A study on sulfur reduction in FCC gasoline using Zn–Mg–Al spinels

It has been previously demonstrated that zinc aluminates are useful additive materials for gasoline sulfur reduction. To enquire about the nature of the catalyst active site in Zn aluminates, in the present work, [Zn(x)2+Mg(1−x)2+]Al2O4, ternary spinels with 0 ≤ x ≤ 1 were synthesized to obtain samples with different Lewis acidity. The Zn–Mg–Al spinels were tested as FCC sulfur reduction additives, using the elimination of sulfur from thiophene at 793 K as model test. The thiophene conversion with the Zn–Al spinel was higher than with ternary Zn–Mg–Al spinels or the commercial cracking catalyst. It was found that although to a small extent, the Zn-free Mg–Al spinel converted thiophene. The IR study on the adsorption of CO2 over Zn–Mg–Al spinels with different amounts of Zn and over ZnO suggested that: (i) no strong Lewis sites are located on Zn and (ii) the Lewis acidity of the ternary spinels is due to aluminum sites and increases with the Zn content. So, it appears that the Lewis acid sites located on aluminum are responsible for the adsorption of thiophene and that one of the benefits of Zn incorporation is the increase of this acidity, which would lead to increased adsorption and reactivity.