H-ZSM-5 zeolite model crystals: Structure-diffusion-activity relationship in methanol-to-olefins catalysis

Enhancing the Acidity Window of Zeolites by Low-Temperature Template Oxidation with Ozone

Revisiting the impact of the first and often deemed trivial postsynthetic step, i.e., a high-temperature oxidative calcination to remove organic templates, increases our understanding of thermal acid site evolution and Al distributions. An unprecedented degree of control over the acidity of high-silica zeolites (SSZ-13) was achieved by using a low-temperature ozonation approach. Fourier transform infrared spectroscopy of adsorbed probe molecules and solid-state NMR spectroscopy reveal the complexity of the thermal evolution of acid sites. Low-temperature activated (ozonated) zeolites maintain the original Brønsted acidity content and high defect content and have virtually no Lewis acidity. They also preserve the "as-made" Al distribution after crystallization and show a clear link between synthesis conditions and divalent cation capacity, as measured with aqueous cobalt ion uptake. The synthesis protocol is found to be the main contributor to Al proximity, yielding record high exchange capacity when ozonated. After conventional calcination at 500-600 °C, however, the presence of water leads to the gradual depletion of Brønsted acid sites, in particular, in small crystals. This work indicates that low-temperature ozonation followed by thermal activation at different temperatures can be used as a novel tool for tuning the amount and nature of acid sites, providing insights into the activity of zeolites in acid-catalyzed reactions, such as CO2 hydrogenation to dimethyl ether, and thereby expanding the possibilities of rational acidity tuning.

Influence of ZSM-5 Crystal Size on Methanol-to-Olefin (MTO) vs. Ethanol-to-Aromatics (ETA) Conversion

Crystal size is a key parameter of zeolites applied as catalysts. Herein, ZSM-5 crystals with similar physicochemical and acid properties, few defects, and aluminum exclusively in tetrahedral coordination are synthesized and the influence of the crystal size on the MTO and ETA conversion is investigated. Short olefins are the main products of the MTO conversion, whereas larger olefins and aromatics dominate the products after ETA conversion. In the case of both feeds, an increased crystal size decreases the catalyst's lifetime. The MTO conversion over larger ZSM-5 altered the product distribution, which was not the case for the ETA conversion. The reason is that the instantly available aromatics during ETA conversion lead to fast coking and zeolite crystals only active in the outer layers. Thus, the different reactivity of different-sized ZSM-5 is direct proof of a different conversion mechanism for both alcohols.

Investigation of ortho-positronium annihilation for porous materials with different geometries and topologies

In this work, we present the results of the ortho-positronium (o-Ps) annihilation lifetimes and nitrogen adsorption measurements for different porous materials and an approach for describing the annihilation of o-Ps in a pore, which results in a surface-volume formula (SVF) for calculating the pore-related o-Ps lifetime. This proposed formula gives the relationship between the o-Ps annihilation rate and the effective pore radius, bulk composition, and pore structure, including pore geometry and topology. The pore-related o-Ps lifetimes of different materials calculated by the SVF are consistent with experimental results for both micro- and mesopores (and macropores) with different geometries and topologies. The SVF is convenient for calculations of pore dimensions for many cases of metal organic frameworks and zeolites. This approach enables us to fully explain the temperature dependence of the o-Ps annihilation lifetime over a wide temperature range, 20-700 K.

Effect of ZSM-5 zeolite porosity on catalytic cracking of n-heptane

The selectivity of ethylene and propylene in cracking of n-heptane is connected to the micropore to mesopore ratioof ZSM-5 structure.

Local and Nanoscale Methanol Mobility in Different H-FER Catalysts

The dynamical behaviour of methanol confined in zeolite H-FER has been studied using quasielastic neutron scattering (QENS) and classical molecular dynamics (MD) simulations to investigate the effects of the Si/Al...

