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The influence of gas/liquid mass transfer on the valorisation reaction of CO2 with epoxides using epichlorohydrin in a stirred batch reactor was investigated in this study. The rate of absorption of CO2 into the liquid was studied in a dynamic way between 50 and 90 °C and at different stirring speeds (100–500 rpm). Two different systems were observed: (i) CO2/epichlorohydrin and (ii) CO2/epichlorohydrin/catalyst, in order to compare and determine the mass transfer coefficient and the enhancement of the absorption when the latter takes place in the presence of a catalyst. The results suggest that the valorisation reaction followed a slow reaction regime in which the reaction did not occur in the mass transfer film but instead took place within the liquid bulk. Therefore, the reaction rate seemed to control the overall process, but according to the specific reaction regime found, both the liquid holdup and the interfacial area should be enhanced to increase the rate of the reaction and the efficiency of the process. Under the conditions studied in this work, the mass transfer coefficient of the liquid phase (kLa) was found to be in the range of 1.0 × 10−3 to 1.0 × 10−2 s−1 and the enhancement factor (E) was between 0.4 and 0.9.

International audience; Cheap and readily available 2-aminopyridine and related compounds can be used as organocatalysts for the conversion of epoxides into cyclic carbonates. This reaction gives high conversions under solvent-free conditions and is amenable to a kilogram-scale conversion under mild conditions.

A structured catalyst consisting of carbon nanofibers grown on the surface of cordierite monoliths was applied in the catalytic ozonation of emerging organic micropollutants. The stability of the catalyst was tested in a long term experiment, showing some initial deactivation related to the formation of oxygenated groups on the carbon surface, but proving to be stable in the long run. The application of the monolith in a triphasic system was demonstrated to be favorable when compared to a biphasic system. The addition of catalyst did not improve the removal of the parent pollutants, but improves the mineralization degree, which is relevant, since the resulting by-products may be more harmful than the parent compounds. The application of the process using a natural water matrix showed some inhibition of the catalytic activity for some pollutants, mainly connected to the radical scavenging properties of some inorganic compounds. However, the catalyst still showed significant activity during these experiments.

We present a study on CoCr–MCM-41 catalysts with stable nm-sized particles. The focus is their promoting effect on the synthesis of Single-Wall Carbon Nanotubes (SWNT). Bimetallic CoCr–MCM-41 catalysts were synthesized by combined grafting and incorporation of metals in the framework. This synthesis allowed an increase in the maximum metal loading in the MCM-41 framework while maintaining nm-sized Co particles stable in high-temperature reactive environments. The SWNT yield was increased by more than 100% from the Co–MCM-41 catalyst. Cobalt is responsible for SWNT nucleation. The role of chromium is to anchor small cobalt particles during reduction and prevent their sintering into large unreactive particles. A larger fraction of the cobalt in the bimetallic catalysts becomes available for the SWNT synthesis when compared to the monometallic one, leading to a significant yield increase. Another effect of the addition of Cr was a shift of the SWNT diameter distribution to smaller nanotubes.

This paper studies the effect of chromium addition to the Co-MCM-41 catalyst in the synthesis of single wall carbon nanotubes (SWNT). The molecular ratios between the two metals have been varied in the catalyst template and their effect on the synthesized SWNT distribution has been studied. By adding Cr to the Co-MCM-41 monometallic catalyst, the diameter distribution of the synthesized SWNT has shifted towards smaller diameter tubes. This shift was correlated with the development of a bimetallic oxide in the MCM-41 framework during catalyst synthesis. By use of fluorescence spectroscopy, the relative abundance of certain tube chiralities has been seen to increase in the bimetallic samples compared to the monometallic ones as for example the (6,5) nanotube. X-ray absorption analysis of the catalyst before, during and after the SWNT synthesis, suggested that the use of a less reducible oxide (chromium oxide) to anchor clusters of a nanotube growth catalyst (cobalt clusters) is an important general tool for engineering the resultant nanotube properties. The addition of chromium has been seen to affect both the reducibility of the cobalt ions and the size of the resultant particles during the SWNT synthesis process.

