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Abstract: A zeolite beta–silicalite-1 composite was prepared by growing polycrystalline silicalite-1 shells on single micron-sized zeolite beta crystals. The obtained core–shell material was employed for the separation of hexane isomers. Gravimetric uptake measurements revealed that the silicalite-1 shell acted as a membrane that controlled the transport to zeolite beta core. The positive impact of the silicalite-1 membrane on the separation of mono- and di-branched hexane isomers was confirmed by breakthrough experiments. The core–shell composite material allowed more selective separation of mono- and di-branched isomers than either of its components alone and had a significantly higher adsorption capacity than silicalite-1. [Copyright &y& Elsevier]

Abstract: Resonant inelastic X-ray scattering (RIXS) was applied to investigate whether the iron–oxygen species created upon reaction of Fe-ZSM-5 with N2O have a (partial) 3d4 configuration, i.e. oxidation state Fe(IV). Fe-ZSM-5 samples with low iron loading were pre-treated at high temperatures before reaction with N2O. Then Fe K-edge XANES spectra were recorded either by selecting the fluorescence of the main Kβ1,3 line or the satellite Kβ′ line in the Kβ emission spectrum. The experiments were performed in situ and imitated the experiments performed in the laboratory reactor. The absence of a pre-edge in the Kβ′ line spectrum proves that the configuration of the active iron–oxygen species is purely 3d5. The result was confirmed for several differently treated Fe-ZSM-5 catalysts. The high reactivity of Fe-ZSM-5 is therefore not due to the formation of high oxidation states of iron, but must be ascribed to the particular oxygen species that is created by the reaction of N2O with the catalyst. [Copyright &y& Elsevier]

Abstract: The hydrothermal stability of WIE-based Fe-ZSM-5 and Fe-BEA for N2O decomposition in the presence of NO, H2O and O2 was studied at 723K. Catalysts were characterized with UV–vis, IR and Al-XANES. The N2O conversion remains at a constant level with Fe–H-BEA even in the presence of large amounts of H2O. Deactivation was, however, observed with Fe–H-ZSM-5 already in the presence of 0.5vol.% water. The analysis of deactivated samples indicated that steam-dealumination and clustering of iron occurred during the reaction with Fe-ZSM-5. Replacement of protons for sodium in Fe-ZSM-5 slowed down the rate of catalyst deactivation significantly. Steam-dealumination is likely to precede the clustering of iron in Fe–H-ZSM-5. The excellent hydrothermal stability of WIE-based Fe–H-BEA relates to the high initial degree of dealumination in the as-received BEA. [Copyright &y& Elsevier]

Abstract: The mechanism of decomposition of N2O on Fe-ZSM-5 prepared by chemical vapor deposition was studied by step and pulse response experiments and by isotope labeling. The results show that only a very small fraction of the iron sites is taking part in the catalytic cycle. N2O deposits its oxygen atoms on these sites, the deposited oxygen atoms migrate over the iron cluster, exchange with other oxygen atoms and then desorb by recombination to O2. On strongly dehydroxylated iron sites also a direct recombination of two oxygen atoms, which were deposited from N2O, is possible. The concentration of these sites increases after treatment of the samples at high temperatures in inert gas. The relation between the sites involved in N2O decomposition and the α-sites, which were first described by the group of Panov, is discussed. We can conclude that the deposition of N2O on Fe-ZSM-5 CVD catalysts creates active oxygen species on the catalyst surface (in particular, after pretreatments at high temperature), but their properties are different from those of α-oxygen. [Copyright &y& Elsevier]

Abstract: Benzene and four trisubstituted aromatic compounds were used as swelling agents for mixed hexadecyl- and dodecyltrimethylammonium micelles. These micelles served as templates for the synthesis of mesoporous M41S materials. By varying the amount and the nature of the aromatic swelling agent, M41S materials with any pore diameter between 3 and 11nm could be synthesized. All materials exhibited specific surface areas around 1000m2/g and large specific pore volumes as it is characteristic for the M41S family. Phases with layered, rod-like, and globular building units were obtained by varying the nature and/or the amount of aromatic swelling agent. A detailed analysis of the trends showed that the hydrophobicity of the swelling agents determines the size and shape of the pores: with the more hydrophobic swelling agents smaller pores with higher curvature are obtained. [Copyright &y& Elsevier]

