Nanoparticles Supported on Sub-Nanometer Oxide Films: Scaling Model Systems to Bulk Materials

Ultrathin layers of oxides deposited on atomically flat metal surfaces have been shown to significantly influence the electronic structure of the underlying metal, which in turn alters the catalytic performance. Upscaling of the specifically designed architectures as required for technical utilization of the effect has yet not been achieved. Here, we apply liquid crystalline phases of fluorohectorite nanosheets to fabricate such architectures in bulk. Synthetic sodium fluorohectorite, a layered silicate, when immersed into water spontaneously and repulsively swells to produce nematic suspensions of individual negatively charged nanosheets separated to more than 60 nm, while retaining parallel orientation. Into these galleries oppositely charged palladium nanoparticles were intercalated whereupon the galleries collapse. Individual and separated Pd nanoparticles were thus captured and sandwiched between nanosheets. As suggested by the model systems, the resulting catalyst performed better in the oxidation of carbon monoxide than the same Pd nanoparticles supported on external surfaces of hectorite or on a conventional Al2 O3 support. XPS confirmed a shift of Pd 3d electrons to higher energies upon coverage of Pd nanoparticles with nanosheets to which we attribute the improved catalytic performance. DFT calculations showed increasing positive charge on Pd weakened CO adsorption and this way damped CO poisoning.

Nanopartikel auf subnanometer dünnen oxidischen Filmen: Skalierung von Modellsystemen

Durch die Abscheidung von ultradünnen Oxidschichten auf atomar‐flachen Metalloberflächen konnte die elektronische Struktur des Metalls und hierdurch dessen katalytische Aktivität beeinflusst werden. Die Skalierung dieser Architekturen für eine technische Nutzbarkeit war bisher aber kaum möglich. Durch die Verwendung einer flüssigkristallinen Phase aus Fluorhectorit‐Nanoschichten, können wir solche Architekturen in skalierbarem Maßstab imitieren. Synthetischer Natriumfluorhectorit (NaHec) quillt spontan und repulsiv in Wasser zu einer nematischen flüssigkristallinen Phase aus individuellen Nanoschichten. Diese tragen eine permanente negative Schichtladung, sodass selbst bei einer Separation von über 60 nm eine parallele Anordnung der Schichten behalten wird. Zwischen diesen Nanoschichten können Palladium‐Nanopartikel mit entgegengesetzter Ladung eingelagert werden, wodurch die nematische Phase kollabiert und separierte Nanopartikel zwischen den Schichten fixiert werden. Die Aktivität zur CO‐Oxidation des so entstandenen Katalysators war höher als z. B. die der gleichen Nanopartikel auf konventionellem Al2O3 oder der externen Oberfläche von NaHec. Durch Röntgenphotoelektronenspektroskopie konnte eine Verschiebung der Pd‐3d‐Elektronen zu höheren Bindungsenergien beobachtet werden, womit die erhöhte Aktivität erklärt werden kann. Berechnungen zeigten, dass mit erhöhter positiver Ladung des Pd die Adsorptionsstärke von CO erniedrigt und damit auch die Vergiftung durch CO vermindert wird.

Synthesis and Characterization of Pd exchanged MMT Clay for Mizoroki-Heck Reaction

We successfully synthesized Pd@MMT clay using a cation exchange process. We characterized all the synthesized Pd@MMT clays using sophisticated analytical techniques before testing them as a heterogeneous catalyst for the Mizoroki - Heck reaction (mono and double). The highest yield of the Mizoroki-Heck reaction product was recovered using thermally stable and highly reactive Pd@ MMT-1 clay catalyst in the functionalized ionic liquid reaction medium. We successfully isolated 2-aryl-vinyl phosphonates (mono-Mizoroki-Heck reaction product) and 2,2-diaryl-vinylphosphonates (double-Mizoroki-Heck reaction product) using aryl halides and dialkyl vinyl phosphonates in higher yields. The low catalyst loading, easy recovery of reaction product and 8 times catalyst recycling are the major highlights of this proposed protocol.

Sodium borohydride-nickel chloride hexahydrate in EtOH/PEG-400 as an efficient and recyclable catalytic system for the reduction of alkenes

An efficient, safe and one-pot convenient catalytic system has been developed for the reduction of alkenes using NaBH₄–NiCl₂·6H₂O in EtOH/PEG-400 under mild conditions. In this catalytic system, a variety of alkenes (including trisubstituted alkene α-pinene) were well reduced and the Ni catalyst could be recycled.

An efficient, safe and one-pot convenient catalytic system has been developed for the reduction of alkenes using NaBH₄–NiCl₂·6H₂O in EtOH/PEG-400 under mild conditions.

Selective hydrogenation of CO2gas to formic acid over nanostructured Ru-TiO2catalysts

Ionic-liquid-mediated TiO₂supported Ru for the selective CO₂hydrogenation reaction and isolation of HCOOH.