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The direct transformation of ethanol to acetaldehyde is an important step in the cascade conversion of bioethanol to higher value chemicals and for the development of sustainable fuels. Herein, zinc oxide supported on alkali cation-exchanged mordenite (ZnO/M–MOR) prepared by a simple wetness impregnation method, is shown to be a selective and stable catalyst for the direct dehydrogenation of ethanol to acetaldehyde at 400 °C under continuous flow conditions. Through variation of the ZnO loading and the zeolite counter-cation (Na, K, Rb, Cs), an optimum catalyst material was identified, ZnO/Rb–MOR loaded at 3.5 wt% Zn. Acetaldehyde productivity (normalised to Zn) could be increased by over 80% and ethylene selectivity reduced to 0.9 % through simple variation of the extra-framework alkali cation. Very low ethylene production leads to low levels of carbonaceous deposits and therefore minimal deactivation at short time on stream (< 5 h). Detailed analysis of the optimized system reveals excellent selectivity and stability beyond 120 h time on stream, resulting in an average acetaldehyde productivity of 16 mmol gcat−1 h−1 and overall acetaldehyde selectivity of 90% whilst operating at an ethanol conversion level of 40 %. Additionally, the use of a zeolite support is shown to greatly improving the usage efficiency of Zn atoms by virtue of an acetaldehyde productivity increase from 20 to 48 mmol mmolZn−1 h−1 for unsupported and supported ZnO, respectively. The new catalyst system shows that ZnO can be tuned to give very low ethylene selectivity and extended lifetimes in ethanol dehydrogenation to acetaldehyde which has not previously been reported.

Expectations for industrial implementation of direct conversion of CH4 to CH3OH are growing with the increasing demand for energy-efficient chemical processes. In this study, catalytic production of CH3OH by direct oxidation of CH4 with O2 was performed using Cu zeolite catalysts in a CH4/O2/H2O flow reaction. Among the various Cu zeolites investigated, the Cu-MOR catalyst exhibited relatively high CH3OH production with a turnover number of 7.4 molCH3OH molCu−1 over 24 h (CH4 conversion: 0.011%). The catalytically active Cu species and catalytic cycle were investigated by in situ simultaneous X-ray absorption and infrared spectroscopy. The results suggest that the key to the catalytic cycle over Cu-MOR is the redox of Cu(I)/Cu(II) species. Furthermore, H2O-adsorption-included dynamic Cu species are revealed to be catalytically active.

Among the many industrially important zeolites, mordenite is found to be interesting because of its unique and exceptional physical and chemical properties. Mordenite (high silica zeolite) is generally prepared by the hydrothermal method using TEA+ cations. TEA+ cations are the best templating agent, though they can create a number of issues, for instance, generating poison and high manufacturing cost, wastewater contamination, and environmental pollution. Hence, it is necessary to find a mordenite synthesis method without using an organic template or low-cost template. In this review, a number of unique sources were used in the preparation of mordenite zeolite, for instance, silica sources (rice husk ash, silica gel, silica fumes), alumina sources (metakaolin, faujasite zeolite) and sources containing both silica and alumina (waste coal fly ash). These synthesis approaches are also based on the absence of a template or low-cost mixed organic templates (for instance, glycerol (GL), ethylene glycol (EG), and polyethylene glycol 200 (PEG)) or pyrrolidine-based mesoporogen (N-cetyl-N-methylpyrrolidinium) modifying the mordenite framework which can create unique properties. The framework properties and optical properties (indium-exchanged mordenite zeolite) have been discussed. Mordenite is generally used in alkylation, dewaxing, reforming, hydrocracking, catalysis, separation, and purification reactions because of its large pore size, strong acidity, and high thermal and chemical stability, although the applications are not limited for mordenite zeolite. Recently, several applications such as electrochemical detection, isomerization, carbonylation, hydrodeoxygenation, adsorption, biomass conversion, biological applications (antibacterial activity), photocatalysis, fuel cells and polymerization reactions using mordenite zeolite were explored which have been described in detail in this review.

It is of great significance to clarify the roles that various seeds play in the induced synthesis of target zeolites from a viewpoint of topological structure. Zeolites, including ZSM-5, β, mordenite, ZSM-35, ZSM-22, SSZ-13, SSZ-24 and analcite, were used as seeds for the template-free synthesis of ZSM-5. It was found that zeolites with lower framework density and identical composite building units (CBUs) and secondary building units (SBUs) could be used as seeds for the successful synthesis of ZSM-5. Zeolites (ZSM-5, β, mordenite, ZSM-35 and ZSM-22) having identical CBUs and SBUs to ZSM-5 were capable of accelerating the crystallization of ZSM-5, whereas zeolites (SSZ-13 and SSZ-24) lacking identical CBUs and SBUs could act as seeds to synthesize ZSM-5 zeolite only if they possessed lower framework density than ZSM-5. As such, zeolites possessing simultaneously identical CBUs and/or SBUs and low framework density had a strong inductive effect in template-free synthesis of ZSM-5.

Two Al-rich mordenite samples were prepared by the same synthesis procedure except for the activation of the gel for which classical stirring and ultrasonic pretreatment was used. The organization of Al atoms both in the synthesis gel and zeolite product was investigated. Although both methods of the gel activation resulted in a similar transformation of Al and Si source according to NMR spectroscopy, stirring provided a significantly higher fraction of AlSiAl sequences in the gel compared to the ultrasonic pretreatment. These sequences were transferred to the zeolite product and were more populated in the conventionally prepared mordenite. Al atoms of AlSiAl sequences face different channels and mainly behave as single Al atoms, but they can also form Al pairs or close unpaired Al atoms, observed for the first time for mordenite.

The formation and reactivities of [Cu–O–M]2+ species (M = Ti–Cu, Zr–Mo and Ru–Ag) in metal-exchanged zeolites, as well as stabilities of these species towards autoreduction by O2 elimination are investigated with density functional theory. These species were investigated in zeolite mordenite in search of insights into active site formation mechanisms, the relationship between stability and reactivity as well as discovery of heterometallic species useful for isothermal methane-to-methanol conversion (MMC). Several [Cu–O–M]2+ species (M = Ti–Cr and Zr–Mo) are substantially more stable than [Cu2O]2+. Other [Cu–O–M]2+ species, (M = Mn–Ni and Ru–Ag) have similar formation energies to [Cu2O]2+, to within ±10 kcal mol−1. Interestingly, only [Cu–O–Ag]2+ is more active for methane activation than [Cu2O]2+. [Cu–O–Ag]2+ is however more susceptible to O2 elimination. By considering the formation energies, autoreduction, cost and activity towards the methane C–H bond, we can only conclude that [Cu2O]2+ is best suited for MMC. Formation of [Cu2O]2+ is initiated by proton transfer from aquo ligands to the framework and proceeds mostly via dehydration steps. Its μ-oxo bridge is formed via water-assisted condensation of two hydroxo groups. To evaluate the relationship between [Cu2O]2+ and other active sites, we also examined the formation energies of other species. The formation energies follow the trend: isolated [Cu–OH]+ < paired [Cu–OH]+ < [Cu2O]2+ < [Cu3O3]2+. Inclusion of Gibbs free-energy corrections indicates activation temperatures of 257, 307 and 327 and 331 °C for isolated [Cu–OH]+, paired [Cu–OH]+, [Cu2O]2+ and [Cu3O3]2+, respectively. The provocative nature of the lower-than-expected activation temperature for isolated [Cu–OH]+ species is discussed.

