Defective Zeolite Research Articles

Defective zeolite TS-1 confined Pt nanoclusters with superior performance for CO and soot catalytic oxidation

Catalytic oxidation is an important reaction in the treatment of diesel exhaust. Herein, a facile self-assembly strategy has been developed to synthesize defective zeolite confined-catalyst Pt@TS-1 with ultra-low Pt loading, which shows super catalytic activity in the CO conversion (T90 = 175 °C) and soot oxidation (T90 = 490 °C). Owing to the confinement effect of zeolite, the obtained catalyst Pt@TS-1 exhibits a high percentage of Pt2+, smaller Pt nanoparticles and sufficient Ti3+-VÖ defects, which can greatly accelerate the adsorption and conversion of CO, and the deep oxidation of soot. In-situ DRIFTS results demonstrate that rich and smaller Pt nanoparticles confined in zeolite may be responsible for excellent CO conversion. Significantly, the catalyst Pt@TS-1 also shows excellent catalytic stability and good resistance to water and sulfur, showing the potential for industrial applications.

Ag and TiO2 nanoparticles co-modified defective zeolite TS-1 for improved photocatalytic CO2 reduction

Photocatalytic CO2 reduction into fuels has been an attractive research topic. Herein, Ag and TiO2 nanoparticles co-loaded zeolite TS-1 (Ag–TiO2/TS-1) were synthesized by the ion-exchange and subsequently in-situ photodeposition method. The obtained Ag–TiO2/TS-1 sample has a high surface area and rich Ti3+-Vo defects and as well as highly dispersed Ag nanoparticles. As expected, the sample Ag–TiO2/TS-1 not only shows high CO2 adsorption capacity, but also improves the separation efficiency of photogenerated electron-hole pairs. As a result, only CO and CH4 can be detected on the sample Ag–TiO2/TS-1 in the photocatalytic CO2 conversion, and the competing H2 evolution can be completely suppressed, suggestive of its high selectivity. The super photocatalytic activity toward CO2 reduction can be ascribed to the synergistic effect among highly dispersed Ag nanoparticle, the support zeolite TS-1 and TiO2 with highly exposed {101} planes.

Effect of Zeolitic Hydroxyl Nests on the Acidity and Propane Aromatization Performance of Zinc Nitrate Impregnation-Modified HZSM-5 Zeolite

A defective HZSM-5 zeolite (SiO2/Al2O3 = 55, crystal size = 300 nm) with a high density of hydroxyl nests and its patched-up counterpart obtained by pretreating the defective zeolite with (NH4)2SiF...

Visible-light-driven zeolite imidazolate frameworks-8@ZnO composite for heavy metal treatment

Hexavalent chromium Cr(VI) is a well-known heavy metal widely existing in wastewater due to various anthropogenic activities. Cr(VI) ions are not biodegradable and tend to be toxic both in flora and fauna. Therefore, effective removal of Cr(VI) has become a very important procedure for treating Cr(VI)-containing wastewater. Here, we developed a facile strategy for constructing ZnO sheets with defective zeolite imidazolate frameworks-8 (ZIF-8) to form visible-light-driven ZIF-8@ZnO composite for efficient photoreduction of Cr(VI). It is widely accepted that both neat ZnO and ZIF-8 show no visible-light photocatalytic activity. However, our study demonstrates that a wide visible-light absorption band is observed in defective ZIF-8@ZnO after introducing self-defects in ZIF-8. Moreover, this strategy of visible-light Zn-based composite photocatalysts can also be used to design other photocatalytic materials for heavy metal treatment.

Design and Synthesis of Acid‐resistant Zeolite T/NaY Composite Membrane for Water/Ethanol Separation

The random distribution of zeolite T on the porous α‐Al2O3 tube during growth greatly limits its application in the industry. In this study, the defective zeolite T layer is modified with zeolite NaY. A continuous and dense zeolite T/NaY composite membrane is obtained through characterization by scanning electron microscope and X‐ray diffraction. The resulting composite membrane exhibits high selectivity and high permeation flux for 90 wt % ethanol/water solution at 75 °C. Water concentration in the permeation side of the as‐synthesized zeolite T/NaY composite membrane is >99.9 wt %, whereas that of primary zeolite T layer is only 60.4 wt %. The water permeation flux of the composite membrane reaches 4.35 kg/m2/h1. The composite membrane displays good stability in acid solution when the pH of the solution is >5.

