Mihaela Florea

Graphenes in the absence of metals as carbocatalysts for selective acetylene hydrogenation and alkene hydrogenation

Catalysis makes possible a chemical reaction by increasing the transformation rate. Hydrogenation of carbon-carbon multiple bonds is one of the most important examples of catalytic reactions. Currently, this type of reaction is carried out in petrochemistry at very large scale, using noble metals such as platinum and palladium or first row transition metals such as nickel. Catalysis is dominated by metals and in many cases by precious ones. Here we report that graphene (a single layer of one-atom-thick carbon atoms) can replace metals for hydrogenation of carbon-carbon multiple bonds. Besides alkene hydrogenation, we have shown that graphenes also exhibit high selectivity for the hydrogenation of acetylene in the presence of a large excess of ethylene.

New Class of Catalysts for the Propane Ammoxidation Process Based on Vanadium Aluminum Oxynitrides

Amorphous high-surface-area vanadium aluminum oxynitrides (VAlON) prepared by nitridation of an amorphous oxide precursor exhibit a high acrylonitrile yield in propane ammoxidation at very low contact time, indicating the participation of ammonia dehydrogenated species in the ammoxidation of alkanes. The productivity of the VAlON catalysts (l of ACN/kg catalyst/h) was markedly improved as compared with known oxide systems.

Graphene from Alginate Pyrolysis as a Metal-Free Catalyst for Hydrogenation of Nitro Compounds.

Graphene obtained by pyrolysis of alginate at 900 °C under inert atmosphere and exfoliation is used as a metal-free catalyst for reduction of nitro to amino groups with hydrogen as a reagent. The process is general for aromatic and aliphatic, conjugated and isolated nitro groups, and occurs with low selectivity over hydrogenation of carbon-carbon double bonds.

Acylation of different amino derivatives with fatty acids on UL-MFI-type catalysts*

Acylation of different amino derivatives (ethanol amine, diethanol amine, N-aminoethylpiperazine) was carried out under green conditions with oleic acid or tail oil fatty acids. The experiments were carried out using as heterogeneous catalysts mesoporous Al-Meso and UL-ZSM-5 with Si/Al ratios between 100 and 20, in the range of the temperatures 80-180 °C without any solvent or in octane or water. The efficiency of the catalysts for the acylation of the investigated substrates appeared to be directly dependent on the Si/Al ratio and the size of the pores. The selectivity toward esters or amides was firstly controlled by temperature, and then by the Si/Al ratios. Additionally, both the conversion and selectivity were controlled by the solvent in which the reaction was carried out. The use of water led mostly to a mixture of esters and amides.

NIR to Vis-NIR up-conversion and X-ray excited emission of Er doped high Z BiOCl

Herein, we investigate the emission properties of Er - BiOCl in the range of ∼500 to 1700 nm under down - (488 and 973 nm) and NIR (telecom - wavelength at ~1500 nm) up - conversion excitation as well high energy X-ray excitation. The dependencies of red (~670 nm) and NIR (~800 nm) to green emission (~543 nm) ratio with Er concentration, excitation mode and delay after laser pulse as well as the up - conversion excitation spectra and decays are analyzed in terms of competitive ground state absorption/excited state absorption and energy transfer up - conversion mechanisms. The CIE chromaticity diagram show single excitation (~1500 nm), delay induced emission color change from yellowish green (delay of 0.001 ms) to reddish orange (delay of 1 ms). The X-ray induced emission of Er - BiOCl presents an atypical red to green emission ratio that exceeds that measured under optical down - conversion excitation by a factor of 13. The potential of Er - BiOCl for optical /X-ray imaging applications is discussed.

Advances in luminescence of lanthanide doped Y 2 O 3 : case of S 6 sites

Although the emission of lanthanide (Ln) ions doped cubic sesquioxides has been subject of extensive studies, there are fundamental issues still to be elucidated. Specifically, compared to the well-understood emission of Ln at C2 sites, the emission at the inversion S6 (C3i) sites, representing ¼ of the total sites, has been identified only for Pr, Nd, Eu, Sm and Yb. Here, we present a first report and improved identification of the emission, excitation and decay properties of Tb, Dy and Pr at S6 sites in Y2O3 by use of time-gated luminescence spectroscopy. The green emission of Tb at S6 sites is characterized by an intensity ratio relative to the cyan band at 490 nm of 10 compared to 2 measured for Tb at C2 sites. Dy at S6 sites displays a relatively intense, near-infrared emission at 765 nm which is red-shifted by ca. 200 nm relative to yellow peaked emission of Dy at C2 sites. The emission lifetimes of 9.4 and 4.8 ms, associated with Tb and Dy at S6 sites, exceed by a factor of 5 and 10 those of C2 counterparts. It is also found that Dy may be regarded as a sensitive probe for the inversion symmetry, comparable with the more recognized Eu. The participation of Ln at S6 sites to the up-conversion emission is revealed for the first time in Sm doped Y2O3 and Eu /Tb, Yb co-doped Y2O3 and explained in terms of successive ground state and excited state absorptions and cooperative energy transfer, respectively.