A hierarchical zeolite composite, MOR@ZSM-5, with two distinct frameworks has been successfully fabricated via the repeated crystallization of ZSM-5 nanocrystals on mordenite surfaces. To avoid their phase separation, the surface of mordenite was pretreated with tetra(n-butyl)ammonium hydroxide (TBAOH) to induce the formation of the ZSM-5 nuclei, and it was subsequently modified by the continuous growth of nanocrystalline ZSM-5 on the entire area of the mordenite surfaces. Interestingly, the fully overgrown MOR@ZSM-5 composite exhibits a remarkable improvement in the ethylbenzene selectivity (>60%) obtained from the alkylation of benzene with ethanol with respect to isolated zeolites and their physical mixture due to the enhanced external surface area and hierarchical porosity as well as the reasonable acidity provided by the fully dispersed ZSM-5 nanocrystals on the mordenite surfaces. Moreover, coke species deposited on the designed composites are likely located at the external surfaces and do not considerably deteriorate the catalytic performance, whereas they are deposited predominantly in the micropores over the incompletely overgrown MOR@ZSM-5 composite. The present study illustrates the advantages of the overgrown zeolite composites of two incompatible frameworks in tailoring the hierarchical porosity, adjusting the acidic properties, and eventually controlling the product selectivity in acid-catalyzed reactions such as the alkylation of benzene with ethanol.

To improve the stability of mordenite (MOR) in the alkylation of benzene with long chain olefin, hierarchical MOR zeolites were synthesized by using organosilane surfactant [3-(trimethoxysilyl)propyl]octadecyldimethyl-ammonium chloride (TPOAC) as the mesopore structure-directing agent. Our findings reveal that the crystal size, hierarchical structure, and acidic properties of the mesoporous MOR zeolites are significantly influenced by the TPOAC/SiO2 molar ratio in the synthesis gel. Moreover, the hierarchical MOR zeolite synthesized under the optimized synthesis conditions presented the pure phase of the MOR framework and uniform mesoporous distribution. More importantly, the catalytic performance evaluated by the alkylation of benzene with 1-dodecene indicates that the optimal mesoporous MOR zeolite shows improved stability and comparable selectivity of 2-phenyl alkane (2-LAB) around 80% compared to the conventional sole microporous MOR zeolite. The improved stability of the mesoporous MOR zeolite can be attributed to the enhanced diffusivity of long chain linear alkylbenzenes and oligomers due to interconnected meso-/microporosity in the MOR.

The selective oxidation of methane directly to methanol is currently one of the most studied topics. A promising approach, which received increasing attention during the past decade, is methane oxidation over copper-exchanged zeolites via chemical looping. In the present study, the kinetics of methane reacting over oxygen-activated copper-exchanged mordenite was studied by means of in situ infrared spectroscopy. Methoxy species and carbon monoxide are the primary reaction products and formed directly from methane. Partial poisoning with water after the oxygen activation and before the methane reaction leads to the decrease of methanol yield, which is associated with the blockage of at least two copper atoms in the active site per one water molecule. However, the poisoning is reversible and the increase of the methane pressure increases the activity of CuMOR due to the competitive adsorption over the active sites. As such, even if the zeolite is not fully dehydrated, low temperature isothermal conversion of methane to methanol via chemical looping becomes possible.

The selective catalytic oxidation of ammonia (NH3-SCO) is the last mitigation step in exhaust treatment using a 4-way catalytic converter to convert any excess and unreacted NH3 (that was used as a reductant of NOx) into environmentally benign N2 and H2O. Here, we report a series of highly reactive and selective nano Cu/zeolites for the NH3-SCO reaction. The NH3-SCO activity was found in the order nano Cu/ZSM-5 (MFI topology) > Cu/Beta (BEA) > Cu/MCM-49 (MWW) > Cu/Y (FAU) > Cu/Mordenite (MOR) > Cu/Ferrierite (FER). The best catalyst, i.e., nano Cu/ZSM-5, achieves 98% NH3 conversion at 250 °C with the N2 yield maintained at >98% even at up to 500 °C. When assessed under practical exhaust conditions in the presence of moisture (5% H2O) as well as that after hydrothermal aging (5% H2O, 850 °C, 8 h), the nano Cu/ZSM-5 exhibited only minor deactivation as a result of its good retention of Cu dispersion, pore structure and specific surface area. Furthermore, small micropore (10-membered ring, 10-MR) topologies were found to be crucial in maintaining high N2 yields. For Cu/Y and Cu/Mordenite, composed of 12-MR pores that are non-interconnected with smaller pores, their N2 yields were compromised by forming NOx at temperatures above 400 °C. Based on the in situ DRIFTS study, the iSCR mechanism appears to be applicable for all fresh and aged Cu/zeolites with the exception of fresh Cu/MCM-49 that follows the imide mechanism.

As Bronsted acid sites in different types of channels exhibit distinct catalytic behaviors in the dimethyl ether (DME) carbonylation reaction over acidic mordenite (H-MOR) zeolites (e.g. acid sites in 8-membered ring channels for carbonylation reaction, acid sites in 12-membered ring channels for methanol-to-hydrocarbons reactions), the identification and regulation of acid site distribution in mordenite zeolites are of great importance to improve the catalytic performance. In this work, we employ the selective ion-exchange method to identify and control the acid site distribution in mordenite zeolites, and the chemical properties of acid sites in different channels are investigated by NH3-TPD and CD3CN FT-IR. Additionally, the effect of selective ion-exchange on the catalytic performance of DME carbonylation reaction is also discussed. The selective ion-exchange is realized by using tetramethylammonium (TMA+) ions, which can selectively remove the counter ions in the 12-membered ring channels but are inaccessible to the counter ions in 8-membered ring channels due to the steric hindrance. The selective ion-exchange reveals that the relative amounts of acid sites in 12-membered ring channels and 8-membered ring channels are 68% and 32%, respectively. Interestingly, it is found that introducing TMA+ into H-MOR zeolites significantly improves the catalytic activity and stability in DME carbonylation reaction as a result of depressing the methanol-to-hydrocarbons reactions. The 3TMA-H-MOR catalyst shows high stability for 210 hours on stream. The present work opens a new avenue for designing carbonylation catalysts with excellent stability in DME carbonylation reaction.

