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We report on the “one step─one pot” synthesis of chain-lengthened aliphatic amines and nitriles from CO/H2/NH3 gas feeds using potassium-promoted Co/MnOx catalysts prepared via MOF-type (metal orga...

We demonstrate Chemical Transient Kinetics as a powerful tool for investigating catalytic reaction kinetics and mechanisms at atmospheric pressure. Quantitation of transient molecular flows while switching feed gas compositions allows key mechanistic steps of the Fischer–Tropsch reaction to be elucidated. Evidence is presented for a CO insertion mechanism operating under hydrogen-deficient reaction conditions. Consequently, formate/carboxylate-derived intermediates are likely involved in chain lengthening. This also agrees with the occurrence of characteristic time profiles when replacing CO by methyl formate or adding ammonia to a CO/H2 feed.

X-ray photoelectron spectroscopy (XPS) was employed to study the thermal decomposition in vacuum of nickel oxalate dihydrate. The process is shown to proceed via mainly two stages. Evaluating the h...

Die Materialität des Schrifterwerbs im Elementarbereich und in der Grundschule ist Gegenstand der Beiträge dieses Sammelbandes. Im Mittelpunkt stehen Beobachtungen zu literalen Praktiken und didaktischen Arrangements in alltäglichen Lernsituationen und die damit verbundene Dynamik, Sozialität und Körperlichkeit. Indem die vorfindlichen Praktiken des Schrifterwerbs in kulturwissenschaftlich-praxeologischer Ausrichtung in den Blick genommen und auf ihre Sinnhaftigkeit für die Erweiterung literalen Handlungsvermögens untersucht werden, tragen die Autorinnen und Autoren zu einer Erweiterung der bisherigen Forschungsperspektiven auf das Lesen- und Schreibenlernen am Schulanfang bei.

We study the hydrogenation of CO under ambient pressure conditions over a Co-MnOx model catalyst using chemical transient kinetics (CTK) under calibrated molecular flow conditions. Alkanes and alke...

In CoCu-based Fischer-Tropsch catalysis, the as-prepared nanoparticles, if allowed to self-assemble, exhibit a Co@Cu core-shell morphology that would render the catalyst inactive for CO hydrogenation. Therefore, a chemical reconstruction has to occur to create the catalytically active phase. While some of the thermodynamically-imposed driving forces for reconstruction have been identified and kinetic mechanisms experimentally probed, a thorough theoretical understanding on the molecular events has yet to be developed. Here, we employ a first-principles statistical mechanics approach to show that the reconstruction of CoCu in CO atmospheres is likely accomplished via subcarbonyl (multiple bonded CO) formation at the step and kink sites of CoCu catalysts. We find that the CO-induced antisegregation of subsurface Co atoms to step sites and the subsequent rupturing of Co subcarbonyls from these sites is thermodynamically feasible under experimentally-relevant CO pressures and temperatures. The results suggest that Co tricarbonyl formation along with its rupturing and diffusion onto the terraces is responsible for reconstruction. These Co tricarbonyls are shown to favorably dimerize, suggesting a potential route for nanoisland formation and morphological changes. Our results illustrate a strong correlation to surface carbonyl and inorganic complex chemistry of Co metal.

Die flucht- und migrationsbedingte Zuwanderung stellt die betroffenen Kinder vor eine hohe Anpassungsleistung, die nicht nur das Sprachenlernen sondern vor allem auch die kulturelle und psychosoziale Integration umfasst. Im Folgenden werden die Zusammenhange von peerkulturellen Kontakten und sprachlich-sozialer Integration untersucht und im Kontext des mehrsprachigen Repertoires von Kindern mit Migrations- und Fluchthintergrund diskutiert.

The interaction of oxygen with a reactive metal is ubiquitous, yet the precise atomic-level mechanisms and pathways leading to the formation of a surface oxide are not well-understood. We report oxygen atom distributions inside Rh single nanoparticles using atom probe microscopy (APM) and demonstrate that mainly facets of the «022¯» crystallographic directions act as oxygen-permeable gateways. The highly anisotropic spatial distribution of incorporated oxygen atoms is in agreement with video-field emission analyses according to which {113} facets of the «022¯» zones act as portals for subsurface diffusion. In addition to providing a more fundamental understanding of the precursor states to metal corrosion, in particular for the case of nanosized metal particles, our studies are also relevant for heterogeneous catalysis where catalytic activity and selectivity conform to reaction-induced structural changes of metal nanoparticles., SCOPUS: ar.j, info:eu-repo/semantics/published

