Catalytic activities of ion-exchanged nickel and iron in low temperature hydrogasification of raw and modified birch chars

Raw, HNO₃ oxidized and carboxymethylated birch woods loaded with nickel or iron by the ion-exchange method were carbonized at 500 °C in a flow of nitrogen, and the resulting chars were hydrogasified in a thermobalance to examine their reactivities below 700 °C. The amounts of ion-exchanged metals on raw char were too small to give high gasification reactivity. However, oxidized and carboxymethylated woods with increased ion-exchange capacity produced much more reactive chars. Both nickel and iron exhibited larger catalytic activities on carboxymethylated chars than on oxidized chars, because better metal dispersion could be achieved on carboxymethylated wood with its larger cation exchangeability. It was noteworthy that only 1 wt% loading of iron, as well as nickel, on carboxymethylated char was sufficient to attain a gasification of 90 wt% at 700 °C. It was also noted that the catalytic effect, up to 600 °C, of iron on the gasification of oxidized and carboxymethylated chars was larger than that of nickel. This is ascribed to two factors; greater catalytic activity of metallic iron formed during the gasification than that of nickel metal, and low ash level in the chars. Above 600 °C, however, serious loss of activity of the iron was observed in the absence of wood ash. This showed the different influence of wood ash on the catalysis of iron in the low and high temperature regions.