OXIDATIVE DESULFURIZATION OF DIESEL WIT OXYGEN: REACTION PATHWAYS ON SUPPORTED METAL AND METAL OXIDE CATALYSTS

摘要

Catalytic oxidative desulfurization (ODS) has most often usednperoxide oxidants with Mo-, V- or Fe-oxides,1-2 or Ti-containingnsilicates.3-6 However, oxygen can react with sulfur heterocycles atntemperatures above ~340 K.7 While there is evidence for somenoxidation at the catalyst surface, much of the reaction seems tonproceed by an autoxidation mechanism through free radicalnintermediates which are initially surface generated. Therefore thenalkylaromatics and nitrogen heterocycles in diesel must also benoxidized to some extent. Here we examine all the oxidation reactionsntaking place during ODS on two typical catalyst classes: supportednPd (on activated carbons or alumina) and titanium silicates. It isnshown that the reaction rate of ODS is heavily influenced by thenother oxidizable components present. Temperatures must be keptnreasonably low (< ~400 K) in order to minimize co-oxidations. Innturn, this requires either higher pressures than typically used fornperoxide-based oxidations, or greatly enhanced gas-liquid mixing.nBoth of these alternatives will be discussed