Tin, niobium and tin-niobium oxides obtained by the Pechini method using glycerol as a polyol: Synthesis, characterization and use as a catalyst in fructose conversion

Abstract

The selective and efficient conversion of fructose into chemicals has been extensively explored, especially from the perspective of a more sustainable industry based on renewable inputs together with a more environmentally friendly process. In this study, mixed metal oxides based on tin and niobium were synthesized by the Pechini method, replacing ethylene glycol with glycerol, a renewable chemical. This replacement allows the use of pure or mixed oxides exhibiting high specific surface areas but did not lead to significant differences in the amount and nature of the acid sites present in each case. Furthermore, the mixed oxides had increased numbers of Lewis acid sites, while the number of Bronsted acid sites decreased. Catalytic tests performed at 150 °C demonstrated that the use of these materials leads to conversion results higher than those observed for pure oxides (SnO2 (EG) = 48.3 %, Nb2O5 (EG) = 51.6 % and SnO2 (G) = 56.8 %, Nb2O5 (G) = 59.6 %) because 78.5 and 75.7 % consumption of fructose for SnNb (EG) and SnNb (G) was attained at 2 h, respectively. In addition, the catalysts show promising 5-hydroxymethylfurfural (5-HMF) selectivity, and the presence of lactic acid was also detected. In addition, recycling experiments were performed, and stability was observed for 4 cycles without structural change in the catalysts.