Nb-based solid acid catalysts for green biomass exploitation
Dispersed Nb2O5 phases in silica matrices were synthesized by different routes: co-precipitation and sol-gel to prepare mixed oxide samples, and wet-impregnation to prepare supported oxide samples. All the Nb2O5-containing catalysts were studied for their main surface and bulk properties and tested in the dehydration reaction of fructose (FRU) to 5-hydroxymethyl-2-furaldehyde (HMF) in water at 100°C. The typical water-tolerant acidity of Nb2O5 was maintained in all the samples. By dispersing different amounts of Nb2O5 into silica, the surface acidity of the samples was modified, in particular the surface acid strength. The Nb2O5-contained samples were active in the FRU dehydration reaction to HMF without the deactivation effects which are observed over bulk niobia catalysts.
In the 19th century the abundance of fossil fuels permitted rapid industrialization, which during the 20th century continued with an increasing consumption of fossil resources. In the 21th century the high demands of energy and chemicals coming from the emerging countries has increased the depletion of oil. Nowadays the defense of our standard of life must take into account both pollution problems and the lack of fuel and chemicals.
Biomass exploitation is the most promising way for the translation from an economy based on fossil to one based on renewable resources, mainly because from biomass it is possible to obtain both fuel and chemicals. The main risks are to remove lands from food production and to convert them to non-food production (e.g. vegetable oil to obtain bio-diesel), or to directly use food biomass for other purposes. Waste products from agriculture should rather be exploited, due to their high carbohydrate content.
Carbohydrates are molecules with the general formula Cm(H2O)n, and compared with oil they have a completely different chemistry. Their exploitation may be ...