Abstract
Biochar (BCR) was obtained from the pyrolysis of a palm-oil-empty fruit bunch at 773 K for 2 h and used as a catalyst for the hydrodeoxygenation (HDO) of guaiacol (GUA) as a bio-oil model compound. Brunauer–Emmet–Teller surface area analysis, NH3 and CO2-temperature-programmed desorption, scanning electron microscope–dispersive X-ray spectroscopy, CHN analysis and X-ray fluorescence spectroscopy suggested that macroporous and mesoporous structures were formed in BCR with a co-presence of hydrophilic and hydrophobic sites and acid–base behavior. A combination of infrared, Raman and inelastic neutron scattering (INS) was carried out to achieve a complete vibrational assignment of BCR. The CH–OH ratio in BCR is ~5, showing that the hydroxyl functional groups are a minority species. There was no evidence for any aromatic C–H stretch modes in the infrared, but they are clearly seen in the INS and are the majority species, with a ratio of sp3–CH:sp2–CH of 1:1.3. The hydrogen bound to sp2–C is largely present as isolated C–H bonds, rather than adjacent C–H bonds. The Raman spectrum shows the characteristic G band (ideal graphitic lattice) and three D bands (disordered graphitic lattice, amorphous carbon, and defective graphitic lattice) of sp2 carbons. Adsorbed water in BCR is present as disordered layers on the surface rather than trapped in voids in the material and could be removed easily by drying prior to catalysis. Catalytic testing demonstrated that BCR was able to catalyze the HDO of GUA, yielding phenol and cresols as the major products. Phenol was produced both from the direct demethoxylation of GUA, as well as through the demethylation pathway via the formation of catechol as the intermediate followed by deoxygenation.
Highlights
Catalysts 2021, 11, 1434 during pyrolysis leads to the formation of bubbles, open and closed pores in BCR, similar to that observed for biochar obtained from palm kernel shells at pyrolysis temperatures higher than 773 K [36]
No metals were immobilized on BCR, we suggest that the iron contained in BCR (9.51 wt%) played a role in the dissociation of H2 during HDO, as our reaction conditions are not far from those generally used in an iron catalyzed FischerTropsch process [58]
BCR from palm oil empty fruit bunches (POEFBs) was developed as a new HDO catalyst
Summary
The world has gradually shifted to renewable energy sources in an effort to reduce dependency on fossil fuels, as well as to address climate change and the global warming caused by excessive greenhouse gas emissions [1]. For example, has rolled out B30, a fuel blend of 30% biofuel from fatty acid methyl esters (FAMEs) and 70%. FAMEs are categorized as first-generation biofuels which rely heavily on food commodities and are, considered to be unsustainable, prompting massive deforestation as a result of industrial plantation expansion [3,4]. Second-generation biofuel, on the other hand, uses abundant and non-competitive biomass waste sources as their precursor. Palm oil empty fruit bunches (POEFBs) are a potential source, since they are rich in lignocellulose feedstock [5]
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