An unprecedented and straightforward strategy towards the activation of metal-organic frameworks UiO-66(Zr) and UiO-66(Hf) in oxidative desulfurization reactions was developed. Post-synthetic treatment of poor-defect pristine UiO-66 materials with chloride-based salts (for example TiCl4) leaded to the preparation of more active and recyclable heterogeneous catalysts for oxidative desulfurization processes. The pristine UiO-66(Hf) showed to be an inactive catalyst; however, after activation treatment 80% of total desulfurization was achieved after 1 h. Also, UiO-66 (Zr) increased appreciably its activity after treatment with chloride-based salts (from 62% to 97% for the sample treated with TiCl4). The insertion of chloride in UiO-66 framework did not retain the counter-cation Ti(IV). The possible interaction of chloride with UiO-66 framework enhances catalytic activity without structural degradation of catalyst, even after consecutive reaction cycles. Chloride activation method opened a new route to activate efficiently catalytic UiO-66 MOFs. This is a cost-effective method capable to be feasible to other MOFs structures, promoting their catalytic capacities and enlarging their catalytic application.