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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 Al 2 O 3 and CeO 2 to investigate the support effect in CO oxidation by in situ diffuse reflectance Fourier-transform infrared spectroscopy (DRIFTS) and mass spectrometry (MS). On Pt/Al 2 O 3 , the carbonate-like intermediates accumulate and do not decompose to CO 2 at the ignition temperature (150 °C) or above; the conversion of CO to CO 2 follows classic Langmuir−Hinshelwood (L–H) mechanism with direct reaction of CO and O 2 on Pt. Whereas for Pt/CeO 2 , the CO conversion to bidentate carbonate (b-CO 3 2−) species followed by decomposition to CO 2 is a main reaction pathway leading to its high reactivity at low temperature (75 °C). CeO 2 facilitates the activation of oxygen to produce the carbonate-like intermediates and further decomposition to CO 2 , which resulted in a lower ignition temperature. [ABSTRACT FROM AUTHOR]

[Display omitted] • The presence of surfactant improved methanol productivity. • Ni-Ga alloys presented activity at ambient pressure. • Smaller particle size led to higher methanol selectivity. • Higher Ni 5 Ga 3 crystalline phase led to higher methanol selectivity. • Ni-Ga alloys mechanism pass by formate and RWGS routes. Ni-Ga alloy catalysts were synthesized by a surfactant-assisted co-precipitation method and were tested in CO 2 hydrogenation to methanol at 10 bar and at ambient pressure. The presence of surfactant in the synthesis led to a decrease in particle size, with the catalyst produced using 1% of surfactant (C_1%) presenting the smallest and most homogeneous particle size. A difference between the catalysts was also observed in the change of the crystalline phase after the reaction, where the C_1% catalyst presented the lowest loss of the Ni 5 Ga 3 active phase. Methanol productivity showed positive relations with smaller particle size and higher quantity of Ni 5 Ga 3 crystalline phase remaining after the reaction, with the C_1% catalyst presenting the highest methanol productivity. Catalytic evaluation under different conditions showed that higher temperature and GHSV values led to poorer selectivity to methanol. The C_1% catalyst also presented good activity at ambient pressure and remained stable after 5 h, with no deactivation. A mechanistic study employing DRIFTS analyses found that the reaction pathway on Ni-Ga alloy involved both the RWGS and formate routes, as shown by the presence of formate, methoxy, and CO intermediates. [ABSTRACT FROM AUTHOR]

[Display omitted] • DRIFTS and XANES analyses shed light on the active Cu species in the PROX. • The oxidation state of Cu catalysts depends on the temperature and Cu content. • A drastic decrease in CO conversion is related to oxidation of Cu species to Cu2+. • Cu+ and Cu0 are active species in co-precipitated catalysts in the PROX reaction. • A PROX mechanism on CuCe catalysts involving Cu0/Cu+ and Ce3+/Ce4+ was proposed. Properties of co-precipitated CuO/CeO 2 catalysts with nominal content of 1–3 wt.% copper were investigated by EDS, XRD, BET, STEM, EDS map, H 2 -TPR, in situ DRIFTS and in situ XANES. By comparing results of DRIFTS, XANES and catalytic performance in the CO-PROX reaction, it was evidenced a relationship between the catalytic behavior and the copper oxidation state of the materials. In situ DRIFTS and XANES analyses shed light on the oxidation state of active copper species involved in the CO-PROX reaction between 120 °C and 200 °C. The investigated catalysts present a balance between Cu° and Cu+ species under PROX conditions and the Cu+ is the main species liable to adsorb CO. Furthermore, our studies indicated that the PROX reaction on CuO/CeO 2 is impacted by the nature of Cu species, which in turn may vary with reaction temperature, depending on the Cu content. From these results, we propose a new mechanism of PROX reaction on CuCe catalysts, including Cu°/Cu+ and Ce3+/Ce4+ redox pairs and direct CO oxidation on Cu°. [ABSTRACT FROM AUTHOR]

