Combined mercury removal and low-temperature NH₃-SCR OF NO with MnO_x/TiO₂ sorbents/catalysts

ABSTRACT

MnO_x/TiO₂ catalysts/sorbents were investigated for flue gas purification via the simultaneous low-temperature NH₃-SCR of NO and elemental Hg capture, in the temperature range 25–300°C. In particular, the effects of the Mn precursor salt (acetate vs. nitrate) and of the TiO₂ support textural properties (nanotubes vs. random mesopores) on both DeNO_x and Hg capture efficiencies were addressed. The catalysts/sorbents were also characterized by means of ICP-MS, SEM-EDX, XRD, BET, H₂-TPR, NH₃ adsorption, and temperature programmed desorption of both NH₃ and Hg. Catalysts prepared by acetate precursor generally displayed a higher reducibility at low temperature which translated into a higher oxidation activity, enhancing mercury capture rate, but adversely affecting the selectivity of the selective catalytic reduction (SCR) process at temperatures above 150°C. Hg was effectively captured up to 250°C and stored on the sorbent in an oxidized form. The original sorption properties could be fully restored by a simple thermal treatment in air at temperatures ≤500°C, releasing elemental mercury. The textural properties of the support were found to have a limited impact on both the Hg capture and SCR performance.

KEYWORDS:

• Hg
• Flue Gas Purification
• DeNOx
• Supported Catalysts
• Regenerable Sorbents

Acknowledgments

Mr. Luciano Cortese and Mr. Fernando Stanzione (IRC-CNR) are gratefully acknowledged for their help in carrying out SEM-EDX, XRD, and ICP-MS characterizations.