IR spectroscopy of CO2 activation by bimetallic clusters

Rising concentrations of greenhouse gases in the atmosphere lead to global warming, one of the most urgent societal problems. The most abundant greenhouse gas is CO 2, which is mainly produced during fossil fuel combustion. The concentration of the atmospheric CO 2, therefore, can be kept constant by recycling it into liquid hydrocarbon fuel. However, the CO 2 molecule is very stable in the gas phase. An additional material, called a catalyst, is required to chemically activate it for further reactions with other molecules. One example of such a process is the reaction of CO2 with H2 to form methanol, which can be used not only as a fuel but also as a feedstock for many chemical reactions. Commercial methanol synthesis nowadays is carried out using a Cu/ZnO catalyst at elevated pressure and temperature. Despite the high energy input that leads to even more CO 2 emissions, the methanol yield is quite low. To make the reaction more efficient, novel catalysts are required. Unfortunately, even for the current catalyst, the reaction mechanism is not well understood. To get the molecular-level understanding of the interaction between CO 2 and a catalyst, we mimic the active site of the catalyst with gas phase clusters, which are agglomerations of several metal atoms. It was already shown that the composition, the electrical charge state and geometrical structure of the cluster plays an important role. Moreover, after extensive study of copper-based catalysts, it has been concluded that bi-metallic catalytic materials might be more interesting candidates for CO2 activation than pure copper. Therefore, in the proposed research, we will study the reaction of CO 2 with copper-based bimetallic clusters. The novel experimental technique will be used to study the change in the geometrical structure of the CO2 molecule due to the presence of the cluster. With other words we will study whether normally linear CO 2 molecule can bend after interaction with a cluster. The cluster- CO2 complexes will be produced in superfluid helium nanodroplets ensuring ultra-low temperature and high-resolution IR-spectroscopy, which makes it possible to measure even the slightest changes in the structure of CO 2. In this way, we will try to find the right composition, charge, and size of the active catalytic site which can be used as a starting point for the designing, of novel, more efficient materials for catalytic CO2 utilization.

Rising concentrations of greenhouse gases in the atmosphere lead to global warming, one of the most urgent societal problems. The most abundant greenhouse gas is CO2, which is mainly produced during fossil fuel combustion. The concentration of atmospheric CO2, therefore, can be kept constant by recycling it into liquid hydrocarbon fuel. However, the CO2 molecule is very stable in the gas phase. An additional material, called a catalyst, is required to chemically activate it for further reactions with other molecules. One example of such a process is the reaction of CO2 with H2 to form methanol, which can be used not only as a fuel but also as a feedstock for many chemical reactions. Commercial methanol synthesis nowadays is carried out using a Cu/ZnO catalyst at elevated pressure and temperature. Despite the high energy input that leads to even more CO2 emissions, the methanol yield is quite low. To make the reaction more efficient, novel catalysts are required. Unfortunately, even for the current catalyst, the reaction mechanism is not well understood. To get a molecular-level understanding of the interaction between CO2 and a catalyst, we mimic the active site of the catalyst with gas phase clusters, which are agglomerations of several metal atoms. It was already shown that the composition, the charge state, and the geometrical structure of the cluster play an important role. Therefore, we started with the evaluation of the cluster formation mechanism in multiply charged superfluid He nanodroplets, to get full control over the production process. As a next step, we have evaluated the properties of the copper clusters formed with that method. The copper was used as a model system since it is one of the most promising catalytic materials for methanol synthesis, and it is considered to be the active site of the current industrial catalyst. Originally anticipated measurements could not be performed due to the fact that the absorption of the light in the IR range by the complexes formed with CO2 was below the detection limit. Instead, we utilized the availability of the laser to study clusters of astronomically relevant molecules like C70 and various polyaromatic hydrocarbons. However, when we gained access to another laser, emitting light with a shorter wavelength, the strongest vibration of CO2 could be covered and the changes in the CO2 structure as a function of the Cu cluster size were investigated.