Oxidation of C213H5OH by NO and O2 on the surface of stepped Pt(332): Relationship to selective catalytic reduction of NO with hydrocarbons

Abstract

Oxidation of C213H5OH by NO and O2 on the surface of stepped Pt(332) was studied using Fourier transform infrared reflection-absorption spectroscopy combined with thermal desorption spectroscopy. Upon annealing, adsorbed C213H5OH molecules undergo stepwise dissociation. Desorption of H2, released from the scission of O–H, C13–H (α-C13), and C13–H (β-C13) bonds in sequence, covers a broad temperature range from ∼260to∼550K. Desorption of C13O gives rise to a peak at 500–510K. This surface process does not change greatly in the presence of O2. Oxidation of C213H5OH and, consequently, the generation of the products are strongly dependent on the pretreatment of C213H5OH. Thermal desorption spectra of H2 and C13O2 indicate that oxidation of C213H5OH to H2O and C13O2 is a primary process in most cases. However, when C213H5OH adsorbed at 90K is preannealed to 250K before being exposed to O2, reaction of O with H predominates. Consequently, oxidation of carbon-related species to C13O2 is completely suppressed. C213H5OH dissociation, in particular, the cleavage of the C13–C3 bonds, is suppressed in the presence of NO. Desorption of H2, released from dehydrogenation of C13Hx (β-C) at surface temperatures above 400K, is not detectable from the co-adlayers following the adsorptions of C213H5OH and NO at 90K. Oxidation of C213H5OH related species with NO to C13O and C13O2 proceeds to a much smaller extent compared to that with O2. The presence of C213H5OH, irrespective of whether it is preadsorbed or postadsorbed, results in more NO desorption from terraces (at 350–360K), due to a site-swapping effect exerted by C213H5OH derivatives (C13O and C13Hx). Nonetheless, NO reduction and subsequent N2 production is promoted in the presence of C213H5OH. This effect, however, does not strongly depend on the exposure of C213H5OH. It is concluded that reduction of NO and subsequent N2 production proceeds through a mechanism of NO dissociation and subsequent O removal, NO dissociation on the steps of the Pt(332) being a rate-limiting step. The reaction of C213H5OH-related species with O effectively scavenges O atoms arising from NO dissociation, therefore giving rise to vacant sites that accommodate O atoms from further NO dissociation. This accounts for the C213H5OH-induced enhancement in N2 production.