• EDTA degradation over TiO 2 was studied through an in-situ DRIFTS-MS analysis. • Gas, relative humidity, irradiation source and EDTA loading used were investigated. • In anaerobic conditions EDTA degradation is minimal and reduced species develop. • In aerobic conditions oxygenated products besides CO 2 and H 2 O were produced. • EDTA degrades under visible light (>410 nm) via ligand-to-metal charge transfer. Ethylenediaminetetraacetic acid (EDTA) is often detected as contaminant in domestic wastewater (DWW) and liquid nuclear waste (LNW). Unfortunately, the existence of EDTA in DWW and LNW was proven to have an adverse impact on the conventional wastewater treatment efficiency. In this work, photocatalytic degradation of EDTA over commercial TiO 2 (Evonik P25) has been investigated by using an irradiated environmental chamber with real-time diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and mass spectroscopy (MS) analysis. The degradation mechanism has been studied by varying different parameters, namely carrier gas, relative humidity, irradiation source and the loading of EDTA adsorbed on TiO 2. Results showed a minimal degradation of EDTA under anaerobic conditions with production of ammonia and short-chained organic molecules (e.g. acetaldehyde). On the contrary, EDTA photooxidation took place under aerobic conditions with carbon dioxide and water as the main products. It is important to note that EDTA forms a visible absorbing complex with P25, which allowed photodegradation of EDTA under pure visible light (wavelength >410 nm). Remarkably, the reaction mechanism was different when the system was irradiated with simulated solar light and near UV light. [ABSTRACT FROM AUTHOR]

• Monitoring the effect of Lewis acid site type II on tungsten oxide catalyst in olefin metathesis. • Understanding the adsorption ability of 1-butene on Lewis acid site type II. • Characterization of the Lewis acid site by in-situ and Operando DRIFT. • Using ammonia coupled with temperature program desorption to specific block on Lewis acid site type II. The types of acidity on WO x /SiO 2 catalysts prepared with different tungsten loadings (5 and 9 wt.% W) and pretreatment atmospheres (N 2 and H 2) were clarified by using the in situ diffuse reflectance infrared Fourier transform spectroscopy with temperature-programmed desorption (in situ DRIFTS-TPD) technique. Ammonia (NH 3) 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 WO x /SiO 2 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. [ABSTRACT FROM AUTHOR]

• Lewis acid transformation occurred over the WO x -supported catalysts. • Lewis acid transformation performances depend on different WO x -supported catalysts employed. • The enhancement of oxygen vacancy improved the Lewis acid transformation. • WO x /HY-500 exhibits the highest Lewis acid transformations. The effect of hydrogen introduction on Lewis acid transformation to Bronsted acid was investigated over the WO x catalysts supported on different supports (HY-15, HY-500, MCM-22, SiO 2 , and Al 2 O 3). The Lewis acid transformation on the catalysts was investigated by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) of adsorbed NH 3 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 WO x catalysts supported on all different supports. It is proposed that the partial reduction of WO x occurred under the hydrogen atmosphere, resulting in the generation of oxygen vacancies sites. The generated oxygen vacancies of the supported WO x 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 WO x 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 H 2 -TPD, H 2 -TPR, O 2 -TPD, UV–vis, XRD, XPS, and TEM-EDS techniques. [ABSTRACT FROM AUTHOR]

Abstract: An operando study of CO oxidation by Ce0.5Zr0.5O2 catalysts under dynamic conditions was performed using a prototype gas flow DRIFTS reaction chamber coupled with a MS. Previous studies conducted under oscillating CO/O2 feedstream conditions, allowed the identification of carbonates as the C-containing storage species on the catalyst surface, with their decomposition being the origin of CO2 evolution dynamics during O2 pulses. A deeper comparison of the time-resolved DRIFTS and MS data revealed some differences that were related to the different observation points of the two detectors. Two methods for the determination of penetration depth of IR radiation in catalysts beds were compared and discussed. From the analysis of DRIFTS data, two main pathways for carbonates decomposition were found at the beginning of the bed of the catalysts: one leading to CO2 and Ce(IV) sites and another to CO and Ce(III). The last one is active only above 673K. The preference of one pathway against the other is strictly related to the Ce(III)/Ce(IV) ratio that shows strong variation during the entire cycle. [Copyright &y& Elsevier]

