Preparation of high catalytic activity biochar from biomass waste for tar conversion

- The highest tar conversion of 94.9% was achieved by activation and Ni loading.
- H2O/CO2 activation created a more porous and hierarchical pore structure of char.
- Better dispersion of Ni particles on char gave a more stable catalytic activity.
- Raw char should be initially activated before used as catalyst or catalyst support.

High catalytic activity biochar from biomass waste by co-processing of H2O/CO2 activation and nickel loading for the conversion of tar model compound (toluene) were prepared. Raw char was produced by pyrolyzing pine wood sawdust at 800 °C for 1 h, then activated by CO2 or H2O (15 vol.% in N2) at 800-900 °C for 20-80 min. The nickel loading amount was 2 mmol/g-char (11.74 wt.%). The catalytic cracking of toluene was carried out in a lab-scale fixed bed reactor at 800 °C with a residence time of 0.13 s. The results showed that activation significantly improved the average toluene conversion from 40.1% by raw char to 93.2% by activated char (H80). High porosity and hierarchical pore structure, more defects in graphene-like carbon structure and oxygen containing groups on the surface (CO) contributed to the higher catalytic activity of activated chars. The nickel loading increased the toluene conversion of raw char (Ni-char) and activated char (Ni-C900) from 40.1 to 80.8% and from 77.7 to 94.9%, respectively, due to the additional supply of active sites. The toluene conversion ratio of Ni-C900 was larger than that of Ni-char due to a more uniform dispersion of nickel on the activated char support. Thus, the raw biochar should be initially activated before used as catalyst or catalyst support to obtain a higher and more stable catalytic activity for tar conversion.