Electrochemically-derived well-crystalline mesoporous silicon carbide (pSiC) was used as a host for cobalt nanoparticles to demonstrate superior catalytic performance during the CO hydrogenation according to Fischer-Tropsch. Colloidal Co nanoparticles (9 ± 0.4 nm) were prepared independently using colloidal recipes before incorporating them into pSiC and, for comparison purposes, into commercially available silica (Davisil) as well as foam-like MCF-17 supports. The Co/pSiC catalyst demonstrated the highest (per unit mass) catalytic activity of 117 µmol.g(CO)-1.g-1(Co).s-1 at 220 °C which was larger by about one order of magnitude as compared to both silica supported cobalt catalysts. Furthermore, a significantly higher C5+ hydrocarbons selectivity was observed for Co/pSiC. The stable performance of the catalyst is attributed to the high dispersion of the active phase and the use of pSiC acting as a thermally conductive and chemically inert mesoporous support., info:eu-repo/semantics/published

The need for a sustainable energy supply in the face of depleting oil reserves has reignited the importance of Fischer–Tropsch (FT) synthesis technology. Presently, the FT process is practiced at the industrial scale to predominately produce synthetic diesel-type fuels and lubricants. More recently, the possibility of hydrogenating CO toward oxygenates, and not just hydrocarbons, has been explored. We have developed a series of CoCuMn and CoMnK catalysts prepared via the oxalate co-precipitation route that are capable of forming oxygenates with desirable selectivity. Upon H2-assisted thermal decomposition of the resultant mixed metal Co1Cu1Mn1 oxalates, catalysts naturally exhibited a cobalt core–copper shell configuration with Mn5O8 dispersed throughout the catalyst nanoparticle as determined via Atom Probe Tomography (APT). We suggest structural changes are induced by the CO and H2 reactants to form the catalytically active phase under real-time reaction conditions as demonstrated by corroborative Density Functional Theory calculations and experimental evidence. APT studies also show that a Co4Mn1K0.1 catalyst post reaction contained a cobalt carbide phase as determined from a Co/C ratio of 2/1. Manganese and potassium were found only in the outermost part of the particle. Both catalysts were found to contain the presence of a Mn5O8 oxidic phase before and post reaction which we attribute to the high activity toward oxygenates of these two catalysts.

Au/TiO2 catalysts were produced by deposition-precipitation using different preparation conditions. Emphasis was laid on producing TiO2 supports via oxalate precursors in the presence or absence of alkali and/or alkali-earth elements to vary on purpose the catalysts’ morphological state, surface composition and electronic structure. The home-made catalysts and a commercial Au/TiO2 were analyzed in a comparative manner by mainly X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) to identify the key parameters responsible for their high activity in the CO oxidation at room temperature. Among these parameters, which were strongly influenced by the catalyst preparation conditions, the abundance of reduced Ti3+ species was ascertained to be overarching along with the availability of negatively charged Au nanoparticles. The abundance of O 2p bonding orbitals in the valence band of TiO2, which was modified by the presence of Au particles, and the extent of the support hydroxylation were also found to have a positive effect on the reaction rate. We further demonstrate that it is the specific area occupied by gold particles on the support surface that has to be taken into account to establish a reliable dependence of the reaction rate on the XPS-derived Au/Ti atomic ratio. All these factors have to be considered when assessing the activity performance of Au/TiO2 catalysts prepared and activated according to different recipes. After-reaction studies, which were also performed with a selected home-made catalyst, show that a slight decrease in its catalytic activity with time-on-stream can be mainly attributed to an appreciable accumulation of various carbon-containing species on the support surface along with a loss of OH groups. In summary, we show that combined XPS/ToF-SIMS studies provide a reliable guide for tailoring the preparation of high-performance Au-supported catalysts.

Mass-spectrometric analysis of a number of atomic, molecular and double-charged ions desorbed from the surface of Mn, Co, Ni and Cu oxalate hydrates under Mg Kα X-ray irradiation was performed. The yield of desorbed ion species was found to steadily increase across the series of oxalates from MnC2O4·2H2O to CuC2O4·xH2O, exhibiting an inverse dependence on the –OCO–Me–OCO– bonds strength. Analysis of X-ray induced ion desorption from the surface of CoC2O4·2H2O annealed at different temperatures was demonstrated to be useful in studying compositional and structural alterations occurring in the topmost surface layer of the oxalate during the process of its thermal decomposition. The temperature dependences of the yield of characteristic ions were shown to be capable of discerning the dehydration and decomposition stages in this process. The probability of desorption and survival of different ions exhibited different dependence on the bonding and structural characteristics of the oxalates. The obtained results are compared with data provided by TG/DTA coupled with mass spectrometry and XPS techniques. Possible mechanisms of X-ray induced ion desorption from oxalates are discussed.

