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• Organic-solvent ditch forms at the RPLC interface due to the hydrophobic effect. • The ditch carries excess of organic solvent compared with bulk mobile phase. • Ditch overlap is studied by molecular dynamics simulations in cylindrical mesopores. • Acetonitrile ditch overlap sets in at larger pore size than methanol ditch overlap. • Ditch has an impact on local and pore-averaged solvent composition and mobility. Mass transport through the mesopore space of a reversed-phase liquid chromatography (RPLC) column depends on the properties of the chromatographic interface, particularly on the extent of the organic-solvent ditch that favors the analyte surface diffusivity. Through molecular dynamics simulations in cylindrical RPLC mesopore models with pore diameters between 6 and 12 nm we systematically trace the evolution of organic-solvent ditch overlap due to spatial confinement in the mesopore space of RPLC columns for small-molecule separations. Each pore model of a silica-based, endcapped, C 18 -stationary phase is equilibrated with two mobile phases of comparable elution strength, namely 70/30 (v/v) water/acetonitrile and 60/40 (v/v) water/methanol, to consider the influence of the mobile-phase composition on the onset of organic-solvent ditch overlap. The simulations show that, as the pore diameter decreases from 9 to 6 nm, the bonded-phase density extends and compacts towards the pore center, which leads to increased accumulation of organic-solvent excess and thus enhanced organic-solvent diffusivity in the ditch. Because the acetonitrile ditch is more pronounced than the methanol ditch, acetonitrile ditch overlap sets in at less severe spatial confinement than methanol ditch overlap. The pore-averaged methanol and acetonitrile diffusivities are considerably raised by ditch overlap in the 6 nm-diameter pore, but also benefit from the ditch (without overlap) in the 7 to 12 nm-diameter pores, whereby local and pore-averaged effects are generally larger for acetonitrile than methanol. [ABSTRACT FROM AUTHOR]

[Display omitted] • Hierarchical ZSM-5/MCM-41 composites with different mesopore sizes were successfully fabricated. • Adsorption capacity of ethyl acetate was significantly enhanced via the introduction of mesopore. • Moderate mesopore was more conductive to desorption and intraparticle diffusion of ethyl acetate. A series of micro-mesoporous structure ZSM-5/MCM-41 composites with different mesopore sizes were successfully fabricated through surfactant-mediated recrystallization method using the template agents with different alkyl chain length. Mesopore pore sizes were tuned from 2.11 nm to 5.09 nm. Taking ethyl acetate as the VOC probe molecule, the adsorption and desorption properties were evaluated by the dynamic adsorption breakthrough curves and TPD experiments. Results showed that the adsorption capacity was enhanced under dry and humid condition owing to the introduction of mesopore size structure. Especially for ZSM-5/MCM-41 (C12), its adsorption capacity reached up to 208.92 mg·g−1 and 82.29 mg·g−1 at dry and saturated humidity (4 v/v% H 2 O). Simultaneously, the hierarchical molecular sieves exhibited an excellent regeneration performance. Even after the fifth cycle, above 86% adsorption capacity remained under humid condition. Moreover, the adsorption kinetics of ethyl acetate on ZSM-5/MCM-41 composites followed the Bangham model. The results indicated that hierarchical composite molecular sieve can be considered as a potential adsorbent for VOCs removal. [ABSTRACT FROM AUTHOR]

A lithium-ion capacitor (LIC) is a device with the dual characteristics of lithium-ion batteries (LIBs) and supercapacitors (SCs), but there is a serious dynamic imbalance between the positive and negative materials. Here, in the research work, γ-Mo2N nanobelts with different grain sizes and mesopore sizes have been prepared to study deeply the electrode dynamics. The results reveal that the reduction of the grain size and mesopore size will lead to a sharp increase in capacitance contribution, excellent rate performance, and structural stability. This is attributed to that the reduction of the grain/mesopore size will promote the oxidation–reduction reaction of the electrode material. Considering this advantage, a high-performance LIC is constructed with a γ-Mo2N-700 anode and a hierarchical porous activated carbon (AC) cathode. This device can achieve the highest energy density of 93.81 Wh kg–1 and a power density of 7513.68 W kg–1, and the excellent specific capacity of up to 87.16% is maintained after 1000 cycles. This work mainly introduces the two parameters of grain size and mesopore size to explore the structure–activity relationship that affects the performance of LIC anode materials, which provides an analysis method for the difference in lithium storage performance. [ABSTRACT FROM AUTHOR]

