Calorimetric Study of Propane and Ethylbenzene on Active Surface on Carbon-Based Catalysts

The use of carbon materials instead of (mixed) metal oxides in selective oxidation catalysis could emerge to be of basic interest for the catalysis community. Low dimensional carbon allotropes such as multiwalled carbon nanotubes (CNTs) with high structural homogeneity provide the characteristics of model catalysts with well defined active sites as compared with polyvalent transition metal oxides featuring complex electronic and spin structures. The oxydehydrogenation (ODH) reaction over carbon has been discovered in 1979 by Alkhazov et al.[1] From the mechanistic point of view, quinone groups are believed be the active site. These nucleophilic oxygen species can selectively abstract hydrogen atoms and the formed phenol groups are subsequently reoxidized by O2. We choose the ODH of propane and ethylbenzene (EB) as the model reactions. Propane is widely investigated as a substrate in this reaction and mechanistic models for the reaction sequence over metal oxide catalysts are nu-merously suggested. It is equipped with a high C–H bond strength (410.5 kJ mol-1). In contrary to the alkane, the weak C-H bond in benzylic position (357.3 kJ mol-1) makes the molecule highly reactive for ODH

Enhancing the Catalytic Activity of Palladium Nanoparticles via Sandwich-Like Confinement by Thin Titanate Nanosheets

As atomically thin oxide layers deposited on flat (noble) metal surfaces have been proven to have a significant influence on the electronic structure and thus the catalytic activity of the metal, we sought to mimic this architecture at the bulk scale. This could be achieved by intercalating small positively charged Pd nanoparticles of size 3.8 nm into a nematic liquid crystalline phase of lepidocrocite-type layered titanate. Upon intercalation the galleries collapsed and Pd nanoparticles were captured in a sandwichlike mesoporous architecture showing good accessibility to Pd nanoparticles. On the basis of X-ray photoelectron spectroscopy (XPS) and CO diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) Pd was found to be in a partially oxidized state, while a reduced Ti species indicated an electronic interaction between nanoparticles and nanosheets. The close contact of titanate sandwiching Pd nanoparticles, moreover, allows for the donation of a lattice oxygen to the noble metal (inverse spillover). Due to the metal–support interactions of this peculiar support, the catalyst exhibited the oxidation of CO with a turnover frequency as high as 0.17 s–1 at a temperature of 100 °C

In situ XRD studies of the effect of catalyst pre-treatment strategies on the bulk structure and performance of Mo-V-Te-Nb catalysts for selective oxidation of propane.

Current research efforts are concentrated towards utilizing propane rather than propylene as the feedstock in the industrial process for producing acrylic acid because of its significant lower price. The discovery of the MoVTe family of catalysts has brought this goal within sight. This study investigates the effect of different calcination protocols using in situ XRD. A series of catalyst precursors were treated at different calcination temperatures and atmospheres, while analysing their structures with XRD. The conditions necessary for crystallization of known active phases were determined. The activity of the same catalysts was also tested using a nanoflow high throughput reactor. A structure – activity study leads to correlations between synthesis, phase equilibria and performance of these Mo-V-Te-Nb catalysts for selective oxidation of propane

From a Molecular Single-Source Precursor to a Selective High- Performance RhMnOx Catalyst for the Conversion of Syngas to Ethanol

The first carbonyl RhMn cluster Na2[Rh3Mn3(CO)18] 2 has been synthesized and structurally characterized, resulting from the salt metathesis reaction of RhCl3 with Na[Mn(CO)5] 1 in 49% isolated yield. The dianionic Rh3Mn3 cluster core of 2 can serve as a molecular single‐source precursor (SSP) for the low temperature preparation of selective high‐performance RhMn catalysts for the conversion of syngas to ethanol (StE). Impregnation of 2 on silica (davisil) led to three different silica‐supported RhMnOx catalysts with dispersed Rh nanoparticles tightly surrounded by a MnOx matrix. With ethanol selectivities of up to 24.1%, the Rh3Mn3 cluster precursor‐derived catalysts show the highest reported selectivity and performance in the conversion of StE for silica‐supported RhMnOx catalysts

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 Al2O3 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