Effects of the size of NiO nanoparticles on the catalytic oxidation of Quinolin-65 as an asphaltene model compound

摘要

In a previous study, the effect of the nanosize of NiO particles on its surface properties for the Quinolin-65 (Q-65) adsorption from toluene-based solution has been investigated and well established. In this work, the effect of nanosize of NiO particles on the catalytic thermo-oxidative decomposition of the adsorbed Q-65 was investigated using TGA/DTA and TGA-MS systems. Virgin Q-65 and Q-65 adsorbed on 5 nm sized NiO particles have been oxidized to the same conversion degree alpha = 0.3, to get the transitional product. FTIR and XPS have been used to characterize the transitional product. Kissinger-Akahira-Sunrise (KAS) isoconversional method was used to describe the oxidation mechanism and to confirm the validity of the catalytic effect of the different-sized NiO nanoparticles. Taken together, the kinetic triplets (i.e., the effective activation energy Ea, the pre-exponential factor A(alpha) and the reaction function, f(alpha)) are necessary specifications to examine and allow meaningful comparisons of the catalytic activity of the different-sized NiO nanocatalysts. The gas analysis TGA-MS system and the thermodynamic parameters suggested that the smaller the particle size is, the higher the catalytic activity, and the faster CO2 formation. The critical NiO nanosize was observed to be between 15 and 30 nm, were the shape become flat and the atomic distribution are barely changed with further increasing of the size. NiO nanoparticles with size <30 nm i.e. 5-15 nm portrayed stronger and faster catalytic effect than of 30-40 nm. The effect of the nanosize on the regeneration process has been studied as well. XRD and BET have been used to characterize the regenerated nanocatalysts. (C) 2017 Elsevier Ltd. All rights reserved.