Periodic Reporting for period 2 - Lewis acid insertion (Designed catalysts for tandem reactions – insertion of Lewis acid centres into the framework of layered double hydroxides for catalytic applications)
Periodo di rendicontazione: 2023-09-01 al 2024-08-31
Among the most pressing challenges facing humanity, ensuring sufficient energy supply seems to be the largely impossible, so in parallel our CO2 emissions must be reduced to – at best - halt climate change. Today, the production of fuels and fine chemicals depends mainly on the accessibility of fossil fuels. In other words: We need to find environmentally friendly and economical but productive alternatives to replace fossil fuel-based technologies. The complete, complex solution is the biorefinery, whose technology is based on the use of renewable sources such as biomass, agricultural, urban and industrial wastes. All these wastes can be converted into fuels or chemicals, even on an industrial scale. The main problem is that efficient technologies are not yet available, as these processes are fundamentally different from established chemical technologies. For this reason, a considerable number of chemists are now engaged in the design and development of effective reactions, mostly catalytic, to carry out these important transformations. Moreover, the above reactions can be classified into a special group of catalytic reactions, which can be called complex or tandem catalytic reactions. This means that the whole process consists of several different chemical reactions, for which, unfortunately, different types of catalysts often have to be used. To simplify these processes, numerous multifunctional catalysts have been developed over the past four decades. Some of these catalysts – mainly based on active noble metal centers – have proven to be suitable for promoting the conversion of plastic waste and biomass into fine chemicals. The only problem is that these catalysts have too low an efficiency to build a valuable technology on. Moreover, the price of these catalysts is very high because they necessarily have to contain noble metals. My project aims to develop a new, noble metal-free technology that is a sustainable alternative to the above-mentioned process. This can be achieved by developing multifunctional catalysts based on layered double hydroxides (LDH) with (Brønsted) basic character in combination with Lewis acids (LA). However, for this purpose, a new synthesis strategy is required to incorporate these LA into the structure of LDH.
The project focuses on the catalytic valorisation of two major biomass components, specifically ketones and aldehydes. For this purpose, two new synthesis strategies for surface-modified LDH with LA considered as active catalysts for these reactions were designed and developed. Using these methods, the incorporation of LA could be realized such a way that LA cations are isomorphously incorporated into the framework of LDH and replace the Al(III) framework cations. By systematically changing the reaction conditions (reaction temperature, reaction time, initial concentrations, etc.), stable, phase-pure multifunctional catalysts with remarkable Lewis acidity and (Brønsted) basicity and well-regulated morphology were synthesized. All the obtained structures were tested in catalytic test reactions, especially aldol condensation and transfer hydrogenation (MPV) reactions. These catalytic reactions are suitable to convert the above-noticed biomass components into more valuable products such as alcohols (MPVO). Each candidate catalyst showed catalytic activity in both test reactions. Their activity could be attributed to the quality of the LA centres. The observed differences in the catalytic performance of the catalyst candidates allowed the selection of the most promising ones, including Ce(IV)- and Sn(IV)-active LA components. By fine-tuning the reaction conditions of the aldol and MPVO reactions promoted by these catalysts, remarkable increases in the conversion of the reactants can be achieved with unchanged, unique selectivities toward the desired products. Moreover, the presented catalysts enabled these reactions under mild reaction conditions, especially at lower temperatures compared to the benchmark catalysts.
We have developed two novel modification methods for LDH that allow the incorporation of various cations with large dimensions that are difficult to incorporate into LDH.
We introduced highly selective aldol condensations by LA/LDH catalysis at relatively low temperature (T = 120°C), which produced the desired products at large scale even for one hour. We set up a high-performance catalytic system to promote MPV reactions that produced alcohols under mild reaction conditions. In both cases, the as-prepared catalysts proved to be at least competitive with benchmark catalysts. In addition, these recyclable solid materials are more affordable compared to promoters containing noble metals.
Although this project is basic research, by further improving the technological quality of the results, the obtained catalysts can provide an alternative way to produce (e-)fuels from biomass. And the utilization of biomass is very important to achieve the goals of the circular economy.
We introduced highly selective aldol condensations by LA/LDH catalysis at relatively low temperature (T = 120°C), which produced the desired products at large scale even for one hour. We set up a high-performance catalytic system to promote MPV reactions that produced alcohols under mild reaction conditions. In both cases, the as-prepared catalysts proved to be at least competitive with benchmark catalysts. In addition, these recyclable solid materials are more affordable compared to promoters containing noble metals.
Although this project is basic research, by further improving the technological quality of the results, the obtained catalysts can provide an alternative way to produce (e-)fuels from biomass. And the utilization of biomass is very important to achieve the goals of the circular economy.