One-Step Synthesis of Nanostructured Cu–Mn/TiO₂ via Flame Spray Pyrolysis: Application to Catalytic Combustion of CO and CH₄

Abstract

Catalytic combustion has been widely applied to remove the trace combustible pollutants. However, the earthabundant and high-performance nanocatalysts are still the main research focus on promoting catalytic efficiency. Herein, the Cu and Mn mixed oxides supported on TiO 2 nanoparticles with various Cu and Mn molar contents synthesized via the flame spray pyrolysis (FSP) technique are utilized in the catalytic oxidation of lean CO and CH 4 . Initially, the Cu−Mn/TiO 2 nanocatalysts are composed of spherical structures with a diameter of about 20 nm, whose specific surface area is between 60 and 90 m 2 /g. The Cu element is more evenly distributed on the TiO 2 surface than the Mn element, owing to the distinctly different ion radii. Both the copper and manganese cations could incorporate into the TiO 2 lattice, which generates oxygen vacancies and enhances the diffusion of oxygen ions, causing the transformation of the antanse to rutile phase. When the molar content of the Cu−Mn increases to less than 30 mol %, the temperature of its reduction peak keeps decreasing due to the hydrogen spillover effect. Moreover, the catalytic performances of the Cu−Mn/TiO 2 with 12 mol % loading (12CMT) are all optimal during the low-temperature and the high-temperature stages, which are superior to the FSP-made copper manganese or copper titanium oxides. This is attributed to the small crystal particles, highly dispersed active components of CuO x and MnO x , and the higher ratios of Cu 1+ /Cu and Mn 4+ −O ads Lewis acid−base pairs. In addition, the strong interaction between Cu−Mn components and rutile phase support can tremendously promote the activity of catalytic combustion. Under the simulated flue gas, the catalytic properties of 12CMT decreases in comparison with those of CO and CH 4 mixed gas due to the introduction of CO 2 . Ultimately, the Cu−Mn/TiO 2 samples exhibit the outstanding water resistance, thanks to the hydrophobization of the catalyst surface.

Deep Insight into the Mechanism of Catalytic Combustion of CO and CH4 over SrTi1–xBxO3 (B = Co, Fe, Mn, Ni, and Cu) Perovskite via Flame Spray Pyrolysis

“…In Figure a, the particle morphology of the SrTi 0.9 Co 0.1 O 3 nanocatalyst includes the overwhelming majority of evenly small 5–15 nm particles, with a few 50–200 nm large particles. The existence of those inhomogeneous particles has been also found in Mn- and Fe-doped samples in Figures S5–S6 as well as other materials synthesized via FSP. , In this work, it is believed that the flame-made perovskites undergo two quite different conversion processes. , On the one hand, large nanoparticles are produced from the partially evaporated droplets pyrolysis by the droplet-to-particle conversion, due to the low enthalpy and high melting point of the selected metal precursors, such as strontium acetate. On the other hand, the fine particles are formed by the evaporated precursor gas, which is dominated by the gas-to-particles mechanism.…”

“…The existence of those inhomogeneous particles has been also found in Mn-and Fe-doped samples in Figures S5−S6 as well as other materials synthesized via FSP. 36,37 In this work, it is believed that the flame-made perovskites undergo two quite different conversion processes. 32,38 On the one hand, large nanoparticles are produced from the partially evaporated droplets pyrolysis by the dropletto-particle conversion, due to the low enthalpy and high melting point of the selected metal precursors, such as strontium acetate.…”

Facile One-Step Flame Synthesis of La1−xSrxMnO3 Nanoparticles for CO Catalytic Oxidation

“…Compared with the XRD characterization before and after the reaction, the intensity and position of diffraction peaks do not change significantly after the cyclic test, which demonstrated that the perovskite structure of samples is retained during the consecutive oxidation test. On the other side, the rapid sintering of precursor sprays in high-temperature flame (>1000°C) increased the dispersion and sintering resistance of Mn active components in perovskite catalysts [32]. Ding et al [28] also reported the preparation of metal oxide-supported single-atom Pt catalysts with high thermal stability by flame spray pyrolysis.…”

Study on Cr₂O₃/γ-Al₂O₃ Catalysts for Mixed Pyrolysis of Coal to Produce Hydrogen-Rich Fuel Gas

“…The results showed that with the increase of pyrolysis temperature, the yields of CO and CO 2 increased first and then decreased, while the yields of CH 4 and H 2 increased gradually. At higher temperature, the prolongation of the residence time will increase the degree of the secondary reaction and influence the distribution of pyrolytic products [5]. The pressure in the pyrolysis system of coal will affect the mass transfer process in the pyrolysis process, and the increase of the pressure will increase the resistance of the release of the primary volatiles, prolong the residence time, and lead to the intensification of the secondary reaction of the volatiles [6].…”