Molecular dynamic simulation studies of adsorption and diffusion behaviors of methanol and ethanol through ZSM-5 zeolite

Due to the importance of synthesis gas's entire conversion to methanol, the separation of methanol from unconverted synthesis gas is an industrial challenge. In this work, the influence of temperature, guest molecules concentrations (methanol and ethanol), and acid site density (Si/Al) of zeolites on the diffusion of methanol and ethanol, pure and binary mixture (80% methanol and 20% ethanol) in silicalite-1 and HZSM-5 (Si/Al = 47 and 23) were studied by using of the COMPASS force-field molecular dynamics method. Also, the adsorption of pure methanol and ethanol and binary mixture through these zeolites has been studied by using the Grand Canonical Monte Carlo (GCMC) method. The calculated adsorption rate and isosteric heat of adsorption for ethanol are lower and higher than methanol, respectively. The results of the binary mixture show that HZSM-5 (Si/Al = 23) has the lowest adsorption selectivity and most diffusion selectivity. The calculated diffusion coefficients of methanol and ethanol guest molecules decreased with rising guest molecule concentration and Si/Al-ratios. The effect of both agents was investigated by analysis of mean square displacement (MSD) and RDF diagram.

Computational elucidation of the aging time effect on zeolite synthesis selectivity in the presence of water and diquaternary ammonium iodide

An example of zeolite selectivity (MFI → MOR) driven by synthesis aging time has been studied. Using N,N,N',N'-tetramethyl-N,N'-dipropyl-ethylenediammonium diiodide (TMDP) as an organic structure-directing agent (OSDA), the zeolite phases obtained at 2 h (MFI 97%), 8 h (MFI 84%, MOR 16%) and 24 h (MFI 43%, MOR 57%) have been characterized by powder X-ray diffraction. The results suggest that at intermediate aging time, namely 8 h and 24 h, the dominant phase (MFI) is displaced by MOR. Different techniques (FT-IR, Raman, ¹³C MAS NMR, TGA/DTG and HC microanalysis) have been employed to verify the OSDA integrity and occlusion inside the zeolite micropores as well as to quantify the water and OSDA loading. The ¹H MAS NMR of the as-made occluded zeolite was compared with the spectra of TMDP and the recovered OSDA from the sample by extraction with water. The comparison indicated that TMDP was not structurally intact, indicating the chemical transformation of TMDP to imidazolinium homologues through the Hofmann degradation process. Furthermore, careful acidic breakdown of the aluminosilicate shell, covered on the zeolite samples by hydrofluoric acid, revealed that the remaining OSDA had been partially degraded to lower molecular weight ammonium salt, confirmed by ¹H NMR and mass spectrometry measurements. A computational study was performed by using a force field based methodology, including accurate loading of water and OSDA in the zeolite (MFI and MOR) unit cells. The results show an important contribution of the presence of water. The samples with larger aging time (8 h and 24 h) incorporate less water and show partial TMDP degradation, whilst at the shortest aging time (2 h), there is a larger water content and TMDP remains intact. The larger accessible volume of MFI justifies that this is the dominant phase at short aging times (large water content) since it can accommodate a larger number of water molecules than MOR. The OSDA partial degradation also plays a role. At longer aging times the partial OSDA decomposition has been considered in the models by including TMDP + Imidaz, which is more stabilized by MOR, whilst at shorter aging times the only OSDA present, TMDP, is better stabilized by MFI.

Superior ZSM-5@γ-Al2O3 Composite Catalyst for Methanol and Ethanol Coconversion to Light Olefins

This paper proposes a ZSM-5@γ-Al₂O₃ composite with a core-shell structure for the high-efficiency cocatalytic conversion of a methanol-ethanol system to light olefins. Using ZSM-5 and γ-Al₂O₃ as sole catalysts for comparison, the effects of physical blending, impregnation, and liquid-phase precipitation coating strategies on the catalytic performance and physicochemical properties of the composite catalysts were systematically investigated. The results indicated that the ZSM-5@γ-Al₂O₃ composite catalyst prepared by a liquid-phase precipitation coating exhibited excellent catalytic performance. When the ethanol content was 25 wt % and the reaction occurred at 350 °C, the conversion rates of methanol and ethanol were 96.1 and 99.9%, respectively; the selectivity and yield of light olefins reached 92.3 and 89.9%, respectively. The introduction of ethanol into methanol enhanced the selectivity of light olefins as target products. The interfacial composite phase formed by in situ nucleation growth of pseudoboehmite produced distinct Brønsted-Lewis acid synergistic active centers. It also increased the mesopore/micropore ratio in the composite catalyst.

