High activity in the dry reforming of methane using a thermally switchable double perovskite and in situ generated molecular level nanocomposite

This work emphasizes the dry reforming of methane (DRM) reaction on citrate sol-gel-synthesized double perovskite oxides. Phase pure La2NiMnO6 shows very impressive DRM activity with H2/CO = 0.9, hence revealing a high prospect of next-generation catalysts. Although the starting double perovskite phase gets degraded into mostly binary oxide phases after a few hours of DRM activity, the activity continues up to 100 h. The regeneration of the original double perovskite out of decomposed phases by annealing at near synthesis temperature, followed by the spectacular retention of activity, is rather interesting and hitherto unreported. This result unravels unique reversible thermal switching between the original double perovskite phase and decomposed phases during DRM without compromising the activity and raises challenge to understand the role of decomposed phases evolved during DRM. We have addressed this unique feature of the catalyst via structure-property relationship using the in situ generated molecular level nanocomposite.

Unraveling the effect of particle size of active metals in Ni/MgO on methane activation and carbon growth mechanism

For dry reforming of methane, the active metal particle size of the catalyst has a significant effect on both the reaction activity and the resistance to carbon deposition. In this study, nickel particles of different sizes (Ni13, Ni25, and Ni37) supported on the MgO(100) slab are used to study the mechanism of CH4 activation and carbon growth based on DFT theoretical calculations. According to the results, the energy of adsorption for reaction intermediates changes depending on the size of the active metal. The adsorption process of CH3, CH2, CH and C on Ni25/MgO has a maximum exothermic value. Furthermore, the energy barriers of CH4 four-step dehydrogenation are lowest on Ni25/MgO during the CH4 activation process. The growth process of carbon deposition on the catalysts is also investigated in this work. The results indicate that the growth of carbon from C5 to C6 is difficult to proceed on Ni13/MgO due to size and active site limitation. Additionally, with an increase in particle size of the active metal, the absolute value of growth energy and average carbon binding energy of Cn increase on both Ni25/MgO and Ni37/MgO. It is proved that smaller particle size presents better resistance to carbon deposition. In the studied size range, Ni25/MgO is demonstrated to have greater catalytic activity and better resistance to carbon deposition.

Resolving the Effect of Oxygen Vacancies on Co Nanostructures Using Soft XAS/X-PEEM

Improving both the extent of metallic Co nanoparticle (Co NP) formation and their stability is necessary to ensure good catalytic performance, particularly for Fischer–Tropsch synthesis (FTS). Here, we observe how the presence of surface oxygen vacancies (O_vac) on TiO₂ can readily reduce individual Co₃O₄ NPs directly into CoO/Co⁰ in the freshly prepared sample by using a combination of X-ray photoemission electron microscopy (X-PEEM) coupled with soft X-ray absorption spectroscopy. The O_vac are particularly good at reducing the edge of the NPs as opposed to their center, leading to smaller particles being more reduced than larger ones. We then show how further reduction (and O_vac consumption) is achieved during heating in H₂/syngas (H₂ + CO) and reveal that O_vac also prevents total reoxidation of Co NPs in syngas, particularly the smallest (∼8 nm) particles, thus maintaining the presence of metallic Co, potentially improving catalyst performance.

Cobalt hybrid catalysts in Fischer-Tropsch synthesis

Currently, cobalt and zeolites are used in Fischer-Tropsch synthesis (FTS) to produce gasoline-range hydrocarbons (GRHs) that constitute clean and environmentally friendly fuels. This technology has earned a great deal of attention from researchers across the world, as it provides a substitute for fuel derived from fossil crudes, which have hitherto been the sole source of the petrol and diesel required by the industry. However, owing to the depletion of the earth’s oil and coal reserves and the unfavourable environmental impact of conventional fuel production, an alternative source of fuel is needed. This article provides a critical review of the technological challenges involved in producing middle isoparaffins and olefins (gasoline hydrocarbons) by FTS. These involve combining cobalt-based catalysts and zeolites to form hybrid catalysts. In this review, we address most of these by setting out each method of creating cobalt and zeolite hybrid catalysts in turn, so that researchers can identify which applications are most effective for producing GRHs.

Investigation of the deactivation behavior of Co catalysts in Fischer–Tropsch synthesis using encapsulated Co nanoparticles with controlled SiO2 shell layer thickness

The deactivation behavior of Co catalysts was clearly elucidated using Co nanoparticles confined by a porous SiO₂ shell layer with varying thickness and different reaction temperatures.

Fischer–Tropsch synthesis using a cobalt catalyst supported on graphitic carbon nitride

The nitrogen atoms in a g-C₃N₄ support improved cobalt reduction in a prepared Co/g-C₃N₄ catalyst.

