摘要
用玻璃外循环无梯度反应器研究了在Pt/Al_2O_3催化剂上乙醇深度氧化稳态动力学.乙醇深度氧化稳态动力学可用乙醇及氧吸附、CO_2吸附阻碍的L-H模型描述.动力学方程(1)式中的参数用正交设计法描述.用脉冲法测定了乙醇、氧及CO_2的吸附热.在实验中观察到在Pt/Al_2O_3催化剂上乙醇深度氧化的振荡现象.
Pt / Al2O3 Catalyst was prepared by the impregnation method.It was calcinated in air and reduced by the hydrogen at temperature 500℃.Pt content is 0.01 %.
The steady-state kinetics of deep oxidation of ethanol on Pt/ Al2O3was investigated in a flow- recirculating gradientless reactor. The temperatures of reaction were in the range of 200-280℃.The effects of partial pressures of ethanol and oxygen on the reaction rate were listed in Table l.The steady-state kinetics of deep oxidation of ethanol was described by the L-H model of adsorption of ethanol and oxygen with inhibition of carbon dioxide.The values of parameters in kinetic equation (2) estimated by the method of orthogonal design are as follows: the energy of activation E= 43. 2kJ/mol, the frequency factor of Arrhenius equationK= 1.29×104, the heats of adsorption of ethanol, oxygen and carbon dioxide are 20.4kJ/mol, 24.7kJ/mol, 43. 8kJ/mol respectively, the frequency factors of Clausius-Clapeyron equation for ethanol, oxygen and carbon dioxide are 4.48 × 10-2 (kPa-1), 1.07 × 10-3(kPa-1) , 1.38 × l0-5(kPa-1) respectively.The calculated values of reaction rate by equation (2) were listed in the last column of Table 1.
Gas-chromatographic method was used to measure the heats of adsorption of ethanol, oxygen and carbon dioxide.The corrected retention volume per g of ethanol, oxygen and carbon dioxide vs. reciprocal temperature for catalyst were shown in Figures1,2, 3 respectively. The beats of adsorption of ethanol, oxygen and carbon dioxide are 19.8kJ/ mol, 25.8kJ/ mol and 44.8 kJ/ mol respectively.These experimental values coincide with the values estimated by the method of orthogonal design.
Oscillations were observed in the deep oxidation of ethanol on Pt/ A12O3.Oscillations of temperature were investigated by a flow-recirculating gradientless reactor. The temperatures of catalyst were measured by the thermocouple placed nearby the catalyst bed. When the amount of catalyst charged to the reactor and the flow rates of ethanol and oxygen are increased to 3 times of that in steady experiments, oscillations of temperature are observed.The results of oscillation experiments of ethanol oxidation over Pt/Al2O3 at 280℃ are listed in Table 2.The relationship between fluctuations of temperature (~△T) and time (t) in experiment no. 5 of Table 2 is shown in Figure 4. Periodical curve with more symmetric form was obtained.The shape of curves of temperature oscillation in the other experiments of Table 2 is similar to Fig.4. The frequency and amplitude of oscillation increase with the partial pressure and conversion of ethanol.
出处
《分子催化》
EI
CAS
CSCD
1989年第2期89-95,共7页
Journal of Molecular Catalysis(China)
基金
国家自然科学基金资助项目
