Low-Temperature Adsorption/Storage of Hydrogen on FAU, MFI, and MOR Zeolites with Various Si/Al Ratios: Effect of Electrostatic Fields and Pore Structures

Jhung, Sung ,Hwa,Yoon, Ji ,Woong,Lee, Ji ,Sun,Chang, Jong-San Wiley - VCH Verlag GmbH & Co. KGaA 2007 Chemistry Vol.13 No.22

<P>Several zeolites, such as faujasite, mordenite, and ZSM-5, with various aluminum contents have been used to analyze the effect of aluminum or cation concentration (strength of electrostatic field) on hydrogen adsorption at low temperature. Irrespective of the zeolite structure, the adsorption capacity, isosteric heat of adsorption (−ΔH<SUB>ads</SUB>), surface coverage, and micropore occupancy increase with increasing aluminum content of a zeolite. Zeolites with a higher amount of aluminum favorably adsorb hydrogen at relatively low pressures. For zeolites with similar aluminum contents, the adsorption capacity, isosteric heat of adsorption, surface coverage, and micropore occupancy are in the order of mordenite>ZSM-5>faujasite, probably due to differing pore sizes and the presence or absence of pore intersections. This work demonstrates that zeolites with strong electrostatic fields and narrow pores without intersections are beneficial for high hydrogen uptake.</P> <B>Graphic Abstract</B> <P>Hydrogen adsorption on zeolites: Irrespective of the zeolite structure, the adsorption capacity, isosteric heat of adsorption (−ΔH<SUB>ads</SUB>), surface coverage, and micropore occupancy increase when increasing the aluminum content of a zeolite (see figure). For zeolites with similar aluminum contents, the adsorption capacities are in the order of mordenite>ZSM-5>faujasite. Zeolites with strong electrostatic fields and narrow pores without intersections are beneficial for high hydrogen uptake. <img src='wiley_img/09476539-2007-13-22-CHEM200700148-content.gif' alt='wiley_img/09476539-2007-13-22-CHEM200700148-content'> </P>

Synthesis of Iron-loaded Zeolites for Removal of Ammonium and Phosphate from Aqueous Solutions

Kwang Soo Kim,Jung O Park,Sang Chul Nam 대한환경공학회 2013 Environmental Engineering Research Vol.18 No.4

This study presents a comparison of different protocols for the synthesis of iron-loaded zeolites, and the results of their application, as well as that of zeolite-A (Z-A), to the removal of ammonium and phosphate from aqueous media. Zeolites prepared by three methods were evaluated: iron-incorporated zeolites (IIZ), iron-exchanged zeolites (IEZ), and iron-calcined zeolites (ICZ). The optimal iron con-tent for preparing of IIZ, as determined via scanning electron microscopy and X-ray photoelectron spectroscopy analyses, expressed as molar ratio of SiO₂:Al₂O₃:Fe, was below 0.05. Ammonia removal revealed that the iron-loaded zeolites have a higher removal capacity than that of Z-A due, not only to ion-exchange phenomena, but also via adsorption. Greater phosphate removal was achieved with IEZ than with ICZ; additionally, no sludge production was observed in this heterogeneous reaction, even though the coagulation process is generally accompanied by the production of a large amount of undesired chemical sludge. This study demonstrates that the developed synthetic iron-loaded zeolites can be applied as a heterogeneous nutrient-removal materials with no sludge production.

Exchanging noble and seminoble cations into zeolites by oxygen vacancy ion exchange (OVIE)

Lee, Gwang Myeong,Heo, Nam Ho,Seff, Karl Elsevier 2017 Microporous and mesoporous materials Vol.244 No.-

<P><B>Abstract</B></P> <P>It is proposed that cation exchanged zeolites can be prepared by reacting their decationized forms, e.g., (SiO<SUB>2</SUB>)<SUB>n</SUB>(Al<SUB>2</SUB>O<SUB>3</SUB>)<SUB>m</SUB>, n ≥ 2m, with noble or seminoble metals and oxygen or ozone. The resulting oxide ions would very exoergically occupy vacancies in the zeolite framework and the cations would go to conventional extraframework positions. The noble metals Rh, Pd, Ir, Pt, and Au and the seminoble metals Ru, Ag, Re, Os, Hg, and Bi are suggested. A sample reaction using decationized zeolite LTA would be: 6Pd + 3O<SUB>2</SUB> + Si<SUB>12</SUB>Al<SUB>12</SUB>O<SUB>42</SUB> → Pd<SUB>6</SUB>Si<SUB>12</SUB>Al<SUB>12</SUB>O<SUB>48</SUB>. Decationized zeolites can be prepared by heating zeolites, especially high-Al zeolites, in their H<SUP>+</SUP> or NH<SUB>4</SUB> <SUP>+</SUP> forms, causing them to lose framework oxygen atoms as H<SUB>2</SUB>O. The reactions may occur by simply heating a mixture of starting materials in flowing oxygen or ozone, e.g., 6Pd + 3O<SUB>2</SUB> + (NH<SUB>4</SUB>)<SUB>12</SUB>Si<SUB>12</SUB>Al<SUB>12</SUB>O<SUB>48</SUB>.nH<SUB>2</SUB>O → Pd<SUB>6</SUB>Si<SUB>12</SUB>Al<SUB>12</SUB>O<SUB>48</SUB> + 12NH<SUB>3</SUB> + (6 + n)H<SUB>2</SUB>O. This method may be extended to other inorganic ion exchangers.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Cations of noble metals may be introduced into zeolites. </LI> <LI> A solid-state reaction is proposed. </LI> <LI> Decationized zeolites (with framework oxygen vacancies) are used. </LI> <LI> There are no leaving cations; this is not ion exchange. </LI> <LI> Success seen with silver may be extended to other metals. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Weak Interactions Between Organic Molecules and Alkali Metal Ions Present in Zeolites Help Manipulate the Excited State Behavior of Organic Molecules

