Coadsorption Of Nitric Oxide Research Articles

Theoretical Studies on the Mechanism of deNOx Process in Cu-Zn Bimetallic System-Comparison of FAU and MFI Zeolites.

In the present study we propose a more promising catalyst for the deNOx process to eliminate harmful nitrogen oxides from the environment. The study was performed with a computer calculation using density functional theory (DFT) based on an ab initio method. Two zeolite catalysts, FAU and MFI, were selected with additional Cu–O–Zn bimetallic dimer adsorbed inside the pores of both zeolites. Based on the analysis of preliminary studies, the most probable way of co-adsorption of nitric oxide and ammonia was selected, which became the initial configuration for the reaction mechanism. Two types of mechanisms were proposed: with hydroxyl groups on a bridged position of the dimer or a hydroxyl group on one of the metal atoms of the dimer. Based on the results, it was determined that the FAU zeolite with a bimetallic dimer and an OH group on the zinc atom was the most efficient configuration with a relatively low energy barrier. The real advantage of the Cu–Zn system over FAU and MFI in hydrothermal conditions has been demonstrated in comparison to a conventional Cu–Cu catalyst.

Coadsorption of CO and NO on the Cu2O(111) surface: A periodic density functional theory study

Coadsorption of carbon monoxide (CO) and nitric oxide (NO) on the Cu(2)O(111) surface was studied using periodic density functional theory calculations. It is interesting to find that CO+NO on Cu(2)O(111) could react to form adsorbed NCO surface species. Coadsorption of CO and NO could give rise to the formation of a O-C...N-O complex well bound to the Cu(2)O(111) surface, in which both the C-O and N-O bonds are greatly activated and the C-N bond is formed. Consequently, the reaction of CO with NO to form adsorbed NCO and CNO species may occur, for which it is disclosed that NCO formation is more possible than CNO formation both thermodynamically and kinetically. In addition, our calculations of searching transition states reveal that it is facile for NCO formation both kinetically and thermodynamically when CO+NO reaction takes place at Cu(CUS) site, and is impossible when this reaction takes places at O(vac) site. Moreover, CO(2) species cannot form when CO+NO reaction occurs at O(vac) site. Therefore, oxygen vacancy on Cu(2)O(111) does not play a positive role on CO+NO reaction to forming NCO, CNO, or CO(2) species.

Coadsorption of nitric oxide and carbon monoxide on the nickel clusters deposited onto MgO(111) film formed on Mo(110)

Coadsorption of NO and CO molecules on the Ni clusters deposited on MgO(111) film formed on a Mo(110) crystal has been studied by reflection–absorption infrared spectroscopy (RAIRS) and temperature programmed desorption (TPD). It is found that adsorption of NO molecules strongly affects the state of CO molecules, which were initially adsorbed on the Ni clusters. The observed features in RAIRS and TPD spectra are attributed to the change of the CO adsorption site and geometry, which is induced by NO adsorption.

CO and NO adsorption and co-adsorption on the Pd(1 1 1) surface

Adsorption and co-adsorption of nitric oxide (NO) and carbon monoxide (CO) on a Pd(1 1 1) surface were studied using pseudopotential density-functional theory calculations. For individual NO and CO molecules we determined the energetically most stable adsorption sites and harmonic frequencies. The results show that at 0.25 monolayer (ML) coverage both the molecules prefer to reside on a hollow site in agreement with experimental and earlier theoretical results. At half of monolayer coverage pure NO occupies only hollow sites but CO molecules have two energetically degenerate structures namely fcc–hcp and bridge–bridge. The harmonic vibrational frequencies were calculated for the most stable structures and the changes of frequencies from 0.25 ML coverage to 0.5 ML were compared to the corresponding experimental shifts. Our results suggest a hollow site adsorption for NO and a hollow–bridge mixture for CO. CO/NO co-adsorption was studied at 0.5 ML coverage with a molecular ratio 1/1. We investigated 16 co-adsorption geometries and found five almost equally stable structures, where NO is mainly on a hollow site, whereas CO occupies either a hollow or a bridge site. For all the examined structures the interaction between co-adsorbed molecules is repulsive. The strength of the repulsion depends on a inter-molecule distance and sharing of the common Pd atom. We calculated harmonic wave numbers for three structures, and found that different adsorbates do not vibrate in resonance.

Coadsorption of CO and NO on the Pd(111) surface: combined ab initio and Monte Carlo study.

