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

Abstract

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.

Modification to Enhance Surface Acidity and Reactive Species of Coal Fly Ash: A Study of Efficient NOX Removal

“…To investigate the adsorption state and species changes of NH 3 on the surface of AB-CFA-9, in situ DRIFTS was utilized to analyze its adsorption behavior and identify acid sites on the surface through the adsorbed species of NH 3 . , As shown in Figure b, the peaks observed at 1650–1690 and 1436–1380 cm –1 are attributed to the asymmetric bending vibration and symmetric bending vibration of the N–H bond in *NH 4 + species formed on Brønsted acid sites, which explains the appearance of a broad band at 503 °C on the NH 3 -TPD. ,, Similarly, peaks at 1605–1592 and 1282–1120 cm –1 are attributed to the symmetric bending vibration and asymmetric bending vibration of the N–H bond in *NH 3 adsorbed on Lewis acid sites, which corresponds to the sharp band at 586 °C on NH 3 -TPD. − The peak at 1547 cm –1 is attributed to −NH 2 species. , Additionally, vibrational peaks at 1060–960 cm –1 are attributed to the adsorbed unstable gaseous NH 3 on the sample surface …”

On-Line Thermally Induced Evolved Gas Analysis: An Update—Part 1: EGA-MS

“…Various characterization methods were used to understand the role of the physicochemical structure of the synthesized catalysts on their De-NOx capability, like scanning electron microscopy, physical adsorption-desorption, and X-ray photoelectron spectroscopy. Furthermore, NH 3 /NO temperature-programmed desorption, NH 3 /NO-thermogravimetric-mass spectrometry, and in situ DRIFTs (Diffuse Reflectance Infrared Fourier Transform Spectroscopy) results showed that the Mn 0.15 Fe 0.05 /FA has relatively high adsorption capacity and activation capability of reactants at low temperatures [ 75 ].…”

Evaluation of the Thermal Behavior, Synergistic Catalysis, and Pollutant Emissions during the Co-Combustion of Sewage Sludge and Coal Gasification Fine Slag Residual Carbon

“…Cai et al [11] also demonstrated that the co-combustions of textile dyeing sludge and waste tea reduced SO 2 emission through thermogravimetric coupled with mass spectrometry (TG-MS) analysis. It is essential to quantify the release of gaseous pollutants in the co-combustion process of sewage sludge and gasification fine slag residual carbon, which can provide important inspiration for the control of pollutants in industrial burner in the future [25][26][27].…”