Platinum nanoparticles entrapped in zeolite nanoshells as active and sintering-resistant arene hydrogenation catalysts

Pt nanoparticles supported on ZSM-5 nanoshells have been prepared by a mild desilication method. The zeolite support is a ZSM-5 crystal with extremely thin walls (ca. 15nm) that contain meso/microporous defects. The 2–3nm diameter Pt nanoparticles are entrapped and highly dispersed in these ZSM-5 nanoshells. The particles are stable up to 750°C in H2 owing to this immobilization. Catalytic activities for toluene hydrogenation were compared with those of reference Pt-based catalysts. The reaction rates obtained on the novel Pt-ZSM-5 nanoshells catalyst were about 100 times higher than those measured over conventional Pt-ZSM-5 catalysts. The highly defective zeolite nanoshell allowed even bulky molecules such as mesitylene to access all the Pt particles. This was in contrast to Pt nanoparticles encapsulated in ZSM-5 hollow single crystals, which were totally inactive due to molecular sieving. This novel Pt-ZSM-5 nanoshell catalyst shows outstanding sintering-resistance and mass transfer properties owing to its hierarchical design.

Factors that Determine Zeolite Stability in Hot Liquid Water.

The susceptibility of zeolites to hot liquid water may hamper their full utilization in aqueous phase processes, such as those involved in biomass conversion and upgrading reactions. Interactions of zeolites with water strongly depend on the presence of hydrophilic moieties including Brønsted acid sites (BAS), extraframework cations, and silanol defects, which facilitate wetting of the surface. However, it is not clear which of these moieties are responsible for the susceptibility of zeolites to liquid water. Previous studies have offered contradictory explanations because the role of each of these characteristics has not been investigated independently. In this work, a systematic comparison has been attempted by relating crystallinity losses to the variation of each of the five zeolite characteristics that may influence their stability in liquid water, including number of BAS, Si-O-Si bonds, framework type, silanol defects, and extraframework Al. In this study, we have systematically monitored the crystallinity changes of a series of HY, H-ZSM-5, and H-β zeolite samples with varying Si/Al ratio, density of BAS, zeolite structure, and density of silanol defects upon exposure to liquid water at 200 °C. The results of this comparison unambiguously indicate that the density of silanol defects plays the most crucial role in determining susceptibility of zeolites to hot liquid water. By functionalizing the silanol defects with organosilanes, the hydrophobicity of defective zeolite is increased and the tolerance to hot liquid water is significantly enhanced.

Isotherms of Fluids in Native and Defective Zeolite and Alumino-Phosphate Crystals: Monte-Carlo Simulations with “On-the-Fly”ab initioElectrostatic Potential

We use periodic Density Functional Theory (DFT) method to generate the electrostatic potentials of adsorption materials and use them in Grand Canonical Monte Carlo simulations of fluid adsorption isotherms. This permits us to consider complex solids showing defects and without a priori knowledge of their electrostatic parameters for the Monte Carlo simulations. We apply the method to aluminophosphate and silicate solids of ZON type and evaluate their affinity to adsorb and separate CO2 -N2 (H2 O) mixtures.

Confined Water Dissociation in Microporous Defective Silicates: Mechanism, Dipole Distribution, and Impact on Substrate Properties

Interest in microporous materials has risen in recent years, as they offer a confined environment that is optimal to enhance chemical reactions. Calcium silicate hydrate (C-S-H) gel, the main component of cement, presents a layered structure with sub-nanometer-size disordered pores filled with water and cations. The size of the pores and the hydrophilicity of the environment make C-S-H gel an excellent system to study the possibility of confined water reactions. To investigate it, we have performed molecular dynamics simulations using the ReaxFF force field. The results show that water does dissociate to form hydroxyl groups. We have analyzed the water dissociation mechanism, as well as the changes in the structure and water affinity of the C-S-H matrix and water polarization, comparing the results with the behavior of water in a defective zeolite. Finally, we establish a relationship between water dissociation in C-S-H gel and the increase of hardness due to a transformation from a two- to a three-dimensional structure.