The Role of Nitrate on the Sol-Gel Spread Self-Combustion Process and Its Effect on the NH3-SCR Activity of Magnetic Iron-Based Catalyst

• Published in: Catalysts 2020-03, Vol.10 (3), p.314
• Main Authors: Ning, Xing, Xiong, Zhi-bo, Yang, Bin, Lu, Wei, Wu, Shui-mu
• Format: Article
• Language: English
• Subjects: Acids; Adsorption; Ammonia; Catalysts; Cerium; Chemical precipitation; Chemical reactions; Citric acid; Coal-fired power plants; Combustion; Crystallites; Decomposition; Fourier transforms; High temperature; Iron; Lewis acid; magnetic γ-fe2o3; nitrate; Nitrate removal; Nitrates; Nitric acid; Nitrogen oxides; Oxidizing agents; Particle size; Pore size; Porosity; Scanning electron microscopy; selective catalytic reduction of nox; sol-gel; Sol-gel processes; the spread self-combustion method; Thermal analysis; Tungsten
• ISSN: 2073-4344; 2073-4344
• DOI: 10.3390/catal10030314

Sol-gel spread self-combustion is the burning of the complexing agent in dried gel and the oxidant. Meanwhile, high temperature takes place during the combustion process, which is harmful to the pore structure of the catalyst. The nitrate from metal nitrate precursors as an oxidant could participate in the spread of the self-combustion process. Therefore, the influence of nitrate from metal nitrate on the spread self-combustion of an iron–cerium–tungsten citric acid gel and its catalytic performance of NOx reduction were investigated by removing nitrate via the dissolution of washing co-precipitation with citric acid and re-introducing nitric acid into the former solution. It was found that the removal of nitrate contributes to enhancing the NH3–SCR activity of the magnetic mixed oxide catalyst. The NOx reduction efficiency was close to 100% for Fe85Ce10W5–CP–CA at 250 °C while the highest was only 80% for the others. The results of thermal analysis demonstrate that the spread self-combustion process of citric acid dried gel is enhanced by re-introducing nitric acid into the citric acid dissolved solution when compared with the removal of nitrate. In addition, the removal of nitrate helps in the formation of γ-Fe2O3 crystallite in the catalyst, refining the particle size of the catalyst and increasing its pore volume. The removal of nitrate also contributes to the formation of Lewis acid sites and Brønsted acid sites on the surface of the catalyst compared with the re-introduction of nitric acid. The in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) demonstrates that both Eley–Rideal (E–R) and Langmuir–Hinshelwood (L–H) mechanisms exist over Fe85Ce10W5–CP–CA at 250 °C with E–R as its main mechanism.