International audience; The reaction of selective hydrogenation of butadiene performed in an excess of propene, which has been extensively studied over gold supported on different oxides and exhibited high selectivity to butenes, has been applied to the case of gold (1 wt%) supported on zinc oxide (8 m2 g−1), a strongly basic oxide, in order to try to thwart deactivation. Our results revealed, for the first time, a catalytic behaviour drastically different from what was previously observed over gold catalysts supported on alumina or titania, i.e. a much poorer activity when the catalyst was activated under usual conditions under hydrogen but a “normal” activity when it was activated in air. An in-depth characterisation study based on different hypotheses to explain the unusual result revealed that at variance with the other catalysts, Au1Zn1 alloy particles formed during activation under hydrogen at 300 °C and were responsible for the loss of activity.

The heats of adsorption of the adsorbed CO species on Ni supported catalysts are rarely studied by using classical analytical methods (i.e. microcalorimetry and temperature programmed desorption (TPD)) due to experimental difficulties linked to different parallel surface reactions to the adsorption/desorption processes. In the present study, the heats of adsorption of the linear and bridged CO species (denoted L and B CO, respectively) on a reduced 20% Ni/Al2O3 catalyst are studied by using the adsorption equilibrium infra red method developed previously. After a stabilization procedure of the catalyst, the evolutions of the IR bands of the L and B CO species: 2053 and 1927 cm−1, respectively, at Ta = 500 K and Pa = 1 kPa, with the adsorption temperature Ta are studied at a constant adsorption pressure Pa. These data provide the evolutions of the coverages θL = f(Ta) and θB = f(Ta) of the two adsorbed CO species with the increase in Ta in isobar conditions. These curves allow us to determine the heats of adsorption E L θ L and E L θ B of the L and B CO species for several values of the coverage θL and θB according to an adsorption model, i.e. EL1 = 100, EL0 = 153, EB1 = 106 and EB0 = 147 kJ/mol at coverages 1 and 0, respectively. These values are consistent with literature data on Ni single crystals. In particular, it is shown that the mathematical formalism of the AEIR method can be applied to literature data on Ni(1 1 1) providing ECOθ values similar to those of the present study showing the limited impact of the Ni particle size on the CO adsorption properties. The presence of hydrogen (2% CO/10% H2/He) during the measurement decreases slightly the coverages of the two CO species at high temperatures due to either a decrease in the heats of adsorption (i.e. EL1 = 97, EL0 = 131, EB1 = 89 and EB0 = 138 kJ/mol) or the perturbation of the adsorption equilibrium by hydrogenation of the adsorbed CO species.

The study concerns modifications of the elementary steps involved in the isothermal oxidation with O2 of linear and bridged CO species adsorbed on a reduced 2.9% Pt/Al2O3 catalyst in the presence of co-adsorbed N-containing species. The rate of the CO2 production at T 350 K : RCO2(t) with time on stream, t, in x% O2/y% Ar/He ( x , y 3 ) presents a decreasing exponential-like profile for a Pt dispersion D 0.26 in the absence of N-containing species. This profile is significantly modified if NO is adsorbed before oxidation of the adsorbed CO species. An induction period is observed, with a characteristic peak defined by the coordinates of its maximum, t m and RCO2 m. This new RCO2(t) profile is unchanged during successive reduction in CO/oxidation in O2 cycles, indicating that the perturbation created by the NO adsorption is permanent at T 350 K . The impact of NO adsorption on RCO2(t) is ascribed to Nads species formed by NO dissociation. Previous studies allow us to show that the modification of the RCO2(t) profile is due to the decreased rate constants of two elementary steps after the adsorption of NO: (a) the desorption of the bridged CO species, which leads to fewer Pt° sites for the activation of oxygen, and (b) the Langmuir–Hinshelwood steps involved in the oxidation of the adsorbed CO species.

