Aerobic Oxidative Desulfurization Of Organo-sulfur Compounds In Iso-octane Over Pt, Cu-based Catalysts

The regulation of sulfur content in fuels which contribute air pollution and acid rain has become more and more stringent along with boosted consciousness of protecting environment.Hydrodesulfurizatin is a mature process for the removal of most organic sulfur compounds from fuels,but it has many disadvantages(e.g.,high temperature,high pressure and hydrogen consumption)and requires larger reactor volume and higher catalyst activity for achieving deep desulsurization.Oxidative desulfurization(ODS)has attracted much attention compared with other non-hydrodesulfurizaion methods due to its mild reaction conditions.However,the ODS technology remains challenging for industrial application because of the need large amount of extraction solvent and expensive H₂O₂ oxidant and safety issues concerning bulk storage of H₂O₂.Using air as oxidant will overcome this shortcoming.In this paper,we wish to demonstrate that the sulfur compounds in the fuels can be selectively converted to SO₂ by mixing the fuel with small amount of air at near 300℃and atmospheric pressure in continuous flow reactor packed with catalysts such as Pt/CeO₂,CuO/CeO-2 and Cu/Ce/SiO-2.Effect of reaction temperature,O-2/S molar ratio and WHSV on the performance of Pt/CeO-2 and CuO/CeO-2 catalyst for aerobic oxidative desulfurization(AODS)of various organo-sulfur blended in iso-octane have been investigated.N-2-BET,XRD and H-2-TPR measurements were performed to determine the catalytically relevant properties of studied catalysts with respect of the specific surface area,phase structure and composition,and reducibility. At 300℃,the performance of Pt/CeO-2,CuO/CeO-2 and 5%Cu/10%Ce/SiO-2 for AODS of various sulfur compounds in iso-octane were examined.In addition,in-situ DRIFTS studies on the adsorption of sufur-containing compounds on the surface of Pt/CeO₂ catalyst were performed for deeply understanding the sulfur transformation chemistry. It was found that reaction temperature was crucial to ensure the maintainance of catalyst reactivity for the AODS process.At reaction temperature below 300℃,the catalyst reactivity degraded quickly,since SO₂ product of AODS would chemisorbed on the catalyst surface to form sulfate or sulfite thereby leading to catalyst poisoning. At reaction temperature of 300℃,however,SO₂ product could escape easily from the catalyst surface with the result that the catalyst reactivity remained along with the reaction time.It is also found that SO₂ is the unique sulfur-containing production in either liquid phase effluent or in the gas phase effluent,ascertained by GC-PFPD and GC-MS analyses.Effects of Ce and Cu contents and the calcination temperature on the AODS performance of Cu/Ce/SiO-2 catalysts have been studied.It was found that the optimal Cu and Ce contents are 5wt%and 10wt%,respectively.The optimal calcination temperatures are all 450℃in the step of loading Ce on SiO-2 and in the subsequent step of loading Cu on the as-made Ce/SiO-2.By correlating the reaction results with the catalyst information provided by N₂-BET,XRD and H₂-TPR measurements,it is suggested that good crystallization of CeO₂,high copper dispersion and strong interaction between Cu and CeO₂ at their interface are favourable for AODS performance of the Cu/Ce/SiO₂ catalysts.In addition,Pt/CeO₂,CuO/CeO₂ and 5%Cu/10%Ce/SiO₂ catalysts all provide good reactivity for AODS of various organo-sulfur compounds blended in iso-octane at 300℃.At equivalent organo-sulfur conversion of 95%at 300℃,over Pt/CeO₂ catalyst the reactivity of various organo-sulfur compounds decrease in the order of 1-pentanthoil＞dibutylsulfide＞benzothiophene＞thiophene＞dibenzothiophene.In situ DRIFTS spectra for adsorption of organosulfur compounds or the surface of Pt/CeO₂ catalyst reveal that the organosulfur compounds can be deeply oxidized by the surface lattice oxygen of the Pt/CeO₂ catalyst into SO₂,CO2 and trace CO. Moreover,the presence of O₂ moleculors facilitates the oxidation of organo-sulfur compounds.