[Display omitted] • ZSM-5 zeolites with similar acidity but different mesoporosity and mesoporous sizes can be synthesized. • Increased zeolitic mesoporosity can improve stability of iron-based/ZSM-5 catalyst by inhibiting coke. • Decreased zeolitic mesoporous size can increase the aromatics selectivity and light aromatics fraction. The utilization of iron-based/ZSM-5 bifunctional catalysts for converting syngas to aromatics (STA) has garnered significant interest because of its cost-effectiveness. This study aims to elucidate the regulatory mechanism of zeolitic pore structure on the performance of the bifunctional catalyst in STA reaction. The relationship among the mesoporosity and mesoporous diameter of hierarchical ZSM-5 zeolite component, product distribution, and catalyst stability is investigated through a range of analyses techniques, including XRD, SEM, TG, Raman, N 2 -adsorption and desorption. The results demonstrate that as the mesoporosity of zeolite increased to 78.9%, the lifetime of the iron-based/ZSM-5 bifunctional catalyst extended beyond 96 h and maintained the aromatics selectivity over 40% at 2 MPa, 320 °C, and 3000 h−1. This outcome can be attributed to the role of high mesoporosity in restraining coke formation in zeolites. Moreover, the reduction in mesopore size from 11.1 to 5.8 nm results in an increased aromatics selectivity from 39.6% to 43.4%, and the fraction of light aromatics rose from 48.8% to 54.5%, indicating that small mesopore size can also expedite the production of aromatics, particularly light aromatics. It is thus concluded that the improvement of aromatics selectivity and stability of iron-based/ZSM-5 bifunctional catalysts in STA reaction can be achieved by increasing the mesoporosity and decreasing the mesopore size of the zeolite component. [ABSTRACT FROM AUTHOR]

Tunable mesoporous silica films were prepared though a sol-gel process directed by the self-assembly of various triblock copolymers. Positron annihilation γ-ray energy spectroscopy and positron annihilation lifetime spectroscopy (PALS) based on intense pulsed slow positron beams as well as ellipsometric porosimetry (EP) combined with heptane adsorption were utilized to characterize the open porosity/interconnectivity and pore size distribution for the prepared films. The consistency between the open porosities was examined by the variations of orthopositronium (o-Ps) 3γ annihilation fractions and the total adsorbed volumes of heptane. The average pore sizes deduced by PALS from the longest-lived o-Ps lifetimes are in good agreement with those by EP on the basis of the Barrett–Joyner–Halenda model, as indicated by a well fitted line of slope k = 1. The results indicate that the EP combined with heptane adsorption is a useful method with high sensitivity for calibrating the mesopore size in highly interconnected mesoporous films, whereas PALS is a novel, complementary tool for characterizing both closed and open pores in them.

MY-x series zeolites with different mesopore diameters were successfully synthesized via a hydrothermal synthesis procedure and the corresponding NiMo/HMY-x series hydrodesulfurization(HDS) catalysts were prepared via incipient co-impregnation method. The synthesized samples were characterized by both wide and small angle XRD, N 2 adsorption-desorption isotherms, pyridine adsorbed FTIR (Py-FTIR), 27 Al MAS NMR, H 2 -TPR, HRTEM and XPS. The results show that the synthesized samples exhibit wide opened mesopores of varying sizes with well crystallized pore walls. The introduction of mesopores caused a slight decline in the interaction between active metals and support (MSI) in the corresponding catalysts, generating higher stacking numbers and a shorter slab lengths among MoS 2 crystals on the corresponding catalyst and favoring both the dispersion and sulfidation of Mo species, particularly favoring the formation of both active edge sites and highly active corner active sites. The reaction network for 4,6-DMDBT HDS over NiMo/HMY-x series catalysts is proposed, and HDS selectivity is found to be related to mesopore size. More specifically, HYD activity is linearly correlated to the number of Mo atoms located along the edge sites of MoS 2 crystals, and DDS activity is linearly correlated with the number of Mo atoms located at the corner sites of MoS 2 crystals. Finally, the active corner sites are approximately 10 times more active than active edge sites. [ABSTRACT FROM AUTHOR]

Novel Mn−Ce−Ti−O composite aerogels with large mesopore size were prepared via a one-pot sol−gel method by using propylene oxide as a network gel inducer and ethyl acetoacetate as a complexing agent. The effect of calcination temperature (400, 500, 600, and 700 °C) on the NH3−selective catalytic reduction (SCR) performance of the obtained Mn−Ce−Ti−O composite aerogels was investigated. The results show that the Mn−Ce−Ti−O catalyst calcined at 600 °C exhibits the highest NH3−SCR activity and lowest apparent activation energy due to its most abundant Lewis acid sites and best reducibility. The NO conversion of the MCTO-600 catalyst maintains 100% at 200 °C in the presence of 100 ppm SO2, showing the superior resistance to SO2 poisoning as compared with the MnOx−CeO2−TiO2 catalysts reported the literature. This should be mainly attributed to its large mesopore sizes with an average pore size of 32 nm and abundant Lewis acid sites. The former fact facilitates the decomposition of NH4HSO4, and the latter fact reduces vapor pressure of NH3. The NH3−SCR process on the MCTO-600 catalyst follows both the Eley−Rideal (E−R) mechanism and the Langmuir−Hinshelwood (L−H) mechanism.

