Speaker
Description
A strategy for the re-use of carbon dioxide is to convert it into a platform chemical, from which valuable products can be prepared. In particular, from all the possible products, light olefins (C2=, C3=) are of great interest as important synthesis building blocks. In the frame of the CatVIC (Catalytic Valorization of Industrial Carbon) project, our goal is to investigate the direct hydrogenation of $CO_2$ into olefins by using a standalone tandem catalyst. To achieve this, the existing knowledge from both methanol synthesis and methanol-to-olefins (MTO) catalysts needs to be integrated. However, to prepare such a tandem catalyst is challenging, since both reactions are incompatible – they sit on a seesaw. Known MTO catalysts work at their best performance at low pressures and high temperatures, whereas the opposite is beneficial for conventional methanol synthesis catalysts. To overcome this issue, novel materials need to be developed. The focus of our work is on the modification of the acidity of the zeolitic/acidic component. However, as a first step, known components were synthesised and compared, as systematic work in this regard is lacking in the literature.$^1$
Methanol synthesis catalysts based on $Cu/ZnO/Al_2O_3,$$^2$ $ZnGa_2O_4$, $ZnO/ZrO_2$ and $ZrO_2/In_2O_3$ were prepared via precipitation. By means of SEM and XRD studies it was demonstrated that no phase segregation occurred, and that all elements are well-distributed in the catalyst precursor. In a first kinetic study, the materials were tested in methanol synthesis from $CO_2/H_2$ and $CO/CO_2/H_2$. $Cu/ZnO/Al_2O_3$ exhibited comparable behaviour to the industrial standard. However, at higher temperatures (350 °C) the other materials show higher methanol space time yields. In particular, $ZnO/ZrO_2$ suffers no deactivation under temperature variations, and exhibits the best performance among all materials. The present results provide a good starting point for performing a study among the possible combinations of known zeotype/metal oxides, with the aim of selecting the most suitable zeotype for targeted modifications of acid site strength and density.
References
1. Zhiqiang Ma and Marc D. Porosoff, ACS Catalysis 9, 2639 (2019).
2. Julia Schumann, Thomas Lunkenbein, Andrey Tarasov, Nygil Thomas, Robert Schlögl, and Malte Behrens, ChemCatChem 6, 2889 (2014).