Sensors based on mesoporous SnO2-CuWO4 with high selective sensitivity to H2S at low operating temperature

Development of new sensitive materials by different synthesis routes in order to emphasize the sensing properties for hazardous H2S detection is one of a nowadays challenge in the field of gas sensors. In this study we obtained mesoporous SnO2-CuWO4 with selective sensitivity to H2S by an inexpensive synthesis route with low environmental pollution level, using tripropylamine (TPA) as template and polyvinylpyrrolidone (PVP) as dispersant/stabilizer. In order to bring insights about the intrinsic properties, the powders were characterized by means of a variety of complementary techniques such as: X-Ray Diffraction, XRD; Transmission Electron Microscopy, TEM; High Resolution TEM, HRTEM; Raman Spectroscopy, RS; Porosity Analysis by N2 adsorption/desorption, BET; Scanning Electron Microscopy, SEM and X-ray Photoelectron Spectroscopy, XPS. The sensors were fabricated by powders deposition via screen-printing technique onto planar commercial Al2O3 substrates. The sensor signals towards H2S exposure at low operating temperature (100°C) reaches values from 105 (for SnWCu600) to 106 (for SnWCu800) over the full range of concentrations (5-30ppm). The recovery processes were induced by a short temperature trigger of 500°C. The selective sensitivity was underlined with respect to the H2S, relative to other potential pollutants and relative humidity (10-70% RH).

Synthesis of Terephthalic Acid by p‐Cymene Oxidation using Oxygen: Toward a More Sustainable Production of Bio‐Polyethylene Terephthalate

The synthesis of terephthalic acid from biomass remains an unsolved challenge. In this study, we conducted the selective oxidation of p-cymene (synthesized from biodegradable terpenes, limonene, or eucalyptol) into terephthalic acid over a Mn-Fe mixed-oxide heterogeneous catalyst. The impact of various process parameters (oxidant, temperature, reaction time, catalyst amount, oxygen pressure) on the selectivity to terephthalic acid was evaluated, and some mechanistic aspects were elucidated. An unprecedented synthesis of biobased terephthalic acid (51 % yield) in the presence of O2 is reported.

A Robust Metal–Organic Framework Constructed from Alkoxo-Bridged Binuclear Nodes and Hexamethylenetetramine Spacers: Crystal Structure and Sorption Studies

A neutral 3D metal-organic framework, (3)(∞)[Cu(2)(mand)(2)(hmt)]·H(2)O (1), was constructed from binuclear Cu(2)O(2) alkoxo-bridged nodes, generated by the doubly deprotonated mandelic acid. The nodes are connected by hexamethylenetetramine (hmt) spacers, which act as biconnective bridging ligands, and by carboxylato groups. Channels are observed along the crystallographic c axis. The water molecules from the channels can be easily removed, preserving the architecture of the crystal, which is stable up to 280 °C. The Langmuir surface area was found to be 610 m(2) g(-1). The sorption ability of 1 was investigated using H(2) and CO(2).

Ru-MCM-41 catalysts for diastereoselective hydrogenation

Abstract Ru-MCM-41 catalysts were prepared by deposition of several complexes from their solvents: of Ru acetylacetonate from its ether solution, of cis -dichlorobis(2,2 ′ -bipyridine) Ru in chloroform, of di-μchlorobis(( p -cymene)chloro Ru(II)) in chloroform and of dichloro(1,5-cyclooctadiene) Ru(II) dissolved in pyridine. The catalysts were characterized as prepared and after several reactions cycles by: adsorption–desorption isotherms of N 2 at 77 K, XRD, FTIR, and XPS. The above catalysts were used in the liquid phase hydrogenation of a F prostaglandin intermediate. A strong leaching of Ru was observed, but after four cycles the catalysts remained unchanged in activity and diastereoselectivity. The stereoselectivity was found to be influenced by the nature of the precursor complex. In the presence of the catalyst prepared from di-μchlorobis(( p -cymene)chloro Ru(II)) the natural-like product was obtained.