Industrially Produced Fe- and Mn-Based Perovskites: Effect of Synthesis on Reactivity in Three-Way Catalysis: Part 2

Abstract

Mn-based perovskites obtained by two different industrial procedures [flame spray pyrolysis (FSP) and co-precipitation (COP)] have been extensively compared in terms of chemical, structural, and morphological properties with the aim of evaluating how the upscale of complex catalysts can affect the functionality. The transition between laboratory and production scale is, in fact, usually not straightforward. The catalytic activity was tested focusing on reactions of relevance in the abatement of pollutants. In particular, CO-assisted NO reduction (which could be also considered as a model reaction) and reactions with a synthetic automotive exhaust mixture, including 10% steam and oxygen, were carried out. The development of three-way catalysts is still a relevant question: noble metal-free, efficient catalysts are even more necessary in hybrid vehicles. For this purpose, the catalytic activity of the samples has been correlated with the characterization results and thus with the peculiar aspects of the production method. Relevant differences have been observed between COP and FSP catalysts, in terms of the specific surface area, surface composition, and presence of surface-active sites. Also, the different efficiencies of inserting dopants in the perovskite unit cell and thus in reducibility and ion mobility are relevant. Despite having the same composition and crystalline structure, the catalytic activity and the effect of pre-treatments are observed to depend on the production procedure.

Optimizing Citrate Combustion Synthesis of A-Site-Deficient La,Mn-Based Perovskites: Application for Catalytic CH4 Combustion in Stoichiometric Conditions

“…The average perovskite composition until a depth of ~1 µm was explored by energydispersive X-ray analysis (EDX), and the average surface composition (depth of 5-10 nm) was explored by X-ray photoelectron spectroscopy (XPS). Element percentages are reported in Table S1 and Table 3, with and without considering the oxygen content, respectively, which is always excessive at the surface as well as in bulk, as usually occurs for perovskite oxides [28,29]. For all samples, all the expected elements (O, La, Mn, Ni/Cu, if any) were detected by both EDX and XPS, without evidence of a significant amount of impurities.…”