Recent progress in the improvement of hydrothermal stability of zeolites

Zeolites have been successfully employed in many catalytic reactions of industrial relevance. The severe conditions required in some processes, where high temperatures are frequently combined with the presence of steam, highlight the need of considering the evolution of the catalyst structure during the reaction. This review attempts to summarize the recently developed strategies to improve the hydrothermal framework stability of zeolites.

Experimental and Theoretical Evidence for the Promotional Effect of Acid Sites on the Diffusion of Alkenes through Small-Pore Zeolites

The diffusion of saturated and unsaturated hydrocarbons is of fundamental importance for many zeolite‐catalyzed processes. Transport of small alkenes in the confined zeolite pores can become hindered, resulting in a significant impact on the ultimate product selectivity and separation. Herein, intracrystalline light olefin/paraffin diffusion through the 8‐ring windows of zeolite SAPO‐34 is characterized by a complementary set of first‐principle molecular dynamics simulations, PFG‐NMR experiments, and pulse‐response temporal analysis of products measurements, yielding information at different length and time scales. Our results clearly show a promotional effect of the presence of Brønsted acid sites on the diffusion rate of ethene and propene, whereas transport of alkanes is found to be insensitive to the presence of acid sites. The enhanced diffusivity of unsaturated hydrocarbons is ascribed to the formation of favorable π–H interactions with acid protons, as confirmed by IR spectroscopy measurements. The acid site distribution is proven to be an important design parameter for optimizing product distributions and separations.

Synergistic effect of Fe and Ga incorporation into ZSM-5 to increase propylene production in the cracking of n-hexane utilizing a microchannel reactor

Comprehensive investigation of the synergistic effect of incorporating Fe and Ga into ZSM-5 in cracking of hexane.

New insight into the inductive effect of various seeds on the template-free synthesis of ZSM-5 zeolite

This work enables us to obtain an improved understanding of the role of seeds in the template-free synthesis of zeolite.

Sustainable one-pot preparation of fully crystalline shaped zeolite catalysts

Fully crystalline shaped zeolite catalysts with MFI, MTT, and TON structures have been successfully prepared via a sustainable one-pot route.

Disentangling Reaction Processes of Zeolites within Single-Oriented Channels

Establishing structure-reactivity relationships for specific channel orientations of zeolites is vital to developing new, superior materials for various applications, including oil and gas conversion processes. Herein, a well-defined model system was developed to build structure-reactivity relationships for specific zeolite-channel orientations during various catalytic reaction processes, for example, the methanol- and ethanol-to-hydrocarbons (MTH and ETH) process as well as oligomerization reactions. The entrapped and effluent hydrocarbons from single-oriented zeolite ZSM-5 channels during the MTH process were monitored by using operando UV/Vis diffuse reflectance spectroscopy (DRS) and on-line mass spectrometry (MS), respectively. The results reveal that the straight channels favor the formation of internal coke, promoting the aromatic cycle. Furthermore, the sinusoidal channels produce aromatics, (e.g., toluene) that further grow into larger polyaromatics (e.g., graphitic coke) leading to deactivation of the zeolites. This underscores the importance of careful engineering of materials to suppress coke formation and tune product distribution by rational control of the location of zeolite acid sites and crystallographic orientations.

