Benjamin Katryniok

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.

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.

Catalytic selective oxidation of isobutane over Csx(NH4)3−xHPMo11VO40 mixed salts

A series of mixed Keggin-type heteropolysalts Csx(NH4)3−xHPMo11VO40 with various ammonia/caesium ratios was prepared by the precipitation method and characterized by TGA, N2 adsorption/desorption, XRD, FT-IR, and NH3-TPD techniques. Correlations between the ammonia/caesium ratio and the specific surface area, as well as with the total number of acid sites, were established. Furthermore, the introduction of Cs to the catalytic formulation was beneficial to the stabilization of the Keggin structure and helped limiting the elimination of the V atoms from the primary structure. The as-prepared samples were applied in the catalytic selective oxidation of isobutane at 340 °C under atmospheric pressure. The best results were obtained over Cs1.7(NH4)1.3HPMo11VO40 with an isobutane conversion of 9.6% and a total selectivity to valuable products (methacrylic acid and methacrolein) of 57.1%. This was explained by the well-balanced acidity and specific surface of this catalyst, promoting the C–H bond activation (adequate acid properties) over a large number of accessible active sites (high acid sites density).

Direct dehydration of 1,3-butanediol into butadiene over aluminosilicate catalysts

The catalytic dehydration of 1,3-butanediol into butadiene was investigated over various aluminosilicates with different SiO2/Al2O3 ratios and pore architectures. A correlation between the catalytic performance and the total number of acid sites and acid strength was established, with a better performance for lower acid site densities as inferred from combined NH3-TPD, pyridine adsorption and 27Al-NMR MAS spectroscopy. The presence of native Bronsted acid sites of medium strength was correlated to the formation of butadiene. A maximum butadiene yield of 60% was achieved at 300 °C over H-ZSM-5 with a SiO2/Al2O3 ratio of 260 with the simultaneous formation of propylene at a BD/propylene selectivity ratio of 2.5. This catalyst further exhibited a slight deactivation during a 102 h run with a decrease in the conversion from 100% to 80% due to coke deposition as evidenced by XPS and TGA-MS, resulting in a 36% loss of the specific surface area.

Ammoxidation of allyl alcohol – a sustainable route to acrylonitrile

The ammoxidation of allyl alcohol was demonstrated over antimony–iron oxide catalysts with a Sb/Fe ratio of 0.6 and 1. Both catalysts showed high performance with 83 and 84% yield of acrylonitrile, respectively, whereby the main difference was found in the initial performance. This was ascribed to the in-operando formation of the SbFeO4 mixed oxide on the catalyst surface under reaction conditions, as proven by XPS analysis.