DRIFT Spectroscopy Research Articles

TWC deactivation by lead: A study of the Rh/CeO2 system

The effect of the incorporation of low amounts of Pb to a Rh/CeO2 catalyst on the typical reactions involved in Three Way Catalysts converters was investigated. The catalytic tests showed no deactivation for CO oxidation and NO reduction whereas for propylene oxidation the deactivation was evident and more intense with the increasing of Pb concentration. The interpretation of this behaviour is discussed on the basis of HREM combined with XEDS analysis, TPR and DRIFT spectroscopy of chemisorbed CO studies. The results provided clear evidence that Pb is not covering the Rh particles neither forming a new phase with Rh nor altering the dispersion of the Rh particles. They also suggest that a mixed oxide is formed in which lead cations are dissolved within the fluorite-like ceria structure. Thus, CeO2 support may act as sink of Pb preventing the formation of a Rh–Pb compound that explains why the CO oxidation and the NO reduction were only slightly affected. However, an electronic interaction between the Rh particles and the Pb-containing CeO2 support is evidenced by TPR and DRIFTS-CO chemisorption data: the Pb present in the Rh-CeO2 interphase as a result of the Pb dissolution in the ceria framework is proposed to be responsible for the electronic donation to Rh metal particles. The possibility that the electronic interaction and/or the modification of the oxygen storage capacity (OSC) of the ceria, both caused by the Pb, bring about the deactivation in the oxidation of propylene is also discussed.

Preparation and evaluation of glibenclamide-polyglycolized glycerides solid dispersions with silicon dioxide by spray drying technique

Solid dispersions (SDs) of glibenclamide (GBM); a poorly water-soluble drug and polyglycolized glycerides (Gelucire ®) with the aid of silicon dioxide (Aerosil ® 200); as an adsorbent, were prepared by spray drying technique. SDs and spray dried GBM in comparison with pure GBM and corresponding physical mixtures (PMs) were initially characterized and then subjected to ageing study up to 3 months. Initial characterization of SDs and spray dried GBM by DSC and XRPD showed that GBM was present in its amorphous form (AGBM). Improvement in the solubility and dissolution rate was observed for all samples. DRIFT spectroscopy revealed presence of hydrogen bonding in SDs. During ageing study, almost no decrease of in vitro drug dissolution was observed, over the period of 3 months as compare with freshly prepared SDs. Slight crystallinity in SDs was observed in the DSC and XRPD studies during ageing. Moreover in vivo study in Swiss Albino mice also justified the improvement in the therapeutic efficacy of amorphous GBM in SDs over pure GBM. Thus, present study demonstrated the high potential of spray drying technique for obtaining stable free flowing SDs of poorly water-soluble drugs using polyglycolized glycerides carriers with the aid of silicon dioxide as an adsorbent.

Study of the supported zirconocene catalysts by means of UV/vis and DRIFT spectroscopy

UV/vis in diffusion reflection mode (DRS) and DRIFT spectroscopy have been used to study the surface zirconocene species formed at the interaction of Me 2Si(Ind) 2ZrCl 2 and Me 2Si(Ind) 2ZrMe 2 complexes with the MAO/SiO 2 support. Effect of additional activation of these catalysts with TIBA has been studied as well. Structure of type [Me 2Si(Ind) 2ZrMe] +[MeMAO] − (C) is formed at the reaction of Me 2Si(Ind) 2ZrMe 2 complex with MAO/SiO 2 (a.b. at 456 nm in UV/vis spectra). Interaction of this complex with TIBA results in the formation of new structure (D) with a.b. at 496 nm in UV/vis spectra. The surface species of different composition and structures are formed at interaction of Me 2Si(Ind) 2ZrCl 2 complex with MAO/SiO 2. The ratio between these species depends on the zirconium content in the Me 2Si(Ind) 2ZrCl 2/MAO/SiO 2 catalysts. According to the DRIFTS data (CO and ethylene adsorption) and ethylene polymerization data these catalysts contain active Zr Me bonds but activity of these catalysts at ethylene polymerization is low. Interaction of Me 2Si(Ind) 2ZrCl 2/MAO/SiO 2 with TIBA leads to the formation of the new cationic structure of type (D) with a.b. at 496 nm in UV/vis spectra and great increasing of activity at ethylene polymerization.