X-ray photoelectron spectroscopy (XPS) was chosen to explore changes occurring in the surface composition, structural and chemical state of atoms during the course of thermal decomposition of CoC2O4·2H2O under ultra-high vacuum conditions. Accordingly, a large set of high-resolution core-level and Auger spectra was recorded as a function of temperature and time. Some Co-related XPS characteristics, including Auger parameter, were found to be sensitive to the local chemical and structural environment of Co atoms, demonstrating non-monotonic variation in the temperature range of intense dehydration. Isothermal decomposition was shown to proceed via formation of a two-phase system composed of metallic Co and oxygen-deficient oxalate and could be described by Avrami–Erofeev or Prout-Tompkins kinetic models. The long-term isothermal decomposition of the oxalate at 380 °C produced nearly oxygen-free Co covered by a substantial amount of carbon in carbidic form (~19 at%) and as graphitic overlayer (~26 at%). On the contrary, heating of the oxalate to 500 °C produced Co particles covered by surface CoO (~29 mol%) with traces of carbidic and graphitic carbon. XRD, TG and DTA coupled with mass spectrometry were employed as complementary techniques.

CoCu-based catalysts are promising candidates for the large-scale application of CO hydrogenation to higher alcohols with varying hydrocarbon chain length. To mimic the Co@Cu core–shell structure of nanosized CoCu particles, we choose a Cu/Co(1012)-oriented slab and find, in agreement with chemical imaging results, that the slab surface is always Cu-terminated, with Co underneath. Using DFT calculations, we observe major surface atom exchange in the presence of adsorbed CO, with up to 50% of the Cu atoms being replaced by Co in the straight-chain steps of the slab surface. Co atom exchange beyond 50% is not observed. More specifically, this work is accomplished by scanning the configurational space of adsorbed CO, surface Co, and surface Cu and then identifying minimum-energy surface configurations. Phase diagrams are also constructed to determine the thermodynamic driving force imposed in the presence of adsorbed CO. The inclusion of surface phonon modes is shown to ensure the correctness of the calcula...

The production of higher terminal alcohols through CO hydrogenation according to the Fischer–Tropsch (F–T) process has been a topic of interest since the Institut Francais du Petrole (IFP) demonstrated short-chain C1–C6 mixed alcohols production over cobalt–copper based catalysts. A number of catalyst formulations were screened for their suitability at that time. In particular, the addition of Cr, Zn, Al, Mn and V to CoCu was investigated. In a number of patents, it was shown that catalyst preparation is crucial in these catalyst formulations and that high alcohols selectivity can only be achieved by carefully respecting the procedures and recipes. This short critical review highlights recent developments in CoCu-based catalysts for higher terminal alcohols synthesis via F–T synthesis. Special attention will be given to catalyst preparation which according to developments in our group is based on oxalate precipitation. This way we show that the close association of Co and Cu on the one hand and promoter/dispersant on the other are of utmost importance to ensure high performance of the catalysts. We shall concentrate on “CoCuMn”, “CoCuMo” and “CoCuNb” catalyst formulations, all prepared via oxalate precipitation and combined with “entrainment techniques” if necessary, and show high total alcohols selectivity can be obtained with tunable Anderson-Schulz-Flory chain-lengthening probability. Either long-chain C8–C14 terminal alcohols as feedstock for plasticizers, lubricants and detergents, or short-chain C2–C5 alcohols as “alkanol” fuels or fuel additives can be formed this way.

While cobalt-based catalysts have been used in industrial Fischer-Tropsch synthesis for decades, little is known about how the dynamics of the Co-Co2C phase transformation drive their performance. Here we report on the occurrence of hysteresis effects in the Fischer-Tropsch reaction over potassium promoted Co/MnOx catalyst. Both the reaction rate and the selectivity to chain-lengthened paraffins and terminally functionalized products (aldehydes, alcohols, olefins) show bistability when varying the hydrogen/carbon monoxide partial pressures back and forth from overall reducing to carbidizing conditions. While the carbon monoxide conversion and the selectivity to functionalized products follow clockwise hysteresis, the selectivity to paraffins shows counter-clockwise behavior. In situ X-ray diffraction demonstrates the activity/selectivity bistability to be driven by a Co-Co2C phase transformation. The conclusions are supported by High Resolution Transmission Electron Microscopy which identifies the Co-Co2C transformation, Mn5O8 layered topologies at low H2/CO partial pressure ratios, and MnO at high such ratios., The question for the structure-reactivity relationship of cobalt-based catalysts for the carbon monoxide hydrogenation is as old as the reaction itself. Here the authors show kinetic hysteresis for a potassium-promoted cobalt-manganese oxide catalyst to be driven by the Co-Co2C phase transition.

