Catalytic decomposition of toluene using a biomass derived catalyst

• Toluene was catalytically decomposed up to 94% at 900 °C using a biochar.
• Activation energy of 91 kJ/mol was required for catalytic decomposition of toluene.
• Biochar has a great potential to use as a commercial tar cracking catalyst.

Pine bark biochar generated by slow pyrolysis (950 °C) was used as a low cost catalyst to decompose toluene (model tar compound) over a temperature range of 600–900 °C. Relative to thermal cracking, fractional toluene conversion increased from 13 to 94% when increasing temperatures from 600 to 900 °C (2500 ppmv, SV = 0.76 s− 1, 3.8 g catalyst) and Arrhenius analysis indicated an activation energy of 91 kJ/mol, comparable to that of synthetic catalysts (e.g., 80.24 kJ/mol for Ni/Mayenite and 196 kJ/mol for olivine) and lower than that of thermal cracking (356 kJ/mol). The reaction rate for toluene decomposition increased linearly from 550 to 700 °C with a concentration range of 1000–4600 ppmv indicating a first order rate law with respect to toluene. Benzene was detected as a potential intermediate in the decomposition of toluene with selectivity ranging from 0 to 28% at temperatures from 600 to 900 °C respectively, and its formation increased with increasing toluene conversion. Toluene conversion ranged between 40 and 95% with benzene selectivity from 0 to 20% at 800 °C during catalyst longevity studies of 6 days. These results indicate that biochar generated from slow pyrolysis of pine bark at high temperature can be used as a low cost catalyst for tar removal from syngas. However, the tar removal rates using the biochar catalyst were lower than that of olivine and nickel based catalysts indicating the need to increase catalytic activity.