Simultaneous removal of NOx and SO2 with H2O2 over silica sulfuric acid catalyst synthesized from fly ash

Specific resistance and adsorption performance of acid-modified fly ash for escaped ammonia in flue gas

Escaped ammonia emission following Selective Catalytic Reduction denitrification significantly influences subsequent flue gas treatment processes. This study investigates the adsorption capabilities of acid-modified fly ash concerning escaped ammonia (NH3) and its consequential impact on specific resistance. Furthermore, the adsorption mechanism of acid-modified fly ash on NH3 was explained. Acid activation facilitated the dissolution of a portion of Fe and Al constituents within the fly ash, the contents of Fe and Al in SFA decrease by 4.91% and 5.64%, respectively. In addition, the specific surface area and porosity of fly ash are obviously improved. The specific surface areas of HFA and SFA increased from 1.83 (OFA) to 4.69 and 7.71 m2/g, respectively. Adsorption kinetics adhered to the pseudo-first-order model. SFA showed the best adsorption performance, with NH3 adsorption up to 10.65 mg/g, which was 4.27 times higher than OFA. The creation of a surface liquid film during NH3 adsorption led to decreased specific resistance values across all fly ash samples after-adsorption. The highest specific resistance values recorded for original fly ash (OFA), hydrochloric acid-modified fly ash (HFA) and sulfuric acid-modified fly ash (SFA) were 6.21 × 1012, 3.37 × 1011 and 5.02 × 1010 Ω·cm, respectively. Sulfuric acid activation makes fly ash have stronger adsorption capacity for escaping ammonia, and SFA maintains good specific resistance characteristics, which has good application prospects in electrostatic precipitation and air pollution control.

Uptake and reactivity of NO2 on the hydroxylated silica surface: A source of reactive oxygen species

We report state-of-the-art first-principles molecular dynamics results on the heterogeneous chemical uptake of NO2, a major anthropogenic pollutant, on the dry and wet hydroxylated surface of α-quartz, which is a significant component of silica-based catalysts and atmospheric dust aerosols. Our investigation spotlights an unexpected chemical pathway by which NO2 (i) can be adsorbed as HONO by deprotonation of interfacial silanols (i.e., -Si-OH group) on silica, (ii) can be barrierless converted to nitric acid, and (iii) can finally dissociated to surface bounded NO and hydroxyl gas phase radicals. This chemical pathway does not invoke any previously experimentally postulated NO2 dimerization, dimerization that is less likely to occur at low NO2 concentrations. Moreover, water significantly catalyzes the HONO formation and the dissociation of nitric acid into surface-bounded NO and OH radicals, while visible light adsorption can further promote these chemical transformations. This work highlights how water-restricted solvation regimes on common mineral substrates are likely to be a source of reactive oxygen species, and it offers a theoretical framework for further and desirable experimental efforts, aiming to better constrain trace gases/mineral interactions at different relative humidity conditions.

Marine oil spill remediation by Candelilla wax modified coal fly ash cenospheres

Biodegradable candelilla wax (CW) was creatively used for hydrophobic modification of coal fly ash cenospheres (FACs), a waste product from thermal power plants, and a new spherical hollow particulate adsorbent with fast oil adsorption rate and easy agglomeration was prepared. CW was confirmed to physically coat FACs and the optimum mass of wax added to 3 g of FACs was 0.05 g. From a series of batch scale experiments, CW-FACs were found to adsorb oil, reaching adsorption efficiency of 80.6% within 10 s, and aggregate into floating clumps which were easily removed from the water's surface. The oil adsorption efficiency was highly dependent on hydrophobicity of the used adsorbent, the adsorption of Venezuela oil onto CW-FACs was found to be a homogenous monolayer, and the capacity and intensity of the adsorption decreased as temperature increased from 10 to 40 °C. The Langmuir isotherm model was the best fit, with the maximum adsorption capacity achieved at 649.38 mg/g. CW-FACs were also found to be highly stable in concentrated acid, alkaline and salt solutions, as well as for spills of different oil products. Furthermore, the retention rate of the oil adsorption capacity of the CW-FACs after 6 cycles of adsorption-extraction was as high as 93.2%. Therefore, CW-FACs can be widely used, easily recycled, and reused for marine oil spill remediation, which is also a good alternative disposal solution for FACs.

