Biomass derived N-doped biochar as efficient catalyst supports for CO2 methanation

Abstract

N-doped biochar with a high nitrogen content and tuned pore structure was obtained from Pinus sylvestris by an in-situ pyrolysis process with simultaneous doping nitrogen and activation where urea was used as a nitrogen precursor and NaHCO3 was employed as the activator. To test the feasibility of N-doped biochars obtained under different pyrolysis temperatures as catalyst supports, a series of Ru catalysts were prepared for use in the methanation and the catalysts were labelled as Ru/N-ABC-x, where x represented the pretreatment temperatures(500, 600 and 700 °C). Besides, the catalytic test of Ru/ABC which was prepared under the same conditions without N modification was also conducted for comparison. The probe reaction test of CO2 methanation showed that the Ru/N-ABC-600 catalyst with the highest pyridinic-N (37.7%) content had superior or comparable catalytic performance to Ru/N-ABC-500 and Ru/N-ABC-700 prepared from N-doped biochar with different pyridinic-N content. A high CO2 conversion of 93.8% with a CH4 selectivity of 99.7% was achieved on Ru/N-ABC-600 under the optimum reaction conditions (380 °C, 1 MPa, n(H2)/n(CO2) of 4, with a gas hourly space velocity of 6000 mL·g-1·h-1). This work provides an effective strategy for the utilization of biochar to develop highly active catalysts for CO2 methanation.