Sodium-doped MgO/NbOPO4 toward highly selective ketonization of aldoses

Abstract

The study aimed to investigate the catalytic effects of alkali metal-doped (Li⁺, Na⁺, and K⁺) magnesia supported by niobium phosphate on the ketonization of aldo-saccharides. The catalytic results showed that Na–MgO/NbP exhibits higher ketose selectivity than Li- and K–MgO/NbP. Compared to undoped MgO/NbP, doping Na⁺ ions at a molar ratio of 5–10% increased both the amount and density of basic sites. The EDS and ESR analyses showed that Na⁺ ions were uniformly distributed on the surface of the xNa–MgO/NbP catalyst, and the oxygen vacancies of xNa–MgO/NbP were increased with an increase in the amount of doped Na⁺ ions, which consequently accelerated the reaction rates. XPS analysis and UV-adsorption measurements indicated that Na⁺ doping had an electron-donating effect, diminishing the positive charge of Mg²⁺ ions. The ketose selectivity increased within the 10–20% Na⁺ doping range, while the yield of ketose remained relatively unchanged when treating aldoses with xNa–MgO/NbP catalysts. Na–MgO/NbP could give a ketose productivity of up to 44.8 g kg-solution⁻¹ h⁻¹ when treating 20.0 wt% glucose with a catalyst loading as low as 0.005 g g-solution⁻¹, achieving a catalyst efficiency of 8.96 g g-catalyst⁻¹ h⁻¹. Further kinetic analysis revealed two types of catalytic sites on the surface: one catalyzed ketonization, while the other is primarily responsible for the decomposition of the saccharides.