Porous cerium oxide (ceria) nanoparticles were prepared with and without manganese (Mn) by using the flash combustion technique. Samples with different loadings (Ce/Mn ratio ranged from 100 to 10) were prepared by using a one-step process and water only as a solvent. Moreover, citric acid was utilized as a fuel in an aqueous medium, and the overall synthesis mixture was dried at 100 °C overnight and then calcinated at 550 °C for 3 h. The obtained final solid product was characterized by inductively coupled plasma (ICP), X-ray powder diffraction (XRD), diffuse reflectance ultraviolet-visible spectroscopy (DR-UV-Vis), and scanning electron microscopy (SEM), which was coupled with Energy Dispersive X-Ray Analysis (EDX), high resolution transmission electron microscopy (HR-TEM), and photoluminescence (PL) analysis. The characterization data showed that Mn ions were totally incorporated into the framework of ceria up to the applied loading. Under visible light illumination, the photocatalytic activity of the prepared samples was tested in the decolorization reaction of methyl green (MG) dye (wavelength greater than 425 nm). The results showed that increasing Mn content improved the photocatalytic activity of ceria. The sample with a Ce/Mn ratio of 10 performed 1.8 times better than bare porous ceria. Finally, the reusability of the best-performing sample was investigated in four consecutive runs without treatment, and slight deactivation was monitored after the fourth run.

A facial one-step synthesis procedure was applied to prepare porous sponge-like ceria (CeO2). The synthesis was performed by mixing cerium nitrate with citric acid, followed by thermal treatment. The produced solid material was characterized by several techniques, such as XRD, SEM, N2 sorption measurement, DR-UV-vis, and Raman spectroscopy. The characterization data showed that the nanoparticles of the porous ceria were formed with a three-dimensional pore system. Moreover, the measured surface area of the porous sample was eight times higher than the commercially available ceria. The photocatalytic performance of the porous ceria was investigated in two different applications under visible light illumination. The first was the decolorization of a methyl green aqueous solution, while the second was the photocatalytic elimination of a gaseous mixture consisting of five short-chain hydrocarbons (C1–C3). The obtained results showed that the photocatalytic activity of porous ceria was higher than that of the commercial sample. Finally, the recycling of porous ceria showed low deactivation (less than 9%) after four consecutive runs.

The prepared porous ceria exhibited high-photocatalytic activity under the illumination of visible light in different applications than commercial ceria. In dye decolorization experiment, methyl green was used as a model compound. It was found that the activity of porous ceria is 3.4 times higher than that of commercial ceria. The second application, the photocatalytic elimination of a gas mixture contains five different short-chain hydrocarbons was applied. Porous ceria was 1.8 times higher than commercial ceria. Currently, our research team is developing the porous ceria by doping with transition elements and the photocatalytic activity is under investigation.

Four different metal nanoparticles (metal = Ag, Ru, Pt, or Rh) were impregnated on the acidic cesium salt of tungstophosphoric acid Cs2.5H0.5PW12O40 (CsPW) with a loading amount of 2 wt%. The prepared catalysts were characterized by using X-ray diffraction (XRD), Fourier transform-infrared spectroscopy (FTIR), N2 sorption measurements, scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX). Results confirmed the formation of highly distributed metallic nanoparticle centres over the acidic CsPW. The catalytic activity of the prepared catalysts were evaluated in the liquid phase hydrogenation of methyl isobutyl ketone (MIBK) to 2-methylpentane (2-MP) at 453 K. Pd-CsPW showed the highest activity compared to other catalysts, where 10% conversion was obtained with 91% selectivity after 4 h’s reaction time.