Hierarchical HZSM-5 membranes were prepared on the inner wall of stainless steel tubes, using amphiphilic organosilane (TPOAC) and mesitylene (TMB) as a meso-porogen and a swelling agent, respectively. The mesoporosity of the HZSM-5 membranes were tailored via formulating the TPOAC/Tetraethylorthosilicate (TPOAC/TEOS) ratio and TMB/TPOAC ratio, in synthesis gel, and the prepared membranes were systematically characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), N2 adsorption⁻desorption, N2 permeation, inductively coupled plasma (ICP), in situ fourier transform infrared (FT-IR), ammonia temperature-programmed desorption (NH3-TPD), etc. It was found that the increase of the TPOAC/TEOS ratio promoted a specific surface area and diffusivity of the HZSM-5 membranes, as well as decreased acidity; the increase of the TMB/TPOAC ratios led to an enlargement of the mesopore size and diffusivity of the membranes, but with constant acid properties. The catalytic performance of the prepared HZSM-5 membranes was tested using the catalytic cracking of supercritical n-dodecane (500 °C, 4 MPa) as a model reaction. The hierarchical membrane with the TPOAC/TEOS ratio of 0.1 and TMB/TPOAC ratio of 2, exhibited superior catalytic performances with the highest activity of up to 13% improvement and the lowest deactivation rate (nearly a half), compared with the microporous HZSM-5 membrane, due to the benefits of suitable acidity, together with enhanced diffusivity of n-dodecane and cracking products.

γ-Al 2 O 3 without amorphous domains was synthesized by cation-anion double hydrolysis method. The mesopore size in the range of 3.9–8.5 nm was easily controlled by regulating crystallization temperature, solution pH value and the concentration of NaAlO 2 . The introduction of MoO 3 to the γ-Al 2 O 3 via impregnation method can lead to a decrease of specific surface areas, pore sizes and pore volumes of the supports. The less steric hindrance of the larger mesopores (particularly 8.5 nm) exhibits the more Lewis acid sites over the γ-Al 2 O 3 . The MoO 3 /γ-Al 2 O 3 possesses more Bronsted acid sites compared to Lewis. The thiophene compounds can be adsorbed both on the supports and catalysts. The acid sites can facilitate the interaction between the thiophene compounds and catalysts (or supports). The more adsorbed thiophene and dibenzothiophene on the catalysts is attributed to the coordinately unsaturated metal sites and Bronsted acid sites on the surface of the catalysts. Of note is the supports and catalysts with larger pore size (especially 8.5 nm) could promote the adsorption of thiophene compounds. It demonstrates that there is pore confinement effect in the hydrodesulfurization catalysts. [ABSTRACT FROM AUTHOR]

As one of the most potential electrode materials for supercapacitors, nitrogen-enriched nanocarbons are still facing challenge of constructing developed mesoporosity for rapid mass transportation and tailoring their pore size for performance optimization and expanding their application scopes. Herein we develop a series of nitrogen-enriched mesoporous carbon (NMC) with extremely high mesoporosity and tunable mesopore size by a two-step method using silica gel as template. In our approach, mesopore size can be easily tailored from 4.7 to 35 nm by increasing the HF/TEOS volume ratio from 1/100 to 1/4. The NMC with mesopores of 6.2 nm presents the largest mesopore volume, surface area and mesopore ratio of 2.56 cm 3 g −1 , 1003 m 2 g −1 and 97.7%, respectively. As a result, the highest specific capacitance of 325 F g −1 can be obtained at the current density of 0.1 A g −1 , which can stay over 88% (286 F g −1 ) as the current density increases by 100 times (10 A g −1 ). This approach may open the doors for preparation of nitrogen-enriched nanocarbons with desired nanostructure for numerous applications. [ABSTRACT FROM AUTHOR]

