Filip de Clippel

Sulfonated silica/carbon nanocomposites as novel catalysts for hydrolysis of cellulose to glucose

Sulfonated silica/carbon nanocomposites were successfully developed as reusable, solid acid catalysts for the hydrolytic degradation of cellulose into high yields of glucose.

Fast and Selective Sugar Conversion to Alkyl Lactate and Lactic Acid with Bifunctional Carbon–Silica Catalysts

A novel catalyst design for the conversion of mono- and disaccharides to lactic acid and its alkyl esters was developed. The design uses a mesoporous silica, here represented by MCM-41, which is filled with a polyaromatic to graphite-like carbon network. The particular structure of the carbon-silica composite allows the accommodation of a broad variety of catalytically active functions, useful to attain cascade reactions, in a readily tunable pore texture. The significance of a joint action of Lewis and weak Brønsted acid sites was studied here to realize fast and selective sugar conversion. Lewis acidity is provided by grafting the silica component with Sn(IV), while weak Brønsted acidity originates from oxygen-containing functional groups in the carbon part. The weak Brønsted acid content was varied by changing the amount of carbon loading, the pyrolysis temperature, and the post-treatment procedure. As both catalytic functions can be tuned independently, their individual role and optimal balance can be searched for. It was thus demonstrated for the first time that the presence of weak Brønsted acid sites is crucial in accelerating the rate-determining (dehydration) reaction, that is, the first step in the reaction network from triose to lactate. Composite catalysts with well-balanced Lewis/Brønsted acidity are able to convert the trioses, glyceraldehyde and dihydroxyacetone, quantitatively into ethyl lactate in ethanol with an order of magnitude higher reaction rate when compared to the Sn grafted MCM-41 reference catalyst. Interestingly, the ability to tailor the pore architecture further allows the synthesis of a variety of amphiphilic alkyl lactates from trioses and long chain alcohols in moderate to high yields. Finally, direct lactate formation from hexoses, glucose and fructose, and disaccharides composed thereof, sucrose, was also attempted. For instance, conversion of sucrose with the bifunctional composite catalyst yields 45% methyl lactate in methanol at slightly elevated reaction temperature. The hybrid catalyst proved to be recyclable in various successive runs when used in alcohol solvent.

Mechanistic Insight into the Conversion of Tetrose Sugars to Novel α‐Hydroxy Acid Platform Molecules

α‐Hydroxy acids (AHAs) such as lactic acid are considered platform molecules in the biorefinery concept and have high‐end applications in solvents and biodegradable polyester plastics. The synthesis of AHAs with a four‐carbon backbone structure is a recently emerging field. New biomass‐related routes towards their production could stimulate their practical use in new polyester plastics. Herein, we report the unique catalytic activity of soluble tin metal salts for converting tetroses, namely erythrulose and erythrose, into new four‐carbon‐backbone AHAs such as methyl vinylglycolate and methyl‐4‐methoxy‐2‐hydroxybutanoate. An in situ NMR study together with deuterium labeling experiments and control experiments with intermediates allowed us to propose a detailed reaction pathway.

Ternary Ag/MgO-SiO2 catalysts for the conversion of ethanol into butadiene.

Ternary Ag/Magnesia-silica catalysts were tested in the direct synthesis of 1,3-butadiene from ethanol. The influence of the silver content and the type of silica source on catalytic performance has been studied. Prepared catalysts were characterized by (29) Si NMR, N2 sorption, small-angle X-ray scattering measurements, XRD, environmental scanning electron microscopy with energy dispersive X-ray analysis (ESEM/EDX), FTIR spectroscopy of adsorbed pyridine and CO2 , temperature-programmed desorption of CO2 and UV/Vis diffuse reflectance spectroscopy. Based on these characterization results, the catalytic performance of the catalysts in the 1,3-butadiene formation process was interpreted and a tentative model explaining the role of the different catalytically active sites was elaborated. The balance of the active sites is crucial to obtain an active and selective catalyst to form 1,3-butadiene from ethanol. The optimal silver loading is 1-2 wt% on a MgO-silica support with a molar Mg/Si ratio of 2. The silver species and basic sites (Mg−O pairs and basic OH groups) are of prime importance in the 1,3-butadiene production, catalyzing mainly the ethanol dehydrogenation and the aldol condensation, respectively.

Tailoring nanohybrids and nanocomposites for catalytic applications

Research on and development of inorganic–organic nanohybrids and nanocomposite materials has attracted increasing attention in recent years. Synthetic strategies for such materials vary from grafting or co-condensation of Si and C sources to the impregnation of silica with polymers. Nanohybrids, prepared using organosilanes, and nanocomposites, obtained by hard or soft templated synthesis, are discussed. Various strategies will be presented that demonstrate how additional carbon properties can be exploited maximising the activity, selectivity and stability of composite materials as solid catalysts. Composite materials allow for the extensive engineering of a catalyst enabling careful tuning of the type, amount and position of active sites, as well as the porosity and hydrophilic nature of the final catalyst. These materials not only combine the advantages of silica (e.g. thermal stability, rigidity, ordering) and carbon (e.g. flexibility, ductility) but also allow their synergetic action in various catalytic applications.

CO2 reverse selective mixed matrix membranes for H2 purification by incorporation of carbon–silica fillers

By filling a PDMS top layer with porous carbon–silica microspheres, a defect-free mixed matrix membrane was created with notable CO2 reverse selective separation properties. For the separation of CO2 over H2 at room temperature and 10 bar inlet pressure, these membranes demonstrate high CO2 gas fluxes up to 3 × 10−7 mol cm−2 s−1, in combination with ideal separation factors in the range of 6 to 9. The present separation data signify an important step forward in the removal of CO2 from H2 using a reverse selective separation strategy. Moreover, they elucidate the potential of such mixed matrix membranes in the emerging field of CO2 separation.

An Eco‐friendly Soft Template Synthesis of Mesostructured Silica‐Carbon Nanocomposites for Acid Catalysis

The synthesis of ordered mesoporous silica‐carbon composites was explored by employing TEOS and sucrose as the silica and carbon precursor respectively, and the triblock copolymer F127 as a structure‐directing agent via an evaporation‐induced self‐assembly (EISA) process. It is demonstrated that the synthesis procedures allow for control of the textural properties and final composition of these silica‐carbon nanocomposites via adjustment of the effective SiO2/C weight ratio. Characterization by SAXS, N2 physisorption, HRTEM, TGA, and 13C and 29Si solid‐state MAS NMR show a 2D hexagonal mesostructure with uniform large pore size ranging from 5.2 to 7.6 nm, comprising of separate carbon phases in a continuous silica phase. Ordered mesoporous silica and non‐ordered porous carbon can be obtained by combustion of the pyrolyzed nanocomposites in air or etching with HF solution, respectively. Sulfonic acid groups can be readily introduced to such kind of silica‐carbon nanocomposites by a standard sulfonation procedure with concentrated sulfuric acid. Excellent acid‐catalytic activities and selectivities for the dimerization of styrene to produce 1,3‐diphenyl‐1‐butene and dimerization of α‐methylstyrene to unsaturated dimers were demonstrated with the sulfonated materials.