Catalytic ozonation of ammonia using biomass char and wood fly ash

Catalytic ozonation of gaseous ammonia was investigated at room temperature using wood fly ash (WFA) and biomass char as catalysts. WFA gave the best results, removing ammonia (11 ppmv NH3, 45% conversion) at 23 °C at a residence time of 0.34 s, using 5 g of catalyst or ash at the lowest ozone concentration (62 ppmv). Assuming pseudo zero order kinetics in ozone, a power rate law of -rNH3=7.2×10-8CNH30.25 (r, mol g−1 s−1, CNH3 mol L−1) was determined at 510 ppmv O3 and 23 °C for WFA. Water vapor approximately doubled the oxidation rate using WFA and catalytic ozonation activity was not measured for the char without humidifying the air stream. Overall oxidation rates using the crude catalysts were lower than commercial catalysts, but the catalytic ozonation process operated at significantly lower temperatures (23 vs. 300 °C). Nitric oxide was not detected and the percentage of NO2 formed from NH3 oxidation ranged from 0.3% to 3% (v/v), with WFA resulting in the lowest NO2 level (at low O3 levels). However, we could not verify that N2O was not formed, so further research is needed to determine if N2 is the primary end-product. Additional research is required to develop techniques to enhance the oxidation activity and industrial application of the crude, but potentially inexpensive catalysts.