Structural/Texture Evolution During Facile Substitution of Ni into ZSM-5 Nanostructure vs. its Impregnation Dispersion Used in Selective Transformation of Methanol to Ethylene and Propylene

AIM AND OBJECTIVE

The effect of two different modification methods for introducing Ni into the ZSM-5 framework was investigated under high-temperature synthesis conditions. The nickel was successfully introduced into the MFI structures at different crystallization conditions to enhance the physicochemical properties and catalytic performance.

MATERIALS AND METHODS

A series of impregnated Ni/ZSM-5 and isomorphous substituted NiZSM- 5 nanostructure catalysts were prepared hydrothermally at different high temperatures and within short times. X-ray diffraction (XRD), Field emission scanning electron microscopy (FESEM), Energy dispersive X-ray (EDX), Brunner, Emmett and Teller-Barrett, Joyner and Halenda (BETBJH), Fourier transform infrared (FTIR) and Temperature-programmed desorption of ammonia (TPD-NH₃) were applied to investigate the physicochemical properties.

RESULTS

Although all the catalysts showed pure silica MFI-type nanosheets and coffin-like morphology, using the isomorphous substitution for Ni incorporation into the ZSM-5 framework led to the formation of materials with lower crystallinity, higher pore volume and stronger acidity compared to using impregnation method. Moreover, it was found that raising the hydrothermal temperature increased the crystallinity and enhanced the more uniform incorporation of Ni atoms in the crystalline structure of catalysts. TPD-NH₃ analysis demonstrated that high crystallization temperature and short crystallization time of NiZSM-5(350-0.5) resulted in fewer weak acid sites and medium acid strength. The MTO catalytic performance was tested in a fixed bed reactor at 460ºC and GHSV=10500 cm³/g_cat.h. A slightly different reaction pathway was proposed for the production of light olefins over impregnated Ni/ZSM-5 catalysts based on the role of NiO species. The enhanced methanol conversion for isomorphous substituted NiZSM-5 catalysts could be related to the most accessible active sites located inside the pores.

CONCLUSION

The impregnated Ni/ZSM-5 catalyst prepared at low hydrothermal temperature showed the best catalytic performance, while the isomorphous substituted NiZSM-5 prepared at high temperature was found to be the active molecular sieve regarding the stability performance.

Effects of Desilication in NaOH/Piperidine Medium and Phosphorus Modification on the Catalytic Activity of HZSM-5 Catalyst in Methanol to Propylene Conversion

BACKGROUND

Propylene is one of the main petrochemical building blocks applied as a feedstock for various chemical and polymer intermediates. The methanol-to-propylene (MTP) processes are reliable options for propylene production from non-petroleum resources. The highsilica ZSM-5 zeolite is found to be a reliable candidate for the methanol to propylene catalysis.

OBJECTIVE

In this study, the mesoporosity was first introduced into a high silica ZSM-5 zeolite via an alkaline treatment by NaOH solution with piperidine to decrease the diffusion limitation, and then the structure of zeolite was stabilized by phosphorus modification to improve the acidic properties and to enhance the catalyst stability.

METHODS

High-silica H-ZSM-5 catalysts (Si/Al = 200) were successfully prepared through microwave-assisted hydrothermal technique in the presence of tetrapropyl ammonium hydroxide (TPAOH) structure-directing agent. The mesoporosity was efficiently introduced into the ZSM-5 crystals via desilication derived from alkaline NaOH/piperidine solution. Then, the acidity of the desilicated ZSM-5 samples was improved using phosphorus modification. The catalysts were subjected to XRD, ICP-OES, FE-SEM, BET, TGA, FT-IR and NH₃-TPD analysis.

RESULTS

The catalytic performance of the prepared catalysts in the methanol to propylene (MTP) reaction was examined in a fixed-bed reactor at 475 °C, atmospheric pressure and methanol WHSV of 0.9 h^-1. The results showed that the alkaline treatment in NaOH/piperidine solution created uniform mesoporosity with no severe damage in the crystal structure. Similarly, phosphorus modification developed the acidic features and led to the optimal catalytic efficiency in terms of the maximum propylene selectivity (49.16%) and P/E ratio (5.97) as well as the catalyst lifetime.

