The selective dehydration of isobutanol to linear butenes catalyzed by acidic ferrierite (H-FER) has been investigated by operando IR spectroscopy under close batch conditions and along a temperature ramp. The employed apparatus permits to alternatively acquire spectra of both the gas phase composition and the species adsorbed on the H-FER surface, thus providing fundamental insights onto the products formation and the reaction intermediates formed on the catalyst surface. In the gas phase, the high selectivity for linear butenes was confirmed in the first phases of the reaction, followed by a slower isomerization to isobutene and by the formation of heavier compounds due to secondary processes. Detailed MCR-ALS analysis of the adsorbed species’ spectra permitted to also identify and quantify adsorbed 2-butanol and trans-2-butene on the H-FER surface, providing a first indication of the alcohol isomerization as a key step in the reaction mechanism. The proposed mechanism was evaluated by microkinetic modelling of both gas phase and surface concentration profiles, showing that the consecutive isomerization of isobutanol to adsorbed 2-butanol followed by its dehydration to trans-2-butene is more favorable than the one-step dehydration-isomerization of isobutanol. In contrast, the direct dehydration of isobutanol to isobutene was found to be slower over the entire investigated temperature range.

Recent models of the Fischer-Tropsch synthesis are able to predict quite accurately the catalyst's initial activity and selectivity. However, these micro-kinetic models rarely consider the performance loss with time on stream and in particular the heavy product selectivity loss. In this study, a deactivation model at the micro-kinetic scale is proposed to represent the effect of carburization on Fischer-Tropsch catalysts performances. Comparison of different mechanisms revealed that termination reactions were the most affected by cobalt carbide formation, before reactants adsorption or chain growth. Both activity and selectivity decline could be accurately described using linear and second-order power laws expressions of active sites concentration and termination kinetic rate constants. The obtained model predicts a monotonous evolution of activity and selectivities from 10% to 80% carburization, above which an important increase of olefin selectivity is observed. The model did not indicate any change of the surface coverages after carburization.

The conversion of isobutanol to light olefins over zeolites was investigated by IR operando spectroscopy. FER zeolites showed a surprisingly high selectivity for the direct conversion of iso-butanol to linear butenes, hence catalyzing dehydration and skeletal isomerization in one step. As a fundamental understanding of the separate reactions is required to design superior catalysts, an in situ and operando FT-IR mechanistic study of the reaction was carried out. The spectroscopic data, the derived species participating and their respective role are analyzed using chemometric (PCA and MCR-ALS) tools. We highlighted the role played by the external acid sites and the requirement of a specific distance between these sites to ensure the n-butene selectivity and point that the internal Brunsted acidity has an adverse effect on the catalyst stability. Moreover, there is no correlation between the carbon species formed on the surface and the exceptional selectivity towards n-butenes, allowing to exclude a "carbon pool" mechanism.

The Front Cover displays a microscopic view of the physico-chemical processes and molecular compounds involved in the Fischer-Tropsch synthesis. In their Full Paper, K. Dembélé et al. report on the direct monitoring of the behavior of cobalt-based nanocatalysts during the reduction step and the following catalytic reaction, by coupling in situ transmission electron microscopy and mass spectrometry and combining additional techniques and catalytic tests. This multiselective approach allows to directly correlate the evolution of the catalytic behavior of the nanoparticles to their structural transformations via processes such as particle fragmentation, migration and coalescence. Our results underline the benefit of using operando microscopy techniques to study the dynamical evolution of catalysts, at the nanoparticle level, under operation conditions. More information can be found in the Full Paper by K. Dembélé et al.

Thanks to their stability and selectivity for long-chains hydrocarbons, supported Co nanoparticles are the most commonly used catalysts in the Fischer-Tropsch synthesis reaction. We report here on the use of in situ transmission electron microscopy (TEM) to address the real-time evolution of cobalt-based catalysts during their reduction under relevant industrial activation condition (10(5) Pa, 430 degrees C), and their operation in syngas (H-2/CO=2, 10(5) Pa, 220 degrees C). To do so, we chose Co3O4-Pt nanoparticles supported on silica or alumina that can be directly compared to some industrial catalysts. By analysing the real space information contained in the TEM images, we have monitored the fragmentation of cobalt aggregates, the disappearance of cavities within the particles, their shape changes, the particle diffusion and coalescence processes, as well as the effect of the support (silica or alumina) on the behaviour of the Co phase. An easier reduction of cobalt catalysts supported on silica as compared to the same catalyst supported on alumina was also observed. During the catalyst operation under syngas, we have noticed the stability of the general shape of the particles. Simultaneously, using a residual gas analyser connected to the TEM holder, the main gas products of the Fischer-Tropsch reaction were systematically analysed. Our findings underline the benefit of the operando TEM to study the dynamical evolution of catalysts, at the nanoparticle level, under operation conditions.

