Xiang He,Aiyilaiti Kudesi,Shuangxi Wang,Xin Liu,Lin Hu
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.
Yuchuan Feng,Penghui Wang,Nana Wang,Xin Guo,Suxia Ma
Reactive force field molecular dynamics (ReaxFF MD) simulation and experiments were employed to deeply reveal the sintering mechanism of Fe2O3 particles during iron-based chemical looping combustion. The sintering process of Fe2O3 particles was simulated at different temperatures (973–1273 K). The results showed that the temperature increase has limited effect on the structure of Fe2O3 particles and slightly increases the atomic irregularity. The sintering process of Fe2O3 particles can be divided into three stages: the proximity phase, rapid formation, and slow growth of the sintering neck. The temperature increase significantly promotes the sintering process of Fe2O3 particles. The mean-square displacement and Arrhenius equations were used to study the atomic diffusion properties of Fe2O3 particles. The diffusion activation energy of surface atoms is lower than that of inner atoms, implying that the surface atoms have stronger diffusion ability. With the increase of temperature, more Fe atoms diffuse toward the interface of Fe2O3 particles. Increasing the temperature can accelerate the diffusion and enrichment of surface atoms, especially Fe, toward the sintering neck region, resulting in more serious sintering of Fe2O3 particles. ReaxFF MD simulation is in good agreement with the experimental results. Inhibiting the atomic diffusion is the key to improving the antisintering ability of Fe2O3 oxygen carriers.
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