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1.
Al-rich ZSM-12 zeolites were synthesized using N,N,N′,N′-tetraethylbicyclo[2.2.2]oct-7-ene-2,3:5,6-dipyrrolidinium diiodide as template under hydrothermal conditions. Their physico-chemical properties were characterized using XRD, ICP-AES, SEM, N2 adsorption, 27Al MAS NMR and NH3-TPD. The results indicated that Al-rich ZSM-12 zeolites with low Si/Al ratios of 8–23 were successfully crystallized. Catalytic properties of the prepared zeolites were studied in the tert-butylation of phenol. Higher para selectivity was obtained on the Al-rich ZSM-12 zeolites compared with other types of zeolites. 相似文献
2.
Moon Hyeon Kim Il Hum Cho Joung Ho Park Sang Ok Choi In-Su Lee 《Journal of Porous Materials》2016,23(2):291-299
Adsorption of CO2 and CO at 25 °C has been conducted using commercially-available (Y, ZSM-5) and laboratory-synthesized (SSZ-13, SAPO-34) H-zeolites with different framework topologies and chemical compositions, and their textual and surface properties have been characterized by N2 sorption and NH3 adsorption techniques. All the zeolites were microporous, although ZSM-5 and SSZ-13 apparently showed a mesoporous sorption behavior due to the interparticle spaces. The zeolites had Si/Al values in the order of SSZ-13 (16.44) > ZSM-5 (16.08) ? Y (2.82) ? SAPO-34 (0.19). Regardless, high CO2 adsorption capacity was obtained for SSZ-13 and SAPO-34 with a CHA framework. The FAU zeolite Y with the highest micropore volume showed less CO2 adsorption than the CHA zeolites and the MFI-type ZSM-5 yielded the poorest performance. Probing acid sites in the H-form zeolites using NH3 disclosed that these all contain both weak and strong acid sites with significant dependence of their strengths and amounts on the topology. The acid strength of the weak acid sites in the CHA zeolites was the weakest, which might allow a stronger interaction with CO2. The H-zeolites gave CO2/CO selectivity factors that were in the range of 4.61–11.0, depending on the framework topology. 相似文献
3.
M. Rutkowska L. Chmielarz M. Jabłońska C. J. Van Oers P. Cool 《Journal of Porous Materials》2014,21(1):91-98
ZSM-5 and Y zeolites were modified with iron by an ion-exchange method and then calcined at 773, 873, 973 and 1,073 K. The obtained materials were characterized with respect to textural parameters (low-temperature N2 sorption), structure (X-ray diffraction, UV–vis–DRS), redox properties (H2-temperature programmed desorption, TPD) and surface acidity (NH3-TPD). The obtained results have shown that the structure of zeolites influenced form, aggregation and content of the introduced iron species. In case of the FAU type structure characterized by wide pores (max. ring size, T-atoms—12) mainly iron in form of mononuclear Fe3+ cations and Fe x 3+ Oy oligonuclear clustered species was found. On the other hand for the MFI type structure characterized by smaller pores (max. ring size, T-atoms—10) significant contribution of iron in the form of bulky Fe2O3 clusters located possibly on the outer surface of ZSM-5 was detected. Such significant differences in distribution of iron species is probably related to various mobility of iron species in the pore systems of both zeolites. The obtained materials were tested as catalysts in the process of N2O decomposition. Calcination of zeolites at different temperatures influenced neither the properties nor the activity of the obtained catalysts. 相似文献
4.
Mehdi Sedighi Mostafa Ghasemi Alireza Jahangiri 《Korean Journal of Chemical Engineering》2017,34(4):997-1003
A series of CeAPSO-34s with various cerium contents was synthesized and characterized by multiple techniques such as XRD, SEM, BET, 29Si MAS NMR, NH3-TPD and CO2-TPD. NH3-TPD spectra showed that a number of acid sites, especially those of strong acidity, is reduced with the increasing of Ce incorporation. Incorporation of metal ions gave rise to more silica-islands in the CeAPSO-34 framework. CO2-TPD showed that basic sites on the surface of modified samples are due to the presence of Ce-containing species incorporation into the framework of CeAPSO-34 molecular sieves. The performance of the catalysts was studied in methanol to olefin reactions at 425 °C under the atmospheric pressure. The results showed that the incorporation of cerium ions had great effects on the structure and acidity of the molecular sieves. All SAPO-34 and MeAPSO-34 molecular sieves were the very active and selective catalyst for light olefins production. Cerium incorporation improved the catalyst lifetime and favored the ethylene and propylene generation. However, an excess Ce content resulted in an inferior catalytic performance and stability. Therefore, there existed optimal cerium content for a specific SAPO-34. 相似文献
5.