Polymeric carbon was deposited over Siralox supported cobalt catalysts by an ethylene treatment at 230 degrees C and 260 degrees C. Cobalt catalysts with cobalt particle sizes of 10 and 14 nm were studied. Temperature programmed hydrogenation and Raman spectroscopy analyses of the deposited species were found to be similar to those formed during Fischer-Tropsch synthesis. The cobalt catalysts were tested in high-throughput 16 parallel reactors at 20 bars and 220 degrees C, using a H-2/CO ratio of 2.12. Data were collected at different space times to compare activities and selectivities at iso-conversion levels. Ethylene treated catalysts showed lower activity that corresponded roughly to the loss of CO adsorption sites. Additionally, a decrease of the heavy products selectivity, an increase in the methane selectivity and a decrease of the olefin to paraffin ratio was observed after the ethylene treatments. Unlike the loss in activity, the deselectivation level was found to depend on the amount of deposited carbon. This phenomenon can be explained by a steric effect of the deposit, but an electronic effect cannot be excluded, but is challenging to prove. (C) 2021 Elsevier Inc. All rights reserved.

Fischer-Tropsch cobalt catalyst deselectivation was studied using accelerated aging treatments dedicated to the carburization phenomenon. Cobalt carbide was successfully obtained by CO treatments, with limited simultaneously carbon deposition nor sintering. Particle sizes were found to influence the catalyst sensitivity to carburization, likely because of a possible core-shell mechanism. An important loss of both activity and selectivity to heavy products was observed after the treatments, making carburization one of the potential mechanisms responsible for deselectivation in Fischer-Tropsch synthesis. Side products were also impacted by cobalt carbide formation, with an increase of CO2 production and a decrease of the selectivity to olefins. The extent of carburization was found to directly dictate the level of the selectivity shift. (C) 2021 Elsevier Inc. All rights reserved.

Two different TiO2/SiO2 compounds containing TiO2 nanodomains dispersed over SiO2 were investigated applying the AEIR method at the adsorption equilibrium of NH3 and H2O from 300 to 723 K, particularly for the measurement of the individual heats of adsorption of the different species on Lewis acidic sites (LAS) and Brønsted acidic sites (BAS) as evaluation of the strength of the sites. It revealed two types of NH3 adsorption sites: the first ones could correspond either to NH3 species H-bonded to free OH groups or to coordinated weak LAS (named L1). The second ones (L2) were attributed to strongest LAS similar to those present at the surface of TiO2 nanocrystallites. They also correspond to the stronger adsorption sites of H2O. Two types of Brønsted acid sites (BAS) were additionally evidenced by the AEIR method and proposed to be specifically located on the Si-O-Ti bridging bonds at the TiO2/SiO2 interface. The heats of adsorption of the different adsorbed species provided by the AEIR method were consistent with literature data on average values of the heats of adsorption of NH3 and H2O from microcalorimetry measurements. The surface acidity of the two compounds in the presence of H2O was determined using NH3-H2O coadsorption. At T ≥ 473 K, the NH3 species on the L2 sites were not significantly displaced from the surface whatever the partial pressure of H2O studied in agreement with the Temkin competitive model using the individual heats of adsorption of the NH3 and H2O species. This model also revealed the presence of a small amount of H2O species adsorbed on L2 sites allowing H2O dissociation or/and hydrolysis of SiOTi or TiOTi bridges, leading to the formation of a much higher amount of BAS. Therefore, this original work combining the AEIR method and the Temkin competitive model provided new insights for understanding water effects on acidic oxide catalysts.

Most industrial hydrocracking catalysts contain metal sulfides. It is commonly accepted that sulfide-based bifunctional hydrocracking catalysts are less well balanced than Pt-based catalysts because of their weak (de)hydrogenation activity. However, the difference in catalytic performances between the two catalysts has never been quantified. In the present work, hydrocracking catalysts were prepared by shaping the USY zeolite CBV720 with an alumina binder. Acidity was varied by changing the USY content. The extrudates were impregnated either with platinum or with nickel-molybdenum-phosphate and evaluated in the hydroconversion of n-hexadecane. In the absence of NH3, NiMo sulfide was unable to supply the acid sites and to avoid cracking reactions. Cracking became the dominating pathway. In the presence of NH3, only a tiny fraction of the acid sites was vacant. This allowed the NiMo sulfide catalysts to become fairly well balanced, if the zeolite loading was low. Increasing zeolite loading led to a deviation from ideality. Pt catalysts were, with one single exception (at very high USY content), always balanced, even in the absence of NH3.

