Preparation of Superhighly Dispersed Co3O4@SBA-15 with Different Morphologies in Supercritical CO2 with the Assistance of Dilute Acids

Development of a novel theory of pressure-induced nucleation in supercritical carbon dioxide

Nucleation was the basis of the fabrication of two-dimensional materials in the bottom-up methods such as chemical vapor deposition and atomic layer deposition etc. Supercritical fluid deposition (SCFD) might provide...

In Search of Factors Determining Activity of Co3O4 Nanoparticles Dispersed in Partially Exfoliated Montmorillonite Structure

The paper discusses a formation of Mt–PAA composite containing a natural montmorillonite structure partially exfoliated by poly(acrylic acid) introduced through intercalation polymerization of acrylic acid. Mt–PAA was subsequently modified by controlled adsorption of Co²⁺ ions. The presence of aluminosilicate packets (clay) and carboxyl groups (hydrogel) led to the deposition of significant amounts of Co²⁺ ions, which after calcination formed the Co₃O₄ spinel particles. The conditions of the Co²⁺ ions’ deposition (pH, volume and concentration of Co(NO₃)₂ solution, as well as a type of pH-controlling agent) were widely varied. Physicochemical characterization of the prepared materials (including X-ray fluorescence (XRF), X-ray powder diffraction (XRD), low-temperature nitrogen adsorption, X-ray photoelectron spectroscopy (XPS) and temperature-programmed reduction (H₂-TPR)) revealed that the modification conditions strongly influenced the content as well as the distribution of the Co₃O₄ active phase, tuning its reducibility. The latter parameter was, in turn, very important from the point of view of catalytic activity in the combustion of aromatic volatile organic compounds (VOCs) following the Mars–van Krevelen mechanism.

Efficient synthesis of sub-5 nm Ag nanoparticles by the desorption effect of supercritical CO2 in SBA-15

Herein, the desorption effect of supercritical CO₂ (scCO₂) was utilized to obtain sub-5 nm Ag nanoparticles (NPs) with a high Ag loading in SBA-15. The size of the Ag NPs decreased from 3.54 ± 0.79 nm (Ag loading of 25.3 wt.% wt.%) to 2.38 ± 0.68 (Ag loading of 10.5 wt%) nm by changing the depressurization curve from 0.1 MPa min^-1 (20-14 MPa) to 3 MPa min^-1 (20-12 MPa). Meanwhile, the intensity of the crystalline Ag characteristic peaks was obviously higher than the latter sample from the x-ray diffraction (XRD) patterns. However, compared with the adsorption kinetics of the two precursors of AgNO₃ and Cu(NO₃)₂ on SBA-15, under the same deposition and depressurization conditions, when the two depositional systems used water as a co-solvent, the time taken to reach the adsorption equilibrium of Ag⁺ on the supports was longer than the time taken by Cu²⁺, which existed in the water as [Cu(H₂O)₄]²⁺. The surface of SBA-15 was hydrophilic, and then the interaction of Ag⁺ and the surface was weaker compared with Cu²⁺, making Ag⁺ highly dispersed on the surface under the scCO₂ desorption effect. After calcination, the size of the Ag NPs decreased, but the morphology of CuO was mainly characterized by nanorods (NRs). Moreover, by comparing the experiments of wetness impregnation, the dispersion ability of the bulk scCO₂ of the reactor was inefficient for Ag⁺ adsorbed on the channels in the depressurization process.

Desorption-dominated synthesis of CuO/SBA-15 with tunable particle size and loading in supercritical CO2

Here, we present a novel method to control the size of CuO nanoparticles (NPs) and Cu loading in SBA-15 via fast desorption of supercritical CO₂ (scCO₂). After calcination, the average size of the CuO NPs (6.47 ± 2.89∼2.18 ± 0.97 nm) decreased with the increase of the depressurization rate (20-14 MPa, 50 °C) from transmission electron microscopy, and the x-ray diffraction results also indicated the decrement of the average particle size (8.6∼4.3 nm by a Scherrer equation). Two reduction peaks situated at 195 °C and 220 °C were found from the temperature-programmed reductions with H₂ profiles, and the intensity of the low-temperature peak increased with increasing the rate for a profile. The hydrogenation of dimethyl oxalate (DMO) to ethylene glycol (EG) was selected to evaluate the catalytic activity of the as-prepared sample. The reaction was conducted at p = 3.0 MPa, T = 200 °C, H₂/DMO = 120, the weight hourly space velocity  = 1.2 h^-1, and the EG selectivity remained at about 90% for over 100 h. The fast desorption of scCO₂ caused mechanical perturbations and crystallization of the adsorbed salt ions on the supports, decreasing the particle size and increasing Cu loading (8∼12 wt%).

Highly efficient Ni–Co oxide nanoparticles on nitrogen-doped FDU-15 for aerobic benzyl alcohol oxidation

Transition bimetal (Ni, Co) oxide nanoparticles immobilized onto nitrogen-doped FDU-15 are high active and show excellent selectivity to the benzaldehyde for the oxidation of benzyl alcohol.

Impregnation of ionic liquids in mesoporous silica using supercritical carbon dioxide and co-solvent

Impregnation of ILs on SBA-15 was successfully prepared in supercritical CO₂. It was superior to the sample prepared using impregnation method.