H. Sasaki H. Jon M. Itakura T. Inoue T. Ikeda Y. Oumi T. Sano 《Journal of Porous Materials》2009,16(4):465-471
The hydrothermal conversion of FAU zeolite into aluminous MTN zeolite is described here. In the presence of both benzyltrimethylammonium
hydroxide (BTMAOH) and sodium chloride (NaCl) the highly crystalline and pure MTN zeolites with Si/Al ratios of 21-23 could
be obtained from the hydrothermal conversion of FAU zeolite. Based on powder XRD refinement and 13C CP/MAS NMR spectra, BTMA+ ions were not present in cages of the obtained zeolites, but TMA+ ions existed instead. It means that BTMAOH underwent degradation during the conversion. Moreover, the effects of Si/Al ratio
of starting FAU zeolite, synthesis parameters (BTMAOH/SiO2 and H2O/SiO2 ratios) and the addition of alkali metal chlorides on the hydrothermal conversion of FAU zeolite into MTN zeolite are discussed.
As compared to amorphous SiO2/γ-Al2O3, which produced impurity, the hydrothermal conversion of FAU zeolite showed a fast crystallization rate and a high selectivity
to MTN zeolite formation. These phenomena indicate that the assembly of locally ordered aluminosilicate species coming from
the decomposition or dissolution of FAU zeolite should be taking part in the conversion process. 相似文献
6.
Medina González Yaocíhuatl Hernández Luna Martín Alcaraz Cienfuegos Jorge 《Catalysis Letters》2006,110(1-2):107-113
Ni/H Zeolites catalysts were prepared by impregnation, starting from HY-Zeolite, Hβ-Zeolite and H-mordenite with nickel precursor salts, NiCl2, NiSO4 and NiCO3. The total number, NTSA, and the acid strength were found dependent on the nickel precursor salt. High catalytic activity,
selectivity and stability of the modified zeolites in isobutene dimerization was attributed to the acidic properties of nickel
modified zeolites. HY-Zeolite modified with NiCO3 resulted more active and selective to dimerization reaction. The prepared catalysts were characterized by EDSX, SEM, and
Adsorption/Desorption of N2 at 77 K, NH3 chemisorption and Ammonia Temperature-Programmed-Desorption (NH3-TPD) and FT-IR of adsorbed pyridine. NH3-TPD and isobutene adsorption revealed an acid sites a new distribution and apparition of acid sites not present in the protonated
zeolites. Catalytic activity and reactor behavior were studied in a continuous downstream fixed bed reactor at 298 K, 27.6 kPa
(4 psig), and WHSV = 0.27 h−1. 相似文献
7.
The nanocatalysts of Pd nanocubes supported on SiO2, TiO2 and MgO were prepared and the CO oxidation activities over the three catalysts were evaluated. The acid–basic properties of the support materials were determined using the temperature-programmed desorptions of NH3 (NH3-TPD) and CO2 (CO2-TPD). The CO adsorptions over the three catalysts were investigated by the diffuse reflectance infrared Fourier transform (DRIFT). It was found that the Pd/MgO catalyst showed the strongest ability to adsorb CO molecules and performed best for CO oxidation. 相似文献
8.
Modified beta zeolites were applied as catalysts for the Fries rearrangement reaction. The properties of the modified zeolites were characterized by NH3-TPD, n-hexane and 1,2,4-trimethylbenzene adsorption. Modification with SiO2 did not block the pores of the beta zeolite but reduced the number of acid sites on the surface. However, when the beta zeolite was modified with Ce2O3, the number of acid sites determined by NH3-TPD increased, which indicated that new acid sites are created by the interaction of cerium oxide and zeolite. Modified beta zeolites and H-beta were applied as catalysts for the Fries rearrangement of phenol acetate. Reaction over H-beta has low selectivity and the catalyst is easily deactivated. SiO2 modification of the catalyst increases the selectivity of the reaction but decreases the conversion. Ce2O3-modified beta zeolites show higher catalytic activity and rearrangement selectivity in the reaction than other catalysts. The stability of the catalyst is also improved after Ce2O3 modification. About 70% selectivity and 60-80% conversion can be achieved over 16 wt% Ce2O3-modified beta zeolite. 相似文献
9.
