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In petroleum refining, middle distillates are produced via hydroisomerization/hydrocracking processes using bifunctional catalysts often containing ultrastable Y (USY) zeolite. Petroleum fractions serving as feedstock for hydrocracking processes contain a majority of (poly)cyclic hydrocarbon molecules. Few studies on reaction mechanisms of hydrocracking of such polycyclic compounds are available. In this study the tricyclic phenanthrene molecule was used as model compound. Phenanthrene was hydrogenated on a Pt/alumina pre‐catalyst to perhydrophenanthrene, and subsequently hydrocracked over Pt/H‐USY zeolite. The feed consisted of 3 wt.% phenanthrene dissolved in n‐heptane. The reaction was performed at 280 °C and 60 bar, with a molar H2 to total hydrocarbon ratio of 7 mol/mol. The reaction products were analyzed using GCxGC‐FID/MS. This detailed analysis enabled identification of the reaction scheme involving skeletal isomerization, ring opening and fragmentation. New mechanistic insight is gained on relative reactivities of bridged and non‐bridged tricyclic naphthenes. Preferential hydrocracking routes were identified. The study provides insight in the products to be expected from polycyclic hydrocarbon isomerization and hydrocracking. [ABSTRACT FROM AUTHOR]

A detailed kinetic model was proposed to analyze experimental data obtained from indole hydrodenitrogenation (HDN) over γ-Al2O3 and amorphous silica-alumina (ASA)-supported NiMo catalysts. The goal was to investigate the support acidity effects on indole HDN and compare with a recent study on quinoline HDN. Similarly to quinoline HDN, indole HDN occurred via hydrogenation of the aromatic ring, followed by N-ring opening and exocyclic C-N bond breaking. The high support acidity of NiMo(P)/ASA exhibited a promoting effect for N-removal steps and adsorption of nitrogen compounds. However, in contrast to quinoline HDN, it did not clearly induce a positive effect for the hydrogenation step. The acidic function of ASA also favored the formation of byproducts such as toluene, cyclohexane, dimer, and trimer of indole. Catalytic conversion of a quinoline and indole mixture revealed a strong inhibiting effect of quinoline on indole HDN, whereas the inhibiting effect of indole on quinoline HDN was weak. The inhibition was weaker over NiMo(P)/Al2O3 than over NiMo(P)/ASA. This result is in agreement with a relative ranking of apparent adsorption constants of quinoline, indole, and their products on NiMo(P)/Al2O3 and ASA. [ABSTRACT FROM AUTHOR]

The adsorption processes for postcombustion CO2 capture are usually based on a temperature or vacuum swing (TSA or VSA). In the present contribution an alternative concept is presented, which is based on the regeneration of the solid sorbent (an immobilized amine) by a purge gas, low pressure vapor, under almost isothermal conditions. Because of the close to isothermal operation, the process consumes significantly less thermal and mechanical energy than conventional TSA and VSA processes, respectively. We present a rough design of such an isothermal concentration swing process based on a simplified, analytical model of a 2-step PSA (pressure swing adsorption) process. The analytical model allows a definition of the range of operating conditions that lead to the best compromise between energy consumption and productivity (size and number of the adsorbers). Moreover, it is possible to define the equilibrium and mass transfer properties of the ideal solid sorbent. The feasibility of the concentration swing process was finally validated by numerical simulations of a full PSA cycle under adiabatic conditions. [ABSTRACT FROM AUTHOR]