The catalytic CO hydrogenation is one of the most versatile large-scale chemical syntheses leading to variable chemical feedstock. While traditionally mainly methanol and long-chain hydrocarbons are produced by CO hydrogenation, here we show that the same reaction can be tuned to produce long-chain n-aldehydes, 1-alcohols and olefins, as well as n-paraffins over potassium-promoted CoMn catalysts. The sum selectivity of aldehydes and alcohols is usually >50 wt% whereof up to ∼97% can be n-aldehydes. While the product slate contains ∼60% n-aldehydes at /pCO=0.5, a 65/35% slate of paraffins/alcohols is obtained at a ratio of 9. A linear Anderson–Schulz–Flory behaviour, independent of the /pCO ratio, is found for the sum of C4+ products. We advocate a synergistic interaction between a Mn5O8 oxide and a bulk Co2C phase, promoted by the presence of potassium, to be responsible for the unique product spectra in our studies., The catalytic CO hydrogenation traditionally produces mainly methanol and long-chain hydrocarbons. Here, the authors show that the same reaction can be tuned to produce long-chain n-aldehydes, 1-alcohols and olefins, as well as n-paraffins over potassium-promoted CoMn catalysts.

Experimental X-ray photoelectron spectroscopy (XPS) and theoretical density functional theory (DFT) calculations reveal the electronic and structural properties of CoCu catalysts before and after CO adsorption. DFT calculations show that, prior to CO adsorption, CoCu has a high tendency to self-assemble into a Co@Cu core-shell structure, which is in accordance with previous atom probe tomography (APT) results for CoCu-based systems and the known mutually low miscibility of Co and Cu. We demonstrate that Co and Cu are electronically immiscible using a density of states (DOS) analysis wherein neither metal's electronic structure is greatly perturbed by the other in “mixed” CoCu. However, CO adsorption on Co is in fact weakened in CoCu compared to CO adsorption on pure Co despite being electronically unchanged in the alloy. Differential charge density analysis suggests that this is likely due to a lower electron density made available to Co by Cu. CO adsorption at coverages up to 1.00 ML are then investigated on a Cu/Co(0001) model slab to demonstrate CO-induced segregation effects in CoCu. Accordingly, a large driving force for a Co surface enrichment is found. At high coverages, CO can completely invert the layer sequence of Co and Cu. This result is echoed by XPS evidence, which shows that the surface Co/Cu ratio of CoCu is much larger in the presence of CO than in H 2 .

The behavior of transition metal oxalates in vacuum, under X-ray irradiation and low-energy Ar+ ion bombardment was studied. A comparative mass-spectrometric analysis was carried out of gas evolution from the surface of Mn, Co, Ni and Cu oxalate hydrates in vacuum, during exposure to X-rays and after termination of X-ray irradiation. The rates of H2O and CO2 liberation from the oxalates were found to be in an inverse correlation with the temperatures of dehydration and decomposition, respectively. X-ray photoelectron spectroscopy (XPS) was employed to study the X-ray induced damage in NiC2O4 and CuC2O4 by measuring the various XP spectral characteristics and surface composition of the oxalates as a function of time of exposure to X-rays. It was shown that Cu oxalate underwent a significantly faster degradation than Ni oxalate and demonstrated a high degree of X-ray induced reduction from the Cu2+ to the Cu1+ chemical state. 500 eV Ar+ sputter cleaning of CoC2O4 for 10 min was found to cause a strong transformation of the oxalate structure which manifested itself in an appreciable alteration of the XP core-level and valence band spectra. The analysis of changes in stoichiometry and comparison of XP spectra of bombarded oxalate with respective spectra of a reference carbonate CoCO3 implied that the bombardment-induced decomposition of CoC2O4 gave rise to the formation of CoO-like and disordered CoCO3-like phases.

Monodisperse Fe(0) nanoparticles with diameters between 1.8 and 9.0 nm were prepared from organometallic {Fe[N(SiMe3)2]2}2 and intercalated into mesoporous MCF-17 silica. We observed high turnover frequencies of the catalytic CO hydrogenation; they increased with Fe particle size. Methane and short-chain olefin selectivities were highest for small particles, while the opposite trend applied to long-chain terminal olefins and oxygenates. The Anderson–Schulz–Flory chain lengthening probabilities were found to increase with Fe particle size for both paraffins and terminal olefins. Reaction-induced sintering of the metal particles was limited and could be explained by the transformation of Fe(0) precursors into (mainly) Fe-carbides. The results cast new light on the structure sensitivity of the catalytic CO hydrogenation.

