Cr Doping MnO_x Adsorbent Significantly Improving Hg⁰ Removal and SO₂ Resistance from Coal-Fired Flue Gas and the Mechanism Investigation

Abstract

A series of binary Mn-based materials (Fe-MnO x , Cu-MnO x , Cr-MnO x , and Mo-MnO x ) were prepared by the coprecipitation method, and the mechanism for elemental mercury (Hg 0 ) removal of Cr-MnO x in the absence and presence of SO 2 was investigated. The physicochemical structure properties of the fresh as well as spent Cr-MnO x samples were well characterized by the methods of N 2 physisorption, XRD, SEM-EDS, FTIR, H 2 -TPR, XPS, and TPD. The experiment results revealed that the loading of Cr into/onto MnO x yielded above 90% of Hg 0 removal efficiency in the presence of SO 2 at 120 °C. However, the appearance of SO 2 would lead to the formation of chromium sulfate/sulfite and manganese sulfate/sulfite although much superior SO 2 resistance was obtained. According to the N 2 physisorption and XRD characterization results, Cr doping can enlarge the BET surface area of MnO x when Cr was doped into/ onto MnO 2 , and the MnCrO 4 mixed oxide material was produced. Moreover, the H 2 -TPR result exhibited that Cr loading into/onto MnO x enhanced the redox property of Cr-MnO x mixed oxides and many more easily reduced species appeared in the mixture. The larger surface area and an abundance of reactive species could benefit from excellent performances of Hg 0 removal and superior SO 2 resistance although the DFT calculation showed almost the same adsorption energies of Hg 0 on MnO 2 (110) and Cr-MnO 2 (110) surfaces. The DFT calculation exhibited that the adsorption energy of SO 2 on the surface of Cr-MnO 2 (110) was much lower than that on MnO 2 (110), implying that Cr doping into MnO 2 would decrease the adsorption behavior of SO 2 , thereby improving its SO 2 resistance performance.

Promoting Effect of the Core-Shell Structure of MnO2@TiO2 Nanorods on SO2 Resistance in Hg0 Removal Process

“…Intensity (a.u.) [29,30]. As shown in Table 3, the ratio of Mn 4+ /Mn is about 37.8% for the fresh αMnO2-NR and it decreases to 33.4% after the SO2 resistance test.…”

“…A doublet due to spin orbital coupling can be detected which corresponds to Mn 2p 3/2 (around 641.24 eV) and Mn 2p 1/2 (around 652.82 eV). Due to the high intensity of Mn 2p 3/2 , it was fitted to give detail information of valence state of Mn and it can be separated into three peaks at 640.2-641.2 eV, 641.2-642.1 eV, and 642.2-643.4 eV corresponding to Mn 2+ , Mn 3+ , and Mn 4+ , respectively [29,30]. As shown in Table 3, the ratio of Mn 4+ /Mn is about 37.8% for the fresh αMnO 2 -NR and it decreases to 33.4% after the SO 2 resistance test.…”

MnO2‐Based Materials for Environmental Applications

“…More importantly, MnO 2 particles have more hydroxyl groups on their surface and a large number of negative charge functional groups, inducing acceptable adsorption performances for cationic heavy metals. [ 227,331 ] Therefore, in recent decades, there has been great interest in using MnO 2 as an adsorbent for the removal of various heavy metals from water aquatic systems, including Cr(VI), [ 332–334 ] Pb(II), [ 312,335–338 ] Cd(II), [ 339,340 ] As(III) and As(V), [ 140,311,341 ] Cu(II), [ 342,343 ] Sb(III) and Sb(V), [ 79,344 ] Hg 0 , [ 310,345 ] Hg(II), [ 346 ] Zn(II), [ 347,348 ] Ni(II), [ 287,349 ] U(VI), [ 192,263,350,351 ] Eu, [ 352 ] etc. ( Table 1 ).…”

Density Functional Theory Study of Elemental Mercury Immobilization on CuSe(001) Surface: Reaction Pathway and Effect of Typical Flue Gas Components

“…Nowadays, quantum chemistry calculations based on density functional theory (DFT) have become a powerful method to provide molecular level interpretations of heterogeneous surface reactions. − The reaction pathways can be hence predicted by facial scaling parameters like adsorption energy; i.e., the adsorbate will be converted into a configuration with higher adsorption energy that is energetically favored . Moreover, the adsorption energy was also demonstrated to be a feasible methodology to predict the influence of typical flue gas components on Hg 0 removal performances over various Hg 0 sorbents. − Compared to conducting experiments, using DFT calculations avoids complicated and time-consuming trial-and-error tests and can even give guidance on sorbent design in a wider and more basic manner . Thus, in this work, a periodic model of the CuSe(001) surface was established, aiming at giving a more in-depth understanding of the Hg-CuSe adsorbate–sorbent system.…”

“…36−39 Compared to conducting experiments, using DFT calculations avoids complicated and timeconsuming trial-and-error tests and can even give guidance on sorbent design in a wider and more basic manner. 40 Thus, in this work, a periodic model of the CuSe(001) surface was established, aiming at giving a more in-depth understanding of the Hg-CuSe adsorbate−sorbent system. The most stable adsorption patterns of Hg 0 over intact and Se-enriched CuSe(001) surfaces were constructed after the binding energy, Hirshfeld charge, and projected density of states (PDOS) analyses were conducted.…”