Hydrothermal Carbon-Coated TiO2 as Support for Co-Based Catalyst in Fischer–Tropsch Synthesis

Hydrothermal Carbon Coating of an Activated Carbon-A New Adsorbent

A new adsorbent material was prepared by coating an activated carbon with hydrothermal carbon obtained from sucrose. The material obtained has different properties from the sum of the properties of the activated carbon and the hydrothermal carbon, which shows that a new material was obtained. It has a high specific surface area (1051.9 m² g^-1) and is slightly more acidic than the starting activated carbon (p.z.c.-point of zero charge 8.71 vs. 9.09). The adsorptive properties of a commercial carbon (Norit RX-3 Extra) were improved over a wide pH and temperature range. The capacity values of the monolayer according to Langmuir's model reached 588 mg g^-1 for the commercial product and 769 mg g^-1 for the new adsorbent.

Highly Efficient Selective Hydrogenation of Cinnamaldehyde to Cinnamyl Alcohol over CoRe/TiO2 Catalyst

Allylic alcohols typically produced through selective hydrogenation of α,β-unsaturated aldehydes are important intermediates in fine chemical industry, but it is still a challenge to achieve its high selectivity transformation. Herein, we report a series of TiO₂-supported CoRe bimetallic catalysts for the selective hydrogenation of cinnamaldehyde (CAL) to cinnamyl alcohol (COL) using formic acid (FA) as a hydrogen donor. The resultant catalyst with the optimized Co/Re ratio of 1:1 can achieve an exceptional COL selectivity of 89% with a CAL conversion of 99% under mild conditions of 140 °C for 4 h, and the catalyst can be reused four times without loss of activity. Meanwhile, the Co₁Re₁/TiO₂/FA system was efficient for the selective hydrogenation of various α,β-unsaturated aldehydes to the corresponding α,β-unsaturated alcohols. The presence of ReO_x on the Co₁Re₁/TiO₂ catalyst surface was advantageous to the adsorption of C=O, and the ultrafine Co nanoparticles provided abundant hydrogenation active sites for the selective hydrogenation. Moreover, FA as a hydrogen donor improved the selectivity to α,β-unsaturated alcohols.

Uniform and dispersible carbonaceous microspheres as quasi-liquid sorbent

Functional colloidal carbon materials find various applications, including the remediation of contaminated water and soil in so-called particle-based in-situ remediation processes. In this study, uniform and highly dispersible micro-sized carbonaceous spheres (CS) were generated by hydrothermal carbonization (HTC) of sucrose in the presence of carboxymethyl cellulose (CMC) as environmentally friendly polyelectrolyte stabilizer. In order to ensure their optimal subsurface delivery and formation of a self-contained treatment zone, a narrow size distribution and low agglomeration tendency of the particles is desired. Therefore, the obtained CS were thoroughly characterized and optimized with respect to their colloidal properties which are a crucial factor for their application as quasi-liquid sorbent. The as-prepared uniform CS are readily dispersible into single particles in water as confirmed by digital microscopy and form stable suspensions. Due to their perfectly spherical shape, particle sedimentation in aqueous suspensions is well predicted by Stokes' law. High sorption coefficients on the synthesized CS K_D,CS were determined for phenanthrene (up to log (K_D,CS/[L kg^-1]) = 5) and other hydrophobic groundwater contaminants. This confirms the application potential of the CS, which were prepared by an economic low-temperature process using sucrose as bio-based precursor, for generating in-situ sorption barriers for groundwater and soil remediation.

TiO2 supported cobalt oxide for olefin epoxidation reaction - characterization, catalytic activities and mechanism - using a DFT model

Metal oxide catalysts are known to trigger C-H bond activation selectively, indicating their suitability for olefin epoxidation. Nano-structured Co₃O₄ supported on TiO₂ was prepared for selective epoxidation of a number of olefins under optimized reaction conditions. An appropriate synthetic procedure yielded a catalytic material (Co-Ti (NP)^HT) with desired crystal size and interface conditions. Incorporation of Co into the Ti matrix resulted in an enhancement in the specific surface of Ti-Co nanoparticles (77.93 m² g^-1). XPS measurements evaluated the surface cobalt atom concentration (5.77%) in Ti-Co(NP)^HT, indicating more dispersion of cobalt oxide species. Catalytic application of the material, using various olefins (under optimized reaction conditions) shows higher conversion (>85%) in a 6-h time interval. The substrate : oxidant (H₂O₂) concentration in an optimized molar ratio of 1 : 2 shows high olefin conversion for the formation of olefin oxide. The reactivity of olefins was found to be in the order: cyclohexene > methylstyrene > styrene > chlorostyrene > p-nitrostyrene. A DFT model compared the HOMO-LUMO energies of styrene and its substituted forms. The reusability of Ti-Co (NP)^HT tested up to four continuous cycles of batch operations indicates a negligible loss (0.25-0.30%) of catalytic activity.