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 mechanism of N2O decomposition was studied on a series of Fe-ZSM-5 catalysts prepared by ion exchange (IE) and chemical vapor deposition (CVD). N2O decomposition activity depends strongly on the extent of autoreduction of the catalyst during the pretreatment in He at high temperatures. The extent of autoreduction is significantly lower for catalysts prepared by CVD compared with that for catalysts prepared by aqueous ion exchange. As a result, the global turnover frequencies of the ion-exchanged catalysts are significantly higher. If the activity is normalized by the concentration of Fe2+ sites, however, then the CVD catalyst is the most active sample. This is attributed to the fact that high iron loading favors the surface migration and recombination of surface oxygen atoms to O2, which is the rate-limiting step of the reaction. O2 formation by slow recombination of two surface oxygen atoms is the dominating mechanism even for IE samples with very low iron loadings. [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: Fe-FER is an active catalyst for the abatement of N2O in the tail gas of nitric acid plants. The activity of Fe-FER can be increased if Ru is added as a second active component. This is a surprising finding, because noble metals are usually strongly inhibited by NO, which is always present in tail gas. Yet the bimetallic FeRu-FER catalyst is more active than the sum of the components, Fe-FER and Ru-FER. A synergy between Fe and Ru can explain this phenomenon. This work discusses the role of Fe and Ru in the reaction mechanism as well as the interplay of these two components. In situ IR measurements show that the preferential adsorption of NO and its reaction products on Fe in the bimetallic catalyst reduces the inhibiting effect of NO on the Ru component; this effect largely contributes to the synergy between Fe and Ru. Moreover, in situ X-ray absorption data are presented, which allow for tracing the average oxidation state of the two active components Fe and Ru under reaction conditions. [Copyright &y& Elsevier]

Abstract: NO-assisted N2O decomposition over four different Fe-ZSM-5 samples prepared by wet ion exchange (WIE) or chemical vapor deposition (CVD) of FeCl3 was investigated by steady-state kinetics, in situ infrared (IR) spectroscopy, and transient response methods. Despite their lower iron loading, the samples prepared by WIE had the highest activity for N2O decomposition in the presence of NO. The in situ IR experiments showed that the most active sample was characterized by a high concentration of adsorbed NO, as well as adsorbed NO2 under reaction conditions. Step response experiments proved that NO2 is an intermediate of the catalytic cycle and functions as intermediate oxygen storage. IR and transient kinetic experiments showed that WIE catalysts behave qualitatively different in NO-assisted N2O decomposition than CVD catalysts. These differences are discussed in terms of the different structure of the iron species in the two types of samples. [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]

The effect of pretreatment conditions on the N2O-decomposition activity of Fe-ZSM-5 prepared by chemical vapor deposition (CVD) was studied by steady-state kinetics and step-response experiments. Pretreatment at 873 K in H2 or He significantly increased the N2O-decomposition activity of Fe-ZSM-5 CVD. In addition to the increased steady-state activity, the catalyst exhibited a very high initial activity in the step-response experiments, which slowly decayed to steady state. This “transient” activity was particularly high after pretreatment of the samples in He, whereas it vanished completely after pretreatment in O2 or exposure to water vapor. This led to the conclusion that the transient activity is related to strongly dehydroxylated Fe2+ sites created by autoreduction at high temperatures. On the basis of isotope-labeling data a mechanism for N2O decomposition is proposed. The first step is the reaction of Fe2+ with N2O to give a Fe3+O- species, which quickly transforms into a Fe2+–peroxo complex. Desorption of O2 occurs upon reaction of the complex with another N2O molecule (mainly during the transient) or via the recombination of two peroxo species after their migration over the iron oxide cluster (mainly during steady state). [Copyright &y& Elsevier]

Iron-containing zeolites were prepared by aqueous ion exchange, sublimation of FeCl3, or hydrothermal synthesis and were modified by steaming at 873 K. The samples contained different kinds of iron species ranging from isolated iron atoms to small clusters that contain a few atoms and somewhat larger oligomers. Yet, the dynamic behavior of all samples in N2O decomposition was qualitatively similar. Pulse experiments showed that a slow and fast pathway of O2 formation, which is the rate-limiting step of the reaction, exists. Both contributed to the overall activity. The fast pathway dominated on isolated iron sites, whereas the contribution of the slow pathway increased on catalysts with high iron loadings. Steaming led to an agglomeration of the iron clusters and increased the activity (with one exception). The steamed samples had a peculiar time-on-stream behavior. They exhibited a very high initial activity and then slowly decayed to steady state. This indicates that steaming did not merely agglomerate the iron clusters, but qualitatively changed the nature of the active sites. [Copyright &y& Elsevier]

The nitration of toluene and 2-nitrotoluene was investigated using different batches of zeolite BEA. In the nitration of toluene, notable differences in the product composition were obtained depending on the batch of BEA used. In the nitration of 2-nitrotoluene, all the catalysts displayed a good selectivity, but different conversions. Steaming improved the performance of the catalysts, but strong dealumination with oxalic acid had a negative effect. The positive effect of steaming was attributed to the enhanced transport of the reaction products out of the pores. Lewis acidity did not seem to play a role in the nitration reaction. A high concentration of Brønsted sites was detrimental, because it slowed down the diffusion of the products, but a small concentration of Brønsted sites was required to catalyze the heterogeneous reaction. [Copyright &y& Elsevier]

