(190b) Effect of Nanosize on Adsorptive and Catalytic Properties of NiO Nanoparticles Towards Heavy Hydrocarbons: Kinetics, Thermodynamics and Mechanistic Insights

The application of nanoparticles in the oil and gas industries has increased in recent years because of their unique physical and chemical properties. Notwithstanding the great deal of interest in the use of nanoparticles as adsorbents and catalysts for enhancing heavy oil upgrading and recovery, still the effect of nanoparticle size on their adsorption and catalytic behaviour towards heavy hydrocarbons remain unclear. This study focused on the effect of NiO nanoparticle size on adsorption and post-adsorption catalytic decomposition of heavy polar hydrocarbons, exemplified by Quinolin-65 (Q-65) and Violanthrone-79 (V-79). In this study, different nanosizes of NiO nanoparticles, ranging from 5-80 nm, were prepared by thermal dehydroxylation of Ni(OH)₂ following the hydrothermal technique. Using batch adsorption equilibrium measurements of Q-65 and V-79 dissolved in toluene coupled with thermogravimetric analysis, we studied the effect of nanoparticle size on the adsorptive and catalytic behavior of the in-house prepared NiO nanoparticles. Adsorption isotherms were described by the Langmuir model and the Solid Liquid Equilibrium model (SLE), and the catalytic behavior of the nanoparticles were compared on the basis of the effective activation energies trends using the isoconversional method of Ozawa−Flynn−Wall (OFW). In addition, computational modeling was conducted to understand the chemistry behind the differences on adsorption capacity and catalytic activity of the different sizes of NiO nanoparticles. In case of V-79, on the surface-area-normalized basis, results obtained in this study revealed that the adsorptive capacity increased with increasing nanosize of NiO particle, while the oxidation activation energy decreased with decreasing of size of NiO particle. On the other hand, an optimum nanosize of NiO nanoparticle was found for Q-65 for which a maximum adsorption capacity and minimum activation energy were obtained. For the case of binary solutions (V-79 and Q-65), for all sizes of NiO nanoparticles, NiO showed higher selectivity towards V-79 than to Q-65 indicating a selective adsorption; which was backed up by the computational modeling The experimental adsorption capacity of V-79 was enhanced in the presence of Q-65, presumably due to new interactions of V-79 in the presence of Q-65 (entangling of aliphatic chains between Q-65 and V-79 seems to reduce the adsoption energy according to the computational study) . 

This study confirms that nanosize plays vital roles in selective adsorption and subsequent catalytic decomposition of heavy hydrocarbons. The study opens up new possibilities for manipulating adsorptive and catalytic performance of metal oxide nanoparticles, and widens our general understanding of their surface functionality and chemical activity.