Phase Controlled Synthesis of Pt Doped Co Nanoparticle Composites Using a Metal-Organic Framework for Fischer–Tropsch Catalysis

Recently, metal nanoparticles embedded in porous carbon composite materials have been playing a significant role in a variety of fields as catalyst supports, sensors, absorbents, and in energy storage. Porous carbon composite materials can be prepared using various synthetic methods; recent efforts provide a facile way to prepare the composites from metal-organic frameworks (MOFs) by pyrolysis. However, it is usually difficult to control the phase of metal or metal oxides during the synthetic process. Among many types of MOF, recently, cobalt-based MOFs have attracted attention due to their unique catalytic and magnetic properties. Herein, we report the synthesis of a Pt doped cobalt based MOF, which is subsequently converted into cobalt nanoparticle-embedded porous carbon composites (Pt@Co/C) via pyrolysis. Interestingly, the phase of the cobalt metal nanoparticles (face centered cubic (FCC) or hexagonal closest packing (HCP)) can be controlled by tuning the synthetic conditions, including the temperature, duration time, and dosage of the reducing agent (NaBH4). The Pt doped Co/C was characterized using various techniques including PXRD (powder X-ray diffraction), XPS (X-ray photoelectron spectroscopy), gas sorption analysis, TEM (transmission electron microscopy), and SEM (scanning electron microscopy). The composite was applied as a phase transfer catalyst (PTC). The Fischer-Tropsch catalytic activity of the Pt@Co/C (10:1:2.4) composite shows 35% CO conversion under a very low pressure of syngas (1 MPa). This is one of the best reported conversion rates at low pressure. The 35% CO conversion leads to the generation of various hydrocarbons (C1, C2–C4, C5, and waxes). This catalyst may also prove useful for energy and environmental applications.

Adsorption of water and n-hexane on pristine and oxidized carbon nanotube supports of cobalt-based Fischer–Tropsch catalysts

Adsorption of water and n-hexane by oxidized and pristine CNTs at different stages of Co/CNT catalyst preparation has been studied to reveal the effect of the support surface functionalization on the catalyst selectivity in Fischer–Tropsch synthesis.

Modeling the kinetics of cobalt Fischer-Tropsch catalyst deactivation trends through an innovative modified Weibull distribution

Since the increase in clean energy demand is driven by environmental concerns, energy management is an ever-lasting issue globally. Among the different scenarios for energy manufacturing, the catalytic route through the famous process named Fischer-Tropsch Synthesis provides beneficial consequences including pollution reduction and economic efficiency, among others. In this regard, catalyst stability must be taken into account as a crucial performance parameter, especially in the expensive cobalt-catalyzed CO hydrogenation processes. As catalyst deactivation seems to be inevitable in catalytic processes, deactivation issues such as the extent, failure rate, or reactivation significantly influence the exploration, development, design, and operation of commercial processes. Accordingly, the deactivation trend of a cobalt-based catalyst was modeled via an innovative Weibull distribution base, which presents a significant advance over the existing macroscopic deactivation models. Being employed to obtain informative equations, the model parameters provide valuable information about the catalyst lifetime, which can be used as a useful predictive tool for industrial control purposes.

Assembly and activation of supported cobalt nanocrystal catalysts for the Fischer–Tropsch synthesis

Low-temperature oxidation of cobalt nanocrystals is the preferred treatment to obtain the most uniformly distributed and active Fischer–Tropsch synthesis catalyst.

Effect of hierarchical meso–macroporous structures on the catalytic performance of silica supported cobalt catalysts for Fischer–Tropsch synthesis

A series of meso–macroporous silica supports with the same macroporous diameter but different mesoporous diameters were prepared by introducing phase separation into a sol–gel process and used to prepare cobalt catalysts for Fischer–Tropsch synthesis.

Advances in the preparation of highly selective nanocatalysts for the semi-hydrogenation of alkynes using colloidal approaches

The present review describes the contributions and perspectives in the field of the selective hydrogenation of alkynes involving the utilization of colloidal methodologies.

Large-scale synthesis of uniformly loaded cobalt nanoparticles on alumina for efficient clean fuel production

The Co/Al₂O₃ nanocatalyst prepared with tens of gram scale in a batch, showed good CO conversion (∼76%), very high CTY value (∼1.4 × 10⁻⁴ mol_CO g_Co⁻¹ s⁻¹) and remarkable hydrocarbon productivity (∼1.0 g_HC g_cat⁻¹ h⁻¹) under controlled FTS conditions.

Effects of macropores on reducing internal diffusion limitations in Fischer–Tropsch synthesis using a hierarchical cobalt catalyst

Internal diffusion limitations in Fischer–Tropsch catalysts strongly affects their catalytic activities and product selectivities.

Highly productive cobalt nanoparticles supported on mesocellular silica foam for the Fischer–Tropsch reaction

The Co/MCF nanocatalyst containing well-dispersed and highly loaded Co nanoparticles exhibits very high hydrocarbon productivity in Fischer–Tropsch synthesis.

Hydrogen Dissociation, Spillover, and Desorption from Cu-Supported Co Nanoparticles

Co-Cu nanoparticles have recently been explored for Fischer-Tropsch synthesis (FTS) as a way to combine the long chain selectivity of Co with Cu's activity for alcohol formation in order to synthesize oxygenated transportation fuels. Depending on particle size, hydrogen dissociation can be a rate-determining step in cobalt-catalyzed FTS. To understand the fundamentals of uptake and release of hydrogen from the Co/Cu bimetallic system, we prepared well-defined Co nanoparticles on Cu(111). We demonstrate that hydrogen spills over from dissociation sites on the Co nanoparticles to the Cu(111) surface via the Co-Cu interface and that desorption of H occurs at a temperature that is lower than from Co or Cu alone, which we attribute to the Co-Cu interface sites. From this data, we have constructed an energy landscape for the facile dissociation, spillover, and desorption of hydrogen on the Co-Cu bimetallic system.

Segregation of Fischer–Tropsch reactants on cobalt nanoparticle surfaces

Scanning tunnelling microscopy reveals segregation of carbon monoxide and hydrogen, the two Fischer–Tropsch synthesis reactants, on cobalt nanoparticles at catalytically relevant coverages. Density functional theory calculations elucidate the energetics.