15 research outputs found
Measurement of radon emanation and impurity adsorption from argon gas using ultralow radioactive zeolite
The amount of radioactive impurities contaminated in the detector gases is
required to be kept at a very low level for rare event particle physics such as
dark matter and neutrino observation experiments. Zeolite is a well-known
adsorbent material and is one of the possible candidates for removing
impurities from these gases. At the same time, the amount of radioactive
impurities released from the adsorbent material needs to be sufficiently small.
In this paper, a development of a new ultralow radioactive zeolite as a product
of the selection of ultralow radioactive materials is reported. Results on the
radon emanation and impurity adsorption from argon gas measurements are also
described.Comment: 8 pages, 7 figure
Incorporation of Si into Iron Oxide-based Microporous Zeolitic Framework for Improving Thermal Stability and Changing Guest Species
Landscape of Research Areas for Zeolites and Metal-Organic Frameworks Using Computational Classification Based on Citation Networks
The field of porous materials is widely spreading nowadays, and researchers need to read tremendous numbers of papers to obtain a "bird's eye" view of a given research area. However, it is difficult for researchers to obtain an objective database based on statistical data without any relation to subjective knowledge related to individual research interests. Here, citation network analysis was applied for a comparative analysis of the research areas for zeolites and metal-organic frameworks as examples for porous materials. The statistical and objective data contributed to the analysis of: (1) the computational screening of research areas; (2) classification of research stages to a certain domain; (3) "well-cited" research areas; and (4) research area preferences of specific countries. Moreover, we proposed a methodology to assist researchers to gain potential research ideas by reviewing related research areas, which is based on the detection of unfocused ideas in one area but focused in the other area by a bibliometric approach. Keywords: research and development management; citation network analysis; bibliometrics; porous materials; zeolites; metal-organic framework
Synthesis of Microporous Zincosilicate *BEA Molecular Sieves from Zincosilicate Gels Co-precipitated in the Presence of an Organic Structure-directing Agent
Catalytic Oxidation of Methane into Methanol over Copper-Exchanged Zeolites with Oxygen at Low Temperature
The direct catalytic conversion of methane to liquid oxygenated compounds, such as methanol or dimethyl ether, at low temperature using molecular oxygen is a grand challenge in C–H activation that has never been met with synthetic, heterogeneous catalysts. We report the first demonstration of direct, catalytic oxidation of methane into methanol with molecular oxygen over copper-exchanged zeolites at low reaction temperatures (483–498 K). Reaction kinetics studies show sustained catalytic activity and high selectivity for a variety of commercially available zeolite topologies under mild conditions (e.g., 483 K and atmospheric pressure). Transient and steady state measurements with isotopically labeled molecules confirm catalytic turnover. The catalytic rates and apparent activation energies are affected by the zeolite topology, with caged-based zeolites (e.g., Cu-SSZ-13) showing the highest rates. Although the reaction rates are low, the discovery of catalytic sites in copper-exchanged zeolites will accelerate the development of strategies to directly oxidize methane into methanol under mild conditions.National Science Foundation (U.S.) (CHE-9808061)National Science Foundation (U.S.) (DBI-9729592
Landscape of Research Areas for Zeolites and Metal-Organic Frameworks Using Computational Classification Based on Citation Networks
Extremely stable zeolites developed via liquid-mediated self-defect-healing
The successful application of zeolites in diverse fields largely relies on their high stability compared with other porous materials. However, the property requirements for zeolites have become stringent due to their diverse and demanding applications. Aluminosilicate zeolites are utilized for adsorptive and catalytic applications, wherein they are sometimes exposed to high-temperature steaming conditions (~1000 °C). Zeolites are exposed to severe steaming conditions in regenerators to remove coke, and over 400,000 t/y of catalysts are discarded due to degradation during the FCC process [1]. Recently, zeolites have been used in exhaust gas treatment processes, such as the selective catalytic reduction of NOx, catalytic oxidation for diesel engines, and hydrocarbon trapping [2], wherein they degrade due to interactions with high-temperature (>800 °C) steam. In automotive applications, degradation is often severe because zeolites are continuously exposed to steam without replacement. Therefore, the development of highly stable zeolites has become an important issue. As the degradation of high-silica zeolites originates from the defect sites in their frameworks, feasible defect-healing methods are highly demanded. Herein, we propose a method for healing defects to create extremely stable high-silica zeolites. High-silica (SiO2/Al2O3 > 240) zeolites with *BEA-, MFI-, and MOR-type topologies could be stabilized by significantly reducing the defect sites via a liquid-mediated treatment without using additional silylating agents. Upon exposure to extremely high-temperature (900–1150 °C) steam, the stabilized zeolites retain their crystallinity and micropore volume, whereas the parent commercial zeolites degrade completely (Figure 1). The proposed self-defect-healing method provides new insights into the migration of species through porous bodies and significantly advances the practical applicability of zeolites in severe environments
A Working Hypothesis for Broadening Framework Types of Zeolites in Seed-Assisted Synthesis without Organic Structure-Directing Agent
Recent research has demonstrated a new synthesis route
to useful
zeolites such as beta, RUB-13, and ZSM-12 via seed-assisted, organic
structure-directing agent (OSDA)-free synthesis, although it had been
believed that these zeolites could be essentially synthesized with
OSDAs. These zeolites are obtained by adding seeds to the gels that
otherwise yield other zeolites; however, the underlying crystallization
mechanism has not been fully understood yet. Without any strategy,
it is unavoidable to employ a trial-and-error procedure for broadening
zeolite types by using this synthesis method. In this study, the effect
of zeolite seeds with different framework structures is investigated
to understand the crystallization mechanism of zeolites obtained by
the seed-assisted, OSDA-free synthesis method. It has been found that
the key factor in the successful synthesis of zeolites in the absence
of OSDA is the common composite building unit contained both in the
seeds and in the zeolite obtained from the gel after heating without
seeds. A new working hypothesis for broadening zeolite types by the
seed-assisted synthesis without OSDA is proposed on the basis of the
findings of the common composite building units in zeolites. This
hypothesis enables us to design the synthesis condition of target
zeolites. The validity of the hypothesis is experimentally tested
and verified by synthesizing several zeolites including ECR-18 in
K–aluminosilicate system