Bert Sels

Efficient catalytic conversion of concentrated cellulose feeds to hexitols with heteropoly acids and Ru on carbon.

A combination of heteropolyacids and Ru on carbon catalyzes the conversion of concentrated cellulose feeds into hexitols under H(2) pressure. Quantitative conversion of ball-milled cellulose was observed with remarkable hexitol volume productivity.

Chemocatalytic conversion of cellulose: opportunities, advances and pitfalls

In recent years, cellulose conversion to useful fuels and chemicals has become a focal point in academic and industrial research. This contribution highlights opportunities for cellulose valorization, summarizes recent advances in its chemocatalytic conversion and discusses the future of the field in the economic context of the first quarter of the 21st century.

Catalytic glycerol conversion into 1,2-propanediol in absence of added hydrogen.

Conversion of glycerol into high yields of 1,2-propanediol in absence of added hydrogen is possible with Pt impregnated NaY zeolite characterized by extra-zeolitic metal particles combined with zeolite Brønsted acidity.

Productive sugar isomerization with highly active Sn in dealuminated β zeolites

A water-tolerant Lewis acid catalyst was synthesized by grafting SnIV in isopropanol under reflux onto dealuminated zeolites with the BEA (β) topology. This synthesis method allows the production of highly active Snβ-type catalysts without the need for long hydrothermal syntheses or hydrogen fluoride, while using cheap Sn-precursors, industrially available β zeolites and standard catalyst synthesis unit operations. Extensive characterization of the best catalyst shows highly dispersed Sn in the zeolite matrix (XRD, 29Si MAS NMR and 1H MAS NMR) without the formation of SnO2 (XRD and UV-Vis). The catalyst was tested for the model isomerization of sugars such as glucose to fructose. The catalytic activity proved to be purely heterogeneous and the catalyst was recycled and reused without significant loss in activity. Isomerization productivities above 4 kg product per kg of catalyst per hour are reported with appreciably low Sn loadings, corresponding to exceptionally high turnover frequencies, viz. 500 cycles per Sn per hour at 110 °C, which surpass the activity per Sn of the original hydrothermally synthesized Snβ.

Hydrolytic hydrogenation of cellulose with hydrotreated caesium salts of heteropoly acids and Ru/C

We recently demonstrated excellent yields of hexitols for the reductive splitting of highly concentrated cellulose mixtures using a combination of commercially available heteropoly acids, viz. H3PW12O40 (H3PW) and H4SiW12O40 (H4SiW), and Ru on carbon (Ru/C) (J. Geboers et al., Chem. Commun., 2010, 46, 3577–3579). Despite their excellent catalytic performance, recovery and reuse of these soluble acid catalysts remains challenging. This contribution evaluates the potential of the so-called insoluble non-stoichiometric caesium salts of HPAs, viz. CsPW and CsSiW, in combination with Ru/C for the conversion of cellulose. As-synthesized CsHPA salts are shown to be even more active than native HPAs and their hydrolytic activity is improved even further by increasing the calcination temperature during synthesis, followed by a hydrotreating procedure. Reactions with CsSiW are highly selective due to suppression of hydrogenolysis side reactions: yields of up to 90% hexitols under mild reaction conditions are achieved using ball-milled avicel cellulose. Whereas recovery of commercial HPAs was not successful, CsPW salts were fully retained after reaction at 170 °C by simple recrystallization at room temperature without the need of an organic solvent.