Investigating the mechanism of the H 2-assisted selective catalytic reduction (SCR) of NOx with octane using fast cycling transient in situ DRIFTS-MS analysis

A mechanistic study of the H-2-assisted Selective Catalytic Reduction (SCR) of NOx with octane as reductant over a Ag/Al2O3 catalyst was carried out using a modified DRIFTS cell coupled to a mass spectrometer Using fast transient cycling switching of H-2 with a time resolution of a few seconds It was possible to differentiate potential reaction intermediates from other moieties that are clearly spectator species Using such a periodic operation mode effects were uncovered that are normally hidden in conventional transient studies which typically consist of a single transient In experiments based on a single transient addition of H-2 to or removal of H-2 from the SCR feed it was found that the changes in the concentrations of gaseous species (products and reactants) were not matched by changes at comparable timescales of the concentration of surface species observed by IR This observation indicates that the majority of sur face species observed by DRIFTS under steady-state reaction conditions are spectators In contrast under fast cycling experimental conditions It was found that a surface isocyanate species had a temporal response that matched that of N-15(2) This suggests that some of the isocyanate species observed by infrared spectroscopy could be important intermediates in the hydrogen-assisted SCR reaction although it is emphasised that this may be dependent on the way in which the infrared spectra are obtained It is concluded that the use of fast transient cycling switching techniques may provide useful mechanistic information under certain circumstances.

Facile in situ synthesis of nanofluids based on ionic liquids and copper oxide clusters and nanoparticles

Two stable nanofluids comprising of mixed valent copper(_I,_II) oxide clusters (<1 nm) suspended in 1-butyl-3-methylimidazolium acetate, [C(₄)mim][OAc], and copper(_II) oxide nanoparticles (<50 nm) suspended in trioctyl(dodecyl) phosphonium acetate, [P-₈₈₈₁₂][OAc], were synthesised in a facile one-pot reaction from solutions of copper(_II) acetate hydrate in the corresponding ionic liquids. Formation of the nanostructures was studied using ¹³C NMR spectroscopy and differential scanning calorimetry (DSC). From a solution of Cu(OAc)₂ in 1-ethyl-3-methylimidazolium acetate, [C₂mim][OAc], crystals were obtained that revealed the structure of [C₂mim][Cu₃(OAc)₅(OH)₂(H₂O)]center dot H₂O, indicating the formation of copper hydroxo-clusters in the course of the reaction. Synthesised nanostructures were studied using transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Physical properties of the prepared IL-nanofluids were examined using IR and UV-VIS spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and densitometry. 

An in situ spatially resolved analytical technique to simultaneously probe gas phase reactions and temperature within the packed bed of a plug flow reactor

This paper reports the detailed description and validation of a fully automated, computer controlled analytical method to spatially probe the gas composition and thermal characteristics in packed bed systems. As an exemplar, we have examined a heterogeneously catalysed gas phase reaction within the bed of a powdered oxide supported metal catalyst. The design of the gas sampling and the temperature recording systems are disclosed. A stationary capillary with holes drilled in its wall and a moveable reactor coupled with a mass spectrometer are used to enable sampling and analysis. This method has been designed to limit the invasiveness of the probe on the reactor by using the smallest combination of thermocouple and capillary which can be employed practically. An 80 mu m (O.D.) thermocouple has been inserted in a 250 mu m (O.D.) capillary. The thermocouple is aligned with the sampling holes to enable both the gas composition and temperature profiles to be simultaneously measured at equivalent spatially resolved positions. This analysis technique has been validated by studying CO oxidation over a 1% Pt/Al2O3 catalyst and the spatial resolution profiles of chemical species concentrations and temperature as a function of the axial position within the catalyst bed are reported.

Catalysis of CO electrooxidation at Pt, Ru, and PtRu alloy. An in situ FTIR study

A comparative study of CO electrooxidation on different catalysts using in situ FTIR spectroscopy is presented. As electrode materials, polycrystalline Pt and Ru and a PtRu (50:50) alloy are used. The latter is one of the well-known active alloys for CO oxidation. The potential dependence of the band frequencies for the CO stretch indicates the formation of relatively compact islands at pure Pt and Ru, and a loose adlayer structure at the alloy. This loose structure has a positive effect on the rate of oxidative desorption. CO submonolayer coverages are obtained by integrating the absorption bands for CO produced upon oxidation of adsorbed CO. The band intensities measured at Pt, Ru, and PtRu indicate an influence of the substrate on the absorption coefficient of the CO stretch. It is shown that for a correct description of the catalyst properties toward CO electrooxidation, it must be distinguished between bulk and adsorbed CO. In contrast to the statement of most of the recent papers that a PtRu alloy (50:50) is the material with the highest activity for CO oxidation, it is demonstrated and rationalized in the present paper that for bulk CO oxidation pure Ru is the best catalyst. © 1999 American Chemical Society.

