Homogeneous Catalysis for the Sustainable Valorization of Biomass
Being the only sustainable hydrocarbon-based source, biomass plays an important role in our energy landscape and has the potential to have a negative carbon footprint. Gaining access to sustainable fuels and chemicals through biomass valorization can be considered as a formula for a swift green transition. In this PhD dissertation, I develop a benign method for converting biomass waste material to fuels and chemicals through the interplay between organometallic pincer catalyst and a Brønsted acid.
Homogeneous transition metal-based Ru-PNP complexes are well known for (de)hydrogenation reactions for small molecule transformation. However, PNP pincer complexes has never been explored for their activity in hydrogenation catalysis under acidic conditions. The main novelty of my projects is represented by the use of Ru-PNP complexes in acidic conditions. I demonstrated that the right combination of Ru-PNP catalyst and a Brønsted acid is able to transform the biomass feedstock directly to GVL (gamma-valerolactone). GVL holds highly promising potential as a future biomass-derived sustainable fuel and feed compound in many chemical industries. It is therefore extremely attractive to directly convert biomass to GVL. However, such a transformation is elusive owing to the high complexity and relatively inert nature of biomass. In concise, low loadings of Ru-MACHO-BH in combination with H3PO4 allows for valorizing woody and starchy biomasses to GVL under mild and sustainable conditions with ≈55% theoretical maximum yields. No chemical treatment or isolation is required for this game-changing method and will represent the state-of-the-art for this transformation or for any transformations of biomass derived substrates for that matter. In addition to the raw biomass feedstock, we also investigated cellulose and hemicellulose as substrates to obtain insight into the underlying mechanisms and performances of the two main reaction pathways for the woody biomass. Synthesis and characterization of a novel Ru-CNC pincer complex have also been demonstrated in the thesis. Exchanging the phosphorus arms with N-heterocyclic carbenes results in a transition metal that is significantly more electron-rich to the extent that the metal-hydrido complex can deliver its hydrogen even under acidic conditions. Based on the preliminary results, this scenario opens for carrying out hydrodeoxygenation (HDO), CO2 hydrogenation and several other potential transformations as well.
The research topics presented in this thesis are highly innovative and interesting subjects for both business and society. Considering this a patent is currently being prepared for filing.