Using X-ray photoelectron spectroscopy we examine the Au 4f spin-orbit components in Au 4f spectra of nanosized Au particles on a TiO2 support. In general, the peak ratios of the Au 4f7/2 and 4f5/2 excitations are found to deviate from the statistical ratio of 4 : 3 and their linewidths (FWHM) are not equal. We reveal that both the FWHM and the Au 4f7/2-to-4f5/2 peak ratios increase appreciably as the Au atomic concentration on the surface of the TiO2 support and the size of Au nanoparticles decrease. On the contrary, the Au 4f spin-orbit splitting remains essentially unchanged. Our findings are discussed in terms of alterations in the electronic band structure.

Porous SiC with uniformly sized 12 nm and 22 nm spherical mesopores was synthesized from nanocomposites of polycarbosilane (PCS) preceramic polymer and xerogels of Ludox® SiO2 nanoparticles as templates. The influence of PCS type (Mw 800 and 2000 Da), PCS : SiO2 ratio, pyrolysis temperature 1200–1400 °C, and addition of Ni complex to the preceramic composite was studied with respect to the SiC porous morphology, crystalline structure and chemical properties. We found that the pore walls of Ni-free por-SiC are composed of relatively large (20 nm) crystallites embedded inside a poorly crystalline SiC/SiC1+x phase. Increasing the pyrolysis temperature resulted in an increase of the large crystallites fraction, as well as of the stability with regard to air oxidation; however, some degradation of the porous morphology was noted too. The presence of Ni (1.5% wt relatively to PCS) noticeably improved the crystallinity of por-SiC prepared at 1200–1300 °C, with no degradation of the porous morphology occurring. On the other hand, higher Ni loadings and temperatures led to the transformation of the porous morphology into aggregates of irregularly packed large crystallites.

X-ray photoelectron spectroscopy (XPS) was employed to characterize the surface composition, atoms’ chemical state and electronic structure of oxalates MeC2O4·nH2O (Me = Mn, Fe, Co, Ni, Cu); their structure was characterized by XRD. Core-level Me 2p, Fe 3p, Fe 3s, C 1s, O 1s, X-ray induced Auger Me LMM, O KVV and valence band spectra are presented along with a number of parameters derived from the spectra analysis. A comparative analysis of FeC2O4 and Fe2(C2O4)3 oxalates is performed. The XPS parameters for the oxalates are compared to those for respective oxides. Variation of spin-orbit splitting, multiplet splitting, energy separation and intensity of satellites in the Me 2p spectra across the series of the compounds is considered in terms of changes in the electronic structure and strength of the Me–O bonding. The strong effect of covalency of the ligand (C2O42– vs. O2–) is demonstrated. Auger parameters α′(Me) and α′(O) are determined and used for estimating the initial state effects in photoemission. The surface charging of the oxalates is shown to be mainly dependent on the surface composition and stoichiometric atomic ratios. In the C 1s and O 1s spectra of the oxalates, intense satellites are revealed for the first time.

Mo2C/graphene nanostructures were used to investigate the nature of gas-phase formic acid decomposition into either CO/H2O or CO2/H2 products. The experimental data show that the Mo2C/graphene can facilitate both decarboxylation and dehydration pathways for the formic acid decomposition reaction. Its selectivity is strongly influenced by the reaction temperature where the decarboxylation predominates at a low temperature (e.g., ≤ 280 °C) and the dehydration predominates at a high temperature (e.g., ≥ 370 °C). These experimental data are compared to Monte Carlo simulations. It was found that the decarboxylation pathway for the production of CO/H2O can be simulated and explained by an Eley-Rideal type mechanism that involves interaction of gas-phase HCOOH with surface H*. Furthermore, the dehydration pathway for the production of CO2/H2 can be simulated and explained by a Langmuir-Hinshelwood type mechanism that involves unimolecular decomposition of surface HCO*O* to form CO2 and H*.

The catalytic hydrogenation of nitrogen oxide (NO and NO 2 ) over platinum nanocrystals is investigated with nanoscale lateral resolution using video-field emission microscopy (field electron microscopy (FEM) and field ion microscopy (FIM)). The ongoing reaction is imaged at the extremity of sharp tip samples mimicking size and morphology of catalyst nanoparticles. The results show a strong sensitivity of the reaction to local surface structures. Fast transitions from nonreactive to reactive conditions, reminiscent of “surface explosions,” are observed. On (001)-oriented Pt samples, such transitions are mainly triggered along zone-lines involving {011}, {012} and kink sites around {001} facets. Explosions are spontaneously repeated without external modifications of the control parameters. FIM investigations demonstrate oscillatory-type behavior with irregular periods for the NO + H 2 reaction. On the other hand, NO 2 hydrogenation, investigated by FEM, shows highly regular surface explosions. Further data analyses indicate that this system bears the features of a noisy chemical oscillator with asymmetric peaks characteristic of relaxation-type oscillations. Surface reconstructions ranging from local surface atom displacements to the transformation of the hemispherical into a polyhedral crystal shape may be observed using FIM. Nonlinear behaviors occur on reconstructed samples as well as on nonreconstructed ones.

