Microwave-Induced Deep Catalytic Oxidation of NO Using Molecular-Sieve-Supported Oxygen-Vacancy-Enriched Fe–Mn Bimetal Oxides

Abstract

A novel microwave (MW) catalytic oxidation denitrification method was developed, which can deeply oxidize NO into nitrate/nitrite with little NO2 yield. A molecular-sieve-supported oxygen-vacancy-enriched Fe2O3–MnO2 catalyst (Ov–Fe–Mn@MOS) was fabricated. Physicochemical properties of the catalyst were revealed by various characterization methods. MW irradiation was superior to the conventional heating method in NO oxidation (90.5 vs 70.6%), and MW empowered the catalyst with excellent low-temperature activity (100–200 °C) and good resistance to H2O and SO2. Ion chromatography analysis demonstrated that the amount of nitrate/nitrite accounted for over 90.0% of the N products, but the main product gradually varied from nitrate to nitrite as the reaction proceeded because of the switching of the main reaction path of NO removal. Mechanism analyses clarified that NO oxidation was a non-radical catalytic reaction: (i) the chemisorbed NO on Mn­(IV) reacted with O2* to produce nitrate and (ii) the excited NO* due to MW irradiation reacted with the active O* generated from Ov···O2 to form nitrite. Density functional theory calculations combined with electron paramagnetic resonance tests revealed the promotional effects of Fe2O3 in (i) boosting the Ov’s quantity; (ii) facilitating O2 adsorption; (iii) increasing the nitrite formation; and (iv) alleviating the suppression of SO2.

Synthesis of Fe–Mn-Based Materials and Their Applications in Advanced Oxidation Processes for Wastewater Decontamination: A Review

“…Molecular sieves (also known as zeolites) are porous crystalline materials composed of silica−aluminates, which have the property of sieving molecules because of their crystal structure with uniform pore size and molecular-scale cavities and channels. 90 Zeng et al prepared nanoparticles Fe, Cu/Fe and Mn/Fe loaded on NaY zeolites (F@Y, CF@Y, and MF@Y) by a two-step method of ion exchange and liquid-phase reduction. 64 The loaded materials were found to exhibit a larger BET surface area compared to nano Fe 0 (nZVI).…”

Electrochemical Reduction of Flue Gas Denitrification Wastewater to Ammonia Using a Dual-Defective Cu2O@Cu Heterojunction Electrode

“…These commercial thermocatalytic pathways can efficiently treat NO x , but fails to recover nitrogen resources in the flue gas. In comparison, wet denitrification emerges as a new approach to convert NO x into nitrate wastewater via a thermal catalytic oxidation (TCO) and subsequent absorption. − These highly concentrated aqueous nitrate, which can accumulate to a millimolar level depending on absorption time, can be recovered as a valuable nitrogen resource via reduction to ammonia (NH 3 ).…”