Catalytic decomposition/regeneration of Pt/Ba(NO3)2 catalysts:: NOx storage and reduction

The introduction of lean-burn engine technology has prompted the development of NO, storage-reduction (NSR) catalysts, which are currently based on a Pt/Ba(NO(3))(2)/Al(2)O(3) system. In this work a series of powdered catalysts based on this system were prepared and their reactivities examined with a pulsed-flow reactor, which was used to carry out temperature programmed desorption (TPD) experiments and to simulate the NSR reaction itself. TPD experiments reveal that Ba(NO(3))(2) is catalytically decomposed by the presence of Pt, at a significantly lower temperature than otherwise (by >200 K), with the extent of the decomposition being dependent on the amount of Pt loaded. The products formed from the decomposition depend on the oxidation state of the Pt; firstly N(2) and N(2)O are evolved (formed from cracking of the NO produced via the Ba(NO(3))(2) decomposition), but as the adsorbed oxygen resulting from their formation builds up, NO and O(2) appear and N(2) and N(2)O are lowered. NO(x) storage has been shown to occur even at room temperature following Ba(NO(3))(2) decomposition from a 0.5 wt. % Pt/Al(2)O(3) catalyst impregnated with 10 wt.% Ba(NO(3))(2). These experiments can be carried out in a reversible way. Simulations of the NSR reaction, using H(2) and CO as reductants, indicate a remarkable difference between the two; CO appears to facilitate Ba(NO(3))(2) decomposition, but not NO(x) reduction, whereas H(2) enables both to take place, with excellent conversion to N(2). The difference between the two reductants in these experiments reflects the difference in binding between the two adsorbates and consequent Pt surface poisoning by CO. (C) 2003 Elsevier Science B.V. All rights reserved.