The present study concerns the characterization, by experiments in the transient regime, at atmospheric pressure, with either a Fourier transform infrared or a mass spectrometer as a detector, of the elementary steps involved in the isothermal oxidation at TOTO lower than 360 K of the superficial species formed by adsorption of CO on reduced Pt/Al2O3 catalysts: linear, bridged, and threefold coordinated CO species. The coverages of the adsorbed species and the rate of the CO2 production are determined during successive adsorption, desorption, and oxidation reactions for different durations. The evolution of the rate of the CO2 production with the duration of the oxidation, RCO2(t), presents a variety of profiles, depending on the Pt dispersion of the catalysts. For Pt dispersions higher than 0.6, an induction period is observed and the RCO2(t ) profile is characterized by a peak with a maximum defined by tmtm and RCO2m. The greater the Pt dispersion is, the longer tmtm is and the lower RCO2m is. For Pt dispersions lower than 0.6, the RCO2(t ) profile is similar to a decreasing exponential, and its highest value is observed at time 0 of the oxidation. The induction period observed for Pt dispersions higher than 0.6 allows us to characterize the Langmuir–Hinshelwood steps between the adsorbed CO and oxygen species by studying the impacts on tmtm and RCO2m of different experimental parameters such as the Pt dispersion, the oxidation temperature, the oxygen partial pressure, and the duration of a desorption stage before oxidation. A kinetic model based on the oxidation of the L CO species by a weakly adsorbed oxygen species formed on the Pt0 sites liberated by the removal of the bridged CO species provides a set of mathematical expressions that provide a reasonable explanation of the impacts of the various experimental parameters on tmtm and RCO2m. As a consequence, this kinetic model reveals how the Pt dispersion affects the elementary step and the turnover frequency of the CO/O2 reaction. A comparison of the present study with similar literature data on a single Pt crystal shows that the differences in the experimental conditions, material and pressure gaps, may lead to a situation in which the Langmuir–Hinshelwood steps that are studied are not the same.

It has been previously shown that the individual heats of adsorption of each adsorbed CO species (linear, bridged and three-fold coordinated) on Pt/Al 2 O 3 catalysts can be obtained from the change of their characteristic IR bands with the adsorption temperature T a (in the range of 300–800 K) at a constant CO partial pressure P a according to a procedure denoted adsorption equilibrium infrared spectroscopy. In the present study, this procedure is used to reveal the impact of the nature of the support TiO 2 , CeO 2 and Y 2 O 3 /ZrO 2 (two solids with high (104 m 2 /g) and low (14 m 2 /g) BET surface area) on the heat of the adsorption of the L CO species that dominates the CO adsorption. These reducible supports have been selected because of their expected interactions with Pt particles according to different SMSI effects. In the wavenumber range characteristic of the L CO species on Pt sites, the FT-IR spectra are dependent on the nature of the support: two strongly overlapped IR bands are detected with an intensity ratio depending on the support. However, it is shown that the nature of the support only has a slight impact on the average heats of adsorption of the L CO species ( 2 O 3 ).

The impact of Pt dispersion (denoted by D ) of Pt/Al 2 O 3 catalysts on the turnover frequency (TOF) of the CO/O 2 reaction and on the elementary steps involved in the catalytic reaction is studied using transient experiments with either a mass or a FTIR spectrometer as a detector. Similar to literature data, it is observed that TOF decreases with an increase in D . The aim of the present study is to correlate this observation with the modifications of the surface elementary steps of two kinetic models, M1 and M2, developed previously for D ≲ 0.6 . The elementary steps considered are (1) adsorption of CO as a linear CO species (denoted by L and involved in models M1 and M2) and as a bridged CO species (denoted by B); (2) the oxidation by O 2 of the adsorbed CO species; and (3) the reduction by CO of the strongly adsorbed oxygen species (denoted by O sads ) involved in model M2. It is shown that D has no significant impact on the heat of adsorption of the L CO species and on the mechanism of the reduction of O sads species by CO. For oxidation of the L CO species by O 2 , it is shown that there is an induction period in the CO 2 production for D ≳ 0.60 not observed for a lower dispersion. This is explained by considering that the rate of formation of the Pt sites, which adsorb O 2 during oxidation, depends on D . These sites, which represent a small fraction of the Pt 0 sites, are associated with the B CO species. It is shown that the heat of adsorption of the B CO species increases with an increase in D . It is suggested that it is the removal of the B CO species (by desorption and oxidation) that controls the induction duration.

