Search

Novel Cu–ZnO–ZrO2/UGSO catalysts for CO2 hydrogenation to methanol were developed using a metallurgical residue as catalytic support, focusing on (i) the synergy of Cu/Zn/Zr and UGSO composition and (ii) UGSO modification, on catalytic activity and stability.

In this study, the kinetics of the esterification of glycolic acid with ethanol homogeneously autocatalyzed and heterogeneously catalyzed are investigated.

Hemicelluloses are a major part of lignocellulosic biomass. Different sugars can be obtained from hemicelluloses: xylose, arabinose, galactose, mannose, glucose. Their catalytic hydrogenation produces polyols: xylitol, arabinitol, dulcitol, mannitol, sorbitol, which are valuable chemicals and platform molecules. In this paper, the hydrogenation of sugars was investigated with a Ru/TiO2 catalyst. The influence of temperature, pressure, xylose concentration and catalyst amount was studied for xylose hydrogenation and a Langmuir-Hinshelwood kinetic model was designed. The comparative study of five hemicellulose sugars showed a strong impact of sugar structure on hydrogenation rate: hexoses (glucose, mannose, galactose) react slower than pentoses (xylose, arabinose).

Industrial Kraft black liquor from maritime pine was oxidised in aqueous, alkaline medium, under air, at 150°C, with or without CuO/TiO2 catalyst. The oxidation products were analysed by HPLC, elemental analysis, SEC, FTIR, NMR. The results showed the depolymerisation of lignin, the formation of phenolic compounds in low yields, with vanillin being the main phenolic compound, and the formation of aliphatic compounds in higher yields, with formic, succinic and tartronic acids being the main identified aliphatic compounds. The presence of the catalyst favoured the formation of phenolic and aliphatic compounds. Replacing Kraft black liquor by pure Kraft lignin as a starting material did not improve the performances of the catalytic oxidation, indicating that lignin purification may not be necessary under our conditions. Switching from a batch reactor to a fixed bed reactor, operating under similar conditions, did not increase the yields of oxidation products but did increase the productivity. This work demonstrates the potential of Kraft black liquor to produce a large panel of compounds, including phenolics, aliphatic acids and oxidised lignin, all of which valuable in chemical industry. For the first time, a catalytic process for the chemical valorisation of Kraft black liquor is presented.

CO2 hydrogenation toward gaseous and liquid hydrocarbons has been experimentally studied over a Fe–K/Al2O3 catalyst in a fixed-bed reactor. At 15 bar, 300 °C, 2080 N mL/gcat/h, and H2/CO2 ratio of ...

The glycerol oxidation reaction was developed leading to selective catalysts and optimum conditions for the production of carboxylic acids such as glycolic acid. However, carboxylic acids are produced in highly diluted mixtures, challenging the recovery and purification, and resulting in high production costs, polymerization, and thermal degradation of some of the products. The protection of the acid function by esterification reaction is one of the most promising alternatives through reactive distillation (RD); this technique allows simultaneously the recovery of carboxylic acids and the elimination of most part of the water. The reactive distillation, experimental and simulation, of glycolic acid was performed, based on kinetic and thermodynamic models developed. For the thermodynamic model, binary parameters of the missing couples were determined experimentally, and the non-random two-liquid (NRTL) model was selected as the most suitable to represent the binary behavior. The kinetic study of the esterification in the presence of homogeneous and heterogeneous catalysis concluded that the heterogeneous reaction can be accurately described either by a pseudo-homogeneous model or the Langmuir–Hinshelwood (L-H) adsorption model. Reactive distillation was conducted in a distillation column filled with random packing sulfonated ion-exchange resin, Nafion NR50®, or with extruded TiO2-Wox. The conversion rate of glycolic acid in reactive distillation increases from 14% without catalyst to 30% and 36% using Nafion NR50® and TiO2-Wox, respectively. As opposed to the batch reactor study, the conversion rate of glycolic acid was better with TiO2-Wox than with sulfonated ion-exchange resin. The better performance was related to an increase in the hydrodynamics inside the column. Tests using water in the feed confirm the hypothesis by increasing the conversion rate because of the decrease in the mass transfer resistance by reducing the average diffusion coefficient. The simulation of the reactive distillation column with ProSim® Plus showed that the yield of the ester increased operating at a low feed rate with reactive stripping. In the presence of water in the feed, nonreactive stages are required, including an enrichment region to separate water vapor.