Ramamurthy, V. Korean Society of Photoscience 2003 Journal of Photosciences Vol.10 No.1

Zeolite is a porous highly interactive matrix. Zeolitic cations help to generate triplets from molecules that possess poor intersystem crossing efficiency. Certain zeolites act as electron acceptors and thus can spontaneously generate radical cations. Zeolites also act as proton donors and thus yield carbocations without any additional reagents. These reactive species, radical cations and carbocations, have long lifetime within a zeolite and thus lend themselves to be handled as ‘regular’ chemicals. Internal structure of zeolites is studded with cations, the counter-ions of the anionic framework. The internal constrained structure and the cations serve as handles for chemists to control the behavior of guest molecules included within zeolites.

Evolution of zeolite crystals in geopolymer-supported zeolites: effects of composition of starting materials

Khalid, Hammad R.,Lee, N.K.,Choudhry, Iqra,Wang, Zhen,Lee, H.K. Elsevier 2019 Materials letters Vol.239 No.-

<P><B>Abstract</B></P> <P>The role of the characteristics of raw materials and starting mix proportion on geopolymerization and evolution of zeolitic crystals from an amorphous geopolymeric gel was investigated. Different types and compositions of metakaolin, fly ash, and slag were activated using same waterglass and NaOH-based alkali activator. The test results showed that the reactivity of alkali-activated raw materials greatly depends on the Si/Al and Si/Na ratios of the starting mix, which affected the strength development and zeolite formation. It was further found that low-Ca class F fly ash was the most suitable to obtain zeolite Na-P1 crystals. Alternatively, high-Ca class C fly ash promoted the synthesis of hydroxysodalite and calcite. Higher porosity (52%) and surface area (99.5 m<SUP>2</SUP>/g) were achieved for the geopolymer-supported zeolites. These materials can be potentially used as membranes/filters for removal of hazardous contaminants (colloidal foulants, macromolecules, heavy metals/radionuclides) from water owing to their porous structure and affinity of zeolites towards cations.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Effects of different starting materials on zeolite evolution in geopolymer binders. </LI> <LI> Compressive strength increased with Si/Al and Si/Na ratios of the starting mix. </LI> <LI> Low Ca fly ash promoted conversion of geopolymeric gel to zeolite Na-P1. </LI> <LI> High Ca fly ash/slag resulted in formation of hydroxysodalite and calcite. </LI> <LI> Synthesized materials have potential to be used as self-supported adsorbents. </LI> </UL> </P>

n-Octane의 개질반응에서 FAU와 MF1 촉매의 탈 알루미늄에 의한 Si/A1비의 영향

유용호 ( Yong Ho Yu ),정우진 ( Woo Jin Chung ),이철우 ( Chul Woo Lee ),오민 ( Min Oh ),이원묵 ( Won Mook Lee ) 한국공업화학회 2003 공업화학 Vol.14 No.2