Metal catalysts may undergo a series of surface and subsurface structural and chemical transformations during a chemical reaction, which inevitably change the surface properties. Understanding such dynamics from a fundamental science standpoint is important to build rational links between chemical/structural surface properties and the desired catalytic performance. The research presented here addresses, the dynamics of early oxide formation on rhodium (Rh) single nanoparticle during O2 exposures revealing the important role that the subsurface plays. O2 dissociative adsorption, as well as its reaction with H2 mainly imply the Rh{012} regions and is directly observable on Rh nanoparticles with the use of Field Ion and Emission Microscopies (FIM/FEM). Adsorbed oxygen atoms (O(ads)) resulting of the O2 dissociative adsorption can migrate to the bulk through the surface. The combination of our observations by FEM and our observations using Atom Probe Tomography (APT) reveals an inter-facet cooperation between Rh{012} and Rh{113} during this process., info:eu-repo/semantics/published

Co nanoparticles of well-defined size were synthesized by temperature-controlled injection of Co2(CO)8 into dichlorobenzene. After intercalation into mesoporous MCF-17 and temperature-programmed oxidation, Co3O4/MCF-17 model catalysts were obtained with cobalt oxide particle sizes varying between 3.5 and 12.2 nm. We demonstrate here the occurrence of a distinct particle size effect for the CO oxidation. Maximum reaction rates of about 0.77 nm–2 s–1 at 150 °C were observed for Co3O4 particles with a size in the range of 5 to 8 nm. The reaction rates decreased for either smaller or larger sizes. X-ray photoelectron spectroscopy allowed establishing a clear correlation between the Co3+ trivalent oxidation state and the CO oxidation rate.

Novel “CoCuNb” ternary catalysts with bimodal nanosized particle structure, in the absence of a generic support material, were designed and successfully tested in higher alcohol production via CO hydrogenation. The selectivities to primary alcohols with an optimized C2–C5 slate usually exceeded the 50 wt % level, and the combined selectivities to 1-alcohols/1-alkenes reached up to ∼73 wt % for CO conversions ranging between ∼5% and nearly 20%. The bimodal nanosized particle distribution, achieved through oxalate coprecipitation, contained Co–Cu particles with sizes ranging from 25 to 40 nm. Smaller particles between 4 and 8 nm were identified as Nb oxides and played the role of a structural dispersant (“spacer”) and promoter of 1-alcohol/1-olefin production. X-ray photoelectron spectroscopy revealed NbOx to contain major amounts of species with Nb in the 4+ oxidation state.

FeRu nanoparticles were prepared according to an organometallic route using {Fe[N(Si(CH3)3)2]2}2 and (η4-1,5-cyclooctadiene)(η6-1,3,5-cyclooctatriene) ruthenium(0) Ru(COD)(COT) precursors followed by their insertion into a mesoporous MCF-17 support host. The resulting nanoparticles had a uniform size of approximately 2 nm, with a relative Ru amount of up to 33 at.%. Steady-state Fischer–Tropsch catalysis at 6 bar total pressure (H2/CO = 1:1) demonstrated light olefins production with a selectivity close to 50 % (ex. CO2) for catalysts with low Ru content (5 at.%). The selectivity pattern changed to long chain-paraffin production with increasing Ru amounts. These catalysts were also more active than those containing few Ru. X-ray photoelectron spectroscopy showed under-parity Ru amounts to effectively cover the surface of Fe nanoparticles. The nanoparticle distribution inside the MFC-17 host was characterized by microtomia/transmission electron microscopy.

A colloidal solution of uniformly sized butoxylated SiO2 nanoparticles in o-xylene was prepared from Ludox HS-30 sol. Using these nanoparticles as a template for nanocasting and polycarbosilane (PCS) as a replica precursor, mesoporous SiC was produced by thermal decomposition of the PCS. More precisely, our synthesis allowed porous SiC to be obtained with uniformly sized (11 nm) spherical pores, high surface area (up to 800 m2/g), and large pore volume (up to 1.25 cm3/g). It is anticipated that such SiC with well-defined texture will find major applications as a mesoporous support for nanosized metal particles in exothermic catalytic reactions.

