Catalyst design for biomass conversion

Catalyst design for biomass conversion

Aura Visan1*, Rob Lammertink1, Pieter Bruijnincx2

1Soft matter, fluidics and interfaces group, University of Twente

2Inorganic chemistry and catalysis group, Utrecht University

*a.visan@utwente.nl

Catalysis is ever-present in industry, up to 90% of the processes use catalysts. However, this valuable experience covers mostly the oil based feedstock processing. For well-known reasons, there is a global interest for more sustainable resources. The catalytic conversion of biomass is a promising alternative for chemical and fuel production. Especially for chemical synthesis this route is highly promising due to the richness and complexity of the chemical composition of biomass waste. This is a clear distinction with respect to oil composition. While oil consists of hydrocarbons and, hence, is hydrophobic, biomass is high in oxygen content and consequently hydrophilic. Therefore, catalysts will have to fulfil completely different requirements in the case of biomass conversion.

Fig. 1 Microchannel 500 µm wide with catalyst patches Fig. 2 High temperature, high pressure setup

The current project attempts to investigate key reactions in the valorification of biomass waste involving platform molecules such as levulinic acid to γ-valerolactone and glucose/fructose to hydroxyl-methylfurfural. The starting point is screening different materials, e.g. probe the potential of abundant metal oxides as catalysts instead of more expensive noble metals. The challenges that will be addressed are the stability of catalyst under aqueous conditions, the effect of hydration as well as other surface functionalities. Nevertheless, the main idea is to study the effect of surface heterogeneity on interfacial transport. It starts from the intuitive idea that consecutive reactions would benefit from alternating catalysts in order to consume intermediates that could potentially poison the catalyst and to generate local gradients that would shift the equilibrium of the reaction increasing overall conversion.

In order to design the optimum interface, the implications of solute – catalyst and solvent – catalyst interactions will also be investigated by changing the catalyst wettability (also alternating solvophobic and solvophilic surfaces), as well as probing the concentration profiles for various catalyst arrangements.

In this project, the effect of catalytic surface heterogeneity (Fig. 1) on interfacial transport is studied on length scales comparable with the boundary layer using a microfluidic platform (Fig. 2). The most challenging aspect for this system is the slow reaction rate. In order to provide a significant consumption flux for the reactant, a high catalytic surface area is necessary. Here the difficulty is to pattern porous materials inside microchannels.

The patterning of the catalytic material using deposition methods compatible with photolithography is straightforward. The important drawback for these deposition methods is the dense material that is obtained. The non-porous layer (Fig. 3) has a low surface area rendering a low catalytic activity to these films. Different approaches will be pursued in order to pattern porous layers inside the microchannels.

Fig. 3: SEM of a sputtered ZrO2 layer Fig. 4 Levulinic acid to GVL over alternating catalysts

The next step after of the fabrication of porous discontinuous layers is alternating two porous materials for tandem reactions (Fig. 4). The effect of catalyst wettability will also be investigated. The catalyst will be hydrophobized by silane surface functionalization.

The oxide porous materials can act as a catalyst directly or serve as a support for metallic nanoparticles. In the later situation, the metal has to be wet impregnated in a second step. Obviously, every fabrication step has to be followed by a thorough characterization procedure. Here, the student will have the opportunity to get acquainted to different characterization techniques from XRD, SEM, EDX, XPS to ellipsometry and TEM.

Please do not hesitate to contact Aura Visan for additional information!

(a.visan@utwente.nl)