Page 117 - Advances in bioenergy (2016)

more loss of protons. 45

Basic Catalysts

Solid acid catalysts are the predominately tested materials in the effort to convert biomass to
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oils using pyrolysis. However, Nokkosmaki et al. and Fabbri et al. also applied basic
oxides in catalytic pyrolysis, ZnO and MgO, respectively. The first group pyrolyzed pine
sawdust with three different zinc oxide (ZnO) catalysts at 600°C, with 30 ms residence time
passing the pyrolysis vapors of pine biomass through a fixed bed of catalyst to investigate
catalysts’ influence on the composition and stability of the bio-oil. They found that ZnO was a
mild catalyst for producing bio-oils showing only a small reduction in the liquid yield with
only a 2 wt% gas increase, but found that the stability of the catalytic oil was significantly
increased. The formation of anhydrosugars and formic acid was reduced when increasing the
temperature of the catalyst. At 500°C, the usual temperature of biomass pyrolysis, neither the
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former nor the latter of the products could be detected. Lu et al. studied the upgrading of
biomass pyrolysis vapors in a Py-GC–MS system using various metal oxides as catalytic

materials and observed different catalytic capabilities. CaO significantly reduced the levels of
phenols and anhydrosugars and eliminated the acids. It also increased the formation of
cyclopentanones, hydrocarbons, and several light compounds. ZnO was found to be a mild
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catalyst and Fe O resulted in the formation of various hydrocarbons. Wang et al. also
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studied CaO by thermo gravimetric analysis-fourier transform infrared spectroscopy analysis
and indeed found that it was very effective in the reduction of acids and promoted the
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formation of hydrocarbons. Finally, Torri et al. investigated the catalytic pyrolysis of pine
sawdust over various metal oxides in a pyrolysis-gas chromatography--microwave induced
plasma--atomic emission detector (Py-GC–MIP–AED) system and observed reduction of
heavy compounds after catalysis at the expense of bio-oil yields. The most interesting
materials from their study were CuO, which exhibited the highest yields in semivolatile
compounds, mixed metal oxide catalysts (Fe O , and mixed metal oxides containing Cu and
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cobalt), and ZnO, which reduced the proportion of heavy fraction in the bio-oil with a limited

decrease in the bio-oil yield. 50

Lu et al. used TiO Rutile, TiO Anatase, and ZrO /TiO catalysts and their modified
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counterparts with incorporation of Ce, Ru, and Pd in a Py-GC–MS system for the upgrading of
biomass pyrolysis vapors. TiO Rutile catalysts, especially the Pd-containing counterpart,
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exhibited very promising effect to convert the lignin-derived oligomers to monomeric phenols
and favored the reduction of aldehydes and sugars, while increasing the ketones, acids, and
cyclopentanones. The ZrO /TiO catalysts reduced the phenol and acid yields remarkably,
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eliminated sugars and meanwhile, increased hydrocarbons, light linear ketones, and
cyclopentanones. 51

The research group of Chemical Process and Energy Resources Institute (CPERI) has also
worked with basic materials, i.e., with TiO , ZrO /TiO , and MgO. The evaluation results of
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these catalysts tested in biomass pyrolysis indicated different deoxygenation pathways