Xylose is a major component of hemicelluloses. In this paper, its hydrogenation to xylitol in aqueous medium was investigated with two Ru/TiO2 catalysts prepared with two commercial TiO2 supports. A strong impact of support on catalytic performances was evidenced. Ru/TiO2-R led to fast and selective conversion of xylose (100 % conversion in 2 h at 120°C with 99 % selectivity) whereas Ru/TiO2-A gave a slower and much less selective transformation (58 % conversion in 4 h at 120°C with 17 % selectivity) with the formation of several by-products. Detailed characterization of catalysts with ICP, XRD, FTIR, TEM, H2 chemisorption, N2 porosimetry, TPR and acid-base titration were performed to elucidate the role of each support. TiO2-R has a small specific surface area with large ruthenium nanoparticles in weak interaction with TiO2 support and no acidity, whereas TiO2-A is a mesoporous material with a large specific surface area, mildly acidic, and bears small ruthenium particles in strong interaction with TiO2 support. The former was very active and selective for xylose hydrogenation to xylitol whereas the latter was less active and poorly selective. Moreover, careful analysis of reaction products also revealed that TiO2 anatase can catalyze undesired side-reactions such as xylose isomerisation to various pentoses, and therefore the corresponding unexpected polyols (arabitol, ribitol) were produced during xylose conversion by hydrogenation. In a first approach of the kinetics, a simplified kinetic model was built to compare quantitatively intrinsic reaction rates of both catalysts. The kinetic constant for hydrogenation was 20 times higher for Ru/TiO2-R at 120°C.

This study investigated the effect of external resistance (Rext) on the dynamic evolution of microbial communities in anodic biofilms of single-chamber microbial fuel cells fueled with acetate and inoculated with municipal wastewater. Anodic biofilms developed under different Rext (0, 330 and 1000 ohms, and open circuit condition) were characterized as a function of time during two weeks of growth using 16S rRNA gene sequencing, cyclic voltammetry (CV) and fluorescence microscopy. The results showed a drastic difference in power output of MFCs operated with an open circuit and those operated with Rext from 0 to 1000 ohms. Two steps during the bacterial community development of the anodic biofilms were identified. During the first four days, nonspecific electroactive bacteria (non-specific EAB), dominated by Pseudomonas, Acinetobacter, and Comamonas, grew fast whatever the value of Rext. During the second step, specific EAB, dominated by Geobacter and Desulfuromonas, took over and increased over time, except in open circuit MFCs. The relative abundance of specific EAB decreased with increasing Rext. In addition, the richness and diversity of the microbial community in the anodic biofilms decreased with decreasing Rext. These results help one to understand the bacterial competition during biofilm formation and suggest that an inhibition of the attachment of non-specific electroactive bacteria to the anode surface during the first step of biofilm formation should improve electricity production.

Lignin is one of the main components of lignocellulosic biomass and corresponds to the first renewable source of aromatic compounds. It is obtained as a by-product in 100 million tons per year, mainly from the paper industry, from which only 2–3% is upgraded for chemistry purposes, with the rest being used as an energy source. The richness of the functional groups in lignin makes it an attractive precursor for a wide variety of aromatic compounds. With this aim, we investigated the Pd-catalyzed depolymerization of lignin under mild oxidizing conditions (air, 150 °C, and aqueous NaOH) producing oxygenated aromatic compounds, such as vanillin, vanillic acid, and acetovanillone. Palladium catalysts were implemented following different strategies, involving nanoparticles stabilized in water, and nanoparticles were supported on TiO2. Significant conversion of lignin was observed in all cases, however, depending on the catalyst nature and the synthetic methods, differences were observed in terms of selectivity in aromatic monomers, mainly vanillin. All these aspects are discussed in detail in this report, which also provides new insights into the role that Pd-catalysts can play for the lignin depolymerization mechanism.

International audience; The methanation of CO over a 20 wt % Ni/Al2O3 catalyst was studied with different transient experiments. CO dissociation was found to be reversible and faster than the formation of methane. SSITKA experiments showed that two pools of surface intermediates lead to the formation of methane. The transient experiments could be adequately described by a microkinetic model based on two distinct adsorbed CO species. One CO species proceeds through direct dissociation, and the other, through hydrogen assisted dissociation to a common CH* intermediate that leads to methane. The model is consistent with literature DFT studies that show that the direct CO dissociation occurs over edge or step sites and hydrogen assisted dissociation occurs over terrace sites.

