Stefano Sterchele

Metal nanoparticles inside microgel/clay nanohybrids: Synthesis, characterization and catalytic efficiency in cross-coupling reactions.

HYPOTHESIS Laponite nanoclay embedded inside soluble crosslinked copolymers (microgels) may act as cation exchanger allowing loading of the microgels with cationic metal precursors, which upon reduction yield tailored ternary colloidal nanocomposites comprising both nanoclay and metal nanoparticles. EXPERIMENTS Microgel nanohybrids with variable Laponite nanoclay content were loaded with cationic precursors of different noble metals (Pd, Pt, Au); subsequent reduction by several methods yielded ternary nanocomposites which were extensively characterized. Nanocomposites based on Pd were also tested as catalysts in standard Suzuki and Sonogashira cross-coupling reactions. FINDINGS The proposed method for the production of ternary nanocomposite microgels has been validated. The factors influencing the final metal nanoparticle size (nature of the reducing agent, clay content in the microgel) have been determined and rationalized. The resulting Pd-containing ternary nanocomposite microgels are viable catalysts of standard cross coupling reactions in water-rich medium.

The influence of catalyst amount and Pd loading on the H2O2 synthesis from hydrogen and oxygen

Palladium catalysts with an active metal content from 0.3 to 5.0 wt.% and supported on a strongly acidic, macroporous resin were prepared by ion-exchange/reduction method. H2O2 direct synthesis was ...

In Situ X‐ray Absorption Fine Structure Spectroscopy of a Palladium Catalyst for the Direct Synthesis of Hydrogen Peroxide: Leaching and Reduction of the Metal Phase in the Presence of Bromide Ions

For the first time a Pd catalyst for the direct synthesis (DS) of H2O2 from H2 and O2 was investigated using in situ Pd K‐edge X‐ray absorption fine structure spectroscopy. The catalyst was loaded into a continuous reaction cell and fed at room temperature and pressure with a mixture of CO2, O2, H2 (86:10:4, v/v), and methanol. Pd and PdO phases are observed in similar and steady proportions (62 and 28 %, respectively). The same is found if the catalyst is either dry or treated with pure methanol only. With 10 ppm of NaBr in the reaction mixture both the Pd edge jump and the fraction of PdO decrease steadily during the DS. This shows that Br− ions promote both the leaching and the reduction of Pd in a monometallic DS catalyst. It also suggests that they are connected to each other and to the ability of Br− ions to promote Pd in the DS. An unprecedented mechanism of protection and remediation supported by Br− ions against the overoxidation of Pd is proposed and discussed in this context.

Influence of Metal Precursors and Reduction Protocols on the Chloride-Free Preparation of Catalysts for the Direct Synthesis of Hydrogen Peroxide without Selectivity Enhancers

Different metal precursors and reducing agents were applied in the preparation of 1 wt % Pd catalysts supported on commercial ion‐exchange resin (Lewatit K2621) and used in the direct synthesis of H2O2. The catalysts were characterized by using TEM and their performance was evaluated in the direct synthesis of H2O2 (in a batch and semi‐batch reactor) to investigate the relationship between the catalyst preparation methods, morphology, and catalytic performance. As expected, both the choice of the Pd precursor and the reduction conditions had a strong influence on the size and size distribution of the resulting supported nanostructured metal nanoparticles and, consequently, on the catalytic performance. The best combination of metal precursor and reduction agent was [Pd(NH3)4]SO4 reduced with hydrogen. This catalyst had the largest average size of the Pd nanoparticles and the broadest size distribution.