This contribution reports on the preparation, physicochemical characterization and catalytic performances of nitrided zeolites
in the Knoevenagel condensation reaction. These basic materials were prepared by subjecting one Y zeolite (Si/Al ratio of
2.6) and two ultrastable Y zeolites (Si/Al ratio of 13 and 37) to nitridation, i.e., treatment with ammonia at high temperature.
Both the amount and the chemical nature of incorporated nitrogen species were controlled by the nitridation temperature. Namely,
an increase of the temperature induces an increase of the nitrogen content and the appearance of nitrogenous species in the
following order of increasing temperature: NH4
+, adsorbed NH3, –NH2, >NH and >N–. The nitridation occurred practically in the same manner whatever the Si/Al ratio of the starting material.
However, from a catalytic point of view different behavior was observed. No direct correlation was found with the nitrogen
content of the samples. Nitrided zeolites were found to exhibit catalytic activity as long as the zeolitic framework was maintained. 相似文献
10.
《Catalysis communications》2007,8(9):1317-1322
Ga2O3–ZrO2 catalysts were prepared by a coprecipitation method. The catalysts were characterized by XRD, Raman, DRS, XPS, SEM, EDX, IR, NH3-TPD, CO2-TPD and N2 adsorption methods. Dehydrogenation of ethylbenzene and propane in the presence of CO2 over these catalysts has been investigated and compared. Ga2O3–ZrO2 catalysts exhibit different catalytic behavior for the two dehydrogenation reactions. 相似文献
11.
Yasutaka Kuwahara Junya Aoyama Keisuke Miyakubo Taro Eguchi Takashi Kamegawa Kohsuke Mori Hiromi Yamashita 《Journal of Catalysis》2012,285(1):223-234
Preparation of highly hydrophobic FAU zeolite has been achieved by a two-step preparation method that comprises predealumination treatment using concentrated mineral acids and subsequent calcination treatment. The hydrophilic/hydrophobic character of the zeolites was estimated by detailed adsorption measurements using water and toluene molecules as adsorbates, which showed the strict hydrophobic nature of the prepared FAU zeolites. By means of TG, FT-IR, and 29Si MAS NMR analyses, it was concluded that the enhancement in hydrophobicity originates from the healing of silanol defect sites and the formation of a refined silica surface with fewer adsorption sites. Thus-prepared FAU zeolite, with high crystallinity, structural and thermal stability, and hydrophobicity, significantly improved the photocatalytic degradation rates of 2-propanol in water and acetaldehyde in air on TiO2 when it was used as a catalyst support. A distinct correlation was found between the hydrophobicity of zeolites and photocatalytic activity of the supported TiO2. 相似文献
12.
Propylene aromatization reaction was performed on various MFI type zeolites containing Ga species. The Ga was introduced into
the zeolites by substitution (Ga-MFI), ion exchange (GIZ) and physical mixing (GPZ). A com-mercialized zeolite (PQZSM-5) was
also used for comparison. The catalysts prepared were characterized by using XRF, XPS, surface area measurement, NH3-TPD, and H2-TPR. Through the Ga substitution, the acidity of the modified catalysts was decreased, and dehydrogenation and aromatization
reactions occurred more easily. The lattice Ga did not react well with hydrogen contrary to the Ga located at the outside
of the lattice. It was also found that Ga-MFI catalysts facilitate alkylation reactions.
This paper is dedicated to Professor Wha Young Lee on the occasion of his retirement from Seoul National University 相似文献
13.
