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No consensus has been reached on the role of reducible and irreducible supports on the reaction pathway of CO oxidation over supported metal catalysts. Here, colloidal ligand-free Pt nanoparticles were deposited on Al2O3 and CeO2 to investigate the support effect in CO oxidation by in situ diffuse reflectance Fourier-transform infrared spectroscopy (DRIFTS) and mass spectrometry (MS). On Pt/Al2O3, the carbonate-like intermediates accumulate and do not decompose to CO2 at the ignition temperature (150 °C) or above; the conversion of CO to CO2 follows classic Langmuir−Hinshelwood (L–H) mechanism with direct reaction of CO and O2 on Pt. Whereas for Pt/CeO2, the CO conversion to bidentate carbonate (b-CO32−) species followed by decomposition to CO2 is a main reaction pathway leading to its high reactivity at low temperature (75 °C). CeO2 facilitates the activation of oxygen to produce the carbonate-like intermediates and further decomposition to CO2, which resulted in a lower ignition temperature.

The effect of hydrogen introduction on Lewis acid transformation to Bronsted acid was investigated over the WOx catalysts supported on different supports (HY-15, HY-500, MCM-22, SiO2, and Al2O3). The Lewis acid transformation on the catalysts was investigated by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) of adsorbed NH3 at 100 °C under atmospheric pressure for 130 min. According to the results of in situ DRIFTS, ammonia migration from Lewis acid sites to Bronsted acid sites occurred over the WOx catalysts supported on all different supports. It is proposed that the partial reduction of WOx occurred under the hydrogen atmosphere, resulting in the generation of oxygen vacancies sites. The generated oxygen vacancies of the supported WOx catalysts were found to play an important role for activating the hydrogen spillover, leading to Lewis acid transformation to Bronsted acid. It was suggested that the selected support is the crucial factor for Lewis acid transformation performances. The results from our experiments showed that the weak interaction between WOx and support led to the easy reduction of W species, which promoted the generation of oxygen vacancies sites. The large amount of oxygen vacancies leads to high Lewis acid transformation. Moreover, the influence of different supports was discussed and investigated by several analytical techniques such as H2-TPD, H2-TPR, O2-TPD, UV–vis, XRD, XPS, and TEM-EDS techniques.

The types of acidity on WOx/SiO2 catalysts prepared with different tungsten loadings (5 and 9 wt.% W) and pretreatment atmospheres (N2 and H2) were clarified by using the in situ diffuse reflectance infrared Fourier transform spectroscopy with temperature-programmed desorption (in situ DRIFTS-TPD) technique. Ammonia (NH3) acted as probe molecules that could block Lewis acid site type II (1620 cm−1) on the studied catalysts. The reactant feed containing 2% trans-2-butene or mixed feed of 2% trans-2-butene and 4% ethylene were used to investigate the reaction pathway on the WOx/SiO2 catalysts. Combining the Operando DRIFTS with gas chromatography-flame ionization detector (Operando DRIFTS-GC-FID) technique and in situ DRIFTS-TPD led to more deeply understanding of the correlation of acid sites and the primary cross metathesis reaction as the main reaction with isomerization of trans-2-butene as the side reaction. The adsorption energy of pulse chemisorption of 1-butene on catalyst by in situ DSC, confirmed the presence of the Lewis acid site type II related to the opportunity of 1-butene adsorption. The results confirmed that the Lewis acid site at 1620 cm−1 was crucial for the secondary metathesis reaction of 1-butene.

In situ DRIFT spectroscopy and mass spectrometry techniques were employed to investigate the mechanisms of the selective catalytic reduction of NO with NH 3 on the FeW oxides catalysts. By integrating the adsorption peaks of NH 3 or NO x , it was found that the coordinated NH 3 and NH 4 + were the main active NH 3 ad-species, while the adsorbed NO x was only obviously detected below 250 °C. That was to say that the reaction mechanisms were totally different at different temperature regions. At the low temperature region ( 2 -SCR” process, involving the formation of NO 2 , complexes NO 2 (NH 3 ) 2 and NO 2 (NH 4 + ) 2 as intermediates. These active complexes could react with gaseous NO to produce N 2 and H 2 O. The oxidation of NO to NO 2 was probably the rate-determining step for the SCR reaction. At the high temperature region (≥250 °C), NH 2 NO species formed from the reaction between surface coordinated NH 3 /NH 4 + species and gaseous NO were the key intermediates, which were further reduced to produce N 2 and H 2 O.

