Influence of temperature on the heterogeneous reaction of toluene to N-containing organic compounds using in situ DRIFTS

Abstract

Heterogeneous reactions of toluene/NO2 with and without O3 on α-Fe2O3 particles was studied as a function of temperature by using in situ diffuse reflectance infrared Fourier transform spectrometry (DRIFTS). The results show that the formation of R-ONO2 group is identified on the α-Fe2O3 particles surface, indicating the formation of benzyl nitrate in the presence of toluene/NO2 with or without O3 at different temperatures from 253 K to 298 K. From the analysis of the spectral changes, the reaction kinetics, such as reaction rate and uptake coefficient are sensitive to temperature. During the heterogeneous reaction of toluene/NO2, the formation rate of organic nitrate increases from (2.38 ± 0.07) × 1017 ions g−1 s−1 to (5.95 ± 0.09) × 1017 ions g−1 s−1 when the temperature decreases from 278 K to 253 K. When the trace gases were toluene/NO2/O3, the reaction rate increases about 3 folds with the increasing of temperature from 253 K to 298 K. In the absence of ozone, nitrification from heterogeneous reaction is exothermic process. However, the addition of ozone dominates the whole reaction process, resulting the different change trends of formation rate at similar range of temperatures. Furthermore, reactive uptake coefficient increases from (6.73 ± 0.02) × 10−7 to (1.64 ± 0.05) × 10−6 with decreasing temperature from 278 K to 253 K during the heterogeneous reaction of toluene/NO2 on α-Fe2O3 particles. The values of activation energy for the heterogeneous reaction of toluene/NO2 and toluene/NO2/O3 are determined to be −8.60 ± 0.91 kJ mol−1 and 15.14 ± 2.51 kJ mol−1, respectively. It implies that the heat change is an important factor in affecting the heterogeneous reaction under the seasonal temperature changes.