Low temperature water-gas shift: Examining the efficiency of Au as a promoter for ceria-based catalysts prepared by CVD of a Au precursor

Increasing the Au loading had a significant positive impact on the catalytic activity. The partial reduction of ceria is necessary for generating bridging OH groups on the surface of ceria, which serve as the active sites. The surface shell reduction process in H 2 was monitored by TPR, XANES, and in situ DRIFTS spectroscopy. Either the oxygen deficiencies are first formed, followed by dissociative adsorption of H 2O to generate the Type II bridging OH groups or, they may be formed directly by spillover of dissociated H 2 from the metal to the ceria surface. For each pair of bridging OH groups formed, two cerium atoms in the surface shell change from the Ce 4+ to Ce 3+ oxidation state. Addition of Au facilitates the surface reduction process and thereby decreases the reduction temperature from 450 °C for the unpromoted catalyst to 100 °C for the 5% Au/ceria catalyst. A systematic decrease in the required temperature for ceria surface shell reduction was observed by increasing the Au promoter loading as follows: 0.1, 0.25, 0.5, 1, 2.5, 5%. Gold and platinum promoted catalysts were compared in a suitable reaction temperature range after first ensuring that metal–oxide interactions were overcome (ca. 5% metal loading). Approximately 20 times the amount of 5% Au/ceria catalyst was required to achieve a lightoff curve similar to that of a 5% Pt/ceria in the temperature range 200–300 °C, and 5% Pt/ceria also exhibited higher steady-state activity (about double that of Au) at 175 °C. This result suggests that, in addition to the role the metal plays in facilitating the formation of the active site bridging OH groups, it also influences the intrinsic rate of the WGS reaction. Transient formate decomposition experiments carried out at 140 °C indicated that the rate of formate decomposition was approximately 20 times higher for 2.5% Pt/ceria than that of 2.5% Au/ceria, suggesting that the metal (in addition to the promoting effect of H 2O previously reported) plays a role in facilitating the decomposition of surface formate intermediates, the proposed rate limiting step of the reaction mechanism.

Organosilane-modified maghemite nanoparticles and their use as co-initiator in the ring-opening polymerization of ɛ-caprolactone

Hydroxyl and amino groups were introduced on maghemite nanoparticles surface by grafting of (3-glycidoxypropyl)trimethoxysilane and N-(2-aminoethyl)-3-aminopropyltrimethoxy silane, in several solvents including water, toluene and N, N-dimethylformamide. Coating of maghemite particles by a biocompatible and biodegradable polyester, namely the poly(ɛ-caprolactone) was then achieved, by an aluminum isopropoxide-catalyzed ring-opening polymerization of ɛ-caprolactone initiated ‘from’ the maghemite particles surface. Silane and polymer coating were characterized by TGA and DRIFT spectroscopy. In this manner, nanocomposites containing up to 0.43 g of polymer per gram of maghemite were obtained.

A MAS NMR and DRIFT study of the Ga species in Ga/H-ZSM5 catalysts and their effect on propane ammoxidation

71Ga, 27Al, and 29Si MAS NMR and DRIFT spectroscopies were used to characterize the state of gallium in Ga/H-ZSM5 catalysts tested for their ability to catalyse the ammoxidation of propane. Ga species were observed in two different possible environments: octahedrally coordinated gallium in small Ga2O3 particles at the external surface of the zeolite crystals, octahedrally coordinated gallium in GaO(OH) or related species, and tetrahedrally coordinated gallium in cationic-exchange positions inside the zeolite. Redox (H2–O2) cycles promote the migration of gallium from the GaO(OH) or Ga2O3 species at the external surface of the zeolite crystals to cationic-exchange sites within the zeolite channels. The redox treatment definitely had a beneficial effect on its catalytic performance for the ammoxidation of propane, which is known to occur via a bifunctional mechanism. The main product was acetonitrile at high Ga and Al contents while acrylonitrile was also observed as a side product at high Ga and low Al contents.Key words: ZSM5, MFI, in situ studies, MAS NMR, DRIFT, propane activation, ammoxidation.

Synthesis and characterization of manganese oxides employed in VOCs abatement

Two MnO2 were prepared by different methods: (i) MnCO3 decomposition; and (ii) oxidation of acid MnSO4 solution. The combined use of X-ray diffraction (XRD), DRIFTS, DRS–UV–vis and TGA techniques revealed: (i) the presence of Mn4+–Mn3+; (ii) a poor crystallinity; and (iii) OH species at temperatures higher than 200°C.The catalysts were tested in the complete oxidation of ethanol to carbon dioxide and water, and the reaction results showed that the catalytic activity of both samples were larger than MnO2 (pyrolusite, β-MnO2) and Mn2O3 (like bixbyite) oxides. The high activity of the prepared oxides can be related to the simultaneous presence of Mn3+ and Mn4+ ions and OH− species generated by Mn4+ vacancies. In addition, in situ DRIFT spectroscopy demonstrated a different mechanism of adsorption-reaction of ethanol between the two synthesized manganese oxides.