Zhang Peiqing Wang Xiangsheng Guo Xinwen Guo Hongchen Zhao Leping Hu Yongkang 《Catalysis Letters》2004,92(1-2):63-68
Nanoscale HZSM-5 zeolite was hydrothermally treated with steam containing 0.8 wt% NH3 at 773 K and then loaded with La2O3 and NiO. Both the parent nanoscale HZSM-5 and the modified nanoscale HZSM-5 zeolites catalysts were characterized by TEM, XRD, IR, NH3-TPD and XRF, and then the performance of olefins reduction in fluidized catalytic cracking (FCC) gasoline over the modified nanoscale HZSM-5 zeolite catalyst was investigated. The IR and NH3-TPD results showed that the amount of acids of the parent nanoscale HZSM-5 zeolite decreased after the combined modification, so did the strong acid sites deactivating catalysts. The stability of the catalyst was still satisfactory, though the initial activity decreased a little after the combined modification. The modification reduced the ability of aromatization of nanoscale HZSM-5 zeolite catalyst and increased its isomerization ability. After 300 h onstream, the average olefins content in the gasoline was reduced from 56.3 vol% to about 20 vol%, the aromatics (C7–C9 aromatics mainly) and paraffins contents in the product were increased from 11.6 vol% and 32.1 vol% to about 20 vol% and 60 vol% respectively. The ratio of i-paraffins/n-paraffins also increased from 3.2 to 6.6. The yield of gasoline was obtained at 97 wt%, while the Research Octane Number (RON) remained about 90. 相似文献
14.
In this research, Ni/SiO2 catalyst was modified with different amount of Gd2O3 and characterized with temperature-programmed desorption of CO2 (CO2-TPD) and NH3 (NH3-TPD), temperature-programmed reduction with H2 (H2-TPR) and X-ray diffraction (XRD). It was found that Gd2O3-modified Ni/SiO2 catalysts possessed higher CO2 adsorption and activation ability due to the formation of surface carbonate species. H2-TPR and XRD characterizations found that the strong interaction among nickel, Gd2O3 and SiO2 took place, which improved the dispersion of Ni. Gd2O3-modified Ni/SiO2 catalysts exhibited higher activity and stability for the combined oxy-CO2 reforming of methane in fluidized-bed reactor. The H2/CO ratio in produced syngas could be controlled via controlling reaction temperature and CO2/O2 ratio in feed. 相似文献
15.
Xiaoxiao Wang Fang Guo Xianxian Wei Zhenmin Liu Wei Zhang Shaoqing Guo Liangfu Zhao 《Korean Journal of Chemical Engineering》2016,33(7):2034-2041
A series of SAPO-11 zeolites with different Si contents were prepared by hydrothermally synthesized method. They were characterized by ICP, XRD, SEM, FT-IR, N2 adsorption-desorption, NH3-TPD and 29Si MAS NMR, and evaluated by the methylation of naphthalene with methanol to 2,6-dimethylnaphthalene (2,6-DMN). According to XRD and SEM results, the crystallinity of SAPO-11 sample increased with increase of the Si content until the SiO2/Al2O3 ratio was up to 0.2. However, a reduction in the crystallinity was observed with further increase of the Si content of the synthesis. N2 adsorption-desorption results showed that all the samples possessed micropores and secondary mesopores. SAPO-11 sample with SiO2/Al2O3 ratio of 0.2 exhibited the largest secondary mesopores size distributions. NH3-TPD and 29Si MAS NMR showed that the Si content was incorporated into the framework affecting not only the acid sites but also the acid strength of SAPO-11. SAPO-11 with SiO2/Al2O3 ratio of 0.2 presented the high catalytic performances for the methylation of naphthalene, which was mainly attributed to the amount of secondary mesopores in the SAPO-11 zeolite. 相似文献
16.
Zhijuan Zhang Shikai Xian Hongxia Xi Haihui Wang Zhong Li 《Chemical engineering science》2011,(20):150
The imidazolate framework ZIF-8 samples were modified separately by using ammonia impregnation and thermal treatment in atmosphere of N2 or H2 in order to improve its adsorption property toward CO2, and the modified samples A-ZIF-8, N-ZIF-8 and H-ZIF-8 were correspondingly available. The modified ZIF-8 samples were characterized, and the surface chemical properties of the ZIF-8 samples were determined separately by FTIR, CO2-TPD, NH3-TPD and H2O-TPD. The isotherms of CO2 on the modified ZIF-8 samples were measured. Results showed that after surface modification, the total amounts of basicity of the modified samples significantly increased, and followed the order: A-ZIF-8>H-ZIF-8>N-ZIF-8>O-ZIF-8. The uptakes of CO2 increased proportionally with the basic groups on the surfaces of the ZIF-8 samples due to CO2 being an acidic molecule. As a consequence of that, the CO2 adsorption capacity of the samples followed the order: A-ZIF-8>H-ZIF-8>N-ZIF-8>O-ZIF-8. The amount adsorbed of CO2 on the modified ZIF-8 sample by ammonia impregnation is the highest, having an increase. 相似文献
17.
