Molybdenum/tungsten-carbide and nickel-phosphide as emerging catalysts for deoxygenation reactions

Abstract

The use of renewable resources has gained attention in the last years due to the increasing worry about the environment. The wider use of renewable resources aims to decrease the crude oil dependency and to attend stricter environmental requirements. While wind, solar and hydropower can provide renewable energy (electricity), they cannot provide (bio)chemical molecules. For that, biomass is the only renewable option. However, biomass needs to be converted into the desired chemical building blocks. In this thesis, deoxygenation of stearic acid was used as model reaction for the conversion of biobased oils such as (non-edible) vegetable oils and waste cooking oils into chemicals. For this reaction, noble metals are efficient catalysts. Nevertheless, noble metals are scarce, hence expensive, which makes it desirable to find more abundant alternatives. Mo/W-carbides and Ni-phosphide are potential replacements of noble metals because they have similar electronic structures and are more available. Although lately Mo/W-carbides and Ni-phosphide have been studied as potential catalysts for deoxygenation reactions, there are still unsolved issues regarding activity, selectivity and stability of these catalysts. In this thesis, I first performed a review study about deactivation routes of carbides in liquid phases reactions. Based on the literature reports, I brought insights in the connection between deactivation routes and carbide properties. In addition to the review, I investigated the influence of several properties in the catalytic performance in stearic acid deoxygenation, such as active phase, support, synthesis method and particle size. I found that those properties had a significant influence on the activity and/or selectivity in stearic acid deoxygenation and provided a deeper understanding on this topic. Those findings enable to steer the selectivity of deoxygenation of fatty acids to specific products such as aldehyde, alcohols, alkanes and alkenes. These molecules are desired by the chemical industry to be used in products such as cosmetics, disinfectant, plastics, solvents and pharmaceutical products. Thus with this thesis I contributed to the further development of a biobased economy.