Massimiliano Comotti

Spatially and Size Selective Synthesis of Fe-Based Nanoparticles on Ordered Mesoporous Supports as Highly Active and Stable Catalysts for Ammonia Decomposition

Uniform and highly dispersed γ-Fe(2)O(3) nanoparticles with a diameter of ∼6 nm supported on CMK-5 carbons and C/SBA-15 composites were prepared via simple impregnation and thermal treatment. The nanostructures of these materials were characterized by XRD, Mössbauer spectroscopy, XPS, SEM, TEM, and nitrogen sorption. Due to the confinement effect of the mesoporous ordered matrices, γ-Fe(2)O(3) nanoparticles were fully immobilized within the channels of the supports. Even at high Fe-loadings (up to about 12 wt %) on CMK-5 carbon no iron species were detected on the external surface of the carbon support by XPS analysis and electron microscopy. Fe(2)O(3)/CMK-5 showed the highest ammonia decomposition activity of all previously described Fe-based catalysts in this reaction. Complete ammonia decomposition was achieved at 700 °C and space velocities as high as 60,000 cm(3) g(cat)(-1) h(-1). At a space velocity of 7500 cm(3) g(cat)(-1) h(-1), complete ammonia conversion was maintained at 600 °C for 20 h. After the reaction, the immobilized γ-Fe(2)O(3) nanoparticles were found to be converted to much smaller nanoparticles (γ-Fe(2)O(3) and a small fraction of nitride), which were still embedded within the carbon matrix. The Fe(2)O(3)/CMK-5 catalyst is much more active than the benchmark NiO/Al(2)O(3) catalyst at high space velocity, due to its highly developed mesoporosity. γ-Fe(2)O(3) nanoparticles supported on carbon-silica composites are structurally much more stable over extended periods of time but less active than those supported on carbon. TEM observation reveals that iron-based nanoparticles penetrate through the carbon layer and then are anchored on the silica walls, thus preventing them from moving and sintering. In this way, the stability of the carbon-silica catalyst is improved. Comparison with the silica supported iron oxide catalyst reveals that the presence of a thin layer of carbon is essential for increased catalytic activity.

Ordered mesoporous Co3O4 as highly active catalyst for low temperature CO-oxidation

Cubic ordered mesoporous Co3O4, prepared via the nanocasting pathway using KIT-6 as hard template, was found to be an excellent catalyst for low temperature CO oxidation, with the activity clearly depending on surface area and pore systems of the catalysts.

Embedded Ru@ZrO2 Catalysts for H2 Production by Ammonia Decomposition

Ammonia can be used as fuel in internal combustion engines (ICEs). In this case, a flame accelerator, such as hydrogen, is needed. H2 can be produced on‐board by partial decomposition of ammonia. In this work, ruthenium nanoparticles were embedded into a lanthanum‐stabilized zirconia (LSZ) support to obtain active and stable heterogeneous catalysts for NH3 decomposition. The effects of the preparation of both Ru nanoparticles and LSZ support were investigated. The embedded catalysts present high metal dispersion and good metal accessibility. Despite the relatively low metal loading (3 wt %), activity was very high in the temperature range 400–600 °C. The activity of the reference catalysts prepared by using classical impregnation was significantly lower under the same working conditions. Although many factors contribute to the final catalyst performances, the data reported confirm that the embedding strategy minimizes the undesirable sintering of the Ru nanoparticles, leading to promising and stable catalytic activity.

Ammonia Decomposition over Iron Phthalocyanine-Based Materials

Iron phthalocyanine‐based materials have been used herein as efficient catalysts for the ammonia decomposition reaction. These materials showed high activity, even superior to that showed by the commercial nickel‐based catalyst and iron‐doped carbon nanotubes, which were used as benchmarks in this study. Catalyst stability under reaction conditions appeared satisfactory, because no deactivation phenomena were observed. The type of the phthalocyanine precursor did not affect the catalytic performance; however, the preparation method had a strong effect. If the resulting material was exposed to the reaction conditions, some structural modification occurred. No clear correlation between phase composition and activity could be established because similar nitrogen content and similar crystalline domains in the sample led to different behaviors. However, the results of extensive characterization suggested that catalytic activities and conversion profiles were most likely dependent on material textural properties and thus on the preparation method used. The accessibility of iron species seems to be limited for catalysts prepared under vacuum. These phenomena are most likely responsible for the activation profile and for the low catalytic activity typical of these materials. In contrast, higher accessibility of iron species, typical of materials prepared under argon, would lead to improved and stable catalytic performance.