Beyond Equilibrium Capacity: A Critical Review of Cyclic Adsorption, Regeneration Performance, and Deployment Readiness of Bio-derived Carbon Adsorbents for Diesel-emission Control

Equilibrium adsorption capacity and specific surface area are insufficient to assess the ability of bio-derived carbon adsorbents to control diesel emissions. While significant advances have been achieved in the selection of the precursors, the thermochemical processing, the design of the pores and the functionalisation of the surfaces, the influence of the mass-transfer limitations, competitive adsorption, humidity, temperature gradient and regeneration-induced degradation is still a crucial issue in assessing operational performance. This review aims to address this limitation by introducing the Cyclic Adsorption–Regeneration Performance (CARP) framework, which frames adsorption performance in four interdependently linked domains: equilibrium storage, transport accessibility, competitive adsorption, and regeneration stability. The advancements in the chemistry of precursors, thermochemical processing, evolution of pore structure, and surface functionality are discussed in the context of adsorption kinetics, breakthrough behavior, multicomponent interactions, and cyclic durability. The synthesis shows that high equilibrium adsorption capacity does not guarantee high usable capacity or sustained performance under dynamic operating conditions. The CARP framework offers an integrated approach to understand these performance trade-offs and identify the factors that contribute to an adsorbent's suitability for diesel-emission control. Areas of interest for research include multicomponent testing under controlled humidity and temperature, performing more adsorption–regeneration cycles, and more integrated development of materials and reactors. More quantitative development and experimental validation are needed to validate the predictive capability and applicability of the framework.