distributions of Co nanoparticle ensembles is an important problem, which has no straightforward solution. In this work, we use the combination of 59Co internal field nuclear magnetic resonance (59Co IF NMR) and ferromagnetic resonance (FMR) spectroscopies on a metallic Co nanoparticle sample with a narrow Co nanoparticle size distribution due to encapsulation within the inner channels of carbon nanotubes. High-resolution transmission electron microscopy (TEM) images showed that the nanoparticles can be represented as prolate spheroids, with the majority of particles having an aspect ratio between 1 and 2. This observation has increased the accuracy of superparamagnetic blocking size calculations from Néel relaxation model by introducing the actual volume of the ellipsoids taken from the image processing. 59Co IF NMR and FMR experiments conducted under different temperatures allowed us to observe the thermal blocking of superparamagnetic particles in full accordance with the TEM particle volume distribution. This proved that these magnetic resonance techniques can be used jointly for characterization of Co nanoparticles in the bulk of the sample.

Direct observation of the evolving metal-support interaction of individual cobalt nanoparticles at the titania and silica interface

Understanding the metal–support interaction (MSI) is crucial to comprehend how the catalyst support affects performance and whether this interaction can be exploited in order to design new catalysts with enhanced properties. Spatially resolved soft X-ray absorption spectroscopy (XAS) in combination with Atomic Force Microscopy (AFM) and Scanning Helium Ion-Milling Microscopy (SHIM) has been applied to visualise and characterise the behaviour of individual cobalt nanoparticles (CoNPs) supported on two-dimensional substrates (SiO_xSi(100) (x < 2) and rutile TiO₂(110)) after undergoing reduction–oxidation–reduction (ROR). The behaviour of the Co species is observed to be strongly dependent on the type of support. For SiO_xSi a weaker MSI between Co and the support allows a complete reduction of CoNPs although they migrate and agglomerate. In contrast, a stronger MSI of CoNPs on TiO₂ leads to only a partial reduction under H₂ at 773 K (as observed from Co L₃-edge XAS data) due to enhanced TiO₂ binding of surface-exposed cobalt. SHIM data revealed that the interaction of the CoNPs is so strong on TiO₂, that they are seen to spread at and below the surface and even to migrate up to ∼40 nm away. These results allow us to better understand deactivation phenomena and additionally demonstrate a new understanding concerning the nature of the MSI for Co/TiO₂ and suggest that there is scope for careful control of the post-synthetic thermal treatment for the tuning of this interaction and ultimately the catalytic performance.

Understanding the metal–support interaction (MSI) is crucial to comprehend how the catalyst support affects performance and whether this interaction can be exploited in order to design new catalysts with enhanced properties.

Theoretically predicted surface morphology of FCC cobalt nanoparticles induced by Ru promoter

The addition of Ru promoter has an important role in tuning the stability of the exposed facets of FCC Co NPs, accompanied by the change of surface morphology.

Transformation of titanium carbide into mesoporous titania for catalysed HBr oxidation

TiC oxidises via a combination of spot-oxidation and shrinking core mechanisms, resulting in a mesoporous, high-performance TiO₂–TiC composite for bromine production via catalysed HBr oxidation.

A nitrogen-doped carbon-coated silicon carbide as a robust and highly efficient metal-free catalyst for sour gas desulfurization in the presence of aromatics as contaminants

A mesoporous N-doped carbon coating for SiC extrudates shows excellent H₂S desulfurization performance along with remarkably high resistance towards deactivation/fouling in the presence of aromatics as contaminant.

Industrial carbon dioxide capture and utilization: state of the art and future challenges

This review covers the sustainable development of advanced improvements in CO₂ capture and utilization.

