Activating reaction intermediates in steam reforming with microwave heating for suppressing coke formation

Microwave heating in steam reforming (SR) could selectively agitate reaction intermediates with polar functionalities including precursors of coke, which might affect tendency of coking and properties of coke. This was verified here by conducting SR of acetic acid, glycerol, toluene, and guaiacol with microwave heating and furnace heating at 300–600 °C with Ni/Mg-Al-LDH as a catalyst. The results showed that microwave heating promoted catalytic activity via enhancing mobilizing reaction intermediates and their collision/reactions. This accelerated gasification of carbonaceous intermediates with steam, forming less coke in SR of all the reactants. Specifically, coke from SR of toluene with microwave heating was only ca. 65 % of that from furnace heating, while the ratio of coke formed from microwave heating to furnace heating in SR of guaiacol even reached ca. 54 %. Enhanced gasification of carbonaceous species with microwave heating also formed aliphatic structures in coke. Generally, the coke from microwave heating was very aromatic with significantly higher C/H ratio and more disordered structures than that from furnace heating. Enhanced aromatization of reaction intermediates to carbon nanotubes was observed in SR of acetic acid with microwave heating, while the coke from furnace heating was highly amorphous. Abundant hydrocarbon intermediates from toluene and oxygen-rich intermediates from glycerol or guaiacol formed nanotube-form coke of smooth or rough surfaces.