Mordenites with framework Si/Al ratios of 6.5–10.2 were hydrothermally synthesized by simply varying the concentrations of silica and alumina sources in the raw gel without using any template. However, their catalytic performance for dimethyl ether carbonylation remained almost identical. Structural analysis and IR characterization revealed that the framework Al atoms preferentially located on the T3 and T4 sites in the 4-ring unit at higher Si/Al ratios, while they positioned on all the four T-sites at lower Si/Al ratios. Accordingly, the correlation between the activity and the specific location of framework Al atoms was established: the Al atom on the T3-site of the 8-MR channel was the active center for DME carbonylation, while the Al atom at the T4-site of the 12-MR channel induced the deactivation via coking. The superfluous Al atoms at T1 and T2 sites did not contribute to either DME conversion or coke deposition, simply acting as spectators. With this regard, mordenite having a framework Si/Al ratio of 11, in which each 8-MR and 12-MR possess of one Al atom siting on the T3 and T4 sites, respectively, would achieve its catalytic activity for DME carbonylation.

An efficient route to obtain aromatic products based on biomass feedstock is a challenge for future biorefineries. Isobutyraldehyde is a promising feedstock available via biotechnological routes based on both carbohydrates and the direct bioconversion of CO2. Herein, we report an efficient process for the aromatisation of isobutyraldehyde over zeolite catalysts in a continuous fixed bed reactor to provide value-added aromatic compounds with a yield of 93%. Benzene, toluene and xylenes are the major compounds formed with 79% yield and a productivity of 65 mmol gcat−1 h−1. Zeolite Y, Beta and Mordenite and ZSM-5 of different modules were studied. Comprehensive catalyst characterisation using XRD, NH3-TPD, N2-physisorption, and ICP-OES enabled establishing structure–performance relationships with a major role of zeolite structure, density of strong acid sites and mesoporosity, respectively. HZSM-5 with Si/Al ratios of 15 to 49 proved effective at the aromatisation possessing a comparable density of strong acid sites of 0.37–0.52 mmol g−1. Superior stability was observed for HZSM-5 zeolites with higher mesopore volumes. The reaction is suggested to mainly proceed via catalytic cracking to C1–C4 alkanes/alkenes, which undergo further oligomerisation, cyclisation, and aromatisation to form the observed alkyl-aromatics. Emphasizing the potential of the concept, long term continuous operation was carried out by alternating 10 hours time on steam operation and catalyst regeneration via in situ calcination.

Understanding the properties of zeolites for cation exchange is important because the ion-exchange performance largely determines their suitability in applications such as catalysis and adsorptive separation. We synthesized a Zn(ii)-incorporated mordenite-framework aluminosilicate zeolite (Zn,Al-MOR), in which both Zn and Al are substituted in the framework, and studied its ion-exchange behavior for multivalent cations. For comparison, the original aluminosilicate mordenite (Al-MOR) was also synthesized with a composition adjusted to ensure that its charge density was similar to that of Zn,Al-MOR. While the incorporation of Zn(ii) led to a slower kinetic process, the selectivities and the exchange capacities toward multivalent cations (especially divalent cations) were significantly improved. Herein, we discussed the mechanism responsible for improving the ion-exchange performance in the presence of Zn(ii) and found that the incorporation of Zn(ii) led to a significant improvement in the ion-exchange temperature dependence of the MOR, which led to the ability to enhance ion-exchange capacity through temperature control during actual application. It was also revealed that the presence of Zn(ii) significantly improves selectivity and spontaneity toward the exchange of multivalent cations, Ni2+. Moreover, XRD and nitrogen-adsorption/desorption analyses revealed that the structures of the materials are maintained during the ion exchange, which is indicative of superior structural stability and tolerance to ion exchange.

Aluminosilicate-based zeolite materials, such as ZSM-5 and mordenite, are well-studied as catalysts. Typical approaches to synthesize these zeolites require either templates or seeds to direct ordered crystal growth and both of these are expensive and add to the complexity of zeolite synthesis. In this paper, we describe a solvent-free and template-free method to synthesize crystalline ZSM-5 and mordenite zeolites without any added seed crystals. Key to the success of this approach is a mechanochemical precursor pre-reaction step. High-energy ball-milling is used to initiate a solid-state metathesis (exchange) reaction between Na2SiO3 and Al2(SO4)3 reagents, forming crystalline Na2SO4 and well-mixed aluminosilicate precursor. The solid precursor mixture is thermally converted to crystalline ZSM-5 or mordenite at moderate 180 °C temperatures without solvents or an organic amine structure directing template. Variations in Si/Al ratios in the precursor mixture and additions of solid NaOH to the mechanochemical reaction were found to influence the subsequent growth of either crystalline ZSM-5 or mordenite zeolites. The crystalline zeolites from this solvent-free and template free method have high ∼300 m2 g−1 surface areas directly from the synthesis without requiring high-temperature calcination. These materials are also comparably active to their commercial counterparts in cellulose and glucose biomass catalytic conversion to hydroxymethylfurfural.

Photocatalysts based on TiO supported on two different synthetic zeolites (faujasite CBV 760: SiO/AlO = 60 and mordenite CBV 21A, SiO/AlO = 20), containing 10 wt% and 40 wt% TiO loading, have been synthesized using a sol-gel method without any further calcination. The structural, textural and optical properties of the samples have been characterized using X-ray diffraction (XRD), elemental analysis (ICP-OES), N adsorption-desorption isotherms, aberration corrected Scanning Transmission Electron Microscopy with High Angle Annular Dark Field imaging combined with Electron Energy Loss Spectroscopy (STEM/HAADF/EELS), and UV-Vis Diffuse Reflectance Spectroscopy (UV-Vis DRS). The characterization data confirmed that an amorphous layer containing polycrystalline anatase TiO was formed efficiently on the surface of the zeolites, showing 2-4 nm crystalline domains. The photocatalytic activities of different samples were tested for the photocatalytic degradation of methyl orange, which showed increased adsorption of the dye molecule, and a faster degradation reaction than the calcined counterparts. Interestingly, although the supported TiO catalysts were not calcined, the best catalysts, 10TZY60nc and 40TZY60nc, showed negligible Ti leaching and their reusability was verified for three cycles without noticeable photocatalytic activity decrement., This work has been partially financed by the Spanish State Research Agency (Agencia Española de Investigación, AEI) and the European Regional Development Fund (Fondo Europeo deDesarrollo Regional, FEDER) through the Project MAT2016-77496-R (AEI/FEDER, UE).

