SiO2 supported niobium oxides with active acid sites for the catalytic acetalization of glycerol.

• The silica supported niobium oxide possessed abundant acid active sites. • The relationship between synthesis parameters and acid properties was investigated. • In-situ experimental trials were introduced to understand the catalytic mechanism. The silica supported niobium oxide catalysts with abundant acid active sites were successfully fabricated and demonstrated catalytic activity in the acetalization of glycerol with acetone to produce solketal. Although Niobium pentachloride which was used as the niobium precursor preferred to aggregate on the surface, the chemical vapor deposition method was introduced to remove the surface chloride. The synthesis parameter of the material affects the structure and the type of the supported niobium oxide on the carrier, and directly changes the amounts of catalytic sites. The effect of calcination temperature/time and loading amount of hydrated niobium oxide on the catalytic performance was investigated. The properties of acid sites on catalysts were characterized, and the catalytic process was directly observed by operando Raman. These in-situ experimental trials could provide deep insight to understand the catalytic mechanism. [ABSTRACT FROM AUTHOR]