Effect of Different Reaction Conditions on the Deactivation of Alumina-Supported Cobalt Fischer–Tropsch Catalysts in a Milli-Fixed-Bed Reactor: Experiments and Modeling

Cobalt oxide-alumina catalysts for the methane-assisted selective catalytic reduction of SO2 to sulfur

Preventing emission of pollutants in any kind, is a way to protect global environment. The objective of this study is to develop cobalt catalysts supported on alumina for the conversion of the toxic gas SO2 into elemental sulfur using methane. Although several useful catalysts have been proposed, there is still a need to synthesize a catalyst with a high sulfur yield that is also persistent during on-stream stability. To this end, four different catalysts were prepared using the wet impregnation technique, with Co3O4 content ranging from 0 to 15 wt%. Catalytic activity tests were carried out at atmospheric pressure and temperatures ranging from 550 to 800 °C. The Al2O3-Co (15 %) catalyst exhibited superior performance, with a sulfur yield of 98.1 % at 750 °C. The catalytic stability of the best catalyst was examined using a 20 h on-stream stability test under the optimized conditions including an SO2/CH4 molar feed ratio of 2 at 750 °C. The structural changes of the used catalyst after the stability test were investigated using XRD and TPO analyses. It was revealed that sulfidation of Co3O4 after a short while, results in decreasing the sulfur yield from 98.1 % to 89.8 %.

Non-porous interpenetrating Co-bpe MOF for colorimetric iodide sensing

MOFs with their accessible voids/channels have been explored immensely for sensing due to their exclusive host-guest chemistry. However, unavailability of pores/voids in interpenetrating non-porous MOFs limits their applications in sensing. We herein report for the first time, hitherto, a non-porous MOF with an interpenetrating ladder structure for iodide sensing. A Co-bpe MOF was synthesized by hydrothermal reaction between cobalt nitrate and 1,2-bis(4-pyridyl)ethylene (bpe) in methanol and tested against colorimetric sensing of halides. The supramolecular structure of the Co-bpe MOF was stabilized through strong hydrogen bonding. We propose a double nucleophilic substitution reaction mechanism for iodide detection, which is one of its own kind. While Co-bpe showed a significant color change from dark maroon to dark green in the presence of iodide, the rest of halides did not display any pronounced colorimetric effect. The limit of detection (LOD) of this material was found to be 2.7 × 10^-7 M. This article focuses on the equal competency of non-porous MOF materials with the porous MOFs in sensing applications.

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.

Kinetic data acquisition in high-throughput Fischer–Tropsch experimentation

The emergence of high-throughput experimentation gives new opportunities for accurate and rapid data acquisition for a wide variety of chemical reactions in different fields of application such as hydrocracking, isomerization and syngas conversion.

Performance of diffusion-optimised Fischer–Tropsch catalyst layers in microchannel reactors at integral operation

Simulation study evaluating impact of diffusion on selectivity and productivity for optimised catalyst layers operated at high conversion.

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.

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.

Size dependent stability of cobalt nanoparticles on silica under high conversion Fischer–Tropsch environment

Highly monodisperse cobalt crystallites, supported on Stöber silica spheres, as model catalysts for the Fischer–Tropsch synthesis were exposed to simulated high conversion environments in the presence and absence of CO utilising an in house developedin situmagnetometer. The catalyst comprising the smallest crystallites in the metallic state (average diameter of 3.2 nm) experienced pronounced oxidation whilst the ratio of H₂O to H₂was increased stepwise to simulate CO conversions from 26% up to complete conversion. Direct exposure of this freshly reduced catalyst to a high conversion Fischer–Tropsch environment resulted in almost spontaneous oxidation of 40% of the metallic cobalt. In contrast, a model catalyst with cobalt crystallites of 5.3 nm only oxidised to a small extent even when exposed to a simulated conversion of over 99%. The largest cobalt crystallites were rather stable and only experienced measurable oxidation when subjected to H₂O in the absence of H₂. This size dependency of the stability is in qualitative accordance with reported thermodynamic calculations. However, the cobalt crystallites showed an unexpected low susceptibility to oxidation,i.e.only relatively high ratios of H₂O to H₂partial pressure caused oxidation. Similar experiments in the presence of CO revealed the significance of the actual Fischer–Tropsch synthesis on the metallic surface as the dissociation of CO, an elementary step in the Fischer–Tropsch mechanism, was shown to be a prerequisite for oxidation. Direct oxidation of cobalt to CoO by H₂O seems to be kinetically hindered. Thus, H₂O may only be capable of indirect oxidation,i.e.high concentrations prevent the removal of adsorbed oxygen species on the cobalt surface leading to oxidation. However, a spontaneous direct oxidation of cobalt at the interface between the support and the crystallites by H₂O forming presumably cobalt silicate type species was observed in the presence and absence of CO. The formation of these metal–support compounds is in accordance with conducted thermodynamic predictions. None of the extreme Fischer–Tropsch conditions initiated hydrothermal sintering. Seemingly, the formation of metal–support compounds stabilised the metallic crystallites and/or higher partial pressures of CO are required to increase the concentration of mobile, cobalt oxide-type species on the metallic surface.

Combined Operando X-ray Diffraction/Raman Spectroscopy of Catalytic Solids in the Laboratory: The Co/TiO2 Fischer-Tropsch Synthesis Catalyst Showcase

A novel laboratory setup for combined operando X-ray diffraction and Raman spectroscopy of catalytic solids with online product analysis by gas chromatography is presented. The setup can be used with a laboratory-based X-ray source, which results in important advantages in terms of time-on-stream that can be measured, compared to synchrotron-based experiments. The data quality was much improved by the use of a relatively high-energy MoKα radiation instead of the more conventional CuKα radiation. We have applied the instrument to study the long-term deactivation of Co/TiO2 Fischer-Tropsch synthesis (FTS) catalysts. No sign of Co sintering or bulk oxidation was found during the experiments. However, part of the metallic Co was converted into cobalt carbide (Co2C), at elevated pressure (10 bar). Furthermore, graphitic-like coke species are clearly formed during FTS at atmospheric pressure, whereas at elevated pressure fluorescence hampered the interpretation of the measured Raman spectra.

Active phase distribution changes within a catalyst particle during Fischer–Tropsch synthesis as revealed by multi-scale microscopy

A new combination of three chemical imaging methods has been developed and applied to fresh and spent co-based Fischer–Tropsch catalysts.

Synthesis of higher alcohols by the Fischer–Tropsch reaction over activated carbon supported CoCuMn catalysts

Activated carbon supported CoCu catalysts with structures containing small-sized Co particles bordering large Cu particles favored the formation of C₂₊ alcohols.