The direct conversion of methane into methanol was studied in a stepwise process over copper-exchanged mordenite. The materials were characterized by X-ray diffraction, nitrogen adsorption–desorption, FTIR of adsorbed NO and X-ray absorption spectroscopy. The methanol productivity and selectivity correlated with the amount of Bronsted acid sites in the zeolite. The in situ FTIR spectroscopy revealed that the presence of Bronsted acid sites increases the stability of formed methanol, hence avoiding its overoxidation into carbon oxides. The best performing material in terms of methanol yield was copper-exchanged mordenite with the highest amount of the Bronsted acid sites showing a methanol productivity of 118 μmol g−1 equivalent to 0.18 mol(MeOH)/mol(Cu) with 95% selectivity towards methanol.

The valorization of hemicellulose into valuable chemicals, such as C5 sugars and furfural, in a one-pot fashion is crucial. In this work, acidic ionic liquids in the presence of water showed high yields of C5 sugars (>80%) with >99% conversion of hemicelluloses at 160 °C. With a water + toluene biphasic solvent system, within 4 h, an 85% furfural yield was obtained directly from hemicellulose in a one-pot fashion using a catalytic amount of 1-methyl-3-(3-sulfopropyl)-imidazolium hydrogen sulfate. It was seen that Bronsted acidic ionic liquids (BAILs) perform better than solid acid [Faujasite and Mordenite zeolites; ion exchange resin, Amberlyst-15] and mineral catalysts [HCl and H2SO4]. The higher activity of BAILs compared to solid acids and mineral acids was correlated to the Hammett acidity function (Ho) and ion-dipole type of interactions. The catalysts were characterized using NMR (1H and 13C), elemental analysis and TGA to confirm that they were stable under reaction conditions and were thus recyclable.

Zeolites representing seven different topologies were subjected to life-time assessment studies as methanol to hydrocarbons (MTH) catalysts at 400 °C, P(MeOH) = 13 kPa and P(tot) = 100 kPa. The following topologies were studied: ZSM-22 (TON), ZSM-23 (MTT), IM-5 (IMF), ITQ-13 (ITH), ZSM-5 (MFI), mordenite (MOR) and beta (BEA). Two experimental approaches were used. In the first approach, each catalyst was tested at three different contact times, all giving 100% initial conversion. The life-time before conversion decreased to 50% at each contact time was measured and used to calculate critical contact times (i.e. the contact time needed to launch the autocatalytic MTH reaction) and deactivation rates. It was found that the critical contact time is strongly correlated with pore size: the smaller the pore size, the longer the critical contact time. The second experimental approach consisted of testing the catalysts in a double tube reactor with 100% initial conversion, and quenching the reaction after 4 consecutive times on stream, representing full, partial, and zero conversion. After quenching, the catalyst bed was divided into four segments, which were individually characterised for coke content (temperature-programmed oxidation) and specific surface area (N2 adsorption). The axial deactivation pattern was found to depend on pore size. With increasing pore size, the main source of coke formation changed from methanol conversion (1D 10-ring structures), to partly methanol, partly product conversion (3D 10-ring structures) and finally mainly product conversion (3D 12-ring structure). As a result, the methanol conversion capacity changed little with contact time for ZSM-5, while it increased with increasing contact time for the catalysts with smaller pore sizes, and decreased with increasing contact time for pore sizes larger than ZSM-5.

International audience; 1 Radioactive iodine species belong to the most dangerous components of nuclear effluents and waste produced by nuclear facilities and this fact motivates a significant effort in development of technologies for their efficient trapping. In this work we use computer simulations at the periodic DFT level to investigate dissociative adsorption of iodomethane on silver exchanged mordenite, which is among the most effective sorbents of iodine species available as of today. The structure, energetics, and mobility of complexes Ag-(CH 3 I) and Ag-(CH 3 I) 2 formed upon adsorption of iodomethane on Ag + sites are investigated using the ab-initio MD approach. The free-energy profiles for the reaction CH 3 I + Ag-MOR → AgI + CH 3-MOR are determined using the blue moon ensemble technique. The AgI species formed as a product of dissociative adsorption are shown to combine spontaneously into small clusters (AgI) n with the dimensions restricted by the size and geometry of confining void. The structure and energetics of the (AgI) n species are analysed in detail and compared with the available experimental and theoretical data. The internal energy of formation of clusters in mordenite is shown to contribute significantly to the shift of equilibrium from undissociated to dissociated form of adsorbed CH 3 I.

A series of Ce@MOR hybrids based on CeOx nanoparticles (1–2.5 nm) encapsulated in mordenite exhibiting a genuine flower-like morphology were prepared by simple hydrothermal synthesis. The cerium content in the catalysts could be easily tuned by adjusting the Si : Al : Ce composition of the preformed gel, affecting the textural properties and the density of acid sites of the catalysts. The genesis of acid sites with medium strength was directly correlated to the catalytic activity for the vapor-phase dehydration of 1,3-butanediol into butadiene. A Ce@MOR hybrid with a Si/Ce atomic ratio of 50 displayed a superior activity and selectivity compared to the parent MOR at a comparable Si/Al atomic ratio (10), as well as to control Ce-MOR catalysts post-synthesized by incipient wetness impregnation from the parent mordenite. A higher density of Bronsted acid sites with medium strength induced by encapsulated CeOx nanoparticles was argued as the main reason for such an enhanced catalytic performance.

Mordenite nanosheets of 20–40 nm thickness significantly shortened the lengths of parallel 12-member and 8-member ring channels and greatly facilitated the diffusion of molecules inside the micropores, and therefore remarkably enhanced the catalytic activity for the carbonylation of dimethyl ether.

Direct methane-to-methanol conversion is a desired process whereby natural gas is transformed into an energy-rich liquid. It has been realised at ambient pressure and temperature in metal ion-exchanged zeolites, where especially copper-exchanged ZSM-5 has shown promising results. The nature of the active sites in these systems is, however, still under debate. The activity has been assigned to a [Cu-O-Cu]2+ motif. One remaining question is whether this motif is general and also active in other metal-exchanged zeolites. Herein, we use first-principles microkinetic modelling to analyse the methane-to-methanol reaction on the [Cu-O-Cu]2+ motif, for Cu and other metals. First, we identify the cluster model size needed to accurately describe the dimer motif. Starting from the [Cu-O-Cu]2+ site, the metal ions are then systematically substituted with Ni, Co, Fe, Ag and Au. The results show that activation of Ag and Au dimer sites with oxygen is endothermic and therefore unlikely, whereas for Cu, Ni, Co and Fe, the activation is possible under realistic conditions. According to the kinetic simulations, however, the dimer motif is a plausible candidate for the active site for Cu only. For Ni, Co and Fe, close-to-infinite reaction times or unreasonably high temperatures are required for sufficient methane conversion. As Ni-, Co- and Fe-exchanged ZSM-5 are known to convert methane to methanol, these results indicate that the Cu-based dimer motif is not an appropriate model system for these metals.

