Chen Lei, a postdoctoral student at the School of Chemical Engineering and Technology, Xi'an Jiaotong University (XJTU), has designed a hollow core-shell manganese-cerium catalyst that can effectively curb the nitrogen oxides produced by the combustion of fossil fuels, which are a serious threat to air quality.

Nitrogen oxides have severely damaged the global environment, causing a series of ecological problems such as photochemical smog and ozone layer destruction. Correspondingly, various denitration technologies have emerged. Among them, selective catalytic oxidation is the core step of the denitration process, and the development of a catalyst with higher performance is the key to solving related problems.

The catalyst designed by Chen introduces cerium dioxide to the outer surface of manganese dioxide to form a hollow core-shell manganese-cerium catalyst with a hierarchical structure that provides the possibility for effective mass transfer, thereby improving thermal catalytic performance.

Synthesis route of hollow core-shell manganese-cerium catalyst

A series of comparative experiments show that the hollow core-shell manganese-cerium catalyst has good catalytic performance at medium and low temperatures.

Compared with commercial platinum/alumina and mullite catalysts, the hollow core-shell manganese-cerium catalyst exhibits higher denitration activity in temperatures ranging from 100°C (212℉) to 350°C (662℉).

The hollow core-shell manganese-cerium catalyst also exhibits good sulfur resistance. In a 100-ppm sulfur dioxide environment, denitrification efficiency does not change significantly. 

Even when the sulfur dioxide concentration is increased to 500 ppm, the denitrification efficiency of the hollow core-shell manganese-cerium catalyst remains at about 90%, showing good prospects for application.

(a, b) The relationship between the denitration efficiency of different samples and the reaction temperature. (c) Arrhenius equation. (d,e) The denitration efficiency of hollow manganese dioxide and hollow core-shell manganese-cerium catalysts with time in the presence of sulfur dioxide. (f) Stability test of hollow core-shell manganese-cerium catalyst.

To clarify the formation of molecular adsorption and reaction intermediates, the researchers studied the in-situ infrared spectra of hollow manganese dioxide and hollow core-shell manganese-cerium catalysts at 275°C (527℉).

In-situ infrared spectroscopy of hollow manganese dioxide and hollow core-shell manganese-cerium catalyst

Through density functional theory calculations, the researchers revealed the influence of the constructed ceria/manganese dioxide composite interface on denitration performance.

(a, b) Electronic localization function (c) Density of state (d) Nitric oxide oxidation potential energy diagram (e) Adsorption model on the catalyst (f) Schematic diagram of the proposed hollow core-shell manganese-cerium catalyst for the oxidation reaction mechanism of nitric oxide

In this study, a highly active nitric oxide catalyst composed of a hollow manganese dioxide core and a mesoporous ceria shell layer was synthesized. The hollow core-shell manganese-cerium catalyst can maximize interface interaction, accelerate electron transport, and generate a large number of active centers at the heterojunction, and has excellent low-temperature catalytic performance.

In addition, due to the protective effect of the mesoporous ceria shell layer, it exhibits excellent sulfur resistance. These results provide a promising strategy for the design of more effective low-temperature catalysts for the treatment of air pollutants.

The results were published in ACS Catalysis with the title "Research on Denitration Performance of Hollow Core-Shell Structure Manganese-Cerium Catalyst".

The first author of the paper is Chen Lei, a postdoctoral fellow at the XJTU School of Chemical Engineering and Technology. The university is the unit of the first author and corresponding author of the paper.

The project was funded by the National Natural Science Foundation of China.

Link to the paper: https://pubs.acs.org/doi/abs/10.1021/acscatal.1c01578