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Hydrophobic Ni2P/SiO2 catalysts with improved stability for bio-oil hydrodeoxygenation

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Dierks,  Michael
Research Department Schüth, Max-Planck-Institut für Kohlenforschung, Max Planck Society;

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Dierks, M. (2017). Hydrophobic Ni2P/SiO2 catalysts with improved stability for bio-oil hydrodeoxygenation. PhD Thesis, Ruhr-Universität Bochum, Bochum.


Cite as: http://hdl.handle.net/21.11116/0000-0001-163D-3
Abstract
Inspired by the concept that hydrophobic surface properties could improve the stability of HDO catalysts, in this thesis the effect of catalyst surface polarity and stability was systematically investigated. In Chapter 3 the influence of catalyst polarity was studied systematically using Ni2P/SiO2 catalysts as a models which deactivated by oxidation through water. For this purpose, a series of organically modified Ni2P/SiO2 catalysts was prepared, modifying a known sol-gel synthesis. Notably, it was found that there is a threshold in terms of hydrophobicity, which has to be reached to stabilize the catalyst against oxidation. Moreover, the modification did also influence the reactivity of the catalysts in HDO reactions. Interestingly, catalysts modified with alkane groups did display a lower reactivity, compared to unmodified catalysts or catalysts modified with benzyl groups. Probably, this is caused by the low polarity of alkane groups, compared to OH groups present on unmodified silica or benzyl modified silica, resulting in a decreased affinity of the relatively polar bio-oil model compounds towards the catalyst. In Chapter 4, a different approach for the synthesis of hydrophobic Ni2P/SiO2 catalysts was introduced. In this approach, the dual role of TOP in the synthesis of Ni2P, starting with a commercial Ni/SiO2 catalyst, was elucidated. The dual role of TOP in this system consists of being the P-source for the conversion of the metallic Ni precursor into Ni2P, and by conferring a hydrophobic character to the catalyst due to the adsorption of excess TOP groups on the catalyst surface. Hence the catalyst with TOP groups on the catalyst could be recycled for 6 times without deactivating. These results are in good agreement with the above mentioned literature reports, as well as the results presented in Chapter 3. Finally, in Chapter 5 ̧ the catalyst introduced in Chapter 4 was applied to real lignin bio-oil feedstocks obtained by a catalytic upstream biorefining process. The optimal reaction conditions described Chapter 4 for a model compound, could successfully be translated into those employed for the conversion of real feedstock. Therefore, either aromatic or aliphatic product mixtures were effectively obtained by applying suitable reaction conditions. Moreover, a new process design was introduced, in collaboration with Dr. Zhenwen Cao, suggesting that steam reforming of the hollocellulose pulp, which is the second product of the catalytic biorefining process, could supply the required hydrogen for the hydrotreatment of the lignin bio-oil. In conclusion, this thesis further substantiates the idea that hydrophobization of HDO catalysts is a suitable method for stabilizing HDO catalysts, which are sensitive to oxidation by water. This concept could also be used for other catalyst systems, which are less sensitive to water, to improve their long-term stability during hydrotreament of real bio-oil feedstocks and, therefore, make this process more feasible for economic purposes.