Influence of temperature on the heterogeneous reaction of toluene to N-containing organic compounds using in situ DRIFTS
Heterogeneous reactions of toluene/NO 2 with and without O 3 on α-Fe 2 O 3 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-ONO 2 group is identified on the α-Fe 2 O 3 particles surface, indicating the formation of benzyl nitrate in the presence of toluene/NO 2 with or without O 3 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/NO 2 , the formation rate of organic nitrate increases from (2.38 ± 0.07) × 10 17 ions g −1 s −1 to (5.95 ± 0.09) × 10 17 ions g −1 s −1 when the temperature decreases from 278 K to 253 K. When the trace gases were toluene/NO 2 /O 3 , 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/NO 2 on α-Fe 2 O 3 particles. The values of activation energy for the heterogeneous reaction of toluene/NO 2 and toluene/NO 2 /O 3 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.
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