Mechanical alloying (MA) has been and continues to be thoroughly examined for creating structural materials, but the production of catalysts is relatively rare. This is especially true for catalysts used in the production of carbon nanofibers (CNFs), a versatile material for applications such as energy storage, catalyst support, advanced composites and others. The application of MA to create CNFs presents a valuable tool in reducing their cost and complexity, and thereby may increase their commercial potential. In this study, the effects of milling duration on CNF deposition are studied by the complementary methods of X-ray diffraction, compositional mapping, electron microscopy, particle size analysis and surface area analysis. These were used to determine microstructural and macroscale evolution of the catalyst powder and its effects on the kinetics and characteristics of carbon deposition using Ni and Ni 30 at % Cu. The results have important implications for low cost catalyst production and provide general guidance on the development of catalytic materials in miscible systems.

Carbon nanofibers were generated over bimetallic catalysts in an atmospheric pressure chemical vapor deposition (APCVD) reactor. Catalyst compositions of Fe 30 at%, Cu and Ni 30 at% and Cu were mechanically alloyed using high-energy ball milling over durations of 4, 8, 12, 16, and 20 h. The catalyst powders were then used to produce carbon nanofibers in ethylene and hydrogen (4:1) at temperatures of 500, 550, and 600 °C. The microstructures of the catalysts were characterized as a function of milling time as well as at deposition temperature. The corresponding carbon deposition rates were assessed and are correlated to the microstructural features of each catalyst. The milling process directly determines the performance of each catalyst toward carbon deposition, and both catalysts performed comparably to those made by traditional co-precipitation methods. Considerations in miscible and immiscible nanostructured alloy systems are discussed.

Bimetallic catalysts can provide enhanced performance, and Co-based catalysts in particular have been studied in various respects for their activity in the deposition of carbon nanofibers (CNFs). The majority of studies on CNF catalysis use co-precipitation to create alloys, but recent work has demonstrated the suitability of mechanical alloying (MA) by ball milling to reduce cost and increase catalytic activity. This work establishes the unique ability of MA to control the microstructure to produce bimetallic composites, which retain distinct metallic phases that improve catalytic activity. It is demonstrated that Co-Pd alloys reach a maximum in catalytic activity at an intermediate time of mechanical activation, where 30 min of milling outperformed samples milled for 5, 15, 60, and 240 min at a reaction temperature of 550 °C and a 1:4 C₂H₄:H₂ reactant ratio. This indicates there is benefit to retaining the metals in distinct phases in close proximity. Ball milling provides a relatively simple and scalable method to achieve these unique microstructures, and in the optimal condition tested here, the activity toward carbon deposition is increased fourfold over prior work. Furthermore, the minimum temperature for deposition is also reduced. The characteristics of these materials, the effects of milling and annealing, and the underlying mechanisms of deposition are discussed.