Abstract: The aim of the present research was to gain further insight into the differences of the trichloroethylene photodegradation routes when using TiO2 (Degussa P25) and protonated titanate nanotubes (H2Ti3O7). These last materials have structural hydroxyls that, along with the surface OH groups present in both photocatalysts, could mediate in the mineralization of the pollutant. In order to obtain a realistic view, an operando Diffuse Infrared Fourier Transform Spectroscopy (DRIFTS) approach has been adopted for surface analysis during the photocatalytic oxidation. The study revealed that the mineralization yield of trichloroethylene on the titanate nanotubes calcined at 300°C was better than the one obtained with the benchmark photocatalyst Degussa P25. In particular, the synthesized nanotubes showed the selective removal of some specific hydroxyl groups, suggesting that their high density and, probably, the specific characteristics of their hydroxyl species can be responsible for the enhanced dechlorination photoactivity exhibited by these nanotubular structures. [Copyright &y& Elsevier]

Abstract: Steady-state isotopic transient kinetic analysis (SSITKA) experiments coupled with in situ DRIFTS and mass spectrometry (operando) were performed for the first time to study essential mechanistic aspects of the water-gas shift reaction (WGSR) over a 0.5wt.% Pt/γ-Al2O3 catalyst. The chemical structure of active and inactive reaction intermediate species present in the carbon-path (“C-path”) from CO to the CO2 product gas (use of 13CO) and in the hydrogen-path (“H-path”) from H2O to the H2 product gas (use of D2O) of the reaction mechanism were determined. In addition, the concentrations (μmol/g) of active species in both the “C-path” and “H-path” of the WGSR at 350°C were measured. Based on the large concentration of active species present in the “H-path” (OH/H located on the alumina support), the latter being larger than 28 equivalent monolayers of the exposed Pt metal surface, the small concentration of OH groups along the periphery of metal-support interface, and the significantly smaller concentration (μmol/g) of active species present in the “C-path” (adsorbed CO on Pt and COOH species on the alumina support and/or the metal-support interface), it might be suggested that diffusion of OH/H species on the alumina support surface towards Pt catalytic sites present in the “H-path” of reaction (back-spillover process) might be considered as a slow reaction step. The latter process was evidenced after conducting the WGS reaction (CO/H2O) in a partially deuterated alumina surface (Pt/γ-Al2O3). At least two kinds of formate (–COOH) species residing on the alumina surface have been identified, one of which was active and leads to the formation of CO2(g) and H2(g), whereas the other kind(s) is/are considered as inactive (spectator) adsorbed reaction intermediate species. [Copyright &y& Elsevier]

Abstract: 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 Brønsted 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 is 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 NO x with proton-adsorbed NH3 via the formation and subsequent thermal decomposition of NH4NO3. [Copyright &y& Elsevier]

Abstract: 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 Ce0.2Zr0.8O2 are mainly present in cationic form but exhibit high reducibility. As found by temperature-programmed surface reaction (TPSR) in CH4 +NO2 atmosphere, the CH4-SCR reaction is initiated at 280°C on Pd/Ce0.2Zr0.8O2 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 O2 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. [Copyright &y& Elsevier]

Abstract: 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 30,000h−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. [Copyright &y& Elsevier]

Abstract: Preliminary characterisation studies are reported regarding a flow switching experiment combined with DRIFTS monitoring, which has been applied for the first time to the study of adsorption and hydrogenation of ethyne and ethene over: (1) a 0.02wt.% Pd/αAl2O3 catalyst and (2) a 2wt.% Pd/γAl2O3 catalyst (Johnson Matthey). The catalysts were pre-reduced under a flow of hydrogen, followed by flushing under helium at 120°C or 200°C. During adsorption of ethyne, a carbonaceous layer was formed on the catalyst in the early stages of the exposure of the catalyst to ethyne, but carbonaceous deposits were not observed during ethene adsorption under identical conditions of freshly reduced catalyst. From the infrared spectra, octane was tentatively identified as being present in the carbonaceous layer. Upon exposing the catalyst to five 5cm3 ‘pulses’ of ethyne, sequential hydrogenation to ethene and ethane occurred during the first two pulses applied even in the absence of gas phase hydrogen, but decreased significantly in the three subsequent pulses. Possible sources of hydrogen for the reaction were retention by the catalyst during the pre-reduction or transfer from the carbonaceous layer. Upon heating the 2wt.% catalyst to 200°C in a flow of helium to remove residual hydrogen from the pre-reduction, then exposing it to ethyne, hydrogenation still occurred with an increased selectivity towards ethane, suggesting that the carbonaceous layer was the more likely source of hydrogen. Less ethane was formed over the 0.02wt.% Pd/α-Al2O3 catalyst compared with the 2wt.% Pd/γ-Al2O3, as the former catalyst is designed to prevent hydrogenation to the alkane through its low metal loading, optimal pore structure and Pd dispersion. The technique gives insights in to the reaction pathways and could potentially be used to derive kinetic and transport parameters for the reaction system. [Copyright &y& Elsevier]

