(721f) Insight into the Effects of Ni-Support Interactions on Enhanced Selectivity of Base-Growth CNTs and COx-Free H2 Production from Thermocatalytic Decomposition of Methane

The abundance of natural gas resources and a surge in demand for CO₂-free hydrogen presents opportunities to develop novel chemical processes for natural gas conversion into more valuable fuels and chemicals. Thermocatalytic decomposition of methane, the major constituent of natural gas, is one potential route as it produces hydrogen and solid carbon in one step and eliminates the need for further CO conversion and/or CO₂ removal. This produces CO₂-free H₂, which has application for low temperature fuel cells, and also generates valuable carbon nanotubes (CNTs) or nanofibers. Commercial processes exist for synthesis of carbon nanotubes, however, are not suitable for large-scale industrial production of hydrogen, since they consume a large amount of energy and do not feed methane into the reactor continuously. Thermocatalytic decomposition of methane using continuous flow reactors is a promising route for large scale production of both hydrogen and carbon nanotube or fiber production. However, no methods have progressed to commercial stage and technical challenges persist.

We have investigated the development of catalyst(s) that promote “base grown” versus “tip grown” CNT formation. Base grown CNTs offer the potential for easier catalyst regenerability while also generating a highly pure and crystalline carbon product. In this presentation we report on a series of Ni-based catalysts prepared using different supports. Supports investigated include gamma-Al₂O₃, Al₂O₃ aerogel, and alumina spinel formulations. Catalysts were characterized using XRD, BET, TPR, HRTEM, and H₂-Chemisoprtion techniques. Catalytic activities were evaluated using different pretreatment methods and operating temperatures; both variables critically affecting catalytic performance. Metal-support interaction was found to influence the resulting nickel metal particle size and distribution, as well as the morphology of produced CNTs (e.g., tip versus base growth). Spent samples were characterized using HRTEM, Raman spectroscopy, and TPO analysis.