MICROPOROUS AND MESOPOROUS MATERIALS
·
2015
·
IF 3.453
Tingting Lu,Ruren Xu,Wenfu Yan
The initial mixture containing fully hydrolysed tetraethyl orthosilicate (TEOS) and tetraethylammonium hydroxide (TEAOH) solution was treated either by heating at 80 °C or by freeze-drying. After adding an appropriate amount of concentrated hydrofluoric acid , the resulting mixture was crystallized at 150 °C. The heating treated mixture produced polymorph A-enriched zeolite beta while freeze-drying treated mixture gave only normal zeolite beta. The 13 C magic angle spinning nuclear magnetic resonance (MAS NMR) analysis and thermogravimetric analysis (TGA) indicated that a partial decomposition of TEAOH to generate triethylamine (TEA) occurred during the heating dehydration process, which was the only difference compared with the freeze-drying process. Together with the reduced TEAOH, different monoamines as a co-template directed the polymorph A-enriched zeolite beta with the freeze-drying process. Diamines as a co-template directed only the normal zeolite beta. The synthesis cost of polymorph A-enriched zeolite beta can be significantly reduced by lowering the usage of expensive TEAOH and using cheaper monoamines.
研究领域:
材料科学
·
化学工程
✓ 已验证
产品关联
DOI
高影响因子
CATALYSIS LETTERS
·
2024
·
IF 2.3
Li Shengpeng,Cheng Shimin,Yuan Long,Tan Guangyu,Cheng Ying,Li Li,Li Yichen,Wang Chuang
In this study, nano-sheet SAPO-34 molecular sieves were synthesized using an aminothermal method. Triethylamine (TEA) was used as the major solvent and template, along with varying amounts of tetraethylammonium hydroxide (TEAOH). Physicochemical properties of the synthesized catalysts were characterized by techniques of XRD, SEM, BET, XRF, and NH 3 -TPD. As the amount of TEAOH increases, the composition of the product changes from a mixture of SAPO-5 and SAPO-34 to pure nano-sheet SAPO-34 molecular sieves. A TEAOH increment causes a reduction in crystallinity and particle size, as well as an increase in acid sites. Additionally, there is a non-linear relationship between the silicon content in molecular sieves and the amount of TEAOH added in the system. In the conversion of methanol to olefins using various SAPO-34 catalysts, the nano-sheet samples with the highest crystallinity and moderate acidity exhibited the longest lifetime and higher selectivity to C 2 = + C 3 = olefins. Graphical Abstract
研究领域:
材料科学
·
催化化学
✓ 已验证
产品关联
DOI
高影响因子
FUEL
·
2024
·
IF 6.7
Zongyang Zhang,Yuping Li,Ze Chen,Fuchao Ji,Xiaohong Liang,Haicheng Xuan,Lina Han,Peide Han
Developing an economical and high-efficiency synthesis pathway of SSZ-13 zeolite is of great significance for the ammonia selective catalytic reduction of nitrogen oxides (NH 3 -SCR of NO x ) reactions. Herein, SSZ-13 zeolite were synthesized using L zeolite as the aluminum source in the presence of a mixed structure directing agent (SDA) composed of N,N,N, trimethtyl-1-adamantammonium hydroxide (TMAdaOH) and tetraethylammonium hydroxide (TEAOH). This synthesis strategy aims to accelerate the crystallization rate through interzeolite transformation, while less expensive TEAOH can play a cooperative structure-directing role, thus reducing the consumption of expensive TMAdaOH template. The results showed that pure SSZ-13 zeolites with high crystallinity can be obtained from L zeolite within 12 h at 160 ℃ under low TMAdaOH/SiO 2 ratio of 0.05 (too low to carry out the synthesis on its own in the current synthesis system) in the presence of TEAOH. Moreover, the crystallization mechanism was also investigated by XRD, FT-IR, SEM and TG-DTG techniques. It was proposed that the crystallization of SSZ-13 occurs through the formation of SSZ-13 nuclei under the direction of TMAdaOH and promotion of TEAOH, subsequently TMAdaOH was incorporated in the framework to further induce the crystal growth of SSZ-13. Especially, the zeolite crystal size can be modulated by the amount of TEAOH added. In addition, After Cu 2+ exchange, the obtained Cu-SSZ-13 sample exhibits superior catalysis performance in the NH 3 -SCR of NO x reaction, and the NO x conversion rate remained over 90 % across a broad range from 200 to 600 °C, demonstrating its significant application potentials in NO x removal from diesel vehicle exhausts.
研究领域:
材料科学
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环境科学
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催化化学
✓ 已验证
DOI
高影响因子
EUROPEAN JOURNAL OF INORGANIC CHEMISTRY
·
2019
·Vol. 2020
·期 3
·318-326
·
IF 2.578
Mingjian Luo,Mingxu Liu,Yadong Fu,Wenxin Chen,Baohui Wang,Guoliang Mao
Graphical Three-stage SAPO-34s have higher purity, smaller crystal size, more acidic sites, longer catalytic lifetime and better olefin selectivity. The crystallization mechanism and the relationship between properties and performance are discussed. Acidity and 2–4 nm mesopores have little effect on MTO performance, which mainly depends on the size and dispersity of the crystallites and the purity of SAPO-34. SAPO-34 zeolites were synthesized by one-, two-, and three-stage crystallization processes with fumed silica (FS), acidic silica sol (AS), basic silica sol (BS) and tetraethoxysilane (TEOS) as silicon sources. Properties of samples were characterized by XRD, SEM, EDX, N 2 -adsorption/desorption, NH 3 -TPD and 29 Si NMR. In contrast with one- and two-stage processes, the three-stage one favors the formation of SAPO-34s with higher purity, higher Si/Al ratio, smaller crystallite/crystal size, better dispersion and more acidic sites. Crystallization mechanism was proposed. It is supposed that three-stage process favors the formation of high supersaturated SBUs (secondary building units) and CBUs (composite building units) before nucleation. Thus massive nuclei are formed during nucleation and well-dispersed small size SAPO-34 crystals are formed in three-stage process. Three-stage SAPO-34s are longer catalytic lifetime and better olefin selectivity in MTO process. TEOS-3 has the best MTO performance. It was found that acidity of sample and mesopores in 2–4 nm range have little effect on the MTO performance of SAPO-34. Catalytic lifetime and olefin selectivity are mainly depending on the size of crystallites, the dispersity of crystallites, and the purity of SAPO-34.
研究领域:
材料科学
·
催化化学
✓ 已验证
产品关联
DOI
高影响因子
危险品化学品经营许可证（带存储）