Simultaneous removal of NOx and SO2 with H2O2 over silica sulfuric acid catalyst synthesized from fly ash.

Considering that the utilization of fly ash in the removal of flue gas pollutants not only provide a way of high value-added utilization of fly ash, but also greatly reduce the cost of removing flue gas pollutant, the synthesis of silica sulfuric acid catalyst from fly ash and its application in simultaneous removal of NOx and SO2 with H2O2 were investigated in this work. Circulating fluidized bed boiler (CFB) fly ash and pulverized coal boiler (PC) fly ash were selected as raw material to prepare silica sulfuric acid catalyst by H2SO4 activation. PC fly ash was difficult to be activated by H2SO4 due to its dense structure, while CFB fly ash could be treated with H2SO4 to promote dealumination, thereby increasing the silica content. Moreover, the -SO3H withdrawing groups were detected on the silica surface by XPS and Py-FTIR technologies, indicating the formation of silica sulfuric acid. Silica sulfuric acid showed higher activity in catalyzing the NO oxidation by H2O2, and a possible reaction mechanism was proposed. Combined with alkali absorption, 99% SO2 and 92% NOx removal efficiencies can be achieved. The effects of activation conditions such as activation temperature, activation time and calcination temperature and removal experimental parameters such as H2O2 concentration, SO2 concentration and simulated flue gas temperature on the catalytic performance were studied. Finally, the catalyst was not found to be deactivated for ten hours in the stability test.

The roles of Brønsted acidity in low-temperature catalytic oxidation of NO over acidic zeolites with H2O2.

In this study, low-temperature catalytic NO oxidation with H2O2 over Na- and H-exchanged Y and ZSM-5 zeolites was investigated at 140 °C which is the average exhaust temperature of coal-fired power plant. Fast catalytic NO oxidation rates were observed over H-zeolites, and catalytic activity was proportional to the amount of Brønsted acid sites. HZSM-5 and HY zeolites show 65% and 95% NO removal efficiency, respectively, but the catalytic stability of HY was lower than HZM-5 due to partial dealumination during the reaction. In-situ DRIFTS analysis showed that NO+ species coordinated at framework sites played a direct role in the catalytic NO oxidation. Moreover, the possible reaction pathway was proposed to elucidate the mechanism of NO oxidation with H2O2 catalyzed over Brønsted acid sites. The effect of reaction temperature, H2O2 concentration, H2O2 flow and SO2 concentration on NO oxidation were investigated over H-zeolites. The experimental results indicated that the NO removal efficiency was increased with the increase of H2O2 concentration, but decreased with the increase of SO2 concentration. The NO removal efficiency first increased and then decreased with the increase of H2O2 flow and reaction temperature.