The mechanism of N2O decomposition over an 18O-labeled Fe-ZSM-5 catalyst was studied. The isotope distribution of the O2 produced during N2O decomposition was statistical. This shows that O2 was formed from a pool of equilibrated surface oxygen atoms. The size of the pool was 1.0 O/Fe, i.e. most or all of the iron clusters took part in the reaction. The reactivity of the oxygen atoms in the pool was low. They did not exchange with 18O2 to a significant extent. [ABSTRACT FROM AUTHOR]

The reaction of Fe-zeolites prepared by sublimation of FeCl3 with N2O was studied by step- and pulse-response experiments. Steps from 0 to 5000 ppm N2O were performed at 673 K, after pretreatment of the catalyst in H2, He, or O2. When the catalysts were prereduced in H2, N2O was first consumed for the reoxidation of the catalyst, before steady-state N2O decomposition started. Also pretreatment in He reduced the catalyst. This autoreduction was not spontaneous, but caused by a small amount of hydrocarbons adsorbed on the catalyst. Prereduced catalysts had a higher steady-state activity, indicating that the incorporation of oxygen from N2O changed the structure of the active sites. Pulse responses proved that O2 desorption is the rate-limiting step of N2O decomposition. O2 desorption was relatively fast from a small fraction of sites, while a second oxygen pool desorbed only slowly from the catalyst. Only the former is responsible for catalytic activity. [Copyright &y& Elsevier]

The nitration of toluene and 2-nitrotoluene with acetyl nitrate was investigated using several solid acid catalysts. In the nitration of toluene, enhanced para-selectivity was observed only with zeolite BEA. For the nitration of 2-nitrotoluene, all the catalysts displayed good para-selectivity, but only BEA led to high yields. The superior performance of BEA was due to the fact that only with this zeolite did the heterogeneously catalyzed reaction compete successfully with the homogeneous nitration in the liquid phase. Geometrical considerations showed that the high para-selectivity of BEA was not caused by classical transition-state selectivity but was induced by the reaction of the arene with a surface-bound acetyl nitrate complex. The existence of this complex was supported by NMR measurements, which showed that its formation is a specific property of zeolite BEA. [Copyright &y& Elsevier]

Keywords: phenanthrene; hydroisomerization; hydrocracking; adamantanes; polycyclic naphthenes; bifunctional catalysis; ultrastable Y zeolite EN phenanthrene hydroisomerization hydrocracking adamantanes polycyclic naphthenes bifunctional catalysis ultrastable Y zeolite 3332 3332 1 07/08/20 20200706 NES 200706 B The Front Cover b shows some of the reaction intermediates involved in the conversion of a tricyclic naphtene, perhydrophenanthrene, over a bifunctional Pt/faujasite (USY) catalyst. In their Full Paper, L. Brito et al. analyze the reaction pathways, which first lead to isomerization products, then to ring-opening and finally to cracking products. Phenanthrene, hydroisomerization, hydrocracking, adamantanes, polycyclic naphthenes, bifunctional catalysis, ultrastable Y zeolite. [Extracted from the article]

Hydroisomerization and hydrocracking of octylcyclohexane (C14H28) were performed over Pt and NiMoS‐supported catalysts, at 300 °C and 60 bar, with a molar H2 to hydrocarbon ratio of 7 mol/mol. The feed, composed of 5 wt.% phenyloctane dissolved in n‐heptane, was initially hydrogenated in situ over a pre‐catalyst, Pt or NiMoS/Al2O3. The C14 naphthene underwent isomerization and cracking under high hydrogen pressure over the bifunctional catalysts, whose acid function was represented by large‐pore zeolities (USY, Beta) or amorphous silica‐alumina (SA). For the Pt‐catalysts, Beta was slightly more active than USY. Both zeolites produced a similar product pattern. Sulfide catalysts were less well equilibrated than Pt ones and hence less active. They led to some over‐cracking, but the cracking selectivity of our naphthene reactant was much less sensitive to the metal‐acid balance than the cracking selectivity of n‐alkanes. The comparison of reactivity of octylcyclohexane with n‐hexadecane and perhydrophenanthrene is also discussed. [ABSTRACT FROM AUTHOR]

