Hydrogen-Assisted Reduction of Metal Oxides: Reaction Mechanisms, Process Optimization, and AI/ML-Enabled Pathways for Sustainable Materials Processing

Abstract

Hydrogen reduction of metal oxides has been identified as a promising approach for producing some engineering (metallic) materials, both through primary production and the reprocessing of waste materials. Such an approach offers a viable promise for the production of value-added materials in a sustainable manner. Unlike in other reduction processes, where obnoxious gases get 2 released as byproducts, hydrogen reduction, on the other hand, generate water vapor as the clean principal byproduct. Such an approach renders the overall mcheaping process inexpensive because of the use of metal oxides as the cheap feedstocks. However, the manufacturing process offers several challenges, upscaling being one of the major ones. In the present review, an attempt has been made to assess the overall reduction process in an integrated manner, which relates thermodynamic principles, reduction mechanisms, reactor-scale phenomena, and specific application requirements. The principles of thermodynamic constraints related to oxide reducibility are described in relation to the role of reduction temperature, gas compositions, and the gas-solid reaction mechanisms to determine rate-controlling processes, diffusion coefficients, and the role of catalysis for the production of metallic materials by primary manufacturing processes and environmental remediation. There is also the consideration of an enabling role of automation, modeling, and digital twin technologies. The manuscript describes practiced hydrogen reduction processes to produce some of the specific metals, such as iron, nickel, cobalt, and refractory metals, but also the need to improve hydrogen access, efficiency, scalability, and ensure catalyst longevity. Enhanced research in hydrogen, renewable power coupling, AI-assisted process control and reactor design are some of the aspects that have been observed to be the major enablers. The manuscript not only describes the status and future projections but also provides a roadmap for improving the status quo.