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

Abstract

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.

Interplay between pore size and nanoparticle spatial distribution: Consequences for the stability of CuZn/SiO2 methanol synthesis catalysts

“…The design and synthesis of catalysts with enhanced stability requires a fundamental understanding of the factors governing metal particle growth [25,26,27,28]. The influence of catalyst composition and structure on metal particle growth has been previously studied for several systems [29,30,31,32].…”

H2 Production via Ammonia Decomposition Using Non-Noble Metal Catalysts: A Review

“…From the data presented in Table 1 for supported systems, the rate of hydrogen formation (at 500°C) is highest for the 6 nm Fe nanoparticles supported on CMK-5 [51], suggesting that small iron nanoparticles are more active for ammonia decomposition although the extent of validity of this conclusion needs to be corroborated by further work in this area. Although, this conclusion is in agreement with computational simulations of iron clusters which suggest that nano-sized particles of iron less than 10 nm in diameter increase catalytic activity [40].…”

“…Research has been mainly focused on carbon materials with metal oxides being used primarily as promoters rather than supports. Carbon materials have high thermal stability and electrical conductivity, making them attractive catalyst supports [51]. Depending on the properties of the carbon support, especially its surface area and porosity, and the iron impregnation method, iron nanoparticles of different sizes have been achieved.…”

“…Depending on the properties of the carbon support, especially its surface area and porosity, and the iron impregnation method, iron nanoparticles of different sizes have been achieved. Iron nanoparticles with average sizes of *6 nm in diameter were stabilised on CMK-5 support (a mesoporous carbon with a dual pore network, which is formed by the templating of SBA-15 porous silica structure and subsequent removal of the template) and carbonised SBA-15 (similar to the previous support but with the SBA-15 template present) [51]. Fe/CMK-5 was found to be a more active catalyst (515 mol H 2 mol …”

Interfacial assembly of mesoporous nanopyramids as ultrasensitive cellular interfaces featuring efficient direct electrochemistry

“…The X-ray photoelectron spectroscopy analysis demonstrates one main peak of O 1s (~533 eV), two peaks of Fe 2p 1/2 and 2p 3/2 in Fe 2 O 3 at~725 and 710 eV, respectively, and peaks of~87.5 and 83.8 eV, which correspond to 4f 5/2 and 4f 7/2 of Au, respectively, and indicate that the NPI films are primarily coated with metal Au 0 particles (Supplementary Figure 11). 47 The electron dispersive X-ray spectra and mapping reveal that the Au nanoparticles are uniformly deposited on the surface of the iron oxide NPIs (Supplementary Figure 12).…”