Effect of Acid Treatment on the Performance of the CuO−MoO3/Al2O3 Catalyst for the Destructive Oxidation of (CH3)2S2

Our previous work confirmed the excellent activity of CuO−MoO 3 /Al 2 O 3 for the destructive oxidation of (CH 3 ) 2 S 2 . This study further investigates the effect of acid treatment on the performance of this catalyst. Four different kinds of inorganic acids (HCl, H 2 SO 4, HNO 3, H 3 PO 4 ) are used to treat the γ-Al 2 O 3 support before impregnating it with copper and molybdenum metal salts. The prepared catalysts are then used for the destructive oxidation of (CH 3 ) 2 S 2 . Experimental results indicate that HCl-treated and H 2 SO 4 -treated catalysts exhibit a higher activity than those without acid treatment. In addition, the H 2 SO 4 -treated catalyst (CuO−MoO 3 /Al 2 O 3 −SO 4 2- ) displays the best stability. As BET surface area analysis demonstrates, the surface area and average pore diameter of the H 2 SO 4 -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−MoO 3 /Al 2 O 3 −SO 4 2- catalyst also has the crystalline structure of Cu 3 Mo 2 O 9 and CuMoO 4 which have been found in CuO−MoO 3 /Al 2 O 3 and which might play a prominent role in the catalyst activity. XPS and TGA analyses suggest that it might have the functional group of SO 4 2- which exists on the surface of the CuO−MoO 3 /Al 2 O 3 −SO 4 2- catalyst. The NH 3 -TPD pattern shows that the acidity is remarkably enhanced when the catalyst is treated with an H 2 SO 4 solution. We believe that the substantial increase in activity is attributed primarily to the presence of the SO 4 2- group and the formation of a copper molybdenum oxide phase on the catalyst surface.