Dispersion State of Catalytic Metal Supported on Bio-Char Elucidated Using Energy Dispersive X-ray Spectroscopy: Effects of Catalyst Type and Heating Process

Abstract

Bio-chars loaded directly with catalytic metals such as K and Fe were gasified with CO₂ at atmospheric pressure after being heated to 1023-1323 K under an Ar flow. The gasification rate constant (K_p) of K-loaded bio char was extremely higher than that of Fe-loaded bio-char. The structure such as surface and cross section of these bio-chars after (1) metal ions were supported on bio-char by the impregnation method (i.e. before heating) and (2) heating under an Ar flow (i.e. just before gasification) were observed using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Before heating, the K atoms were uniformly distributed with no crystal formation. Even after heating under an Ar flow, the distribution of K atoms on the surface and inside of bio-chars remained uniform, suggesting the efficient formation of active sites for CO₂ gasification, although the K content on the surface decreased because of releasing. In contrast, even before heating, the Fe atoms were nonuniformly supported as α-FeOOH and α-Fe₂O₃ particles on the surface. After heating under an Ar flow, the Fe content on the surface decreased because Fe oxide particles moved into mesopore, suggesting the decrease in the number of active sites and the restriction of the accessibility of CO₂ to active sites because of the existence of large Fe oxide particles in mesopores.