Bimetallic CoCu model catalysts were investigated for the synthesis of higher alcohols using catalytic CO hydrogenation according to the Fischer–Tropsch technology. Emphasis was placed on revealing the influence of the activation conditions. Accordingly, catalyst precursors were activated in argon, hydrogen, syngas (CO/H2), and CO under atmospheric conditions and at elevated temperatures (370 °C). All catalyst precursors were prepared via oxalate coprecipitation in the absence of a classic support. Alcohol selectivities between 30 and ∼40% (up to ∼50% for the sum of alcohols and alkenes) were obtained with an Anderson–Schulz–Flory (ASF) chain lengthening probability maximizing the slate up to C6. Detailed catalysis and characterization studies were performed using a Co2Cu1 catalyst composition. The catalytic performances of the H2- and syngas-activated Co2Cu1 catalyst were similar. While the CO-activated catalyst shows significantly higher catalytic activity and ASF chain lengthening probability, the alco...

X-ray photoelectron spectroscopy (XPS) was employed to study the changes in the surface composition and electronic structure of a TiO2-promoted Pd/SiO2 catalyst following methane oxidation under lean-burn conditions (up to 600 C) and SO2 treatment at 350 C. Overnight exposure of the activated catalyst to SO2 was found to cause the formation of a layer of palladium sulfate and sulfate/sulfite species on the support surface, leading to its deactivation. A single cycle of methane combustion over the SO2-treated catalyst gave rise to its reactivation due to the effective decomposition of Pd sulfate and desorption of SO2 at relatively low temperatures. In the stabilized and restored states, the catalyst exhibited a high and stable activity, had the largest proportion of metallic versus oxidic palladium species, a high density of Pd 4d states near the Fermi level, and the smallest extent of surface hydroxylation. The catalytic reaction over an as-prepared or SO2-treated catalyst was revealed to cause a partial and reversible 'encapsulation' of Pd particles by TiOx suboxide moieties from the mixed oxide support. The encapsulation resulting from strong metal-support interaction was enhanced by the SO2 treatment of the Pd/(SiO2 + 10 wt% TiO 2) catalyst. © 2014 Elsevier Inc. All rights reserved.

We studied the catalytic reduction of NO2 with hydrogen on platinum model catalysts by means of field emission techniques. Atomic resolution field ion microscopy (FIM) was used to characterize Pt s...

In this work, we investigate the catalytic hydrogenation of NO over palladium and platinum and of NO2 over platinum surfaces. Samples are studied using field emission techniques including field emission/ion microscopies (FEM/FIM). The aim of this study is to obtain detailed information on the non-linear dynamics during NOx hydrogenation over nanocrystallites at the atomic scale. The interaction between Pd and pure NO has been studied between 450 K and 575 K and shows the dissociative adsorption of NO. After the subsequent addition of hydrogen in the chamber, a surface reaction with the oxygen-adlayer can be observed. This phenomenon is reversible upon variation of the H2 pressure, exhibits a strong hysteresis behaviour but does not show any unstable regime when control parameters are kept constant. On platinum, NO is dissociated and the resulting O(ads) layer can also react with H2. Although occurring on both Pd and Pt metals, the reaction mechanism seems to be different. On palladium, NO dissociation takes place on the whole visible surface area leading to a “surface oxide” that can be reacted off by raising the H2 pressure whereas on Pt, the catalytic reaction is self-sustained and restricted to 〈001〉 zone lines comprising {011} and {012} facets and where self-triggered surface explosions are observed. Two kinetic phase diagrams were established for the NO–H2 reaction over palladium and platinum samples under similar experimental conditions. Their shapes reflect a different chemical reactivity of metal surfaces towards oxygen species resulting from the dissociation of NO. NO2 hydrogenation is followed over Pt samples and shows self-sustained kinetic instabilities that are expressed as peaks of brightness that are synchronized over the whole active area (corresponding to the 〈001〉 zone lines as in the NO case) within 40 ms, the time resolution of the video-recorder used for this work.

The dynamic exchange of hydrogen and deuterium is used to determine metal surface areas of solid catalysts. The measurements are carried out in situ, i.e. no transfer of the catalyst from the catalytic reactor to a probing chemisorption device is necessary. This makes the method suitable for measurements at any instant of catalyst activation or kinetic testing. The principle of operation is to perform gas switches from H2 to D2 (deuterium) at various hydrogen partial pressures under dynamic flow conditions using Ar as balance. When switching the gas, D2 reacts with the adsorbed H atoms and with H2 remaining in the gas phase, producing HD molecules. The exchange is followed mass spectrometrically. A linear relationship between the number of detected HD molecules and the hydrogen partial pressure is observed. The extrapolation to $${\text{p}}_{{{\text{H}}_{2} }}$$ = 0 gives access to the number of H atoms adsorbed on the catalyst surface before switching gases. Provided the hydrogen/metal adsorption stoichiometry is known the specific surface area of the metal can be determined. This approach is methodically new and has been validated by comparing the surface areas of pure metallic Co samples (without any support) and their BET surface areas from measurements in the same experimental set-up. We finally demonstrate the usefulness of the methodical approach to determine “active” surface areas of Co-based catalysts after various pretreatments and kinetic tests.

