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High-silica zeolites, some of the most important and widely used catalysts in industry, have potential for application across a wide range of traditional and emerging technologies. The many structural topologies of zeolites have a variety of potential uses, so a strong drive to create new zeolites exists. Here, we present a protocol, the assembly-disassembly-organization-reassembly (ADOR) process, for a relatively new method of preparing these important solids. It allows the synthesis of new high-silica zeolites (Si/Al >1,000), whose synthesis is considered infeasible with traditional (solvothermal) methods, offering new topologies that may find novel applications. We show how to identify the optimal conditions (e.g., duration of reaction, temperature, acidity) for ADOR, which is a complex process with different possible outcomes. Following the protocol will allow researchers to identify the different products that are possible from a reaction without recourse to repetitive and time-consuming trial and error. In developing the protocol, germanium-containing UTL zeolites were subjected to hydrolysis conditions using both water and hydrochloric acid as media, which provides an understanding of the effects of temperature and pH on the disassembly (D) and organization (O) steps of the process that define the potential products. Samples were taken from the ongoing reaction periodically over a minimum of 8 h, and each sample was analyzed using powder X-ray diffraction to yield a time course for the reaction at each set of conditions; selected samples were analyzed using transmission electron microscopy and solid-state NMR spectroscopy.

Zeolites are an important class of materials that have wide ranging applications such as heterogeneous catalysts and adsorbents which are dependent on their framework topology. For new applications or improvements to existing ones, new zeolites with novel pore systems are desirable. We demonstrate a method for the synthesis of novel zeolites using the ADOR route. ADOR is an acronym for Assembly, Disassembly, Organization and Reassembly. This synthetic route takes advantage of the assembly of a relatively poorly stable that which can be selectively disassembled into a layered material. The resulting layered intermediate can then be organized in different manners by careful chemical manipulation and then reassembled into zeolites with new topologies. By carefully controlling the organization step of the synthetic pathway, new zeolites with never before seen topologies are capable of being synthesized. The structures of these new zeolites are confirmed using powder X-ray diffraction and further characterized by nitrogen adsorption and scanning electron microscopy. This new synthetic pathway for zeolites demonstrates its capability to produce novel frameworks that have never been prepared by traditional zeolite synthesis techniques.

The high activity and selectivity of zeolites in the cyclisation of unsaturated alcohols is reported for the first time; the details of a reaction mechanism based on quantum chemical calculations are also provided. The high efficiency of zeolites MFI, BEA and FAU in the cyclisation of unsaturated alcohols (cis-decen-1-ol, 6-methylhept-5-en-2-ol and 2-allylphenol) to afford oxygen-containing heterocyclic rings is demonstrated. The best catalytic performance is found for zeolites with the optimum concentration of Brønsted acid sites (ca. 0.2 mmol g(-1)) and the minimum number of Lewis acid sites. It is proposed that the efficiency of the catalysts is reduced by the existence of the so-called dual site, at which a molecule of unsaturated alcohol can simultaneously interact with two acid sites (an OH group with one and the double bond with the other Brønsted site), which increases the interaction strength. The formation of such adsorption complexes leads to a decrease in the catalyst activity because of (i) an increase in the reaction barrier, (ii) an unfavourable conformation and (iii) diffusion limitations. A new procedure for the preparation of tetrahydrofurans and pyrans over zeolite catalysts provides important oxygen-containing heterocycles with numerous applications., (Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The catalytic performance of a set of metal-organic frameworks [CuBTC, FeBTC, MIL-100(Fe), MIL-100(Cr), ZIF-8, MIL-53(Al)] was investigated in the Prins condensation of β-pinene with formaldehyde and compared with the catalytic behavior of conventional aluminosilicate zeolites BEA and FAU and titanosilicate zeolite MFI (TS-1). The activity of the investigated metal-organic frameworks (MOFs) increased with the increasing concentration of accessible Lewis acid sites in the order ZIF-8