In silico screening of CO2 adsorbents is a very powerful method for preselecting the most promising porous solids for experimental studies. Because of increased computational power, it is now possible to investigate a large number of adsorbents in a fairly short time. However, it remains difficult to rationalize structure-performance correlations because the complexity of such porous materials cannot be reduced to a few simple descriptors. In this paper, we present a different approach that was applied to the design of an optimal adsorbent for CO2 separation from gas mixtures. A CO2-CH4 mixture was used as the feed. We constructed a simplified model of the porous material by adopting a spherical pore geometry. From the dispersion-repulsion point of view, the spherical pore was modeled by homogeneously distributed Lennard-Jones sites. Besides, a charge distribution was introduced to mimic the electrostatic behavior. The selected charge distribution is constituted of negative charges homogeneously distributed over the surface of the pore. The total negative charge is counterbalanced by eight positive discrete charges placed on the corners of the cube inscribed in the sphere. This model can be characterized by two main descriptors: the pore size and the cation charge. For this model, the adsorbate-adsorbent interaction potential due to electrostatic and dispersion-repulsion interactions was determined. Then, the Henry constants of CO2 and CH4 are calculated from statistical thermodynamics and substituted in the Ruthven statistical model, which allows calculation of the binary adsorption isotherms. Finally, the adsorbed quantities are used to estimate the performance indexes of the pressure swing adsorption (PSA) process, such as the working capacity and separation factor. We show how these two parameters depend on the pore size and cation charge. For a medium-pressure PSA process, the optimal adsorbent has a large pore volume and is highly charged, which provides high working capacity and selectivity. The high cationic charge allows one to efficiently fill the large pore volume and assures high CO2 selectivity. [ABSTRACT FROM AUTHOR]

Environmental regulations concerning fuel‐related sulfur emissions are currently experiencing worldwide expansion. This is motivating the research and development of improved hydrotreating (HDT) catalysts with carefully engineered synthesis methods that maximize activity as ultimate goal. In this contribution, the effect of phosphorus doping and triethylene glycol (TEG) incorporation on the genesis of the CoMoS phase of model HDT catalysts is assessed. Following a surface‐science approach, α‐Al2O3 single crystals with four orientations: C(0001), A(112‾ 0), M(101‾ 0), and R(11‾ 02) are used as model supports of the traditional γ‐Al2O3 support for the study of active phase‐support interactions at the molecular scale. The model catalysts are prepared by traditional impregnation of a solution containing metal and phosphorus precursors and TEG. The catalysts are characterized in the sulfide phase by XPS, XAS, TEM, and AFM, revealing that the calcination step is key in the emergence of distinctive metal‐support interactions, which are directly related to the nature of alumina surface sorption sites. In addition, TEG incorporation on dried catalysts increases metal sulfidation and enhances promotion with respect to non‐additivated systems, especially at mild sulfidation temperatures. The catalytic activity of the model catalysts is tested in a thiophene hydrodesulfurization reaction, revealing the following activity trend with respect to alumina surface orientations: A112‾0 ≫ M101‾0 >R11‾02 , C(0001). This trend is identical to the one observed for non‐phosphorus doped non‐TEG additivated model systems, confirming the predominance of surface effects on the catalytic activity over those exerted by P and TEG. By transposing these results to the industrial γ‐Al2O3 support, the (100) facet would provide surface sites that lead to better performing catalysts. This could result in the development of novel supports, engineered to expose surface sites that maximize hydrotreating activity. [ABSTRACT FROM AUTHOR]