The adsorption of CO at several adsorption temperatures (T a ) in the range of 300-550 K on several reduced 5 wt % Cu/Al 2 O 3 solids, with and without residual chlorine, is studied by FTIR spectroscopy. Whatever the solid,the main adsorbed species is a linear (denoted by L) CO species adsorbed on Cu° sites. On the Cl-free solids, the L CO species is detected at 2095 cm - 1 , while the presence of Cl leads to a shift to higher wavenumbers. The evolution of the coverage θ L of the L CO species with the adsorption temperature for a constant CO partial pressure (P C O = 1 kPa) allows us to determine the heat of adsorption of the L CO species as a function of the coverage on the various Cu-containing solids by using the AEIR method. It is shown that the presence of residual Cl has no impact on the heat of adsorption at low coverages (82 kJ/mol), while it decreases slightly the heat of adsorption at high coverages from 57 to 45 kJ/mol.

[EN] Structured hierarchical catalysts were developed for efficient reduction of bromates in water. In the catalysts a small amount of active metal, 0.3 wt.% Pd, is supported onto carbon nanofibres grown either on sintered metal fibres or on a carbon cloth. In both cases high rates of reaction and high selectivity were achieved, allowing a significant reduction in the amount of catalyst required for the treatment of a set volumetric flow of polluted water, compared to a conventional Pd/Al2O3 catalyst. Manufacture of carbon nanofibres grown on a hierarchical structured support was scaled to 10 g batches. Cradle-to-gate life cycle assessment (LCA) study was performed to compare potential water treatment processes based on two catalyst types, and to identify the areas for future optimisation of the novel technology based on structured hierarchical catalysts., The research leading to these results has received funding from the European Community's Seventh Framework Programme [FP7/2007-2013] for MONACAT under Grant agreement no NMP4-SL-2009-226347. We would like to thank Drs Dana Kralisch and Denise Ott for their advice on Umberto LCA methods.

Emerging micropollutants have been recently the target of interest for their potential harmful effects in the environment and their resistance to conventional water treatments. Catalytic ozonation is an advanced oxidation process consisting of the formation of highly reactive radicals from the decomposition of ozone promoted by a catalyst. Nanocarbon materials have been shown to be effective catalysts for this process, either in powder form or grown on the surface of a monolithic structure. In this work, carbon nanofibers grown on the surface of a cordierite honeycomb monolith are tested as catalyst for the ozonation of five selected micropollutants: atrazine (ATZ), bezafibrate, erythromycin, metolachlor, and nonylphenol. The process is tested both in laboratorial and real conditions. Later on, ATZ was selected as a target pollutant to further investigate the role of the catalytic material. It is shown that the inclusion of a catalyst improves the mineralization degree compared to single ozonation.

6 pages, 2 tables., The aim of this work is to study the activity of new Pd catalysts, supported on two different nano structured carbon materials, for bromate catalytic hydrogenation. The influence of the support has been studied, obtaining the best results with a palladium catalyst supported on carbon nanofibers (CNF) grown in sintered metal fibers (SMF). The results have shown the importance of the catalyst support in order to minimize the mass-transfer limitations ensuring an efficient catalyst use. In this way the most active catalysts are those with a mesoporous structure containing high dispersed Pd nanoparticles. The activity of this catalyst for bromate reduction has been tested in different types of water, namely, distilled water, natural water and industrial wastewater. It has been shown that the catalyst activity depends on the water matrix and bromate reduction rate depends on the hydrogen partial pressure. The potential use of the catalyst has been studied in a continuous reactor. It has been observed that the catalyst is active without any important deactivation at least during 100. h of reaction, but is necessary to avoid salt precipitation and plugging problems., The authors thank the European Union (European Community’s Seventh Framework Programme FP7/2007-2013 under Grant Agreement No. 226347 Project) for financial support.