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Hollow Y zeolite single crystals have been obtained from a conventional NaY zeolite following a three-step process involving a severe dealumination of the zeolite with silicon tetrachloride (step #1), followed by an acid washing under mild conditions (step #2) and finally a selective dissolution of the crystals core in the presence of protective Al species (step #3). Crystals are characterized by the presence of a regular internal cavity with 0.1–0.2 nm thick microporous walls. They contain a relatively low framework Al content but significant amounts of extraframework Al oxide species mainly located on the external surface of the crystals. Hollow crystals have been mixed with a Pt-supported alumina binder and used as catalysts in the hydroisomerization of n-hexadecane. Compared to the corresponding bulk crystals obtained after step #2, their higher activity has been attributed to a better efficiency, directly resulting from the presence of the cavity.

[Display omitted] • The surface of cobalt was monitored by operando IR under CO 2 -CO-H 2 mixtures. • The selectivity to methane decreased monotonously with CO surface coverage. • The state of the cobalt metallic surface remained unaffected by the CO/CO2 ratio. An operando IR study was carried out to investigate the loss of selectivity to higher hydrocarbons observed over cobalt-based Fischer-Tropsch catalysts when CO is replaced with CO 2. Our data unambiguously show that the structure and oxidation state of the surface of metallic cobalt remains the same whether CO 2 or CO are cofed with H 2. The selectivity to CH 4 appears to increase monotonously with decreasing surface coverage of adsorbed CO. The switch from Fischer-Tropsch synthesis to methanation using CO 2 -rich feeds over metallic cobalt can therefore be assigned to surface coverage effects only, assuming that most, if not all, hydrocarbons products are formed on metallic cobalt. [ABSTRACT FROM AUTHOR]

Abstract: The paper addresses current needs in Natural Gas (NG) treating. Basic principles of Pressure Swing Adsorption (PSA) separation processes are described. A state of the art of microporous adsorbents in the frame of NG treating is given. It includes reference and advanced zeolites, carbon based materials and Metal-Organic Frameworks (MOFs). The pros and cons of each material category are discussed. Guidelines to develop on-purpose materials are given from thermodynamics and material state of the art. Finally, PSA applicability to inert (nitrogen and carbon dioxide) rejection from NG is discussed. [Copyright &y& Elsevier]

A simple kinetic model based on the zeolite acid strength, the number of Brønsted acid sites, and the catalyst efficiency was developed for the cracking of n-hexane. A series of HY zeolites with a mesopore volume from 0.04 to 0.32 cm3/g was synthesized and characterized by various physical-chemical methods and tested for n-hexane cracking. The generation of mesoporosity influenced several other important parameters, such as acidity and extra-framework aluminum. Zero-length column diffusion measurements for mesitylene showed a large decrease in the characteristic diffusion time upon the introduction of mesoporosity, which changed only slightly with a further increase in mesoporosity. Similar n-hexane physisorption enthalpies were measured for all samples. The highest initial activity for n-hexane cracking per catalyst volume was observed for the sample with an intermediate mesopore volume of 0.15 cm3/g. The three mesoporous H-USY zeolites showed the same value of the intrinsic rate constant and the same activation energy. The difference in initial activity of the mesoporous zeolites was caused by the difference in the number of Brønsted acid sites. The increase in initial activity for the mesoporous zeolites compared to a microporous zeolite was caused by an increase in the acid strength. [ABSTRACT FROM AUTHOR]

Silver nanoparticles are currently one of the most studied nanostructured nanomaterials. Because nanoparticle size and dispersion act together in determining a material's physical and chemical properties, there is a continuous quest to develop size-controlled synthesis methods. Nonetheless, the instability of the nanometer-sized particles, which is caused by their tendency to aggregate irreversibly into larger particles, remains a recurrent problem. The use of confining scaffolds, such as the regular system of cages in a crystalline zeolite-type material, is often reported in the literature as an efficient solution to overcome particle migration at the surface. Silver nanoparticles encapsulated in ZSM-5 (Ag@ZSM-5) represent a new generation of adsorbent for Xe enrichment from the atmosphere that is currently being developed at the pilot scale in a Temperature Swing Adsorption (TSA) process. In this study, we have found that the presence of Cl-containing compounds in the air (VOCs) leads to a poisoning of the active silver phase by the formation of silver chloride. By a careful study of process parameters, we have found that most of the chlorine can be removed by heat treatment above 573 K so that the adsorption properties of silver are regenerated. That said, when applying 573 K temperature regeneration at the pilot scale, we observe a very minor but observable decay of xenon adsorption capacity that continues cycle after cycle. The mechanism of capacity decay is discussed in terms of (i) the residual presence of Cl at the surface of silver nanoparticles, (ii) the aggregation of silver nanoparticles into larger particles (sintering mechanism), and (iii) the acceleration of silver particle migration to the surface and sintering. [ABSTRACT FROM AUTHOR]

