The fabrication of supported catalysts consisting of colloidal iron oxide nanocrystals with tunable size, geometry, and loading—homogeneously dispersed on carbon nanotube (CNT) supports—is described herein. The catalyst synthesis is performed in a two-step approach. First, colloidal iron and iron oxide nanocrystals with a narrow size distribution are produced. Second, the nanocrystals are attached to CNT grains serving as support structure. Important features, like iron loading and nanocrystal density on the CNT support, are controlled by changing the nanocrystal concentration and ligand concentration, respectively. The Fischer–Tropsch performance reveals these new materials to be active, selective toward lower olefins (60% C of hydrocarbons produced in the absence of promoters), and remarkably stable against particle growth.

A major cause of supported metal catalyst deactivation is particle growth by Ostwald ripening. Nickel catalysts, used in the methanation reaction, may suffer greatly from this through the formation of [Ni(CO)₄]. By analyzing catalysts with various particle sizes and spatial distributions, the interparticle distance was found to have little effect on the stability, because formation and decomposition of nickel carbonyl rather than diffusion was rate limiting. Small particles (3–4 nm) were found to grow very large (20–200 nm), involving local destruction of the support, which was detrimental to the catalyst stability. However, medium sized particles (8 nm) remained confined by the pores of the support displaying enhanced stability, and an activity 3 times higher than initially small particles after 150 h. Physical modeling suggests that the higher [Ni(CO)₄] supersaturation in catalysts with smaller particles enabled them to overcome the mechanical resistance of the support. Understanding the interplay of particle size and support properties related to the stability of nanoparticles offers the prospect of novel strategies to develop more stable nanostructured materials, also for applications beyond catalysis.

A major cause of supported metal catalyst deactivation is particle growth by Ostwald ripening. Nickel catalysts, used in the methanation reaction, may suffer greatly from this through the formation of [Ni(CO)₄]. By analyzing catalysts with various particle sizes and spatial distributions, the interparticle distance was found to have little effect on the stability, because formation and decomposition of nickel carbonyl rather than diffusion was rate limiting. Small particles (3–4 nm) were found to grow very large (20–200 nm), involving local destruction of the support, which was detrimental to the catalyst stability. However, medium sized particles (8 nm) remained confined by the pores of the support displaying enhanced stability, and an activity 3 times higher than initially small particles after 150 h. Physical modeling suggests that the higher [Ni(CO)₄] supersaturation in catalysts with smaller particles enabled them to overcome the mechanical resistance of the support. Understanding the interplay of particle size and support properties related to the stability of nanoparticles offers the prospect of novel strategies to develop more stable nanostructured materials, also for applications beyond catalysis.

Pd nanoparticles were synthesized on nonfunctionalized and functionalized SBA-15 grafted with thiol or amine groups. The resulting materials were used as catalysts to study the influence of these functional groups for a similar Pd particle size of approximately 2 nm on the Heck reaction that uses iodide substrates. The nonfunctionalized catalysts lost their activity quickly because of Pd leaching and particle growth. However, if a mixed solvent that consisted of toluene and DMF was used and thiol groups were grafted on SBA-15, we were able to reduce the Pd leaching and particle growth to thus obtain a more stable catalyst in which an important role of the ligands was to recapture Pd. However, heterogeneity tests, such as a hot filtration test and poisoning experiments, gave a strong indication that Pd still leached from the support and that homogeneous Pd species were mainly responsible for the activity. Pd on S-functionalized SBA-15 was able to catalyze the Heck reaction using different substrates to achieve good activity and selectivity in most cases.

Bulk lanthanum oxide and lanthanum oxide supported on carbon nanofibers were studied as solid base catalysts. The impact of synthesis parameters on the supported catalysts, deposition method, aging, washing, and heat treatment temperature were investigated and evaluated by studying the catalytic activities in the self-condensation reaction of acetone to diacetone alcohol. The initial activity of the carbon nanofiber (CNF) supported lanthanum oxide catalysts (48 mmol_DAA h⁻¹ g_catalyst⁻¹, DAA=diacetone alcohol) was up by one order of magnitude compared to the activity of the bulk lanthanum oxide (4.4 mmol_DAA h⁻¹ g_catalyst⁻¹). The most active catalyst reported here was 12 wt % La₂O₃/CNF, prepared from a lanthanum nitrate precursor by precipitation with ammonia, followed by washing, drying, and heating at temperatures between 600–700 °C in nitrogen to activate the catalyst. Initial enthalpies for CO₂ adsorption, determined by using micro calorimetry, are approximately 155 kJ mol⁻¹ (CO₂ uptake 0–5 μmol g⁻¹) for supported samples with 12 wt % La₂O₃. TEM revealed well-distributed and small (≈4 nm) lanthanum oxide particles on the support.

The efficiency of filling carbon nanotubes (CNTs) by ultrasound-assisted wet impregnation is quantified by electron tomography (ET). For image analysis, a method that combines edge detection with single-value thresholding is proposed and validated. A high proportion (80 wt %) of the ruthenium was deposited inside the tube at an average particle size of 2–4 nm. Particles located on the outer surface of the CNT had a size of 1–3 nm. The local ruthenium loading measured by ET (3.2 wt %) closely matched the value from elemental analysis (3.5 wt %). In addition, a few 1 nm-sized ruthenium particles were detected inside the carbon wall, which contained pores/cracks. Direct imaging and quantification is a powerful tool to understand and possibly model the unique properties of CNT-based catalysts.