Abstract: Pd-Ni catalysts supported on Al2O3 and (Ce,Zr)O x /Al2O3, 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 C3H6 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. [Copyright &y& Elsevier]

DRIFTS data were collected on the interaction of NO and CO over Au/TiO2 prepared by a deposition–precipitation procedure. Reduction of Au/TiO2 in hydrogen at 300 °C for 30 min did not completely reduce the catalyst and both ionic and metallic gold sites were found to be present. Adsorption of NO is dominated by the formation of dinitrosyl complexes. CO readily adsorbs on Au/TiO2 leading to multi-bonded carbonyl species. These species readily react with gaseous O2 to form carbonate species. Displacement of adsorbed CO by gaseous NO showed no interaction between the two adsorbates and there is no experimental evidence for the formation of isocyanate species. This is rationalized in terms of the low tendency of NO to undergo dissociation on Au/TiO2. [Copyright &y& Elsevier]

Abstract: 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 S BET 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. [ABSTRACT FROM AUTHOR]

Abstract: La, V, Zn, Cu, Fe, Li and Ag promoted Rh/SiO2 catalysts were investigated for the synthesis of ethanol during CO hydrogenation at 230°C and 1.8atm. 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/SiO2 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/SiO2 catalyst may primarily be caused by an increase in the concentration of the adsorbed CO species in the presence of H2, 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/SiO2 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/SiO2, leading apparently to the much reduced activities for CO hydrogenation observed. [Copyright &y& Elsevier]

PtIr/TiO 2 catalyst was prepared and investigated for the selective catalytic reduction of NO x by H 2 (H 2 -SCR) in the presence of O 2. It was found that PtIr/TiO 2 exhibited higher H 2 -SCR activity as well as wider activity temperature window than Pt/TiO 2 and Ir/TiO 2 catalysts, and the optimum mass ratio of Pt/Ir was 1:1. Characterization of the catalyst showed that metallic Pt and Ir were generated on PtIr/TiO 2 , both of which were favorable active sites in H 2 -SCR process. In situ DRIFTS studies showed that more NO x species, NH 3 and NH 4 + species were formed on PtIr/TiO 2. All of these lead to the superior catalytic activity of PtIr/TiO 2 catalyst. [Display omitted] • PtIr/TiO 2 is more active than Pt/TiO 2 and Ir/TiO 2 for H 2 -SCR of NO x. • The optimum mass ratio of Pt/Ir was 1:1 over PtIr/TiO 2 catalyst. • Pt0 and Ir0 active sites were generated on PtIr/TiO 2 catalyst. • More NO x species, NH 3 and NH 4 + species were formed on PtIr/TiO 2. [ABSTRACT FROM AUTHOR]

[Display omitted] • Microfibrous-structured Cu-ZSM-5/Al-fiber catalysts with different Si/Al molar ratios were synthesized for SCR reaction. • Adsorbed bridged nitrates species is in accordance with the enhanced NO degradation activity. • Microstructured Cu-ZSM-5 catalysts are more active at high-throughout conditions due to the enhanced mass transfer. Selective catalytic reduction of NO x with NH 3 (NH 3 -SCR) is one of the most efficient technologies to remove NO x emissions. The copper ion-exchanged zeolites with broad temperature windows and high N 2 selectivity are very promising for this process. In this work, we synthesized a series of microfibrous-structured Cu-ZSM-5/Al-fiber catalysts for SCR reaction by changing the Si/Al molar ratios. The in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) of NH 3 adsorption results show that the Cu-ZSM-5/Al-fiber catalysts with higher Si/Al molar ratios have higher NH 3 adsorption capacity. The subsequent NO adsorption results show that the amount of adsorbed bridged nitrates species is in accordance with the enhanced NO x degradation activity. At moderate temperature, Cu-ZSM-5/Al-fiber catalyst shows better NH 3 -SCR performance under higher gas hourly space velocity (GHSV), indicating microstructured Cu-ZSM-5 catalysts are more active at high-throughout conditions due to the enhanced mass transfer. [ABSTRACT FROM AUTHOR]