Thechoice of an appropriate adsorbent for CO2separationby pressure-swing adsorption remains a field of intense research.In this work, several FAU and LTA zeolites with different Na contents(Si/Al ratios) are studied for the separation of CO2frommixtures of CO2, CO, and CH4by means of breakthroughexperiments. The breakthrough experiments were carried out between1 and 5 bar at 303 K using two feed mixtures: 50/50 (v/v) CO2/CH4and 75/15/15 (v/v/v) CO2/CH4/CO. The most polar zeolites, i.e., those with high Na content, exhibitthe highest adsorption capacity and selectivity for CO2, but their regeneration is difficult; hence, their working capacityis low. The opposite is true for the least polar zeolites, i.e., thosewith low Na content. In order to quantify the trade-off between theselectivity and working capacity, the Ruthven statistical model (RSM)was used. It satisfactorily reproduced the experimental trends. We,therefore, used the RSM to identify the properties of the adsorbentthat lead to an optimal compromise between the working capacity andseparation factor. The critical parameter is the concentration ofextraframework cations, which, in turn, depends on the framework chargeof the zeolites FAU and LTA. The optimal trade-off zone is definedin terms of the Henry constant of CO2(KCO2). It is found that this zone is placedbetween KCO2= 5 × 10–3and 50 × 10–3molecules·bar–1·Å–3. This interval correspondsto a heat of adsorption of CO2at zero coverage between27 and 32 kJ·mol–1. In our study, this optimalrange of Henry constants was achieved for the zeolites Na-USY, SAPO-37,LTA (Si/Al = 5), and EMC-1. [ABSTRACT FROM AUTHOR]

• 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]

[Display omitted] • Co promotion do not alter metal-support interactions compared to non-promoted systems. • Co promotion is not surface-dependent but contingent to the formation of MoS 2. • Highest catalytic activity for metal-support interactions of intermediate strength. The current environmental and industrial contexts require constant revision and improvement of hydrotreating processes for obtaining cleaner (bio)fuels through the development of supported transition metal sulfide (TMS) catalysts. The present work proposes a surface-science approach to describe the surface-dependent genesis of the cobalt-promoted active phase (CoMoS) supported on α-Al 2 O 3 single crystals used as surrogates of the industrial γ-Al 2 O 3 support. Co-Mo precursor solutions are deposited by aqueous-phase impregnation onto four α-Al 2 O 3 single crystals of C(0001), A (11 2 ¯ 0) , M (10 1 ¯ 0) , and R (1 1 ¯ 02) orientations, which display specific OH sorption sites. The model catalysts are characterized in the oxide and sulfide states by XPS, AFM, and TEM revealing a surface dependent sulfidation and dispersion as a result of metal-support interactions of diverse nature. The surfaces can be ranked following metal-support interactions of increasing strength C(0001) < A (11 2 ¯ 0) , M (10 1 ¯ 0) < R (1 1 ¯ 02) in good agreement with model non-promoted catalysts. However, AFM and TEM imaging also reveal that cobalt incorporation leads to an increase in the stacking of CoMoS particles with respect to non-promoted catalysts. The activity of the model catalysts in thiophene hydrodesulfurization cannot be simply related to the common features of the active phase (sulfidation, dispersion, promotion extent) but a volcano-shape curve is obtained when plotting the activity as a function of metal-support interactions. These results suggest that high activity is obtained on surfaces with intermediate metal-support interactions that lead to an optimal metal-sulfur bond energy in agreement with the Sabatier principle. Transposing these results to the traditional γ-Al 2 O 3 support suggests an enhanced activity of the (1 0 0) facet, which can lead to the development of improved supports for hydrotreating catalysts. [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]

The constant improvement of hydrotreating (HDT) catalysts, driven by industrial and environmental needs, requires a better understanding of the interactions between the oxide support (mostly alumina) and the MoS 2 active phase. Hence, this work addresses the support-dependent genesis of MoS 2 on four planar single-crystal α-Al 2 O 3 surfaces with different crystal orientations (C (0 0 0 1), R ( 1 1 ¯ 0 2 ) , M ( 1 0 1 ¯ 0 ) , and A ( 1 1 2 ¯ 0 ) ). In contrast to classical surface science techniques, which often rely on UHV-type deposition methods, Mo is introduced by impregnation from an aqueous solution in order to mimic standard incipient wetness impregnation. Comparison between different preparation routes, impregnation vs. equilibrium adsorption (selective adsorption), is also considered. Atomic force microscopy, X-ray absorption spectroscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy show that the α-Al 2 O 3 orientation has a clear impact on the strength of metal–support interactions in the oxide state with consequences for the sulfidation, size, stacking, and orientation of MoS 2 slabs. Aggregation of molybdenum oxide particles is observed on the C (0 0 0 1) plane, suggesting weak metal–support interactions leading to a high sulfidation degree with large slabs. Conversely, the presence of well-dispersed individual oxide particles on the R ( 1 1 ¯ 0 2 ) plane implies stronger metal–support interactions, leading to a low sulfidation degree and shorter MoS 2 slabs. Both A ( 1 1 2 ¯ 0 ) and M ( 1 0 1 ¯ 0 ) facets, of similar crystallographic structure, display intermediate behavior in terms of sulfidation rate and MoS 2 size, in line with intermediate metal–support interactions. Polarization-dependent grazing-incidence-EXAFS experiments, as well as high-angle annular dark-field (HAADF) scanning transmission electron microscopy analysis, allow us to demonstrate a surface-dependent orientation of MoS 2 slabs. Predominant basal bonding is suggested on the C (0 0 0 1) plane, in agreement with the existence of weak metal–support interactions. Conversely, a random orientation (edge and basal bonding) is observed for the other planes. Generalization of these conclusions to industrial catalysts is proposed, based on comparison of the surface structure of the various model α-Al 2 O 3 orientations used in this work and the predominantly exposed γ-Al 2 O 3 surfaces ((1 1 0), (1 0 0), and (1 1 1)). [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]

