ZnO Clusters Encapsulated inside Micropores of Zeolites Studied by UV Raman and Laser-Induced Luminescence Spectroscopies

ZnOx overlayer confined on ZnCr2O4 spinel for direct syngas conversion to light olefins

ZnCrOx oxides coupled with zeolites (OXZEO) allow direct conversion of syngas into light olefins, while active sites in the composite oxides remain elusive. Herein, we find that ZnO particles physically mixed with ZnCr2O4 spinel particles can be well dispersed onto the spinel surfaces by treatment in syngas and through a reduction-evaporation-anchoring mechanism, forming monodispersed ZnOx species with uniform thickness or dimension on ZnCr2O4 up to a dispersion threshold ZnO loading of 16.0 wt% (ZnCr2O4@ZnOx). A linear correlation between CO conversion and surface ZnO loading clearly confirms that the ZnOx overlayer on ZnCr2O4 acts as the active structure for the syngas conversion, which can efficiently activate both H2 and CO. The obtained ZnCr2O4@ZnOx catalyst combined with SAPO-34 zeolite achieves excellent catalytic performance with 64% CO conversion and 75% light olefins selectivity among all hydrocarbons. Moreover, the ZnOx overlayer is effectively anchored on the ZnCr2O4 spinel, which inhibits Zn loss during the reaction and demonstrates high stability over 100 hours. Thus, a significant interface confinement effect is present between the spinel surface and the ZnOx overlayer, which helps to stabilize ZnOx active structure and enhance the catalytic performance.

Role of Hydroxyl Groups in Zn-containing Nanosized MFI Zeolite for the Photocatalytic Oxidation of Methane

The effective conversion of methane to a mixture of more valuable hydrocarbons and hydrogen under mild conditions is a significant scientific and practical challenge. Here, we synthesized Zn-containing nanosized MFI zeolite for direct oxidation of methane in the presence of H2O and air. The presence of the surface hydroxyl groups on nanosized MFI-type zeolite and their significant reduction in the Zn-containing nanosized MFI zeolite were confirmed with Infrared Fourier Transform (FTIR) spectroscopy. Incorporation of zinc atoms into the framework of nanosized MFI zeolite is revealed by Nuclear Magnetic Resonance, X-ray Diffraction and UV-Vis Spectroscopy. Unexpectedly, pure silica MFI zeolite exhibited the highest photocatalytic performance. Our findings demonstrated that large number of isolated silanol groups and silanol nests increase the formation of ⋅OH, and enhance the productivity of oxygenate compounds and C2H6, while the Zn incorporated into the zeolite framework or attached to the silanol nests of the nanosized zeolites are less efficient. A mechanism of photocatalytic methane oxidation is proposed. These findings provide insights into the development of active nanosized zeolite photocatalysts with an extended amount of surface hydroxyl groups that can play a key role in photocatalytic methane conversion.

Combination of Hollow Capsule Structure and Zn Uniform Load for the Conversion of Methanol to Aromatics over Zn/ZSM-5 Zeolites

As an important nonoil route for acquiring aromatics, the highly efficient conversion of methanol to aromatics over Zn/ZSM-5 zeolites remains an ongoing challenge. In this work, we developed a uniform loading approach of zinc and further combined it with a hollow capsule structure to design the high-performance Zn/ZSM-5 catalyst. The electrostatic assembly among EDTA3-, n-butylamine+ and negative silica-alumina gel gave rise to an "Inorganic-Organic Hybrid Sphere" in form of Na(l+m+n+3x)-(y+z)·{[(SiO)4Al-]l/(SiO-)m(n-butylamine+)y(EDTA3-)x(n-butylamine+)z(SiO-)n, which further transformed into mesoporous aluminosilicates sphere (MASS) through calcination. The characteristic of abundant mesopore guaranteed MASS fantastic ability to evenly incorporate Zn ingredient inside, and the resultant Zn/MASS further served as a "hard template" for the direct synthesis of Hollow Zn/ZSM-5 capsules, rather than after impregnation. When tested in the methanol-to-aromatics (MTA) process, the direct synthesis method not only facilitated the homogeneous dispersion of the Zn ingredient, but also benefited for the generation of more (ZnOH)+ sites and strengthened their synergism with zeolite acid for the superior aromatics selectivity (50.63%). Meanwhile, the hollow capsule structure increased the contact time of MTA intermediate products with the Zn/ZSM-5 shell, and it increased the coke-admitting capacity and suppressed the coke rate, which maintained quite an excellent stability (131 h). Therefore, the above combination of hollow capsule structure and uniform load of Zn ingredient brings forward a wide prospect to develop zeolite materials with excellent properties in catalysis.

