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

Cataloged from PDF version of article.The nature of the NOx 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 NOx 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 CuSO4/ZrO2 catalyst are characterized by significantly lower thermal stability than the nitro-nitrato species on the Cu2+/ZrO2 sample. The difference in the thermal stability of the NOx- 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 CuSO4/ZrO2 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. (C) 2002 Elsevier Science B.V. All rights reserved

Routes of formation and composition of NOx complexes adsorbed on palladium-promoted tungstated zirconia

Cataloged from PDF version of article.Surface species obtained during the adsorption of NO and NO/O2 coadsorption at room temperature on Pd-free (WZ) and Pd-promoted tungstated zirconia (Pd/WZ) are identified by means of in situ FT-IR spectroscopy. The WZ and Pd/WZ samples have a tetragonal structure and contain randomly distributed mesoporous phase. Dispersed palladium(II) species are present in two different environments: (i) Pd2+ ions, which have only Zr4+ ions in their second coordination sphere and (ii) Pd2+ ions, which are linked to both zirconium and tungsten ions via oxygen bridges. On the Pd/WZ sample, NO undergoes oxidation to various NOx species depending on the temperature. The compounds formed at room-temperature oxidation are adsorbed N2O3 and products of its self-ionization, NO+ and NO2-. In this process W(VI) is involved, being reduced to W(IV). At high temperature N2O3 decomposes, restoring the WO species. Under these conditions, NO undergoes oxidation to NO2 by the Pd(II) ions, which are reduced to Pd(I). The nitrosyls of Pd(I) display high thermal stability and do not disappear upon evacuation at 623 K. During NO/O2 coadsorption on the Pd/WZ catalyst at room temperature, the amounts of surface nitrates and NO2/N2O4 formed in the gas phase are significantly lower than those observed under identical conditions in the presence of tungstated zirconia. It is concluded that promotion of tungstated zirconia with palladium(II) suppresses the oxidation of NO by molecular oxygen at room temperature due to the elimination of acidic protons involved in the process. © 2005 Elsevier B.V. All rights reserved

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

Cataloged from PDF version of article.In order to evaluate the effect of sulfate ions in zirconia-supported cobalt catalysts on the reactivity of adsorbed NOx species toward methane, experiments involving the interaction of the hydrocarbon with NOx-free and NOx-precovered catalysts are performed. The nitrate species formed at room-temperature adsorption of NO/O-2 over the CoOx/ZrO2 catalysts are inert toward the methane in the 573-723 K temperature range. Over NOx-precovered CoOx/SO42--ZrO2 catalysts, oxidation of the hydrocarbon starts at 573-623 K with the participation of reactive nitro-nitrato species coordinated to cobalt sites. It is proposed that in the catalytic reduction of NO over the sulfated cobalt catalysts, the activation of methane occurs on cobalt sites and the products of the latter process-formate species and formic acid-are key intermediates capable of selectively reducing the nitro-nitrato species. (C) 2004 Elsevier Inc. All rights reserved

Characterization of Zr6Nb2O17 synthesized by a peroxo route as a novel solid acid

Cataloged from PDF version of article.The impregnation of hydrated zirconia at pH 0.5 with a solution of peroxoniobium(V) complex, [Nb2(O2)3] 4+, ensuring a ZrO2:Nb2O5 mole ratio of 6:1 followed by calcination at 873 K resulted in the formation of a Zr6Nb2O17 solid solution. The structure of this compound was confirmed by XRD. The surface acidity was investigated by in situ FT-IR spectroscopy using 2,6-dimethylpyridine (lutidine). Zr6Nb2O17 has a sufficient amount of Brønsted acid sites necessary for the stabilization of dispersed Pd(II) species. The potential of the Pd-promoted Zr6Nb2O17 as a catalyst for the reduction of NO with methane was evaluated by studying the reactivity of adsorbed NOx species toward the hydrocarbon. 2007 Elsevier B.V. All rights reserved

XPS and FTIR characterization of manganese ions deposited on alumina

Cataloged from PDF version of article.By application of XPS and FTIR spectroscopy of adsorbed CO the effect of preparation conditions on the state and localization of manganese ions deposited on h-Al2O3 is studied. Both Mn21 and Mn31 ions are observed on the impregnated sample. The sample obtained by ion exchange contains only Mn31 ions. The adsorbed CO species are identified. q 1999 Elsevier Science B.V. All rights reserved

Spectroscopic characterization of VOx/ZrO2 catalysts prepared using vanadium(V) oxo complexes