Long-term effect of sewage sludge application on soil humic acids

Sewage sludges are used in agriculture because they act as a fertilizer. Long-term studies are needed to evaluate the effect of sewage sludge on soil properties by paying particular attention to the soil organic matter. Soil plots were amended for 10 years with 1 Mg dry matter ha −1 year −1 of sewage sludge. Chemical parameters such as total organic carbon (TOC), N, C/N ratio and CEC were determined when this period ended. Moreover, TOC was fractionated into humified and non-humified fractions. Humic acids (HA) were isolated and studied by elemental analysis, DRIFT, 1H NMR and CPMAS 13C NMR spectroscopies. At the end of the tests, compared to the control soil, the sludge-amended soil did not exhibit change in total organic C and related humified fractions. However, the HA composition of the soil treated with sludge had developed an HA composition closer to that of the HA-sludge as a result of the enrichment of recalcitrant fractions contained in the sludge.

Heat‐damage assessment of carbon‐fiber‐reinforced polymer composites by diffuse reflectance infrared spectroscopy

AbstractDiffuse reflectance infrared Fourier transform (DRIFT) spectroscopy was used to assess the effects of heat damage on carbon‐fiber‐reinforced polymer composites. Moisture‐saturated graphite–epoxy laminates with a quasi‐isotropic lay‐up were heat‐damaged above their upper service temperatures. The loss of matrix‐dominated mechanical properties due to heat exposure was investigated in the laboratory under environmental testing conditions with mechanical tests, ultrasonic C‐scanning, and DRIFT spectroscopy. The reduction of the mechanical strength of the composite materials was accompanied by an increase in the carbonyl band integral and a decrease in the phenyl ratio and hydroxyl and hydrocarbon band integrals, as shown by the DRIFT spectra. DRIFT was confirmed to be more effective than ultrasonic inspection in evaluating the extent of heat damage, and a good correlation was found between the mechanical test results and DRIFT spectra. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1222–1230, 2005

Temperature-programmed desorption (TPD) of carbon dioxide on alkali-metal cation-exchanged faujasite type zeolites

Using temperature-programmed desorption (TPD), we have investigated the interaction of carbon dioxide with alkali-metal cation-exchanged faujasite type zeolites (LSX, X and Y). TPD in the temperature range between 300 and 500 K results in desorption profiles of different intensities depending on the kind of cation and the aluminium content of zeolites. For NaX the desorbed amount corresponds to about one percent of the saturation capacity at 298 K. In case of NaX and X type zeolites exchanged with Cs+ ions an additional desorption peak above 500 K could be observed. Taking into account desorption curves of different heating rates, desorption energy distribution functions were calculated by using an extended integral equation. Initial adsorbed CO2 could be assigned to carbonate species in different environments by DRIFT spectroscopy.

Nature of cadmium cationic sites in cadmium-modified ZSM-5 zeolite according to the DRIFT studies of molecular hydrogen adsorption

The samples of CdZSM-5 prepared by ion-exchange, incipient wetness impregnation, and the interaction of HZSM-5 with cadmium vapor were studied by DRIFT spectroscopy using molecular hydrogen as a probe adsorbed at 77 K. Three different cadmium cationic species were detected. Dicadmium Cd 2 2 + ions most weakly perturb adsorbed hydrogen molecules. They are characterized by a band at 4102 cm −1. Two other kinds of isolated Cd 2+ sites are characterized by bands at 3982 and 3940 cm −1. The former band was ascribed to isolated Cd 2+ cations which compensated the negative charges of neighboring aluminum–oxygen tetrahedra. The latter band corresponds to isolated Cd 2+ cations which compensate the negative charges of distantly separated aluminum–oxygen tetrahedra. The calcination of samples containing Cd 2 2 + species in oxygen converts these species into cadmium oxocations [Cd 2O x ] 2+. Hydrogen molecules dissociate at room temperature on the isolated Cd 2+ cations which most strongly perturb adsorbed hydrogen molecules at 77 K.