• An accelerated deactivation protocol at the pilot plant scale was developed to study hydrocracking catalyst deactivation in a short time of 30 days. • The organic nitrogen content of the feedstock to the hydrocracking process deactivates the catalyst acid function permanently by coke deposition. In contrast, nitrogen compounds have just an inhibitory effect on the metal function. The deactivation of the metal function is mainly due to nickel depromotion. • The balance in the ratio of the metal/acid sites determines the amount and the type of formed coke. The lower the ratio, the higher the coke production rate with a more aromatic structure. • Along the catalytic bed, the metal/acid balance decreases from bed inlet to bed outlet, the bed outlet contains a higher amount of coke, which is more aromatic. A representative accelerated experimental deactivation procedure was developed to understand the activity loss of bifunctional vacuum gasoil (VGO) hydrocracking catalysts over time. Experiments were performed in an up-flow fixed-bed pilot unit with a typical vacuum gas oil feedstock. The deactivation was measured by tracking the decrease of VGO conversion (370 °C+) with time on stream. The catalyst consisted of nickel-molybdenum sulfide particles dispersed on a carrier containing USY zeolite. The impact of temperature, liquid hourly space velocity (LHSV), hydrogen to hydrocarbon (H 2 /HC) ratio and organic nitrogen (N org) on the catalyst deactivation rate was first studied. The variables with the most significant impact on conversion loss were temperature and space velocity. Temperature directly influences the production rate of coke precursors, whereas space velocity affects the local concentration of feed contaminants along the reactor. Based on these results, the following operating conditions were selected to establish the final accelerated deactivation experimental protocol: T = 418 °C, LHSV = 3 h−1, H 2 /HC = 1500NL/L, P = 14 MPa, organic nitrogen content (Norg) = 150 ppm weight, total nitrogen content = 2500 ppm weight and a total time on stream of 30 days. Spent samples from this procedure presented similar properties to some industrial catalysts submitted to cycle lengths between 12 and 18 months. Both types of samples yield similar values of surface area and pore volume loss as well as a similar amount and nature of coke deposits. These results led to the qualitative validation of the protocol representativeness. This experimental procedure was then used to get more insight into the deactivation phenomenon. It was found that the organic nitrogen content of the feedstock is crucial, as it determines the ratio between available metal and acid sites. This ratio determines the reactions that take place and, therefore, the type of coke produced. [ABSTRACT FROM AUTHOR]

Abstract: The N2O decomposition activity of the Fe-ZSM-5 catalysts, prepared by chemical vapor deposition (CVD) and aqueous ion exchange (IE), was studied after steaming and high temperature treatment at 1218K (HT) and compared with the activity of the corresponding non-steamed catalysts after pretreatment at 873K. FTIR spectra showed that dehydroxylation and/or dealumination took place during steaming and high temperature treatment of the catalysts, which leads to the formation of oxygen vacancies (i.e. lattice defect). These lattice defects leads to a change in electronic properties of the iron sites, which are associated with electron withdrawing Al Lewis centers. The iron sites in close proximity of defects are responsible for the initial higher N2O decomposition (transient activity) of the steamed and HT catalysts. The increase in steady-state activity over steamed and HT catalysts can be mainly attributed to an increase in the number of active sites created by autoreduction of the iron centers during steaming and high temperature treatment. The above-mentioned trends are valid for both CVD and IE samples. [Copyright &y& Elsevier]

Abstract: Mesoporous materials were synthesized from solutions containing ZSM-5 precursors in the presence of a micellar template (CTACl). The effect of different parameters like aluminum content, aging conditions and hydrothermal treatment conditions on the properties of the final materials was investigated by dynamic light scattering (DLS), N2 physisorption, XRD, 27Al MAS-NMR, TEM and IR. In addition two catalytic test reactions (cracking of isopropylbenzene and 1,3,5-triisopropylbenzene) and acidity measurements via pyridine adsorption were carried out. We observed a transition of the initially formed mesoporous structure containing protozeolitic seeds to a zeolitic phase during hydrothermal treatment. The rate of zeolitization strongly depended on the conditions of the aging period and on the composition of the synthesis solution: the more protozeolitic seeds were formed during the aging procedure the faster the zeolitization. Catalytic test reactions and acidity measurements showed that the XRD amorphous materials with protozeolitic seeds in the mesoporous structure are more active and more acidic than mesoporous materials prepared without ZSM-5 precursors, but far less active and acidic than zeolites. A combination of high activity and accessibility of most active sites was found for samples containing small zeolite crystals. [Copyright &y& Elsevier]

