Modification Of Manganese-based Catalyst For VOCs Catalytic Combustion And Its Performance

PM2.5 and O3 have become the main secondary atmospheric pollutants. VOCs as an important precursor played a key role in the formation process of the composite atmospheric pollution. Toluene accounted for the largest proportion in the 31 million tons of VOCs emissions in 2015. Noble metal catalysts used for toluene catalytic combustion was considered to have high catalytic activity at low temperature, but it were expensive and easy poisoning. Developing a catalyst with excellent toluene catalytic activity, high resistant to toxicity and low cost is of great significance and high application value. Manganese-based catalysts were reported to have good oxidation-reduction properties with low price. But the single manganese metal oxide catalyst exhibited low activity. It was easy to change crystal phase and deactivated in high temperature. So the modification of manganese base catalysts to improve its thermal stability and catalytic combustion efficiency would have good research significance and practical value.In this research, the modified manganese metal oxide catalysts were prepared by introducing non-noble metal Zr and Ce. A series of characterization, such as SEM, BET, XRD, TEM, XPS. TGA-DSC and H2-TPR. were used to explore the influence of different element modification on the morphology, specific surface area, pore volume, crystal phase, elements composition as well as the thermal stability and oxidation reduction of manganese base catalysts. The results showed that Ce and Zr can influence the formation of the manganese catalysts morphology, and change its lattice structure. The generation of Mn4+ and lattice oxygen were also promoted by modification. The introduction of Zr improved the thermal stability of manganese-based catalyst, while the catalyst with Ce modified exhibited an obvious improvement on oxidation-reduction performance. In the aspect of catalyst activity characterized for the model VOCs pollutant of toluene, ethyl acetate and chlorobenzene, the activity of Zr modified manganese base catalyst only had distinct improvement in the catalytic reaction of chlorobenzene. Although the Ce modified manganese catalysts exhibited better catalytic activities in the combustion of toluene and ethyl acetate, it was poor resistance to chlorine poisoning. As a result, uniform mesoporous structure, large specific surface area and pore volume, high Mn4+ and lattice oxygen content, as well as the best thermal stability property and oxidation-reduction property were found in the Mn-Zr-Ce catalyst. It can resist chloride toxic and regenerate easily when deactivation occurred.The transition elements Cu was also used to further modified Mn-Zr-Ce catalyst. Results showed that catalyst with 25% Cu modified had the highest specific surface area and pore volume. The active component distributed in the catalyst uniformly, and the surface active oxygen content, thermal stability, oxidation-reduction properties were also further improved. The activity experimental results showed that Cu modified was beneficial to improve the toluene catalytic activity, and the toluene degradation rate stabled in more than 90% after 48 hours continuous operation under 260?. When compared to the noble metal catalyst,25%Cu-Mn-Zr-Ce catalyst had equal high toluene catalytic activity. At the same time, the degradation pathway of toluene on 25% Cu-Mn-Zr-Ce catalyst was also discussed.