In situ characterisation of carbon-containing species formed on chromia/alumina during propane dehydrogenation

The formation of carbon-containing species was studied during propane dehydrogenation on a chromia/alumina catalyst with 13.5 wt% chromium. The deposition was monitored by in situ DRIFT spectroscopy combined with mass spectrometry, and by in situ Raman spectroscopy combined with gas chromatography. The reduction of chromates by propane resulted in the formation of adsorbed acetone, formates, and acetates. Acetates/carboxylates and hydrocarbon species—aliphatic, unsaturated/aromatic, and graphite-like species—were present under dehydrogenation conditions. The deposition of the hydrocarbon species was gradual, consistent with the continuous deactivation of the catalyst observed during the measurements. Hydrogen prereduction of the chromia/alumina catalyst slowed the formation of acetates/carboxylates, but it had no detectable effect on the deposition of the hydrocarbon species.

Factors influencing selectivity in naphthalene hydrogenation over Au- and Pt–Au-supported catalysts

The effects of the support (γ-Al 2O 3 and SiO 2) and of the preparation method (the reduction of metal precursors by ethanol in the presence of polyvinylpyrrolidone (PVP) versus impregnation (IMP)) on the activity and selectivity of the Au and Pt–Au catalysts in naphthalene hydrogenation ( P = 2.0 MPa, T = 448 K, WHSV = 45.7 h −1) were studied. The physico-chemical characteristics of the catalysts were evaluated by X-ray diffraction, N 2 adsorption–desorption isotherms, DRIFT spectroscopy of the adsorbed CO, thermogravimetric (TG) and X-ray photoelectron spectroscopy techniques. Activity data for the target reaction showed that the SiO 2-supported catalysts are slightly better than the γ-Al 2O 3-supported counterparts. The monometallic Au/Al catalyst prepared by the IMP method displayed comparable selectivity but larger activity (mmol s −1 moles Au(Pt) −1) than its homologue prepared by the PVP method. As derived from X-ray line broadening analysis, this is due to much better dispersion of gold particles when using the IMP method. For SiO 2-supported catalysts prepared by PVP method, the initial activity followed the trend: 1Au > 1Pt–1Au > 2Pt. Both the monometallic Au/Si and 2Pt/Si exhibited quick deactivation contrary to the binary 1Pt–1Au/Si-pvp sample exhibiting higher activity at long time on stream. In this sample a synergy effect between Pt and Au was attributed to Pt 50Au 50 alloy formation. The factors controlling the selectivity in naphthalene hydrogenation on gold catalysts are discussed.

A Systematic Study of the Interactions between Chemical Partners (Metal, Ligands, Counterions, and Support) Involved in the Design of Al2O3-Supported Nickel Catalysts from Diamine−Ni(II) Chelates

1.5 Ni wt %/Al2O3 catalysts have been prepared by incipient wetness impregnation using [Ni(diamine)x(H2O)(6-2x)]Y2 precursors (diamine = 1,2-ethanediamine (en) and trans-1,2-cyclohexanediamine (tc); x = 0, 1, and 2; Y = NO3- and Cl-), to avoid the formation, during calcination, of difficult-to-reduce nickel aluminate. N2 was chosen for thermal treatment to help reveal and take advantage of the reactions occurring between Ni2+, ligands, counterions, and support. In the case of [Ni(en)2(H2O)2]Y2 salts used as precursors, in situ UV-vis and DRIFT spectroscopies show that after treatment at 230 degrees C Ni(II) ions are grafted to alumina via two OAl bonds and that the diamine ligands still remain coordinated to grafted nickel ions but in a monodentate way, bridging the cation with the alumina surface. With Y = Cl-, the chloride counterions desorb as hydrogen chloride, and hydrogen released upon decomposition of the en ligands is able to reduce a fraction of nickel ions into metal as evidenced by XPS. In contrast, with Y = NO3-, compounds such as CO or NO are formed during thermal treatment, indicating that nitrate ions burn the en ligands. After thermal treatment at 500 degrees C, a surface phase containing Ni(II) ions forms, characterized by XPS and UV-vis spectroscopy. Temperature-programmed reduction shows that these ions can be quantitatively reduced to the metallic state at 500 degrees C, in contrast with the aluminate obtained when the preparation is carried out from [Ni(H2O)6]2+, which is reduced only partly at 950 degrees C. On the other hand, a total self-reduction of nickel complexes leading to 2-5-nm metal particles is obtained upon thermal treatment via the hydrogen released by a hydrogen-rich ligand such as tc, whatever the Y counterion. An appropriate choice of the ligand and the counterion allows then to obtain selectively Ni(II) ions or a dispersed reduced nickel phase after treatment in N2, as a result of the reactions occurring between the chemical partners present on alumina.

