Catalytic Reduction of SO_3 Stored in SO_x Transfer Catalysts - A Temperature-Programmed Reaction Study

摘要

A laboratory test method has been developed to assess the efficiency of SO_x transfer catalysts for the reduction of SO_3 stored in the catalysts. The test method is based on the temperature-programmed reaction (TPR) with propane over a presulfated catalyst. The reaction products released during the test were determined by means of mass spectrometry (MS). Using this technique, we have appraised the oxides of four transition metals, V, Cr, Fe, and Ce, each impregnated on microspheres of a ternary oxide containing Mg, La, and Al. Based solely on the onset temperature for H_2S release, the ranking in catalyst efficiency found was V > Ce > Fe > Cr. In good contrast to this, the ranking based on thermogravimetric analysis (TGA) test for the SO_2 oxidaiton / SO_3 trapping was Ce>Cr>V>Fe. Using the TPR/MS test method, we have also examined a sample of DESOX~(TM), the leading commercial SO_x transfer catalyst consisting of (MgO)_2Al_2O_3 and oxides of Ce and V. The onset temperature for H_2S release was approximately 450 deg C when propane was the reactant. It was approximately 580 deg C when H_2 or CH_4 was used. These data imply that the rate of H_2S release is limited by the supply of active hydrogen. Thus, the data further suggest that the primary role of catalytic metal oxide for the reduction of SO_3 stored in the catalyst is to facilitate C-H bond cleavage on the catalyst by activating hydrocarbons.