Controlled synthesis of niobium and rare earth mixed oxides for catalytic combustion of chlorinated VOCs in the synthesis process of polyether polyol and polyurethane

Abstract

Catalytic technique is an effective and economical method to deal with air pollution. This work investigated the effect of recombination of rare earth (RE ​= ​Y, La, Ce, Pr and Nd) and Nb element, different calcination temperature and preparation methods on the physical/chemical properties of RENbO4+δ mixed oxides. These materials were used for catalytic combustion of chlorinated VOCs (using monochlorobenzene and 1,2-dichloroethane as representative examples), and the structure-performance relationship was explored. The results showed that the optimal catalyst was the oxygen-rich Ce–Nb–O mixed oxide. It was gradually sintered above 700 ​°C to form CeNbO4+δ compound, and its apparent catalytic activity decreased with the increase of calcination temperature. The high dispersion of Nb2O5 into CeO2 matrix lead to strong interaction between Ce, Nb and O elements, and thus more active oxygen species were obtained, which was beneficial to improving redox property and catalytic performance of catalyst. The apparent catalytic activity decreased in the order of CeNbO-hp (homogeneous precipitation of urea)＞CeNbO-cp (co-precipitation of (NH4)2CO3)＞CeNbO-sg (citric acid based sol-gel method)＞CeNbO-mm (simple mechanical mixing of Nb2O5 and CeO2)＞pure Nb2O5, CeO2. In the continuous reaction of 100 ​h, both monochlorobenzene and 1,2-dichloroethane could be completely destroyed at 320 ​°C to form HCl, CO2 and H2O on the optimized CeNbO-hp.