We present herein an ultrafast, organic structure-directing agent (OSDA)-free synthesis of mordenite zeolite in a tubular reactor capable of fast heating. Using a typical Na2O/SiO2/Al2O3 system, the synthesis time was shortened to 10 min, which is much shorter than the time required by conventional methods (tens of hours). The addition of milled seeds, which have a smaller crystal size (200 nm), was found to be more effective in enhancing the crystallization than the micrometer-sized raw seeds (2 μm). The fast-synthesized mordenite possesses properties similar to those of mordenite synthesized by conventional methods in terms of crystallinity while having a comparably small crystal size. In addition, the effects of the alkalinity and SiO2/Al2O3 ratio of the initial reactant mixture on the crystallization rate were evaluated, but no significant effects were observed. On the contrary, the yield and SiO2/Al2O3 ratio of the product were dependent on the alkalinity and SiO2/Al2O3 ratio of the initial reactant mixture. Based on these observations, the crystallization behavior of mordenite, obtained from an ultrafast, OSDA-free synthesis method, is discussed.

Modified mordenites have been used in the direct conversion of glucose into 5-hydroxymethylfurfural (5-HMF) in two different media: the ionic liquid 1-butyl-3-methylimidazolium bromide ([BMIM]Br) and a biphasic system composed of water–acetone and ethyl acetate. The results revealed that there are crucial differences in the final catalytic performances. Modified mordenite treated with 1 M NH4Cl only, with a moderate Si/Al ratio of 11.2 and a high content of strong Bronsted acid sites (TPDNH3 acidity of 1.39 mmol g−1), possessed the highest catalytic activity resulting in 64% 5-HMF yield with 97% glucose conversion in the ionic liquid system. On the other hand, the mordenite treated with 1 M NH4Cl and 2.4 M NH4F, with a total acidity of 1.51 mmol g−1, mainly due to Lewis acid sites, gave 50% 5-HMF yield with 98% conversion in the biphasic system. The presence of strong Lewis acid sites has a major effect on the catalytic activity in aqueous–organic biphasic medium, in agreement with earlier works that showed that the reaction proceeds via Lewis acid-catalyzed isomerization followed by Bronsted acid-catalyzed dehydration. In contrast, the quick adsorption and strong interaction of the ionic liquid with the zeolite, which hinders the diffusion of the products, enhances the role of zeolite mesoporosity in the catalytic activity when the reaction is carried out in ionic liquid solution.

Seed-assisted synthesis has been demonstrated as a green and facile route to produce useful zeolites with several frameworks, and meanwhile shows the potential to selectively template the formation of specific structured crystals. In view of the difficulty of directly synthesizing zeolite mordenite (MOR) with short 1D, 12-MR channels, we proposed a plausible synthetic route of exotic seed-assisted conversion (ESAC), starting from aluminosilicate gel containing zeolite beta (BEA) seeds to MOR nanocrystals. Through judiciously adjusting the synthetic conditions, including NaF/Si, OH−/Si, hydrothermal temperature and added zeolite BEA seeds, nano-crystallite assembled zeolite MOR nanoparticles with rich inter-crystallite mesoporosity, high crystallinity, perfect framework, and high catalytic activity for low-density polyethylene cracking, were fast transformed under a low seeded, organic template-free system. The combined investigation of synthetic conditions and the crystallization process deepened the understanding on this special crystallization behaviour.

N-Methyl amines play a major role in the production of medicines, pesticides, surfactants and dyes. N-Methylation of primary or second amines with methanol is considered to be a green path for the synthesis of N-methyl amines and the catalyst is key. In this article, the combined Al2O3–mordenite catalyst (mass fraction of alumina is 40%) with good activity, selectivity, lifetime and stability was prepared for N-methylation of various amines with methanol in a hydrogen free system in a fixed bed reactor, and characterized by XRD, N2 adsorption and NH3-TPD. Furthermore, the methanol adsorption was investigated by in situ FTIR, and the result indicated that methoxyl species may be the active species for the N-methylation of amines.

Copper mordenite was used for the conversion of methane to methanol in a cyclic operation. Repeated cycling was possible using catalysts having different loadings prepared via aqueous ion exchange using copper(II) acetate (Cu-MORA) and solid state ion exchange using copper(I) chloride (Cu-MORS). For Cu-MORA, the yield increased by at least 30% on the second cycle and remained constant afterwards. Linear combination fitting of the XANES identified a similar increase in the fraction of CuI formed upon reacting with methane on the second cycle. For Cu-MORS residual chlorine initially hindered the production of methanol. Successive cycles removed chlorine and yielded significantly more methanol per copper than Cu-MORA. Over successive cycles of Cu-MORS, the fraction of the CuII species that was reduced to CuI upon reacting with methane correlated well with the amount of methanol produced. Although commonly done, analyzing only one reaction cycle is not representative of the long-term performance of methane to methanol over copper mordenite. Copper species equilibrate with cycling.

It is shown that control of the degree of coking can lead to the observation of hyperfine structures in the carbonaceous residues deposited from methanol over mordenite (H-MOR) at temperatures relevant to the conversion of methanol to hydrocarbons. EPR measurements of the catalyst samples at various times on stream have been recorded, with a rich hyperfine splitting pattern observed in the early stages of the reaction. Interpretation of the EPR data with the aid of density functional theoretical calculations has afforded the first definitive assignment of the radical cations formed in high temperature coke. The results detail a shortlist of six species: 2,3/2,6/2,7-dimethylnaphthalenium, 2,3,6-trimethylnaphthalenium, 2,3,6,7-tetramethylnaphthalenium, and anthracenium radical cations whose proton hyperfine splitting profiles match the experimental spectra; 2,3,6,7-tetramethylnaphthalenium showed the best agreement. The observation of these particular isomers of polymethylnaphthalene suggest the formation of more highly branched polyaromatic species is less likely within the confines of the H-MOR 12-membered ring channel. These radicals formed when the catalyst is active may constitute key intermediates in the conversion of methanol to light olefins.