Abstract: The surface of mesoporous M41S silica material was functionalized with 3-aminopropyl and methyl groups and with mixtures of both. The ratio of the two groups on the silica surface could be adjusted by changing the molar ratio of the corresponding alkoxysilanes in the reaction mixture. The fraction of 3-aminopropyl on the surface was always larger than in the functionalization reaction mixture. Moreover, functionalization with the 3-aminopropyl group or with mixtures of the 3-aminopropyl and methyl groups led to higher molar coverages of the silica surface than functionalization with the methyl group alone. One reason for these effects is that the amino group base-catalyzes the hydrolysis of the alkoxysilanes and thereby enhances the reaction of the silanes with the silica surface. The 3-aminopropyl/methyl—functionalized materials showed a very high stability against hydrolysis in boiling water because the siloxane bonds of the silica framework were protected by the organic moieties. [Copyright &y& Elsevier]

The effect of various acid treatments and of two different sodium silicate sources on the pore characteristics and the hydrothermal stability of pure silica MCM-41 was investigated. The best material was obtained by addition of acetic acid after 24 h of the synthesis, which lasted in total 96 h at 100 °C. There was a correlation between the pore characteristics and the hydrothermal stability. The material with the best pore characteristics as revealed by nitrogen adsorption and XRD also showed the best hydrothermal stability during steaming and refluxing in water. The relative loss of pore volume after 6 h of steaming at 500 °C was only 15%. The positive effect of the acid treatment on the pore characteristics and the hydrothermal stability is mechanistically explained by two factors, (i) the shift of the equilibrium of silica condensation and (ii) the decrease in electrostatic repulsion among the negatively charged silicate species in the alkaline synthesis gel. In the comparison of the two silica precursors, better results were obtained using the sodium silicate solution containing larger silicate species. [Copyright &y& Elsevier]

In order to meet the demand for cleaner fuels, it is necessary to develop high performing hydrotreating catalysts. Although organic additives are often used to improve the performances of hydrotreating catalysts, bio-polymer additives have not yet been thoroughly investigated. We recently showed that dopamine, a neurotransmitter molecule, which is also frequently found in adhesive bio-polymers, efficiently coats the surface of an alumina carrier material and modifies the interaction with active components of hydrotreating catalysts, i.e . cobalt and molybdenum. The catalytic performance of the CoMoS/Al 2 O 3 catalysts could, thus, be improved. In the present paper we extend the strategy to other carrier materials (silica and titania). The catalysts prepared on (poly)dopamine (Pdop) coated silica showed enhanced activity for the hydrogenation of toluene reaction and the selective HDS of FCC gasoline model feed. Pdop coating lowers the MoS 2 nanocrystallites' stacking on silica, thereby improving the accessibility of active edge sites. The origin of this increase in catalytic activity may be found in the higher capacity of Pdop's functional groups to interact with metallic precursors leading to a better dispersion of the active phase. On the contrary, when the interaction between the dopamine and the support is too strong (as observed for TiO 2 ), the functional groups of Pdop are not available for interaction with Co and Mo species, resulting in decreased catalytic activity. [ABSTRACT FROM AUTHOR]

A detailed kinetic study of the hydrodenitrogenation (HDN) network of quinoline was carried out over Ni-promoted MoS 2 catalysts supported either on γ-Al 2 O 3 or on amorphous silica alumina (ASA), the objective is to identify the role of the support acidity in HDN reactions. The kinetic data obtained from catalytic tests in a batch reactor were analyzed by a model including the liquid-vapor mass transfer. The adsorption constants of all intermediates and the kinetic constants of all elementary steps were estimated. We found that the NiMo(P)/ASA exhibited a higher rate constant in the hydrogenation of tetrahydroquinoline, which was the rate determining step of the main reaction pathway, and in exocyclic carbon-nitrogen bond cleavage reactions, than the NiMo(P)/Al 2 O 3 . Characterization data by Infra-Red spectroscopy of CO suggested that this result might be related to the modification of the electronic properties of promoted NiMoS phase due to higher acidity of ASA. However, the stronger self-inhibiting effect due to stronger adsorption of nitrogen compounds over NiMo(P)/ASA and its lower content of NiMoS phase decreased its global catalytic activity. [ABSTRACT FROM AUTHOR]

• VGO from conversion processes have a very different distribution of neutral nitrogen species than straight run VGOs. • Transition of neutral to basic N-species was observed for heavy coker gas oil. • DBE shift in basic nitrogen species depends on the number of the carbon atoms. • Neutral species with high DBE convert into carbazoles, which are "refractory". • Isomeric characterization is necessary for the selection of the reactivity descriptors. This paper is a part of a study on reactivity descriptors in vacuum gas oil hydrotreatment (VGO HDT). It aims to understand the differences in feeds of various process origins and the corresponding hydrotreated effluents on a molecular level. Four different vacuum gas oils were hydrotreated over a sulfided NiMo/Al 2 O 3 catalyst at a wide range of temperatures and residence times in order to collect HDT effluents at a broad range of hydrodenitrogenation (HDN) conversions. Vacuum gas oils and HDT effluents have been analyzed by Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) in positive ESI(+) and negative ESI(-) electrospray ionization modes to characterize the basic and neutral nitrogen-containing species and the subtleties of HDT transformations depending on the feedstock type. [ABSTRACT FROM AUTHOR]

