Cr2O3-Al2O3催化剂半导性对催化性能的影响

在剖析Cr_2O_3-Al_2O_3系催化剂微观结构的基础上,通过对Cr_2O_3 Al_2O_3的电导测定、热磁分析研究了Cr_20_3-Al_2O_3催化剂的半导性及它对临氢脱烷基催化过程的影响。实验结果表明,氧化态Cr_2O_3为p型半导体,在还原气氛中,将转化为n型。其转变温度随Cr_2O_3含量的增加而提高。催化甲苯临氢脱烷基的活性中心为Cr(Ⅱ)。具有尖晶石结构的γ-Cr_2O_3比α-Cr_2O_3的活性更好。在甲苯气氛中,载流子Cr(Ⅱ)越多,活性越高;在苯气氛中,载流子Cr(Ⅱ)相对越少,其对苯的选择性越好。

EFFECT OF SEMICONDUCTIVITY OF Cr_2O_3-AI_2O_3 CATALYSTS ON THEIR CATALYTIC PERFORMANCE

Based on the microstructure analysis of Cr2O3-Al2O3 catalyst by XRD and TEM, the semiconduetivity of Cr2O3-Al2O3 catalyst and its connection with catalytic properties for toluene hydro-dealkylation have been investigated by means of electric conductance deteimination and tbermomagnetic analysis. The results reveal that Cr2O3-Al2O3 catalysts are p-type semiconductor in oxidizing atmospheres, whereas, they are converted to n-type in reducing atmospheres and the transformation temperature increases with increasing the Cr2O3 content of Cr2O3-Al2O3. A relation between the semiconductance and the catalytic property of catalyst was observed. The activity of Cr2O3-A]2O3 catalysts increases with the increase of electric conductance in toluene atmosphere, and the selectivity increases with the decrease of electric conductance in benzene atmosphere. The active sites of Cr2O3-Al2O3 responsible for toluene demethylation are proposed to be Cr(E). The spinel-type lattice Y-Cr2O3 is more active than the corundum-type lattice a-Cr2O3.