제올라이트에서 Si/Al의 조성비는 산도에 큰 영향을 주므로 촉매의 활성 및 선택도도 큰 영향을 받는다. 본 연구에서는 상용화된 FAU 및 MFI 제올라이트를 탈 알루미늄 하여 산도를 변화시킨 후 노르말 옥탄의 개질 반응에서의 촉매특성을 살펴보았다. FAU와 MFI 제올라이트의 탈 알루미늄은 각각 열처리, 수증기 처리, 그리고 질산 처리 등 세 가지 서로 다른 방법으로 수행하였고, 처리된 제올라이트의 물성은 BET, XRE, SEM-EDS, TPD, FT-IR 등을 사용하여 측정하였다. 변형된 제올라이트 촉매들은 본 제조 조건에서 결정성을 그대로 유지하였으며, Si/Al 비는 3에서 30까지 증가하였고 산도는 크게 감소하였다. n-Octan의 개질 반응에서 촉매의 활성은 MFI계 촉매가 FAU계 촉매보다 더 우수하였고, 열처리한 경우가 수증기 처리한 경우보다 활성이 더 크게 나타났다. 수증기 처리한 경우는 열처리한 경우보다 촉매의 활성은 낮았지만 BTX 생성 억제 효과는 더 우수하였고, 산도가 높은 FAU 촉매는 분해반응에서 우수한 활성을 나타내었다. 개질 반응에서 일어나는 분해반응, 탈 수소반응 그리고 이성화반응 등을 종합적으로 고려하면 열처리에 의하여 변형된 MFI계 촉매가 가장 우수하였다. The catalytic activity and selectivity of zeolites are significantly influenced by the Si/Al ratio, because it has strong effects on the acidity of zeolites. In this research, the catalytic characteristics were investigated by using dealuminated FAU and MFI zeolites as the catalysts in the reforming of n-octane. Dealumination of zeolites was carried out in three different processes, i. e., thermal, steam, and nitric acid treatment, and their properties were measured by BET, XRD, SEM-EDS, TPD and FT-IR. The crystalline structure of zeolites was maintained after dealumination. Si/Al ratio was increased from 3 to 30, and the acidity was decreased drastically as Si/Al ratio increased. The catalytic activity of dealuminated MFI zeolite was superior to that of FAU zeolie. Steam treated catalyst showed lower activity than thermally treated one, but it showed better performance in the inhibition of BTX generation. FAU zeolite with high acidity showed good selectivity to the decomposition reaction. In conclusion, thermally treated MEI zeolite showed the highest activity in the n-octane reforming, considering all the reactions; decomposition, dehydrogenation and isomerization.

Catalytic properties of microporous zeolites in the synthesis of octyl glucoside from D-glucose with 1-octanol by single-step direct glucosidation

Chung, K.H.,Lee, S.J.,Lee, H.,Kim, H.,Park, Y.K.,Kim, B.H.,Jung, S.C. Elsevier 2016 Microporous and mesoporous materials Vol.233 No.-

<P>Catalytic properties of various microporous zeolites consisted of different acidic properties and pore topologies were studied in the synthesis of octyl glucoside from D-glucose with 1-octanol by single-step direct glucosidation. The influences of acidic properties and pore topologies of the zeolite catalysts were evaluated relating to the conversion of glucose and selectivities of octyl glucosides. The octyl glucosides could be synthesized conveniently by the single-step direct glucosidation through aging of reactants without further pre-treatment or additional supply of reactant. The reusability of the zeolite catalyst was evaluated to the used zeolite. The high conversion of D-glucose was obtained on H+ ion exchanged FAU (H-FAU) zeolite which has a mild acid strength. The conversion and yield were improved with increasing of acid site amount of the zeolite catalysts. H-FAU zeolite catalysts exhibited high octyl glucopyranoside selectivity owing to relatively a large pore cavity and a high concentration of mild acid sites. The selectivities of the octyl glucoside isomers were mainly depended on the differences of pore structure and concentration of acid sites of the zeolite catalysts. The zeolite used in the reaction was able to reuse through the regeneration process. (C) 2016 Elsevier Inc. All rights reserved.</P>

Dry-gel synthesis of mesoporous MFI zeolite nanosponges using a structure-directing surfactant

Han, Seung Won,Kim, Jaeheon,Ryoo, Ryong Elsevier 2017 Microporous and mesoporous materials Vol.240 No.-

<P><B>Abstract</B></P> <P>The synthesis of mesoporous MFI zeolite nanosponges was investigated in a dry-gel conversion process using C<SUB>18</SUB>H<SUB>37</SUB> N<SUP>+</SUP>(CH<SUB>3</SUB>)<SUB>2</SUB> C<SUB>6</SUB>H<SUB>12</SUB> N<SUP>+</SUP>(CH<SUB>3</SUB>)<SUB>2</SUB> C<SUB>4</SUB>H<SUB>9</SUB> as a micropore-mesopore hierarchical structure-directing surfactant. The initial synthesis mixture was converted at 333 K to a mesoporous material exhibiting a structure similar to that of MCM-41. The mesoporous material was filtered, dried at 373 K, and subsequently heated at 423 K in an autoclave with controlled humidity. In this process, precise control of the relative chamber humidity and the pH of the precursor gel was necessary to achieve full crystallization of the zeolite. The final product was composed of three-dimensional networks of 2.5-nm thick MFI nanolayers and exhibited a high surface area and narrow distribution of mesopore diameters centered at 4 nm. The zeolite crystallization behavior at 423 K was investigated after various heating times with X-ray diffraction, gas adsorption, and electron microscopy. The results indicated that under controlled humidity, crystallization took place through a pseudomorphic transformation, where the initial gel morphology was maintained throughout. The overall quality of the dry-gel product was similar to that of a conventional hydrothermal product. The Si/Al ratios of the zeolite could be controlled over the range of 50 ∼ ∞. Furthermore, in a 100-g synthesis batch, the dry-gel method had the advantage of compact autoclave size for large-scale synthesis.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Mesoporous MFI zeolite nanosponges were synthesized by dry-gel conversion at relative chamber humidity above 80%. </LI> <LI> At 80% humidity, zeolite formation took place through a pseudomorphic transformation. </LI> <LI> The dry-gel synthesis allowed significant reduction of autoclave volume and pressure. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Influence of the zeolite type on the mechanical–thermal properties and volatile organic compound emissions of natural-flour-filled polypropylene hybrid composites

