Monometallic cerium layered double hydroxide supported Pd-Ni nanoparticles as high performance catalysts for lignin hydrogenolysis

Monometallic cerium layered double hydroxides (Ce-LDH) supports were successfully synthesized by a homogeneous alkalization route driven by hexamethylenetetramine (HMT). The formation of the Ce-LDH was confirmed and its structural and compositional properties studied by XRD, SEM, XPS, iodometric analyses and TGA. HT-XRD, N-2-sorption and XRF analyses revealed that by increasing the calcination temperature from 200 to 800 degrees C, the Ce-LDH material transforms to ceria (CeO2) in four distinct phases, i.e., the loss of intramolecular water, dehydroxylation, removal of nitrate groups and removal of sulfate groups. When loaded with 2.5 wt% palladium (Pd) and 2.5 wt% nickel (Ni) and calcined at 500 degrees C, the PdNi-Ce-LDH-derived catalysts strongly outperform the PdNi-CeO2 benchmark catalyst in terms of conversion as well as selectivity for the hydrogenolysis of benzyl phenyl ether (BPE), a model compound for the alpha-O-4 ether linkage in lignin. The PdNi-Ce-LDH catalysts showed full selectivity towards phenol and toluene while the PdNi-CeO2 catalysts showed additional oxidation of toluene to benzoic acid. The highest BPE conversion was observed with the PdNi-Ce-LDH catalyst calcined at 600 degrees C, which could be related to an optimum in morphological and compositional characteristics of the support

Finding a suitable catalyst for on-board ethanol reforming using exhaust heat from an internal combustion engine

Ethanol steam reforming with pure ethanol and commercial bioethanol (S/C = 3) was carried out inside the housing of the exhaust gas pipe of a gasoline internal combustion engine (ICE) by using exhaust heat (610–620 °C). Various catalytic honeycombs loaded with potassium-promoted cobalt hydrotalcite and with ceria-based rhodium–palladium catalysts were tested under different reactant loads. The hydrogen yield obtained over the cobalt-based catalytic honeycomb at low load (F/W 200 h) at high load (F/W = 150 mLliq·gcat-1·h-1, GHSV = 2.4·103 h-1) showed that promotion of the ceria-supported noble metal catalyst with alumina and zirconia is a key element for practical application using commercial bioethanol. HRTEM analysis of post mortem honeycombs loaded with RhPd/Ce0.5Zr0.5O2–Al2O3 showed no carbon formation and no metal agglomeration.Postprint (author's final draft

Highly selective hydrogenation of furfural over supported Pt nanoparticles under mild conditions

The selective liquid phase hydrogenation of furfural to furfuryl alcohol over Pt nanoparticles supported on SiO₂, ZnO, γ-Al2O₃, CeO₂ is reported under extremely mild conditions. Ambient hydrogen pressure, and temperatures as low as 50 °C are shown sufficient to drive furfural hydrogenation with high conversion and >99% selectivity to furfuryl alcohol. Strong support and solvent dependencies are observed, with methanol and n-butanol proving excellent solvents for promoting high furfuryl alcohol yields over uniformly dispersed 4 nm Pt nanoparticles over MgO, CeO₂ and γ-Al₂O₃. In contrast, non-polar solvents conferred poor furfural conversion, while ethanol favored acetal by-product formation. Furfural selective hydrogenation can be tuned through controlling the oxide support, reaction solvent and temperature

Electrical properties and reactivity under air–CO flows of composite systems based on ceria coated carbon nanotubes

Nanocomposite systems of ceria nanoparticles and Double Walled Carbon Nanotubes (DWNTs) coated with nanoceria (nCeO2) were elaborated using a classical sol gel method. Three samples noted as [nCeO2 + xDWNTs] with variable weight fractions x = 0, 5 and 15 wt.% of DWNTs were obtained. The samples were characterized by Xray diffraction and electron microscopy. The electrical conductivity of [nCeO2 + xDWNTs] compacted pellets systems was determined from electrical impedance spectrometry, under air, between 120 and 400 °C. In this temperature range, all samples were semiconducting with a weak variation of activation energy. However, the conductivity strongly increased with the weight fraction of ceria coated carbon nanotubes. Finally, the solid–gas interactions between air–CO flows and these systems were studied as a function of time and temperature, by means of Fourier transform infrared (FTIR) spectroscopy. The oxidation kinetics of CO into CO2 was analyzed from the evolutions of FTIR absorption band intensities. As the carbon nanotube fraction x increased, the conversion efficiency was strongly improved

Surface characterization and properties of ordered arrays of CeO2 nanoparticles embedded in thin layers of SiO2

We demonstrated the surface composite character down to the nanometer scale of SiO2-CeO2 composite high surface area materials, prepared using 5 nm colloidal CeO2 nanoparticle building blocks. These materials are made of a homogeneous distribution of CeO2 nanoparticles in thin layers of SiO2, arranged in a hexagonal symmetry as shown by small-angle X-ray scattering and transmission electron microscopy. Since the preparation route of these composite materials was selected in order to produce SiO2 wall thickness in the range of the CeO2 nanoparticle diameter, these materials display surface nanorugosity as shown by inverse chromatography. Accessibility through the porous volume to the functional CeO2 nanoparticle surfaceswasevidenced throughanorganic acid chemisorption technique allowing quantitative determination of CeO2 surface ratio. This surface composite nanostructure down to the nanometer scale does not affect the fundamental properties of the functional CeO2 nanodomains, such as their oxygen storage capacity, but modifies the acid-base properties of the CeO2 surface nanodomains as evidenced by Fourier transform IR technique. These arrays of accessible CeO2 nanoparticles displaying high surface area and high thermal stability, along with the possibility of tuning their acid base properties, will exhibit potentialities for catalysis, sensors, etc

Tetravalent doping of CeO2 : the impact of valence electron character on group IV dopant influence

Fluorite CeO2 doped with group IV elements is studied within the density functional theory (DFT) and DFT + U framework. Concentration-dependent formation energies are calculated for Ce(1-x)Z(x)O(2) (Z = C, Si, Ge, Sn, Pb, Ti, Zr, Hf) with 0 <= x <= 0.25 and a roughly decreasing trend with ionic radius is observed. The influence of the valence and near valence electronic configuration is discussed, indicating the importance of filled d and f shells near the Fermi level for all properties investigated. A clearly different behavior of group IVa and IVb dopants is observed: the former are more suitable for surface modifications and the latter are more suitable for bulk modifications. For the entire set of group IV dopants, there exists an inverse relation between the change, due to doping, of the bulk modulus, and the thermal expansion coefficients. Hirshfeld-I atomic charges show that charge-transfer effects due to doping are limited to the nearest-neighbor oxygen atoms