CONCLUSION

The results showed an excellent catalytic activity in terms of 99.21% methanol conversion, good propylene selectivity up to 49.16%, a high ratio of P/E of 5.97 and a low selectivity to C5 + hydrocarbons of 11.57% for ZS-D-PI-P sample.

Lower olefins from methane: recent advances

Modern methods for methane conversion to lower olefins having from 2 to 4 carbon atoms per molecule are generalized. Multistage processing of methane into ethylene and propylene via syngas or methyl chloride and methods for direct conversion of CH4 to ethylene are described. Direct conversion of syngas to olefins as well as indirect routes of the process via methanol or dimethyl ether are considered. Particular attention is paid to innovative methods of olefin synthesis. Recent achievements in the design of catalysts and development of new techniques for efficient implementation of oxidative coupling of methane and methanol conversion to olefins are analyzed and systematized. Advances in commercializing these processes are pointed out. Novel catalysts for Fischer – Tropsch synthesis of lower olefins from syngas and for innovative technique using oxide – zeolite hybrid catalytic systems are described. The promise of a new route to lower olefins by methane conversion via dimethyl ether is shown. Prospects for the synthesis of lower olefins via methyl chloride and using non-oxidative coupling of methane are discussed. The most efficient processes used for processing of methane to lower olefins are compared on the basis of degree of conversion of carbonaceous feed, possibility to integrate with available full-scale production, number of reaction stages and thermal load distribution.

The bibliography includes 346 references.

Effects of crystal size on methanol to hydrocarbon conversion over single crystals of ZSM-5 studied by synchrotron infrared microspectroscopy

Operando synchrotron infrared microspectroscopy (OIMS) was used to study the conversion of methanol over coffin-shaped HZSM-5 crystals of different sizes: large (∼250 × 80 × 85 μm3), medium (∼160 × 60 × 60 μm3) and small (∼55 × 30 × 30 μm3). The induction period, for direct alkene formation by deprotonation of surface methoxy groups, was found to decrease with decreasing crystal size and with increasing reaction temperature. Experiments with a continuous flow of dimethylether showed that evolution of the hydrocarbon pool and indirect alkene formation is also strongly dependent on crystal size. These measurements suggest that the hydrocarbon pool formation and indirect alkene generation should be almost instantaneous at reaction temperatures used in practical catalysis with crystal sizes typically ∼1 μm3.

PFG-NMR as a Tool for Determining Self-Diffusivities of Various Probe Molecules through H-ZSM-5 Zeolites

The understanding of major zeolite applications is partially based on diffusion of molecules inside or outside microporous networks. However, it is still a challenge to measure such phenomena. The diffusion ordered nuclear magnetic resonance spectroscopy (DOSY) technique has been reported to measure a probe molecule's diffusion inside porous solids. Pulsed-field gradient (PFG)-NMR has been used herein to measure the self-diffusivity of different probe molecules, such as neopentane, benzene, toluene and 1-dodecene with increasing dynamic diameter, respectively, on a series of H-ZSM-5 zeolites. The latter materials exhibit different crystal sizes, Si/Al ratios and the presence (or absence) of crystalline defects. In addition, shaped zeolite bodies representing industrial catalysts were compared with the afore-mentioned samples.

Synthesis of ZSM-5 Zeolite Using Coal Fly Ash as an Additive for the Methanol to Propylene (MTP) Reaction

Using ZSM-5 zeolites as catalysts for the methanol to propylene (MTP) reaction is being widely investigated and has been industrially applied. In this study, pure ZSM-5 zeolite was successfully synthesized by a direct hydrothermal method using the fly ash of coal gasification as an additional raw material. Various analysis methods such as X-ray diffraction, N2 sorption, scanning electron microscopy, and infrared spectroscopy, were employed to characterize the physicochemical properties of parent and modified zeolites. Then, the prepared ZSM-5 catalysts were tested in the MTP reaction. The results showed that pure ZSM-5 could be directly synthesized in the optimized conditions using fly ash as additional silicon and aluminum sources, and those ZSM-5 catalysts turned out to be candidate catalysts for the MTP reaction. Whereas their catalytic lifetimes were not good enough due to the strong acid sites and needed improving.