Oxidative Dehydrogenation of Ethane with CO2 over Mo/LDO Catalyst: The Active Species of Mo Controlled by LDO

A series of the layered double oxides supported molybdenum oxide catalysts were synthesized and evaluated in the oxidative dehydrogenation of ethane with CO2 (CO2-ODHE). The 22.3 wt% Mo/LDO catalyst delivered a 92.3%selectivity to ethylene and a 7.9% ethane conversion at relatively low temperatures. The molybdenum oxide catalysts were fully characterized by XRD, BET, SEM, TEM, UV–vis, Raman TG, and XPS. Isolated [MoO4]2− dominated on the surface of the fresh 12.5 wt% Mo/LDO catalyst. With the increase of the Mo content, the Mo species transformed from [MoO4]2− to [Mo7O24]6− and [Mo8O26]4− on the 22.3 wt% and 30.1 wt% Mo/LDO catalysts, respectively. The redox mechanism was proposed and three Mo species including [MoO4]2−, [Mo7O24]6−, and [Mo8O26]4− showed quite different functions in the CO2-ODHE reaction: [MoO4]2−, with tetrahedral structure, preferred the non-selective pathway; [Mo7O24]6−, with an octahedral construction, promoted the selective pathway; and the existence of [Mo8O26]4− reduced the ability to activate ethane. This work provides detailed insights to further understand the relationship between structure–activity and the role of surface Mo species as well as their aggregation state in CO2-ODHE.

Highly Dispersed CoO Embedded on Graphitized Ordered Mesoporous Carbon as an Effective Catalyst for Selective Fischer–Tropsch Synthesis of C5+ Hydrocarbons

Herein, we report the high Fischer–Tropsch synthesis performance of the Co-based catalysts supported on graphitized ordered mesoporous carbon (GMC-900) by using a facile strategy. Compared with CMK-3 and active carbon (AC), the obtained GMC-900 by using pollution-free soybean oil as a carbon source exhibited enhanced catalytic performance after loading Co species due to its highly crystallized graphitic structure and uniform dispersion of CoO. As a result, Co/GMC-900 was an effective catalyst with the maximum C₅₊ selectivity of 52.6%, which much outperformed Co/CMK-3 and Co/AC. This research provides an approach to produce advanced Co-based catalysts with satisfactory performance for efficient Fischer–Tropsch synthesis.

Photo-assisted thermal catalytic Fischer-Tropsch Synthesis over Co-Cu/CeO2

Generally, the increase in temperature in the Fischer-Tropsch synthesis accelerates the conversion of CO but reduces the selectivity of high value-added products due to the increase in the percentage of...

Functionalized Carbon Materials in Syngas Conversion

Functionalized carbon materials are widely used in heterogeneous catalysis due to their unique properties such as adjustable surface properties, excellent thermal conductivity, high surface areas, tunable porosity, and moderate interactions with guest metals. The transformation of syngas into hydrocarbons (known as the Fischer-Tropsch synthesis) or oxygenates is an exothermic reaction and is typically catalyzed by transition metals dispersed on functionalized supports. Various carbon materials have been employed in syngas conversions not only for improving the performance or decreasing the dosage of expensive active metals but also for building model catalysts for fundamental research. This article provides a critical review on recent advances in the utilization of carbon materials, in particular the recently developed functionalized nanocarbon materials, for syngas conversions to either hydrocarbons or oxygenates. The unique features of carbon materials in dispersing metal nanoparticles, heteroatom doping, surface modification, and building special nanoarchitectures are highlighted. The key factors that control the reaction course and the reaction mechanism are discussed to gain insights for the rational design of efficient carbon-supported catalysts for syngas conversions. The challenges and future opportunities in developing functionalized carbon materials for syngas conversions are briefly analyzed.

An Efficient Catalyst Derived from Carboxylated Lignin-Anchored Iron Nanoparticle Compounds for Carbon Monoxide Hydrogenation Application

Catalytic activity and target product selectivity are strongly correlated to the size, crystallographic phase, and morphology of nanoparticles. In this study, waste lignin from paper pulp industry is employed as the carbon source, which is modified with carboxyl groups at the molecular level to facilitate anchoring of metals, and a new type of carbon-based catalyst was obtained after carbonization. As a result, the size of the metal particles is effectively controlled by the chelation between -COO- and Fe3+. Furthermore, Fe/CM-CL with a particle size of 1.5-2.5 nm shows excellent catalytic performance, the conversion of carbon monoxide reaches 82.3%, and the selectivity of methane reaches 73.2%.

Arming wood carbon with carbon-coated mesoporous nickel-silica nanolayer as monolithic composite catalyst for steam reforming of toluene

Steam reforming is an effective measure for biomass tar elimination as well as H₂-rich syngas (H₂ + CO) production. However, the granular or powdery Ni-based catalysts are prone to deactivation, which is caused by inappropriate mass transfer and clogging of catalyst bed. Herein, monolithic wood carbon (WC) with low-tortuosity microchannels is armed with a carbon-coated mesoporous nickel-silica nanocomposite (Ni-SiO₂@C) layer via an evaporation-induced self-assembly and calcination procedure for toluene (tar model compound) steam reforming. The quality of the Ni-SiO₂@C layer growing on the surface of WC microchannel is affected by the molar ratios of Si/Ni feed. A uniform thin-layer coverage is obtained on the Ni-15SiO₂@C/WC (Si/Ni = 15) catalyst, where highly dispersed Ni nanoparticles (average size of 6.6 nm) with appropriate metal-support interaction and remarkable mechanical strength are achieved. The mass transfer, coke resistance, and hydrothermal stability of the Ni-15SiO₂@C/WC catalyst were significantly improved by the multilevel structure assembled from the WC microchannels and the secondary ordered SiO₂ mesopores. A stable toluene conversion over 97% with an H₂ yield of 135 μmol/min was obtained at 600 °C on the Ni-15SiO₂@C/WC catalyst. This work opens a new window for facilely constructing high-performance wood carbon-based monolithic tar reforming catalyst.

