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Four groups of catalysts have been tested for hydrodeoxygenation (HDO) of phenol as a model compound of bio-oil, including oxide catalysts, methanol synthesis catalysts, reduced noble metal catalysts, and reduced non-noble metal catalysts. In total, 23 different catalysts were tested at 100 bar H2 and 275 °C in a batch reactor. The experiments showed that none of the tested oxides or methanol synthesis catalysts had any significant activity for phenol HDO under the given conditions, which were linked to their inability to hydrogenate the aromatic ring of phenol. HDO of phenol over reduced metal catalysts could effectively be described by a kinetic model involving a two-step reaction in which phenol initially was hydrogenated to cyclohexanol and then subsequently deoxygenated to cyclohexane. Among reduced noble metal catalysts, ruthenium, palladium, and platinum were all found to be active, with activity decreasing in that order. Nickel was the only active non-noble metal catalyst. For nickel, the effect of support was also investigated and ZrO2 was found to perform best. Pt/C, Ni/CeO2, and Ni/CeO2-ZrO2 were the most active catalysts for the initial hydrogenation of phenol to cyclohexanol but were not very active for the subsequent deoxygenation step. Overall, the order of activity of the best performing HDO catalysts was as follows: Ni/ZrO2 > Ni-V2O5/ZrO2 > Ni-V2O5/SiO2 > Ru/C > Ni/Al2O3 > Ni/SiO2 ≫ Pd/C > Pt/C. The choice of support influenced the activity significantly. Nickel was found to be practically inactive for HDO of phenol on a carbon support but more active than the carbon-supported noble metal catalysts when supported on ZrO2. This observation indicates that the nickel-based catalysts require a metal oxide as a carrier on which the activation of the phenol for the hydrogenation can take place through heterolytic dissociation of the O–H bond to facilitate the reaction.

The interest in utilizing biomass as a CO 2 neutral fuel by combustion, gasification, or pyrolysis processes is increasing due to concern about the emission of greenhouse gases from fossil fuel combustion. In thermal fuel conversion, pyrolysis is an important step which determines the split of products into char, tar, and gas. In this work, a combination of thermogravimetry and evolved gas analysis by Fourier transform infrared analysis (TG-FTIR) has been applied to study the influence of potassium chloride (KCl) on wheat straw pyrolysis. Raw straw, washed straw, and washed straw impregnated with KCl have been investigated. To facilitate interpretation of the results, pyrolysis of biopolymers (cellulose, xylan, lignin) in the presence and absence of KCl was investigated as well. The raw straw decomposed in a single broad featureless peak. By washing, two peaks appeared in the derivative weight loss curve, corresponding to the decomposition of hemicellulose and cellulose components in the straw. Washing reduced the char yield from 23 wt % (daf) to 12 wt % (daf), reduced the yields of gases, and increased the tar yield from 32 wt % (daf) to 66 wt % (daf). Adding 2 wt % (daf) KCl to the washed straw resulted in a char yield which was close to that of the raw straw, and the yields of tar and gases were between those from the raw and washed straw. Furthermore, the peaks corresponding to hemicellulose and cellulose decomposition moved to lower temperatures, from 670 to 633 K for the cellulose peak, but did not collapse to a single peak as in the raw straw. The influence of KCl on the peak temperature of hemicellulose and cellulose decomposition was not observed with the single biopolymers. This indicates that minerals in straw influence the interaction between the biopolymers in whole biomass. Combustion of the char remaining after pyrolysis showed that char combustion is catalyzed by the minerals present in wheat straw. Char from the washed straw with KCl added burned with two peaks in the derivative weight loss curve corresponding to a catalyzed and noncatalyzed part, indicating that the added salt did not behave in the same way as the inherent minerals in the straw.

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