Said Laassiri

Clear microstructure-performance relationships in Mn-containing perovskite and hexaaluminate compounds prepared by activated reactive synthesis.

Microstructural properties of mixed oxides play essential roles in their oxygen mobility and consequently in their catalytic performances. Two families of mixed oxides (perovskite and hexaaluminate) with different microstructural features, such as crystal size and specific surface area, were prepared using the activated reactive synthesis (ARS) method. It was shown that ARS is a flexible route to synthesize both mixed oxides with nano-scale crystal size and high specific surface area. Redox properties and oxygen mobility were found to be strongly affected by the material microstructure. Catalytic activities of hexaaluminate and perovskite materials for methane oxidation were discussed in the light of structural, redox and oxygen mobility properties.

Solvent free synthesis of nanocrystalline hexaaluminate-type mixed oxides with high specific surface areas for CO oxidation reaction

Nanocrystalline hexaaluminate-type mixed oxides having crystallite sizes of around 20 nm and high surface areas (>77 m2 g−1) were synthesized using an original mechanosynthesis technique. These nanocrystalline materials were evidenced to be highly active heterogeneous catalysts compared to the conventional parent materials.

Waste-free scale up synthesis of nanocrystalline hexaaluminate: properties in oxygen transfer and oxidation reactions

Synthesis of nanocrystalline hexaaluminate is reported using an original activated reactive synthesis process. Starting from a classical ceramic solid, exhibiting low surface area and a micrometric crystal size, a two-step grinding process allows reduction of the crystal size down to a few nanometers and development of high surface areas. The synthetic process was then used to produce transition metal- and noble metal-doped structures. The effects of (i) morphological and structural properties and (ii) substitution on oxygen transfer properties and catalytic properties in CO and CH4 oxidation reactions were studied. Crystal size was shown to be a key parameter in controlling the bulk oxygen transfer. Study of the catalytic properties in low and high temperature oxidation reactions also shows the crucial effect of the morphological parameters. Highest activities were achieved over nanocrystalline high surface compositions. Finally, even if less active than classical palladium supported solids, these new structures exhibited extremely high thermal stability.

Role of Mn+ cations in the redox and oxygen transfer properties of BaMxAl12−xO19−δ (M = Mn, Fe, Co) nanomaterials for high temperature methane oxidation

BaMxAl12−xO19−δ (M = Mn, Fe, Co, x = 1, 2) hexaaluminate nanomaterials were successfully prepared using the ARS (Activated Reactive Synthesis) process, a top-down and solvent free original synthesis route. The crystal sizes of the nanomaterials range at 24 ± 2 nm, which allows them to display high surface area (from 60 to 100 m2 g−1). The role of Mn+ cations in the redox and oxygen transfer properties of the nanomaterials was studied by H2-TPR and 18O/16O isotopic exchange, respectively. The nature of the transition metal as well as its content is observed to play a key role in the oxygen transfer properties. The catalytic properties of the nano-hexaaluminates, evaluated for methane oxidation, a reaction involving severe conditions (high temperature), resulted from multiple factors including oxygen transfer properties and transition metal valence and concentration on the surface.

Methane Cracking over Cobalt Molybdenum Carbides

The catalytic behaviour of Co3Mo3C, Co6Mo6C, Co3Mo3N and Co6Mo6N for methane cracking has been studied to determine the relationship between the methane cracking activity and the chemical composition. The characterisation of post-reaction samples showed a complex phase composition with the presence of Co3Mo3C, α-Co and β-Mo2C as catalytic phases and the deposition of different forms of carbon during reaction.Graphical Abstract