The morphology of silica monoliths determines their mass transport properties. While eddy dispersion can be related to the size and structural heterogeneity of the macropores, longitudinal diffusion and trans-skeleton mass transfer resistance are influenced by the physical appearance of the mesopore space. We used two small analytes (uracil, naphthalene) and a large one (lysozyme) to characterize the column performance of a set of six second-generation analytical silica monoliths with systematically varied mean mesopore size from 5.5 to 25.7 nm. Within this set of sample columns, the mean macropore size was conserved at about 1.2 μm. Longitudinal diffusion and trans-skeleton mass transfer resistance were derived from peak parking experiments. Both contributions to the overall plate height are affected by the structural hindrance in the mesopores, which increases with smaller mesopore size. For the weakly retained naphthalene, this effect is counteracted by surface diffusion, which increases with the surface area of the mesopore space. Additivity of individual plate height contributions allows for the determination of eddy dispersion by subtraction of the other terms from the overall plate height curves. Column performance for lysozyme is limited by mass transfer resistance, which increases strongly with smaller mesopore size until lysozyme becomes totally excluded from the smallest (5.5 nm) pores. [ABSTRACT FROM AUTHOR]

Highlights: [•] Compared with conventional method, PCSA method yields KIT-6 with tunable pore size of 8–10nm, and. [•] Improved ordering with increased interval time (1–5h) for a given addition combination of 7-xh-3. [•] Higher meso-orderings, when prepared with hydrothermal treatment at 140°C. [•] Particle sizes 1–2 orders of magnitude smaller. [•] Simplicity and directness without changing other synthetic conditions. [ABSTRACT FROM AUTHOR]

ZSM-5/MCM-41 zeolite composites with varying mesopore sizes were prepared through alkali-desilication and surfactant-directed recrystallization with different chain length of alkyltrimethylammonium bromide. XRD and TEM revealed that the composites possessed the characteristics of both ZSM-5 and mesoporous MCM-41 with hexagonal symmetry. N-adsorption-desorption, Al MAS NMR, NH-TPD and in situ FT-IR results suggested that the sizes of the mesopores and the accessibility of acid sites could be affected greatly by the chain length of alkyltrimethylammonium bromide used. Catalytic cracking of n-dodecane over ZSM-5/MCM-41 composites was studied in the form of coatings on the inside of a tubular reactor at 550 °C and 4 MPa. The conversion of n-dodecane increased gradually with increasing the mesopore sizes of ZSM-5/MCM-41 composites, implying a positive effect of the mesopores on the diffusion inside pore channels and the accessibility of acid sites by the reactants. Graphical Abstract: [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Abstract: Two carbon xerogels (CX) with different pore size distributions were prepared by the conventional approach (condensation of resorcinol and formaldehyde). The key variable to control those sizes is the pH of the aqueous solution. Gold nanoparticles were supported on the prepared CXs by the sol immobilization method and tested in the selective oxidation of glycerol, with the main purpose of evaluating the influence of the textural properties on the activity and selectivity. Mesopore sizes of the support have a strong effect on the distribution of products: wide pores enhance the formation of dihydroxyacetone whereas narrow mesopores favor the oxidation towards glyceric acid. Additionally, the selectivity results obtained with carbon xerogels were compared with those achieved with other carbon supports (activated carbon and multi-walled carbon nanotubes) and the same trend was observed. Therefore, it seems that the distribution of products can be controlled by the adequate choice of the support. For this purpose, carbon xerogel is a promising material since its pore size can be easily modified in a controllable way during the preparation stage. [Copyright &y& Elsevier]

• Octadecyl methacrylate (ODM) was re-tested to functionalize silica monoliths. • ODM-monoliths with 3 different mesopore sizes can be prepared without clogging. • The present ODM-monoliths show an enhanced retention compared to literature. • The efficiency (H = 6 μm) is higher than that of the ODM-columns in literature (H = 10 μm). • ODM-phase showed a lower diffusivity than ODS-phase, explaining the steeper C -term. We report on the possibility to enhance the phase ratio and retention factor in silica monoliths. According to pioneering work done by Núñez et al. [1] , this enhancement is pursued by applying a stationary phase layer via radical polymerization with octadecyl methacrylate (ODM) as an alternative to the customary octadecylsilylation (C18-derivatization). The difference in band broadening, retention factor and separation selectivity between both approaches was compared. Different hydrothermal treatment temperatures for the column preparation were applied to produce monolithic silica structures with three different mesopore sizes (resp. 10, 13, and 16 nm, as determined by argon physisorption) while maintaining similar domain size (sum of through-pore and skeleton size). It has been found that the columns with the poly(octadecyl methacrylate)-phase (ODM columns) provided a 60 to 80% higher retention factor in methanol-water mixture compared to the octadecylsilylated (ODS) columns produced by starting from similar silica backbone structures. In acetonitrile-water mixture, the enhancement is smaller (15 to 30% times higher), yet significant. By adjusting the fabrication conditions (for both the preparation of the monolithic backbones and the surface functionalization), the achieved retention factors (up k = 4.89 for pentylbenzene in 80:20% (v/v) methanol/water) are obviously higher than obtained in the pioneering study on ODM monoliths of Núñez et al. [1] , and column clogging could be completely avoided. In addition, also separation efficiencies were significantly higher than shown in Ref. [1] , with plate heights as low as 5.8 μm. These plate heights are however inferior to those observed on the ODS-modified sister columns. The difference can be explained by the slower intra-skeleton diffusion displayed by the ODM-modified columns, in turn caused by the larger obstruction to diffusion originating from the thicker stationary phase layer. [ABSTRACT FROM AUTHOR]

