Industrial applications of solid adsorbents for direct capture of CO2 from the atmosphere require lowering the regeneration temperature (typically 80–100 °C) to save the energy and operation cost. The addition of ionic liquid (IL) to silica functionalized with polyethylenimine (PEI) was found to lower the temperature of CO2 desorption. Modulation excitation infrared spectroscopy evidenced that the presence of IL weakens the C–N bond in carbamate/carbamic acid species formed by reaction of amine groups of PEI and gaseous CO2 and, thus, facilitates the CO2 desorption at a low temperature. The newly developed PEI–IL composite adsorbent enabled a complete regeneration at 50 °C.

Operando infrared spectroscopy is an invaluable tool to provide a deep insight into underlying mechanisms in heterogeneous catalysis. Recent advances in spectroscopic techniques enabled operando analysis under elevated pressure and temperature. In this study we compared a conventional steady-state IR analysis with a transient IR analysis by modulation excitation spectroscopy (MES) using a model reaction, CO2 hydrogenation to methanol at 30 bar and 250 °C. The steady-state IR spectra provide information about surface properties of catalysts while the transient IR spectra are a powerful tool to unveil the kinetics of surface species involved in catalytic cycles and therefore to determine rate-limiting step. Operando MES-IR spectroscopy evidenced that under the reaction conditions (30 bar, 250 °C) hydrogenation of surface methoxy species (CH3O−) is the rate-limiting step for the Cu–Zn based catalyst. We herein demonstrate that comparative analysis of both steady-state and transient spectra at elevated pressure provides a solid understanding of surface processes, allowing a rational catalyst design.