The use of preformed nanoparticles in the production of heterogeneous catalysts

Abstract

Preformed iron oxide nanoparticles have been successfully assembled onto alumina and MCM-41 support materials. The particles are found to disperse evenly over the surface of the silicate; however, in the case of the alumina we find that in addition to areas of even distribution there is also some clustering of the particles. The materials are stable under heat treatment, with no signs of further aggregation during calcination. We investigate the reducibility of the materials through H 2 -TPR studies and we find that the particles are reducible around 500-550 o C. The reduction process is complete at temperatures where MCM-41 can undergo degradation, supporting that the alumina based materials are more suited to the multiple base oxidation reduction steps in the catalytic cycle.

Fabrication of Fischer–Tropsch Catalysts by Deposition of Iron Nanocrystals on Carbon Nanotubes

“…The literature offers a few examples of the use of colloidal nanocrystals for heterogeneous catalysis and in particular to improve the nanocrystal dispersion in FT catalysts . In these contributions, the deposition of the nanocrystals on the substrate is performed by deposition precipitation or impregnation of the substrate with a suspension of nanocrystals in the liquid phase, or by destabilizing the colloidal suspension by the addition of a nonsolvent, which can eventually cause aggregation of the nanocrystals.…”

Supported heterogeneous catalysts: what controls cobalt nanoparticle dispersion on alumina?

“…On addition to the support, the black nanoparticle suspension instantaneously became colourless, suggesting particles adhered to the support quickly in comparison to systems based on iron that typically took a few to several hours. 18,19,21 Bright field TEM images of typical uncalcined nanomaterial are shown in Fig. 1.…”

“…Despite the ease of preparation of these materials and the demonstrated stability during calcination, there are few reports involving the assemblage of preformed particles onto a support. [17][18][19][20][21][22] Catalytic performance is not only determined by composition, size and shape of the metal species. Dispersion is also a key consideration for the development of catalysts.…”

“…Traditional FT catalysts based on metal clusters, have been known to aggregate 10 but preformed nanoparticle catalysts have shown both good dispersion in addition to aggregation. 21 How particles assemble over a support and the rate at which this occurs is the result of a number of factors including surfactant choice, particle size and morphology, zeta potential, support surface, and temperature. 21 These factors influence the competing interactions (van der Waals, steric, magnetic and electrostatic interactions) that occur between the nanoparticles themselves and the nanoparticles and the substrate.…”

“…21 How particles assemble over a support and the rate at which this occurs is the result of a number of factors including surfactant choice, particle size and morphology, zeta potential, support surface, and temperature. 21 These factors influence the competing interactions (van der Waals, steric, magnetic and electrostatic interactions) that occur between the nanoparticles themselves and the nanoparticles and the substrate. 24 This competition results in the complex particle dynamics manifesting in deposition patterns on the support material.…”