SSCI-VIDE+ING+AMS:FRM:YSC; International audience; Preferential oxidation of CO (PROX) in hydrogen-rich mixtures was studied over alumina-supported Pt and Pt-Sn catalysts, which exhibited a well-defined metal particle size. The reaction rate was much faster over Pt-Sn/Al2O3 than over Pt/Al2O3. Significantly different apparent activation energies and oxygen reaction orders were found for both samples. Whereas the CO PROX kinetics over Pt/Al2O3 could be described by oxygen adsorption as being rate-determining step, this was not the case for Pt-Sn. In situ Diffuse Reflectance Infrared Fourier Transformed Spectroscopy (DRIFTS) showed that Pt-Sn, initially under a mixture of 1% CO/80% H-2, segregated upon the introduction of 2% O-2, even at temperatures where the alloy was stable under reducing conditions. For the CO PROX reaction over Pt-Sn/Al2O3 a bifunctional mechanism is proposed with CO and H being adsorbed on the platinum sites and oxygen being channeled from neighboring SnOx sites. This work suggests a Mars-Van Krevelen type of mechanism for the SnOx, site, in agreement with the low value of 0.2 for the oxygen reaction order over Pt-Sn. (C) 2015 Elsevier B.V. All rights reserved.

CuO/CeO 2 -TiO 2 catalysts have been widely studied for the thermocatalytic NO reduction with CO. Here, we examine to what extent this reaction can be photocatalytically enhanced beyond the mere thermocatalytic activity by irradiating the catalyst with UV light under reaction conditions while observing the reaction progress via DRIFTS (diffuse reflectance infrared Fourier transform spectroscopy). The reaction was studied in a batch reactor at four temperatures (35, 65, 100, and 200 °C). The most pronounced effect of photocatalytic enhancement was observed at 65 °C where an enhanced CO conversion of 64.4% was achieved, compared with 11.5% CO conversion without UV irradiation. The photocatalytic enhancement of the CO conversion diminished as the temperature increased to 200 °C, where the CO conversion process became entirely dominated by thermal catalysis. The promoting effect of ceria on the CO + NO reaction has been revealed and rationalized on the basis of physical and chemical characterizations results. XPS and TPR results suggest that the electronic state interaction between Ce and the other two components (Ti and Cu) in the catalysts might lead to a higher oxygen vacancy concentration that facilitates oxygen transport from ceria to copper species resulting in the high catalytic activity for NO reduction by CO.

In the last years there has been an increasing interest for the use of ethanol not only as biofuel but also as raw material for the production of petrochemicals. In the present work the conversion of ethanol into hydrocarbons was investigated over zeolites with different acidic properties and porous structure (HZSM-5 and HMCM-22). The samples used were active for ethanol conversion and both their acidic properties and porous structure played an important role on product selectivity. HZSM-5 zeolite was the most promising catalyst for propene formation. Raman spectroscopy and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) were also employed to investigate the carbon species deposited on the zeolites and the adsorbed species formed during the reaction, respectively. DRIFTS results show that coke formation was severely inhibited by the pore structure of HZSM-5 justifying the high stability of this zeolite.