Adsorption and coadsorption of nitric oxide (NO) and carbon monoxide (CO) on the Pd(111) surface are studied by combining first principles (FP) calculations and Monte Carlo (MC) simulations. From FP adsorption energies and molecule-molecule interactions we construct an interaction model, which is used in MC. We do several simulations with different coverages and CO/NO ratios. The simulations provide 0.75 monolayer (ML) for a saturation coverage, which is in excellent agreement with experiments. The results indicate that at 0.75 ML coverage, NO molecules take over the hollow sites and push CO molecules mainly onto bridge sites.

IR spectroscopic study of NO and CO adsorptions on nonstoichiometric nickel–copper manganites

The adsorptions and co-adsorption of nitric oxide and carbon monoxide on nonstoichiometric nickel and nickel–copper manganites have been investigated in situ by transmission infrared spectroscopy. Time-dependent and temperature-dependent data have been acquired to investigate the nature of the molecule–surface interactions. The surface chemistry of NO was found to be particularly rich, involving numerous surface species (mononitrosyls, dinitrosyls, adsorbed N2O, nitrites/nitrates), whereas that of CO was somewhat simpler. The competitive adsorption of NO and CO was evidenced. However, with time, NO tended in all cases to colonize the surface of the samples, and Cu+ cations were shown to be the only access points of CO to the surface of such oxides in the presence of NO. Finally, a time sequence of reactions was shown in the case of NO adsorption.

Site switching and restructuring of oxygen adlayers induced by high coverage NO on Co{101̄0} at 100 K

We have employed reflection–absorption IR spectroscopy (RAIRS) as the principal technique as well as low energy electron diffraction (LEED) and temperature programmed desorption (TPD) as diagnostic tools to study the adsorption and reaction of nitric oxide (NO) on oxygen precovered Co{101̄0} surfaces at 100 K. The presence of oxygen adatoms greatly attenuates the occupation of two-fold sites in favor of atop sites, but O adatoms do not show any significant blocking effect for NO adsorption, and the NO coverage is close to 0.5 ML, as found on the clean surface. Beyond a critical coverage of NO, whatever the initial O coverage, a new IR band appears at ∼1876 cm−1 which is indicative of a strong NO–O interaction. The coadsorption of NO with various precoverages of oxygen (0.15–1.0 ML) including three ordered oxygen overlayers, c(2×4) (θO≈0.5 ML), p(2×1) (θO≈0.5 ML), and p(2×1)-g (θO≈1.0 ML), reveals an NO-induced surface restructuring process, in which O adatoms are driven from overlayer to underlayer sites at high NO coverages. This restructuring process increases the O effective diameter to up to ∼10 Å, this being the range over which the NO–O interaction is strong, producing the 1870 cm−1 N–O band.

Coadsorption of nitric oxide and oxygen on the Ag(110) surface

The coadsorption of NO and O2 on Ag(110) surface has been studied by X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS) and in situ Raman spectroscopy. The existence of oxygen enhances the adsorption of NO by forming the NOx species, that is, NO2 and NO3, and the NO in turn as a promotor facilitates the cleavage of the dioxygen bond, forming the surface atomic oxygen species having the same spectral characteristics as those produced using oxygen at high pressure. The oxygen species generated by the interaction is composed of two parts. One is produced directly by the decomposition of surface NO–O2 complex at ca 625K, which raised an O1s feature at 530.5eV and is absent at ca 800K, while the another with an O1s binding energy of 529.2eV emerges at higher temperatures and shows similar properties as the reported γ-state oxygen which bound tightly on restructured silver surface. The exposure to NO and O2 causes noticeable changes in the morphology of the Ag(110) surface and the flat terraces superseded by small (ca 0.1μm) pits, and particles with typical diameters of a few micrometres were formed at elevated temperatures.

Fourier transform-infrared study of the adsorption and coadsorption of nitric oxide, nitrogen dioxide and ammonia on vanadia-titania and mechanism of selective catalytic reduction

The adsorption of nitric oxide, nitrogen dioxide and ammonia and their coadsorption on vanadia-titania have been studied by FT-IR spectroscopy. Upon nitric oxide adsorption, a surface nitrosyl species is formed rapidly and nitrates are formed slowly by oxidation. Nitrogen dioxide adsorption forms nitrate species by oxidation and nitric oxide. Lewis-bonded molecular species and ammonium ions are formed upon ammonia adsorption. Coordinated ammonia is thermally more stable than ammonium ions and can lose an hydrogen atom to give an amide species. Adsorption on a water-covered sample shows that ammonia displaces water from Lewis sites. Experiments of nitric oxide adsorption on ammonia-covered vanadia-titania show that ammonia poisons the nitric oxide adsorption sites and that NO 3- species are formed by nitric oxide oxidation on vanadyl sites. By heating the ammonia-covered sample in the presence of gaseous nitric oxide coordinated ammonia reacts via the amide species, while ammonium ions do not. The following reaction mechanism is proposed: VO 2+ + NH 3 = [HO-V-NH 2] 2+ NO + [HO-V-NH 2] 2+ = [HO-V-NH 2-NO] 2+ [HO-V-NH 2-NO] 2+ = N 2 + H 2O + [VOH] 2+ [VOH] 2+ +1/4 O 2 = VO 2+ +1/2 H 2O This reaction sequence is believed to operate during the selective catalytic reduction of NO x over vanadia-titania based catalysts.

