A Transient Kinetic Study of the Mechanism of the NO+H2 Reaction over Pt/SiO2 Catalysts: 1. Isotopic Transient Kinetics and Temperature Programmed Analysis

Abstract The NO+H 2 reaction has been studied over a supported Pt catalyst using temperature programmed reaction (TPR xn ), temperature programmed desorption (TPD), and steady state and non-steady state isotopic transient kinetic analysis (SSITKA and NSSITKA). N 2 , N 2 O, and NH 3 formation are noted during the TPR xn . N 2 O is the most prevalent species formed at lower temperatures while N 2 is most prevalent at higher temperatures. NH 3 is formed in relatively low yields at intermediate temperatures. The SSITKA shows that N 2 O is the isotopically first product and that N 2 is isotopically second. The concentration of sites producing N 2 O and N 2 increases with temperature, and the increase in the effective activity of the sites is greater for those sites producing N 2 than those sites producing N 2 O. The chemisorption of NO is also found to be a reversible process under actual reaction conditions. Non-steady state transient kinetic experiments show that after removal of the gas phase NO, there is a conversion of some of the residual NO on the surface into N 2 precursors following a short treatment in a H 2 whereas N 2 O precursors on the surface are destroyed by this treatment. It is concluded that the formation of N 2 O requires the presence of gas-phase or very weakly adsorbed NO.

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