Microporous and Mesoporous Materials最新文献

The bimetallic Ni(Zn)-MOF-74 nanoparticles were fabricated by the metal substitution method and doped into a polyether-polyamide block copolymer (Pebax 1657) matrix to obtain mixed matrix membrane (MMM) for CO₂/CH₄ separation. The pore structure and chemical properties of Ni(Zn)-MOF-74 nanoparticles were controlled by changing the molar ratio of Ni/Zn, and the effect of heterometallic on the gas separation performance of MMMs was studied. In particular, when the molar ratio of Ni/Zn was 2:1, the Pebax/Ni(Zn)-MOF-74-21 MMMs has the optimal CO₂ separation performance. The main reason was that Ni(Zn)-MOF-74-21 has the smallest pore size (0.68 nm) and abundant CO₂ adsorption sites, which could effectively prevent the entry of CH₄ molecules after preferentially adsorbing one or two CO₂ molecules, and improve the selectivity of CO₂/CH₄ molecules. Furthermore, the unreplaced pore size of 1.48 nm and the increased polymer chain spacing in Ni(Zn)-MOF-74-21 nanoparticles could provide a fast transport channel for CO₂ and improve the permeability of MMMs. The developed Pebax/Ni(Zn)-MOF-74-21 MMMs loaded with 2 wt% filler displayed a CO₂/CH₄ selectivity of 33.7 and a high CO₂ permeability of 719.9 barrer, exceeding the gas separation performance of many previously reported MOF-74-based MMMs. The results showed that the development and design of bimetallic organic framework was an important way to obtain high performance MOF-74-based MMM.

A synthetic approach to production of monolithic (NH₄)₃H(Ge₇O₁₆)(H₂O)_x and (NH₄)₂Ge₇O₁₅ aerogels is developed. Production of the aerogels with the germanate zeolite-like structure is reported for the first time. Thermal decomposition of (NH₄)₂Ge₇O₁₅ leads to formation of GeO₂ aerogel, which has been obtained before using much more complex and expensive process of alkoxide hydrolysis. The suggested synthetic route might be used for production of novel luminescent, catalytic and anode materials. Luminescent properties of all obtained aerogels revealed excitation dependence. Based on excitation wavelengths it could exhibit blue, yellow-green and red luminescence. Luminescent properties for (NH₄)₃H(Ge₇O₁₆) (H₂O)_x and (NH₄)₂Ge₇O₁₅ are reported for the first time.

Sn-based zeolite have been prepared by incipient wetness impregnation by studying the role of the starting precursor either Sn(II) or Sn(IV) chlorides. Catalysts have been deeply characterized through XRD, FT-IR, UV–vis-NIR, SEM-EDXS, FE-SEM-EDXS, and IR of probe molecules i.e., pyridine and CO, by also investigating the reaction at the surface in static conditions. As well catalytic activity has been carried out by investigating the role of GHSV that has been varied between 2700 and 8500 h⁻¹, obtaining linear variation of product distribution as a function of contact time. Small amounts of Sn improve the catalytic activity of H-ZSM-5 zeolite in converting ethanol to higher hydrocarbons. In particular, the addition of Sn⁴⁺ ions increases the conversion of ethanol to C₆–C₈ aromatic hydrocarbons up to a very interesting 34 % selectivity at 100 % ethanol conversion. In fact, bioethanol conversion over Sn–H-ZSM-5 zeolite represents a potentially interesting way to produce a high-octane biogasoline, as well as aromatic (BTX) cut useful as a renewable intermediate in future biorefinery-derived processes. It is proposed that ethylene, the main product, is the key intermediate in the acid-catalyzed route, and Sn-ions are favoring the cyclization and dehydrogenation of ethylene-derived oligomers.

