Christine Lancelot

A long-life catalyst for glycerol dehydration to acrolein

While the initial catalytic performances of silica-supported silicotungstic acid are high in the glycerol dehydration reaction, they rapidly decrease with time on stream and the acrolein yield quickly decreases.

The nature of cobalt species in carbon nanotubes and their catalytic performance in Fischer–Tropsch reaction

The nature of cobalt species in the catalysts supported by multi-wall carbon nanotubes and their catalytic performance in Fischer–Tropsch synthesis were investigated using nitrogen adsorption, X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, high resolution transmission electron microscopy, in situ magnetic method, X-ray absorption and temperature programmed reduction. The catalysts were prepared by incipient wetness impregnation using solutions of cobalt nitrate assisted by sonochemical process followed by calcination in nitrogen. The characterization techniques uncovered that acid pretreatment oxidized the carbon nanotube surface and removed impurities. Small cobalt oxide particles of 8–10 nm diameter and irregular shape anchored to the outer surface of carbon nanotubes were detected in the calcined samples by several characterization techniques. The catalysts displayed high cobalt reducibility, which was slightly affected by the pretreatment with nitric acid and nanotube outer diameter. Cobalt catalysts supported on carbon nanotubes exhibited high catalytic activity in Fischer–Tropsch synthesis. Pretreatment with nitric acid leads to a 25% increase in hydrocarbon yield, while carbon nanotube diameter does not seem to significantly affect the Fischer–Tropsch performance of the resulting catalysts.

Transesterification of Diethyl Oxalate with Phenol over Sol–Gel MoO3/TiO2 Catalysts

The transesterification of diethyl oxalate (DEO) with phenol to form diphenyl oxalate (DPO) has been carried out in the liquid phase over very efficient MoO(3)/TiO(2) solid-acid sol-gel catalysts. A selectivity of 100 % with a remarkable maximum yield of 88 % were obtained, which opens the route to downstream phosgene-free processes for the synthesis of polycarbonates. Interpretation of the results of various acidity measurements (NH(3) and pyridine desorption, methanol oxidation as a probe reaction) allowed us to identify the catalytic sites as Lewis acid sites.

The Role of Steric Effects and Acidity in the Direct Synthesis of iso‐Paraffins from Syngas on Cobalt Zeolite Catalysts

This study focuses on the effects of the localization of Co species, zeolite structure, and acidity on the performance of Co bifunctional catalysts promoted with Pt for the direct synthesis of iso‐paraffins from syngas. ZSM‐5, MOR, and BEA were chosen as zeolites with different structures and pore diameters. The catalysts were prepared either by incipient wetness impregnation or by the mechanical mixing of the zeolite with a conventional silica‐supported Co catalyst. The increase in the pore size and open character of the zeolite structure from ZSM‐5 to BEA resulted in a higher fraction of Co located inside the pores of the catalysts prepared by impregnation. The catalytic performance was affected strongly by the zeolite acidity, pore structure, and Co distribution between the pores and the external surface. The selectivity to short‐chain iso‐paraffins is affected principally by the zeolite acidity, whereas the selectivity to long‐chain branched hydrocarbons mostly depends on steric effects.

Tuning Hydrodesulfurization Active‐Phase Dispersion using Optimized Mesoporous Titania‐Doped Silica Supports

Solids composed of TiO2 nano‐crystallites (10–40 wt %) dispersed in an SBA‐15 matrix were synthesised and used as hydrodesulfurisation (HDS) active‐phase supports. Well‐dispersed polymolybdate species were detected by Raman spectroscopy on all the CoMo‐based oxidic precursors. Undesirable bulk CoMoO4 mixed oxide was also detected on the surface of low‐TiO2‐content materials, which suggests the enhancement of the Mo oxidic species dispersion as a result of the presence of TiO2. After activation under H2/H2S, the obtained catalysts were tested in the HDS of thiophene. An optimum conversion was observed for the catalyst supported on the solid that contained 20 wt % TiO2, which outperformed the homologous samples supported on TiO2 and SBA‐15. This clearly highlights the beneficial effect of using such nano‐TiO2‐SBA‐15 composite supports, in which SBA‐15 confers adequate textural properties to the system, and the active phase benefits from the dispersive effect of TiO2.

Fischer–Tropsch synthesis on a ruthenium catalyst in two-phase systems: an excellent opportunity for the control of reaction rate and selectivity

The activity and selectivity of Fischer–Tropsch synthesis over hydrophobic Ru/C catalysts were efficiently controlled in the reaction medium consisting of organic and aqueous phases. A higher reaction rate was observed in two-phase systems compared to Fischer–Tropsch synthesis in the organic phase; however, catalyst localization in the organic phase leads to higher and tuneable selectivity to long-chain hydrocarbons.