A method for deposition of vanadium(V) oxo species on zirconia using different vanadium(V) precursor ions is described. The samples are synthesized by suspension of the support (powder) in solutions containing: (i) the dioxovanadium(V) ion, VO2+; (ii) the yellow diperoxo anion, [VO(O-O)2]- and (iii) the red monoperoxo cation, [VO(O-O)]+. The application of vanadium(V) peroxo complexes significantly increases the uptake of vanadium by zirconia. The state and localization of the VOx species on the surface of zirconia have been studied by FTIR, UV-Vis and XP spectroscopies. © 2001 Elsevier Science B.V

Spectroscopic characterization of vanadium(v) oxo species deposited on zirconia

A method for deposition of vanadium(v) oxo species from acidic solutions of ammonium metavanadate on zirconia is described. The samples are synthesized by suspension of the support (powder) in solutions containing three different vanadium(V) precursor ions: the dioxovanadium(V) ion, VO2+, the yellow diperoxo anion [VO(O-O)2]- and the red monoperoxo cation [VO(O- O)]+. Application of vanadium(V) peroxo complexes increases significantly the uptake of vanadium by zirconia. The state and localization of the VO(x) species on the surface of zirconia were studied by FTIR, UV/VIS and XP spectroscopies. The materials prepared from VO2+ ions contain isolated VO4 groups and domains of orthovanadate species, (VO4)(n). The FTIR spectra of adsorbed CO revealed that the number of exposed Zr4+ ions decreased markedly when vanadium(v) peroxo ions were used as precursors. The predominant surface structure in this case was identified as pyrovanadates, V2O7. On all of the samples studied no separate phase of V2O5 was detected

Structure control of silica-supported mono and bimetallic Au–Pt catalysts via mercapto capping synthesis

Cataloged from PDF version of article.SiO2-supported monometallic and bimetallic platinum-gold catalysts are prepared by deposition of metal nanoparticles stabilized by mercaptopropyltriethoxysilane (MPTES) after different aging time of the solution containing metal ions and MPTES. The materials are tested in the hydrodesulfurization (HDS) reaction of thiophene and compared with corresponding catalysts prepared by the conventional deposition-precipitation (DP) method. The monometallic Pt and the bimetallic Au-Pt prepared by DP have comparable activity. With respect to the platinum catalyst prepared by DP, the corresponding platinum catalyst prepared by MPTES particle stabilization exhibits a substantial enhancement of the activity regardless the solution aging time. On the contrary, the MPTES-assisted Au-Pt catalysts have different activities, depending on the solution aging time, with the most active being the one obtained with the 5-day-aged solution. In accord with XRD, XPS, and FTIR, the aging time of the solution, through the different interaction of Pt or Au precursors with the mercapto groups, has a crucial effect on the structure and on the surface of the catalysts. The observed differences in the catalytic activity are related to the structural and compositional changes of the bimetallic particles. (C) 2012 Elsevier Inc. All rights reserved

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

The interaction of methane at various temperatures with NO x species formed by room temperature adsorption of NO + O2 mixture on tungstated zirconia (18.6 wt.% WO3) and palladium(II)-promoted tungstated zirconia (0.1 wt.% Pd) has been investigated using in situ FT-IR spectroscopy. A mechanism for the reduction of NO over the Pd-promoted tungstated zirconia is proposed, which involves a step consisting of thermal decomposition of the nitromethane to adsorbed NO and formates through the intermediacy of cis-methyl nitrite. The HCOO- formed acts as a reductant of the adsorbed NO producing nitrogen. © Springer Science+Business Media, LLC 2007

Characterization of LaMnAl11O19 by FT-IR spectroscopy of adsorbed NO and NO/O-2

Cataloged from PDF version of article.The nature of the NOx species produced during the adsorption of NO at room temperature and during its coadsorption with oxygen on LaMnAl11O19 sample with magnetoplumbite structure obtained by a sol–gel process has been investigated by means of in situ FT-IR spectroscopy. The adsorption of NO leads to formation of anionic nitrosyls and/or cis-hyponitrite ions and reveals the presence of coordinatively unsaturated Mn3+ ions. Upon NO/O2 adsorption at room temperature various nitro–nitrato structures are observed. The nitro–nitrato species produced with the participation of electrophilic oxygen species decompose at 350 8C directly to N2 and O2. No NO decomposition is observed in absence of molecular oxygen. The adsorbed nitro–nitrato species are inert towards the interaction with methane and block the active sites (Mn3+ ions) for its oxidation. Noticeable oxidation of the methane on the NOx -precovered sample is observed at temperatures higher than 350 8C due to the liberation of the active sites as a result of decomposition of the surface nitro–nitrato species. Mechanism explaining the promoting effect of the molecular oxygen in the NO decomposition is proposed. (c)2005 Elsevier B.V. All rights reserved