Promoted Ru–hydroxyapatite: designed structure for the fast and highly selective oxidation of alcohols with oxygen

Ru-containing hydroxyapatite (HAp) catalysts have been developed for the oxidation of alcohols with molecular oxygen in an organic solvent. The working hypothesis has been that fine-tuning of the location and surroundings of the active Ru species would provide outstanding performance. The highest oxidation activity was achieved when (i) the contact time between the metal salt solution and HAp was limited to a few minutes to minimize restructuring via dissolution–redeposition, (ii) low Ru content was applied, (iii) Co 2+ and Pb 2+ promoters were incorporated to occupy the poorly accessible “hidden” sites in HAp before the introduction of Ru 3+, thus facilitating egg-shell-type Ru distribution in the particles, and (iv) after Ru incorporation the catalysts were dried at moderate temperature to avoid restructuring induced by dehydration of the active sites and their neighborhood. It is assumed that the active sites are Ru(OH) 2+ species stabilized by the phosphate O atoms and adsorbed (H-bonded) water. Various methods have been used for characterization of these catalysts, including XPS, DRIFT spectroscopy, inductively coupled plasma optical emission spectroscopy (ICP-OES), XRD, thermogravimetry combined with mass spectroscopy (pulse thermal analysis), and nitrogen adsorption. One of the two best catalysts (RuCoHAp-10min) was used in the partial oxidation of benzylic, allylic, aliphatic and cycloaliphatic alcohols. Most carbonyl compounds were produced in excellent yields without the formation of any detectable by-product. The catalytic activity seems to be higher than that of other Ru-based solid catalysts developed for the aerobic oxidation of alcohols.

SiO 2-supported dodecatungstophosphoric acid and Nafion-H prepared by ball-milling for catalytic application

Dodecatungstophosphoric acid (HPW) and Nafion-H were supported on SiO 2 using the ball-milling technique. Samples were characterized by physical (BET surface, SEM, DSC, XRD, DRIFT and Raman spectroscopies) and chemical (acid–base titration) methods. Catalytic properties were studied in a range of chemical transformations, which can be induced by electrophilic catalysts including Friedel–Crafts reactions (alkylation of toluene with benzyl alcohol, acylation of anisole with acetic anhydride) and the dimerization of α-methylstyrene. Milling conditions (stainless steel or polystyrene apparatus, milling time), loading of the active components, and the type of support were found to have profound effects on the physical characteristics and catalytic performance of the samples. Ball-milled HPW-SiO 2 samples prepared under appropriately selected conditions exhibit catalytic properties similar to catalysts made by impregnation. HPW in ball-milled samples, in turn, proved to be more resistant to extraction with polar solvents (hot methanol) and these catalysts display higher stability in recycling studies. Supported Nafion-H samples prepared by ball-milling show high activities in test reactions. The best catalyst exceeds SAC-13 in the selective synthesis of 1,1,3-trimethyl-3-phenylindane in the dimerization of 2-phenylpropene. Catalysts with high catalytic performance require the use of optimal milling time, because particle coalescence and the resulting decrease in BET surface area hinder the accessibility of the active sites.

Plasma modification of diamond surfaces

Because of its extreme hardness, diamond is a very interesting material for many industrial applications. One way to extend the field of diamond application and optimize the process conditions in diamond tool production is to enhance its surface reactivity. Low-pressure oxygen-plasma treatments were applied to equip the diamond surfaces with chemically reactive groups to improve their adhesion properties. XPS and DRIFT spectroscopy investigations showed that oxygen plasmas were suitable to oxidize the diamond surface. Combining derivatization reactions and solvatochromic dye adsorption studies, the introduction of alcoholic groups was confirmed. Besides the surface oxidation, the plasma treatment initiates decomposition of the diamond lattice which is followed by a re-arrangement of the carbon atoms in a graphite-like structure. The planar graphite structure supports the formation of carbonyl groups.

