Synergy effects of basic graphitic-C3N4 over acidic Al2O3 for a liquid-phase decarboxylation of naphthenic acids

Abstract

Synergy effects of a basic graphitic-carbon nitride (g-C3N4) supported on a Lewis acidic γ-Al2O3 (Al@CN) were investigated to remove naphthenic acids (NAs) in a highly acidic model crude oil (dodecane used as model component) through a liquid-phase decarboxylation, where a novel bifunctional Al@CN catalyst effectively reduced the acidity of the model crude oil. Among the well-known elimination methods of NAs in acidic crude oils, catalytic decarboxylation of NAs has been largely attracted due to its simple process scheme by using Lewis acid catalysts. Even though γ-Al2O3 itself having with mesoporous structures was effective for NAs removal, the activity was largely enhanced by an incorporation of the basic g-C3N4 nanoparticles on the Lewis acidic γ-Al2O3 surfaces at an optimal 20 wt% g-C3N4/Al2O3 through the synergy effects of two active sites. The main roles of the highly dispersed g-C3N4 nanoparticles on the γ-Al2O3 surfaces were to reduce coke depositions and to adjust the adsorption strength of NAs on the newly formed defected carbon surfaces formed on the Al@CN during a liquid-phase decarboxylation reaction. A proper amount of the thermally stable g-C3N4 species on the acidic γ-Al2O3 surfaces not only enhanced the catalytic activity by adjusting the acidic and basic sites on the bifunctional Al@CN but also helped in preserving the pristine basic g-C3N4 structures by strongly interacting with the Lewis acidic γ-Al2O3 surfaces.