Increase of the Ni/W Ratio in Heteropolyanions Based NiW Hydrocracking Catalysts with Improved Catalytic Performances

Abstract In the present work, we investigated the influence of the increase of Ni/W ratio by the addition of nickel nitrate on heteropolycompound (HPC) based catalysts. Synthesized catalysts were characterized by Raman, XPS and HRTEM techniques and were examined in the model reaction of toluene hydrogenation. The Ni2SiW12O40 based catalyst with a ratio of 0.36 obtained by addition of nickel nitrate was found to have the best catalytic activity compared to the most efficient of the HPC based catalysts with a stoichiometric Ni/W ratio of 0.36. Raman spectroscopy showed that the SiW12O404− HPA was decomposed during the drying step in SiW11O398− species. Graphical Abstract

Synthesis and characterization of zirconia-grafted SBA-15 nanocomposites

The preparation of highly ordered mesoporous zirconia is of special interest when targeting applications in catalysis. Nevertheless, most of the previously reported attempts led to materials with a low hydrothermal stability. Herein, we accordingly report about the benefit of using mesoporous silica as a host support in which accessible zirconia crystallites are stabilized on the surface. The zirconia surface coverage could be tuned and optimized by playing on the most sensitive synthesis parameters, namely the quantity of zirconia, the calcination temperature and the pore diameter of the host support. The acid properties of the so-obtained materials were determined, showing a remarkable linear relationship between the amount of introduced zirconia and the number of acid sites, which evidenced a high accessibility of the acid sites in the nano-composite, due to a homogeneous dispersion of the zirconia phase in the pores of the silica host support.

Plasma Synthesis of Highly Dispersed Metal Clusters Confined in Nanosized Zeolite

Metal-containing zeolites (and, more generally, porous materials) are very important for catalysis, electronics, and sensors, but their preparation is still a problem. Reproducibility and control of the properties of the metal cluster is difficult. Broad size distribution of the metal particles together with a low stability of the clusters is often observed. New methods have been reported, such as UV photolysis and g irradiation of hydrated metal complex ions incorporated within the microporous molecular sieves. Organic templates such as tetraalkylammonium cations can stabilize separate metal clusters and prevent agglomeration and also limit the metal loading in the material. However, such solids still need to be heat treated (calcined), which may result in a slow agglomeration of the clusters and a possible migration to the outer surface of the matrix, with pore blocking and low energy efficiency. Postsynthetic treatment by nonthermal plasma was recently applied to metal-loaded templated mesoporous materials (MCM and SBA-15). The plasma is believed to dissociate and ionize residual water molecules in the mesoporous matrix, creating hydrated electrons e ðaqÞ and radicals H· for reduction of the metal ions to clusters. The authors however still needed to use additional water and apply a final thermal treatment to remove residual impurities, resulting in partial sintering of the metal clusters. We report herein a one-step environmentally friendly approach for the preparation of active and highly dispersed metal clusters confined predominantly in the channels of nanosized BEA type zeolite (diameter of individual particles of 10 nm) by plasma treatment. This approach, which was discovered using operando FTIR in the plasma reactor, leads to a fast and simultaneous calcination of the nanosized molecular sieve (removal of the organic template) and reduction of the metal cations to clusters. Prior to calcination, the nanosized pure BEA and Pt-containing BEA (Pt/BEA, 0.75 wt% Pt) zeolites were directly subjected to Ar or O2 cold plasma treatments at low pressure (350 Pa). The changes in the samples under plasma treatment followed by operando FTIR spectroscopy are shown in Figure 1. The initial spectra of the pure BEA and Pt/BEA samples exhibit the methyl stretching modes at 3100–2800 cm 1 originating from the tetraalkylammonium (TEA) organic template (Figure 1). From the beginning of the plasma ignition, the intensity of the CH bands decreased due to the removal of the TEA template. In oxygen plasma, the IR feature of acidic Bronsted sites appeared at 3600 cm 1 (Figure 1b, c). This phenomenon is better pronounced in the Pt-containing BEA samples (Figure 1b). The degree of degradation of the organic template (D%) could be calculated by integrating the total absorbance, AHC, in the region of 3100–2800 cm 1 as a function of time according to the Equation (1):

Potential of templated mesoporous aluminas as supports for HDS CoMo catalysts

Aluminas, exhibiting different textural properties, were prepared using a template assisted sol–gel method. In the presence of a triblock copolymer as a porogen, and owing to the control of the synthesis parameters, alumina textural properties can be adjusted up to values higher than those of conventional alumina. Among obtained supports, some were selected in order to cover surface area values from 350 to 450 m2 g−1, and pore diameters from 5.4 to 9.0 nm. CoMo derived catalysts, prepared by impregnation with a (Co2Mo10O38H4)Co3 solution, with a concentration corresponding to a molybdenum density of 4 atMo nm−2 (or 3 when not possible to achieve 4), exhibit decreased textural parameters. However, despite the changes induced by the preparation step, the final catalysts always display attractive textural properties. Activities in thiophene hydrodesulfurization (HDS) can be increased by a factor three, depending on the textural properties of the supports used and possibly to some extend on the residual carbon content in the material. The performance of the most efficient solid in the HDS of thiophene was evaluated in the HDS of a straight run gas oil (SRGO) and was found higher than that of a commercial alumina based catalyst and close to that of a commercial catalyst modified by a chelating agent, evaluated under the same conditions.