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

Abstract

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.

Solution combusted ultrathin Co3O4/CoO heterophase electrocatalyst for solar‐energy driven bifunctional water electrolysis

“…Addition of nitric acid (NO 3À ) increased the oxidizing environment and increased the rate of oxidation: NO 3À provides in-situ oxidizing atmosphere for the breakdown of organic matters and triggered the sol-gel to complete combustion process. [24,25] Finally, the dry gel starts to auto-combustion (high exothermic) for about 1-2 mins, after that the burnt gel was turned to crispy powder of SCSCOs.…”

Study of the Structural and Magnetic Properties of a Novel Cola/Lah Nanocomposite Material

“…The DSC graph reveals two peaks, one endothermic at 25 °C due to water loss and one exothermic at 300-375 °C due to metal nitrate combustion with urea. 31 As a result, the formation temperature of the studied sample was over 400 °C. As a consequence, the nano-sample was prepared at 500 °C.…”

Rational design on photo(electro)catalysts for artificial nitrogen looping

“…Different from NRR, however, the products of NOR are nitrates rather than ammonia, which can not only provide nitrogen sources and nutrition for soil but also play a crucial role in numerous manufactures, for example, making gunpowder, curing coronary heart disease, and so on. 108,[112][113][114][115] It has been suggested that N 2 is oxidized to nitrate by the following two steps: the first step is to activate the N≡N triple-bond, converting the inert N 2 to active NO * intermediates ( * represents to active sites). The second step is a redox reaction, in which NO * is transformed into nitrate over the active sites.…”

“…In addition to this route, nitrogen oxidation to nitrate (ie, NOR) has also been considered a feasible way to achieve the same goal of fixing nitrogen. Different from NRR, however, the products of NOR are nitrates rather than ammonia, which can not only provide nitrogen sources and nutrition for soil but also play a crucial role in numerous manufactures, for example, making gunpowder, curing coronary heart disease, and so on 108,112‐115 . It has been suggested that N 2 is oxidized to nitrate by the following two steps: the first step is to activate the N≡N triple‐bond, converting the inert N 2 to active NO * intermediates ( * represents to active sites).…”