Jimei Xue Xiaowei Yin Fang Ye Litong Zhang Laifei Cheng 《Journal of the American Ceramic Society》2013,96(3):979-986
A thermodynamic calculation on the chemical vapor deposition of the SiCl4–NH3–CH4–H2–Ar system was performed using the FactSage thermochemical software databases. Predominant condensed phases at equilibrium were SiC, Si3N4, graphite, and Si. The equilibrium conditions for the deposition of condensed phases in this system were determined as a function of the deposition temperature, dilution ratio (δ), and reactant ratios of CH4/SiCl4 and NH3/SiCl4. The CVD phase diagrams were used to understand the reactions occurring during the formation of Si–C–N from the gas species and determine the area of SiC–Si3N4. The concentration of condensed‐phase products was used to determine the deposition conditions of CVD SiC–Si3N4. The present work was helpful for further experimental investigation on CVD Si–C–N. 相似文献
18.
N. V. Vlasenko Yu. N. Kochkin A. M. Puziy P. E. Strizhak 《Chemical Engineering Communications》2017,204(8):937-941
Catalytic activity of different zeolites: H,NH4-form of mordenite-containing rock (H-CMK) and H-Beta with a Si/Al ratio of 15–407 (H-ВЕА) in ethyl tert-butyl ether (ETBE) synthesis in a packed-bed flow reactor at 80–180°C and 1?MPa has been studied. Acid characteristics of zeolites were determined by stepwise (Quasi-Equilibrium) ammonia thermodesorption. Three types of acid sites of different strength has been found, which is marked as weak (ENH3?=?60–75?kJ/mol), medium (ENH3?=?86–123?kJ/mol), and strong (ENH3?=?112–145?kJ/mol). The correlation between ETBE productivity and the concentration of weak acid sites has been found. Thereby, it was established that weak acid sites of zeolites are the active sites in ETBE synthesis. 相似文献
19.
《Catalysis communications》2007,8(3):416-423
12-Molybdophosphoric acid (PMo), Ni and Ni–PMo loaded on nanoscale HZSM-5 zeolites were prepared and characterized by BET, IR, XRD, Py-IR, NH3-TPD, TG and SEM. The hydroconversion of n-octane over various catalysts was investigated in order to obtain light isomers alkanes and aromatics products with high-octane-number. The acid amounts of the catalysts were modified after the loading of PMo and Ni, and its relation to the activity of the reaction was discussed. It is concluded that the stability of aromatization is improved, and the yield of light iso-alkanes is enhanced due to the introduction of PMo and Ni. The improved activity of n-octane hydroconversion over PMo and Ni loaded nanoscale HZSM-5 zeolites could be attributed to the increase of the acid amounts and the synergetic effect between Brønsted and Lewis acid sites. 相似文献
20.
《Journal of the European Ceramic Society》2004,24(12):3409-3417
The Si/B/C/N/H polymer T2(1), [B(C2H4Si(CH3)NH)3]n, was reacted with different amounts of H3Al·NMe3 to produce three organometallic precursors for Si/B/C/N/Al ceramics. These precursors were transformed into ceramic materials by thermolysis at 1400 °C. The ceramic yield varied from 63% for the Al-poor polymer (3.6 wt.% Al) to 71% for the Al-rich precursor (9.2 wt.% Al). The as-thermolysed ceramics contained nano-sized SiC crystals. Heat treatment at 1800 °C led to the formation of a microstructure composed of crystalline SiC, Si3N4, AlN(+SiC) and a BNCx phase. At 2000 °C, nitrogen-containing phases (partly) decomposed in a nitrogen or argon atmosphere. The high temperature stability was not clearly related to the aluminium concentration within the samples. The oxidation behaviour was analysed at 1100, 1300, and 1500 °C. The addition of aluminium significantly improved the oxide scale quality with respect to adhesion, cracking and bubble formation compared to Al-free Si(/B)/C/N ceramics. Scale growth rates on Si/B/C/N/Al ceramics at 1500 °C were comparable with CVD–SiC and CVD–Si3N4, which makes these materials promising candidates for high-temperature applications in oxidizing environments. 相似文献