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Wastewater detoxication and sulfate purification of flue gas desulfurization wastewater by the simultaneous catalytic oxidation of SO32− and separation of Se is desirable for the circular economy, but still faces many challenges. Here, an oxygen-vacancy-enriched cobalt-ceria (OV-CoO/CeO2) bimetallic oxide was fabricated that increased the catalytic oxidation rate of SO32− to 0.1735 mmol L−1 s−1, 13 times that of the uncatalyzed reaction. The Se adsorption efficiency reached 92% with an adsorption capacity over 120 mg g−1. The homogeneous surface diffusion model predicted the Se adsorption behavior, and the surface diffusion coefficient was 4.17 × 10−13 cm2 s−1. The free energy for Se adsorption on OV-CoO/CeO2 was 10.09 kJ mol−1, indicating chemisorption. Characterization of the catalyst showed that the ceria dioxide (CeO2) induced the formation of cobalt oxide (CoO) nanoclusters, which were highly dispersed on the CeO2 lamella matrix, creating more available Co sites and oxygen vacancies (OVs). The Ce4+/Ce3+ redox pair coupled with the abundant OVs increased the Co2+-induced catalytic oxidation of SO32− by increasing the yield and transfer of O* by OV-O2. The contribution of different components to Se adsorption was in the order CeO2 > CoO > OVs. The surface –OH on Ce4+/Ce3+/Co2+ dominated the Se adsorption by forming Me–O–SeOx2−, and the reaction between Me–O* and Se also contributed to Se adsorption. This dual functional material may provide a new method for the simultaneous production of high-quality sulfate and separation of toxic Se from flue gas desulfurization wastewater. [ABSTRACT FROM AUTHOR]

Oxidation of magnesium sulfite is a key step in the wet magnesia desulfurization. Using the mixture of waste corn stalk (CS) and activated sludge (AS) as a support, the cobalt‐based catalyst was prepared by the impregnation method to promote the oxidation rate. The results indicated that the catalysis performance is highly dependent on the ratio of CS/AS in which 8:2 is the optimal, and that with the cobalt loading of 0.6% dominates the catalytic activity. The physicochemical properties of catalyst were identified by FTIR, XRD, TEM and XPS to reveal the catalytic mechanism. The catalyzed oxidation kinetics of magnesium sulfite was investigated in a bubbling tank. The reaction orders with respect to catalyst, magnesium sulfite and oxygen were achieved to be 0.75, 0 and 0.67, respectively. The apparent activation energy were derived as 34.9 kJ·mol−1. Integrating with a three‐phase reaction model, it was inferred that the overall oxidation is controlled by the inner diffusion of oxygen. The research results can serve as a reference for the development of low‐cost catalytic techniques for the magnesia desulfurization. © 2018 American Institute of Chemical Engineers Environ Prog, 38: 201–207, 2019 [ABSTRACT FROM AUTHOR]

Sulfur dioxide (SO2) emission has become a crucial problem, especially in developing countries since it is one of the main reasons for the formation of acid precipitation and the secondary formation of fine particulate matter (PM2.5). Wet magnesia desulfurization stands out as a widely used practical approach for the control of SO2 due to its high removal efficiency, low operating cost and potential valuable by-products. However, the effluent of magnesium sulfite (main by-product) can reemit SO2 and cause water pollution. Thus, it is important, but challenging, to enhance the oxidation rate to improve the utilization of MgSO4 for sustainable resources and meanwhile downsize the absorbing tower. Herein, we report a series of graphitic carbon nitride (g-C3N4)-assembled transition metal catalysts (M–C3N4) for the first time via a facile and environmentally friendly synthetic route as a new generation of catalysts for the oxidation of magnesium sulfite. We have performed both theoretical evaluation and deep experimental validation of the series of M–C3N4 materials, and in particular, the cobalt–C3N4 material since it possesses the best catalytic activity reported to date, which is comparable to that of aqueous precious metal benchmarks but only with a 2.4 wt% cobalt loading. Additionally, the ability to recycle the Co–C3N4 complex is investigated to facilitate its practical application. This fabrication method is expected to provide a new concept for the construction of multifunctional nanocomposites for a large variety of industrially relevant desulfurization applications. [ABSTRACT FROM AUTHOR]

