*3.3. Catalytic Activity Measurements*

Catalytic performances were evaluated in the gas phase toluene oxidation reaction. A mass of catalyst equal to 0.200 g was positioned in a fixed bed reactor and was heated from 25 ◦C to 330 ◦C for30 min (2 ◦C·min−1) under synthetic air flow. Then, the reaction flow, composed of 1000 ppmv of toluene diluted in synthetic air, was stabilized at a flow rate of 100 mL·min−<sup>1</sup> (given a Weight Hourly Space Velocity of 30,000 mL·h−1·g−1) and the reactor temperature was allowed to decrease from 300 ◦C to 150 ◦C at a constant temperature decrease rate of <sup>−</sup>0.5 ◦C·min<sup>−</sup>1. Stability experiments were performed during 70 h at a constant temperature of 285 ◦C. Exhaust gases were analyzed by gas chromatography and the results were expressed in terms of toluene conversion into carbon dioxide: X(%) = 100·[CO2]out/(7·[C7H8]in). To quantify the resistance against deactivation an activity coefficient a285 was defined as the ratio between the toluene conversion after 70 h reaction to that at initial time.

## **4. Conclusions**

Mn- and Fe-containing perovskite were synthesized by a three-step reactive grinding process followed by calcination at 400 ◦C for 3 h. The reactive grinding process involved a first step resulting in the obtention of a crystalline perovskite at high temperature (solid state reaction) followed by a second step of HEBM affording a mean crystal size decrease to end up with a LBEM step performed in wet conditions for surface area improvement. Nanocrystalline LaMnO3.15 and LaFeO3 were obtained (crystal size range of 14–22 nm obtained after milling steps). The most efficient LEBM was found for the LaFeO3 formulation allowing it to reach a SSA of 18.8 m2·g<sup>−</sup>1. It was noted that the TM reducibility was significantly affected by the HEBM step through the lowering of the crystal size leading to a decrease of the temperature of reduction of the Mn(+IV) and Fe(+III) species. XPS analysis evidenced the important effect of the grinding steps on the surface composition. Catalytic tests provided evidence of the importance of the catalyst SSA for the conversion of toluene. Then, while comparable activation energies were estimated for both perovskite compositions (Mn and Fe), from the overall results it was

found that: (i) a higher intrinsic activity for the Mn-compositions than for the Fe-compositions due to a better redox behavior; (ii) a higher weight activity for Fe-compositions due to higher surface areas. Finally, while Mn-formulations deactivated significantly (−30% after 70 h on stream), far better stability was reported for Fe-formulations.

**Author Contributions:** B.H. prepared the materials, conducted the experiments and wrote the first draft of the paper. J.-F.L., S.R. and H.A. supervised the work. All authors contributed to the data interpretation, the discussion and the revision of the paper.

**Funding:** B.H. thanks Laval University (Canada) and Lille University (France) for funding his joint PhD. The "DepollutAir" project (grant number 1.1.18) of the European Program INTERREG V France-Wallonie-Flanders (FEDER), Chevreul institute (FR 2638), Ministère de l'Enseignement Supérieur et de la Recherche and Région Hauts-de-France are acknowledged for the funding and their support for this work.

**Conflicts of Interest:** The authors declare no conflict of interest.
