Investigation of Particle Atomic Layer Deposition of Metal Precursor on Silica Supports for Catalytic Decomposition of Methane

In the United States, natural gas that exceeds demand is readily burned or flared, contributing GHGs such as methane and CO₂ to the atmosphere. Over the past ten years, this value has exceeded an average of 300,000 million cubic feet¹. To reduce GHG emissions and increase profitability in utilizing this waste flare gas stream, we are investigating a comprehensive chemical vapor deposition process in which methane is converted to hydrogen and carbon nanoproducts (CNPs) through the catalytic decomposition of methane (CDM), which relies on a precisely designed metal catalyst.

We propose synthesizing this catalyst using particle atomic layer deposition (ALD) of a transition metal precursor onto a silica support in a fluidized bed reactor. Particle ALD facilitates precise nanoparticle deposition on a substrate through repeated self-limiting half reactions in which a metal precursor is first deposited onto the substrate, followed by a second half reaction in which the remaining metal precursor ligand is removed, leaving a supported metal catalyst. The metal precursor is introduced to the fluidized bed reactor through the sublimation of a metallocene in a heated chamber. Dosing cycles of the metal precursor and reducing agent are repeated until the desired metal particle size, dispersion, and loading are reached. ALD is evaluated via mass spectrometry and carbon combustion analysis, metal loading on the silica support is measured via ICP-OES, and metal nanoparticle size and distribution is qualitatively measured with SEM-EDS. Metal loading and distribution is further evaluated by comparing silica substrates of varied physical properties such as surface area and density.

The investigation of particle ALD performance with this metal and substrate will inform optimal catalyst designs through precision of metal loading and metal nanoparticle distribution. Furthermore, results from this investigation will contribute to the ongoing experiments in producing hydrogen and carbon nanoproducts via catalytic decomposition of methane.

¹ “U.S. Natural Gas Vented and Flared.” U.S. Energy Information Administration, 30 Sept. 2022, https://www.eia.gov/dnav/ng/ng_prod_sum_a_EPG0_VGV_mmcf_a.htm. Accessed 13 Oct. 2022.