Catalytic ozonation of ammonia using biomass char and wood fly ash

Abstract

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 NH 3, 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 - r NH 3 = 7.2 × 10 - 8 C NH 3 0.25 ( r, mol g −1 s −1, C NH3 mol L −1) was determined at 510 ppmv O 3 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 NO 2 formed from NH 3 oxidation ranged from 0.3% to 3% (v/v), with WFA resulting in the lowest NO 2 level (at low O 3 levels). However, we could not verify that N 2O was not formed, so further research is needed to determine if N 2 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.