The mobility of the pentane isomers in the hydroxylated UiO-66 metal-organic framework has been characterized. ²H NMR spectroscopy was applied to measure the jump rate of alkanes guest molecules between adjacent cages and estimate the diffusivity. It is inferred that the difference in diffusion coefficients defines the kinetic separation selectivity, which is higher for the linear alkanes. The adsorption of pentane isomers in UiO-66 has been modeled with molecular dynamics (MD) simulation. The adsorbed quantity of isopentane is higher than that for n-pentane, providing the possibility of separation with selectivity α ≈ 8 in stationary conditions. The impact of the UiO-66 MOF hydroxylation state on the mobility of pentane isomers has been characterized by comparison with results obtained for the dehydroxylated UiO-66 material. The hydroxylated state of UiO-66 MOF has 6-time higher separation selectivity for pentane isomers compared to its dehydroxylated state (α_hyd ≈ 76). MD calculations show that hydroxylated UiO-66 MOF is more efficient, as the separation selectivity is 4 times lower in the dehydroxylated material. The UiO-66 hydroxylation effect is compared for the mobility of C₄ and C₅ alkanes. The optimal conditions for C₄/C₅ alkanes kinetic separation by UiO-66 MOF are established.

Nanospherical mesoporous AlMCM-41 (SAM-41) was prepared by a one-step method and employed as a support to prepare NiMo catalysts for hydrodesulfurization (HDS) of 4,6-dimethyldibenzothiophene. Characterization revealed that SAM-41 demonstrated a size of around 70 nm and possessed a higher content of framework Al compared to the reference supports. The aggregation of active metals on SAM-41 was mitigated, promoting the dispersion and sulfidation of the metals. Consequently, a large number of highly dispersed type II NiMoS phases with shorter slab lengths and lower layers were easily generated on NiMo/SAM-41, providing a wide distribution of active sites and ensuring effective HDS reactions. Additionally, NiMo/SAM-41 possesses easily accessible active sites and well mass transfer. Therefore, NiMo/SAM-41 exhibited superior catalytic activity for 4,6-dimethyldibenzothiophene HDS, with a 96.5 % conversion. Besides, NiMo/SAM-41 displayed the high reusability. Furthermore, NiMo/SAM-41 showed the highest direct desulfurization selectivity due to the highest proportion of Brønsted acid and corner sites.

A novel process for coating spherical silica cores with a thick, mesoporous shell to obtain core-shell type mesoporous silica particles (C-MSPs) was developed. The solution pH during the sol-gel reaction in the presence of cetyltrimethylammonium bromide (CTAB), which was used for micelle templates, was measured to model the concentrations of ionic species. Silicate ions were of particular interest because their concentration rapidly increased by the hydrolysis of tetraethyl orthosilicate (TEOS) at high concentrations. The silicate ions present in the reaction mixture were determined by rate equations for the hydrolysis of TEOS and the condensation of silica. Estimating the ionic strength based on the modeled concentrations of ionic species in the solution allowed us to design an appropriate process of coating particles with a mesoporous silica shell. Mesoporous shells were effectively thickened by the continuous addition of TEOS at controlled feeding rates, where the concentration of silicate ions was kept lower than the solubility of silica, which helped suppressing the generation of secondary particles (by-products). Micron-sized C-MSPs with a mesoporous shell around a submicron-sized silica core were successfully obtained by the co-addition of TEOS and CTAB. An approximately 400 nm thick mesoporous shell with a porosity similar to that of conventional thin shells was formed onto 460 nm spherical cores. The concept of controlling the ionic strength of the reaction solution can also be applied to other cores, which offers a practical approach to synthesize core-shell type mesoporous particles required in various future applications.

The environmentally-friendly preparation of high performance catalytic dodecahydro-N-ethylcarbazole (12H-NEC) dehydrogenation catalysts is consistent with green chemistry. Beta zeolite loaded ultrafine palladium nanocatalysts (Pd/Beta) were fabricated by ultrasound in-situ reduction (USR) in the absence of chemical reducing and stabilizing agents, and used to efficiently catalyze 12H-NEC dehydrogenation. The catalysts were characterized by XPS, XRD, TEM, SEM and FT-IR, which revealed that Pd nanoparticles (NPs) were highly dispersed on the surface of Beta zeolite with an average particle size of 1.84 nm. The USR method facilitated the metal-carrier interaction, which led to better catalytic activity and stability for dehydrogenation of 12H-NEC, the efficiency of dehydrogenation was 100 % at 6 h and the TOF achieved 70.44 min⁻¹, when it still reached 94 % after 7 cycles.

