Synthesis and Separation Performance of Y-type Zeolite Membranes by Pre-Seeding Using Electrophoresis Deposition Method

Y-type zeolite membranes were synthesized by a two-step approach in which a particle seed layer was prepared by electrophoresis deposition(EPD) at first, followed by densification through secondary growth. The pre-seeding adopted the directing agent for Y-type zeolite synthesis serving as seeds. The effects of aging time of the directing agent, electrophoresis voltage and electrophoresis deposition time on seed layers quality as well as the quality of zeolite membranes were investigated. The results indicated that the zeolite seeds derived from the directing agent could be evenly deposited on substrate under certain EPD conditions. The XRD patterns of the seeded substrates after the secondary growth showed that the pure as-synthesized Y-type zeolite membranes had successfully grown on the substrates. The SEM images indicated that the substrate was covered by the highly intergrown zeolite crystals when the seeding solution employed the directing agent with an aging time of 2 days. The separation performance of zeolite membrane was evaluated using a CO_2/N2 mixture(with a mole ratio of 1:1) at different temperatures. Furthermore, the pervaporation measurements were carried out for the dehydration of isopropanol aqueous solutions with different mass fractions. The as-synthesized Y-type zeolite membranes exhibited a relatively high selectivity of water from isopropanol and sustainable permeation flux.

Infrared Spectroscopy Study of Structural Nature of Geopolymeric Products

The bonding status and chemical environment of SiO4 and AlO4 tetrahedras of three types of geopolymeric products were systematically investigated by infrared spectroscopy. The relationship between amorphous geopolymeric products and zeolite crystals with the same overall chemical compositions was also discussed. The infrared evidence shows that SiO4 tetrahedra is partially bonded by AlO4 during the hydration process of geopolymeric cement. The two types of tetrahedras jointly construct the three dimensional framework structures of the geopolymeric products. The mutual transformation between geopolymeric products and corresponding zeolite crystals will take place once the reaction condition is suitable, which reveals that the nature ofgeopolymeric products are probably the amorphous equivalent of the corresponding zeolite crystals.

Accelerating the detection of unfeasible hypothetical zeolites via symmetric local interatomic distance criteria

In silico prediction of potential synthetic targets is the prerequisite for function-led discovery of new zeolites. Millions of hypothetical zeolitic structures have been predicted via various computational methods, but most of them are experimentally inaccessible under conventional synthetic conditions.Screening out unfeasible structures is crucial for the selection of synthetic targets with desired functions.The local interatomic distance（LID） criteria are a set of structure rules strictly obeyed by all existing zeolite framework types. Using these criteria, many unfeasible hypothetical structures have been detected. However, to calculate their LIDs, all hypothetical structures need to be fully optimized without symmetry constraints. When evaluating a large number of hypothetical structures, such calculations may become too computationally expensive due to the forbiddingly high degree of freedom. Here, we propose calculating LIDs among structures optimized with symmetry constraints and using them as new structure evaluation criteria, i.e., the LIDsymcriteria, to screen out unfeasible hypothetical structures. We find that the LIDsymcriteria can detect unfeasible structures as many as the original non-symmetric LID criteria do, yet require at least one order of magnitude less computation at the initial geometry optimization stage.

Efficient adjustment of product selectivity using controllable Pd nanoparticles in nitroarene hydrogenation

Product selectivity adjustment is a much-studied topic in mesoscience that is critical for industrial processes and strongly related to reaction intermediates formed by interactions between catalytic active sites and reactants.Herein,we report efficient adjustment of the product selectivity in the hydrogenation of substituted nitroarenes via rational reaction intermediates achieved using controllable Pd nanoparticles.Pd nanoparticles fixed within zeolite Beta crystals(Pd@Beta)afforded rational Pd-NO2 interactions,in which the Pd nanoparticle-adsorbed substituted nitroarenes,such as nitrobenzaldehyde,were reasonably hydrogenated into the corresponding aminobenzaldehyde.However,for Pd nanoparticles supported on the external surfaces of zeolite beta crystals,various side products were obtained owing to the coexistence of Pd-NO2 and Pd-C=O interactions.When Pd nanoparticles were artificially controlled in various positions in a fixed-bed reactor,the product selectivity was significantly affected.These results demonstrate the importance of molecular adsorption and diffusion processes in adjusting product selectivity in catalytic reactions.