Impact of Acidic/Basic Sites of the Catalyst on Properties of the Coke Formed in Pyrolysis of Guaiacol: A Model Compound of the Phenolics in Bio-oil

Acidic and basic sites are important factors influencing the reaction network and properties of coke. In this study, the catalytic pyrolysis of guaiacol, a model compound of lignin derivatives, was conducted over SBA-15, layered double hydroxides (LDHs), and Al2O3 with distinct distribution of acidic and basic sites. The results show that the acidic sites in SBA-15 and the basic sites in LDHs significantly promoted coking and evolution of heavier organics with π-conjugated structures. The Al2O3 catalyst with less acidic/basic sites does not have such an effect. At low pyrolysis temperature, the coke formed over SBA-15 or LDHs is very aliphatic and thermally unstable, while the increase of the pyrolysis temperature enhanced the aromatization degree of coke. Additionally, the acidic sites in SBA-15 are more effective than the basic sites in LDHs in catalyzing the condensation of reaction intermediates and enhancing the aromatic degree of coke, rendering the coke with higher thermal stabilities and reactivity toward oxidation.