Supported Molybdenum Carbide and Nitride Catalysts for Carbon Dioxide Hydrogenation.

Catalysts based on molybdenum carbide or nitride nanoparticles (2-5 nm) supported on titania were prepared by wet impregnation followed by a thermal treatment under alkane (methane or ethane)/hydrogen or nitrogen/hydrogen mixture, respectively. The samples were characterized by elemental analysis, volumetric adsorption of nitrogen, X-ray diffraction, and aberration-corrected transmission electron microscopy. They were evaluated for the hydrogenation of CO2 in the 2-3 MPa and 200-300°C ranges using a gas-phase flow fixed bed reactor. CO, methane, methanol, and ethane (in fraction-decreasing order) were formed on carbides, whereas CO, methanol, and methane were formed on nitrides. The carbide and nitride phase stoichiometries were tuned by varying the preparation conditions, leading to C/Mo and N/Mo atomic ratios of 0.2-1.8 and 0.5-0.7, respectively. The carbide activity increased for lower carburizing alkane concentration and temperature, i.e., lower C/Mo ratio. Enhanced carbide performances were obtained with pure anatase titania support as compared to P25 (anatase/rutile) titania or zirconia, with a methanol selectivity up to 11% at 250°C. The nitride catalysts appeared less active but reached a methanol selectivity of 16% at 250°C.

Supported Cobalt Catalysts for Acceptorless Alcohol Dehydrogenation.

The acceptor-less dehydrogenation of 2-octanol was tested over cobalt supported on Al2 O3 , C, ZnO, ZrO2 and various TiO2 substrates. The catalysts were characterized by ICP, XRD and TGA-H2 . For Co/TiO2 P25, the effects of passivation, aging (storage at room temperature), and in situ activation under H2 were investigated. The catalysts must be tested shortly after synthesis in order to prevent deactivation. Cobalt supported on TiO2 P25 was the most active and 69 % yield of 2-octanone was obtained, using decane as a solvent. Selectivities for 2-octanone were observed in the range of 90 % to 99.9 %. Small amounts of C16 compounds were also formed due to aldol condensation/dehydration reactions. The catalysts exhibited higher conversion in the dehydrogenation of secondary alcohols (65-69 %), in comparison to primary alcohols (2-10 %). The dehydrogenation of 1,2-octanediol led to 1-hydroxy-2-octanone, with a selectivity of 90 % and 69 % for Co/TiO2 P25 and Co/TiO2 P90, respectively.

Heterogeneous catalytic hydrogenation of biobased levulinic and succinic acids in aqueous solutions.

Supported noble-metal catalysts (Ru, Pd or Pt) and the corresponding Re-promoted catalysts exhibit a high activity for the hydrogenation of biobased carboxylic acids. Levulinic acid and succinic acid are converted into the lactones or the diols depending on the nature of the catalyst and the reaction conditions. The highest selectivity to 1,4-pentanediol of 82 % is achieved at 140 °C in the presence of the 1.9 % Ru-3.6 % Re/C catalyst.

Cellulose conversion with tungstated-alumina-based catalysts: influence of the presence of platinum and mechanistic studies.

The performances of platinum supported on tungstated alumina (Pt/AlW) in the hydrothermal conversion of cellulose at 190 °C under H2 pressure were evaluated and compared to that of Pt-free tungstated alumina (AlW). We show that the presence of Pt significantly increased the extent of conversion and led to a different product distribution with the formation of acetol and propylene glycol as the main products and a global yield of up to 40 %. Based on previous reports, we propose the formation of pyruvaldehyde on the Lewis acid sites of the tungstated alumina as a key intermediate. Pyruvaldehyde can then be transformed to acetol and propylene glycol or lactic acid depending on the presence or absence of supported Pt.

Tailoring metal-organic framework catalysts by click chemistry.

We successively introduce new catalytic centers through click reaction into MOFs and modify their environment by addition of lipophilic groups. The resulting bifunctionalized MOF provides an optimized balance between basicity and lipophilicity and shows outstanding performance for the transesterification reaction.

Green synthesis of xylan hemicellulose esters.

The esterification of xylan type hemicelluloses, isolated from birchwood, was carried out firstly in homogeneous conditions using N,N-dimethylformamide (DMF) and lithium chloride (LiCl) in the presence of 4-dimethylaminipyridine (DMAP). The degree of substitution (DS) of xylan acetates ranged between 0.9 and 2.0 as a function of experimental conditions. Due to the problems of toxicity and recycling of DMF, an alternative method of esterification is reported in the second part of this work, performing in the absence of organic solvent and using DMAP or methanesulfonic acid (MSA) as catalysts. Acetylation reaction catalyzed by MSA was developed through an experimental design in order to achieve the highest DS under the mildest conditions. The significant factors and their interactions were identified. The optimization of reaction parameters allowed to obtain a high DS (1.6) and maximal yield (85%). Moreover, the reactivity of propionic and hexanoic anhydrides was evaluated and hydrophobic xylan esters with low degrees of substitution were obtained.