In situ FTIRS investigations of surface processes of Rh electrode - Novel observation of geminal adsorbates of carbon monoxide on Rh electrode in acid solution

With the help of in situ multi-step FTIR Spectroscopy, two types of adsorbed geminal CO have been observed for the first time at an electrochemically modified Rh electrode. A doublet band of two broad peaks at 2166 and 2112cm is assigned to geminal CO on Rh surface oxide (or hydroxide) produced by the electrochemical modification process, and a doublet band of two peaks near 2103 and 2033cm is ascribed to geminal CO on surface clusters of Rh formed by reduction of Rh surface oxide. Based on the evolution of FTIR spectra with the electrode potential, the surface processes of a Rh electrode, subjected to a potential cycling treatment at 1.5Vs between -0.275 and 2.4V for 2min, have been elucidated. The present results at the solid/liquid electrochemical interface were compared with those obtained at the solid/gas interface, and consistent conclusions were achieved.

In situ FTIR studies of the effect of temperature on the adsorption and electrooxidation of CO at the Ru(0001) electrode surface

The adsorption and electrooxidation of CO at a Ru(0001) electrode in perchloric acid solution have been investigated as a function of temperature, potential and time using in situ FTIR spectroscopy. This builds upon and extends previous work on the same system carried out at room temperature. As was observed at room temperature, both linear (CO) and 3-fold-hollow (CO) binding CO adsorbates (bands at 2000-2045 cm and 1768-1805 cm, respectively) were detected on the Ru(0001) electrode at 10°C and 50°C. However, the temperature of the Ru(0001) electrode had a significant effect upon the structure and behavior of the CO adlayer. At 10°C, the in-situ FTIR data showed that the adsorbed CO species still remain in rather compact islands up to ca. 1100 mV vs Ag/AgCl as the CO oxidation reaction proceeds, with oxidation occurring only at the boundaries between the CO and active surface oxide/hydroxide domains. However, the IR data collected at 50°C strongly suggest that the adsorbed CO species are present as relatively looser and weaker structures, which are more easily electro-oxidized. The temperature-, potential-, and coverage-dependent relaxation and compression of the CO adlayer at low coverages are also discussed.

In situ FTIR spectroscopic studies of the oxidation of CO adsorbates on Ru(0 0 0 1) electrodes under open circuit conditions

This paper reports the first observation, using in situ FTIR spectroscopy, of the oxidation of CO adsorbates on the Ru(0001) electrode to CO under open circuit (oc) conditions in both perchloric acid and sulphuric acid solution at 20 and 55 °C. While the significant oc oxidation of the adsorbed CO on the Ru(0001) electrode was observed in perchloric acid solution, much less oc oxidation took place in sulfuric acid solution due to the specific adsorption of bisulfate at the Ru surface which inhibits the surface oxidation and reduces the reactivity of the surface towards the oxidation of CO . The oc oxidation of the CO depends strongly on the oxygen concentration in the solution and the temperature. The data so obtained are compared to those observed at the gas|solid interface, as well as to those obtained from the electro-oxidation of CO , and possible new catalytic oxidation reaction mechanisms are discussed. In addition, it is shown that the C-O frequency of the adsorbed CO may be used as an effective probe of the open circuit potential. © 2003 Elsevier B.V. All rights reserved.

In situ FTIR studies on the effect of temperature on the electro-oxidation of small organic molecules at the Ru(0001) electrode

The adsorption and electro-oxidation of formaldehyde, formic acid and methanol at the Ru(0001) electrode in perchloric acid solution have been studied as a function of temperature, potential and time using in situ FTIR spectroscopy, and the results interpreted in terms of the surface chemistry of the Ru(0001) electrode and compared to those obtained during our previous studies on the adsorption of CO under the same conditions. It was found that no dissociative adsorption or electro-oxidation of methanol takes place at Ru(0001) at potentials 1000 mV, both the oxidation of formic acid to CO and the oxidation of formaldehyde to both CO and formic acid were significantly increased, and the oxidation of methanol to CO and methyl formate was observed, all of which were attributed to the formation of an active RuO phase on the Ru(0001) surface.

The electro-oxidations of methanol and formic acid at the Ru(0001) electrode as a function of temperature:In-situ FTIR studies

The electro-oxidations of methanol and formic acid at a Ru(0001) electrode in perchloric acid solution have been investigated as functions of temperature, potential and time using in-situ FTIR spectroscopy, and the results compared to those obtained during our previous studies on the adsorption and electro-oxidation of CO under the same conditions. It was found that no dissociative adsorption or electro-oxidation of methanol takes place at the Ru(0001) at potentials 1000 mV, the oxidation of formic acid to CO was significantly increased, and the oxidation of methanol to CO and methyl formate was observed, both of which were attributed to the formation of an active RuO phase on the Ru(0001) surface.

High energy resolution fluorescence detection XANES - an in situ method to study the interaction of adsorbed molecules with metal catalysts in the liquid phase

The change in the Pt electronic structure following the adsorption of an a,ß-unsaturated aldehyde and ketone was followed by in situ HERFD-XANES in the liquid phase. The resulting shift in the Pt Fermi energy is in good agreement with the molecule adsorption energy trends calculated by DFT and provides insight into the reaction selectivity.