Amine-based scrubbing technique is recognized as a promising method of capturing CO 2 to alleviate climate change. However, the less stability and poor acidity of solid acid catalysts (SACs) limit their potential to further improve amine regeneration activity and reduce the energy penalty. To address these challenges, here, we introduce two-dimensional (2D) cobalt-nitrogen-doped carbon nanoflakes (Co-N-C NSs) driven by a layered metal-organic framework that work as SACs. The designed 2D Co-N-C SACs can exhibit promising stability, superhydrophilic surface, and acidity. Such 2D structure also contains well-confined Co-N 4 Lewis acid sites and -OH Brønsted acid sites to have a synergetic effect on C-N bond disruption and significantly increase CO 2 desorption rate by 281% and reduce the reaction temperatures to 88 °C, minimizing water evaporation by 20.3% and subsequent regeneration energy penalty by 71.7% compared to the noncatalysis.

Cobalt (Co)-based catalysts can efficiently reduce the heat waste from sulfate concentration by enhancing sulfite oxidation during wet flue gas desulfurization system. However, arsenic (As) can poison such catalysts and migrate into the sulfate by-products, resulting in severe secondary pollution. In this study, a zero-valent Co/iron (Fe)-based nanoparticle (NZV-Co 2 Fe 1 ) was fabricated and applied as a bifunctional catalyst/adsorbent. The catalytic stability of the Co-based catalyst was enhanced by the introduction of Fe because the poisonous effect of As was substantially suppressed because of the high adsorption capacity of Fe for As. Compared with the noncatalytic benchmark, the presence of 0.5 g/L NZV-Co 2 Fe 1 can increase the rate of MgSO 3 oxidation by approximately 12-fold even at a high concentration of As (2.5 mg/L). The Langmuir model was fitted to the As adsorption isotherms, indicating that As uptake is a single-layer adsorption process. The pseudo-second-order kinetic model indicated that As was removed through chemisorption. The oxidation pathway of As(III) involves reactive radicals (mainly OH, SO 4 - and SO 5 - ) and ligand-to-metal charge transfer between SO 3 2- and Co 2+ . The availability of MgSO 3 improved the removal efficiency at high concentrations of As(III) (1 mg/L). These results indicate that using NZV-Co 2 Fe 1 as a catalyst to purify the by-products of flue gas desulfurization can effectively prevent secondary pollution., Competing Interests: Declaration of competing interest Lidong Wang reports financial support was provided by Foundation for Innovative Research Groups of the National Natural Science Foundation of China. Lidong Wang reports financial support was provided by The Fundamental Research Funds for the Central Universities. Tieyue Qi reports financial support was provided by The Natural Science Foundation of Hebei Province. Tieyue Qi reports financial support was provided by Foundation for Innovative Research Groups of the National Natural Science Foundation of China. Lidong Wang reports a relationship with Foundation for Innovative Research Groups of the National Natural Science Foundation of China that includes: funding grants. Lidong Wang reports a relationship with Fundamental Research Funds for the Central Universities that includes: funding grants. Tieyue Qi reports a relationship with The Natural Science Foundation of Hebei Province that includes: funding grants. Tieyue Qi reports a relationship with Foundation for Innovative Research Groups of the National Natural Science Foundation of China that includes: funding grants., (Copyright © 2022. Published by Elsevier B.V.)

