1138511 - Simultaneous Removal of hg⁰ and NO by Self-prepared tio₂{001} and ceo₂/tio₂{001} at High Temperatures

This study prepared a new CeO2/TiO2{001} to simultaneously remove Hg0 and NO in the flue gases emitted from coal-fired power plants, which can be used in selective catalytic reduction (SCR) for higher oxidation efficiency and better thermal stability. TiO2{001} was firstly prepared with the addition of hydrofluoric acid (HF) to explore the optimum amount of HF addition for achieving higher Hg0 oxidation efficiency. The synergetic redox reaction mechanisms of Hg0 and NOx were further explored for different NO and NH3 concentration ratios. TiO2 was initially prepared by hydrothermal method without adding HF, which is composed of octahedral bipyramide-shaped nanocrystals in the size range of 10-20 nm. As the amount of HF addition increased, its shape turned to a rectangular flake with the size range of 100-150 nm and was characterized as a high purity anatase (>99.9%). XPS analysis showed that chemisorbed oxygen (Oα) overwhelmed lattice oxygen (Oβ) and thus dominated the oxidation of Hg0. The displacement of Ti atoms showed the formation of oxygen vacancies and Ti3+. Moreover, Ce doped TiO2 can promote the formation of Ce3+ and Oα. The oxidation efficiency of Hg0 with reaction temperatures was ordered as η100℃>η150℃>η200℃ in the atmosphere of N2+Hg0. After doping by CeO2, 7%CeO2/TiO2{001} had higher oxidation efficiency and better thermal stability. As the molar ratio of[NH3]/[NO]=1:1, the addition of 5% O2 and 7%CeO2/TiO2{001} enhanced the reduction of NO. XPS analysis showed that 7%CeO2/TiO2{001} favored the formation of HgO on the surface of photocatalysts. Simulated by the L-H kinetic model, the reaction rate constant (kr) increased and the equilibrium constant (KHg0) decreased with reaction temperature. It showed that the adsorption efficiency of Hg0 on the surface of photocatalysts reduced with reaction temperatures, which was controlled by the physical adsorption mechanism. In summary, the newly developed novel photocatalysts combining with UV/TiO2 could increase the simultaneous removal of Hg0 and NO in SCR, and Hg2+ can be further removed by the follow-up wet scrubber, which is an innovative air pollution control technology.