Laser-Generated InO_x/ZrO₂ Catalysts for CO₂ Hydrogenation: Role of In Situ Fragmentation and Ripening Control

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 InOx/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 InOx 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 InOx 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 InOx particles with a significantly higher degree of amorphousness. Further size quenching and increased amorphous content of the InOx nanoparticles were observed when micromolar concentrations of phosphates were additionally present during ablation. After supporting the InOx 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.