The emergence of high-throughput experimentation gives new opportunities for accurate and rapid data acquisition for a wide variety of chemical reactions in different fields of application such as hydrocracking, isomerization and syngas conversion.

Ferrierite was shown to be highly efficient in the conversion of isobutanol to butenes with selectivity values higher than 98%. Furthermore, its isomerisation activity is remarkable since proportion of linear butenes higher than 80% was obtained in the present study confirming patents claims. This selectivity was shown to increase with temperature and contact time as well as with time on stream. Neither water added to the feed nor water generated by dehydration has an impact on the structure of ferrierite as shown by XRD and Al-27 NMR. A slight enhancement of catalytic activity was observed below 250 degrees C and could be due to an increase in the number of BAS as suggested by in situ acidity measurements achieved at the reaction temperatures in presence of water vapor while competition of adsorption would inhibit the catalytic activity above 250 degrees C. Furthermore, water was shown to improve dramatically selectivity to linear butenes at low conversion. We propose that water inhibits the proton shift of isobutylcarbenium ions or deprotonation sites leading to isobutene but not acid sites able to isomerize isobutylcarbenium ions into linear carbocations leading to linear butenes. At high conversions, both coke formation and water generated by dehydration could improve selectivity to linear butenes by neutralization of unselective sites responsible for proton-shift reaction.

The Cover Feature shows the combination of in situ transmission electron microscopy and mass spectrometry used to follow the dynamic process occurring on a catalytic material in real time at nanometric scale. In their Full Paper, K. Dembele et al. studied the thermal behavior and surface reactivity of Co nanocatalysts under a syngas (H2/CO=2) atmosphere. The catalyst was stable on the time-scale of the experiment at standard operating temperature of 220 °C for 2 h. Upon increasing the temperature to 400 °C, carbon layers encapsulated the Co nanoparticles. Once the temperature was increased to 500–700 °C, the surface reactivity drastically changed and the Co NPs catalyze the growth of carbon nanotubes (CNTs), following the tip-growth mechanism. In addition, it was found that the presence of hydrogen increases three times the growth rate of CNTs. More information can be found in the Full Paper by K. Dembele et al. on page 4004 in Issue 18, 2018 (DOI: 10.1002/cctc.201800854).

Colloidal chemistry is very efficient in providing nanocrystals of well-controlled structural characteristics. Although nanoparticles are essential components of heterogeneous catalysts, colloidal methods are rarely employed for their preparation. We have employed a seed-mediated growth approach for modifying the structural characteristics of a conventional cobalt-based Fischer-Tropsch catalyst. The Co particles of this catalyst can play the role of seeds for the overgrowth of shape- and structure-controlled cobalt nanostructures by using a simple wet chemical method involving a molecular cobalt precursor and stabilizing agents. Thus, cobalt nanorods exhibiting the hexagonal compact structure were selectively grown on the immobilized Co particles of a reference Co/Al2O3-SiO2 catalyst. The as-obtained catalyst shows a better stability than a reference catalyst for the Fischer-Tropsch reaction. The removal of most of the ligands from the nanorod catalyst allows the catalyst activity to be improved while maintaining its stability. This is a proof of concept concerning the implementation of wet chemistry nanoparticle synthesis for the modification of heterogeneous catalysts.

Here the thermal behaviour and the surface reactivity of cobalt catalysts supported by alumina-silica and promoted by platinum were investigated by insitu transmission electron microscopy (insitu TEM) in a syngas environment. At the standard operating temperature of 220 degrees C, atomic diffusion and sintering processes onto the support are quite limited on the time scale of the TEM experiment. At temperatures between 350 and 450 degrees C, particles encapsulation occurred due to a higher CO dissociation and conversion into graphitic layers. Beyond 500 degrees C, carbon nanotubes (CNTs) growth is activated and the particles undergo (i) morphological changes through continuous elongation and contraction; and (ii) microstructural changes with the appearance of cobalt carbide. By comparing reactions under pure CO and a mixture CO-H-2, it was shown that the addition of dihydrogen to CO increased the rate of CNTs growth and modified the structure of the nanotubes. These results clearly demonstrate the strong ability of the insitu TEM to provide the main lines of the reactivity synopsis of nanocatalysts at a nanometric scale under temperature and reactive gas.

