Different anions of potassium salts render distinct capability for creating pore structures in activation of cellulose and lignin

Several potassium salts such as KOH, K 2 C 2 O 4, and K 2 CO 3 are capable to activate biomass to form activated carbon (AC) with developed pore structures, but their different anions render their unique decomposition kinetics or pathways, affecting their capability for generating pores. Such differences were investigated herein by conducting the activation of cellulose and lignin at 800 °C. The results showed that KOH was superior to K 2 C 2 O 4 or K 2 CO 3 for creating pore structures in activation of cellulose (1507.8 m 2 /g with KOH versus 1180.5 m 2 /g with K 2 C 2 O 4 or 1307.7 m 2 /g with K 2 CO 3 ) or lignin (1109.1 versus 583.4 or 873.2 m 2 /g). This was due to rapidly releasing K + and OH − from KOH at lower temperature, which enhanced severity of cracking reactions, diminishing yields of AC (i.e. 10.3 % with KOH versus 18.1 % with K 2 C 2 O 4 in cellulose activation) as well as aliphatic organics and phenolics in bio-oil. K 2 C 2 O 4 and K 2 CO 3 exhibited delayed K + availability from their stepwise decomposition behaviors, suppressing early-stage cracking/gasification and forming higher yields of AC with limited pore development. In-situ IR revealed that KOH was more active in promoting dehydration/deoxygenation, while slow kinetics for K + release from K 2 C 2 O 4 /K 2 CO 3 preserved more oxygen-containing functionalities in the resulting AC. Additionally, cellulose of aliphatic nature enabled superior potassium permeation, intensifying etching through synergistic cracking/gasification, forming AC of higher S BET but lower yields than that from lignin of aromatic nature.