In-situ Monitoring of Solid Oxide Electrolysis Cells

High temperature co-electrolysis of steam and carbon dioxide using a solid oxide cell (SOC) has been shown to be an efficient route to produce syngas (CO + H-2), which can then be converted to synthetic fuel. Optimization of co-electrolysis requires detailed understanding of the complex reactions, transport processes and degradation mechanisms occurring in the SOC during operation. Thermal imaging, Raman spectroscopy and Diffuse Reflectance Infrared Fourier Transform Spectroscopy are being developed to probe in-situ both the reactions occurring during operation and any associated changes within the structure of the electrodes and electrolyte. Here we discuss the challenges in designing experimental apparatus suitable for high temperature operation with optical spectroscopic access to the areas of the SOC that are of interest. In particular, issues with sealing, temperature gradients, signal strength and cell configuration are discussed and final designs are presented. Preliminary results obtained during co-electrolysis operation are also presented.

Evaluation of an in situ spatial resolution instrument for fixed beds through the assessment of the invasiveness of probes and a comparison with a micro-kinetic model

This paper reports the detailed description and validation of a fully automated, computer controlled analytical method to spatially probe the gas composition and thermal characteristics in packed bed systems. This method has been designed to limit the invasiveness of the probe, a characteristic assessed using CFD. The thermocouple is aligned with the sampling holes to enable simultaneous recording of the gas composition and temperature profiles. This analysis technique has been validated by studying CO oxidation over a 1% Pt/Al2O3 catalyst. The resultant profiles have been compared with a micro-kinetic model, to further assess the strength of the technique. 

In situ ATR-FTIR study of H2O and D2O adsorption on TiO2 under UV irradiation

The adsorption of water and deuterium oxide on TiO2 surfaces was investigated in the dark as well as under UV(A) irradiation using in situ ATR-FTIR spectroscopy under oxygen and oxygen free conditions. Adsorption of H2O-D2O mixtures revealed an isotopic exchange reaction occurring onto the surface of TiO2 in the dark. Under UV(A) irradiation, the amount of both OH and OD groups was found to be increased by the presence of molecular oxygen. Furthermore, the photocatalytic formation of hydroperoxide under oxygenated condition has been recorded utilizing Attenuated Total Reflection Fourier Transformed Infrared (ATR-FTIR) spectroscopy which appeared as new band at 3483 cm-1. Different possible mechanisms are discussed in terms of the source of hydroxyl groups formed and/or hydration water on the TiO2 surface for the photocatalytic reaction and photoinduced hydrophilicity.

Complete filling of zeolite frameworks with polyalkynes formed in situ by transition-metal ion catalysts

We report the use of transition-metal-exchanged zeolites as media for the catalytic formation and encapsulation of both polyethyne and polypropyne, and computer modeling studies on the composites so formed. Alkyne gas was absorbed into the pores of zeolite Y (Faujasite) exchanged with transition-metal cations [Fe(II), Co(II), Cu(II), Ni(II), and Zn(II)]. Ni(II) and Zn(II) were found to be the most efficient for the production of poly-ynes. These cations were also found to be effective in polymer generation when exchanged in zeolites mordenite and beta. The resulting powdered samples were characterized by FTIR, Raman, diffuse reflectance electronic spectroscopy, TEM, and elemental analysis, revealing, nearly complete loading of the zeolite channels for the majority of the samples. Based on the experimental carbon content, we have derived the percentage of channel filling, and the proportion of the channels containing a single polymer chain for mordenite. Experimentally, the channels for Y are close to complete filling for polyethyne (PE) and polypropyne (PP), and this is also true for polyethyne in mordenite. Computer modeling studies using Cerius2 show that the channels of mordenite can only accept a single polymer chain of PP, in which case these channels are also completely filled.

Observing the in situ chiral modification of Ni nanoparticles using scanning transmission X-ray microspectroscopy

Enantioselective heterogeneous hydrogenation of Cdouble bond; length as m-dashO bonds is of great potential importance in the synthesis of chirally pure products for the pharmaceutical and fine chemical industries. One of the most widely studied examples of such a reaction is the hydrogenation of β-ketoesters and β-diketoesters over Ni-based catalysts in the presence of a chiral modifier. Here we use scanning transmission X-ray microscopy combined with near-edge X-ray absorption fine structure spectroscopy (STXM/NEXAFS) to investigate the adsorption of the chiral modifier, namely (R,R)-tartaric acid, onto individual nickel nanoparticles. The C K-edge spectra strongly suggest that tartaric acid deposited onto the nanoparticle surfaces from aqueous solutions undergoes a keto-enol tautomerisation. Furthermore, we are able to interrogate the Ni L2,3-edge resonances of individual metal nanoparticles which, combined with X-ray diffraction (XRD) patterns showed them to consist of a pure nickel phase rather than the more thermodynamically stable bulk nickel oxide. Importantly, there appears to be no “particle size effect” on the adsorption mode of the tartaric acid in the particle size range ~ 90–~ 300 nm.