A_(1-3x)^(2+)A_(2x)^(3+)φ_xMoO_4催化体系热处理方法对丙烯氨氧化的影响

Study on Influence of Heat Treatment Method on Ammoxidation of Propylene in A_(1-3x)^(2+)A_(2x)^(3+)Φ_xMoO_4 Catalytic System

以Pb_1 _(3x)Bi_(2xφx)MoO_4为例,研究了白钨矿A_1^(2+)_(3x)A_(2x)^(3+)φ+xMoO_4型催化剂的热处理方法对丙烯氨氧化制丙烯腈催化活性的关系。利用DTA及XRD研究温度对PbMoO_4晶体生长的影响以确定焙烧温度。阳离子空位x=0.04对催化性能最佳,丙烯转化率76%,丙烯睛收得率51%。没有空位的PbMoO_4(x=0)基本上没有催化活性。研究了焙烧温度、时间和气氛对30X催化剂比表面和表面总酸度的影响,并与催化性能相关联,从而优化了此催化体系的焙烧条件。在空气气氛中650℃停留25min获得的催化剂(比表面约为43m^2/g,表面总酸度0.33mmol/g)用于氨氧化反应,丙烯转化率大于99.5%,丙烯睛收得率约86%。

The heat treatment method of scheelite type catalyst A_(1-3x)^(2+)A_(2x)^(3+)φ_xMoO_4 has been studied by using Pb_(1-3x)Bi_(2x)φ_xMoO_4 as model compound. Also, the relationship between the crystal growth of PbMoO_4 and temperature when x = 0, and the relatiónship between x value and catalytic activity when the range of x is from 0 to 0.08 have been studied. Experimental results show that the best catalytic activity was observed at x = 0.04 when the active phase existed as a form of Mo-Bi-Pb-mixed oxide solid solution. The influences of calcination temperature, time, atmosphere over the specific surface area and the total surface acidity have also been studied, and were correlated with the catalytic properties. The calcination conditions of this catalytic system have been optimized; when calcined in air stream at 650℃ for 25 min, the propylene conversion is more than 99.5% and the selectivity or acrylonitrile is 86%.