Study On Microporous Materials For NO Catalytic Oxidation And CO₂ Capture

NOx including NO and NO₂, as the primary pollutant in the atmosphere, have severely threatened our life and living environment, resulting in acid rain, O3 depletion, photochemical smog, respiratory diseases, and secondary pollutants such as PM2.5 and PM10. How to control the NOx emissions from power plant becomes challenging. The traditional and prevalentl selective catalytic reduction technology（SCR） with V2O5-WO3/TiO2 suffers from catalyst deactivation by fly ash and high costs for gas-reheating to reach the ideal temperature for SCR. Comparably, catalytic oxidation at low temperature combined with subsequent liquid absorption is attractive due to the low-temperature characteristic and the potential of simultaneous removal of co-existing pollutants（e.g., Hg, dioxins）. However, the mechanism of NO oxidation is still in debate. Here, based on the novel study of carbon and zeolite catalyzed NO oxidation, confinement mechanism for NO oxidation and new catlaysts for NO oxidation with good SO2 resistance is proposed and developed. This finding make the technology practical in industrial use.In this paper, activated carbon fiber cloth（ACFC-10, pore size 7?） was selected as the catalyst for NO oxidation. In-situ three cyclic experiments, NO2 pre-treatment combined with subsequent NO oxidation, and NO2 pre-treatment in different atmospheres were employed. It is shown that the physical properties of the activated carbon control its steady-state NO oxidation kinetics, while carbon’s adsorption and surface reaction properties impact the transient kinetics by adsorbing and reacting with formed NO2 to regenerate NO. A consequtive mechanism was firstly proposed that includes NO rapid oxidation to NO2 in the micropores and NO2 subsequent oxidation over activated carbon along with the release of NO and formation of surface functional groups. This theory challenges the previous accepted concept that NO2 is formed through the decomposition of adsorbed NO3- species.Zeolites with different physical and chemical properties（ZSM-5, beta, USY, NaY, SAPO-11, SAPO-34, SAPO-5, MOR, ZSM-22, MCM-22 and MCM-41） were investigated as catalysts for NO oxidation. All the zeolites can catalyze NO to NO2 in spite of the differences in steadystate oxidation kinetics. The steady state oxidation kinetics is strongly related to the physical properties（surface area, pore volume, pore size and cavity size）. An unprecedented mechanism that NO oxidation is achieved via a transition state approach was proposed, and the conversion efficiency is shown to be different because of the extent to which the confinement of transition state determines the energy of transition state. The confinement decreases the free energy required for the formation of transition state, then accelerates the reaction rates. By means of the selection rule of the match between transition state and void space in zeolite, 82 zeolites from the database of international zeolite association was selected for further potential study.Activated carbon and zeolites with micropore features can catalzye NO oxidation through the pathway of the confinement of transition state. Therefore, metal-organic framework material-UiO-66 was frist proposed as the catalyst for NO oxidation. As expected, UiO-66 can catalyze NO oxidation with a conversion efficiency of 28.3 oC at 25 oC under the conditions of 400 μL·L-1NO and 10 vol% O2. With the NO concentration increasing, the oxidation efficiency increases, and the reaction order of NO is 2. Despite that activated carbons, zeolites, and UiO-66 have microporous structure, the discrepancies in chemical properties result in different behaviors on NO2 adsorption. Activated carbon demonstrated the highest NO2 adsorption capacity, while zeolites and UiO-66 can effective inhibit the release of NO during NO2 adsorption.SO₂ poisoning is a universal issue when developing catalysts for the abatement of NOx. Activated carbons and zeolites were systematically investigated about the SO2 resistance during NO oxidation. Regarding the activated carbon, SO2 can cause the irreservisble deavtivation along with the oxidation efficiency finally approaching zero. In contrast, high silica zeolite shows good SO2 tolerance with slight conversion decrease of 8.5% ratio, and the SO2 tolerance is influenced by the zeolite structure and aluminum content.Carbon capture and sequestration is another process for post-treatment of flue gas in power plant. Here, a biomass-based carbon with natural nitrogen was prepared and selected as the sorbent for CO2 capture. This biomass-based carbon was prepared from Enteromorpha prolifera – a biomass waste collected from Qingdao coastal. Characterization reveals that the biomassbased carbon have 3-D connective structures with micropores, mesopores and macropores. Under the conditions of 15 vol% CO2 in N2, the dynamic capacity is 105 mg/g and 61.4 mg/g at 0 oC and 25 oC, respectively. A mild regeneration procedure at room temperature with He can restore 91% of initial uptake after eight cycles, showing a good recyclability and longevity.