Supported gold and platinum particles on titanium oxide catalysts were evaluated in the oxidative depolymerization of lignins toward high added value aromatics under mild conditions (T: 150 °C, Pair: 20 bar, CNaOH: 10 g/L, 1 h). Kraft and ethanol Organosolv lignins were engaged in the study. Gold catalyst showed a strong tendency to further oxidize aromatics produced from lignin depolymerization to volatile compounds leading to very low yield in target molecules. On the contrary, platinum-based catalysts were allowed to observe enhanced yields that were attributed to its ability to preserve lignin’s substructure during the reaction. A kinetic model was constructed based on the results observed, which allowed us to identify the occurrence of condensation reactions during lignin oxidation and degradation of the produced aromatic compounds as the main limitations to reach high product yields. Insights on lignin oxidation and the catalyst’s role lead through this study would help to reach higher control over lignin valorization.

International audience; Carboxylic acids are one of the most important building blocks and feedstocks for fine chemicals, flavors and polymers, yet their production largely relies on petrochemical derivatives or processes that require large amounts of energy or chemicals. To ensure their long-term sustainable production, it is necessary to explore different options of renewable feedstocks. An alternative solution is the recovery of carboxylic acids present in black liquor. These compounds are formed as by-products during the cooking stage in the Kraft pulping process; they are later burnt along with the other compounds present in black liquor to be transformed into energy. However, usually an energy surplus is generated due to the large amounts entering the unit, therefore their recovery and later use as renewable feedstocks could be considered as an advancement in waste valorisation. Furthermore, the extraction of carboxylic acids from black liquor can increase pulp production, boosting the efficiency of the Kraft process. This review aims to examine the different technologies to recover carboxylic acids from black liquor as well as the challenges associated with their incorporation into paper and pulp mills in order for them to become integrated forest biorefineries.

International audience; Commercially available open-cell polyurethane foams (OCPUF) have been successively functionalized with bio-inspired polydopamine coating (OCPUF@PDA), and activated with cobalt nanoparticles (OCPUF@PDA@Co). The resulting soft structured catalytic support (S2CS) has been used as a highly efficient tool for the release of dihydrogen from a commercially available alkaline sodium borohydride solution at room temperature. With a diluted solution containing 0.4 wt% NaBH4 and 0.4 wt% NaOH, the hydrogen generation rate was of 76.4 ± 3.18 L h−1 gcat−1 after stabilization of the catalytic activity. The catalytic tool could be used for 10 runs.

SSCI-VIDE+CDFA+LDJ; International audience; Several lignin samples of varying botanical nature (softwood, hardwood, or annual plants) and extraction procedures (Kraft, Organosolv, or soda) were fully characterized by complementary techniques and engaged in “catalyst-free” depolymerization in air under basic conditions. Treatment of the complex reaction mixture was optimized to ensure reproducibility, careful analyses, and accurate data. After an optimization of the reaction conditions, we were able to recover high amounts of aromatic compounds (up to 19%wt). Additionally, we demonstrated a relation between lignin’s structure, i.e., the accessible phenol moieties and inter-unit linkages, and the yields of aromatic compounds, thus showing the importance of the extraction process to optimize lignin’s potential. This work provides valuable reference for developing further lignin depolymerization under basic media.

In the framework of limiting the concentration of CO2 in the atmosphere, the utilization of CO2 as a feedstock for the synthesis of different products, such as methanol, dimethyl ether and liquid fuels, is gaining a lot of interest. In particular, the Power-to-Liquid (PtL) concept which combines the CO2 hydrogenation with the production of hydrogen from water electrolysis, powered by renewable sources, seems a very interesting solution for the production of liquid fuels and chemicals. It also represents a storage solution for the intermittent renewable energies. In this work, the techno-economic feasibility of the CO2 hydrogenation into long-chain hydrocarbons, compared to the synthesis of other liquid or gaseous products (methanol, DME, hydrogen, methane…) is studied, as well as that of PtL compared to other renewable fuels production pathways. Even if the PtL process is not economically competitive on the market yet, some economic considerations predict a decrease in the production cost of PtL fuels, thus it is worth to study the synthesis of liquid fuels from CO2 and H2 for its several advantages in terms of efficiency and sustainability of the process, especially for middle or long term prospects and for their potential applications as fuel for the heavy-duty, marine and aviation transport, but also as feedstock for the chemical industry. The review is then focused on the hydrogenation of CO2 into liquid fuels. A review of the performances of Fe and Co catalysts is also given, pointing up that iron catalysts are more suitable for the production of long-chain hydrocarbons, especially when potassium-promoted. A state-of-the-art about the kinetic modeling of the reaction and the current industrial demonstrators has also been reported. However, very few data are available and further investigation in this field should be done. This work, summarizing general information about the hydrocarbon synthesis from CO2 hydrogenation, shows the complexity of such a process and points out that further studies about the reaction mechanism, kinetics and the development of a highly active catalyst selective towards long-chain hydrocarbons are needed. This will help to increase the techno-economic feasibility of this challenging process.