Kim, Hee-Soo,Kim, Hyun-Joong Wiley Subscription Services, Inc., A Wiley Company 2008 Journal of applied polymer science Vol.110 No.5

<P>The physicomechanical properties, thermal properties, odor, and volatile organic compound (VOC) emissions of natural-flour-filled polypropylene (PP) composites were investigated as a function of the zeolite type and content. The surface area and pore structure of the natural and synthetic zeolites were determined by surface area analysis and scanning electron microscopy, respectively. With increasing natural and synthetic zeolite content, the tensile and flexural strengths of the hybrid composites were not significantly changed, whereas the water absorption was slightly increased. The thermal stability and degradation temperature of the hybrid composites were slightly increased with increasing natural and synthetic zeolite content. At natural and synthetic zeolite contents of 3%, the various odors and VOC emissions of the polypropylene/rice husk flour and polypropylene/wood flour hybrid composites were significantly reduced because of the absorption of the odor and VOC materials in the pore structures of the natural and synthetic zeolites. These results suggest that the addition of natural and synthetic zeolites to natural-flour-filled thermoplastic polymer composites is an effective method of reducing their odor and VOC emissions without any degradation of their mechanical and thermal properties. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008</P>

Catalytic hydrodeoxygenation of 2-methoxy phenol and dibenzofuran over Pt/mesoporous zeolites

Lee, Hyung Won,Jun, Bo Ram,Kim, Hannah,Kim, Do Heui,Jeon, Jong-Ki,Park, Sung Hoon,Ko, Chang Hyun,Kim, Tae-Wan,Park, Young-Kwon Elsevier 2015 ENERGY Vol.81 No.-

<P><B>Abstract</B></P> <P>The hydrodeoxygenation of 2-methoxy phenol and dibenzofuran, which are representative model compounds of bio-oil, was performed using two different Pt/mesoporous zeolite catalysts, Pt/mesoporous Y and Pt/mesoporous MFI. The reforming of 2-methoxy phenol and dibenzofuran via catalytic hydrodeoxygenation was investigated using a batch reactor at 40 bar and 250 °C. The characteristics of the catalysts were analyzed by N<SUB>2</SUB> adsorption-desorption, X-ray diffraction, and NH<SUB>3</SUB> temperature programmed desorption. Pt/mesoporous zeolite catalysts containing both strong acid sites and mesopores showed the higher conversion of 2-methoxy phenol than Pt/SiO<SUB>2</SUB> and Pt/Si-MCM-48 with no acid sites, Pt/γ-Al<SUB>2</SUB>O<SUB>3</SUB>, and a mixture of mesoporous Y and Pt/SiO<SUB>2</SUB>, indicating the importance of both Pt and strong acid sites for high catalytic activity. Among the two Pt/mesoporous zeolite catalysts tested, the conversion of 2-methoxy phenol to cyclohexane over Pt/mesoporous Y was much higher than that over the Pt/mesoporous MFI. This was attributed to the better textural properties, such as surface area, pore volume and micropore size, compared to those of Pt/mesoporous MFI. The catalytic conversions of dibenzofuran obtained using two Pt/mesoporous zeolite catalysts were similar and the main products were 1,1′-bicyclohexyl, cyclopentylmethyl-cyclohexane and cyclohexane. In addition, the reaction mechanisms of 2-methoxy phenol and dibenzofuran over Pt/mesoporous zeolite were suggested.</P> <P><B>Highlights</B></P> <P> <UL> <LI> HDO of 2-methoxy phenol and dibenzofuran was performed over Pt/mesoporous zeolites. </LI> <LI> Pt/mesoporous zeolites have mesopores and strong acid sites. </LI> <LI> Main product of HDO of 2-methoxy phenol was cyclohexane. </LI> <LI> Main products of HDO of dibenzofuran were bicyclohexyl (BCH), <I>i</I>-BCH, and cyclohexane. </LI> </UL> </P>