Nanostructured Pd/SiO2 xerogel catalysts prepared via cogelation were characterized by X-ray photoelectron spectroscopy. The preparation route allowed highly porous silica particles to be formed along with embedded Pd nanocrystals. After heat-treating the catalysts in vacuum, Pd was found to be in the metallic state. To obtain information on the xerogel catalyst texture and, in particular, on the size of the silica particles, a theoretical formalism was developed based on measuring the relative intensities of Pd 3d doublet and the associated background tail due to inelastically scattered photoelectrons. The suggested procedure also involved the measurement of the background tails accompanying Si 2p and O 1s spectral lines as internal standards. Using the developed formalism, the size of the silica particles in the catalysts after different treatments was evaluated and compared with TEM data. The results obtained indicate that the textural properties of the sol–gel catalysts start to develop already at the level of co-condensation of alkoxides with the network-forming reagent. Calcination causes these properties to run to completion.

In this paper, we report the colloidal synthesis and detailed characterization of 11 nm bimetallic CoCu nanoparticle catalysts. Presently Co and Cu is an attractive combination because of their respective properties for industrially important Fischer–Tropsch and methanol synthesis reactions of CO (and CO2) with H2. We report the preparation of catalysts by deposition of bimetallic metal nanoparticles, both within mesoporous silica (MCF-17) and on the native oxide surface of a silicon wafer. Subsequent phase separation into phase-segregated (i.e., dimer) particles is found to occur upon redox treatment. These nanoparticle catalysts have then been investigated using an array of techniques including synchrotron-based ambient pressure X-ray photoelectron spectroscopy (APXPS) and in situ near edge and extended X-ray absorption fine structure (NEXAFS/EXAFS) spectroscopies. CO2 hydrogenation is used as a probe reaction. All three techniques combine to show that an oxygen atmosphere segregates copper to the surface. In doing so the oxygen produces oxides of both Co and Cu metals. Significant hydrogen pressure and temperature are required to fully rereduce both metals to a metallic state as demonstrated by NEXAFS spectroscopy. Under the conditions of the CO2/H2 reaction monitored in situ using NEXAFS spectroscopy, both metals exist in a fully reduced state at 2.7 bar, 1:3 CO2:H2, and 260 °C.

We show that the CO hydrogenation over CoCu-based catalysts can be tuned so as to produce either short- or long-chain 1-alcohols with high selectivities. This breakthrough is achieved by “alloying” these catalysts with Mn or Mo thereby creating either “CoCuMn” or “CoCuMo” in various relative composition. Catalysts are prepared via co-precipitation of mixed oxalate precursors, except “CoCuMo” for which the co-precipitation of CoCu oxalate is combined with the precipitation of MoO x using solubility effects. Both “CoCuMn” and “CoCuMo” catalysts produce 1-alcohols or combined 1-alcohols/1-alkenes with selectivities of more than 60 % at temperatures between 170 and 240 °C. CoCuMo catalysts show a double Anderson–Schulz–Flory (ASF) chain-lengthening distribution. Under conditions of low CO conversion, the overall selectivity of 1-alcohols may rise to over 95 % for Co1Cu5Mo1 catalysts. The ASF chain-lengthening probability for Co1Cu1Mn1 may be adjusted to ~0.6–0.7 so as to maximize the C8–C14 1-alcohol slate as feedstock for plasticizers, lubricants or detergents.

This work investigates experimentally the mechanism by which chemical oscillations emerge in a nanometric system. We monitor the spatiotemporal dynamics of an oscillating reaction on the surface of a nanosized three-dimensional Pt model catalyst. Using high-resolution field emission techniques, we are able to show that the oscillations are generated by nanoscale chemical target patterns of much shorter characteristic time than the period with which the oscillations occur. Our observations are made for a specific reaction system---${\mathrm{NO}}_{2}$ reduction with hydrogen---and represent the first experimental evidence for the presence of target patterns at the nanoscale. They can be seen as an experimental demonstration of reaction-diffusion mechanisms to hold at the nanoscale as they do at the macroscale. These results shed new light on the emergence of complexity through different time and length scales.