• Ag/ZSM-5 and Ag/BEA are able to adsorb C 3 H 6 but not NO in the presence of H 2 O. • Pd/BEA is able to adsorb both C 3 H 6 and NO in significant amounts (presence of H 2 O). • H 2 O inhibits the interaction of NO, C 3 H 6 and –OH groups of ZSM-5 and BEA zeolites. • Ag preferentially adsorbs C 3 H 6 over NO, whereas C 3 H 6 and NO compete for Pd sites. • Oxidation reactions occur over Ag, Pd containing ZSM-5 and BEA during desorption. Silver and palladium ion-exchanged BEA zeolites (Si/Al = 12.5) and silver ion-exchanged ZSM-5 zeolites (Si/Al = 15) were studied for their ability to adsorb and desorb propylene and NO under simulated diesel exhaust conditions. The adsorption experiment results demonstrated the excellent ability of bare BEA zeolites to adsorb propylene, but only a small amount of NO. The presence of H 2 O inhibited the adsorption of both C 3 H 6 and NO. Ion-exchanging BEA zeolites with Ag (1.2 and 5.1 wt.% Ag/BEA) attenuated the inhibiting effect of H 2 O on C 3 H 6 adsorption, while NO storage remained inhibited. Adsorption experiments indicated that C 3 H 6 and NO competed with each other for Pd sites with C 3 H 6 showing stronger adsorption compared to NO, whereas Ag sites preferentially adsorbed C 3 H 6. DRIFTS data indicated the formation of nitrate, formate and acetate species on Ag and Pd, while C 3 H 6 and NO adsorption was also observed on the zeolite hydroxyl groups in the absence of H 2 O. However, the C 3 H 6 and NO adsorption on the zeolite hydroxyl groups was significantly inhibited in the presence of H 2 O. Additionally, nitrosyl, acrolein and carbonate species were formed over 1.0 wt.% Pd/BEA. The effluent analysis during the temperature-programmed desorption in the DRIFTS reactor revealed that adsorbed C 3 H 6 and NO reacted during the release to form oxidation reaction byproducts. The 1.0 wt.% Pd/BEA zeolite showed the greatest oxidation ability during desorption with the majority of stored C 3 H 6 converted to CO 2. [ABSTRACT FROM AUTHOR]

[Display omitted] • Co-Ce-Ti composite oxide catalyst with redox cycle was developed for NH 3 -SCR of NO x. • Co-Ce-Ti catalyst is more active than Co-Ti and Ce-Ti catalyst for NH 3 -SCR of NO x. • The synergetic effect between Co and Ce leads to improved redox property and enhanced acidity. • More reactive NH 3 /NH 4 + species formed over Co-Ce-Ti catalyst. A novel Co-Ce-Ti composite oxide catalyst prepared by the hydrothermal method has been developed for the selective catalytic reduction of NO x by NH 3. Co-Ce-Ti catalyst exhibited high NH 3 -SCR performance in a wide temperature window, which is superior to that of Co-Ti and Ce-Ti catalysts. Catalyst characterization results revealed that over Co-Ce-Ti catalyst the redox cycle (Co3+ + Ce3+↔ Co2+ + Ce4+) plays an important role for the high catalytic NH 3 -SCR performance. The synergetic effect between Co and Ce over Co-Ce-Ti catalyst resulted in both improved reducibility and increased acidity. In situ DRIFTS results clarified that over Co-Ce-Ti catalyst more reactive NH 3 /NH 4 + species is formed, thus promoting the NH 3 -SCR of NO x to proceed. The present Co-Ce-Ti catalyst has great potential to be used for practical deNO x application. [ABSTRACT FROM AUTHOR]

