Reactive Grinding Synthesis of LaBO3 (B: Mn, Fe) Perovskite; Properties for Toluene Total Oxidation

Abstract

LaBO3 (B: Mn, Fe) perovskites were synthesized using a three-step reactive grinding process followed by a calcination at 400 °C for 3 h. The three successive steps are: (i) solid state synthesis (SSR); (ii) high-energy ball milling (HEBM); (iii) low-energy ball milling (LEBM) in wet conditions. The impact of each step of the synthesis on the material characteristics was deeply investigated using physico-chemical techniques (X-ray diffraction (XRD), N2-physisorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), temperature-programmed reduction (H2-TPR), X-ray photoelectron spectroscopy (XPS)) and the catalytic performances of the synthesized materials were evaluated for the toluene total oxidation reaction. Starting from single oxides, microcrystalline perovskite phase, exhibiting negligible surface areas, is obtained after the SSR step. The HEBM step leads to a drastic reduction of the mean crystal size down to ~20 nm, along with formation of dense aggregates. Due to this strong aggregation, surface area remains low, typically below 4 m2·g−1. In contrast, the second grinding step, namely LEBM, allows particle deagglomeration resulting in increasing the surface area up to 18.8 m2·g−1 for LaFeO3. Regardless of the perovskite composition, the performance toward toluene oxidation reaction increases at each step of the process: SSR < HEBM < LEBM.

Reactive Grinding synthesis of La(Sr,Ce)CoO3 and their properties in toluene catalytic total oxidation

“…In agreement with the Sr and Ce promotional effects, lower activation energy values are obtained for the Sr‐ and Ce‐doped catalysts, ranging from 166 to 153 kJ ⋅ mol −1 . Theses Ea values are slightly higher than the ones observed for LaMnO 3 and LaFeO 3 systems in the exact same conditions or La 1‐x Ca x BO 3 (B=Fe, Ni) systems by Pecchi et al. .…”

“…Calculated values are in the range of 15 to 20 nm, the unsubstituted sample having the lowest value of 15 nm. Those values are consistent with already reported perovskite synthesized by reactive grinding…”

“…The gain from the low energy ball milling process is dependent of the perovskite composition and substitution is commonly found to increase specific surface area up to a certain extent . The absence of change in SSA underlines the key role of the medium, ethanol instead of water, used during the LEBM process for the particle deagglomeration and affording a constant value of surface area whatever the perovskite composition.…”

Mechanochemical Synthesis of Catalytic Materials

“…Serendipitously, this led to the formation of an exotic mixed perovskite (LaCo 1− x Fe x + ϵ O 3− δ ), highlighting the great potential of mechanochemical processing for the preparation of complex systems [126–128] . In fact, other mixed LaMO 3 (M=Co, Mn, Fe, Mg, or Ti) perovskites—such as LaCo 1− x Cu x O 3 , LaCo 1− x Pd x O 3 , LaMn 1− x Cu x O 3 , LaFe 1− x Cu x O 3 , LaTi 0.5 Mg 0.5 O 3 , and LaTi 0.4 Mg y Fe x O 3 —were produced by ball milling [129–136] . Interestingly, the synthesis of ABO 3 perovskites, with A=Ca, Bi, or Ba and B=Mn, Ti, Zr, or Fe, was also achieved mechanochemically [137–139] .…”

Catalysis by Metals on Perovskite-Type Oxides

“…A series of LaCo Finally, a three-step reactive grinding process including solid-state synthesis, high-energy ball milling, and low-energy ball milling in wet conditions followed by calcination at 400 • C is used to prepare LaMnO 3 and LaFeO 3 by Heidinger et al [9]. In both cases, the catalytic performance for toluene oxidation increases after each synthesis step of the process in line with the increase in specific surface area that reaches ca.…”