Zeolites are often investigated as potential adsorbents for CO(2) adsorption and separation. Depending on the zeolite topology and composition (Si/Al ratio and extra-framework cations), the CO(2) adsorption heats at low coverages vary from -20 to -60 kJ mol(-1), and with increasing surface coverage adsorption heats either stay approximately constant or they quickly drop down. Experimental adsorption heats obtained for purely siliceous porous solids and for ion-exchanged zeolites of the structural type MFI, FER, FAU, LTA, TUN, IMF, and -SVR are discussed in light of results of periodic density functional theory calculations corrected for the description of dispersion interactions. Key factors influencing the stability of CO(2) adsorption complexes are identified and discussed at the molecular level. A general model for CO(2) adsorption in zeolites and related materials is proposed and data reported in literature are evaluated with regard to the proposed model., (Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Cyclohexylphenols are valuable intermediate chemicals applied in the manufacture of dyes, resins, and pharmaceutical drugs. However, they are synthesized using raw chemicals derived from fossil fuels rather than sustainable sources (e.g., lignin-derived phenol). In this article, we report a one-pot synthesis of cyclohexylphenols via phenol-assisted conversion with isopropyl alcohol over the tandem catalytic system formed by RANEY® Nickel plus hierarchical Beta zeolite. Over this tandem catalytic system, cyclohexylphenols were synthesized with remarkable selectivity (∼70%) at high conversion rates (64%) after 1 h of reaction at 150° C. In contrast, higher temperatures (175 °C) were required to obtain alkylphenols over the Al-SBA-15 catalyst, which is highly accessible thanks to its uniform mesoporous structure, albeit with weaker Lewis acid sites. Additionally, selectivity to cyclohexylphenols over Al-SBA-15 was far lower (19%) than over hierarchical Beta zeolite, and cresols were instead the most abundant alkylphenol (26%). Therefore, the combination of suitable accessibility and Brønsted acidity of hierarchical Beta with the hydrogenating ability of RANEY® Ni through catalytic hydrogen transfer from isopropyl alcohol drives the selectivity of this tandem system towards the production of cyclohexylphenols. [ABSTRACT FROM AUTHOR]

Research activities and recent developments in the area of three-dimensional zeolites and their two-dimensional analogues are reviewed. Zeolites are the most important industrial heterogeneous catalysts with numerous applications. However, they suffer from limited pore sizes not allowing penetration of sterically demanding molecules to their channel systems and to active sites. We briefly highlight here the synthesis, properties and catalytic potential of three-dimensional zeolites followed by a discussion of hierarchical zeolites combining micro- and mesoporosity. The final part is devoted to two-dimensional analogues developed recently. Novel bottom-up and top-down synthetic approaches for two-dimensional zeolites, their properties, and catalytic performances are thoroughly discussed in this review. [ABSTRACT FROM AUTHOR]

The inter-layer interactions and the possible arrangements of MWW-type layers were investigated computationally at the non-local density functional theory level. Powder XRD patterns were simulated for structures obtained computationally and compared with experimental data. The MCM-22P material corresponds to the layers bound with relatively strong hydrogen bonds between surface silanol groups that is an energetically preferred structure in the presence of a structure directing agent (hexamethyleneimine). The powder XRD pattern of MCM-56 is best matched for relatively disordered (in the ab plane) MWW layers that are partially condensed. The appearance of the powder XRD pattern in the 2 range of 7.5-10° depends on the extent of interlayer condensation. The combination of density functional investigation of interactions between MWW layers together with simulation of powder XRD patterns brings atomistic insight into the inter-layer arrangement and better understanding of the effects responsible for the differences between various layered materials of the MWW family. [ABSTRACT FROM AUTHOR]

Modification of HMCM-22 zeolite by alkaline treatment was investigated by various characterization techniques and in toluene disproportionation and alkylation with isopropyl alcohol. This ‘desilication’ process led for mild alkaline concentrations (~0.10–0.20 M NaOH at 323 K for 45 min) to the partial destruction of the zeolite framework, but also to the formation of additional mesoporosity. Furthermore, the accessibility/availability of Lewis acid sites, investigated by d3-acetonitrile and pyridine adsorption using FTIR spectroscopy, increased for these mild alkaline treatments, while the Brønsted acidity decreased. Higher alkaline concentrations (up to 0.50 M NaOH) led to a too severe framework and pore destruction and a decrease of both the Lewis and Brønsted acid site concentration. Decomposition and deconvolution of 29Si MAS-NMR spectra confirmed the Si extraction and partial framework destruction, since more Q3 SiOH groups were formed at the expense of the Q4 T-atoms in the framework. Furthermore, the T6 and T7 Si-atoms were preferentially extracted, which would indicate that an interconnection between the intralayer and the interlayer and/or outer surface is formed. The toluene conversion in its disproportionation reaction increased for the mildly treated sample, while the selectivity to xylene isomers (and cymene and n-propyltoluene isomers in the alkylation reaction with isopropyl alcohol) was similar to the thermodynamic equilibrium, suggesting that the reaction primarily occurs at outer surface cups of the HMCM-22 zeolite. [ABSTRACT FROM AUTHOR]