Thiol-ligated Au38(SC12H25)24 clusters were synthesized and supported on a microporous TiO2 support by incipient wetness impregnation. After a reductive pretreatment designed to remove the thiol ligands, the activity of catalyst was tested using CO oxidation in a fixed-bed reactor at 30 and 60 °C. CO oxidation was also performed at similar conditions in an in situ FTIR (DRIFTS) cell to monitor the species that were formed during the reaction, and results were compared to commercially available Au/TiO2 catalyst. Our Au/TiO2 was less active than this commercial catalyst for CO oxidation, likely due to the presence of bidentate carbonate species. DRIFTS studies on the commercial catalyst showed strong peaks at 1718 and 1690 cm−1 that are not present in our catalyst. We propose that these bands are due to bridging CO2 between Au Ti and Au Au centers formed via direct oxygen atom transfer from the titania surface to Au CO. On the surface of our catalyst, however, a different reaction mechanism involving sulfur-mediated oxygen transfer at the Au-TiO2 interface has been proposed.

La, V, Zn, Cu, Fe, Li and Ag promoted Rh/SiO 2 catalysts were investigated for the synthesis of ethanol during CO hydrogenation at 230°C and 1.8 atm. As is well known, the activity and selectivity depend heavily on the choice of promoter. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) was used to probe the effects of La, V, Zn and Cu on CO adsorption and hydrogenation. From the IR study, it was found that the behavior of CO adsorbed on the differently promoted catalysts was very different. While La enhanced total CO adsorption, the addition of V, Zn and Cu suppressed CO adsorption to different extents. The doubly promoted Rh-La/V/SiO 2 showed only moderate CO adsorption. Results from DRIFTS suggest that the higher catalytic activity (compared to the non-promoted catalyst) observed for the La singly promoted Rh/SiO 2 catalyst may primarily be caused by an increase in the concentration of the adsorbed CO species in the presence of H 2+ possibly due to the formation of new active sites at the LaO x -Rh interface. The higher catalytic activity of the V singly promoted Rh/SiO 2 catalyst could be ascribed to an increased desorption rate/reactivity of the adsorbed CO species. The La and V doubly promoted catalyst showed both new adsorbed CO species and increased desorption rate/reactivity of the adsorbed species during CO hydrogenation due to a synergistic promoting effect of La and V. The addition of Zn or Cu promoters significantly reduced the desorption rate/reactivity of the adsorbed CO species on Rh/SiO 2 , leading apparently to the much reduced activities for CO hydrogenation observed.

In this study, the parameters governing the activity of Pd/ceria-zirconia catalysts in the selective catalytic reduction (SCR) of NO x assisted by methane are investigated using a combination of temperature-programmed spectroscopic and thermogravimetric techniques and transient SCR conditions. By DRIFTS of adsorbed CO, it is established that Pd species on Ce 0.2 Zr 0.8 O 2 are mainly present in cationic form but exhibit high reducibility. As found by temperature-programmed surface reaction (TPSR) in CH 4 + NO2 atmosphere, the CH 4 -SCR reaction is initiated at 280 °C on Pd/Ce 0.2 Zr 0.8 O 2 and yields almost 100% N2 above 500 °C. DRIFTS-MS and TGA experiments performed under transient SCR conditions show that DeNO x activity is due to a surface reaction between some methane oxidation products on reduced Pd sites with ad-N x O y species presumably located on the support. The detrimental effect of 02 on DeNO x is explained by the promotion of the total combustion of methane assisted by the ceria-zirconia component at the expense of the SCR reaction above 320 °C.

Fe–Ce–Mn/ZSM-5 catalysts were prepared and performance of catalysts in NO selective catalytic reduction by NH3 was tested in the temperature range of 100–500 °C. NO conversion reached 96.6% and 98.1% at 200 °C and 300 °C respectively at a GHSV of 30,000 h−1. In situ diffuse reflectance infrared transform spectroscopy (DRIFTS) study was carried out for revealing the reaction mechanism. Two possible reaction pathways were proposed. One was that NO2 could react with NH4+ on Bronsted acid sites and the formed NO2[NH4+]2 would react with NO, producing N2 and H2O. Another way was that NH3 was adsorbed and then reacted with NO or HNO2. Possible intermediate NH4NO2 and NH2NO were unstable and would decompose into N2 and H2O. The addition of Mn in Fe–Ce–Mn/ZSM-5 catalysts could contribute to provide more Bronsted acid sites which was beneficial for the adsorption of NH3. The addition of both Fe and Ce could obviously increase the conversion of NO to NO2. Introduction of Fe increased the oxidation of NH3 slightly and the addition of Ce increased the oxidation of NH3 significantly. The combination of manganese, iron and cerium could significantly enhance the low temperature SCR activity.