The role of the oxide support on the structure of the MoS2 active phase (size, morphology, orientation, sulfidation ratio, etc.) remains an open question in hydrotreating catalysis and biomass processing with important industrial implications for the design of improved catalytic formulations. The present work builds on an aqueous-phase surface-science approach using four well-defined a-alumina single crystal surfaces (C (0001), A (1120), M (lOlO), and R (1102) planes) as surrogates for y-alumina (the industrial support) in order to discriminate the specific role of individual support facets. The reactivity of the various surface orientations toward molybdenum adsorption is controlled by the speciation of surface hydroxyls that determines the surface charge at the oxide/water interface. The C (0001) plane is inert, and the R (1102 ) plane has a limited Mo adsorption capacity while the A (1120) and M (1010) surfaces are highly reactive. Sulfidation of model catalysts reveals the highest sulfidation degree for the A (1120) and M (1010) planes suggesting weak metal/support interactions. Conversely, a low sulfidation rate and shorter MoS2 slabs are found for the R (1102) plane implying stronger Mo-O-Al bonds. These limiting cases are reminiscent of type I/type II MoS2 nanostructures. Structural analogies between α-and γ-alumina surfaces allow us to bridge the material gap with real Al203-supported catalysts. Hence, it can be proposed that Mo distribution and sulfidation rate are heterogeneous and surfacedependent on industrial γ-Al203-supported high-surface-area catalysts. These results demonstrate that a proper control of the γ-alumina morphology is a strategic lever for a molecular-scale design of hydrotreating catalysts. [ABSTRACT FROM AUTHOR]

New developments and breakthroughs in the design of hydrotreating (HDT) catalysts for complying with fuel specifications and reduced sulfur contents ask for a continuous improvement in the molecular scale description of the active phase both at the oxide and sulfide states. HDT catalysts are mainly based on alumina-supported molybdenum nanophases and the present contribution is dedicated to review the surface science approaches that have helped gain a molecular-scale insight into the structure of the active-phase (mainly molybdenum) and the role of metal-support (mainly alumina) interactions through the use of well-defined surfaces and surface sensitive analysis techniques. The main focus of this Review is placed on model systems that can bridge the gap with industrial catalysts, that is, oxide-supported active phases prepared in aqueous conditions, as opposed to more traditional surface-science studies that consider metal-supported nanophases prepared in UHV conditions. The synthesis and structure of well-defined alumina surfaces (thin films and single crystal wafers) is first presented before discussing aqueous-deposition of Mo precursors on flat surfaces. The detailed role of the oxide support is then addressed with an emphasis on the genesis and structure of the MoS2 phase namely sulfidation rate, stacking, and orientation. [ABSTRACT FROM AUTHOR]