Cu-Exchanged zeolites are known as active materials for methane oxidation to methanol. However, understanding of the formation of Cu active species during synthesis, dehydration and activation is fragmented and rudimentary. We show here how a synthesis protocol guided by insight in the ion exchange elementary steps leads to highly uniform Cu species in mordenite (MOR).

A cost-effective K1.5Mg/SiO2 catalyst with a K2MgSiO4 component was employed to help transfer several hexoses into hydroxylmethylfurfural (HMF) in a biphasic water/butanol system. The solid catalysts with rod-like structures and moderate base sites could promote the aldose–ketose isomerization of glucose and have potential for the synthesis of lactic acid via a retro-aldol condensation. In the presence of sulfonated titania/mordenite solid acid, the K1.5Mg/SiO2 catalyst presented heat-stability and prolonged activity in the one-pot conversion of glucose to HMF, leading to an optimal yield of 62.2%. The one-pot catalysis of saccharides from the enzymatic hydrolysate of poplar sawdust achieved a high HMF yield of 56.9% at a glucose conversion of 91.6%.

The conventional methods used in preparing zeolite membranes, such as the secondary growth and in situ crystallization methods, involve long and complex procedures that require the preparation of the zeolite aluminosilicate gel prior to the fabrication process and often result in membranes which contain pin holes. Here we report a simple, cheap, and less time-consuming technique to fabricate zeolite A and mordenite membranes on a porous stainless steel support. In addition, the technique makes it possible to fabricate types of zeolite membranes that have been previously difficult to synthesise. A clinoptilolite membrane was fabricated to demonstrate the ability to manufacture a zeolite membrane from an existing crystalline zeolite (natural or synthetic). All three membranes were subjected to separation tests, (ethanol dehydration, ethanol–cyclohexane and phenol removal from water) to demonstrate the efficacy of membrane synthesis. The fluxes obtained and separation factors which were achieved are comparable with literature values but as with most zeolite membranes there is a trade-off between high flux and separation.

The pyrolysis of whole biomass—pine wood and bark—with mordenite (M), beta (β) and Y zeolites has been examined at 600 °C. The GPC results indicated that the pyrolysis oils upgraded by Y and β zeolites have a very low average molecular weight range (70–170 g mol−1). Several NMR methods have been employed to characterize the whole portion of pyrolysis products. After the use of these two zeolites (Y and β), the two main products from the pyrolysis of cellulose—levoglucosan and HMF—were eliminated; this indicates a significant deoxygenation process. When a mixture of zeolites (Y and M) was used, the upgraded pyrolysis oil exhibited advantages provided by both zeolites; this pyrolysis oil represents a biofuel precursor that has a very low average molecular weight and a relatively low acidity. This study opens up a new way to upgrade pyrolysis oils by employing mixtures of different functional zeolites to produce biofuel/biochemical precursors from whole biomass.

A series of Fe-modified mordenite zeolite samples were synthesized by a template-free method and employed in dimethyl ether (DME) carbonylation reaction for the production of methyl acetate (MAc). XRD, UV-Vis, and UV-Raman characterization studies proved that Fe atoms have been introduced into the mordenite zeolite framework by partial substitution of Al atoms, which led to evident changes of activity and MAc selectivity. With the increase of iron content (as metal) from 0.0 to 3.6 wt%, DME conversion first increased and then decreased. MAc selectivity and catalyst stability were enhanced for all Fe-modified samples. TG and GC-MS analysis of deactivated catalysts showed that the amount of coke retained in the catalysts decreased as the iron content of the zeolites increased. The enhancement effects were expounded in terms of the decrease of the acid strength and acid density in the 12MR channels of mordenite after introduction of Fe, resulting in the reduction of carbon deposition.

The hydrodeoxygenation (HDO) of various ketones (acetone, methyl ethyl ketone and cyclohexanone) to olefins via hydrogenation–dehydration was conducted in a fixed bed reactor at 373–573 K under H2. A ketone can be hydrogenated over the metal function to an alcohol intermediate that is subsequently dehydrated to an olefin over the acidic function. A preliminary study on hydrogenation of acetone to 2-propanol over metal/SiO2 catalysts (Cr, Fe, Co, Ni, Cu and Pd) shows that Ni and Cu are active at >373 K. Although Ni possesses an activity higher than that of Cu, it promotes olefin hydrogenation and alcohol hydrogenolysis at >473 K. Hydrogenolysis of alcohol intermediate is suppressed over the Ni–Cu alloy catalyst. An optimum conversion with 100% selectivity to alcohol, can be obtained at 448 and 473 K for Ni and Cu, respectively. The dehydration of 2-propanol to propylene over proton zeolites (ZSM-5, Y, Mordenite and β) can be achieved at >398 K. The zeolites with three-dimensional pore structure (β and Y) provide relatively higher activity (>90% conversion). However, a bimolecular dehydration to ether is also promoted. Only HZSM-5 shows excellent selectivity to propylene (98%). Hydrodeoxygenation of ketones was tested with (i) a double bed of 5%Ni/SiO2 and HZSM-5 (Si/Al ~ 13), (ii) a physical mixed bed of 5%Cu/SiO2 and HZSM-5 (Si/Al ~ 13) and (iii) a bi-functional catalyst of 5%Cu/HZSM-5 (Si/Al ~ 250). It was found that high alkene selectivity was readily obtained at 448 K. While, over the physical mixed bed and bi-functional catalyst, the hydrogenation activity was enhanced as the alcohol intermediate was removed from the system. The reactivity of the ketone depends on its adsorption on the metal surface and steric hindrance, i.e. acetone > cyclohexanone > methyl ethyl ketone.

The mechanism of stepwise mordenite recrystallization has been studied by a complex of physicochemical methods: multinuclear MAS NMR, X-ray diffraction (XRD), X-ray fluorescence (XRF), transmission electron microscopy (TEM), thermogravimetric analysis (TGA) and nitrogen adsorption–desorption. The recrystallization procedure included 4 steps: (1) treatment in alkali, (2) treatment in the presence of cetyltrimethylammonium bromide (CTAB) surfactant; (3) hydrothermal treatment and (4) hydrothermal treatment after pH adjustment to 8. Intermediate products were recovered during each reaction step and thoroughly investigated. The results pointed to the dissolution/re-assembling mechanism. The comparison with one-step recrystallization discussed previously suggests that the stepwise addition of NaOH and the surfactant does not affect significantly the recrystallization mechanism. In contrast, stepwise hydrothermal treatment with the intermediate pH regulation enhances the condensation of siliceous species formed during desilication, leads to their rearrangement into an ordered mesoporous phase and results in the product yields of 100%. Depending on the degree of zeolite dissolution and the extent of mesoporous phase overgrowth, two different types of materials were obtained: coated mesoporous zeolites and mesoporous materials containing small zeolitic fragments in the walls. It was shown that the latter could be obtained only using a stepwise procedure.

