281319 Mercury Oxidation Over Cupric Chloride-Impregnated Alumina Catalyst for Mercury Emissions Control
CuCl2 has demonstrated excellent mercury oxidation performance in our previous studies. This work aims to advance the fundamental mechanistic understanding of the heterogeneous catalytic oxidation by using the reaction between Hg(0) vapor and CuCl2 impregnated on both α-Al2O3 and γ-Al2O3. The CuCl2/Al2O3 catalysts (both fresh and spent) were characterized by SEM-EDX, TGA-MS, TPR, XRD, and XPS.
The CuCl2 crystallites formed onto α-Al2O3 were found to be very stable up to 300 °C, and undergo the thermal reduction process from Cu(II) to Cu(0) via Cu(I). In the absence of HCl and O2 gases, CuCl2 was found to follow a Mars-Maessen mechanism by consuming lattice chlorine of CuCl2 for Hg(0) oxidation and to be reduced to CuCl. In the presence of 10 ppmv HCl, 2,000 ppmv SO2, and 6% O2 gases, the CuCl2/α-Al2O3 sample works as an Hg(0) oxidation catalyst exhibiting >90% conversion with good resistance to SO2 at 140 °C. The reduced CuCl was found to be re-chlorinated to CuCl2 under HCl and O2 gases by following the Deacon reaction. CuCl2 is expected to be able to be used as a catalyst by impregnating onto non-carbonaceous substrates in a temperature window after the air preheater.
Multiple copper species were found to be formed when γ-Al2O3 is used as a substrate as opposed to one Cu(II) species on α-Al2O3. At low CuCl2 loading, strong interaction exists between CuCl2 and γ-Al2O3 surface, resulting in a thermally-stable copper aluminate phase. At higher loadings (e.g. 10% CuCl2/γ-Al2O3), amorphous CuCl2 overlaps the surface aluminate and exists in the forms of highly dispersed CuCl2 and Cu2(OH)3Cl phases . The CuCl2/γ-Al2O3 catalysts with low CuCl2 loadings showed low catalytic performances in mercury oxidation. In contrast, high loading CuCl2/γ-Al2O3 catalysts showed almost complete Hg(0) oxidization in the presence of 10 ppmv HCl and 6%(v) O2 gas balanced with N2 gas, regardless of the presence of 2,000 ppmv SO2 gas over 140 hrs of the performance evaluations.