Synthesis of Nb2O5 based solid superacid materials for catalytic combustion of chlorinated VOCs

Abstract Nb 2 O 5 based solid superacids (Nb 2 O 5 -MO x , M = Ti, W, Zr, Si, Al and Ca, respectively) were synthesized by sol-gel method using citric acid as the cross-linking agent, and then were investigated for catalytic combustion of 1,2-dichloroethane (abbreviation: DCE), one of the typical examples for chlorinated VOCs pollutants. The research results of the structure-performance relationship show that mesopore and amorphous state structure are formed for Nb 2 O 5 -MO x , and the metal elements are highly dispersed, which contribute to enhancing the metal-metal interaction and modifying the physicochemical properties of the catalysts. The order for the inherent catalytic activity is: Nb 2 O 5 -WO 3 ＞Nb 2 O 5 -ZrO 2 ＞Nb 2 O 5 -TiO 2 ＞Nb 2 O 5 -SiO 2 ＞Nb 2 O 5 -Al 2 O 3 ＞Nb 2 O 5 ＞Nb 2 O 5 -CaO. There exists synergistic catalytic effect: the mesopore and surface acidity facilitate the adsorption, activation and destruction of the C Cl bond in the reactants to form HCl and byproduct C 2 H 3 Cl (or carbocation intermediate), and then the redox sites promote deep oxidation of the byproduct/intermediate to convert to CO 2 and H 2 O. Especially, the Nb 2 O 5 -TiO 2 catalyst represents the highest apparent catalytic degradation activity. It also represents good thermal stability and durability for DCE destruction as well as good resistance to water vapor.