We propose a method for analyticallypredicting single-componentadsorption isotherms from molecular, microscopic and structural descriptorsof the adsorbate–adsorbent system and concepts of statisticalthermodynamics. Expressions for Henry’s constant and the heatof adsorption at zero coverage are derived. These functions dependon the pore size, pore shape, chemical composition, and density ofthe adsorbent material. They quantify the strength of the solid–fluidinteraction, which governs the low-pressure part of the adsorptionisotherm. For intermediate and high pressures, the fluid–fluidinteractions must also betaken into account. Both solid–fluid and fluid–fluidinteractions are combined within the framework of the Ruthven statisticalmodel (RSM). The RSM thus constructs theoretical adsorption isothermsthat are entirely based on microscopic molecular and structural descriptors.The theoretical results that we obtained are compared with experimentaldata for the adsorption of pure CO2and CH4onall-silica zeolites. The developed methodology allows for the estimationof the optimum properties of a nonpolar adsorbent for the adsorptionof CO2in cyclic adsorption processes. [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]

The objective of this work was to study the adsorption and separation of the most important families of hydrocarbon compounds on metal-organic frameworks (MOFs), in comparison with zeolites. For this purpose, we have selected four probe molecules, each of them representing one of these families, i.e., o- and p-xylene as aromatics, 1-octene as an alkene, and n-octane as an alkane. The separation of these four molecules was studied by binary breakthrough experiments. To represent the large diversity of MOF structures, the experiments were carried out with (i) two MOFs with coordinatively unsaturated metal sites (CUS), i.e., Cu-btc (HKUST-1) and CPO-27-Ni, (ii) a MOF with an anionic framework and extraframework cations, i.e. RHO-ZMOF, and (iii) two rather apolar zeolitic imidazolate framework (ZIF) materials with different pore sizes, i.e. ZIF-8 and ZIF-76. Zeolite NaY and zeolite β were used as polar and apolar reference adsorbents, respectively. The results can be briefly summarized as follows: ZIFs (not carrying any polar functional groups) behave like apolar adsorbents and exhibit very interesting and unexpected molecular sieving properties. CUS-MOFs behave like polar adsorbents but show the specificity of preferring alkenes over aromatics. This feature is rationalized thanks to DFT+D calculations. MOFs with extraframework cations behave like polar (cationic) zeolites. [ABSTRACT FROM AUTHOR]

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 separation of paraffin isomers is a very importanttopic inthe petrochemical industry. Zeolite 5A is industrially used to sievealkane isomers, but its pore size does not allow the separation ofmonobranched and dibranched alkanes by a kinetic mechanism. In thispublication, we compare three ZIF materials in the separation of C6-paraffinisomers: ZIF-8, ZIF-76, and a new material called IM-22. The performanceof the materials is evaluated by a breakthrough curve of binary mixturesof n-hexane, 3-methylpentane, and 2,2-dimethylbutane.We show that ZIF-8 is a very attractive alternative to zeolite 5Abecause it exhibits a high (kinetic) selectivity for the adsorptionof linear alkanes and at the same time a high adsorption capacity.The new material IM-22, a ZIF with CHAtopology, seemsto be particularly suited for the separation of mono- and dibranchedparaffin isomers. [ABSTRACT FROM AUTHOR]

The present study attempts to understand the use of the flexible porous chromium terephthalate Cr(OH)(O2C--C6H4--CO2) denoted MIL-53(Cr) (MIL = Material from Institut Lavoisier) for the separation of mixtures of CO2 and CH4 at ambient temperature. The coadsorption of CO2 and CH4 was studied by a variety of different techniques. In situ synchrotron X-ray Powder Diffraction allowed study of the breathing of the solid upon adsorption of the gas mixtures and simultaneously measured Raman spectra yielded an estimation of the adsorbed quantities of CO2 and CH4, as well as a quantification of the fraction of the narrow pore (NP) and the large pore (LP) form of MIL-53. Quantitative coadsorption data were then measured by gravimetry and by breakthrough curves. In addition, computer simulation was performed to calculate the composition of the adsorbed phase in comparison with experimental equilibrium isotherms and breakthrough results. The body of results shows that the coadsorption of CO2 and CH4 leads to a similar breathing of MIL-53(Cr) as with pure CO2. The breathing is mainly controlled by the partial pressure of CO2, but increasing the CH4 content progressively decreases the transformation of LP to NP. CH4 seems to be excluded from the NP form, which is filled exclusively by CO2 molecules. The consequences in terms of CO2/CH4 selectivity and the possible use of MIL-53(Cr) in a PSA process are discussed. [ABSTRACT FROM AUTHOR]

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]

Review: 158 refs. [ABSTRACT FROM AUTHOR]