The characterization of hydrodynamics in Trickle-Bed-Reactors is a complex task due to the opacity of the medium. In particular, the determination of pressure drop, liquid hold-up, wetting of the catalyst surface and catalyst shape effect on these parameters is very important for optimal catalyst use and reactor operation. Measurements under industrial conditions are limited to indirect estimations, and direct measurement methods are limited to near-ambient conditions. In this context, the objective of the present article is to use Computational-Fluid-Dynamics to investigate pressure drop, liquid saturation and wetting efficiency in Trickle-Bed-Reactors and to improve existing correlations, with a special focus on the catalyst shape effect and wetting prediction. The Volume-Of-Fluid approach was used to simulate two-phase flow through particle loadings of spherical, trilobe and quadrilobe-shaped particles. The numerical model was validated against literature correlations in terms of pressure drop, liquid holdup and wetting efficiency. The CFD model was then employed to explore two effects that does not reach out a consensus in existing literature, i.e effects of particle shape and gas-phase velocity on wetting efficiency. As a result, it was shown that CFD provides good predictions of pressure drop and liquid saturation for different catalyst particle shapes, the achieved deviations between CFD results and correlation estimations are below 20%. A new wetting efficiency correlation is also proposed. This new correlation is able to predict wetting efficiency with a precision of 6.99% for a wide range of liquid velocities (from 0.2 to 0.8cm/s) and gas velocities (from 5 to 20cm/s) and three particle shapes.

Heterogeneously catalyzed cellulose hydrolysis into value added chemicals has addressed intensive efforts of research for the past ten years. However, the mechanism of cellulose transformation promoted by a solid catalysts is far to be solved. We are thinking that this is most likely due to analysis issues. Indeed, cellulose conversion is never measured directly but deduced from TOC analysis of the aqueous phase or by weighing the solid residue at the end of the reaction. This does not correctly represent the cellulose transformation, which leads, very often, to the formation of solid products. In the present work, we report our efforts to develop a simple analytic tool based on FTIR to measure directly the cellulose conversion and the amount of solid carbon products, an essential data, rarely quantify to date. With these new analytic tools, the observed evolutions of cellulose conversion and of the products distribution with time definitively show that the solid catalyst ZrW accelerates i-the initial rate of cellulose conversion ii- the initial formation of the three main products families: chemicals detectable by HPLC, soluble polymers and solid carbon products. However, the key issue of the contact between the solid substrate and the catalyst surface is put forward by these kinetic data but remains not solved.

SSCI-VIDE+CDFA+FRA:NES; International audience; The objective of this work was to investigate the ability of supercritical (SC) ethanol conditions to attack preferentially the lignin fraction against the carbohydrate fraction and their effects on the product distribution among gases, light products, bio-oils, and chars. In this study, the conversion of each pinewood component was determined by the analysis of solid residues to quantify cellulose, hemicellulose, lignin, and char contents. It is shown that, by tuning the temperature, hemicellulose and lignin are already transformed in subcritical ethanol conditions, lignin being more reactive than hemicellulose. In contrast, native wood cellulose is recalcitrant to liquefaction in SC ethanol near the critical point (Tc = 241 °C and Pc = 61 bar), but 20% of native wood cellulose is converted in SC ethanol at 280 °C. Besides, the severity of the conditions, in terms of temperature and treatment time, does not significantly influence the yields of gases, light products, and bio-oils but strongly enhances char formation. Interestingly, the increase in SC ethanol density does not change the conversion of biomass components but has a marked effect on bio-oil yield and prevents char formation. The optimum fractionation conditions to convert the lignin component, while keeping unattacked the cellulose fraction with a minimum formation of char, are dense SC ethanol, at 250 °C for 1 h, in batch conditions. However, although lignin is more reactive than hemicellulose under these conditions, these fractions are converted, in a parallel way, to around 50% and 60%, respectively.

An extractive-reaction process for the synthesis of HMF from fructose was implemented in microreactor. Experimental conditions were 10 wt.% fructose in water, MIBK as extracting solvent and HCl as catalyst in a temperature window of 120–160 °C, a MIBK/H2O ratio 1 to 9 and an HCl concentration of 0.25–2 M. The dehydration of fructose to HMF is achieved in less than 40s with a total HMF yield higher than 90% at 150 °C. Aqueous and organic phase spontaneously separate at the outlet of the reactor and HMF is obtained in MIBK with a yield of 80% and a purity of 92%.