Zinc Oxide Nanoclusters Encapsulated in MFI Zeolite as a Highly Stable Adsorbent for the Ultradeep Removal of Hydrogen Sulfide

Often, trace impurities in a feed stream will cause failures in industrial applications. The efficient removal of such a trace impurity from industrial steams, however, is a daunting challenge due to the extremely small driving force for mass transfer. The issue lies in an activity-stability dilemma, that is, an ultrafine adsorbent that offers a high exposure of active sites is favorable for capturing species of a low concentration, but free-standing adsorptive species are susceptible to rapidly aggregating in working conditions, thus losing their intrinsic high activity. Confining ultrafine adsorbents in a porous matrix is a feasible solution to address this activity-stability dilemma. We herein demonstrate a proof of concept by encapsulating ZnO nanoclusters into a pure-silica MFI zeolite (ZnO@silicalite-1) for the ultradeep removal of H2S, a critical need in the purification of hydrogen for fuel cells. The Zn species and their interaction with silicalite-1 were thoroughly investigated by a collection of characterization techniques such as HADDF-STEM, UV-visible spectroscopy, DRIFTS, and 1H MAS NMR. The results show that the zeolite offers rich silanol defects, which enable the guest nanoclusters to be highly dispersed and anchored in the silicious matrix. The nanoclusters are present in two forms, Zn(OH)+ and ZnO, depending on the varying degrees of interaction with the silanol defects. The ultrafine nanoclusters exhibit an excellent desulfurization performance in terms of the adsorption rate and utilization. Furthermore, the ZnO@silicalite-1 adsorbents are remarkably stable against sintering at high temperatures, thus maintaining a high activity in multiple adsorption-regeneration cycles. The results demonstrate that the encapsulation of active metal oxide species into zeolite is a promising strategy to develop fast responsive and highly stable adsorbents for the ultradeep removal of trace impurities.

Antimicrobial and Virus Adsorption Properties of Y-Zeolite Exchanged with Silver and Zinc Cations

The antimicrobial activity of silver and zinc exchanged cations in Y-zeolite (Ag/CBV-600, Zn/CBV-600) is evaluated against Staphylococcus aureus (gram (+)) and Escherichia coli (gram (-)) bacteria along with their adsorption capacity for viruses: brome mosaic virus (BMV), cowpea chlorotic mottle virus (CCMV), and the bacteriophage MS2. The physicochemical properties of synthesized nanomaterials are characterized by inductively coupled plasma optical emission spectroscopy (ICP-OES), UV-Vis spectroscopy, X-ray diffraction (XRD), and scanning electron microscopy (SEM). According to the obtained results, the main species associated with the exchanged ions are Ag+ and Zn2+ cations with the concentration of around 1 atomic %. The incorporation of cations does not modify the Y-zeolite framework. The Ag/CBV-600 and Zn/CBV-600 materials show an inactivation of 90% for both gram (+) and gram (-) bacteria at 16 h at a relatively low concentration of nanomaterial (0.5 mg/mL). Moreover, the samples present good adsorption capacity for BMV, CCMV, and MS2 viruses showing adsorption higher than 40% after 2 h of interaction with the viruses. These prominent results allow the further usage of nanomaterials as an effective remedy to inhibit and reduce the spread of viruses such as SARS-CoV-2 or other gram (+) or gram (-) bacteria.

SAPO-34 and Zn/ZSM-5 synergistic catalysis of methanol to aromatics from light olefins

A schematic diagram of different methanol to aromatics reaction processes.

