(Invited) Nanowire Catalysts and Adsorbents
Authors: Sunkara Mahendra , Nouduri Abhinav , Kannapu Hari Prasad Reddy , Meduri Praveen 
Published: August 2024

The unique properties of nanowire materials like fast charge transport, short diffusion length, controlled surface sites and single crystal nature make them ideal for designing high performance catalysts, adsorbents and electrocatalysts by design. To realize any of these applications, one would need either large quantities of nanowire powders or nanowire arrays on large areas. In this presentation, we will highlight our group’s efforts with scalable methods for continuous manufacturing of nanowire powders and arrays for oxides1 and III-nitride materials.2 The process for producing metal oxide nanowires has been scaled up to ton-scale. The resulting nanowire powders can be used to formulate unique catalyst and adsorbent products.
Zinc oxide nanowires alloyed with catalytically active metals and have been formulated into ultra-deep desulfurization catalytic adsorbents.3,4 These materials exhibited ultra-deep desulfurization with sulfur removal down to 1 ppm or below for liquid hydrocarbons (diesel, gasoline and naphthalene) and to less than 1 ppb for natural gas. The desulfurization mechanism does not involve formation of H2S species unlike that typically observed with hydro-desulfurization process involving sulfided catalysts.
Titania nanowires supported with nickel and molybdenum clusters have also shown to exhibit high activity and durability as hydro-desulfurization catalysts for removal of sulfur from hydrocarbons by forming H2S.5 The synergistic activity with MoS2 and titania are expected to contribute to enhanced activity with desulfurization.
Alloying of nanowires with other elements is also studied to produce compound and alloyed nanowires. Fundamental studies have shown that alloying process occurs at much lower temperatures than decomposition temperatures for precursors used. Alloying studies have clearly shown that the solubility in nanowires to be much more than that expected for bulk materials systems. This presentation will provide several examples in which nanowires were alloyed with elements at compositions more than that expected for thermodynamic solubility.
In the case of CO2 sorbents, alkali metal oxide nanowires have shown high capacity for CO2 sorption as high as 75% by wt. The alkali metal oxide nanowires have been alloyed with alkali hydroxides to produce alkali metal oxide compound nanowires. These solid sorbents showed selective CO2 sorption from a variety of streams including air, exhausts containing CO2 at various concentrations. Nanowire geometry for these nanowires allow for non-sinterability, and smaller length scales for rapid diffusion of alkali ions allow for fast kinetics and regenerability. 6,7

Acknowledgements: Authors also acknowledge contributions from Drs. Juan He, Sivakumar Vasireddy, Vivekanand Kumar, Veerendra Atla and Tu Nguyen. Partial support from National Science Foundation (NSF) and US Department of Energy (DOE) EPSCOR programs and full support from NSF and DOE SBIR programs and Kentucky Cabinet for Economic Development for Advanced Energy Materials, LLC are highly appreciated.
References:

V. Kumar, J-H. Kim, C. Pendyala, B. Chernomordik, and M.K. Sunkara, “Gas-Phase, Bulk Production of Metal Oxide Nanowires and Nanoparticles Using a Microwave Plasma Jet Reactor”, J. Phys. Chem. C., 112, 46, 17750-17754 (2008).

S. Calero-Barney, A. Andriotis, M. Menon and M.K. Sunkara, “Plasma assisted vapor liquid phase epitaxy of dilute anion alloyed GaSbxN1-x and GaBixN1-x alloys: confirmation of discontinuity in band gap reduction”, Physical Review B, 105 (8), Article No. 085307 (2022). DOI: 10.1103/PhysRevB.105.085307.

M. Gupta, T. Nguyen, F. Petzold, D. Fonseca, J. Jasinski and M.K. Sunkara, “Nanowire Based Bi-functional Catalysts for Ultra-deep HydroDesulfurization and Aromatic Hydrogenation”, Applied Catalysis B; Environmental, 180, 246–254 (2016)

M.K. Sunkara, S. Vasireddy and J. He, “Desulfurization and Sulfur Tolerant Hydrogenation Processes for Hydrocarbon Feedstocks”, US Patent 11,254,880 B1, Issued February 2022.

A. Nambo, J. He, V. Atla, T. Q. Nguyen, T. Druffel, and M. Sunkara, “Ultrafast carbon dioxide sorption kinetics using lithium silicate nanowires”, 17 (6), 3327–3333, Nano Letters (2017).

M.K. Sunkara, V. Kumar, J. He and S. Vasireddy, “Nanowire-based Hydrodesulfurization Catalysts for Hydrocarbon Fuels”, US Patent 11,306,261 B2, Issued April 19, 2022.

J. He, T. Nguyen, M.K. Sunkara, “Novel CO2 Sorbent Materials for Advanced Carbon Capture Technologies and Dielectric Barrier Discharge (DBD) Plasma Based Processes”, US Patent 11,305,229 B1, Issued April 19, 2022.