Modelling of bitumen fragment adsorption on Cu+ and Ag+ exchanged zeolite nanoparticles

We investigate bitumen desulfurisation on zeolite chabazite nanoparticles that contain Ag+ and Cu+ by using periodic density functional theory. The large bitumen molecules that contain thiophene derivative impurities and useful aromatic hydrocarbons cannot enter into zeolite pores but adsorb on the outer surface of the zeolite. The zeolite nanoparticle surface can be optimised for efficient impurities removal and bitumen upgrading, as we have shown recently. On chabazite nanoparticle surface, Ag+ that reside near the main channel enhance the bitumen fragment adsorption in the order benzene < thiophene < benzothiophene < dibenzothiophene. For Cu+, the bitumen fragment adsorption strength increases in the order benzene < dibenzothiophene < benzothiophene < thiophene. The different trends arise from the spatial constraint of the surface termination and the smaller ionic radius of Cu+ relative to Ag+. Our results show that zeolite surface modifications allow for stronger adsorption of thiophenes relative to hydrocarbons. Our results can be applied toward the rational design of zeolite nanoparticles for bitumen upgrading. We conclude that the preferred configurations of organic macromolecules adsorbed on zeolite outer surfaces can be safely predicted by using Fukui functions.