Abstract: The present work describes the adsorption and separation of xylene isomers by ZIF-8. Although the formal pore diameter of ZIF-8 is much smaller than the molecular diameter of the xylene isomers, ZIF-8 is able to separate the isomers by molecular sieving. A structural study indicates that the diffusion of the xylenes into the pore structure of ZIF-8 happens via a transitory deformation of the pore aperture which is based on a tilt of the imidazolate linkers, followed by a return to the initial conformation. The rate of adsorption depends on the size of the isomer, i.e. it decreases from para- to meta- and to ortho-xylene. The separation of the xylene isomers is good in the gas phase. In liquid phase breakthrough experiments, the quality of the separation is deteriorated. Moreover, as expected for a separation based on molecular sieving, para-xylene cannot be well separated from ethyl-benzene. [Copyright &y& Elsevier]

Abstract: The crystal chemistry of divalent metal N,N′-piperazinebis(methylenephosphonates) of the STA-12 family, (M2(H2O)2(O3PCH2NC4H8NCH2PO3)·xH2O, M=Mg, Mn, Fe, Co, Ni) is compared. The different metal analogues are isostructural in the hydrated forms, possessing symmetry, but their reversible dehydration behaviour and resultant porosity are strongly dependent on the metal cation. Whereas the Co and Ni forms change symmetry to triclinic upon dehydration, giving permanent porosity to N2 of 0.14cm3 g−1 and 0.27cm3 g−1, respectively, the Mn and Fe forms remain rhombohedral but exhibit a strong decrease in unit cell volume (e.g. 23% for STA-12(Mn)). Structure determination of dehydrated STA-12(Mn) indicates a topotactic transformation with a change in coordination of the phosphonate O atoms. Negligible permanent porosity is observed in either dehydrated STA-12(Mn) or (Fe), suggesting the presence of non-crystallographic pore blocking. Dehydration of STA-12(Mg) results in loss of some long range order, preventing structural determination of the fully dehydrated form, but does give appreciable permanent porosity for N2 of 0.20cm3 g−1. Infrared spectroscopy (and for STA-12(Mg) solid-state NMR spectroscopy) have been used to follow the changes upon dehydration. Applications of the most porous and stable STA-12 structure, the Ni form, have also been investigated. CO2 adsorption selectivity over CH4 and CO has been measured via analysis of breakthrough curves, and a Porous Layer Open Tubular (PLOT) gas chromatographic column has been prepared and used to separate a mixture of low molecular weight alkanes. [Copyright &y& Elsevier]

Abstract: ZIF-76, Zn(Im) x (5-ClbIm) y (Im=imidazolate, 5-ClbIm=5-chlorobenzimidazolate), is, among the known ZIF structures, one of the few materials that combine a relatively large pore aperture with a large pore volume. Moreover, it is thermally stable up to 400°C and can be stored under ambient atmosphere without undergoing a measurable degradation. ZIF-76, therefore, appears to be an interesting material for applications in adsorption and separation. The published synthesis protocol leads to very low yields and is, thus, not applicable on a larger scale . In this work, we have succeeded in preparing ZIF-76 in suitable yields by changing the solvent and adding NaOH to the synthesis mixture. The addition of the base increases the yield and leads to smaller crystal sizes, by favoring nucleation over crystal growth. By using the same synthesis strategy, four new isomorphs of ZIF-76 were obtained, with different substituents on the benzimidazole ligand (Me, Br and NO2) and different metal sources (Co and Zn). All the samples were tested in the adsorption and separation of CO2/CH4 in order to highlight the influence of the linker and of the metal center on the adsorption/separation properties. [Copyright &y& Elsevier]

The texture of a series of dealuminated macrocrystalline beta zeolites has been investigated by N2 physisorption, transmission electron microscopy, and electron diffraction. Hydrothermal dealumination creates a secondary mesoporous system in zeolite BEA. N2 physisorption together with DFT calculations indicated the presence of pores with an estimated size of 2–4 nm after steaming. After subsequent leaching, TEM revealed the newly formed cylindrical mesopores. As determined by electron diffraction, the new porous network consists of pores lying in the (0 0 1) plane. [Copyright &y& Elsevier]