Substantial energy penalty of valuable sulfate recovery restricts the efficiency of wet desulfurization and increases the risk of Hg 0 reemission. Although the enhanced sulfite oxidation rate with cobalt-based materials can increase the energy efficiency, inactivation and poisoning of catalyst due to the competition of reactant must be addressed. Here we obtained a superwetting two-dimensional cobalt-nitrogen-doped carbon (2D Co-N-C) nanosheet featuring confined catalysis/adsorption sites for the energy-efficient sulfite oxidation and Hg 2+ adsorption. The designed structure exhibits enhanced surface polarity, availability and short reactant diffusion path, thus enabling the significant catalytic TOF value of 0.085 s -1 and simultaneous mercury removal ability of 143.26 mg·g -1 . The catalyst nanosheets present regenerating stabilities to improve cost-efficiency. By deployment of the Co-N-C catalysts, a marked reduction of heat penalty up to 69% can be achieved, which makes this catalytic pathway for sulfur resource recovery economically feasible in real industry scenario.

High energy duty restricts the application of amine-based absorption in CO 2 capture and limits the achievement of carbon neutrality. Although regenerating the amine solvent with solid acid catalysts can increase energy efficiency, inactivation of the catalyst must be addressed. Here, we report a robust metal-organic framework (MOF)-derived hybrid solid acid catalyst (SO 4 2- /ZIF-67-C@TiO 2 ) with improved acidity for promoting amine regeneration. The TiO 2 coating effectively prevented the active components stripping from the surface of the catalyst, thus prolonging its lifespan. The well-protected Co-N x sites and protonated groups introduced onto the TiO 2 surface increased the amount and rate of CO 2 desorption by more than 64.5 and 153%, respectively. Consequently, the energy consumption decreased by approximately 36%. The catalyzed N-C bond rupture and proton transfer mechanisms are proposed. This work provides an effective protection strategy for robust acid catalysts, thus advancing the CO 2 capture with less energy duty.

The re-emission of NH 3 and SO 2 caused by the decomposition of (NH 4 ) 2 SO 3 is a crucial concern in ammonia-based desulfurization. In this study, a novel Co 3 O 4 -NPs@KIT-6 catalyst with a three-dimensional two-helix structure is proposed for converting (NH 4 ) 2 SO 3 into (NH 4 ) 2 SO 4 . The oxidation rate of (NH 4 ) 2 SO 3 with the catalyst was 7.5 times that without any catalyst, and this improvement was attributed to appropriately dispersed Co 3 O 4 nanoparticles with a size of 4-10 nm that interacted with the KIT-6 support. Therefore, the number of active sites with substitution and hole defects was substantially increased, which is advantageous for high catalytic activities. Consequently, the amount of NH 3 and SO 2 re-emission during (NH 4 ) 2 SO 3 oxidation was reduced by 43.9%, which considerably reduced potential environmental risks. The results of this study serve to advance ammonia desulfurization by improving the desulfurization efficiency, downsizing the oxidation tank, and generating considerable profit from efficient reclaiming of (NH 4 ) 2 SO 4 as a fertilizer.

The forced oxidation of magnesium sulfite (MgSO 3 ) aims to not only reclaim the by-product in the magnesia desulfurization, but also lower the risk of secondary pollution. The non-porous titanium dioxide nanoparticle was used as a support to prepare the cobalt catalyst (Co-TiO 2 ) in order to expedite the oxidation rate. This fabricated Co-TiO 2 was characterized by inductively coupled plasma optical emission spectroscopy (ICP-OES), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), and energy dispersive spectroscopy (EDS) to figure out its catalytic mechanism. The results revealed that the cobalt nanoparticles were uniformly dispersed on the surface of the TiO 2 in forms of Co 3 O 4 and Co 2 O 3 . The kinetics of the MgSO 3 oxidation catalyzed by the prepared Co-TiO 2 was investigated in a bubbling tank reactor, indicating that the oxidation rate was dependent on the catalyst concentration, oxygen partial pressure, pH value, and the reaction temperature. Compared with the reported porous catalyst (Co-CNTs), the activation energy with the Co-TiO 2 (17.29kJmol -1 ) decreased by 50.9%, resulting in a good catalytic performance in sulfite oxidation. The findings will help advance the industrial application of the novel magnesia desulfurization process., (Copyright © 2017 Elsevier B.V. All rights reserved.)