A Comparative Study of Water- and Benzene-Saturated Mesoporous Silicas by 1H NMR Spectroscopy

1H NMR investigations have been carried out on water- and benzene-saturated mesoporous sillicas with a wide range of pore sizes (13–42 Å). The freezing point of the bound water increases with the pore size, approaching that of bulk water at large pore sizes. With large pore sizes, there is more than one transition due to the bound water species. The benzene-saturated samples show a behavior similar to that of water-saturated samples, although the freezing point depression is significantly greater. The pore size distribution generally becomes broader with the increase in pore size. The original Kelvin equation is satisfactory to estimate the pore radii both in the case of water and benzene-saturated samples.     

水热处理过程中Y分子筛的骨架脱铝、补硅及二次孔的形成

在过去、现在乃至将来很长一段时间内,Y分子筛在多相催化领域都是极为重要的一种固体酸催化剂。超稳Y分子筛是其最为重要的应用形式。文章简要综述了Y分子筛骨架在水热处理过程中的结构变化历程,其中包括骨架脱铝、补硅的发生、非骨架铝的产生以及二次孔的形成。重点总结了近几年在实验、理论方面与水热脱铝相关的研究进展,强调了继续深入研究Y分子筛的后处理改性的必要性。     

Organosilane surfactant-assisted synthesis of mesoporous SSZ-39 zeolite with enhanced catalytic performance in the methanol-to-olefins reaction

SSZ-39 zeolite with AEI framework structure is a good catalyst candidate for the methanol-to-olefins (MTO) reaction. However, the diffusion limitation and coke formation often results in fast deactivation of the SSZ-39 zeolite catalyst. One solution for this challenge is to introduce mesoporosity in the SSZ-39 zeolite. Herein, we report the synthesis of mesoporous SSZ-39 zeolite using an organosilane surfactant, N,N-dimethyl-N-(3-(trimethoxysilyl)propyl)octan-1-aminium chloride, as a mesopore template and N,N-dimethyl-cis-2,6-dimethylpiperidinium as a micropore template. The obtained zeolites were characterized by X-ray diffraction, N₂ sorption, scanning electron microscopy, temperature programmed desorption of ammonia, and magic angle spinning nuclear magnetic resonance of ²⁷Al. The results show that the mesoporous SSZ-39 zeolite has high crystallinity, meso/microporosity, high surface area, cuboid morphology, and abundant acidic sites. More importantly, this mesoporous SSZ-39 zeolite exhibits enhanced catalyst lifetime in the MTO reaction due to the presence of mesoporosity for fast mass transfer, compared with a conventional SSZ-39 zeolite without mesoporosity.     

Surface-Enhanced Raman Scattering from Dye Molecules in Silicon Nanowire Structures Decorated by Gold Nanoparticles

Silicon nanowires (SiNWs) prepared by metal-assisted chemical etching of crystalline silicon wafers followed by deposition of plasmonic gold (Au) nanoparticles (NPs) were explored as templates for surface-enhanced Raman scattering (SERS) from probe molecules of Methylene blue and Rhodamine B. The filling factor by pores (porosity) of SiNW arrays was found to control the SERS efficiency, and the maximal enhancement was observed for the samples with porosity of 55%, which corresponded to dense arrays of SiNWs. The obtained results are discussed in terms of the electromagnetic enhancement of SERS related to the localized surface plasmon resonances in Au-NPs on SiNW’s surfaces accompanied with light scattering in the SiNW arrays. The observed SERS effect combined with the high stability of Au-NPs, scalability, and relatively simple preparation method are promising for the application of SiNW:Au-NP hybrid nanostructures as templates in molecular sensorics.     

Cl2 Adsorption and Desorption over Ordered Mesoporous Carbon Materials as an Indicator for Catalytic Phosgene Formation

The presented work evaluates the implementation of adsorption and desorption experiments with Cl₂ over carbon materials towards the development of more active and stable catalysts for industrial phosgene synthesis. By using a soft templating method as a tool, ordered mesoporous carbon materials with tunable porosity, surface area, and degree of graphitization were synthesized and utilized as model system. The Cl₂ adsorption/desorption properties of these materials were studied and compared to commercial activated carbon. To draw correlations between Cl₂ adsorption/desorption behavior and catalytic performance, the materials were further tested in the phosgene formation in a plug flow reactor. However, the chemical reaction of Cl₂ with carbon during the adsorption/desorption experiment hinders a direct correlation.     

Hierarchical ZSM-5 zeolite with radial mesopores: Preparation,formation mechanism and application for benzene alkylation

Hierarchical ZSM-5 zeolite with radial mesopores is controllably synthesized using piperidine in a NaOH solution. The piperidine molecules enter the zeolite micropores and protect the zeolite framework from extensive desilication. The areas containing fewer aluminum atoms contain fewer piperidine protectant molecules and so they dissolve first. Small amounts of mesopores are then gradually generated in areas with more aluminum atoms and more piperidine protectant. In this manner, radial mesopores are formed in the ZSM-5 zeolite with a maximal preservation of the micropores and active sites. The optimal hierarchical ZSM-5 zeolite, prepared with a molar ratio of piperidine to zeolite of 0.03, had a mesopore surface area of 136 m²·g⁻¹ and a solid yield of 80%. The incorporation of the radial mesopores results in micropores that are interconnected which shortened the average diffusion path length. Compared to the parent zeolite, the hierarchical ZSM-5 zeolite possesses more accessible acid sites and has a higher catalytic activity and a longer lifetime for the alkylation of benzene.     

Influence of swelling agents on pore size distributions of porous silica-alumina hollow sphere particles in acid-promoted hydrolytic generation of hydrogen from ammonia borane

We studied the influence of swelling agents on pore size distributions in the shell of porous silica-alumina hollow sphere particles for acid-promoted hydrolytic generation of hydrogen from ammonia borane. Their well-ordered porous shells were formed with micelle templates of cetyltrimethylammonium bromide on spherical polystyrene (PS) particle templates, and swelling agents were introduced into the micelle templates for expanding the pores. Non-polar agents (hexane and toluene) did not significantly influence the size of the pores, whereas, polar agents (1-dodecanol and 1-dodecylamine) effectively expanded the pores. The hollow sphere particles formed with 1-dodecylamine possessed narrow pore distribution with a high peak pore volume. The activity of the hollow sphere particles in the hydrolytic generation of hydrogen increased according to increasing pore size with a narrow distribution, and the hollow sphere particles formed with 1-dodecylamine showed an approximately five times higher TOF for the hydrogen evolution than those formed without a swelling agent.     

Formation of Chiral Mesopores in Conducting Polymers by Chiral‐Lipid‐Ribbon Templating and “Seeding” Route

Conducting polymer nanofibers with controllable chiral mesopores in the size, the shape, and handedness have been synthesized by chiral lipid ribbon templating and “seeding” route. Chiral mesoporous conducting poly(pyrrole) (CMPP) synthesized with very small amount of chiral amphiphilic molecules (usually < 3%) has helically twisted channels with well‐defined controllable pore size of 5–20 nm in central axis of the twisted fibers. The structure and chirality of helical mesopores have been characterized by high‐resolution transmission electron microscope (HRTEM), scanning electron microscope (SEM) and electron tomography. The average pore diameters of chiral mesopores were approximately estimated from the N₂ adsorption–desorption data and calculated by the conversion calculation from helical ribbons to a rectangular straight tape. The pore size of CMPP has been controlled by choosing different alkyl chain lengths of chiral lipid molecules or precisely adjusting the H₂O/EtOH volume ratio.