The migration of Zn species on Zn/ZSM-5 catalyst during the process of ethylene aromatization

The Zn species in the Zn/ZSM-5 catalyst undergo reciprocal transformation of ZnO clusters and ZnOH+ during the ethylene aromatization process. They then migrate to form large-grain ZnO on the outer surface, and finally lost as Zn vapor.

Boosting propane dehydroaromatization by confining PtZn alloy nanoparticles within H-ZSM-5 crystals

A Pt–Zn@H-ZSM-5 catalyst with Pt–Zn alloy nanoparticles confined in H-ZSM-5 crystals exhibits a significantly improved performance in the propane dehydroaromatization reaction.

Catalytic conversion of ethane to valuable products through non-oxidative dehydrogenation and dehydroaromatization

Chemical utilization of ethane to produce valuable chemicals has become especially attractive since the expanded utilization of shale gas in the United States and associated petroleum gas in the Middle East. Catalytic conversion to ethylene and aromatic hydrocarbons through non-oxidative dehydrogenation and dehydroaromatization of ethane (EDH and EDA) are potentially beneficial technologies because of their high selectivity to products. The former represents an attractive alternative to conventional thermal cracking of ethane. The latter can produce valuable aromatic hydrocarbons from a cheap feedstock. Nevertheless, further progress in catalytic science and technology is indispensable to implement these processes beneficially. This review summarizes progress that has been achieved with non-oxidative EDH and EDA in terms of the nature of active sites and reaction mechanisms. Briefly, platinum-, chromium- and gallium-based catalysts have been introduced mainly for EDH, including effects of carbon dioxide co-feeding. Efforts to use EDA have emphasized zinc-modified MFI zeolite catalysts. Finally, some avenues for development of catalytic science and technology for ethane conversion are summarized.

Ethane aromatization and evolution of carbon deposits over nanosized and microsized Zn/ZSM-5 catalysts

Nanosized Zn/HZSM-5 facilitated the faster escape of light aromatics from zeolite channels and exhibited higher product yield and improved stability.

Operando dual beam FTIR spectroscopy unravels the promotional effect of Zn on HZSM-5 in iso-butane aromatization

Experimental and theoretical results showed that there are special interactions between olefins (as intermediate precursors) and the Zn modified HZSM-5 zeolites, which were absent in the parent HZSM-5.

A highly active and stable Zn@C/HZSM-5 catalyst using Zn@C derived from ZIF-8 as a template for conversion of glycerol to aromatics

Zn@C/HZSM-5 showed excellent catalytic activity (54.7% aromatics yield) and high catalytic stability (8.5 h lifetime) due to the synergy between ZnOH⁺, intra-crystalline mesopores and HZSM-5 zeolite.

Silicalite-1 zeolite acidification by zinc modification and its catalytic properties for isobutane conversion

Silicalite-1 zeolite was successfully acidified by zinc modification, the prepared Znx/S-1 catalysts exhibited excellent catalytic performances in both isobutane dehydrogenation and butene isomerization reactions.

Highly active and stable Zn/ZSM-5 zeolite catalyst for the conversion of methanol to aromatics: effect of support morphology

The regulation of the morphology of HZSM-5 zeolite supports on the modification effect of zinc, as well as their subsequent catalytic performance for the methanol-to-aromatics (MTA) process were investigated.

Isobutane aromatization over a complete Lewis acid Zn/HZSM-5 zeolite catalyst: performance and mechanism

Operando DB-FTIR and DFT results certificate that the isobutane aromatization could be exclusively catalyzed by (Zn–O–Zn)²⁺ Lewis acid site over Zn/HZSM-5.

Mesoporous Silica Matrix as a Tool for Minimizing Dipolar Interactions in NiFe₂O₄ and ZnFe₂O₄ Nanoparticles

NiFe₂O₄ and ZnFe₂O₄ nanoparticles have been prepared encased in the MCM (Mobile Composition of Matter) type matrix. Their magnetic behavior has been studied and compared with that corresponding to particles of the same composition and of a similar size (prepared and embedded in amorphous silica or as bare particles). This study has allowed elucidation of the role exerted by the matrix and interparticle interactions in the magnetic behavior of each ferrite system. Thus, very different superparamagnetic behavior has been found in ferrite particles of similar size depending on the surrounding media. Also, the obtained results clearly provide evidence of the vastly different magnetic behavior for each ferrite system.

