Catalytic conversion of CO, NO and SO 2 on supported sulfide catalysts : II. Catalytic reduction of NO and SO 2 by CO

Abstract

To investigate the possibility of simultaneous catalytic reduction of NO and SO 2 by CO, reactions of NO, NOCO, and NOSO 2CO were performed on γ-alumina-supported sulfides of transition metals including Co, Mo, CoMo and FeMo. NO was decomposed into N 2O and N 2 accompanied with the formation of SO 2; this serious oxidation of lattice sulfur resulted in the deactivation of the catalysts. The addition of CO to the NO stream suppressed SO 2 formation and yielded COS instead. A stoichiometric conversion of NO and CO to N 2 and CO 2 was observed above 350°C on the CoMo and the FeMo catalysts. Although the CO addition lengthened catalyst life, it was not enough to maintain activity. After the NOCO reaction, an XPS analysis showed the growth of Mo 6+ and SO 4 2− peaks, especially for the sulfided FeMo/Al 2O 3; the FeMo catalyst underwent strong oxidation in the NOCO reaction. The NO and the NOCO reactions proceeded non-catalytically, consuming catalyst lattice sulfur to yield SO 2 or COS. The addition of SO 2 in the NOCO system enabled in situ regeneration of the catalysts; the catalysts oxidized through abstraction of lattice sulfur experienced anew reduction and sulfurization through the SO 2CO reaction at higher temperature. NO and SO 2 were completely and catalytically converted at 400°C on the sulfided CoMo/Al 2O 3. By contrast, the sulfided FeMo/Al 2O 3 was easily oxidized by NO and hardly re-sulfided under the test conditions. Oxidation states of the metals before and after the reactions were determined. Silica and titania-supported CoMo catalysts were also evaluated to study support effects.