Improving stability of Nb2O5 catalyst in fructose dehydration reaction in water solvent by ion-doping

Acidity modulation of the niobic acid surface, Nb2O5 center dot nH(2)O (NBO), by ion doping was pursued with the aim to limit the deactivation observed in fructose dehydration reaction performed in water due to insoluble humin formation and deposition on the NBO surface. Three series of K-, Ba-, and Nd-doped NBO catalysts prepared with different ion loading (from 1 to 15 atom nm(-2)) have been characterized and tested in the fructose dehydration reaction. Catalyst effective acidity, measured in water by 2-phenyl-ethylamine (PEA) adsorption, was in relation to the catalyst activity, with a clear effect on the fructose conversion. The long-term catalyst stability (up to 200 h of reaction time) was studied in a flow reactor with fixed catalytic bed at constant temperature of 100 degrees C by controlling activity, and in particular, selectivity to 5-hydroxymethylfurfural (HMF). The kinetic rate constants of deactivation were obtained; they have been associated with a faster (0.004 < k(deact,1)/ h(-1) < 0.058) and a slower (0.001 < k(deact,2)/h(-1) < 0.005) deactivation phenomenon. Comparison among the samples in terms of activity and effective acidity, measured in water, in long term reaction is here presented.