Selectivity Control in the Tandem Aromatization of Bio-Based Furanics Catalyzed by Solid Acids and Palladium

Bio-based furanics can be aromatized efficiently by sequential Diels-Alder (DA) addition and hydrogenation steps followed by tandem catalytic aromatization. With a combination of zeolite H-Y and Pd/C, the hydrogenated DA adduct of 2-methylfuran and maleic anhydride can thus be aromatized in the liquid phase and, to a certain extent, decarboxylated to give high yields of the aromatic products 3-methylphthalic anhydride and o- and m-toluic acid. Here, it is shown that a variation in the acidity and textural properties of the solid acid as well as bifunctionality offers a handle on selectivity toward aromatic products. The zeolite component was found to dominate selectivity. Indeed, a linear correlation is found between 3-methylphthalic anhydride yield and the product of (strong acid/total acidity) and mesopore volume of H-Y, highlighting the need for balanced catalyst acidity and porosity. The efficient coupling of the dehydration and dehydrogenation steps by varying the zeolite-to-Pd/C ratio allowed the competitive decarboxylation reaction to be effectively suppressed, which led to an improved 3-methylphthalic anhydride/total aromatics selectivity ratio of 80 % (89 % total aromatics yield). The incorporation of Pd nanoparticles in close proximity to the acid sites in bifunctional Pd/H-Y catalysts also afforded a flexible means to control aromatic products selectivity, as further demonstrated in the aromatization of hydrogenated DA adducts from other diene/dienophile combinations.

Impact of hierarchical pore structure on the catalytic performances of MFI zeolites modified by ZnO for the conversion of methanol to aromatics

The increase in the pore hierarchy of ZnO/hierarchical H-ZSM-5 catalysts increased the catalyst stability and the yield of aromatics, particularly BTX, from methanol.

Ethane and ethylene aromatization on zinc-containing zeolites

The importance of balance between the number of Zn and Brønsted acid sites for aromatization of ethane and ethylene on Zn-ZSM-5 is discussed.

Catalytic conversion of methanol to aromatics over nano-sized HZSM-5 zeolite modified by ZnSiF6·6H2O

ZnSiF₆-modified nano-sized HZSM-5 zeolites (NZ2, NZ3 and NZ4 catalysts) were prepared and investigated as catalysts for the conversion of methanol to aromatics.

Effect of zinc oxide amounts on the properties and antibacterial activities of zeolite/zinc oxide nanocomposite

Nanocomposites of zinc oxide loaded on a zeolite (Zeolite/ZnO NCs) were prepared using co-precipitation method. The ratio effect of ZnO wt.% to the Zeolite on the antibacterial activities was investigated. Various techniques were used for the nanocomposite characterization, including UV-vis, FTIR, XRD, EDX, FESEM and TEM. XRD patterns showed that ZnO peak intensity increased while the intensities of Zeolite peaks decreased. TEM images indicated a good distribution of ZnO-NPs onto the Zeolite framework and the cubic structure of the zeolite was maintained. The average particle size of ZnO-nanoparticles loaded on the surface of the Zeolite was in the range of 1-10nm. Moreover, Zeolite/ZnO NCs showed noticeable antibacterial activities against the tested bacteria; Gram- positive and Gram- negative bacteria, under normal light. The efficiency of the antibacterial increased with increasing the wt.% from 3 to 8 of ZnO NPs, and it reached 87% against Escherichia coli E266.

Mesoporous ZnZSM-5 zeolites synthesized by one-step desilication and reassembly: a durable catalyst for methanol aromatization

A mesoporous ZnZSM-5 zeolite synthesized by simple alkaline desilication and CTAB-mediated reassembly shows obviously improved catalytic stability for methanol aromatization.

The growth mode of ZnO on HZSM-5 substrates by atomic layer deposition and its catalytic property in the synthesis of aromatics from methanol

The resulting ZnO film on zeolites could effectively prevent exposing the HZSM-5 framework to steam during the reaction and regeneraton processes.