Co-TPP/TiO_2对CO在常温下氧化的催化作用

CATALYTIC ACTIVITY OF Co-TETRAPHENYL-PORPHYRIN SUPPORTED ON TiO_2 FOR THE OXIDATION OF CARBON MONOXIDE AT ROOM TEMPERATURE

生物体内存在的各种金属卟啉配合物对酶的催化反应起着重要作用.它的储氧和载氧功能已被广泛研究,与血红蛋白一样,它对O_2、CO和NO等有络合活化能力.众所周知,CO和NO都是污染环境的有毒气体.近年来用金属卟啉和金属酞菁等含氮大环配合物将NO直接分解或用H_2,CO等作还原剂与NO进行氧还反应的研究十分活跃.我们在前报的基础上继续开展了CO常温氧化催化剂的研究.本工作是将四苯基卟啉钴(Co-TPP)负载于无定形的TiO_2载体上作为催化剂,研究了它在室温下对CO氧化的催化性能.确定了催化剂的最佳活化温度和再生条件,考察了反应温度和反应物浓度变化对活性的影响.求得CO常温氧化的速率方程.讨论了催化剂活性增强的主要原因.

The catalytic activity of cobalt - tetraphenylporphyrin ( Co TPP ) supported on TiO2 for the oxidation of carbon monoxide at 20℃ has been studied. Titania was prepared from hydrolysis of titanium sulfate.The precipitate which was calcined at different temperatures had different surface area and crystal modification.Experimental results indicate that titania support which was calcined at 110℃ had large surface area ( 350 m2/g ) and amorphous structure. Co TPP impregnated onto this support exhibits a significant exhancement of catalytic activity for the oxidation of CO with O2·It has the rate of 3×10-1m mole/g·cat .min at 20℃. CoTPP was impregnated onto TiO2 using a benzene solution to give a concentration of 3.5% ( w./w. ) and activated by evacuating at various temperatures before reaction.The maximum activity of the catalyst was obtained by heat treatment at 300℃ for 2h under vacuum ( 1 × 10-1 Torr). This treatment appears to favor the interaction between the complex and the support thereby causing the extraordinary high activity. The catalytic reaction was carried out in a circulating reactor (vol. 1225ml, circulation rate 1000ml/min ) the partial pressures of CO and O2 were 18 and 24 Torr respectively .Conversion of CO and yields of CO2 were analyzed by a gas chromatograph. The catalytic activity of the same catalyst in the second run was decreased to about 65% of the initial activity.The evacuation of the catalyst at 300℃ for 2 h before the repeated use restored the initial activity, indicating adsorption of some catalyst poisons such as CO2would cause the partial deactivation of the catalyst. Rates under various partial pressures of CO and O2 were observed. The kinetic equation for the conversion of CO is r = 6.1×10-3P_co^0:51P_o^2~0:78 mmole/g·cat.min. The rate increased scarcely above 30℃.No reaction was found to take place at all over Co TPP or TiO2 alone, or on the supported Co TPP/ A12O3 and Co TPP/SiO2 under the same conditions. These results suggest that the chemical interaction between the complex and support is the major reason to increase the activity.