**1. Introduction**

Volatile organic compounds (VOCs) are responsible of important environmental and health issues such as greenhouse gas effect, tropospheric ozone accumulation or CMR (carcinogenic, mutagenic or reprotoxic) behavior on animals and human beings. Those chemicals are generated from both natural and anthropogenic sources, the latter being the most significant. Industry is a major contributor to the VOC emissions, with a huge consumption of chemicals, especially benzene, toluene and xylene (BTX) mainly used as precursors or organic solvents [1,2]. Toluene is, for example, a potential CMR and has consequent greenhouse power [3,4]. Professional exposure limits have been set up to protect workers with respectively 50 and 100 ppmv values for the long- and short-term exposition for the European Union [5]. Over the last two last decades, VOC emissions have been highly reduced to fit the stringent environmental regulations [2,6]. While chemical substitution has to be privileged, this alternative is difficult to adapt to industrial processes which are already well-optimized. Then, catalytic oxidation processes as a post-treatment solution, play a major role in VOC emissions control with attractive characteristics: limited energy consumption as well as complete and selective elimination of pollutants. Supported noble metal catalysts are active catalysts even at low temperature [7] but they generally suffer from a deactivation over time by poisoning [8,9]. Increasing the cost and rarefication

of these resources limit their wide use [10]. Alternatives to noble metal catalysts are transition metal oxides, being of lower cost and some of them showing interesting catalytic performances in oxidation reactions [11,12]. Among them are perovskites-like mixed oxides, commonly described by the general formula ABO3 where A is an alkaline, an alkaline earth or a rare-earth cation and B is a transition metal. With numerous possible A and B associations, properties of perovskite-like materials can be fine-tuned regarding the targeted application [13–15]. Properties of perovskites are closely related to their synthesis method [16–18]. Parameters being identified as crucial are specific surface area (SSA), crystal domain size and transition metal surface accessibility, all parameters having an effect on cation reducibility and then on catalytic activity. Among the different compositions, LaMnO3.15 and LaFeO3 are of particular interest. LaMnO3.15 shows excellent catalytic performances related to MnIV/MnIII mixed valence stabilized in the structure (charge neutrality being reached with cationic vacancies). Considering a lower reducibility of the iron cations in the crystal (leading to a lower activity than those of the Co- and Mn-counterparts), LaFeO3 is far less studied, except for high temperature application due to its good stability [14].

As the important parameter that directly impacts the catalytic activity is the specific surface area. While solid state reaction route produces material with low specific surface area, not ideal in view of a catalytic application, solution-mediated synthesis routes give access to materials with better textural properties, but they can hardly be considered as a sustainable solution because of the consumption of solvent. On the other hand, reactive grinding (RG) is a common approach used in metallurgy that shows attractive features such as flexibility, low temperature, atmospheric pressure, no use of solvents (or in a small amount) [19,20]. Reactive grinding has then already been proved to be efficient to produce catalysts such as MnO2, several hexaaluminates and perovskites [21–24]. In this work, nanocrystalline LaMnO3 and LaFeO3 perovskites-type mixed oxides, exhibiting high specific surface areas, are obtained by a three-step reactive grinding synthesis. The selected synthesis sequence consists in: (1) a solid-state reaction step, starting with selected single oxides to obtain the perovskite phase, (2) the structural modification (crystal size decrease) with high-energy ball milling (HEBM) step, and finally, (3) a low-energy ball milling (LEBM) for surface area development. Solids are characterized at each step of the synthesis, and catalytic performances as well as stability behavior of LaMnO3.15 and LaFeO3, are reported for the toluene total oxidation reaction.
