Insights into new catalysts and materials at the molecular level through in-situ infrared spectroscopy

This thesis focused on gaining insights into new catalysts and materials at the molecular level. These systems were investigated using in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and ambient pressure (polarization modulation-) infrared reflection absorption spectroscopy ((PM-)IRAS). Dehydrogenation of the hydrogen-rich compound perhydro dibenzyltoluene (H18-DBT) releases pure H2. Therefore, H18-DBT is a promising compound for long term H2-storage. However, the deactivation of the catalyst is still a challenge to be overcome in order to be able to use the system for a simple and long term industrial process. S as surface dopant increases the stability and selectivity of the catalyst Pt/Al2O3 for the dehydrogenation of H18-DBT. Moving on to the substrate TiO2 enables strong metal-support interactions (SMSI) between the substrate and the catalyst Pt. In course of this thesis, different S loadings were used to study the adsorption position of S on the Pt nanoparticles (NPs). The in-situ CO DRIFTS measurements suggest the preferred binding of S at low coordinated step/defect sites. Higher S loadings were required to block the terrace sites of the Pt NPs. Furthermore, a bare-eye H2 sensor consisting of a supraparticulate system was characterized and investigated with DRIFTS. The supraparticles (SPs) were synthesized from bimetallic Au-Pd NPs, SiO2 NPs, and resazurin, a redox dye. Additionally, the presence and amount of H2O in the system influences the sensitivity of the H2 sensor. Thus, the reaction mechanism and the changes in sensitivity with increasing H2O content was investigated with in-situ DRIFTS. The experiments show the (ir)reversible reduction of resazurin to resorufin and hydroresorufin caused by H2 exposure. Furthermore, the variation of the H2O content in the DRIFTS experiments and molecular dynamics (MD) simulations demonstrates the importance of a three-phase system, SP, H2O, and H2, for the functionality of the sensor. This enables the application of H2-safety systems even in remote places and places without power supply and increasing the overall safety of applications using H2. Solid catalysts with ionic liquid layer (SCILL) systems show improved selectivity in comparison to their ionic liquid (IL)-free counterparts. Thus, it is important to understand the interaction, permeability, and stability of the IL on the surface in or close to operating conditions. In this thesis, the IL [C4C1Pyr][NTf2] on Pd(111), as well as, the pristine Pd(111) were investigated using CO as probe molecule at atmospheric pressure and heated to 670 K to focus on the permeability of the IL film. CO is able to penetrate the IL layer at near ambient pressure and at RT due to a change in the film morphology. With increasing temperature, the partially depleted IL multilayer areas increase. This structural change of the IL layer increases the permeability of the system and allows the adsorption and desorption of CO already at temperatures below the multilayer desorption. The IL wetting layer is still present up to 540 K. Thus, a detailed picture of the interactions at the Pd/IL interface at relevant conditions was obtained. Furthermore, supported ionic liquid phase (SILP) catalysts for hydrogenation reactions were investigated. Different Wilkinson-type catalysts in [C4C1Im][NTf2] on SiO2 were studied using in-situ DRIFTS up to 140 °C and in reductive/reaction gas atmosphere. The formation of Rh-NPs at elevated temperature was observed. The molecular catalyst decomposes to isolated Rh+ on the SiO2 support. Rh+ is reduced and agglomerates to Rh-NPs. In order to retain the characteristics and advantages of the homogeneous catalyst, the addition of CO as a ligand and in the gas phase increases the stability. The use of the chelating ligand xantphos yields the highest stability within the investigated samples. A SILP system for the generation of high-purity H2 via the water gas shift reaction (WGSR) was investigated. The WGSR is catalyzed by SILP systems containing homogeneous Ru complexes at ultra-low reaction temperature. The addition of organic additives, such as methylene blue (MB), doubled the catalytic effect. The interaction of the additives with the Ru catalysts was further investigated via ATR IR spectroscopy. Comparison of the ATR spectra of the various components and mixtures thereof with the DFT-calculated IR spectra leads to the conclusion that no covalent bond exists between MB and the precursor/monomer. Weak H-bonding interactions stabilize a hydride transition state. With these investigations it is now possible to apply the gained knowledge in the future design of improved catalysts.