The illicit manufacture of drugs in the 21st century presents a danger to first responders, bystanders and the environment, making its detection important. Electronic noses based on metal oxide semiconducting (MOS) sensors present a potential technology to create devices for such purposes. An array of four thick film MOS gas sensors was fabricated, based on zinc oxide inks. Production took place using a commercially available screen printer, a 3 × 3 mm alumina substrate containing interdigitated electrodes and a platinum heater track. ZnO inks were modified using zeolite β, zeolite Y and mordenite admixtures. The sensors were exposed to four gases commonly found in the clandestine laboratory environment; these were nitrogen dioxide, ethanol, acetone and ammonia. Zeolite modification was found to increase the sensitivity of the sensor, compared to unmodified ZnO sensors, all of which showed strong responses to low ppm concentrations of acetone, ammonia and ethanol and to ppb concentrations of nitrogen dioxide. Machine learning techniques were incorporated to test the selectivity of the sensors. A high level of accuracy was achieved in determining the class of gas observed.

The morphology-controlled synthesis of mordenite (MOR) zeolites was achieved using the acidic hydrolysis route, which was started by acid-catalyzed hydrolysis of tetraethylorthosilicate (TEOS), followed by switching the synthetic gel to basic conditions for hydrothermal crystallization. The synthesis by using tetraethylammonium hydroxide as the template resulted in a series of large MOR crystals with different morphologies, such as bulky sphere, circular pie, flat prism, hexagonal star-like prism and ellipsoid. Moreover, column, elongated spindle, short spindle, petal and circular pie shaped MOR crystals could be obtained without using an organic template in the above synthetic route. Among these morphologies, the bulky sphere, hexagonal star-like prism and petal shaped crystals were generated on MOR zeolites for the first time. The obtained products were characterized by XRD, SEM and N2 adsorption experiments. Various synthetic parameters were systematically investigated, including hydrolysis conditions for TEOS, molar composition of the initial gel, crystallization time and temperature. The results demonstrated that MOR zeolites can be synthesized through the acidic hydrolysis route, and their morphology can be facilely controlled through tuning the elemental synthetic conditions.

Propofol (2,6-diisopropylphenol/DIPP) is the world's most widely used intravenous general anesthetic and is typically synthesized by isopropylation of phenol over an acid catalyst. It is highly difficult to stabilize bio-oil containing phenolic compounds. The isopropylation of this phenol (a model compound representing species in bio-oils) is one of the options to stabilize the bio-oil and convert it into valuable products. Probably for the first time, H-beta- and H-mordenite-catalysed vapour phase isopropylation of phenol with isopropyl alcohol (IPA) was studied to selectively synthesize DIPP. The optimization of various operating parameters such as molar ratio (phenol : IPA), weight hourly space velocity (WHSV), reaction temperature and time on stream were performed. H-beta (94% phenol conv. and 56% DIPP sel.) was found to be a potential and more active catalyst than H-mordenite (68% phenol conv. and 43% DIPP sel.) at optimized process parameters. A kinetic model is proposed to probe the intricate reaction kinetics and validated (R2 > 0.98) by the experimental results. H-beta catalyst was observed to be stable for more than 25 h with 94% phenol conversion and 56% selectivity towards DIPP at optimized process parameters. The phenol conversion and DIPP selectivity obtained in the present study are higher than those reported so far. The activation energy obtained for isopropylation of phenol with IPA over H-beta is calculated to be 25.39 kJ mol−1.

Rearrangement of cyclopropylcarbinyl bromide over proton and ammonium-exchanged mordenite (H-MOR and NH4-MOR) was studied at different temperatures. The product distribution analysis revealed a similar profile to what is found in solution, with prevalence of cyclobutyl over allylcarbinyl bromide. The activation parameters showed that compared with 80% aqueous ethanol solution, the zeolites present lower enthalpy of activation and higher entropy of activation, but yielding a significantly lower . The results may be explained in terms of the ability of zeolites to serve as solid solvents, providing a polar nanoenvironment for ionic reactions to occur.

Biotemplating with carbonized wood is a novel way of zeolite adsorbent and catalyst production, with uniform, hierarchically ordered macro- and micropore structure, having low diffusional resistances against mass transport of adsorptives, reactants and products around the zeolite crystallites. Pinewood (Picea abies) cubes of 1-cm size edges were carbonized at 700 °C in nitrogen flow. The obtained charcoal cubes contain parallel channels of 20–30 μm diameter, separated by about 1–3 μm thick carbon walls. The hydrophobic character of the channel walls was effectively reduced using oxidative treatment with nitric acid. Following saturation with zeolite synthesis solution the carbon cubes were exposed to hydrothermal conditions. Mordenite/carbon composite materials were formed where Na-mordenite microcrystals coated the walls of the carbon macropores. The thickness and density of the zeolite layer was controlled by varying the synthesis conditions. Owing to reduced diffusional resistance, the preparations are favourable adsorbents and catalysts.

The direct crystallization of high-silica mordenite (MOR) zeolite using both tetraethylammonium and fluoride ions was investigated by varying the primary variables of the hydrothermal synthesis such as Si∶Al and H2O∶SiO2 ratios in the starting synthesis mixture. Under well-optimized conditions, highly crystalline MOR zeolites with a Si∶Al ratio of approximately 25 were successfully prepared. From evaluation of the thermal stabilities of the MOR zeolites obtained, it was also found that there is a good relationship between the thermal stability and the bulk Si∶Al ratio of MOR zeolites and that any NaF remaining in the zeolite crystals considerably reduces the thermal stability.

The influences of aliphatic alcohols (ROH) on the synthesis of mordenite (MOR) type zeolite were investigated using a starting synthesis mixture with the chemical compositions (0–3 ROH∶0.035 Na2O∶0.005–0.01 Al2O3∶SiO2∶40 H2O). Highly crystalline single crystals of MOR were successfully synthesized using ethanol, 1-propanol and 1-butanol. Under well-optimized conditions, pure uniform and large single crystals up to ca. 50 μm in length were obtained. From sorption experiments of nitrogen, water, benzene and Se, it was found that the single large MOR obtained is not the large-port type MOR and that the effective sorption capacity is markedly influenced by the carbon chain length of aliphatic alcohol used in the crystallization.