Enhancing the selectivity of noble metal containing heterogeneous catalysts in the nitro group hydrogenation of functionalized nitroarenes is challenging due to high dependence of selectivity on the catalyst structure. Most reports focus on the influence of metal nanoparticles (NPs) size, confinement, and support-metal interactions, while the effect of support polarity remains unclear. Herein we investigate, for the first time, the influence of support polarity on the selective hydrogenation of NO₂ in 3-nitrostyrene over Pt-based heterogeneous catalysts and compare it to the effects of Pt NPs size and location. To achieve this, we confined Pt NPs in the channels of the nonpolar Silicalite-1 (S-1) and benchmarked against catalysts with NPs of various sizes supported on polar SiO₂ and nonpolar S-1.

We demonstrate that support polarity is the key factor determining selectivity, surpassing the roles of Pt particle size and confinement. Catalysts with the nonpolar Silicalite-1 support exhibit higher NO₂ selectivity compared to SiO₂-based ones, with a threefold increase observed for Pt@S–S-1 compared to a commercial Pt/SiO₂. DRIFT spectroscopy-monitored adsorption experiments and hydrogenation experiments of nitrobenzene and styrene model molecules show that the S-1 support favors the adsorption of –NO₂ and the –NH₂ formed during the reaction, impeding C=C hydrogenation. To a lower extent, the size of Pt NPs contributed to the obtained results with decreased C=C hydrogenation observed over smaller Pt NPs. Finally, confining Pt in the zeolite restricts the NPs growth during catalyst activation, resulting in a further decrease of particles size and C=C hydrogenation activity.

During the methylcyclohexane (MCH)-toluene interconversion over a Pt/Al₂O₃ catalyst, a part of MCH is isomerized to undesirable five-membered ring compounds, which accumulate as impurities and lower the energy efficiency of the liquid organic hydrogen carrier system. In this study, we focused on the shape selectivity of zeolite materials to improve the selectivity for the hydrogenolysis of methylcyclopentane (MCP) and chose Si-ITQ-1 zeolite (MWW topology) with 10-ring micropores. The hydrothermal synthesis of an ITQ-1 zeolitic precursor (ITQ-1P) with a relatively high Ir content inside the micropores was possible when using N,N,N-trimethyl-1-adamantammonium and hexamethyleneimine as organic structure-directing agents (OSDAs). A direct H₂ treatment at 400 °C promoted the reduction of cationic Ir to highly dispersed Ir⁰ clusters (ca. 0.9 nm), followed by the removal of OSDAs inside the micropores via catalytic hydrogenolysis by Ir⁰ species. The Ir/ITQ-1 catalyst showed high activity and selectivity for the hydrogenolysis of MCP in the presence of excess MCH at 200 °C.

High-temperature thermal exfoliation is a simple, rapid, and cost-efficient method for transforming graphene oxide (GO) materials into reduced graphene oxide (rGO) materials. In this study, GO materials were dispersed with alkali metal nitrates (MNO₃), leading to the preparation of porous rGO materials characterized by high specific surface area (SSA) and pore volume via high-temperature thermal exfoliation. Experimental data indicate that the metal cations of MNO₃ tend to react directly with the oxygen functional groups (OFG) of GO, modulating the OFG content. Simultaneously, nitrate anions have preferential interaction with alkali metal ions and adhere to the surface of the GO. The presence of MNO₃ on the surface of GO facilitates the thermal exfoliation process and leads to the formation of structures with an extremely high proportion of mesoporous content. The isothermal gas adsorption results show that the exfoliation efficiency of the samples activated with different nitrate salts decreases in the order rGO-KNO₃ > rGO-NaNO₃ > rGO-LiNO₃. Among these samples, rGO modified with KNO₃ exhibited the greatest exfoliation efficiency, with a mesopore-to-micropore volume ratio of 22.4, more than 1.7 times that of rGO. Its SSA and pore volume were 359 m² g⁻¹ and 1.26 cm³ g⁻¹, respectively. These values significantly surpass those of rGO. Our research findings demonstrate that activation with MNO₃ significantly increases the SSA and pore volume of the GO material after high-temperature annealing.