Journal of the Indian Chemical Society 100 (2023) 100801 Available online 17 November 2022 0019-4522/© 2022 Indian Chemical Society. Published by Elsevier B.V. All rights reserved. Adsorptive denitrogenation of indole from model fuel oil over Co-MAC: Adsorption mechanisms and competitive adsorption Prerana Sikarwar a, b , Meena Nemiwal c , Vijayalakshmi Gosu a, ** , Verraboina Subbaramaiah a, * a Department of Chemical Engineering, Malaviya National Institute of Technology Jaipur, Jaipur, 302017, India b Department of Chemical Engineering, National Institute of Technology Raipur, Raipur, 492010, India c Department of Chemistry, Malaviya National Institute of Technology Jaipur, Jaipur, 302017, India A R T I C L E INFO Keywords: Indole Adsorptive denitrogenation Co-MAC Competitive adsorption ABSTRACT The present research article depicts the adsorptive denitrogenation of indole-containing model oil using cobalt- incorporated acid-activated carbon (Co-MAC). The active metal incorporated acetic acid-activated bio-sorbent showed a signifcant adsorption capacity for indole from model fuel oil than mere activated carbon. In a batch study, maximum 96% indole removal was achieved with an initial indole concentration of 500 mg/L, catalyst dose of 10 g/L, time of 4 h, and reaction temperature of 303 K. The non-linear regression analysis was opted to ft the experimental equilibrium data into various adsorption isotherms, including Langmuir, Freundlich, Temkin and Redlich, and Peterson. Thermodynamic parameters of adsorption were investigated, and the entropy and heat of adsorption change were determined to be 0.26 kJ/mol K and 57.31 kJ/mol, respectively. Besides, a plausible adsorption mechanism of indole was also explored. 1. Introduction Fossil fuels consumption has been increased immensely due to the rapid growth of the world’s population as well as industrialization. These fuels contain the most obnoxious contaminants, namely, sulfur and nitrogen compounds. Upon combustion, the nitrogen and sulfur compounds present in fuel produce NO x and SO x emissions, and these emissions are accountable for acid rain, haze, and global warming [1,2]. Removal of sulfur and nitrogen compounds from fossil fuels has gained considerable attention of researchers owing to its harmful effect on both environment and human health [3,4]. Especially, nitrogen compounds should be removed since they act as a threat to catalysts in hydro- desulfurization process. Nitrogen compounds present in fuel compete with sulfur compounds to get-adsorb on active sites of the catalyst and therefore hinder the in-depth desulfurization process [5,6]. It has been shown in various studies that the presence of nitrogen compounds, even in trace amounts, can severely inhibit the production of fuel with low sulfur [7,8]. Hydrodenitrogenation (HDN) is currently employed in re- fneries to reduce the nitrogen content of liquid fuels [9]. HDN is an expensive and energy intensive process. Moreover, HDN is a kinetically slow process, and more energy is required than the hydrodesulfurization process [10]. Therefore, an alternative technology needs to be devel- oped to reduce the nitrogen content of liquid fuels. Adsorption is a one of the alternative technique, and it has large footprint to remove undesired compounds from the solution, including toxic contaminants like heavy metals, dyes, organic solvents, phenolic and nitrogenous compounds have been addressed [11–14]. Further- more, adsorption gaining signifcant attention for the removal of un- desirable compounds such as sulfur and nitrogenous compounds, from the fuel oil to meet current BS V1 norms. Adsorptive denitrogenation (ADN) process has been adopted in various studies to mitigate nitroge- nous compounds from liquid fuels. Moreover, adsorptive denitrogena- tion process does not require high temperature, high pressure, expensive hydrogen, and catalyst when compared to conventional HDN process. Therefore, more economical as compared to the HDN process. A wide variety of adsorbents have been explored to carry out the denitrogena- tion of liquid fuels, such as activated alumina’s [15], metal-organic frameworks [16], ion exchange resins [17], mesoporous molecular sieve [18], activated carbon (AC) [19,20], zeolite-based materials [21], Ni supported granular activated carbon [22], Co-MCM-41 [23], metal organic frameworks [24], activated carbon modifed by oxygen [24]. Activated carbon is one of the promising adsorbents for the removal ** Corresponding author. * Corresponding author. E-mail addresses: 2015rch9503@mnit.ac.in (P. Sikarwar), vlakshmi.chem@mnit.ac.in (V. Gosu), vsr.chem@mnit.ac.in (V. Subbaramaiah). Contents lists available at ScienceDirect Journal of the Indian Chemical Society journal homepage: www.journals.elsevier.com/journal-of-the-indian-chemical-society https://doi.org/10.1016/j.jics.2022.100801 Received 26 June 2022; Received in revised form 4 November 2022; Accepted 9 November 2022