表面氧浓度对负载型金属催化剂活化甲烷反应性能的影响

Effect of Surface Oxygen Concentration on Activation of Methane over Supported Metal Catalysts

利用脉冲 质谱在线分析技术考察了无气相氧条件下负载型金属催化剂上脉冲CH4的反应结果表明 ,对于Rh/SiO2 催化剂 ,不管是氧化态还是还原态 ,除第 1次脉冲生成较多的CO2 外 ,从第 2次脉冲开始 ,只有CO生成 ;对于Ru/SiO2 催化剂 ,无论是氧化态还是还原态 ,每次脉冲均有一定量的CO2 生成 .这可能是由于Rh和Ru两种金属对氧的亲合力不同所致 .甲烷在负载型催化剂表面的活化以及产物的选择性主要受催化剂表面活性氧物种覆盖度的影响 .

Activation of methane over supported metal catalysts was investigated using MS pulse technique on line. Oxygen free CH 4 pulsing reactions were carried out over both Rh/SiO 2 and Ru/SiO 2 at 700 ℃. Large amounts of CO and CO 2 were observed at the first pulse of CH 4 over oxidized Rh(O)/SiO 2 catalyst. However, no CO 2 formation was observed at the second pulse and thereafter. Similar to the response of Rh(O)/SiO 2 catalyst, the intensity of CO and CO 2 was strong at the first pulse over reduced Rh/SiO 2 catalyst, and CO 2 appeared also only at the first pulse over Rh/SiO 2 catalyst. No CO 2 was detected at the second pulse and thereafter. CH 4 pulsing over Ru(O)/SiO 2 catalyst also produced CO and CO 2. CO and CO 2 were detected from the first pulse, and their intensity was much stronger than that of CO and CO 2 produced over Rh/SiO 2 catalyst. However, unlike Rh/SiO 2 catalyst, CO 2 was formed at every pulse over Ru(O)/SiO 2 catalyst. Pulsing CH 4 over Ru/SiO 2 catalyst also produced both CO and CO 2 at every pulse. This difference between Rh and Ru catalysts may be due to the difference in the bond strength of Ru O (528 4 kJ/mol ) and Rh O (405 1 kJ/mol) and in their relative oxygen affinities, Ru 0 can be more easily oxidized by O 2 than Rh 0 owing to the greater oxygen affinity of Ru. Surface oxygen should play an important role in the activation of methane and the product distribution.