Application of Inverse Gas Chromatography (IGC) for inner surface characterization on porous glass and zeolite catalysts

• Applicants: Professor Dr. Bernd Abel; Professor Dr. Dirk Enke
• Subject Area: Solid State and Surface Chemistry, Material Synthesis ; Physical Chemistry of Solids and Surfaces, Material Characterisation ; Theoretical Chemistry: Molecules, Materials, Surfaces
• Term: from 2019 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 413114936

For elucidating catalytic processes and enhancing process efficiency, the characterization of porous catalysts is crucial. As an alternative for contact angle measurements, the inverse gas chromatography (IGC) is a sensitive gas phase method to investigate surface properties of particles, granulates or fibers. With the assistance of well-characterized probe molecules, the IGC is able to detect even small differences of largely identical materials. Thus, the IGC is often applied for characterization of drugs, minerals, polymers and composites. However, there is only a limited number of studies on micro- and mesoporous catalysts or catalyst supports, regardless of the well suited properties of several probe molecule for the investigation of the inner surface of porous materials. The IGC method is able to determine a large number of physico-chemical properties, for example, surface energies (dispersive and polar), acid/base/polar functionality of surfaces, adsorption enthalpy/entropy, sorption isotherms and BET surface areas.Mesoporous glasses (PG), small-, medium- and large-pore zeolites will be investigated by the IGC to examine the influence of an additional surface modification by grafting with different silanes. These materials are characterized by well-defined surface properties and pore structures. For potential catalytic, drug delivery and sensor applications an extensive characterization is necessary. IGC studies will be performed to obtain surface properties like the dispersive amount of the surface energy γ_s^d and the free enthalpy of adsorption 〖ΔG〗_ads^sp to estimate the strength of the interactions between adsorption sites and different adsorptives. Furthermore, the acid/base characteristics (γ_s^+/γ_s^-) of the surface accord¬ing to the nonlinear VAN OSS approach are determined to calculate the specific surface energy using both monopolar and amphoteric probe molecules and a weighted least-square method. In addition, DFT calculations on adsorption will be applied to obtain information regarding the arrangement and adsorption strength of nonpolar and polar adsorptives on a silanol-free and silanol-containing silica surface.Regarding the catalytic application of small-, medium- and large-pore zeolites, gas phase dehydration on butanol will be accomplished to investigate the influence of the pore structure on catalytic activity, selectivity and long-term stability. The effects of a liquid phase grafting with silanes on the materials hydrophilicity/hydrophobicity and acidity will be compared with the results of the IGC measurements (surface energy, acidity/basicity parameter (KA/KB) according to the GUTMANN approach).

• DFG Programme: Research Grants