It is desirable to reduce the reliance on fossil fuels and to develop alternative methods to yield valuable chemicals. CO2 hydrogenation to methanol is a promising approach, where In2O3/ZrO2 catalysts have attracted increasing attention due to their high selectivity and stability. However, the activity of indium-based catalysts is very susceptible to the preparation method, which is typically wet impregnation. Here, we explore a laser-based synthesis route to prepare InO x /ZrO2 catalysts of varying indium size and load. The respective particle sizes were either adjusted by in situ fragmentation with a more (ns-VIS-laser) or less (ns-IR-laser) efficient laser wavelength or by using micromolar concentrations of phosphate as an electrostatic stabilizer. The InO x colloids were subsequently deposited onto ZrO2 Our results demonstrate that the pulsed laser ablation with ns-IR-laser pulses yielded larger ∼45 nm crystalline cuboid InO x supported on zirconia. The frequency-doubled ns-VIS-pulses on the other hand caused an augmented in situ fragmentation during ablation, which led to catalysts with spherical ∼14 nm InO x particles with a significantly higher degree of amorphousness. Further size quenching and increased amorphous content of the InO x nanoparticles were observed when micromolar concentrations of phosphates were additionally present during ablation. After supporting the InO x nanoparticles onto ZrO2, the laser-generated catalysts were found to perform equally well as their wet-chemically prepared counterparts for methanol synthesis in a slurry phase, although crystalline In species performed slightly better in the catalytic reaction. In conclusion, in situ fragmentation does not only provide opportunities for independent studies of size and composition but also ripening control and structural modifications such as amorphization.

Both oxygen vacancies and surface hydroxyls play a crucial role in catalysis. Yet, their relationship is not often explored. Herein, we prepare two series of TiO 2 (rutile and P25) with increasing oxygen deficiency and Ti 3 + concentration by pulsed laser defect engineering in liquid (PUDEL), and selectively quantify the acidic and basic surface OH by fluoride substitution. As indicated by EPR spectroscopy, the laser-generated Ti 3 + exist near the surface of rutile, but appear to be deeper in the bulk for P25. Fluoride substitution shows that extra acidic bridging OH are selectively created on rutile, while the surface OH density remains constant for P25. These observations suggest near-surface Ti 3 + are highly related to surface bridging OH, presumably the former increasing the electron density of the bridging oxygen to form more of the latter. We anticipate that fluoride substitution will enable better characterization of surface OH and its correlation with defects in metal oxides.

Sowohl oberflächennahe Sauerstofffehlstellen als auch Hydroxylgruppen an der Oberfläche spielen eine entscheidende Rolle in der Katalyse. Dennoch bleiben die genauen Zusammenhänge durch die limitierte analytische Zugänglichkeit dieser Struktureigenschaften oft wenig verstanden. Zur selektiven Quantifizierung der sauren und basischen Oberflächenhydroxide wurde in dieser Studie deshalb eine Fluoridsubstitution am Beispiel zweier Serien von TiO 2 (Rutil und P25) untersucht, welche eine zunehmende Dichte an Ti 3 + -Sauerstofffehlstellen aufwiesen. Die Materialien sind durch gepulster Laserdefekt-Engineering in Flüssigkeit (PUDEL) hergestellt worden. Aus EPR-und EEL-Spektroskopie geht hervor, dass sich die lasergenerierten Ti 3 + beim Rutil potentiell in der Nähe der Partikeloberfläche befinden, während diese beim P25 tiefer in den Partikeln vorzuliegen scheinen. Anhand der pH-abhängigen Fluoridsubstitution zeigt sich, dass sich auf dem laserbehandelten Rutil zunehmend saure (verbrückende) Hydroxylgruppen gebildet haben, welche potentiell auf die Hydrierung der lasergenerierten, oberflächennahen Ti 3 + -Zentren zurückgeht. Beim P25 blieb die Dichte an Hydroxylgruppen trotz nachweislicher Bildung von Ti 3 + -Zentren bei der Laserbehandlung unverändert. Wir gehen davon aus, dass die hier eingesetzte pH-abhängige Substitutionsmethode von Hydroxiden durch Fluoride zukünftig eine einfache und robuste Charakterisierung von Oberflächen-OH und deren Korrelation mit Defekten in Metalloxiden zulassen wird.