Unravelling the mechanism of glycerol hydrogenolysis over rhodium catalyst through combined experimental-theoretical investigations.

We report herein a detailed and accurate study of the mechanism of rhodium-catalysed conversion of glycerol into 1,2-propanediol and lactic acid. The first step of the reaction is particularly debated, as it can be either dehydration or dehydrogenation. It is expected that these elementary reactions can be influenced by pH variations and by the nature of the gas phase. These parameters were consequently investigated experimentally. On the other hand, there was a lack of knowledge about the behaviour of glycerol at the surface of the metallic catalyst. A theoretical approach on a model Rh(111) surface was thus implemented in the framework of density functional theory (DFT) to describe the above-mentioned elementary reactions and to calculate the corresponding transition states. The combination of experiment and theory shows that the dehydrogenation into glyceraldehyde is the first step for the glycerol transformation on the Rh/C catalyst in basic media under He or H(2) atmosphere.

Generic postfunctionalization route from amino-derived metal-organic frameworks.

This study deals with the development of a soft, generic, one-pot postfunctionalization method for metal-organic frameworks (MOFs) starting from compounds with an amino group on the linker. The first step consists of transforming the amino group into azide (N(3)) by an unconventional route using tBuONO and TMSN(3). In the same vessel, the desired functionalized MOF then is obtained by the Huisgen 1,3-dipolar cycloaddition of azides to alkynes, otherwise known as the "click" reaction. The method was applied to DMOF-NH(2) and MIL-68(In)-NH(2), which represent two distinct and important classes of MOF. For both, the functionalization was complete (>90% grafting) and the crystallinity was maintained. Thanks to the large diversity and availability of cyano- and acetylene-based chemicals, this method opens the door to tailor-made functionalized MOFs.

Palladium-catalyzed telomerization of butadiene with polyols: from mono to polysaccharides.

The telomerization of butadiene with alcohols is an elegant way to synthesize ethers with minimal environmental impact since this reaction is 100% atom efficient. Besides telomerization of butadiene with methanol and water that is industrially developed, the modification of polyols is still under development. Recently, a series of new substrates has been involved in this reaction, including diols, pure or crude glycerol, protected or unprotected monosaccharides, as well as polysaccharides. This opens up the formation of new products having specific physicochemical properties. We will describe recent advances in this field, focusing on the reaction of renewable products and more specifically on saccharides. The efficient catalytic systems as well as the optimized reaction conditions will be described and some physicochemical properties of the products will be reported.

Telomerization of butadiene with starch under mild conditions.

The design of industrial products based on bioresources is a challenging issue. Modification of starch, by hydrophobic chemical substituents, results in an innovative hydrophobic material. Herein, the hydrophobic part of the derivative, comprised of octadienyl chains, is introduced through catalytic butadiene telomerization. The process is efficiently conducted on starch in its granular form in an aqueous medium using hydrosoluble palladium complexes. After optimization, a turnover number (TON) of up to 550 was achieved in the presence of [(pi-allyl)PdCl](2) catalyst and, unusually, by using dimethylisosorbide as a cosolvent.

Metal-organic frameworks: opportunities for catalysis.

The role of metal-organic frameworks (MOFs) in the field of catalysis is discussed, and special focus is placed on their assets and limits in light of current challenges in catalysis and green chemistry. Their structural and dynamic features are presented in terms of catalytic functions along with how MOFs can be designed to bridge the gap between zeolites and enzymes. The contributions of MOFs to the field of catalysis are comprehensively reviewed and a list of catalytic candidates is given. The subject is presented from a multidisciplinary point of view covering solid-state chemistry, materials science, and catalysis.

Total synthesis of rapamycin.

For over 30 years, rapamycin has generated a sustained and intense interest from the scientific community as a result of its exceptional pharmacological properties and challenging structural features. In addition to its well known therapeutic value as a potent immunosuppressive agent, rapamycin and its derivatives have recently gained prominence for the treatment of a wide variety of other human malignancies. Herein we disclose full details of our extensive investigation into the synthesis of rapamycin that culminated in a new and convergent preparation featuring a macro-etherification/catechol-templating strategy for construction of the macrocyclic core of this natural product.

Direct synthesis of tricyclic 5H-pyrido[3,2,1-ij]quinolin-3-one by domino palladium catalyzed reaction.

Unexpectedly, the palladium catalyzed coupling reaction of acrolein with 8-bromoquinoline gave 5H-pyrido[3,2,1-ij]quinolin-3-one in a single step.