A Study on the Oxidative Decomposition of Dimethyl Disulfide over Supported Copper-Molybdenum Oxide Catalysts

• Main Authors: Wang, Ching-Huei, 王清輝
• Other Authors: Hung-Shan Weng
• Format: Others
• Language: zh-TW
• Published: 1998
• Online Access: http://ndltd.ncl.edu.tw/handle/38946124733791505522

博士 === 國立成功大學 === 化學工程學系 === 86 === ABSTRACT The incipient wetness impregnation and the coprecipitation method were employed0 to prepare catalysts. Catalytic activities of the prepared catalysts for oxidative decomposition of dimethly disulfide were measured by a packed-bed reactor. The results indicate that active species (CuO), support and promoter (metal oxide) are important factors affecting catalyst activity. CuO/Al2O3 was the most active catalyst among eight prepared supported single metal oxide catalysts (CuO, MoO3, Cr2O3, Fe2O3, MnO2, NiO, ZnO, Co3O4). Among nine metal oxides (MoO3, Cr2O3, NiO, MnO2, La2O3, Fe2O3, Co3O4, SrO, and ZnO) MoO3 has the best promoting effect to CuO/Al2O3. The CuO-MoO3/Al2O3 catalyst exhibits a higher activity and a better resistance to deactivation by sulfur compounds than a commercial platinum catalyst. A formation of Cu3Mo2O9 and CuMoO4, as confirmed by XRD , TPR and XPS analyses, plays a prominent role in the catalyst activity. Such a formation markedly enhanced the catalytic activity when the added amount of Mo is not too large. However, the activity declines when the content of Mo exceeds 10 wt %. Furthermore, NH3-TPD demonstrates that adding of Mo to CuO/Al2O3 elevates the catalyst''s acidity and acidic strength. A kinetic study on the oxidation decomposition of dimethyl disulfide over CuO(5)-Mo03(10)/Al2O3 catalyst was carried out in a differential reactor. Power-rate law, Langmuir-Hinshelwood, and Mars-Van Krevelen models were used to analyze the results of oxidative decomposition of dimethyl disulfide. The results show that the Mars-Van Krevelen model is suitable for oxidative decomposition of dimethyl disulfide. The reaction rate can be expressed by: Where a=5.5, CR and CO are the concentrations of (CH3)2S2 and O2 , respectively. Knowing that a higher acidity might benefit the catalyst to catalyze the reactions involving cracking and decomposition, we further investigated the effect of acid treatment on the performance of CuO-MoO3/Al2O3 catalyst. Four different kinds of inorganic acids (HCl, H2SO4, HNO3, H3PO4) were used to treat the (-Al2O3 support before impregnating it with copper and molybdenum metal salts. The prepared catalysts were then used for the destructive oxidation of (CH3)2S2. Experimental results indicate that HCl-treat ed and H2SO4-treated catalysts exhibit a higher activity than those without acid treatment. In addition, the H2SO4-treated catalyst (CuO-MoO3/sulfated-Al2O3) displays the best stability. As BET surface area analysis demonstrates, the surface area and average pore diameter of the H2SO4-treated catalysts are larger than those without treatment; however, the increase in surface area is not the main factor in promoting the activity. XRD analysis reveals that the CuO-MoO3/sulfated-Al2O3 catalyst also has the cryst alline structure of Cu3Mo2O9 and CuMoO4 which have been found in the CuO-MoO3/Al2O3. XPS and TGA analysis suggest that it might have the functional group of SO4-2 which exists on the surface of the CuO-MoO3/sulfated-Al2O3 catalyst. The NH3-TPD pattern shows that the acidity is remarkably enhanced when the catalyst is treated with an H2SO4 solution. We believe that the substantial increase in act ivity is attributed primarily to the presence of SO4-2 group on the