加压下甲烷部分氧化反应中催化剂上积碳形态的研究

Formation of Carbon Deposit during Partial Oxidation of Methane to Syngas under Pressure

用XRD和TEM等方法对不同压力下甲烷部分氧化催化剂上积碳的形态进行了表征 ,发现积碳中有石墨相和类金刚石相存在 ,其中金刚石相的含量随压力的升高而增加 .讨论了甲烷裂解和CO歧化两个反应产生积碳的可能性 ,探讨了非石墨相碳与实验条件的关系 .结果表明 ,甲烷部分氧化积碳主要来源于甲烷分解 。

With the development of energy industry, more and more attention has been paid to the partial oxidation of methane(POM). However, the exact forms of carbon deposit and mechanism of carbon deposition were rarely studied. This paper attempted to study the forms of carbon deposit during the POM to syngas under different pressure, so that the insight could be offered to further studies of the conditions and mechanism of carbon deposition. The POM reaction took place on 10%Ni-1%Pt/Al_2O_3 at (1～10)×10 5 Pa. With increasing pressure, the activity and the selectivity of the catalyst decreased. From the TEM pictures of carbon deposit, it could be seen that there were mainly three forms of carbon deposit, i.e., carbon fiber, nano-carbon tube and amorphous carbon with diameter of 20～60 nm. When the pressure increased from 1.8×10 5 to 5.5×10 5 Pa, the carbon fiber and nano-carbon tube were observed only. When the pressure increased to 8×10 5 Pa, the carbon deposit was entirely made up of amorphous nano-carbon of 20 nm. The carbon deposition was controlled by dynamics. The decomposition of methane made main contribution to the carbon deposition. The main cause of the breaking of carbon fiber and tube, and the formation of amorphous carbon was the existence of oxygen. From the XRD patterns of carbon deposit, the characteristic peaks of diamond increased with the increase in pressure. The pressure did not influence the conformation of diamond much. Under the same experimental conditions, the amount of diamond increased when the partial pressure of oxygen increased in POM reaction. All these results proved that the oxygen played a great role in the conformation of diamond in carbon deposition of POM, which was also supported by the calculated graphitization degree of carbon deposit.