A TDS study on the reaction intermediates in the catalyzed gasification of activated charcoal

Abstract

Catalytic coal gasification was studied by using thermal desorption spectroscopy (TDS) under high vacuum conditions. Activated charcoal was used as a model compound of coal, and Na2CO3 and K2CO3 as catalysts. Catalysts enhanced oxygen adsorption and decomposed at temperatures below their own decomposing temperatures. After pretreatment of the catalyst at high temperature the CO2 desorption pattern represented characteristics of reaction intermediates. There were two peaks, α-peak and β-peak, in CO2 TDS curves. From the experimental results, α-peak was interpreted to the result from intercalated metal-carbon (M-C) complex, and β-peak from metal-oxygen (M-O-C) complex. A higher pretreatment temperature led to decrease both the number of M-O-C complex and its thermal stability. The increase of catalyst loading in Na2CO3-containing sample resulted in relative increase of the number of M-O-C complex than that of intercalated M-C complex, and also increase of thermal stabilities of both reaction intermediates. Major difference between K2CO3 and Na2CO3 appeared in α-peak, intercalated M-C complex. That is, the contribution of intercalated metalcarbon complex to total reaction intermediates was larger in K2CO3 than Na2CO3. This could be attributed mainly to the better intercalating ability of potassium due to its lower ionization potential.