An investigation was carried out to determine whether the adsorptive properties of zeolites could be used to separate nucleosides and nucleotides, more specifically adenosine, adenosine 5′-monophosphate (AMP) and adenosine 5′-triphosphate (ATP). Separation using the molecular sieving properties of the zeolites makes use of the difference in size of the nucleosides and nucleotides but more importantly the increasing polarity, adenosine being the least and ATP the most polar. Zeolites X, Y and mordenite were used to investigate the effect of pore size opening and Si/Al ratio on the sorption of the nucleosides and nucleotides. A range of cations of increasing charge density were ion exchanged into the channels of the zeolites to investigate the effect of modifying the electrostatic field within the zeolite. Quantitative analysis of the aqueous equimolar solutions of adenosine and AMP and adenosine and ATP after exposure to zeolites was by HPLC employing a mobile phase of 40% methanol–water. Equimolar solutions of AMP and ATP were analysed using a mobile phase consisting of 0.02 M KH2PO4/0.05 M tetrabutylammonium phosphate (pH=5)∶methanol in the ratio 70∶30.

A series of Y, Beta, mordenite and ZSM-5 zeolites containing different amounts of nanosized TiO2 clusters have been prepared by TiO2+ exchange followed by condensation. The presence of TiO2+ and its subsequent oligomerization can be followed in Raman spectroscopy by the appearance of the band at ca. 530 cm−1 and its replacement by others at 394, 460 and 637 nm. X-ray diffractograms of the solids show a considerable intensity decrease as the amount of TiO2 present increases. High-resolution transmission electron microscopy (HRTEM) shows that no isolated TiO2 particles are present in the case of zeolite Y, while the sample of mordenite at the highest Ti loading contains isolated TiO2 particles distinguishable by HRTEM. Diffuse reflectance UV-Vis spectroscopy indicates that the bandgap and the apparent extinction coefficient depend remarkably on the Ti content as well as on the zeolite crystal structure. Quantum chemical calculations at the semiempirical level also predict large variations in the HOMO–LUMO energies as a function of the number of Ti atoms. It has been found that the photoactivity of TiO2@Y and TiO2@mordenite is higher than that of commercial anatase for the photooxygenation of thianthrene to thianthrene oxide (λex>200 nm), but smaller for the hoseradish peroxidase photodeactivation in aqueous buffer (λex=350 nm). These variations in the photocatalytic activity of TiO2 illustrate the potential that inclusion of TiO2 nanoclusters within zeolites has to modulate its photoactivity.

The photoionization of N,N,N′,N′-tetramethyl-p-phenylenediamine (TMPD) and N,N,N′,N′-tetramethylbenzidine (TMB) in synthetic H-, Na- and Na,K-mordenite molecular sieves was examined at room temperature. It results in the formation of TMPD+ and TMB+ cation radicals, identified by EPR and diffuse reflectance spectroscopy. Alkali metal ion-exchanged mordenites assist in the formation and stabilization of TMPD+ and TMB+ cation radicals compared to H-mordenite. An electron hopping mechanism from TMPD/TMB to the mordenite surface mediated by alkali metal ions is suggested. The photoyield depends on the nature of the photoactive electron donor and the nature of the alkali metal.

The siting of Cu(II) in mordenite has been studied by ab initio calculations on large cluster models, representing the cation exchange sites in mordenite. Partial geometry optimizations, based on density functional theory (DFT), were performed to obtain the structure of the coordination environment of Cu(II) at the different sites. The ligand field spectra and EPR g-tensors of these clusters were then calculated by means of multiconfigurational perturbation theory (CASPT2). The calculated results were compared with experimental information, obtained by diffuse reflectance spectroscopy (DRS) and EPR. The calculations indicate that at low exchange levels Cu(II) is coordinated to oxygen six-rings in the main channel of mordenite, in the presence of two aluminiums. At higher loadings, six- or five-rings containing only one aluminium also become occupied, where Cu(II) is coordinated as a single ion, not as (Cu–OH)+. The calculations indicate also that in fully dehydrated mordenite, the twisted eight-ring (site A) is not occupied by Cu(II).

Upon polymerisation of acetylene and propyne inside the channels of Ni2+-exchanged mordenite and mesoporous MCM-41 spontaneous doping and formation of antiferromagnetic NiO clusters are observed to various extents. The population of polarons present in the final polymer/zeolite composite: (i) is higher for polyacetylene than for polypropyne; (ii) increases with polymerisation temperature in the range 100 to 335 °C; (iii) increases with the C content; and (iv) is higher for mordenite than for MCM-41 under the same conditions. The use of Ni(0),H+-mordenite for polymer formation enhances the polaron population of the resulting polymer by over one order of magnitude. Doped polyacetylene encapsulated in mordenite or MCM-41 was found to be persistent for periods of over three months after its preparation.

Liquid and solid state NMR studies of the nitration of toluene with a mixture of nitric acid and acetic anhydride have been performed in homogeneous solution and in a heterogeneous system using zeolite beta (small and large crystalline Al-beta with Si/Al = 13 and pure silicon beta), mordenite (Si/Al = 74 and 5) and ZSM-5 (Si/Al = 20) as catalysts. Acetyl nitrate proved to be the reactive species, although it decomposed slowly to tetranitromethane which was not active in the nitration. No NMR evidence for the presence of isolated nitronium ions, often thought to be the nitrating species, was found in the liquid phase. In the absence of acetic anhydride, nitric acid interacted strongly with the framework aluminium of the zeolite leading to a complex of one nitrate per aluminium. In contrast to free nitric acid, this species did not seem to take part in the nitration of toluene. Introduction of acetic anhydride converted the strongly bonded nitrate to the more reactive acetyl nitrate and acetic acid which were coordinated to the framework aluminium of the zeolite. Heterogeneous zeolite-catalysed nitration of toluene by acetyl nitrate improved the para- to ortho-nitrotoluene ratio compared to the homogeneous liquid phase nitration. The best para-selectivity was obtained with Al-beta and to a lesser extent with dealuminated mordenite, suggesting that the selectivity may be related to the presence of flexible lattice aluminium in these large pore zeolites.

ITQ-2 is a novel delaminated zeolite whose crystalline sheets (2.5 nm depth) define a large external surface (∽720 m2 g−1) having 12-membered ring (MR) open cups together with a reduced microporosity due to a 10 MR channel system. This feature is the reverse of that of classical zeolites (i.e., much larger internal area compared to the external surface). Herein, we have used tetrathiafulvalene and triphenylamine to probe the capability of layered ITQ-2 zeolite to generate persistent organic radical cations compared to conventional Y, mordenite and ZSM-5 zeolites as well as to Al/MCM-41 (3.2 nm diameter) and amorphous silica–alumina. By selective silylation of the external cups, it has been found that formation of a significant concentration of persistent organic radical cations in ITQ-2 is a property that occurs within the open cups of the external surface rather than inside the 10 MR pores.