Temperature rise characteristics of coal-KOH adduct under microwave heating and the properties of resultant activated carbon for catalytic methane decomposition

Temperature rise characteristics of subbituminous coal impregnated with KOH in a wide range of KOH/coal ratio (w/w, 0.25∼2) under microwave (MW) heating were investigated and the catalytic performance in methane decomposition (CMD) over the resultant activated carbon (AC) was measured. The results showed that with the increase of KOH content, the temperature rise ability of the coal-KOH adduct under MW-field increases gradually, and the maximum temperature that can be increased from 170℃ to 880℃. The increase of aromaticity due to the structural rearrangement of the coal aromatic layers during KOH impregnation and the release of volatiles during MW-heating provides the main driving force for the continuous increase of temperature. When KOH/coal ratio is 1.5, it took 224 s for coal-KOH adduct to rise from room temperature to 800℃, with the development of specific surface area (S_BET) and pore volume to the maximum of 661.8 m²/g and 0.512 cm³/g, respectively. However, the catalytic activity of AC with the largest S_BET for CMD is not the highest. At 800℃ and higher temperatures, the increase of active site number on the surface by the potassium intercalation mechanism promotes the catalytic activity of AC. Therefore, the research core of carbon-based catalysts from coal is to increase the number of active site, not the S_BET alone.