Catalytic Performance Of Modified Activated Carbon For CO₂ Reforming Of CH₄

When it comes to CO₂ and CH₄ emissions, China beat all the others around the world. CO₂ and CH₄ are not only the main greenhouse gas, but also are an invaluable resource. CO₂ and CH₄ resource utilization has great significance for solving environmental risks, security of energy resources and chemical raw materials security,so as to make greater contributions to Chinese sustainable development. The last decade, the world’s researchers have made some progress in dry reforming of methane, but limited to laboratory research stage. Development of low-cost and high activity catalysts of reforming reaction is an important prerequisite to achieve industrialization.Carbon material as dry reforming of methane catalyst has attracted wide attention because of cheap, rich pore structure and large specific surface area in recent years. In this paper, activated carbon is modified by various modified methods. Modern instrumental analysis is used to analyze activated carbon structure and functional groups, and to explore the reaction mechanism of CH₄-CO₂ reforming, The main conclusions are as follows:1. Activated carbon showed different surface acidity and reactivity after different modified methods. The activated carbon surface is basic after modified by NaOH, NaHCO₃, Na2CO₃, HNO₃, KMnO4, it is beneficial for the adsorption and activation of carbon dioxide, thus showing higher activity in the CH₄-CO₂ reforming reaction. The activated carbon surface is acidic after modified by HCl, H3PO4, C2H₄O₃, NaClO, it is not beneficial for the adsorption and activation of carbon dioxide, thus showing lower activity in the CH₄-CO₂ reforming reaction.2. The activated carbon modified by HNO₃ and KMn O4, compared to NaOH, NaHCO₃, Na2CO₃, have the higher activity. At a reactor temperature of 800 ℃, CH₄ conversion obtained a more than 7.45%, CO₂ conversion obtained a more than 20.28%, the CO yield obtained a more than 20.46%, the H2 yield obtained a more than 1.39%, by using the KMn O4 modified activated carbon. After the HNO₃ modified activated carbon, CH₄ conversion obtained a more than 10.84%, CO₂ conversion obtained a more than 16.14%, the CO yield obtained a more than 28.33%, the H2 yield obtained a more than 5.23%.3. The optimization preparation condition of HNO₃ modified activated carbon is: the concentration of HNO₃ is wt. 8%, calcination temperature is 800 ℃, calcination time is 80 min. After nitric acid modification, activated carbon surface tends higher degree of graphitization, the content of C-O, O-H, alkyl C-H are decreased, but generate ionic OH-, pyridine, pyrrole and amino nitrogen functional groups; after reforming reaction, modified activated carbon surface become the more obvious the graphitized degree, the more serious the damage of activated carbon structure and the number of ionic OH- and nitrogen functional groups are decreased.4. The optimization preparation condition of KMnO4 modified activated carbon is: the concentration of KMn O4 is 0.06mol/L, pH≥7. After potassium permanganate modification, activated carbon surface present honeycomb, and generate alkaline active substances suah as ionic OH-, their cooperation improves the catalytic activity of modified activated carbon. After reforming reaction, the content of ionic OH- and Mn Ox are decreased.5. The effect of modified activated carbon surface’s alkaline nitrogen functional groups pyridine, pyrrole and alkyl ammonium on the activation of methane and carbon dioxide molecules are discussed. The lone pair of their nitrogen has more intense electrophilic reaction with the hydrogen in methane and makes methane activation; moreover due to the nitrogen electronegativity, which makes the ortho carbon electron cloud density decrease, so easy to nucleophilic reaction with CO₂, makes carbon dioxide activation; Alkaline amino more conducive to the adsorption and activation of carbon dioxide.6. The effect of modified activated carbon surface ionic OH- and carbonyl on the activation of methane and carbon dioxide molecules are discussed. The electronegativity of ionic OH- make easier to react with hydrogen of methane and makes methane activation; Ionic OH- with strong polarity, which is conducive to the adsorption of polar carbon dioxide; Additional, carbon dioxide is acidic gas, which is easy to react with alkaline ionic OH-, further to activate carbon dioxide, formate transition-state intermediate of high energy; Carbonyl and ionic OH- can provide active oxygen, which promote CH₄ activation.7. Two reaction mechanisms of dry reforming of methane catalyst over modified activated carbon were proposed based on the study of activation path of methane, carbon dioxide molecules by surface functional groups.