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The adsorption of CO in the temperature range of 300–713 K on the PtSn particles of a reduced (H2, 713 K) 1.2%Pt-2.7%Sn/Al2O3 catalyst is studied by FTIR spectroscopy to reveal the geometric and electronic effects of Sn on the Pt sites. By comparison with a 1.2% Pt/Al2O3 it is shown that Sn (a) suppresses the Pt sites forming bridged CO species due to a geometric effect and (b) displaces the IR band of a linear CO species on Pt sites at 300 K from 2066 cm−1 to 2044 cm−1 due to an electronic effect. According to the AEIR method, the change in the IR band on the PtSn particles with the increase in Ta in isobaric condition (PCO = 1 kPa) provides the heats of adsorption of the linear CO species (named L1PtSn) at high (58 kJ/mol) and low (130 kJ/mol) coverages. By comparison with the values of the linear CO species on Pt particles (named LPt): 220 and 106 kJ/mol at low and high coverages, respectively, these values reveal the strong impact of the electronic effect of Sn on the heats of adsorption of CO. For Ta > 463 K there is a reconstruction of the PtSn particles due to the segregation of Sn as SnOx species associated with an enrichment of the surface in Pt. On the reconstructed PtSn particles, a new IR band is observed at 2057 cm−1 after adsorption of CO at 300 K ascribed to a new L2PtSn CO species. Its heats of adsorption are significantly higher than those of the L1PtSn species: 165 and 65 kJ/mol at low and high coverages. Moreover, successive reconstruction/H2 reduction at 713 K cycles leads to a sintering of the PtSn particles associated to the progressive increase in the heats of the L2PtSn CO species until a value at low coverage: 210 kJ/mol similar to that of the LPt species whereas at high coverage a significant difference exists between the two species (70 and 115 kJ/mol for L2PtSn and LPt, respectively). These data show that the impacts of Sn on the heat of adsorption of the linear CO species on the Pt sites are dependent on (a) the Pt/Sn surface ratio which changes with reconstruction and the particle size and (b) the coverage of the Pt sites. The comparison of the heats of adsorption of the L CO species on the fresh, reconstructed and aged PtSn particles with experimental and theoretical literature data reveals that they are consistent with some of them.

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.

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 linear and bridged CO species adsorbed on Ag0 sites of a reduced 3% Ag/Al2O3 catalyst and of the linear CO species on Ag+ sites of the oxidized catalyst are determined as the function of their respective coverages by using the adsorption equilibrium infrared spectroscopy method previously developed. The evolutions of the intensities of the IR bands of each adsorbed species: 2045 cm-1 and 2000 cm-1 at 300 K, for the linear and bridged CO species, respectively, on Ag0 sites of the reduced solid and 2168 cm-1 for a linear CO species on Ag+ sites of the oxidized solid are determined as a function of the adsorption temperature Ta, at a constant CO adsorption pressure PCO. This provides the evolutions of the coverages of each adsorbed CO species with Ta in isobar conditions that give the individual heats of adsorption of the three adsorbed CO species at several coverages according to an adsorption model. The heats of adsorption of the linear and bridged adsorbed CO species on Ag0 sit...

International audience; The heats of adsorption at several coverages of the linear and bridged CO species (denoted L and B, respectively) adsorbed on the Pt0 sites of the 2.9 wt% Pt/10% K/Al2O3 catalyst are determined using the Adsorption Equilibrium Infrared spectroscopy method. The addition of K on 2.9% Pt/Al2O3 modifies significantly the adsorption of CO on the Pt particles: (a) the ratio L/B is decreased from 8.4 to 1, (b) a new adsorbed CO species is detected with an IR band at 1763 cm−1, (c) the heats of adsorption of L and B CO species are significantly altered and the positions of their IR bands are shifted. The heats of adsorption of L CO species are decreased: i.e. 206 and 105 kJ/mol at low coverages on Pt/Al2O3 and Pt/K/Al2O3 respectively. Two B CO species denoted B1 and B2, with different heats of adsorption are observed on Pt/K/Al2O3. The heats of adsorption of B2 CO species (major B CO species) are significantly larger than those measured in the absence of K: i.e. 94 and 160 kJ/mol at low coverages on Pt/Al2O3 and Pt/K/Al2O3 respectively, whereas those of B1 CO species (minor species) are similar: 90 kJ/mol at low coverages. These values are consistent with the qualitative High Resolution Electron Energy Loss Spectrometry literature data on Pt(1 1 1) modified by potassium.

[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.

International audience; This paper deals with the study of the conditions of obtention of small metal copper particles on ZnO using easy synthesis methods and activation treatments, which were found "efficient" for the preparation of copper particles on silica, that is, deposition-precipitation with urea and incipient wetness impregnation. For the latter, four different copper precursors were used: copper(II) nitrate, acetylacetonate, bis-ethylenediamine, and tetraamine. Activation treatments were performed under different gas reducing conditions (H2 or CO in N2), temperatures between 280 and 350 °C, and isotherm between 1 min and 2 h, with or without a precalcination step. Transmission electron microscopy (TEM), UV-visible spectroscopy, and X-ray diffraction (XRD) techniques were used to characterize the samples at the different stages of the synthesis route. The TEM results showed that it is not as easy as on silica to make small copper particles on ZnO. However, some experimental conditions were found to lead to particles around 4 nm: impregnation with copper acetylacetonate or copper bis-ethylenediamine, followed by calcination before reduction in H2. The important result of this work is that depending on the final temperature of reduction under hydrogen, it was possible to form either metal Cu particles (280 °C) or Cu3Zn alloy particles (350 °C); this was directly proved by XRD and indirectly by UV-visible spectroscopy. However, the formation of Cu3Zn could be avoided if the reducing gas H2 was replaced by CO in N2. To our knowledge, this is the first time that the formation of Cu3Zn alloy particles is evidenced in Cu/ZnO samples.