Dissociative adsorption of water in CaNaA zeolites studied by TG, DRIFTS and 1H and 27Al MAS NMR spectroscopy

Three CaNaA zeolites, in which, respectively, 49%, 65% and 83% of the Na + cations were exchanged with Ca 2+ ions, along with a NaA sample were studied by thermogravimetry, temperature-programmed DRIFT spectroscopy and MAS NMR. Thermogravimetric desorption profiles of the Ca 2+ exchanged zeolites show a low-temperature peak between 423 and 508 K as well as two high-temperatures peaks at 853 and 973 K, which are missing in case of the NaA sample. Three main bands at 3603–3611, 3495–3510 and 3552–3565 cm −1, of which the first two are due to bridging Si–OH–Al groups located in 8- and 6-rings, respectively, whereas the third corresponds to Ca(OH) + groups dominate the DRIFT spectra of zeolite samples exchanged with Ca 2+ ions. The intensity of the band at 3603–3611 cm −1 decreases significantly until it vanishes almost completely at 823 K. A simultaneous decreases of the intensity of the band of Ca(OH) + groups is indicative of a low-temperature dehydroxylation process between these two species. The intensity of the other Si–OH–Al group bands at 3495–3510 cm −1 shows almost no change up to 823 K, thus suggesting that these groups participate in a high-temperature dehydroxylation process. A weak band in the region 3670–3680 cm −1 is attributed to Al–OH groups of extra-framework aluminum species formed during dehydration of the CaNaA zeolites. Peaks at 4.3 and 5.2 ppm in the 1H MAS NMR spectra are assigned to Si–OH–Al groups in 8- and 6-rings, respectively. 27Al MAS NMR spectra show two main peaks at 57.3 and 78.7 ppm, which are due to tetrahedrally coordinated aluminum and calcium alumosilicate groups. A weak signal between 12 and 13 ppm ascribed to octahedrally coordinated aluminum disappears at higher temperatures.

Characterization of Al- and Ti-modified MCM-41 using adsorption techniques

The influence of aluminium and titanium dopants on the structure and properties of MCM-41 silica has been evaluated and compared with previously published results. The acidity and basicity of the surface states (adsorption sites) were of special interest. The total acidity was studied by using temperature-programmed ammonia desorption (NH 3-TPD). Additionally, organic probe molecules with known Lewis and/or Brϕnsted acid or base functional groups were adsorbed on the powder samples in dry cyclohexane. Both UV–vis spectroscopy and microcalorimety were used to quantify the adsorption. The adsorption data of the monofunctional probes were fitted with Langmuir-, Freundlich- and Henry-corrected Langmuir isotherms providing both the number of the surface sites and strength of probe molecule adsorption. The surface charge densities, relating to Brϕnsted acidity and basicity, were determined for the doped samples in water using potentiometric titration. DRIFT spectroscopy was used to identify the type of the surface sites. The hexagonal pore structure of the doped MCM-41 samples was observed to remain roughly unaltered for all samples. The NH 3-TPD analysis indicates that the acidity increases as a result of modification. The probe adsorption showed that the number of sites increases and the strength of adsorption enhances with surface modification. It seems that the simple Langmuir-isotherm is sufficient for the surface state analysis in most cases. In a few cases, the Freundlich- or the Henry-corrected Langmuir isotherm gave, however, a superior fit to the experimental surface excess data. The DRIFT-analysis confirmed the existence of Lewis sites and the formation of Brϕnsted type acid sites with enhanced Al- or Ti-doping, which was supported by the other methods used.

Spectrokinetic Investigation of Reverse Water-Gas-Shift Reaction Intermediates over a Pt/CeO2 Catalyst

The reactivity of the surface species present over a 2%Pt/CeO2 catalyst during the reverse water-gas-shift (RWGS) reaction was investigated by a detailed operando spectrokinetic analysis. A single reactor common for the kinetic and the spectroscopic measurements was used. The reactor employed was a modified high-temperature diffuse reflectance FT-IR (DRIFT) cell from SpectraTech. The reactivity of the surface species was monitored by DRIFT spectroscopy (DRIFTS) and mass spectrometry (MS) using steady-state isotopic transient kinetic analysis (SSITKA) techniques, i.e., switching between 1% CO2 + 4% H2 reaction mixtures containing either 13CO2 or 12CO2. The combination of these techniques allowed time-resolved simultaneous monitoring of the variation of the coverage of 12C and 13C-containing surface intermediates and the concentration of the gas-phase products 12CO(g) and 13CO(g) due to the isotope exchange. These results clearly indicated that surface formates observed by DRIFTS were not the main reaction ...