An improved method for the oxidation of benzylic and aliphatic alcohols using concentrated bleach (1.6 M NaOCl) using 2-step continuous flow microreactors is reported herein. Enhancement of the reaction rate was obtained by on-line pH adjustment. In the first step, the pH of the bleach was precisely decreased to pH 8.5 using CO2. Such pH is a compromise between oxidative properties, chemical stability and unwanted precipitation. The aqueous bleach solution was subsequently used for the oxidation of benzyl alcohols in EtOAc using catalytic amounts of TBAB (n-Bu4N+Br−) in a segmented flow microreactor. The total conversion of benzyl alcohols was obtained in less than 1 min using 2 eq. of NaOCl at r.t. without any metal catalysts. Selective benzyl alcohol oxidation (>98%) was demonstrated on primary and secondary alcohols. For aliphatic alcohols, 0.1 mol% TEMPO was used as a co-catalyst in synergy with TBAB and a total conversion with high selectivity (>98%) was achieved in less than 2 min.

The review describes the most significant recent results achieved in France in the field of heterogeneous catalysis over the last 10 years. It focusses on the research carried out in the French academic laboratories, often in close collaboration with some industrial partners.

SSCI-VIDE+CDFA+YSW:CNG:TVU:FRA:MET:PFO:NES; International audience; The objective of the present work was to determine if wood sawdust can be used instead of isolated cellulose in the general solid-acid-catalyzed production of chemicals. The kinetics of model cellulose and pine-wood sawdust liquefaction into lactic acid were determined in the presence of a solid Lewis acid, ZrW. The catalytic hydrolysis of pine wood was performed at 190 degrees C in a large-scale batch reactor (2.5 L). Similar kinetic curves of lactic formation were obtained for cellulose and wood as substrates. Moreover, the initial lactic acid production rate of pine-wood sawdust was higher than that of model cellulose, proving that, in spite of the presence of lignin/hemicellulose, the catalyst drives the transformation towards lactic acid formation. However, our results give also evidence of solid-catalyst deactivation for both cellulose and wood substrates. This result indicates that if wood pretreatment can be bypassed, the bottleneck will be the solid-catalyst regeneration and recycling.

BACKGROUND Unlike Pt and Au, Ag has been recently reported to be an active catalyst for the synthesis of glycolic acid from the liquid phase oxidation of glycerol (GLY>). In order to provide comparative information about the kinetics of this reaction using Pt, Au or Ag,> a kinetic model was performed for each catalyst (Ag/, Pt/ and Au/Al2O3), using the experimental results obtained at different temperatures. RESULTS A power-law kinetic model was proposed for each catalyst, which included the Khang-Levenspiel model to evaluate potential catalyst deactivation. All the three kinetic models predicted well the experimental concentrations. Pt/ and Au/Al2O3 showed higher kinetic rate constants, being the highest value that of the production of glyceric acid. The lower the metal particle size, the higher the kinetic rate constant of the production of glyceric acid was. Deactivation parameters played an important role in the model of Pt/Al2O3, so that Au/ and Ag/Al2O3 seemed to be more resistant to deactivation. CONCLUSIONS This work reports the first kinetic model for the oxidation of GLY using a Ag-based catalyst. It showed a noticeable kinetic rate constant for the production of glycolic acid. The activation energies obtained were in the range 48–97 kJ/mol.

SSCI-VIDE+CDFA:ING+MLF:FBG:NOG:PFO:MIL; International audience; A new membrane preparation method based on mechanical pore-plugging of the supports with appropriate sized seeds followed by secondary zeolite growth by hydrothermal synthesis was optimized for the production of hydroxy-sodalite (hydroxy-SOD) membranes. A series of parameters were investigated during membrane production, including seed loading, presence of Teflon on the coarse side of the support, top-layer orientation in the autoclave, autoclave agitation, synthesis time and temperature, membrane post-synthesis treatment, and nature and pore size of the support (TiO2/SS, SS, Al2O3 and ZrO2/TiO2). Zeolite seeds and synthesized membranes were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and gas permeation. The gas permselective separation ability of these membranes was demonstrated from H-2, N-2, CO2 and H2O permeation tests at temperature up to 250 degrees C. The membranes fabricated with the optimized parameters achieved H2O/N-2, H2O/CO2, and H2O/H-2 ideal gas permselectivities of 5.1, 4.8 and 1.4 at 250 degrees C, while providing a high water permeance (Pi(H2O) of 1.26 x 10(-7) mol Pa-1 m(-2) S-1) at the same temperature. (C) 2016 Elsevier Inc. All rights reserved.