Fourier transform infrared study of the adsorption and coadsorption of nitric oxide, nitrogen dioxide and ammonia on TiO 2 anatase

The adsorption and coadsorption of NO, NO 2 and NH 3 on TiO 2 anatase has been studied by Fourier-transform infrared (FT-IR) spectroscopy. Upon NO adsorption, nitrosyl species adsorbed on two different Lewis sites are observed, together with N 2O produced via the reduction of NO by Ti 3+, and NO 3- formed by oxidation of NO by Ti 4+. Adsorption of NO 2 produces several distinct adsorbed nitrate ions with different thermal stabilities. NH 3 molecularly coordinated on two different Lewis sites is observed upon NH 3 adsorption. Nitrosyls are not formed by contacting the NH 3-covered surface of TiO 2 with gaseous NO. Coadsorption of NH 3 with NO and NO 2 causes only a few perturbations, attributed to changes in the coordination of nitrates and of NH 3 species. No evidence is found for the reaction of NO x with NH 3 to 523 K, in line with the poor catalytic activity of TiO 2 in the Selective Catalytic Reduction (SCR) of NOx by NH 3.

Coadsorption of nitric oxide and benzene on Ru(001)

The coadsorbate system NO + benzene has been studied on Ru(001) at various relative coverage ratios using HREELS, ΔΦ, TPD and LEED. A strong mutual influence of the two molecules is found as indicated by appreciable shifts of the vibrational frequencies. Benzene retains C 6v symmetry in the mixed layer, but it shows a strongly altered behavior concerning molecular desorption and dehydrogenation. In particular, a much higher amount of benzene than for the pure layer desorbs molecularly. In the mixed layer, three states of adsorbed NO are formed, with electron accepting species being favored. Characteristic shifts of the N-O stretch frequencies to lower values indicate an enhanced occupation of the antibonding 2π ∗ orbital of NO which presumably results from indirect charge transfer from benzene to NO through the substrate. During thermal evolution a transformation of NO occupying bridge sites to the terminally bound linear NO δ+ species is found.

Observation of an NH 3NO complex on the Pt(111) surface

The coadsorption of nitric oxide and ammonia has been studied on the Pt(111) surface using electron energy loss spectroscopy and thermal desorption spectroscopy to characterize the surface complex which forms between adsorbed molecular ammonia and adsorbed molecular nitric oxide. A stretching frequency of the surface complex occurs at 1280 cm −1 and is formed by the coalescence of the bridge-bonded nitric oxide stretching mode at 1490 cm −1 and the symmetric deformation mode of the low-coverage, high-temperature form of molecular ammonia at 1090 cm −1. The thermal stabilities of some of the adsorbed nitric oxide and the low-coverage, high-temperature form of adsorbed molecular ammonia are increased as evidenced by the appearance of new high-temperature desorption peaks for both NO and NH 3 at 350 K. Thermal desorption experiments with coadsorbed nitric oxide and ammonia indicate that no nitrogen formation occurs directly from the surface complex. With heating, the NH 3NO complex simply decomposes at 350 K, and desorption of molecular ammonia and nitric oxide occurs. Ammonia decomposition has been observed on this surface only above 400 K, and therefore it appears that NH 3 decomposition may be necessary to initiate the NONH 3 reaction on this surface.

多結晶タングステン表面への一酸化窒素，窒素及び酸素の共吸着について

The coadsorption of nitric oxide, nitrogen, and oxygen on a polycrystalline tungsten filament was studied using flash desorption mass spectroscopy. Oxygen or nitrogen does not adsorb on tungsten saturated with nitric oxide, whereas nitric oxide adsorbs on tungsten saturated with nitrogen or oxygen. The strength of the chemisorption bond between tungsten and adsorbed species becomes weaker in the order of nitric oxide, oxygen and nitrogen. When oxygen is adsorbed on the tungsten surface saturated with nitrogen, the Tp of nitrogen desorption spectrum shifted to a lower temperature.