Designing a Mesoporous Zeolite Catalyst for Products Optimizing in n-Decane Hydrocraking

Mesoporous ZSM-5 zeolite is developed to enhance the catalytic performance in a hydrocracking reaction. The generated mesopores and mesoporous channels in the new catalyst supply more opportunities for reactant accessing the active sites according to the better mass transfer and diffusion. Meanwhile, the acidity of the mesoporous catalyst is also weakened because of the removal of Si and Al species from its MFI structure, which makes the products distribution drift to more valued chemicals such as olefins. In the modified mesoporous ZSM-5 zeolites via different metallic promoters, the olefins’ selectivity increases as the alkalinity of the catalyst increases. The reason for this is that the formed olefins will be further hydrogenated into corresponding alkanes immediately over the extremely acidic zeolite catalyst. Hence, the moderate alkalinity will limit this process, while at the same time the remaining olefins products will too. Furthermore, the Pd-based mesoporous ZSM-5 zeolite shows an excellent n-decane conversion and high propane selectivity due to the occurrence of hydrogen spillover via the Pd promoter. The phenomenon of hydrogen spillover supplies more chemisorbed sites of hydrogen atoms for hydrocracking and hydrogenating in this reaction. In short, this study explores the important effect factors in n-decane hydrocracking reaction activity and products distribution. It also shows a potential for the further industrial application of petroleum-derived fuel hydrocracking according to the optimized products distribution under metallic promoted mesoporous zeolite.

Studying Proton Mobility in Zeolites by Varying Temperature Infrared Spectroscopy

We report a varying temperature infrared spectroscopic (VTIR) study with partial deuterium isotopic exchange as a method for characterizing proton mobility in acidic materials. This VTIR technique permits the estimation of activation energies for proton diffusion. Different acidic materials comprising classical proton-conducting materials, such as transition metal phosphates and sulfonated solids, as well as different zeolites, are tested with this new method. The applicability of the method is thus extended to a vast library of materials. Its underlying principles and assumptions are clearly presented herein. Depending on the temperature ranges, different activation energies for proton transfer are observed irrespective of the different materials. In addition to the well-studied transition metal phosphates, Si-rich zeolites appear to be promising proton-transfer materials (with E_act < 40 kJ mol⁻¹) for application in high-temperature (>150 °C) PEM fuel cells. They significantly outperform Nafion and sulfonated silica, which exhibit higher activation energies with E_act ~ 50 and 120 kJ mol⁻¹, respectively.

CO2 Adsorption Capacities in Zeolites and Layered Double Hydroxide Materials

The development of technologies that allow us to reduce CO₂ emissions is mandatory in today's society. In this regard, we present herein a comparative study of CO₂ adsorption over three types of materials: zeolites, layered double hydroxides (LDH), and zeolites coated LDH composites. The influence of the zeolite Si/Al ratio on zeolites sorption capacity along with the presence of mesopores was investigated. By comparing these results with the well-known performance of LDHs, we aim to provide insights on the factors that may influence the CO₂ capture capacity over zeolites, thus providing useful tools for tuning their properties upon post-treatments.

