Green preparation of PtRu and PtCu/SBA-15 catalysts using supercritical CO 2

PdRu Bimetallic Nanoparticles/Metal-Organic Framework Composite through Supercritical CO2-Assisted Immobilization

Metal-nanoparticle (NP)/metal-organic framework (MOF) composites have attracted considerable attention as heterogeneous catalysts. Compared with porous carbon, silica, and alumina, the charge-transfer interaction between the metal NPs and the MOF accelerated the catalytic activity. In this study, PdRu bimetallic NPs were successfully immobilized on MOFs such as MIL-101(Cr) by using supercritical carbon dioxide. The STEM-EDX images show a uniform 3D distribution of the PdRu bimetallic NPs on MIL-101(Cr). The resulting PdRu@MIL-101(Cr) catalyst exhibited higher CO oxidation than monometal/MOF composites such as Pd@MIL-101(Cr) and Ru@MIL-101(Cr). Furthermore, PdRu@MIL-101(Cr) exhibited higher catalytic activity than PdRu@SiO2. This is because the particle size of the PdRu bimetallic NPs in MIL-101(Cr) was within the range of 2-3 nm. The synergistic effects were based on the combination of two metals, Pd and Ru, small bimetal particle formation, and charge-transfer interactions between the bimetal NPs and the MOF. These factors enhance the catalytic activity of the bimetal/MOF composites.

Deposition of Pd, Pt, and PdPt Nanoparticles on TiO2 Powder Using Supercritical Fluid Reactive Deposition: Application in the Direct Synthesis of H2O2

In this study, we investigated the catalytic properties of mono- and bimetallic palladium (Pd) and platinum (Pt) nanoparticles deposited via supercritical fluid reactive deposition (SFRD) on titanium dioxide (TiO2) powder. Transmission electron microscopy analyses verified that SFRD experiments performed at 353 K and 15.6 MPa enabled the deposition of uniform mono- and bimetallic nanoparticles smaller than 3 nm on TiO2. Electron-dispersive X-ray spectroscopy demonstrated the formation of alloy-type structures for the bimetallic PdPt nanoparticles. H2O2 is an excellent oxidizing reagent for the production of fine and bulk chemicals. However, until today, the design and preparation of catalysts with high H2O2 selectivity and productivity remain a great challenge. The focus of this study was on answering the questions of (a) whether the catalysts produced are suitable for the direct synthesis of hydrogen peroxide (H2O2) in the liquid phase and (b) how the metal type affects the catalytic properties. It was found that the metal type (Pd or Pt) influenced the catalytic performance strongly; the mean productivity of the mono- and bimetallic catalysts decreased in the following order: Pd > PdPt > Pt. Furthermore, all catalysts prepared by SFRD showed a significantly higher mean productivity compared to the catalyst prepared by incipient wetness impregnation.

Green Fabrication of Supported Platinum Nanoparticles by Supercritical CO₂ Deposition

Pt nanoparticles were successfully deposited on uncatalyzed carbon paper by the supercritical CO₂ deposition (SCD) method using platinum (II) acetylacetonate as a precursor followed by thermal conversion. A full 2⁴ factorial design (four factors, each with two levels) was used to investigate the main effect of four factors (deposition temperature, deposition time, reduction temperature, and reduction time) and the interaction effects between them. The morphological structures and surface properties of the Pt/carbon paper composite were analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM)/energy-dispersive X-ray spectroscopy analyzer (EDS), and high-resolution transmission electron microscopy (HR-TEM). The results of the 2⁴ factorial design showed that Pt loading on the substrate correlated significantly with deposition time, while Pt aggregation slightly increased with the thermal reduction temperature. Data obtained from both XRD and HR-TEM were in good agreement and showed that Pt nanoparticles were homogeneously dispersed on the substrate with diameters of 7.2–8.7 nm.