程序升温技术研究Mo/HZSM-5催化剂上甲烷无氧芳构化反应积炭的化学特性

对经过程序升温表面甲烷无氧芳构化反应(TPSR)后的Mo/HZSM-5催化剂上的积炭进行了程序升温加氢反应(TPH)和程序升温CO₂反应(TPCO₂),并对相应催化剂上的积炭进行了程序升温氧化反应(TPO)和热重(TG)实验.TPH实验及TPCO₂实验表明,H₂主要对高温烧炭峰发生作用.CO₂则可同时对这两种烧炭峰产生影响,对低温峰积炭的影响尤其明显.对不同Mo含量的催化剂进行上述实验的结果表明,Mo担载量的变化及不同的实验过程都会影响催化剂上两种温峰的积炭在总积炭量中所占的比例.由TG实验数据计算出的动力学结果说明,无论是TPH还是TPCO₂实验都可以降低烧炭过程的一级反应起始温度,并减少其活化能.此外,催化剂中Mo担载量的变化也会对开始温度和烧炭活化能产生明显影响.

Chemical Characteristics of Coke on Mo/HZSM-5 Catalysts for Methane Dehydroaromatization Under Nonoxidative Conditions by TP Techniques

Over Mo/HZSM-5 catalysts, various carbonaceous depositions occurred during the course of methane dehydroaromatization(MDA). These species of surface carbon formed on HZSM-5 zeolite or Mo/HZSM-5 catalysts with different Mo loadings were investigated by means of TPH, TPCO₂ and TPOin combination with thermal gravimetric analysis(TG). The results of TGrevealed that, the total amount of coke formed on 6Mo/MCM 22 during TPSRis larger than those formed on HZSM-5 zeolite, 2Mo/HZSM-5 and 10Mo/HZSM-5 catalysts. The TPOprofiles recorded during the procedure of coke burning off show two different temperature peaks. The results of TPOand TGafter TPHsuggested that, the TPHexperiments only had an effect on the coke burnt off at a high temperature, but didn′t result in the diminishing of the coke burnt off at low temperature peak. On the other hand, the result of the coked catalyst after succeeding TPCO₂ experiments exhibited an obvious reduction in the areas of both the high and low temperature peaks, particularly in the area of the low temperature peak. The study on the catalysts with different Mo loadings suggested that, the percentage of the coke burnt off at a low temperature turned larger with the increase of Mo loading, respectively. And the change trend of the coke burnt off at a high temperature was opposite exactly. By using the experiments of TPSR, TPH, TPCO₂ and TG, quantitative analysis of the coke and the kinetics of its burning off process have been done. The results show that, either TPHor TPCO₂ can diminish the starting temperature and decrease the activation energy, and there are some differences among the catalysts with various Mo loadings.