Whereas the synthesis principles of supported metal catalysts are well documented in the open literature, impregnation protocols on shaped bodies represent sensitive industrial know-how and are, therefore, rarely found. We investigated various synthesis parameters for both wetness (WI) and dry (DI) impregnations to prepare Pd/γ–Al2O3 alumina beads. Two kinds of catalysts were achieved: homogeneously dispersed catalysts with no metal gradient across the beads and eggshell catalysts. A combination of optical images, Castaing microprobe analysis, elemental analysis, and TEM made it possible to discriminate between catalysts according to their metal loading, location across the bead diameter, and metal dispersion. Regardless of the macropore structure of the alumina beads, we found that volatile solvents (acetone) were preferred for preparing homogeneous catalysts by WI, whereas the use of a viscous aqueous solution (water/glycerol) in DI resulted in an eggshell-type catalyst. The atomic layer deposition (ALD) method was also investigated as a physical vapor phase deposition method for preparing eggshell catalysts. Representative-shaped catalysts were tested for CO oxidation as a model reaction in order to highlight the differences between catalysts with a homogeneous metal distribution (no metal gradient) and eggshell-type. [ABSTRACT FROM AUTHOR]

Despite the development of selective catalyst formulations for oxidative coupling of methane (OCM), kinetic and reactor design studies have been hampered by a lack of data for truly isothermal reaction conditions. Because of the high exothermicity, the temperature of a fixed-bed reactor filled with Mn-Na 2 WO 4 /SiO 2 catalysts will show hot-spots with a loss of selectivity. The objective of this study is to measure catalyst activity under relevant reaction conditions of pressure (3 bar), biogas composition (no dilution) and contact time, while keeping the process isothermal. To this aim, we have synthesized and shaped a trilobed Mn-Na 2 WO 4 /α-Al 2 O 3 catalyst, which may be used as is at industrial scale, and measured its performance in a single-pellet reactor. We found that the presence of CO 2 did not degrade the catalyst performance, even on the long run, which should enable the use of a CO 2 -rich stream such as biogas. Actually, higher methane conversions have been obtained in the presence of CO 2 , likely due to a possible contribution of methane dry reforming reaction. We also noticed a slow catalyst activation over the first 100 h, while selectivity was kept constant. [Display omitted] • Oxidative methane coupling in the presence of carbon dioxide was studied. • A single pellet reactor was used to avoid temperature gradients. • Carbon dioxide does not impact the catalyst performance. • Opens the pathway for biogas applications. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights: • Numerical models are developed for all porous solid oxide fuel cells. • Electrolyte porosity changes are investigated for the solid oxide fuel cells. • Criterion of safe operations are considered in the simulation. • Effects of operating parameters for the solid oxide fuel cells are studied. • A novel design is proposed to improve the performance of solid oxide fuel cells. Abstract Conventional solid oxide fuel cells (SOFCs) could suffer from carbon deposition when fueled with hydrocarbons. For comparison, a new type of SOFC with porous electrolyte can resist carbon deposition because it allows oxygen molecules to transport from the cathode to the anode. As the transport of O 2 to the anode lowers the fuel cell performance and causes the risk of explosion, the rate of O 2 transport must be well controlled to ensure efficient and safe operation. Following our previous model, this paper focuses on electrolyte porosity optimization under various inlet methane mole fractions, inlet oxygen mole fractions and inlet gas flow rates. Furthermore, a new design with a partial porous electrolyte is proposed and numerically evaluated. The new design significantly improves the electrochemical performance compared with all-porous one. A conversion rate >90% from methane to syngas is achieved at the 0.33 inlet CH 4 mole fraction with the new design. The results enhance the understanding of all porous solid oxide fuel cells and the mechanism underlying, inspiring novel designs of solid oxide fuel cells. [ABSTRACT FROM AUTHOR]

Two cobalt imidazolate metal-organic frameworks were evaluated as a bactericidal material against the growth of the Gram-negative bacteria Pseudomonas putida and Escherichia coli. Under the most unfavourable conditions, within the exponential growth phase and in the culture media for both microorganisms, the growth inhibition reached over 50% for concentrations of biocidal material in the 5-10mgL−1 range. The release of metal gives excellent durability with the antibacterial effect persisting after 3months. Both cobalt-based materials can be prepared with simple, cheap and easily accessible commercial ligands, leading to a more affordable possible future application as antimicrobial materials. [ABSTRACT FROM AUTHOR]

Abstract: This paper exploits the suitability of three perovskite materials Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF), GdBaCo2O5+δ (GBC) and Ba0.5Sr0.5Mn0.7Fe0.3O3−δ (BSMF) as SOFC cathodes in the single-chamber configuration operating at the intermediate temperature range. TG analysis showed high thermal stability depending on the crystalline phases of the materials. The catalytic activity of these three materials for hydrocarbon conversion was investigated under a realistic feed, i.e. with hydrocarbon, oxygen, water and carbon dioxide. Electrochemical impedance spectroscopy of the various cathodes tested in symmetric cell configuration revealed a B-site dependence of the electrode catalytic activity for oxygen reduction. High temperature (1000°C) powder reactivity tests over a gadolinium doped-ceria (CGO) and perovskite cathode revealed excellent chemical compatibility of BSMF and CGO. Catalytic tests associated with thermal and structural characterization attest to the suitability of these materials in the single-chamber configuration. [Copyright &y& Elsevier]