Insight into the Transformation Behaviors of Dioxins from Sintering Flue Gas in the Cyclic Thermal Regeneration by the V<sub>2</sub>O<sub>5</sub>/AC Catalyst-sorbent

Carbon-based catalysts have been extensively used for flue gas desulfurization (FGD) and have exerted great importance in controlling SO2 emissions over the past decades. However, many fundamental details about the nature of the active sites and desulfurization mechanism still remain unclear. Here, we reported the experimental and theoretical identifications of active sites in FGD on carbon catalysts. Temperature-programmed decomposition allowed us to modulate the number of oxygen functional groups on carbon catalysts and to establish its correlation with desulfurization activity. Selective passivation further demonstrated that the ketonic carbonyl (CO) groups are the intrinsic active sites for FGD reaction. Combined with transient response experiments, quasi-in situ X-ray photoelectron spectroscopy, and density functional theory simulations, it was revealed that desulfurization reaction on carbon catalysts mainly proceeded via the Langmuir–Hinshelwood mechanism, during which the nucleophilic ketonic CO groups served as active sites for chemically absorbing SO2 and their adjacent sp2-hybridized carbon atoms dissociatively activated O2. It also turned out that the formation of H2SO4 is the reaction barrier step. The output of this study should not only advance the understanding of desulfurization at the atomic scale but also provide a general guideline for the rational design of efficient carbon catalysts for FGD.

Section: Methodsmentioning

confidence: 99%

Identification of Active Sites over Metal-Free Carbon Catalysts for Flue Gas Desulfurization

Yuan

Chen

Wang

et al. 2023

Section: Introductionmentioning

confidence: 99%

“…In industrial applications, NO x is usually purified via a moving bed system with simultaneous removal of SO 2 (Figure S1), and carbon materials undergo sequential processes of desulfurization, regeneration, and NH 3 -SCR. , It is widely accepted that H 2 SO 4 is the end product of the desulfurization process over carbon when O 2 and H 2 O coexist and gradually accumulates in the pores. , Obviously, regeneration plays a crucial role in the long-term operation of an integrated removal system. , Li et al investigated the impact of the cyclic desulfurization and regeneration (C-S–R) process on denitration performance and proposed that the enhanced SCR activity could be attributed to the increase in O-containing groups . It is noteworthy that the content and type of S-containing functional groups also developed during the C-S–R process. ,, In other words, in situ S-doping is induced by the C-S–R process.…”

Section: Introductionmentioning

confidence: 99%

In Situ S-Doping Engineering for Highly Efficient NH₃–SCR over Metal-Free Carbon Catalysts: A Novel Synergetic Promotional Mechanism

Zhu,

Yuan,

Peng

et al. 2023

Cyclic desulfurization−regeneration−denitrification based on metal-free carbon materials is one of the most promising ways to remove NO x and SO 2 simultaneously. However, the impact of S-doping induced by the cyclic desulfurization and regeneration (C-S−R) process on the selective catalytic reduction (SCR) is not well understood. Herein, it is demonstrated that the C-S−R process at 500 °C induces in situ S-doping with a significant accumulation of C−S−C structures. NO x conversion was dramatically enhanced from 18.95% of the original sample to 84.55% of the S-doped sample. Density functional theory calculations revealed that the C−S−C structure significantly regulates the electronic structure of the C atom adjacent to the ketonic carbonyl group, thereby significantly altering the NH 3 adsorption configuration with superior adsorption capacity. Moreover, Sdoping induces an extra electron transfer between the N atom of the NH 3 molecule and the C atom of the carbon plane, thereby promoting the activation of NH 3 over the ketonic carbonyl group with a reduced energy barrier. This study elucidates a synergetic promotional mechanism between the ketonic carbonyl group and the C− S−C structure for SCR, offering a novel design strategy for high-performance heteroatom-doped carbon catalysts in industrial applications.

“…Currently, SCR technology with carbon catalysts has been applied to steel sintering through a reaction–regeneration process which consists of a catalytic reactor along with a regenerator. ,, In general, both NO x reduction and SO 2 adsorption occur over carbon catalysts in the catalytic reactor, followed by recycling sulfur from the used carbon catalysts in the regenerator. The regeneration process, in which the used carbon catalysts are thermally treated under N 2 , is critical for preserving long-term operations and decreasing operation costs.…”

Section: Introductionmentioning

confidence: 99%

Potential Risk of NH₃ Slip Arisen from Catalytic Inactive Site in Selective Catalytic Reduction of NO_x with Metal-Free Carbon Catalysts

Yuan

Wang

et al. 2022

Ammonia emissions from industrial processes have rapidly increased in the past years. Recent advances have used carbon-based selective catalytic reduction (SCR) technology combined with a reaction−regeneration process to reduce NO x from sintering flue gas, while NH 3 slip is seldom accounted for in this process. This study demonstrates that although the electrophilic carboxyl groups (−COOH) on metal-free carbon catalysts exhibit strong adsorption toward NH 3 , they do not participate in the SCR reaction. As a result of the competitive adsorption of NH 3 in the reaction step, these catalytic inactive carboxyl groups not only prolong the time to the SCR steady state, but also result in the potential risk of NH 3 slip. A linear relationship with the equimolar ratio between carboxyl groups and slipped NH 3 was established in the regeneration steps. The slip of NH 3 could be alleviated by the decomposition of carboxyl groups, and special attention should be paid to the presence of inactive sites with strong NH 3 adsorption on industrial-employed carbon catalysts. In addition to advancing the understanding of the NH 3 −SCR mechanism, this work also provides valuable opportunities for the control of ammonia emissions from industrial processes.