Liquid phase Friedel-Crafts acylation of cyclohexene and 1-methylcyclohexene was investigated over zeolites and mesoporous molecular sieves. The effect of the structure and concentration and type of active sites on the conversion and selectivity of cyclohexene and 1-methylcyclohexene was investigated. In addition, the effect of the chain length of acylating agent was studied. Catalytic experiments were carried out at temperature 80 °C and at atmospheric pressure. The highest conversion was reached over zeolite Beta with Si/Al ratio 37.5 (cyclohexene conversion 78.7%, 1-methylcyclohexene conversion 54.1%). It was found that with increasing chain length of the acylating agent cyclohexene as well as 1-methylcyclohexene conversions decrease. No direct relationship between the conversion of cyclohexene or 1-methylcyclohexene and the concentration of Lewis acid sites was found. [ABSTRACT FROM AUTHOR]

SSZ-33 based-catalyst, after modification with Mo and alumina binder, was evaluated in long-run tests in the toluene disproportionation in the presence of hydrogen as a carrier gas. The activity and selectivity of this catalyst were compared with those of ZSM-5 and mesoporous ZSM-5 prepared with the same concentration of Mo and alumina. Formation of the final catalysts decreased the void volume of micropores in order SSZ-33 > ZSM-5 > ZSM-5/Meso. Simultaneously, the concentration of Lewis acid sites increased due to the addition of alumina to the catalyst. The highest toluene conversion was achieved with SSZ-33 catalyst comprising 12-12-10-ring channels, which is the result of high acidity of this zeolite together with increased mass transport through large pores. ZSM-5 zeolite exhibited lower toluene conversion while only a low activity was found for mesoporous ZSM-5 probably due to the limitations of the access to the zeolite channels after modification with alumina. [ABSTRACT FROM AUTHOR]

Cyclohexylphenol (CHP) is a high added-value chemical, extensively used for the preparation of dyes, resins and biocides. This molecule is currently synthetized by phenol alkylation with cyclohexene/cyclohexanol using highly polluting mineral Brønsted acids as catalysts. The present contribution reports the one-pot production of cyclohexylphenol via hydroalkylation, using phenol as the only organic reactant, over a number of bifunctional catalysts consisting of Co 2 P (5 wt% Co) supported over different zeolites (ferrierite, mordenite, beta and MCM-22). Phenol conversion increased in the order: Co 2 P/Mordenite (30%) < Co 2 P/Ferrierite (65%) < Co 2 P/Beta (77%) < Co 2 P/MCM-22 (90%), which reflects enhancing dispersion of cobalt phosphide phase and accessibility of acid centres with evolving external surface in nanocrystalline zeolite supports. On the other hand, remarkable differences were observed between the catalysts in terms of CHP formation. The highest values of CHP yield and selectivity (Y CHP =43% and S CHP =56%) were attained over the Co 2 P/Beta catalyst, due to the combination of three-dimensional microporosity, large external surface area (as a consequence of its nanocrystalline nature) and highly dispersed Co 2 P nanoparticles. In addition, it is envisaged that the formation of CoAlPO phases might favour a balanced performance of metal and acid sites for the CHP production. [Display omitted] • Co 2 P/zeolites were applied as catalysts for phenol hydroalkylation. • Mordenite, ferrierite, beta and MCM-22 were used as supports. • Phenol conversion favoured over materials with high accessibility and small Co 2 P particles. • Cyclohexylphenol production required an adequate balance of metal and acid sites. • Highest selectivity and yield to cyclohexylphenol were achieved over Co 2 P/Beta. [ABSTRACT FROM AUTHOR]

Micro/mesoporous composite material is prepared via reaction of zeolite Beta seeds solution and mesoporous precursor solution under hydrothermal conditions. The resulted micro/mesoporous composite contains nanoparticles with a mean radius of about 90 nm, while pure zeolite Beta and MCM-41 have particles with size of about 50 and 230 nm, respectively. The presence of highly cross-linked silicon framework walls and tetrahedrally coordinated aluminum in the framework structure are confirmed with solid-state 29Si and 27Al NMR investigations. Adsorption measurements show the presence of micropores, mesopores and high interparticle porosity due to the nanometer-sized particles in the micro/mesoporous composite. Various techniques such as dynamic light scattering, scanning electron microscopy, X-ray diffraction, FT-IR, NMR spectroscopy and nitrogen sorption measurements were carried out in order to investigate the properties of the prepared material. [Copyright &y& Elsevier]