The organocatalyzed aerobic oxidation of aldehydes to acids was reproduced from the original report. In- and ex-situ analysis of the reaction mixture as the function of time reveals that, unlike the claim in the publication, the aerobic oxidation of aromatic and aliphatic aldehydes leads predominantly to the formation of peracids. The latter are transformed into the corresponding carboxylic acids during the workup procedure. The buildup of peracids in solution poses safety problems that should not be overlooked. This finding has also an influence on the way new catalysts are investigated to improve this reaction as well as on aerobic aldehyde-mediated co-oxidation.

Platelet millimetric reactors (PMR, 18 mm × 5 mm × 24 or 120 mm) packed with open cell foam supporting Pt nanoparticles have been studied with a model reaction (formic acid oxidation). The hydrodyn...

The aim of this work is to show the feasibility of a one-pot reaction in three phase hybrid catalysis, one step being an oxidation. The model reaction proposed is a two-step reaction: an enzymatic catalysed isomerisation of fructose to glucose followed by a heterogeneously catalysed oxidation of glucose to gluconic acid. The reaction medium required for the enzymatic step was shown to be compatible with the oxidation catalyst. Kinetic parameters were estimated from experimental data to run simulation using an isothermal one-pot slurry model. Finally, a one-pot test was performed which showed that combining both steps is possible.

International audience; The monitoring of chemical reactions can be arduous especially when sampling is required with highly reactive compounds. Online spectroscopic methods provide efficient and non-invasive ways to record the composition of reactive mixtures, yet their use is often limited by the interpretation of spectroscopic data. Herein, we report an easy access and reproducible method for the online analysis of organic transformations through FTIR spectroscopy. Spectra are treated with a multivariate approach to lead to the accurate quantification of the chemicals involved. Further, the technique was applied to the acceptorless dehydrogenation coupling (ADC) of alcohol and allows the first in situ quantitative assessment of the aldehyde intermediate.

International audience; Glycerol valorization through partial oxidation is a good way of obtaining many different molecules with high added value such as glyceric acid, tartronic acid, dihydroxyacetone, etc. Among the potential products, glyceraldehyde is an interesting chemical compound for its various applications in different domains such as organic chemistry, medical, and cosmetic industries. In the present paper, we studied the effect of different supports on the glycerol oxidation reaction in a batch reactor applying base-free conditions. The tested catalysts were Pt-based materials deposited on various supports (i.e., SiO2, TiO2, ZSM-5, γ-Al2O3), which were synthesized using a deposition method followed by a chemical reduction. The catalysts were extensively characterized (BET, ICP, XRD, TEM, XPS), highlighting differences in terms of specific surface areas, textural properties, and Pt nanoparticles sizes. We evidenced a direct relation between glycerol conversion and glyceraldehyde selectivity (i.e., an increase in glycerol conversion leads to a decrease in glyceraldehyde selectivity). The Pt/γ-Al2O3 catalysts exhibited the highest activity, but their selectivity to glyceraldehyde significantly decreased with time on stream. Pt/SiO2 presented the highest selectivity to glyceraldehyde owing to a slower reaction rate, which allows envisioning technical opportunities to continuously extract the formed glyceraldehyde from the mixture.

The continuous selective aerobic oxidation of benzyl alcohol in flow was developed using an immobilized Ru0 catalyst. After optimization of the reaction conditions, the stability and productivity of the equipment were examined over time using tert-amyl alcohol as solvent, and no deactivation occurred. A cumulative TON close to 15 000 was obtained with a constant activity (TOF = 4 min−1). A semi-empirical kinetic rate expression was proposed.

The solvolysis of technical lignins was evaluated using water/ethanol solvent mixture with the aim of producing monomeric aromatic compounds in a continuous flow bench reactor. Four lignins issued from various biomasses (softwood, wheat straw) and extracted using different pulping processes (kraft, soda, organosolv) were engaged in the study. Before being converted, these lignins (two kraft, a soda, and an organosolv) were characterized by a multitechnique approach coupling compositional analysis, NMR, IR, GC, and SEC. Data thus obtained allowed us to point out the main differences in terms of structure and chemical composition. Based on its high solubility in water and water/ethanol mixture, alkaline lignin (i.e., from the kraft process) was used to optimize the reaction parameters. Thus, we found out that working at 225 °C under 8 MPa nitrogen using a 1-wt% basic solution of lignin allowed to operate the reactor without difficulties (no foam formation, no char) when a 1/1 water/ethanol mixture was used. Under these conditions, alkaline lignin was converted up to 76%. Other lignins were then evaluated leading to conversions between 46 and 74%. The reaction mixture obtained was fractioned to PM (precipitated matter), OP (organic products), and AP (aqueous phase soluble products) to allow careful analyses of the products. Analytical data obtained showed particularly that the number of β-O-4 linkages in the remaining solid material (PM) decreases significantly (up to − 95%) that correlated with the formation of monomeric organic compounds in OP, however in low amount due to over reactions leading to compounds evolving in the aqueous phase. Generally, whatever the lignin, guaiacol is the main aromatic compound observed under all reaction conditions evaluated.