Two-dimensional-related catalytic materials for solar-driven conversion of COx into valuable chemical feedstocks

The discovery of improved chemical processes for CO and CO2 hydrogenation to valuable hydrocarbon fuels and alcohols is of paramount importance for the chemical industry. Such technologies have the potential to reduce anthropogenic CO2 emissions by adding value to a waste stream, whilst also reducing our consumption of fossil fuels. Current thermal catalytic technologies available for CO and CO2 hydrogenation are demanding in terms of energy input. Various alternative technologies are now being developed for COx hydrogenation, with solar-driven processes over two-dimensional (2D) and 2D-related composite materials being particularly attractive due to the abundance of solar energy on Earth and also the high selectivity of defect-engineered 2D materials towards specific valuable products under very mild reaction conditions. This review showcases recent advances in the solar-driven COx reduction to hydrocarbons over 2D-based materials. Optimization of 2D catalyst performance demands interdisciplinary research that embraces catalyst electronic structure manipulation and morphology control, surface/interface engineering, reactor engineering and density functional theory modelling studies. Through improved understanding of the structure-performance relationships in 2D-related catalysts which is achievable through the application of modern in situ characterization techniques, practical photo/photothermal/photoelectrochemical technologies for CO and CO2 reduction to high-valuable products such as olefins could be realized in the not-too-distant future.

The Fischer–Tropsch synthesis performance over cobalt supported on silicon-based materials: the effect of thermal conductivity of the support

The effect of thermal conductivity of support on the catalytic performance of supported Co-based Fischer–Tropsch catalysts is investigated.

Incorporating silicon carbide nanoparticles into Al2O3@Al to achieve an efficient support for Co-based catalysts to boost their catalytic performance towards Fischer–Tropsch synthesis

The SiC nanoparticles modified Al₂O₃@Al composites were used as an efficient supports for Co-based catalysts to boost the FTS performance via a synergy effect.

Co-Based Catalysts Derived from Layered-Double-Hydroxide Nanosheets for the Photothermal Production of Light Olefins

Solar-driven Fischer-Tropsch synthesis represents an alternative and potentially low-cost route for the direct production of light olefins from syngas (CO and H₂ ). Herein, a series of novel Co-based photothermal catalysts with different chemical compositions are successfully fabricated by H₂ reduction of ZnCoAl-layered double-hydroxide nanosheets at 300-700 °C. Under UV-vis irradiation, the photothermal catalyst prepared at 450 °C demonstrates remarkable CO hydrogenation performance, affording an olefin (C_2-4⁼ ) selectivity of 36.0% and an olefin/paraffin ratio of 6.1 at a CO conversion of 15.4%. Characterization studies using X-ray absorption fine structure and high-resolution transmission electron microscopy reveal that the active catalyst comprises Co and Co₃ O₄ nanoparticles on a ZnO-Al₂ O₃ mixed metal oxide support. Density functional theory calculations further demonstrate that the oxide-decorated metallic Co nanoparticle heterostructure weakens the further hydrogenation ability of the corresponding Co, leading to the high selectivity to light olefins. This study demonstrates a novel solar-driven catalyst platform for the production of light olefins via CO hydrogenation.

Nickel Sulfides Decorated SiC Foam for the Low Temperature Conversion of H₂S into Elemental Sulfur

The selective oxidation of H₂S to elemental sulfur was carried out on a NiS₂/SiC^foam catalyst under reaction temperatures between 40 and 80 °C using highly H₂S enriched effluents (from 0.5 to 1 vol.%). The amphiphilic properties of SiC foam provide an ideal support for the anchoring and growth of a NiS₂ active phase. The NiS₂/SiC composite was employed for the desulfurization of highly H₂S-rich effluents under discontinuous mode with almost complete H₂S conversion (nearly 100% for 0.5 and 1 vol.% of H₂S) and sulfur selectivity (from 99.6 to 96.0% at 40 and 80 °C, respectively), together with an unprecedented sulfur-storage capacity. Solid sulfur was produced in large aggregates at the outer catalyst surface and relatively high H₂S conversion was maintained until sulfur deposits reached 140 wt.% of the starting catalyst weight. Notably, the spent NiS₂/SiC^foam catalyst fully recovered its pristine performance (H₂S conversion, selectivity and sulfur-storage capacity) upon regeneration at 320 °C under He, and thus, it is destined to become a benchmark desulfurization system for operating in discontinuous mode.

