Catalytic carbon gasification by air: explaining rate jumps as a catalyst nanoparticle effect

Abstract

It is easier to optimize reactions when the mechanism is well understood. Nowadays, catalytic carbon gasification is an area of industrial importance. The mechanism based on C-bulk diffusion has been recently updated. The relevance of the Tammann temperature to get efficient carbon/catalyst nanoparticle contact is now better understood. However, the interaction between kinetics and thermodynamics still needs some clarification. Rate jump is a kinetic phenomenon observed in some cases in catalytic carbon gasification by air or oxygen following a minor increase in temperature (v.g. Delta T = 5 degrees C). This occurrence has been reported, but the phenomenon is not well understood. In this short review, we show that the rate jumps can be consistently explained by the "carbon-worm" mechanism due to a jump in the temperature of the moving nanocatalyst particles. The carbon bulk diffusion step is then much faster and the external film mass transfer becomes the rate-limiting step. The reaction order changes from zero to one. The nature and role of catalyst-carbon contact in catalytic carbon gasification is discussed.