Tungstated zirconia, ZrW, is reported as an efficient solid acid catalyst in the conversion of cellulose into lactic acid in hydrothermal conditions. The active phase of ZrW is generally ascribed to more or less polymerized WOx domains dispersed on zirconia. In this study, commercial uncalcined and calcined tungstated zirconia were used as catalysts for the conversion of cellulose under hydrothermal conditions at 190 °C. Their activities were also compared with uncalcined zirconium oxyhydroxide, ZrO2-x(OH)2x and calcined zirconia, ZrO2. Contrary to the expected results, it is disclosed that uncalcined ZrW exhibits higher catalytic activity and stability than calcined ZrW. Modifications in the products distribution were observed as glycolic acid formation at the expense of lactic acid formation upon ZrW calcination. Even more surprising, the catalytic activity of W free amorphous zirconium oxyhydroxide ZrO2-x(OH)2x is similar to uncalcined ZrW, with lactic acid as the main product while ZrO2 does not have any catalytic activity. These results suggest that the active phase of these catalysts might combine the couple Zr4+ and OH− species while the role of W species would be of secondary importance.

International audience; This work investigates Gas-Liquid-Solid mass transfer coupled to heterogeneous catalytic reaction using Computational Fluid Dynamics (CFD). The numerical model is based on the Volume-of-Fluid (VOF) approach, coupled with a convection–diffusion equation for mass transfer resolution. First, the numerical method is validated on a falling liquid film over a semi-infinite planar surface. Then, a micro-structured reactor with α-methylstyrene hydrogenation is studied. A good agreement is found between experimental data of Tourvieille et al. (2013) and simulation results. Afterwards, a vertical spherical beads string is investigated. Convective transport by transversal velocities is identified as an important contributor to the overall Gas-Liquid-Solid mass transfer. While the film model is applicable in pure diffusion regimes, the resistances-in-series model is not relevant and over-estimates the real mass transfer by nearly 30% when mass transfer occurs in liquid film flow without bulk.The present work shows how CFD can be an effective tool for predicting hydrodynamic and catalyst geometry effect on mass transfer in Gas-Liquid-Solid reactors.

SSCI-VIDE+CDFA+LZH:GRA:YSW:LCD:PFO; International audience; Base-free catalytic acceptorless dehydrogenative homo-coupling of alcohols to esters under neat conditions was investigated using a combined organometallic synthesis and kinetic modelling approach. The considered bifunctional ruthenium aliphatic PNP complexes are very active, affording TONs up to 15,000. Notably, gas mass transfer issues were identified, which allowed us to rationalize previous observations. Indeed, the reaction kinetics are limited by the rate of transfer from the liquid phase to the gas phase of the hydrogen co-produced in the reaction. Mechanistically speaking, this relates to the interconverting couple amido monohydride/amino bishydride. Overcoming this by switching into the chemical regime leads to an initial turnover frequency increase from about 2000 up to 6100 h(-1). This has a significant impact when considering assessment of novel or reported catalytic systems in this type of reaction, as overlooking of these engineering aspects can be misleading. (C) 2016 Elsevier Inc. All rights reserved.

A new reactor design is proposed to carry out hybrid catalysis. It involves a two-basket reactor, one filled with an heterogeneous catalyst and the other with a supported enzymatic catalyst The physical transfer properties ( k L a , mixing time,…) have been studied experimentally and the velocity, mixing time and thermal behavior simulated by CFD. Volumetric oxygen mass transfer ( k L a ) between 0.02 s−1 and 0.035 s−1 are obtained. The simulated mixing times are in good agreement with the experimental ones. The mass flow field are simulated in various conditions of stirring. The thermal behavior of the reactor is also simulated, allowing for the observation of two zones (cold and hot) with a Δ T of up to 15 K while keeping good mass transfer characteristics.

Hydrolysis of hemicelluloses is a key step in biorefineries processes. In this paper, TiO2-based catalysts were prepared and applied to the hydrolysis of a model compound, cellobiose, and then to xylan from corncob. Hydrolysis of cellobiose yielded glucose (60%), hydroxy-methylfurfural (HMF) and humins in various amounts depending on the catalyst nature. Activity and selectivity to glucose varied with the nature of dopant (W or Zr) and the calcination temperature of the catalyst. A kinetic model was built to elucidate the formation of humins and showed that the direct pathway “cellobiose to humins” is predominant in our reaction conditions. TiO2–W catalyst was then applied to xylan hydrolysis. Xylan reacted much faster than cellobiose and yielded xylose and furfural with low humins production.