A Comparative Study of MFI Zeolite Derived from Different Silica Sources: Synthesis, Characterization and Catalytic Performance

In this paper, a comparative study of MFI zeolite derived from different silica sources is presented. Dry gel conversion (DGC) method is used to synthesize silicalite-1 and ZSM-5 with MFI structure. Two kinds of silica sources with different particle sizes are used during the synthesis of MFI zeolite. The as-prepared samples were characterized by X-ray diffraction (XRD), N2-sorption, Fourier transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM) and X-ray fluorescence spectrometer (XRF). From the characterization results, it could be seen that the high-quality coffin-like silicalite-1 was synthesized using silica sphere with particle size of 300 nm as silica source, with crystallization time being shortened to 2 h. The schematic diagram of silicalite-1 formation using silica sources with different particle sizes is summarized. ZSM-5 was obtained by adding Al atoms to raw materials during the synthesis of MFI zeolite. The performance of aqueous phase eugenol hydrodeoxygenation over Pd/C-ZSM-5 catalyst is evaluated.

Dense and thin 13X membranes on porous α-Al2O3 tubes: preparation, structure and deep purification of oxygenated compounds from gaseous olefin flow

The low contact efficiency, large mass transfer resistance and high operational cost of traditional 13X molecular sieve particle adsorbents (MSPs) have greatly limited their application in deep purification of trace oxygenated compounds from gaseous olefins. Herein, we successfully fabricated dense and thin 13X molecular sieve membranes on a porous α-Al₂O₃ tube (MSCMs) by a combination of 3-aminopropyl triethoxy silane (APTES) surface modification and vacuum pre-coating sol technology for purifying the above impurities. By a solid–solution transformation process, 13X molecular sieve membranes on MSCMs that were continuous and integral without any cracks, pinholes or other defects, and mainly composed of 1–1.5 μm regular 13X crystals with a thickness of 5–6 μm have been achieved. The purification performance of the MSPs, non-APTES functionalized MSCMs (nMSCMs) and MSCMs was evaluated by dynamic adsorption of N₂ or C₂H₄ feed flow containing dimethyl ether, methanol and propanal impurities at room temperature. The results demonstrated that both the nMSCMs and MSCMs could deeply purify the trace amounts of the three oxygenated compounds to below 1 × 10⁻⁶ (mol mol⁻¹) from gaseous olefins at an initial concentration of 20 × 10⁻⁶ (mol mol⁻¹), exhibiting much more excellent purification performance than that of MSPs. In particular, the breakthrough times of MSCMs for dimethyl ether, methanol and propanal were 7 h, 32 h and 51 h in a N₂ system, and 12.1 h, 53 h and 90 h in a C₂H₄ system. The cumulative adsorption amounts of MSCMs for dimethyl ether, methanol and propanal were 12.108 mg g⁻¹, 35.812 mg g⁻¹ and 103.129 mg g⁻¹ in a N₂ system, and 25.88 mg g⁻¹, 94.19 mg g⁻¹ and 256.26 mg g⁻¹ in a C₂H₄ system, respectively. The regeneration experiment also indicated that the MSCMs had a more stable structure and a longer lifetime. The excellent purification performance of MSCMs could be attributed to the continuous 13X molecular sieve layers without non-adsorption interfacial voids. Hence, the MSCMs have great potential for future industrial application of trace oxygenated compound removal from gaseous olefins.

Dense and thin 13X molecular sieve membranes on porous α-Al₂O₃ tubes were successfully fabricated by a combination of 3-aminopropyl triethoxy silane surface modification and vacuum pre-coating sol for purifying trace oxygenated compounds from gaseous olefins.

Probing Gas Adsorption in Zeolites by Variable-Temperature IR Spectroscopy: An Overview of Current Research

The current state of the art in the application of variable-temperature IR (VTIR) spectroscopy to the study of (i) adsorption sites in zeolites, including dual cation sites; (ii) the structure of adsorption complexes and (iii) gas-solid interaction energy is reviewed. The main focus is placed on the potential use of zeolites for gas separation, purification and transport, but possible extension to the field of heterogeneous catalysis is also envisaged. A critical comparison with classical IR spectroscopy and adsorption calorimetry shows that the main merits of VTIR spectroscopy are (i) its ability to provide simultaneously the spectroscopic signature of the adsorption complex and the standard enthalpy change involved in the adsorption process; and (ii) the enhanced potential of VTIR to be site specific in favorable cases.