Pd-Ni catalysts supported on Al 2 O 3 and (Ce,Zr)O x /Al 2 O 3 , both in fresh and thermally aged states, were examined with the main aim of determining the effects of Ni and Ce-Zr mixed oxide on the catalytic activity for CO and C 3 H 6 oxidation, and NO reduction reactions under stoichiometric conditions. For this purpose, catalytic activity results were analysed in conjunction with DRIFTS and XANES spectra recorded under reaction conditions to obtain information on the processes occurring in the catalysts during the course of the reactions. While a nickel-induced promotion of the formation of contacts between palladium and the Ce-Zr mixed oxides generally enhances the CO oxidation performance of the catalyst, it results detrimental to the NO reduction activity. This has been related to the higher difficulty in achieving the most active metallic palladium state for comparatively similar particle sizes in the presence of such contacts. Comparison of DRIFTS spectra under various reactant mixtures and between fresh and aged systems was shown to explain in a unique way the detrimental catalytic effects of hydrocarbon self-poisoning and sintering of the active components in the catalysts.

DRIFT spectroscopy combined with mass spectrometry was used to investigate the oxidation of adsorbed ammonia by NO2, NO+O2 and NO2+O2 on a copper ion exchanged SSZ 13 (Cu-SSZ-13) zeolite. Compared with both NO2 and NO, the adsorption of ammonia is much stronger on the Cu-SSZ-13 zeolite. Two adsorbed ammonia species were found over the Cu-SSZ-13 zeolite studied here; notably ammonia on Bronsted acid sites (proton) and ammonia on Lewis acid sites (copper ions). These adsorbed ammonia species present different activity profiles and selectivity to N2 during NH3 oxidation. The results obtained suggest that ammonia adsorbed onto copper ions in Cu-SSZ-13 are more active at low temperatures than proton-adsorbed NH3, and give rise to a higher selectivity to N2. The formation of N2O is associated primarily with the reaction of NOx with proton-adsorbed NH3 via the formation and subsequent thermal decomposition of NH4NO3. Financial support was provided by the US Department of Energy (DOE), Office of Energy Efficiency and Renewable Energy, Vehicle Technologies Program. Portions of this work were performed in the Environmental Molecular Sciences Laboratory (EMSL) at Pacific Northwest National Laboratory (PNNL). The EMSL is a national scientific user facility supported by the US DOE, Office of Biological and Environmentalmore » Research. PNNL is a multi-program national laboratory operated for the US DOE by Battelle.« less

A series of catalysts based on combinations between copper and cerium oxides, in which the former has been modified by doping with Co, Zn and Sn, have been prepared by a microemulsion method and characterized by XRD and SBET measurements. Their catalytic activity as well as details of redox processes taking place during the course of the reaction has been examined by means of operando-DRIFTS-MS under CO-PROX conditions. The results reveal differences in the characteristics of carbonyl species formed through a reductive process during the course of the reaction which are employed to rationalize catalytic properties of the systems.

In this study, the nature of surface intermediates generated by adsorption of NO and NO2 on a commercial ceria–zirconia powder of composition Ce0.69Zr0.31O2 was investigated using Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS). The conditions of occurrence of the main adsorbed species, i.e. nitrites and nitrates, are studied semi-quantitatively as a function of catalyst pre-treatment and/or type of adsorbed NOx molecule. On the partially reduced ceria–zirconia, the primary role of NOx is to re-oxidize the surface via adsorption/decomposition on reduced sites. By contrast, the formation of nitrites and nitrates readily occurs on oxidized surfaces, the latter kind of species being strongly promoted in the case of NO2 adsorption only.