Lactic acid esterification over three carbon based solid acid catalysts were compared: sulfonated carbonised wood, graphene oxide (GO) and Amberlyst 15(A15) with the aim to address their water tolerance related to their acidity and hydrophobicity. The acidic properties of the carbon materials were measured by calorimetry of NH3 adsorption and their hydrophobicity was evaluated by water vapor adsorption isotherms. Here, we disclose the exceptional strong acidity of GO with differential heat of NH3 adsorption (QdiffNH3) higher than 200 kJ mol−1 while A15 and sulfonated carbon have significant lower acid strength with QdiffNH3 lower than 150 kJ mol−1. The super-acidity of GO is tentatively ascribed to the presence of “free” protons explained by the delocalization of the negative charges of counter anions within the graphene sheet. In presence of the minimum water content (3 mol L−1), GO is the most active catalyst with a TOF of 52 h−1 and its activity is also less inhibited upon water addition compared to A15. These results are rationalized considering that TOF depends intrinsically on the strength of Br∅nsted active sites and on the active site accessibility more or less controlled by the its micro-environment hydrophobicity seen to be equivalent for A15, sulfonated carbon and GO.

Magnesium and rare earth mixed oxides (Mg3REOx (RE = La, Y, Ce)) were prepared and characterized by X-ray diffraction (XRD), N2 adsorption–desorption, infrared spectra and microcalorimetry of CO2. The results reveal that the Mg3CeOx catalyst is present in the form of Mg-Ce-O solid solution, while the Mg3LaOx and Mg3YOx catalysts are probably rare earth oxides dispersed on MgO surface. As a result, among the calcined Mg3REOx catalysts, the Mg3CeOx catalyst presents the highest rate constant for acetone aldolization, which is well correlated to its more homogeneous distribution of basic sites. In contrary, the Mg3YOx catalyst exhibit the lowest catalytic activity for acetone aldolization. Upon hydration pre-treatment, the basic properties on the surface of the Mg3REOx catalysts were changed markedly. The Mg3YOx catalyst after hydration treatment shows the highest amount of basic sites on catalyst surface, and then exhibits the highest activity among the hydrated Mg3REOx catalysts. These results make it possible to fine-tune basic sites for acetone aldolization.

An attractive approach to reduce anthropogenic emission of carbon dioxide (CO2) would be to valorize it into added-value products (e.g. alcohols or dimethylether) by chemical recycling. However, in most of these important reactions, water is produced as a by-product that limits CO2 conversion thermodynamically and can lead to the deactivation of catalysts. Water removal in sorption-enhanced reaction process (SERP) would allow the overcoming of these drawbacks and several zeolites (SOD, LTA, and FAU) have been selected to assess their potential to adsorb water in-situ at high temperature. This work aims to study the water adsorption capacity and kinetics in a large temperature range of 25–250 °C and evaluate the potential of the selected adsorbents for in-situ water removal in the reverse water gas shift (RWGS) reaction. For all zeolites, the water uptake showed an important decrease at higher temperatures but the capacity at 250 °C was still significant. While the poor adsorption kinetics of SOD limit its use, FAU-13X powder gave better results than LTA-4A, which were confirmed by a more important increase of CO concentration at the exit of the reactor for the RWGS reaction. Transient adsorption data obtained in this study were fitted by a double stretched equation and the kinetic constants were determined. These results are essential to model and design an efficient SERP process and determine the optimal reaction conditions. This article is protected by copyright. All rights reserved

International audience

Five alumina-supported Co catalysts with different particle sizes and structures were synthesized. The catalysts showed different activities during long-term Fischer-Tropsch experiments. Steady-state isotopic transient kinetic analysis (SSITKA) (CO)-C-12/H-2 -> (CO)-C-13/H-2 experiments were performed during these long-term runs. The number of active sites for CO adsorption and activation was estimated through the summation of all surface intermediates derived from the SSITKA results. Rather than comparing turnover frequencies, a kinetic analysis was performed. A simple kinetic rate equation based on the in situ number of active sites described the steady-state CO conversion over the five catalysts adequately. Thus the difference in the catalytic performance could not be attributed to a difference in particle size, phase orientation (face-centered cubic or hexagonal close packed), or Pt-promotion effect but instead was only because of the number of reduced Co atoms exposed during the reaction. Similarly, the selectivity depended on the CO conversion level and temperature and not on the catalyst structure.