In situ and operando diffuse reflectance FT-IR (DRIFTS) studies are often carried out over samples that may undergo changes in optical properties due to stronger absorptivity (darkening), for instance when coking or being reduced. The variation of IR optical pathlength of two Fe and Co-based Fischer-Tropsch catalysts treated at different temperatures was investigated through the use of an internal standard CaCO 3 that was physically mixed with the catalyst. The CaCO 3 overtone band at 1795 cm-1 was used, exhibiting an integral molar absorption coefficient ε = 2.68 × 105 cm mol-1. The IR penetration depth was negligible over the iron oxide sample once reduced above 400 °C, due to the formation of a strongly absorbing material. A reduction of the cobalt sample up to 350 °C revealed large changes of optical pathlength (dropping four-fold from 66 to 16 µm), likely related to the onset of cobalt oxide deep reduction. These data indicate that changes in optical pathlength should be considered when attempting quantitative DRIFTS analyses and that mixing a small concentration of CaCO 3 , e.g. 2 wt%, is a suitable way of doing so. [Display omitted] • Optical pathlengths may vary greatly during DRIFTS analyses. • Using an internal standard such as CaCO 3 can easily solve this limitation. • Iron oxide sample becomes too dark for DRIFTS upon reduction. [ABSTRACT FROM AUTHOR]

• PdZn/ZrO 2 catalyst showed ˜100 selectivity to methanol at 230 °C, 30 bar. • PdZn alloy formation was observed. • Calcium serves as an excellent promoter. • In situ DRIFTS shows surface carbonates and formates. • Reaction mechanism follows formate route. PdZn-based catalysts have evolved as a very effective catalytic material for CO 2 hydrogenation to methanol. ZrO 2 -supported PdZn and Ca-PdZn catalysts, synthesized by the simple impregnation method, exhibited excellent catalytic activity with impressive selectivity to methanol when tested for direct CO 2 hydrogenation reaction. These catalysts were able to achieve up to 97–100 % methanol selectivity with significant CO 2 conversion (single-pass of more than 10% in the case of Ca-doped PdZn/ZrO 2) under reaction conditions of 20–30 bar, 2400 mL/g-h, H 2 /CO 2 = 3:1, 220–270 °C. Addition of calcium to PdZn/ZrO 2 catalyst had a positive impact on overall catalytic performance and catalyst lifetime. Ca-doped PdZn/ZrO 2 catalyst also showed high stability for at least 100 h (on stream) implying the catalyst was very stable and resistant to sintering. The catalysts were characterized using BET, CO-chemisorption, CO 2 -TPD, XRD, XPS, SEM-EDS and TPR. Whereas, in-situ DRIFT study identified surface reaction transient intermediates, formates and methoxy species, and therefore, a reaction mechanism of formate pathway is proposed based on the DRIFT analysis. [ABSTRACT FROM AUTHOR]

• Au showed a promoting effect on Pd/TiO 2 catalyst for H 2 -SCR of NO x. • PdAu alloy and the highly dispersed active sites account for the improved activity. • Reactive chelating bidentate nitrate and NO 2 formed over Pd-Au/TiO 2 catalyst. • NH 3 and NH 4 + play important roles in H 2 -SCR of NO x over Pd-Au/TiO 2 catalyst. Au promoted Pd/TiO 2 catalysts with different Pd loading were investigated for the selective catalytic reduction of NO x by hydrogen (H 2 -SCR). The results showed that 1%Pd-0.5%Au/TiO 2 catalyst exhibited the highest NO x conversion and N 2 selectivity, as well as a wide activity temperature window. Moreover, the 1%Pd-0.5%Au/TiO 2 catalyst offered remarkable resistance to high gas hourly space velocity (GHSV). XRD, XPS and TEM results illustrated that the excellent H 2 -SCR performance of 1%Pd-0.5%Au/TiO 2 catalyst was closely related to the formed PdAu alloy and the higher dispersion of active sites compared with 1%Pd/TiO 2. In-situ DRIFTS results revealed that more and new adsorbed nitrogen oxides species, as well as more adsorbed NH 3 and NH 4 + active species generated over 1%Pd-0.5%Au/TiO 2 catalyst, thus accelerating the ability to active H 2 atom and the subsequent reaction with adsorbed nitrogen oxides species. [ABSTRACT FROM AUTHOR]

