Sébastien Paul

Glycerol dehydration to acrolein in the context of new uses of glycerol

Catalytic dehydration of glycerol to acrolein has the potential to valorise the glut of crude glycerol issuing from biodiesel production. This reaction requires catalysts with appropriate acidity, and intensive research activities have been focused on the application of families of catalysts including zeolites, heteropolyacids, mixed metal oxides and (oxo)-pyrophosphates, as their acidic properties are well-known. Nevertheless, their deactivation by coking remains the main obstacle in the way of large-scale industrial applications. Considering this important issue, various technologies have been proposed for regenerating the catalysts. This review shows that a well-balanced combination of an appropriate catalytic system together with an adapted regeneration process could put large-scale industrial applications within reach.

Selective catalytic oxidation of glycerol: perspectives for high value chemicals

Due to its three hydroxyl groups, glycerol is a potential starting material for various high value fine chemicals such as dihydroxyacetone, tartronic acid and mesoxalic acid. The corresponding oxidation reactions are catalysed by various metals such as palladium, platinum, bismuth or gold. Nevertheless, the selectivity not only depends on the type of the active phase, but is also influenced by numerous parameters such as the metal particles size, the pore size of the support and the pH of the reaction medium. This review not only describes the recent developments in the field of research for new catalysts but also spotlights the role of the reaction conditions as well as the possible transport limitations in this tri-phasic system. Furthermore, an economical analysis of some processes is given, which shows that this is realistic to envision sustainable production of, e.g., dihydroxyacetone.

Towards the Sustainable Production of Acrolein by Glycerol Dehydration

The massive increase in biodiesel production by transesterification of vegatable oils goes hand-in-hand with the availability of a large volume of glycerol, which must be valorized. Glycerol dehydration to acrolein over acid catalysts is one of the most promising ways of valorization, because this compound is an important chemical intermediate used in, for example, the DL-methionine synthesis. In this Minireview, we give a detailed critical view of the state-of-the-art of this dehydration reaction. The processes developed in both the liquid and the gas phases are detailed and the best catalytic results obtained so far are reported as a benchmark for future developments. The advances on the understanding of the reaction mechanism are also discussed and we further focus particularly on the main obstacles for an immediate industrial application of this technology, namely catalyst coking and crude glycerol direct-use issues.

A long-life catalyst for glycerol dehydration to acrolein

While the initial catalytic performances of silica-supported silicotungstic acid are high in the glycerol dehydration reaction, they rapidly decrease with time on stream and the acrolein yield quickly decreases.

Highly efficient catalyst for the decarbonylation of lactic acid to acetaldehyde

The gas phase decarbonylation of lactic acid was performed over various silica-supported heteropolyacids. The obtained performances were, by far, higher than those previously described in the literature. In particular, the best results were obtained for silicotungstic acid-based catalysts, which showed very high yields of acetaldehyde (81–83%) at high lactic acid conversion (up to 91%).

Selective oxidation of 5-hydroxymethylfurfural to 2,5-diformylfuran over intercalated vanadium phosphate oxides

The selective oxidation of 5-hydroxymethylfurfural (5-HMF) to 2,5-diformylfuran (DFF) was studied over vanadium phosphate oxide (VPO)-based heterogeneous catalysts in the liquid phase. The selectivity to DFF was highly increased when using intercalated vanadium phosphate oxides under mild conditions (1 atm of oxygen, 110 °C) in an aromatic solvent. We found that the length of the intercalated ammonium alkyl chain had no clear influence on the catalytic performances, and a maximum yield of 83% could be achieved over C14VOPO4 and C14VOHPO4 after 6 h of reaction. Recycling of the catalyst was successfully performed, and we further obtained some insights in the reaction pathway: while the desired oxidation reaction indeed proceeded over the catalyst, the formation of by-products was linked to the presence of free radicals in solution.

Catalytic Conversion of Alcohols into Carboxylic Acid Salts in Water: Scope, Recycling, and Mechanistic Insights

The catalytic conversion of alcohols into carboxylic acid salts in water was performed in the presence of ruthenium complexes supported by aliphatic PNP pincer ligands preformed or formed in situ. High activity toward a wide substrate scope was achieved with turnover number values of up to 4000. The air-stable catalytic system can be recycled by using toluene as a catalyst-immobilizing phase; the activity is maintained after five consecutive runs. Finally, mechanistic studies allowed some fundamental aspects related to water activation to be unveiled and to the mechanism postulated.

The role of carbon atoms of supported iron carbides in Fischer–Tropsch synthesis

High reactivity of iron carbides enhances the Fischer–Tropsch reaction rate on supported iron catalysts. Highly dispersed carbide is easily hydrogenated to methane in a hydrogen atmosphere with subsequent regeneration in the presence of CO. Carbon atoms in iron carbide are involved in the initiation of chain growth in Fischer–Tropsch synthesis.

Regeneration of silica-supported silicotungstic acid as a catalyst for the dehydration of glycerol.

The dehydration reaction of glycerol to acrolein is catalyzed by acid catalysts. These catalysts tend to suffer from the formation of carbonaceous species on their surface (coking), which leads to substantial degradation of their performances (deactivation). To regenerate the as-deactivated catalysts, various techniques have been proposed so far, such as the co-feeding of oxygen, continuous regeneration by using a moving catalytic bed, or alternating between reaction and regeneration. Herein, we study the regeneration of supported heteropolyacid catalysts. We show that the support has a strong impact on the thermal stability of the active phase. In particular, zirconia has been found to stabilize silicotungstic acid, thus enabling the nondestructive regeneration of the catalyst. Furthermore, the addition of steam to the regeneration feed has a positive impact by hindering the degradation reaction by equilibrium displacement. The catalysts are further used in a periodic reaction/regeneration process, whereby the possibility of maintaining long-term catalytic performances is evidenced.

Room Temperature Hydrogen Production from Ethanol over CeNiXHZOY Nano‐Oxyhydride Catalysts

CeNiXHZOY nano‐oxyhydride catalysts were developed for the highly efficient sustainable hydrogen production from ethanol and water in the oxidative steam reforming reaction. After an in situ treatment in hydrogen in the temperature range of 200–300 °C, the cerium–nickel binary mixed oxides became hydrogen reservoirs, which were called oxyhydrides, in the presence of hydrogen species of the hydride nature in the anionic vacancies of mixed oxides. A novel technology was developed for the room temperature hydrogen production by using the chemical energy released from the reaction between CeNiXHZOY nano‐oxyhydride catalysts and oxygen, which completely converted ethanol specifically at 60 °C (oven temperature) and simultaneously produced hydrogen, carbon dioxide, and carbon monoxide along with small amounts of methane and ethanal. CeNiXHZOY nano‐oxyhydride catalysts demonstrated excellent catalytic stability, which was attributed to the graphitic filamentous carbon formed during the reaction. The unique activation phenomenon of the reaction (a huge variation in the temperature between the catalyst bed and the oven) was demonstrated in detail. Finally, the correlations among the catalyst properties, the catalytic performances, and the characterizations were thoroughly discussed.