Sampling the structure and chemical order in assemblies of ferromagnetic nanoparticles by nuclear magnetic resonance

Assemblies of nanoparticles are studied in many research fields from physics to medicine. However, as it is often difficult to produce mono-dispersed particles, investigating the key parameters enhancing their efficiency is blurred by wide size distributions. Indeed, near-field methods analyse a part of the sample that might not be representative of the full size distribution and macroscopic methods give average information including all particle sizes. Here, we introduce temperature differential ferromagnetic nuclear resonance spectra that allow sampling the crystallographic structure, the chemical composition and the chemical order of non-interacting ferromagnetic nanoparticles for specific size ranges within their size distribution. The method is applied to cobalt nanoparticles for catalysis and allows extracting the size effect from the crystallographic structure effect on their catalytic activity. It also allows sampling of the chemical composition and chemical order within the size distribution of alloyed nanoparticles and can thus be useful in many research fields.

As nanoparticles possess technological applications from catalysis to medical therapies, methods to probe their structural properties are crucial. Here, the authors extend a nuclear magnetic resonance method to extract such properties for specific size ranges of noninteracting magnetic particles.

Silicon carbide foam as a porous support platform for catalytic applications

This review provides an overview of the use of foam-structured SiC as a porous support platform in some typical catalytic processes both for gas-phase and liquid-phase reactions, such as H₂S selective oxidation, Friedel–Crafts benzoylation and Fischer–Tropsch synthesis.

Thermal stability and hcp-fcc allotropic transformation in supported Co metal catalysts probed near operando by ferromagnetic NMR

Despite the fact that cobalt based catalysts are used at the industrial scale for Fischer-Tropsch synthesis, it is not yet clear which cobalt metallic phase is actually at work under operando conditions and what is its state of dispersion. As it turns out, the different phases of metallic cobalt, fcc and hcp, give rise to distinct ferromagnetic nuclear magnetic resonance. Furthermore, within one Co metal particle, the occurrence of several ferromagnetic domains of limited sizes can be evidenced by the specific resonance of Co in multi-domain particles. Consequently, by ferromagnetic NMR, one can follow quantitatively the sintering and phase transitions of dispersed Co metal particles in supported catalysts under near operando conditions. The minimal size probed by ferromagnetic Co NMR is not precisely known but is considered to be in the order of 10 nm for supported Co particles at room temperature and increases to about 35 nm at 850 K. Here, in Co metal Fischer-Tropsch synthesis catalysts supported on β-SiC, the resonances of the fcc multi-domain, fcc single-domain and hcp Co were clearly distinguished. A careful rationalization of their frequency and width dependence on temperature allowed a quantitative analysis of the spectra in the temperature range of interest, thus reflecting the state of the catalysts under near operando conditions that is without the uncertainty associated with prior quenching. The allotropic transition temperature was found to start at 600-650 K, which is about 50 K below the bulk transition temperature. The phase transition was fully reversible and a significant part of the hcp phase was found to be stable up to 850 K. This anomalous behavior that was observed without quenching might prove to be crucial to understand and model active species not only in catalysts but also in battery materials.

Silicon carbide supported cobalt for Fischer–Tropsch synthesis: probing into the cause of the intrinsic excellent catalytic performance

The Si_xO_y layer on the surface of SiC plays a great role in the intrinsic excellent catalytic performance of Co/SiC.

Silicon carbide coated with TiO2 with enhanced cobalt active phase dispersion for Fischer–Tropsch synthesis

The introduction of a thin layer of TiO₂ on β-SiC allows a significant improvement of the cobalt dispersion. This catalyst exhibits an excellent and stable catalytic activity for the Fischer–Tropsch synthesis (FTS) with high C₅₊ selectivity, which contributes to the development of a new active catalyst family in the gas-to-liquid process.