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摘要
Purple tungsten oxide (WO2.72) is an important intermediate product during the reduction of WO3 to tungsten carbide (WC) catalysts, and the systematic analysis of the reaction behavior of WO3 to WO2.72 is an essential step for the efficient preparation of high-quality WC. In this work, the reaction mechanism and kinetics of the reduction of WO3 to WO2.72 by CO-15%CO2 mixed gases were analyzed with the adaptation of model fitting, TG-DTA, XRD, FE-SEM and thermodynamic calculations methods. The results show that the reaction of WO3 with CO-15% CO2 mixed gases is consisted of two steps in the temperature range from1015 K to 1131 K: the first step is the reduction of WO3 to WO2.9, and the second step is the reduction of WO2.9 to WO2.72, i.e., WO3→WO2.9→WO2.72, which are proceeded independently. The kinetic analysis results show that the reductions of WO3 to WO2.9 and WO2.9 to WO2.72 are both controlled by the interfacial chemical reactions with the extracted apparent activation energies of 142.182 kJ/mol and 128.235 kJ/mol, respectively. The current model is also suitable to analyze the kinetics of the non-isothermal reaction, and its apparent activation energies is extracted to be 124.638 kJ/mol, which is in good agreement with the isothermal experimental results. Adding a certain content of Nb2O5 (0~0.5%) is beneficial for the increase of the reaction rate, however, the reaction rate will be decreased when the content is beyond the limitation(> 0.5%). Combining the phase transition and morphology evolution law of the reaction products during the reaction process, the possible reaction mechanism of the reduction of WO3 to WO2.72 by CO-15%CO2 mixed gases is proposed. ? 2022, China Science Publishing & Media Ltd. All right reserved.
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