Helena Kaper

High‐Surface‐Area SiO2–ZrO2 Mixed Oxides as Catalysts for the Friedel–Crafts‐Type Alkylation of Arenes with Alcohols and Tandem Cyclopropanation Reactions

The catalytic activity of SiO2–ZrO2 mixed oxides was studied for the Friedel–Crafts‐alkylation reaction between anisole and benzylic or allylic alcohols. In particular, the influence of Zr content on the catalytic activity was studied. The catalyst with the lowest Zr content (5 mol % ZrO2) showed the highest activity with high selectivity for the alkylated product and good recyclability. We used this catalyst in the reaction of 1‐phenyl‐1‐ethanol with toluene and xylene. We also studied the possibility of a tandem process that involved a Friedel–Crafts alkylation and the subsequent trans‐hydrogenation of trans‐1,3‐diphenyl‐2‐propen‐1‐ol for the synthesis of substituted cyclopropanes.

The role of lattice oxygen in CO oxidation over Ce18O2-based catalysts revealed under operando conditions

Ceria-based materials are today the most prominently used catalyst supports for CO oxidation and NOx reduction in three-way catalytic converters (TWCs) worldwide. Acting as oxygen buffer compounds, the underlying reaction mechanism and especially the distinct role of surface and lattice oxygen for catalytic reactions are still under debate. This is partially related to the complexity of the real CeO2 surface containing important amounts of water and carbonates. Combining TG-MS, Raman spectroscopic experiments and isotope labeling pulse temperature programmed oxidation reaction (ILPOR), coupled with mass spectrometric analysis of 18O-doped ceria, we explored here the oxygen uptake/release behavior under operando conditions, together with the catalytic activity related to surface and/or lattice oxygen mobility and exchange. Specific changes in the lattice dynamics induced by 18/16O isotope exchange were analyzed by Raman spectroscopy, allowing the temperature-dependent onset of lattice oxygen mobility and isotope exchange behavior to be studied selectively. For Pt-supported nano-ceria, we evidenced high catalytic performance for CO oxidation, activated slightly above ambient conditions without significant lattice oxygen participation. The distinct role of surface and lattice oxygen in the catalytic reaction of ceria catalysts is discussed as a function of temperature, grain size, Gd doping and Pt impregnation.

In situ generated catalyst: Copper (II) oxide and Copper (I) supported on Ca2Fe2O5 for CO oxidation

Two sets of copper oxide–brownmillerite Ca2Fe2O5 catalysts are prepared and studied for CO oxidation. The first set of catalysts is prepared by classical wet impregnation of the Ca2Fe2O5 support. The second set is prepared by Ca2Fe2O5 B-site doping. The active catalyst species are generated during hydrogen treatment. The two sets of catalysts behave very differently in CO oxidation. The performance of the impregnated catalysts is independent of the Cu content, while the performance of the doped catalysts can be tuned by the copper content. The best performing catalyst is a doped-reduced catalyst with 40 mol% Cu. Detailed characterization of the catalysts is carried out using nitrogen physisorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and in situ X-ray absorption fluorescence spectroscopy (XAFS).

Enhancement of Oxygen Activation and Mobility in CaTi x Fe 1− x O 3− δ Oxides

The study of oxygen activation and mobility in CaTi0.9Fe0.1O3−δ was investigated by using the isotopic exchange technique. The thermomechanical and chemical stability of CaTi0.9Fe0.1O3−δ makes it a promising mixed ionic and electronic conducting oxide for catalytic membrane reactors. However, its oxygen flux performance is still lower than that of reference membranes. Two strategies were studied to improve oxygen transport in this perovskite oxide, that is, higher Fe doping and utilization of a dual‐bed system composed of LaMnO3/CaTi0.9Fe0.1O3−δ.