Tunable mesoporous silica films were prepared though a sol-gel process directed by the self-assembly of various triblock copolymers. Positron annihilation γ-ray energy spectroscopy and positron annihilation lifetime spectroscopy (PALS) based on intense pulsed slow positron beams as well as ellipsometric porosimetry (EP) combined with heptane adsorption were utilized to characterize the open porosity/interconnectivity and pore size distribution for the prepared films. The consistency between the open porosities was examined by the variations of orthopositronium (o-Ps) 3γ annihilation fractions and the total adsorbed volumes of heptane. The average pore sizes deduced by PALS from the longest-lived o-Ps lifetimes are in good agreement with those by EP on the basis of the Barrett–Joyner–Halenda model, as indicated by a well fitted line of slope k = 1. The results indicate that the EP combined with heptane adsorption is a useful method with high sensitivity for calibrating the mesopore size in highly interconnected mesoporous films, whereas PALS is a novel, complementary tool for characterizing both closed and open pores in them. [ABSTRACT FROM AUTHOR]

Novel Mn–Ce–Ti–O composite aerogels with large mesopore size were prepared via a one-pot sol–gel method by using propylene oxide as a network gel inducer and ethyl acetoacetate as a complexing agent. The effect of calcination temperature (400, 500, 600, and 700 °C) on the NH3–selective catalytic reduction (SCR) performance of the obtained Mn–Ce–Ti–O composite aerogels was investigated. The results show that the Mn–Ce–Ti–O catalyst calcined at 600 °C exhibits the highest NH3–SCR activity and lowest apparent activation energy due to its most abundant Lewis acid sites and best reducibility. The NO conversion of the MCTO-600 catalyst maintains 100% at 200 °C in the presence of 100 ppm SO2, showing the superior resistance to SO2 poisoning as compared with the MnOx–CeO2–TiO2 catalysts reported the literature. This should be mainly attributed to its large mesopore sizes with an average pore size of 32 nm and abundant Lewis acid sites. The former fact facilitates the decomposition of NH4HSO4, and the latter fact reduces vapor pressure of NH3. The NH3–SCR process on the MCTO-600 catalyst follows both the Eley–Rideal (E–R) mechanism and the Langmuir–Hinshelwood (L–H) mechanism. [ABSTRACT FROM AUTHOR]

Hierarchical HZSM-5 membranes were prepared on the inner wall of stainless steel tubes, using amphiphilic organosilane (TPOAC) and mesitylene (TMB) as a meso-porogen and a swelling agent, respectively. The mesoporosity of the HZSM-5 membranes were tailored via formulating the TPOAC/Tetraethylorthosilicate (TPOAC/TEOS) ratio and TMB/TPOAC ratio, in synthesis gel, and the prepared membranes were systematically characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), N2 adsorption–desorption, N2 permeation, inductively coupled plasma (ICP), in situ fourier transform infrared (FT-IR), ammonia temperature-programmed desorption (NH3-TPD), etc. It was found that the increase of the TPOAC/TEOS ratio promoted a specific surface area and diffusivity of the HZSM-5 membranes, as well as decreased acidity; the increase of the TMB/TPOAC ratios led to an enlargement of the mesopore size and diffusivity of the membranes, but with constant acid properties. The catalytic performance of the prepared HZSM-5 membranes was tested using the catalytic cracking of supercritical n-dodecane (500 °C, 4 MPa) as a model reaction. The hierarchical membrane with the TPOAC/TEOS ratio of 0.1 and TMB/TPOAC ratio of 2, exhibited superior catalytic performances with the highest activity of up to 13% improvement and the lowest deactivation rate (nearly a half), compared with the microporous HZSM-5 membrane, due to the benefits of suitable acidity, together with enhanced diffusivity of n-dodecane and cracking products. [ABSTRACT FROM AUTHOR]