The Fischer-Tropsch synthesis (FTS) is a structure-sensitive exothermic reaction that enables catalytic transformation of syngas to high quality liquid fuels. Now, monolithic cobalt-based heterogeneous catalysts were elaborated through a wet chemistry approach that allows control over nanocrystal shape and crystallographic phase, while at the same time enables heat management. Copper and nickel foams have been employed as supports for the epitaxial growth of hcp-Co nanowires directly from a solution containing a coordination compound of cobalt and stabilizing ligands. The Co/Cufoam catalyst was tested for Fischer-Tropsch synthesis in a fixed-bed reactor, showing stability and significantly superior activity and selectivity towards C5+ compared to a Co/SiO2 -Al2 O3 reference catalyst under the same conditions.

H 4 SiW 12 O 40 heteropolyanions, WO 3 , TiO 2 and SnO 2 were supported over SiO 2 at high loading by wet impregnation or grafting methods and evaluated in the dehydration of isobutanol to butenes. Their structural and textural properties were determined by different techniques such as XRD, TEM, IR, XPS and N 2 liquid physisorption respectively. Most of the prepared compounds contained amorphous oxide clusters of few nanometers lying over SiO 2 and were mesoporous. Their acidic properties (nature, density and strength) were investigated by pyridine and CO adsorption followed by FTIR. H 4 SiW 12 O 40 /SiO 2 contained strong Brønsted acid sites while mostly moderate Lewis acid sites were present on TiO 2 /SiO 2 and SnO 2 /SiO 2 . WO 3 /SiO 2 had a mixed character with both moderate Brønsted and Lewis sites. The catalytic activity was related to the Brønsted acidity and the best selectivity to butenes close to 100% were obtained for the catalysts containing moderate and weak sites (WO 3 /SiO 2 and TiO 2 /SiO 2 ). Except for SnO 2 /SiO 2 catalysts, which were unstable and unselective to dehydration products, a significant selectivity to linear butenes (ca 30%) was obtained. This isomerisation activity was mainly related to equilibrium between carbocations formed after E 1 elimination of water. Its slight increase for H 4 SiW 12 O 40 /SiO 2 (and to a lesser extent WO 3 /SiO 2 ) was attributed to strong Brønsted acid sites able to convert isobutene to linear butenes.

We reveal the presence of significant variations in Brønsted catalytic activity within and between individual H‐ZSM‐5 zeolite crystals. Fluorescence microscopy in combination with a fluorogenic probe was used to resolve the catalytic activity at the nanoscale. The observed variations in catalytic activity could be directly linked to structural parameters and crystal morphology observed in scanning electron microscopy and by specifically staining crystal defects. The obtained results are directly compared with ensemble averaged information from techniques such as pyridine IR spectroscopy and nitrogen physisorption, typically used to characterize acid zeolites. The inter‐ and intra‐particle heterogeneities resolved by the employed fluorescence approach remain unaddressed by bulk characterization. Our experimental results relate the heterogeneous catalytic activity to variation in both the Si/Al ratio and mesoporosity induced during the zeolite synthesis.

The understanding of water effects on solid acid catalysts is a key issue in developing efficient processes to produce olefins by bio-alcohols dehydration. In this work, the effects of water on TiO2/SiO2 catalysts for the gas phase conversion of isobutanol into linear olefins have been unraveled, using for the first time in situ acidity measurements achieved with a flowing NH3 probe and water vapor containing gas mixtures at adsorption equilibrium in the temperature range of the reaction. Such compounds, prepared by grafting titania onto mesoporous silica, contain well-dispersed TiO2 amorphous clusters anchored by Ti-O-Si linkages, leading to much higher catalytic activity than TiO2 and SiO2. They yielded only dehydration products, among which 30% were linear butenes. Furthermore, their activity was significantly improved by addition of water into the feed, whatever the contact time. Acidity measurements indicated that TiO2/SiO2 mixed oxides were mostly of Lewis type after activation at 450 degrees C. However, in situ FTIR acidity measurements showed that addition of H2O to NH3/He gas mixture has no influence on the number of Lewis sites, while weak Bronsted sites were formed on other sites. This formation, due to a shift of equilibrium depending on both the temperature and the H2O partial pressure, corresponds to the hydrolysis of Ti-O-Si bonds, generating OH acidic groups and enhancing catalytic activity under water vapor. The novel type of acidity measurements used in this work appear powerful and can be applied to other acidic heterogeneous catalysts. (C) 2016 Elsevier Inc. All rights reserved.