Metal Organic Framework (MOF)/Wood Derived Multi-cylinders High-Power 3D Reactor

3D monolithic reactor has shown great promise for varied heterogeneous catalysis reactions including water treatment, energy generation and storage, and clean fuel production. As a natural porous material, macroporous wood is regarded as an excellent support for inorganic catalyst due to its abundant polar functional groups and channels. On the other hand, a metal organic framework (MOF) has been widely used as heterogeneous catalyst due to its high specific surface area and large amount of microporosities. Combining macroporous wood and a microporous MOF is expected to produce a high-performance 3D reactor and is demonstrated here for Fischer-Tropsch synthesis. The carbonized MOF/wood reactor retains the original cellular structure with over 180 000 channels/cm². When being decorated with hexagonal-shaped core-shell Co@C nanoparticles aggregates derived from Co-MOF, the MOF/wood reactor resembles a multi-cylinders reactor for Fischer-Tropsch synthesis. Because of the unique combination of macro- and microporous hierarchical structure, the 3D MOF/wood reactor demonstrates exceptional performance under high gas hourly space velocity (81.2% CO conversion and 48.5% C₅₊ selectivity at 50 L·h^-1·g_cat^-1 GHSV). This validates that MOF/wood can serve as a multi-cylinders and high-power reactor for catalytic reactions, which is expected to be applicable for environmental and energy applications.

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.

Highly efficient solar light-driven photocatalytic hydrogen production over Cu/FCNTs-titania quantum dots-based heterostructures

The need for clean and eco-friendly energy sources has increased enormously over the years due to adverse impacts caused by the detrimental fossil fuel energy sources on the environment. This work reports the safest and most efficient route for hydrogen generation using solar light receptive functionalized carbon nanotubes-titania quantum dots (FCNT-TQDs) as photocatalysts under the influence of solar light irradiation. Predominantly, dual capability of CNT as co-catalyst and photo-sensitizer reduced the recombination rate of charge carriers, and facilitated the efficient light harvesting. The bulk production of hydrogen via water harvesting is considered, wherein photocatalyst synthesized was tuned by the optimum addition of copper to achieve higher production rate of hydrogen up to 54.4 mmol h^-1g^-1, nearly 25-folds higher than that of pristine TiO₂ quantum dots. Addition of copper has a crucial role in improving the rate of hydrogen generation. The ternary composite exhibited 5.4-times higher hydrogen production compared to FCNT-TQDs composite.

Stabilizing Optimal Crystalline Facet of Cobalt Catalysts for Fischer-Tropsch Synthesis

Developing efficient catalysts with a stable optimal crystalline facet is highly promising yet challenging for the Fischer-Tropsch synthesis (FTS). Here, we demonstrate a coating strategy to fabricate a stable optimal cobalt-facet catalyst. The catalyst (Co@C-SiO₂) is composed of a single crystalline core, a wrapped carbon layer, and an amorphous silica shell. The moderate metal-support interaction endowed by carbon, combining the confined effect of the silica shell, protects and maintains the single-crystal structure and optimal crystalline facet of the core, that is, Co(10-11). Due to the unique core-shell nanostructure and optimal cobalt facets, our Co@C-SiO₂ catalyst shows a remarkable low methane selectivity (5.3%), high activity (TOF = 4.0 × 10^-2 s^-1), C₅₊ selectivity (88.9%), and more importantly, excellent stability (TOS = 168 h) in FTS.

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.

New Understandings of the Relationship and Initial Formation Mechanism for Pseudo-lignin, Humins, and Acid-Induced Hydrothermal Carbon

The generation of pseudo-lignin as byproduct during the lignocellulose acidic pretreatment has been proposed for many years. However, the detailed formation mechanism is still unclear. Moreover, there is a lack of understanding in the initial reaction during the formation of humins (byproducts in furfural production) and acid-induced hydrothermal carbon (carbon material). In this work, the initial formation of these three substances were investigated. We first found the common feature of their formation process was that carbohydrate-hydrolyzed compounds could form black polymers by condensing in acidic media, but the difference was dependent on the reaction degree. Furthermore, the results revealed that oxidation was an accelerator for condensations during producing black polymers because oxidized compounds could enhance the acidity of the reaction system. However, condensations of oxidized compounds were more difficult to proceed. Meanwhile, during the initial stage, the dominating pathway was that furfural condensed with itself and isomerized xylose via aldol-condensation.