Hydrogenation in water of mono- and disaccharides to polyols using Ni-Fe/SiO 2 catalysts Achraf Sadier 1 , François Robert 2,3 , Catherine Amiens 2,3 , Karine Philippot 2,3 , Robert Wojcieszak 1 and Eric Marceau 1 1 Univ. Lille, CNRS, Centrale Lille, Univ. Artois, France, 2 CNRS, LCC (Laboratoire de Chimie de Coordination), France, 3 Université de Toulouse, France Besides costly noble metals, Ni is used to catalyze the hydrogenation of sugars to polyols, but is poorly stable. Compared with Ni, supported Ni-Fe alloyed nanoparticles were recently reported to present high conversion and selectivity in the hydrogenation of glucose to sorbitol. [1] Investigating if benefits also exist for the hydrogenation of xylose and maltose to, respectively, xylitol and maltitol, two molecules of interest for the food and pharmaceutical industries, is the purpose of the present work. The activity, selectivity and stability in water of a Ni/SiO 2 catalyst and a bimetallic Ni 62 Fe 38 /SiO 2 catalyst prepared by deposition-precipitation (Ø particles =5-7 nm) were compared as a function of experimental parameters (T=50- 150 °C, P H2 =10-30 bar). For xylose hydrogenation, [2] the only product detected was xylitol, while for maltose, [3] maltitol was the major product, but maltose hydrolysis to glucose occurred in the upper range of temperature. A reaction temperature of 80 °C allowed minimizing nickel leaching at full conversion and unwanted side-reactions. The presence of reduced Fe at the surface of the bimetallic nanoparticles increased the first-order apparent rate constant k and the adsorption constant of the sugar compared with the Ni catalyst, by a factor 2 to 3, indicating a stronger interaction with the oxophilic Ni-Fe surface. However, the rate constant for maltose hydrogenation was lower by a factor 5 to 6 compared with xylose. Another major difference in the case of maltose was a reaction order of 0.5 with respect to P H2 on Ni-Fe/SiO 2 compared with a zero-order on Ni/SiO 2 , stressing significant differences in H 2 coverage of the bimetallic surface. A dilution of Ni domains among Fe atoms can explain the difficulty to find adsorption sites for maltose, a bulky disaccharide, hence the low value of k despite maltose strong adsorption, and the limited coverage in hydrogen atoms apt to ensure the hydrogenation. The presence of Fe also promoted the catalyst stability. The activity of Ni/SiO 2 strongly declined upon formation of a Ni(II) phyllosilicate. No deactivation was found for the Ni-Fe catalyst. Nevertheless, the size of the metal particles and the Fe proportion in the surface layers increased, suggesting a flattening and coalescing of the particles over the silica surface. A comparison with SiO 2 -supported Ni-Fe nanoparticles tailored via an organometallic route (hydrogenation of [Ni(COD) 2 ] and {Fe[N(SiMe 3 ) 2 ] 2 } 2 ; Ø particles =3-4 nm) led to similar results and emphasized the importance of keeping the two metals in their reduced form for an optimum activity, the beneficial role of Fe-enriched surfaces; and the higher performance of a Ni 70 Fe 30 formulation. References
1. Y. Fu et al., Appl. Catal. B 2021 , 288 , 119997. 2. A. Sadier et al., Appl. Catal. B 2021 , 298 , 120564. 3. A. Sadier et al., Appl. Catal. B 2022 , 313 , 121446.
P11
© The Author(s), 2022
Made with FlippingBook Learn more on our blog