Rh/SiO_2催化剂上甲烷部分氧化制合成气反应

利用程序升温脱附、程序升温还原、程序升温表面反应、程序升温反应和化学捕获反应等手段 ,对Rh/SiO2 催化剂上甲烷部分氧化制合成气反应进行了研究 .结果表明 ,Rh/SiO2 催化剂上甲烷部分氧化制合成气机理属于热解 氧化反应机理 .甲烷首先在催化剂上发生解离吸附 ,产生具有不同H/C比的化学吸附物种CHx(x =1～ 3) .其中 ,具有较高H/C比的CHx 可能是甲烷部分氧化反应的活性物种 ,而具有较低H/C比的CHx 可能是催化剂上积碳并导致催化剂失活的来源 .活性物种CHx在活性氧物种的作用下 ,生成含氧中间体物种CHxO或继续脱氢 .含氧中间体物种进一步分解 ,即生成CO和H2 ;CO2 也可由CHx 或CHxO物种进一步氧化生

Rh/SiO_2催化剂上甲烷部分氧化制合成气反应

利用程序升温脱附、程序升温还原、程序升温表面反应、程序升温反应和化学捕获反应等手段 ,对Rh/SiO2 催化剂上甲烷部分氧化制合成气反应进行了研究 .结果表明 ,Rh/SiO2 催化剂上甲烷部分氧化制合成气机理属于热解 氧化反应机理 .甲烷首先在催化剂上发生解离吸附 ,产生具有不同H/C比的化学吸附物种CHx(x =1～ 3) .其中 ,具有较高H/C比的CHx 可能是甲烷部分氧化反应的活性物种 ,而具有较低H/C比的CHx 可能是催化剂上积碳并导致催化剂失活的来源 .活性物种CHx在活性氧物种的作用下 ,生成含氧中间体物种CHxO或继续脱氢 .含氧中间体物种进一步分解 ,即生成CO和H2 ;CO2 也可由CHx 或CHxO物种进一步氧化生

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

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

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

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

Partial oxidation of methane to syngas over Rh/SiO2 catalyst

Partial oxidation of methane (POM) over Rh/SiO2 Catalyst was investigated by using several techniques, such as TPD, TPR, TPSR and trapping agent, combined with MS. At the beginning of POM reaction, only gaseous CO2 can be detected over the catalyst. With the increase in space velocity, the conversion of CH4 and the selectivity for CO and H-2 increase, while the selectivity for CO2 decreases. During the pulse reaction with CH4 as reactant, over the catalyst prereduced at 700 degreesC, CO and H-2 can be detected as main products with trace C2H6 and C2H4. When the catalyst is exposed to CH4-He, there are two kinds of carbonaceous species formed, and they are designated CHalpha and CHbeta, as identified by their hydrogenation temperature of 210 similar to 260 degreesC and 450 similar to 800 degreesC, respectively. The CHalpha is assigned to H-rich form and the CHbeta is assigned to H-deficient form. When the catalyst is exposed to CH4-O-2-He, the carbonaceous species are mainly CHalpha with trace CHbeta. The two kinds of carbonaceous species may play different roles in POM reaction. The CHbeta accumulated during CH4 activation is the possible cause for catalyst deactivation, and the CHalpha may be responsible for CO formation. The CHx may be the intermediate of POM reaction. In the trapping reaction, a series of ions with M-r/z = 2 similar to 46 have been detected at 300 similar to 600 degreesC. The CHxO (x = 1 similar to 3) may be the O-containing intermediate of POM reaction. Based on the above results, the POM mechanism has been proposed. Over the reduced catalyst, CH4 is firstly dissociated, forming the surface species CHx. By reacting with the active species OH-, the CHalpha is oxidized to O-containing intermediate, CHxO, which can be dehydrogenated to give the adsorbed and gaseous CO

Effect of surface oxygen concentration on activation of methane over supported metal catalysts

Activation of methane over supported metal catalysts was investigated using MS-pulse technique on-line. Oxygen-free CH4 pulsing reactions were carried out over both Rh/SiO2 and Ru/SiO2 at 700 degreesC. Large amounts of CO and CO2 were observed at the first pulse of CH4 over oxidized Rh(O)/SiO2 catalyst. However, no CO2 formation was observed at the second pulse and thereafter. Similar to the response of Rh(O) /SiO2 catalyst, the intensity of CO and CO2 was strong at the first pulse over reduced Rh/SiO2 catalyst, and CO2 appeared also only at the first pulse over Rh/SiO2 catalyst. No CO2 was detected at the second pulse and thereafter. CH4 pulsing over Ru(O)/SiO2 catalyst also produced CO and CO2. CO and CO2 were detected from the first pulse I and their intensity was much stronger than that of CO and CO2 produced over Rh/SiO2 catalyst. However, unlike Rh/SiO2 catalyst, CO2 was formed at every pulse over Ru(O)/SiO2 catalyst. Pulsing CH4 over Ru/SiO2 catalyst also produced both CO and CO2 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