Spray-Flame Synthesis of LaMnO_3+δ Nanoparticles for Selective CO Oxidation (SELOX)

Abstract

LaMnO3+δ nanoperovskites were prepared via the continuous and scalable spray-flame synthesis (SFS) technique from metal nitrate-based solutions by using either ethanol (EtOH) as solvent or a mixture of ethanol (50 vol %) and 2-ethylhexanoic acid (50 vol %) (EtOH/2-EHA). Solutions based on pure EtOH generated a mixture of several phases and a broad and multimodal particle size distribution, which is attributed to a combination of gas-to-particle and droplet-to particle formation of particles. The product contained a bimodal distribution of the orthorhombic (Pnma II) LaMnO3 perovskite-like phase and additional, unwanted phases such as La2O3 and sub-20 nm Mn-rich amorphous/poorly crystalline particles. The incorporation of 2-EHA led to high surface area (>100 m2 g–1), small, and crystalline LaMnO3+δ nanoparticles with sizes ranging between 4 and 15 nm in the presence of few sub-200 nm particles (<10 wt %). This sample is mainly composed of the orthorhombic Mn4+ rich (Pnma I) LaMnO3+δ phase, and it counts with a very high specific surface area that makes it highly promising for catalytic applications. FTIR and UV–VIS spectroscopy of the precursor solutions revealed the oxidation of the Mn2+ precursor in advance of the particle formation process along with the esterification of the solvent mixture. It is assumed that the observed liquid-phase oxidation supports the formation of Mn4+-rich perovskites. According to O2-TPD and H2-TPR measurements, the EtOH/2-EHA sample presented a much higher formation of adsorbed active oxygen species and higher reducibility than the EtOH-made material, leading to a superior performance for both the catalytic oxidation of CO and the selective oxidation (SELOX) of CO.

Virtual Special Issue of Recent Advances in Gas-Phase Synthesis of Functional Materials for Energy

“…Three papers demonstrate the outstanding possibilities provided by gas-phase synthesis for the generation and applications of tailored materials. Angel et al present the synthesis of LaMnO 3+δ nanoperovskites in spray flames and demonstrate excellent catalytic activity for selective CO oxidation. Deligiannakis et al showcase a sequential-deposition spray-flame technique to produce PdO/Pd 0 /TiO 2 nanocrystals for the application of H 2 production via HCOOH dehydrogenation at near-ambient pressure and temperature.…”

“…Ren et al10 present a single-droplet model to describe multicomponent droplet combustion with the consideration of micro explosion, precursor reaction, and particle formation, aiming to elucidate the droplet-to-particle conversion route in spray-flame synthesis of nanoparticles.Three papers demonstrate the outstanding possibilities provided by gas-phase synthesis for the generation and applications of tailored materials. Angel et al11 present the synthesis of LaMnO 3+δ nanoperovskites in spray flames and demonstrate excellent catalytic activity for selective CO oxidation. Deligiannakis et al12 showcase a sequentialdeposition spray-flame technique to produce PdO/Pd 0 /TiO 2 nanocrystals for the application of H 2 production via HCOOH dehydrogenation at near-ambient pressure and temperature.…”

Manganese Oxide-Based Catalysts for Soot Oxidation: A Review on the Recent Advances and Future Directions

“…Furthermore, Mn-based materials can be easily modified by other elements due to their high structure flexibilities. Therefore, it is not surprising that many different Mn-based oxides have been synthesized through various methods such as the flame spray pyrolysis and sol–gel method and more. , …”

“…Therefore, it is not surprising that many different Mn-based oxides have been synthesized through various methods 39 such as the flame spray pyrolysis and sol−gel method and more. 40,41 The soot−catalyst oxidation process is sensitive to various influential factors, such as the soot composition, soot−catalyst contact conditions, and structure of the very catalyst. For example, the catalytic activities of manganese oxides may be enhanced by adding dopants or incorporating various elements into the crystal lattice.…”

Facile synthesis of nanostructured perovskites by precursor accumulation on nanocarbons

“…The low-temperature calcination of the gel yielded nanosized perovskites. In addition to the sol–gel method, other solution-based approaches, such as coprecipitation, 10,14,15 combustion, 16–18 flame-spray, 19–22 and microemulsion methods, 23,24 have been explored. Recently, other novel processes to synthesize nano-perovskites have also been reported, such as solid-state gelation and molten-salt-protected pyrolysis.…”