The effects of calcination temperature on Pd/γ-alumina catalysts were studied using a variety of techniques to measure particle sizes, surface species, and activity in methane combustion. Pd/Al 2 O 3 catalysts were synthesized using a new impregnation-vortexing method. Three catalysts containing 3.3 wt.% Pd/Al 2 O 3 were calcined at 150 °C, 250 °C, and 500 °C. The light-off temperature for methane combustion was 250-255 °C for all catalysts and 100% methane combustion was achieved at 275 °C in 20 min with the 3Pd/Al 2 O 3 250 °C catalyst under lean methane conditions. X-ray photoelectron spectroscopy showed PdO x and PdO on the catalysts surface, and conversion of some PdO x to PdO and Pd0 after reaction. Particle sizes and dispersions were different in the three fresh and spent catalysts as shown by scanning transmission electron microscopy (STEM) and CO pulse chemisorption. In situ and o perando diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) showed that after high temperature calcination, dormant monodentate carbonates are formed at the interface of Pd and alumina on the 3 Pd/Al 2 O 3 500 °C catalyst, which are absent on the 3Pd/Al 2 O 3 250 °C catalyst during reaction. Temperature-responsive CO species were observed for both 3Pd/Al 2 O 3 catalysts, evidencing restructuring of the 3Pd/Al 2 O 3 250 °C catalyst upon heating in accordance with the STEM results. The results indicate a varying degree of strong metal-support interactions, resulting in different adsorbed species over the catalysts during methane oxidation reaction. We suggest that, over the 3Pd/Al 2 O 3 250 °C catalyst, the desorption of carbonates frees OH groups at the Pd-Al 2 O 3 interface, which can react (with other OH or H) and desorb as water, a step which can be rate limiting on methane oxidation over Pd/Al 2 O 3 at low temperatures. This research study highlights the possibility of altering catalytic properties and surfaces through calcination at different temperatures. [Display omitted] • Pd/alumina catalysts calcined at three temperatures had different methane activity. • Calcination temperature changed nanoparticle sizes and surface species. • Operando DRIFTS showed dormant carbonate species adsorbed on Pd/Al 2 O 3 500 °C catalyst • Evolution of adsorbed CO species evidenced restructuring of Pd/Al 2 O 3 250 °C catalyst • Complete methane combustion was achieved at 275 °C with Pd/Al 2 O 3 250 °C catalyst [ABSTRACT FROM AUTHOR]

[Display omitted] • Au restructuration is not sufficiently considered when investigated Au-based samples. • CO dissociation occurs on many metals near room temperature. • Surface segregation and phase segregation can be triggered by CO adsorption. • Surface modifiers such as Zn and Sn lead to strong geometric effects. This contribution reviews some of the structural features of supported bimetallic catalysts that could be unravelled using IR spectroscopy of CO adsorption. The few examples presented are focussed on active metals such as Au, Pd, Pt and Co and modifications by inert elements such as Sn or Zn. The difficulty in interpreting the IR spectra during CO adsorption over Au-Pt and Au-Pd is underlined, because of Au restructuring that leads to bands typically in the range associated with Pt and Pd carbonyls. Crucial aspects of metal dispersion and surface segregation can yet be obtained, such as active metal site isolation by the disappearance of bridged or multi-bonded CO. The use of IR spectroscopy of CO adsorption to investigate the surface of bimetallics or alloys remains yet challenging and not conclusive in many instances. Firstly, this results from the complexity of the spectra obtained (even over single metals) that depends on many parameters. Secondly, CO adsorption often results in modifications of both surface structure and composition of nanoalloys via reconstruction, as in the case of monometallic surfaces, or surface segregation when one of the metals exhibits a greater affinity for CO. CO dissociation near room temperature has also been documented on many metals, including cobalt and more surprisingly Pt, Ag and Au-based materials. [ABSTRACT FROM AUTHOR]