Oxidation-absorption process for simultaneous removal of NOx and SO2 over Fe/Al2O3@SiO2 using vaporized H2O2

3% Fe/Al₂O₃ and 3% Fe/Al₂O₃@SiO₂ were prepared to investigate the performance in simultaneous removal of NO_x and SO₂ using vaporized H₂O₂. Certain paraments were changed to explore the activity of catalysts, including temperature, H₂O₂ concentration, GHSV and coexistence gases component. A 24-h durability test was conducted on 3% Fe/Al₂O₃@SiO₂. Moreover, a series of characterizations were employed to analyze the physical and chemical properties of catalysts, including XRD, BET, SEM, TEM, FTIR and XPS. Compared with 3% Fe/Al₂O₃, 3% Fe/Al₂O₃@SiO₂ exhibited more excellent catalytic activity, which could achieve the peak removal efficiency of 100% for SO₂ and 93.76% for NO_x. Moreover, 3% Fe/Al₂O₃@SiO₂ kept stable simultaneous removal efficiency in a 24-h test. The characterization results indicated that the BET area was greatly improved and the core-shell structure was synthesized with the formation of more micropores and mesopores by the coating of SiO₂, which could improve the activity of catalyst at high temperature and high SO₂ concentration. Besides, the mechanism of SO₂ molecules on simultaneous removal was investigated. On one hand, a part of H₂O₂ was consumed by SO₂ molecules without catalyst, which resulted in the drop of NO_x removal by the decrease of oxidants. The main products were sulfites and bisulfites, which were broken down into SO₂ over the catalyst. On the other hand, the presence of SO₂ was beneficial for NO_x removal by increasing oxygen vacancies on the catalyst surface and facilitating the absorption of NO₂ by NaOH solution.

Candida rugosa lipase immobilized on hydrophobic support Accurel MP 1000 in the synthesis of emollient esters

OBJECTIVES

To immobilize Candida rugosa lipase in Accurel MP 1000 (CRL-AMP) by physical adsorption in organic medium and apply in the synthesis of wax esters dodecanoyl octadecanoate 1 and hexadecanoyl octadecanoate 2 in a heptane medium, as well as evaluating the stability and recyclability of CRL-AMP in six reaction cycles.

RESULTS

The specific activity (A_sp) for CRL-AMP was 200 ± 20 U mg^-1. Its catalytic activity was 1300 ± 100 U g^-1. CRL-AMP was used in the synthesis of esters in heptane medium with a 1:1 acid:alcohol molar ratio at 45 °C and 200 rpm. In synthesis 1, conversion was 62.5 ± 3.9% in 30 min at 10% m v^-1 and 56.9 ± 2.8% in 54 min at 5% m v^-1; while in synthesis 2, conversion was 79.0 ± 3.9% in 24 min at 10% m v^-1, and 46.0 ± 2.4% in 54 min at 5% m v^-1. Reuse tests after six consecutive cycles of reaction showed that the biocatalyst retained approximately 50% of its original activity for both reaction systems.

CONCLUSIONS

CRL-AMP showed a high potential in the production of wax esters, since it started from low enzymatic load and high specific activities and conversions were obtained, in addition to allowing an increase in stability and recyclability of the prepared biocatalyst.

Silica–sulfuric acid and alumina–sulfuric acid: versatile supported Brønsted acid catalysts

–SO3H functionalized silica and alumina have emerged as efficient and eco-compatible heterogeneous solid acid catalysts for the construction of various important molecular skeletons.

A Study on Mn-Fe Catalysts Supported on Coal Fly Ash for Low-Temperature Selective Catalytic Reduction of NOX in Flue Gas

A series of Mn0.15Fe0.05/fly-ash catalysts have been synthesized by the co-precipitation method using coal fly ash (FA) as the catalyst carrier. The catalyst showed high catalytic activity for low-temperature selective catalytic reduction (LTSCR) of NO with NH3. The catalytic reaction experiments were carried out using a lab-scale fixed-bed reactor. De-NOx experimental results showed the use of optimum weight ratio of Mn/FA and Fe/FA, resulted in high NH3-SCR (selective catalytic reduction) activity with a broad operating temperature range (130–300 °C) under 50000 h−1. Various characterization methods were used to understand the role of the physicochemical structure of the synthesized catalysts on their De-NOx capability. The scanning electron microscopy, physical adsorption-desorption, and X-ray photoelectron spectroscopy showed the interaction among the MnOx, FeOx, and the substrate increased the surface area, the amount of high valence metal state (Mn4+, Mn3+, and Fe3+), and the surface adsorbed oxygen. Hence, redox cycles (Fe3+ + Mn2+ ↔ Mn3+ + Fe2+; Fe2+ + Mn4+ ↔ Mn3+ + Fe3+) were co-promoted over the catalyst. The balance between the adsorption ability of the reactants and the redox ability can promote the excellent NOx conversion ability of the catalyst at low temperatures. Furthermore, NH3/NO temperature-programmed desorption, NH3/NO- thermo gravimetric-mass spectrometry (NH3/NO-TG-MS), and in-situ DRIFTs (Diffuse Reflectance Infrared Fourier Transform Spectroscopy) results showed the Mn0.15Fe0.05/FA has relatively high adsorption capacity and activation capability of reactants (NO, O2, and NH3) at low temperatures. These results also showed that the Langmuir–Hinshelwood (L–H) reaction mechanism is the main reaction mechanism through which NH3-SCR reactions took place. This work is important for synthesizing an efficient and environmentally-friendly catalyst and demonstrates a promising waste-utilization strategy.