Abstract
Catalytic ozonation is a new method used for removal of NH4OH solution. Therefore, high catalytic performance (activity and selectivity) should be achieved. In this work, we report the synthesis and catalytic performance of Fe2O3-Co3O4 modified dolomite in the catalytic ozonation of NH4OH solution. Dolomite was successfully activated and modified with Fe2O3 and Co3O4. Firstly, dolomite was activated by heating at 800°C for 3 h and followed by KOH treatment. Activated dolomite was modified with Fe2O3 by the atomic implantation method using FeCl3 as Fe source. Fe2O3 modified dolomite was further modified with Co3O4 by precipitation method. The obtained catalysts were characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), energy-dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM), N2 adsorption–desorption (BET), and temperature-programmed reduction (H2-TPR). From SEM image, it was revealed that nano-Fe2O3 and Co3O4 particles with the size of 80–120 nm. Catalytic performance of activated dolomite, Fe2O3 modified dolomite, and Fe2O3-Co3O4 modified dolomite in catalytic ozonation of NH4+ solution was investigated and evaluated. Among 3 tested catalysts, Fe2O3-Co3O4 modified dolomite has the highest NH4+ conversion (96%) and N2 selectivity (77.82%). Selectivity toward N2 over the catalyst was explained on the basis of bond strength M-O in oxides through the standard enthalpy ΔH°f of oxide. Catalyst with lower ΔH°f value has higher N2 selectivity and the order is the following: Co3O4 (ΔH°f of 60 kcal (mole O)) > Fe2O3 (ΔH°f of 70 kcal (mole O)) > MgO (ΔH°f of 170 kcal (mole O)). Moreover, high reduction ability of Fe2O3-Co3O4 modified dolomite could improve the N2 selectivity by the reduction of NO3- to N2 gas.
Highlights
Agricultural and industrial effluents containing ammonia (NH4+-N) discharged from production operation, dairy processor, and fertilizer plants could reduce water quality and cause a danger to human health [1]
We report the synthesis and catalytic performance of Fe2O3-Co3O4 modified dolomite in the catalytic ozonation of Co3O4
In X-ray diffraction pattern (XRD) of raw dolomite (Figure 1(a)) appeared the peaks at 30.9°, 41.1°, 44.9°, and 51.3° which are characteristic for CaMg(CO3)2
Summary
Agricultural and industrial effluents containing ammonia (NH4+-N) discharged from production operation, dairy processor, and fertilizer plants could reduce water quality and cause a danger to human health [1]. Methods for removal of NH4OH solution such as biological nitrification processes, ion exchange, membrane separation, chlorination, and catalytic degradation have often been used [2,3,4,5,6]. Ion exchange and membrane separation methods require expensive operating costs and can cause secondary pollution, while biological methods require a long treatment time and strict operation control [3,4,5]. Liu et al investigated the employing of MgO as an effective catalyst for the catalytic ozonation of NH4+ solution. This MgO catalyst exhibited high NH4OH conversion (95%) but the N2 selectivity was very low; nitrites and nitrates were the main products [6]. Ichikawa et al have examined a Fe2O3, and series of CuO for metal oxides such catalytic ozonation as of
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