• Vapor phase acylation of guaiacol with acetic acid over acidic zeolites. • MFI and BEA zeolites with different acidic and textural properties have been explored. • Microcrystalline zeolites activity was poor because of the steric/diffusion limitation. • Zeolites with larger external/mesopore surface are more active. • HMAPs production is favoured over MFI zeolites with a ratio of Lewis to Brønsted sites in the 0.45-0.7 range. Vapor phase acylation of guaiacol with acetic acid was explored over a series of micro, nanocrystalline, and hierarchical MFI and BEA zeolites with different acidic and textural properties using a continuous flow reactor. The main products formed over these zeolites were i) guaiacol acetate, which is produced via O-acylation; ii) Hydroxymethoxyacetophenones (HMAPs), which are of pharmaceutical interest and mainly formed by C-acylation of guaiacol and to lesser extent by Fries rearrangement of guaiacol acetate and iii) catechol, which derives from the demethylation/demethoxylation of guaiacol. Both microcrystalline zeolites activity was poor because of the steric/diffusion limitation. Nanocrystalline and hierarchical MFI zeolites with improved accessibility and optimised acid strength and Lewis/Brønsted acid sites ratio were the most suitable catalysts for the continuous production of HMAPs. Although the guaiacol conversion slightly declines along the time on stream, the HMAPs selectivity and yield are enhanced due to deactivation affecting in higher extent to secondary reactions. [ABSTRACT FROM AUTHOR]

• Amines and dipodal moieties favor organosilane-protozeolitic nanounits interactions. • Dipodal organosilanes produce non-completely crystalline ZSM-5 materials. • Organosilane combining phenyl and amine groups generate more uniform mesopores. • Uniform h-ZSM-5 properties lead to LDPE cracking in a narrow temperature range. Crystallization of hierarchical ZSM-5 zeolite has been performed under hydrothermal conditions from silanized protozeolitic units. The role of amine and phenyl groups present in the organosilanes, as well as the use of dipodal silanization agents, on the creation of mesoporosity in the zeolite samples has been investigated. The presence of amine groups and dipodal moieties in the organosilane increases their interactions with the protozeolitic nanounits in the gel, which results in hierarchical zeolites showing enhanced secondary porosity and a higher degree of modification of the textural properties. Nevertheless, dipodal organosilanes hinder strongly the aggregation of the nanounits, leading to non-completely crystalline materials. In contrast, the combination of phenyl and amine groups into a single organosilane has shown to be effective for the generation of more uniform mesopores. Thus, N -(2 -N- Benzylaminoethyl)-3-aminopropyltrimethoxysilane (Ph-2A) has been found as the best silanization agent, affording a hierarchical zeolite with a narrow mesopore size distribution and a high concentration of strong Brønsted acid sites. Moreover, during LDPE catalytic cracking in TGA tests, the latter material allowed the conversion of the polymer to occur in a narrow temperature range as a consequence of its more uniform acid and textural properties. Likewise, this sample exhibited a high activity in LDPE cracking at 340 °C using a laboratory scale reaction system to produce mainly gasoline-range hydrocarbons and light olefins. [ABSTRACT FROM AUTHOR]

Abstract: Adsorption isotherms of carbon dioxide on the Na-A zeolite were measured in the temperature range from 273 to 333K. Henry’s constants and isosteric adsorption heats calculated from the temperature dependence of CO2 isotherms were combined with results of the variable temperature IR spectroscopy to obtain a spectroscopic signature of adsorption complexes and corresponding thermodynamic characteristics. The adsorption of CO2 in Na-A zeolite was also investigated computationally, using a periodic density functional model improved for the proper description of dispersion interactions. Based on a good agreement between experimental and calculated adsorption heats and shifts of asymmetric CO2 stretching frequency due to adsorption the following model of CO2/Na-A system is proposed: (i) CO2 adsorption complexes formed at a low coverage involves interaction of CO2 with three Na+ cations in the LTA supercage; they are characterized by the IR band at 2349cm−1. (ii) CO2 adsorption complexes at higher coverages are formed between a pair of Na+ cations; they are characterized by the IR band centered at 2360cm−1. Almost half of the interaction energy between CO2 and Na-A is due to the dispersion interaction. [Copyright &y& Elsevier]

