Title : Catalytic hydrodeoxygenation of benzoic acid as a typical bio-oil model compound: Reaction and kinetics
Abstract:
The realisation of biofuels and chemicals requires the development of highly active and selective catalysts that are resistant to deactivation. Herein, the effects of support properties during the hydrodeoxygenation (HDO) of benzoic acid as a bio-oil model compound have been investigated. Three catalysts, m-Ni/ZSM-5, h-Ni/ZSM-5, and Ni/SiO2 were prepared, characterised, and tested. While the mesoporous zeolite support (h-ZSM-5) showed an improved surface area and pore volume following the treatment of the microporous support (m-ZSM-5) with NaOH, nickel impregnation caused an evident decrease in the surface area and total pore volume for all the supports, suggesting successful deposition of nickel. Similarly, the NaOH treatment improved the concentration of acid sites on the h-Ni/ZSM-5 catalyst. Activity tests clearly demonstrate the influences of support acidity, porosity, and the active metal sites. The highest conversion of 97% was recorded over the h-Ni/ZSM-5 catalyst. Benzoic acid transformation proceeds via deoxygenation to benzaldehyde, hydrogenation to benzyl alcohol, deoxygenation to toluene, demethylation to benzene, and hydrogenation to cyclohexane. It is obvious that the synergetic effect of the support acidity and metal sites promotes the demethylation (C-C cleavage) reaction in toluene and, subsequently, the hydrogenation of the benzene to cyclohexane. Higher activity in the less acidic catalyst, Ni/SiO2 (91% conversion) compared to the more acidic catalyst, m-Ni/ZSM-5 was attributed to the mesoporous nature of the SiO2 support, which gives the bulk benzoic acid molecule more access to the available catalytic active sites. In a kinetic study, the rate of benzoic acid disappearance on the h-Ni/ZSM-5 was found to be non-linear with a fractional order 0.21–0.55. Furthermore, a kinetic model was developed using the Langmuir–Hinshelwood–Hougen–Watson approach. A mechanism assuming dual-site adsorption of dissociatively adsorbed hydrogen was shown to be the most accurate representation of the three-phase benzoic acid HDO. The observed activation energy from the model was 137.23 kJ mol-1.
Audience Takeaway Notes:
- The audience will understand the need for alternative sources of energy, especially liquid carbon.
- Understand the prospect and the present state of bio-oil development.
- The presentation will highlight the research opportunities (research gaps) in the area of bio-oil development.
- The audience will be provided with new information to assist in the design of new catalysts for bio-oil upgrading processes.
