FT-IR spectroscopic investigation of the reactivity of NOx species adsorbed on Cu2+/ZrO2 and CuSO4/ZrO2 catalysts toward decane

Abstract

The nature of the NO x species produced on NO adsorption and its co-adsorption with O 2 at room temperature on zirconia-supported copper(II) catalysts has been studied by means of in situ FT-IR spectroscopy. The samples were prepared by impregnation of zirconia with aqueous solutions of copper(II) nitrate and sulfate. The structural identification of the surface NO x complexes exhibiting absorptions in the fundamental nitro-nitrato region was performed by analyzing the combination bands of the nitrate species. In order to understand which factors control the selectivity of the catalysts in the catalytic reduction of NO by longer chain hydrocarbons, the stability of surface nitro-nitrato species and their reactivity toward adsorbed decane at various temperatures was investigated. The nitrates on the CuSO 4 /ZrO 2 catalyst are characterized by significantly lower thermal stability than the nitro-nitrato species on the Cu 2+ /ZrO 2 sample. The difference in the thermal stability of the NO x − species (x is 2 and 3) parallels their reactivity toward the adsorbed decane. The sulfate-free catalyst contains bidentate nitro species that are inert toward the hydrocarbon. The bidentate nitro species start to decompose to NO at temperatures higher than 523 K. In contrast, the nitrate species formed on the CuSO 4 /ZrO 2 catalyst are able to oxidize the adsorbed decane completely at 523 K producing acetates, formates, adsorbed CO and isocyanate species. It is proposed that the presence of stable nitro species on the sulfate-free copper(II)-zirconia catalyst is associated with its non-selective behavior above 573 K in the reduction of NO with decane in an excess of oxygen reported in the literature.

FT-IR spectroscopic investigation of the surface reaction of CH4 with NO x species adsorbed on Pd/WO3–ZrO2 catalyst

“…The intensities of these bands do not change synchronously with the increase in the temperature. Therefore, they are assigned to the m as (NO 2 ) modes of two types of inorganic bidentate nitrito species [20,42]. It should be pointed out that no adsorbed NO x compounds have been detected during the high-temperature adsorption of NO on the WZ sample [20] which confirms that the species associated with the bands at 1250 and 1220 cm )1 originate from the thermal transformation of the cismethyl nitrite.…”

“…A broad, unresolved absorption develops, which appears with maxima at 1255 and 1227 cm )1 at 250°C. In analogy with the WZ sample, these two bands are assigned to the m as (NO) 2 modes of two types of inorganic bidentate nitrito species [20,42]. At 300°C the adsorbed NO and cis-CH 3 ONO disappear from the spectrum which is accompanied by decrease in the intensities of the formate bands.…”

NOx storage and reduction pathways on zirconia and titania functionalized binary and ternary oxides as NOx storage and reduction (NSR) systems

“…4a. The spectral region between 1700 and 1200 cm −1 is characteristic for the nitrate and nitrite species coordinated on TiO 2 and ZrO 2 [28][29][30]. The observed frequencies at 1644 and 1209 cm −1 can be attributed to bridging nitrates, while the features at 1578, 1550 and 1280 cm −1 can be assigned to bidentate nitrates [8,31].…”

Cobalt supported on zirconia and sulfated zirconia II. Reactivity of adsorbed NOx compounds toward methane

“…The results of our previous investigation [7] have shown that the presence of sulfate ions in zirconia-supported copper(II) catalysts strongly modifies the reactivity of adsorbed NO x species toward saturated long-chain hydrocarbon (decane). The aim of this paper is to investigate the effect of sulfate ions in zirconia-supported cobalt catalysts on the reactivity of adsorbed NO x species toward methane.…”

“…In general, the mechanism of selective catalytic reduction of nitrogen oxides in excess oxygen on various oxide catalysts involves the interaction of strongly adsorbed NO x − species (x is 2 or 3) with the hydrocarbon [3][4][5][6][7][8][9]. The results of our previous investigation [7] have shown that the presence of sulfate ions in zirconia-supported copper(II) catalysts strongly modifies the reactivity of adsorbed NO x species toward saturated long-chain hydrocarbon (decane).…”