To be support or promoter: the mode of introducing ceria into commercial V2O5/TiO2 catalyst for enhanced Hg0 oxidation

Unraveling the anti-poisoning mechanism of highly dispersed Ni atoms enhanced porous MnOx catalysts in the selective reduction of NOx by NH3

Rationally designing catalysts suitable for flue gas purification at low temperatures and unraveling the anti-poisoning mechanism at the atomic level remain challenges. Here, a highly dispersed Ni-doped MnOx catalyst (Ni0.1Mn0.9Ox) was constructed and applied for selective catalytic reduction (SCR) of nitrogen oxides (NOx). The long-term stability of Ni0.1Mn0.9Ox is up to 80% (180 °C) after 18 h under SO2 and H2O conditions. This is due to the fact that the highly dispersed Ni atoms enhance the redox and surface acidity of MnOx, and modulate the electronic structure of the active Mn sites. The denitrification reaction on Ni0.1Mn0.9Ox mainly follows the Eley-Rideal mechanism. The anti-poisoning mechanism is that the introduction of Ni weakens the electron transfer between the Mn site and SO2, thereby inhibiting the adsorption of SO2. In particular, the H2O adsorbed on the Ni sites is decomposed to replenish the depleted Brønsted acid sites, which facilitates the adsorption of NH3. However, an excess of H2O can have an inhibitory effect. In addition, the mesoporous structure may increase the mass transfer rate and reduce the accumulation of harmful substances. This study provides viable insights for the design of SCR catalysts with excellent anti-poisoning ability.

Simultaneous analysis of sulfur and mercury occurrence forms in coal by sequential chemical extraction procedures combined with plasma low-temperature ashing and their correlation study

Sulfur and mercury are two pollution elements with affinity, and their correlation studies are crucial for understanding their migration, transformation, and directional regulation during coal thermal conversion. Studies on the correlation between sulfur and mercury in coal have been inconsistent, so it is necessary to classify the occurrence forms of sulfur and mercury in coal simultaneously and study the correlation between the same form of sulfur and mercury. The sequential chemical extraction procedures (SCEPs) combined with plasma low-temperature ashing (PLTA) have obvious advantages in simultaneous analysis of the occurrence forms of sulfur and mercury in coal containing fine-grained pyrite. The content accuracy of form sulfur and form mercury is increased by 11.59 % and 6.22 %, respectively. The total contents of organic S and sulfide S, organic matrix-bound Hg and sulfide-bound Hg in coal are 56.73 %-85.51 % and 65.49 %-90.86 %, respectively. There is a significant positive correlation between organic S and organic matrix-bound Hg, sulfide S and sulfide-bound Hg, and the correlation index is 0.9996 and 0.9998, respectively. This study lays a theoretical foundation for the migration and transformation of sulfur and mercury in the process of thermal conversion.

Remove elemental mercury from simulated flue gas by CeO2-modified MnOx/HZSM-5 adsorbent

In this study, we synthesized a Ce-modified Mn/HZSM-5 adsorbent via the ultrasound-assisted impregnation for Hg0 capture. Given the addition of 15% CeO2, ~ 100% Hg0 efficiency was reached at 200 °C, suggesting its promotional effect on Hg0 removal. The doped Ce introduced additional chemisorbed oxygen species onto the adsorbent surfaces, which facilitated the oxidation of Hg0 to HgO. Even though adding CeO2 led to a weakened adsorbent acidity, yet it appeared that this negative affect could be completely overcome by the enhanced oxidative ability, which finally endowed Ce-modified Mn/HZSM-5 with a satisfactory Hg0 removal performance within the whole investigated temperature range. During the Hg0 capture process, chemisorption was predominant with Mn4+operating as the main active site for oxidizing Hg0 to Hg2+. Finally, the 15Ce-Mn/HZSM-5 adsorbent exhibited good recyclability and stability. However, its tolerance to H2O and SO2 appeared relatively weak, suggesting that some modification should be conducted to improve its practicality.

Three-dimensional porous CuO-modified CeO2-Al2O3 catalysts with chlorine resistance for simultaneous catalytic oxidation of chlorobenzene and mercury: Cu-Ce interaction and structure

Chlorine poisoning effects are still challenging to develop efficient catalysts for applications in chlorobenzene (CB) and mercury (Hg⁰) oxidation. Herein, three-dimensional porous CuO-modified CeO₂-Al₂O₃ catalysts with macroporous framework and mesoporous walls prepared via a dual template method were employed to study simultaneous oxidation of CB and Hg⁰. CuO-modified CeO₂-Al₂O₃ catalysts with three-dimensional porous structure exhibited outstanding activity and stability for simultaneous catalytic oxidation of CB and Hg⁰. The results demonstrated that the addition of CuO into CeO₂-Al₂O₃ can simultaneously enhance the acid sites and redox properties through the electronic inductive effect between CuO and CeO₂ (Cu²⁺+Ce³⁺↔Cu⁺+Ce⁴⁺). Importantly, the synergistic effect between Cu and Ce species can induce abundant oxygen vacancies formation, produce more reactive oxygen species and facilitate oxygen migration, which is beneficial for the deep oxidation of chlorinated intermediates. Moreover, macroporous framework and mesoporous nanostructure dramatically improved the specific surface area for enhancing the contact efficiency between reactants and active sites, leading to a remarkable decrease of byproducts deposition. CB and Hg⁰ had function of mutual promotion in this reaction system. In tune with the experimental results, the possible mechanistic pathways for simultaneous catalytic oxidation of CB and Hg⁰ were proposed.