Bio-Oil Upgrading Using Methane: A Mechanistic Study of Reactions of Model Compound Guaiacol over Pt–Bi Bimetallic Catalysts

Abstract

Biomass and shale/natural gas will be two important alternative resources for fuel and chemical production for at least the next century. Bio-oil, deriving from the fast pyrolysis of lignin, is a key second generation biofuel, containing high oxygen content. Hydrodeoxygenation (HDO) is typically employed to improve the quality of bio-oils, while the high cost of hydrogen prevents its commercialization. On the other hand, although it is the primary component of shale and natural gas, methane direct conversion to higher hydrocarbons has remained a challenge since the 1980s. Following our recent work, in the present study, methane is used to upgrade guaiacol, a well-known model compound of bio-oils, over Pt–Bi bimetallic catalysts supported on activated carbon (AC). Various characterization techniques, including transmission electron microscopy (TEM), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), H2 temperature-programmed desorption (H2-TPD), H2–O2 titration, inductively coupled plasma atomic emission spectroscopy (ICP-AES), temperature–programmed oxidation (TPO) and temperature–programmed surface reaction (TPSR), were utilized to obtain catalyst structure and properties. It was found that as compared to the Pt catalyst, Pt–Bi bimetallic catalysts exhibited relatively stable (no significant deactivation) guaiacol upgrading performance for 8 h TOS (time on stream), generating partially deoxygenated products along with ethane. The addition of Bi suppresses coke formation, improving catalyst stability. The isotopic labeling tests demonstrate that ethane is produced either from coupling of two methane molecules (20–25%) or from a methane molecule combining with a methyl from guaiacol (75–80%).