Bimetallic Ru:Ni/MCM-48 catalysts for the effective hydrogenation of d-glucose into sorbitol

Abstract

Most of the sorbitol processing at industrial scale is performed by hydrogenation of d-glucose using Raney–nickel catalysts. Noble metals (Ru, Rh, Pd and Pt) and non-noble metals (Fe, Ni, Cu or Co) have been used in hydrogenation reactions. Nickel catalysts have achieved a good piece of attention according to their low cost and moderate to good catalytic activity. Nevertheless, nickel catalysts are susceptible to show deactivation after its recycling due to leaching of the active nickel into the reaction media, sintering of the active metal and poisoning of metallic nickel surface. The current trend consists on the preparation of ruthenium catalysts, which show catalytic activities per mass of active metal 20 – 50 times higher in comparison with nickel. However, the high price of noble metals is the main drawback. Thus, the development of novel bimetallic nickel catalysts with comparable high activity to noble metal catalysts still remains a technological challenge. In this work, three bimetallic Ru:Ni catalysts supported on a mesoporous silica MCM-48 were prepared by consecutive wet impregnations, with a total metal loading of ca. 3% (w w−1). Ru:Ni ratios spanned in the range of 0.15–1.39 (w w−1) and were compared with the corresponding monometallic Ni/MCM-48. The catalysts so prepared were characterized by XRD, TEM, adsorption/desorption of N2, H2-TPR, NH3− TPD and Atomic Absorption, and tested in the liquid phase hydrogenation of d-glucose into sorbitol in the temperature range 120–140 ºC under 2.5 MPa of H2 pressure (Figure 1). Bimetallic catalysts with Ru:Ni ratios higher than 0.45 enhanced the catalytic behaviour of the monometallic Ni/MCM-48 in the reaction, increasing the reaction rate and showing complete selectivity to sorbitol by minimizing the production of mannitol. Ru:Ni/MCM-48 (0.45) was recovered from the reaction media and tested for three reaction cycles, showing good stability under the selected experimental conditions.