Design And Prepration Of Niobium Based Materials And Application

Recently, the niobium based catalyst has been widely used in oxidative dehydraogenenation, photocatalysis and acid-catalyzed reaction. Among nobium based materials, niobium phosphate has been known as an excellent water-resistant solid acid. Therefore looking for alternative approach to prepare high surface areas niobium phosphate material, and exploring novel applications is a hot topic.In this thesis, we developed a series of novel high surface areas niobium catalysts using cheap niobium source and further investigated the transformation of sugars towards5-HMF. The main contants include:1. Novel mesoporous niobium phosphate was prepared by using niobium tartrate as precursor. Thus prepared niobium phosphate was amorphous, with the surface area up to302m2/g. Meanwhile, the growth mechanism of porous material was also investigated. The presence of niobium tartrate ligand played an important role in the assemble process. The niobium catalyst exhibit good hydrothermal stability and can be used in fructose dehydration. It exhibited excellent catalytic performance even in aqueous system. After catalyst recycled for5times, it just had a slight deactivation, and the used catalyst can be almost regenerated by calcination at500℃2. The precise control of surface acid features (amount and the ratio of acid types) was realized by tuning the synthesis pH value. When the precursor’s pH increased, the total amount of acidic solid acid is indeed reduced, while the ratio of the Lewis acid to Bronsted acid was increased. To identify the origin of acid sites, niobium pentoxide and Na-exchanged niobium phosphate were also investigated. All results showed that Bronsted acid was derived from P-OH in surface, while Lewis acid was origined from the high valence of NbOx cluster. Applicated in the dehydration of glucose, the catalyst showed excellent activity and stability. Furthermore, this catalyst also displayed good performance on trasfer other carbohydrates towards HMF.