Abstract: Two types of MFI zeolitic materials with improved accessibility, hierarchical zeolites and hybrid ordered mesoporous materials are here compared in terms of textural, acidic and catalytic properties. In both cases, protozeolitic units were employed as starting building blocks, the growth of which was perturbed by a silanization agent (hierarchical ZSM-5) or controlled by assembling around surfactant micelles (hybrid ordered mesoporous material, HZM). Likewise, two standard samples (nanocrystalline ZSM-5 and Al-MCM-41) were used as reference. Nitrogen adsorption measurements confirmed the presence of a secondary porosity and a high share of non-microporous surface area in hierarchical ZSM-5, whereas no significant amount of micropores was detected in the hybrid HZM sample. However, 27Al MAS NMR measurements indicated that zeolitic fragments are present within the walls of the latter sample. The acidic properties of the materials under study were extensively investigated by adsorption–desorption of different base probe molecules. Specifically, FTIR spectra taken after pyridine adsorption show the presence of a high population of strong Lewis acid sites in both hierarchical ZSM-5 and HZM samples. This fact, along with a high accessibility to the active sites, is proposed to be mainly responsible for the enhanced catalytic activity exhibited by these materials in 1,2-epoxyoctane rearrangement and anisole acylation. The results obtained clearly indicate the strong and positive influence of the textural and acidic features of the hierarchical materials on their catalytic properties. [Copyright &y& Elsevier]

Abstract: The synthesis of N-substituted imidazoles via alkylation of imidazole with 1-bromobutane using sonochemical and thermal activations over zeolites (H-ZSM-5, Mordenite, H-Beta and H-Y) is reported. The effect of the acidity and channel size of zeolites on the activity and selectivity of imidazole alkylation was investigated in a liquid phase. The N-alkylimidazoles are important intermediates in the synthesis of pharmaceuticals with antiviral properties. N-alkylimidazoles were obtained in high yields (>80%) as main product (100% selectivity) under mild conditions, ultrasound (US) activation at 333K in only 1h, when Mordenite and NH4Y zeolites were used as catalysts. [Copyright &y& Elsevier]

Hierarchical ZSM-5 zeolite has been synthesized by hydrothermal crystallization of protozeolitic nanounits previously functionalized with two types of commercially available organosilanes. The first one (N , N -diethyl-3-aminopropyl-trimethoxysilane, DEAMP) is a monopodal organosilane that contains a tertiary amine group, whereas the second one (1,2-bis(trimethoxysilyl)decane, BTMDC) includes a long aliphatic chain and two tri-alkoxysilyl groups (dipodal organosilane). The properties of the samples obtained have been compared with two nanocrystalline ZSM-5 materials as references. While both organosilanes are effective in generation of a secondary porosity, enhancing strongly the textural properties of ZSM-5 zeolite, DEAMP affords for more uniform nanounits in the aggregates with narrower mesopore size distribution compared to BTMDC. On the other hand, varying the concentration of DEAMP during the silanization step (in the range of 2.5–10 mol%, referred to the silica content of the synthesis gel) it has been possible to synthesize hierarchical ZSM-5 samples showing progressively smaller size of the nanounits in the aggregates. This fact has led to important changes in both the textural and acid properties of the zeolite samples. In particular, a decrease in the Brønsted/Lewis acid sites ratio has been observed with increasing the concentration of DEAMP introduced in the synthesis gel. These materials have been tested as catalysts for low-density polyethylene (LDPE) cracking, showing enhanced catalytic activity in comparison with the two reference nanocrystalline ZSM-5 samples. A maximum of the LDPE conversion has been obtained with the h-ZSM-5 zeolite prepared with 5 mol% of silanization agent as this material exhibits an optimum combination of acidic features and accessibility. Image 1 • Organosilane type has a crucial role in the properties of hierarchical ZSM-5. • Tertiary amine – containing organosilane produces mesopores with narrow PSD. • Acidic and textural properties can be tailored adjusting the organosilane content. • Accessibility-acidity compromise determines the maximal LDPE cracking activity. [ABSTRACT FROM AUTHOR]