Catalytic cracking of acetic acid and its ketene intermediate over HZSM-5 catalyst: A density functional theory study

Catalytic cracking of carboxylic acids is regaining great interest in the upgrading of biomass-derived oxygenates. Herein, the catalytic cracking mechanism of acetic acid on HZSM-5 catalyst was studied by density functional theory (DFT). It is found that acetic acid is firstly protonated, followed by the alpha-hydrogen transferring to produce 1,1-ethylene glycol, which is subsequently dehydrated to form ketene. The ketene-formation step of this mechanism is found to be the rate-determining step with an activation barrier of 45.23 kcal/mol. The as-formed ketene intermediate continues to react with the HZSM-5 catalyst, generating acetyl cation with a small activation barrier of 3.00 kcal/mol. Moreover, it is found that the as-formed acetyl cation is difficult to be further decomposed, resulting in the accumulation of intermediate products of acetyl cation and ketene. Meanwhile, the ketene further reacts with methoxide, resulting in the final formation of carbon monoxide and ethylene. (C) 2017 Elsevier B.V. All rights reserved.