共查询到20条相似文献,搜索用时 46 毫秒
1.
Howon Lee Ji Chul Jung Heesoo Kim Young-Min Chung Tae Jin Kim Seong Jun Lee Seung-Hoon Oh Yong Seung Kim In Kyu Song 《Korean Journal of Chemical Engineering》2009,26(4):994-998
Oxidative dehydrogenation of n-butene to 1,3-butadiene over ZnFe2O4 catalyst mixed with Cs
x
H3−x
PW12O40 heteropolyacid (HPA) was performed in a continuous flow fixed-bed reactor. The effect of Cs
x
H3−x
PW12O40 addition on the catalytic performance of ZnFe2O4 was investigated. Cs
x
H3−x
PW12O40 itself showed very low catalytic performance in the oxidative dehydrogenation of n-butene. However, addition of small amount
of Cs
x
H3−x
PW12O40 into ZnFe2O4 enhanced the catalytic performance of ZnFe2O4 catalyst. The catalytic performance of ZnFe2O4-Cs
x
H3−x
PW12O40 mixed catalysts was closely related to the surface acidity of Cs
x
H3−x
PW12O40. Among the catalysts tested, ZnFe2O4-Cs2.5H0.5 PW12O40 mixed catalyst showed the best catalytic performance. Strong acid strength and large surface acidity of Cs2.5H0.5PW12O40 was responsible for high catalytic performance of ZnFe2O4-Cs2.5H0.5PW12O40 mixed catalyst. Thus, Cs2.5H0.5PW12O40 could be utilized as an efficient promoter and diluent in formulating ZnFe2O4 catalyst for the oxidative dehydrogenation of n-butene. 相似文献
2.
Joongwon Lee Sunhwan Hwang Dong Ryul Park Jeong Gil Seo Min Hye Youn Ji Chul Jung Sang-Bong Lee Jin Suk Chung In Kyu Song 《Korean Journal of Chemical Engineering》2010,27(3):807-811
Palladium-exchanged heteropolyacid (Pd0.15Cs
x
H2.7−x
PW12O40) catalysts were prepared by an ion-exchange method with a variation of cesium content (x=2.0, 2.2, 2.5, and 2.7) for use
in the production of middle distillate through hydrocracking of paraffin wax. Surface acidity of Pd0.15Cs
x
H2.7−x
PW12O40 catalysts determined by NH3-TPD experiments showed a volcano-shaped trend with respect to cesium content. Surface acidity of the catalysts played an
important role in determining the catalytic performance in the hydrocracking of paraffin wax. Conversion of paraffin wax increased
with increasing surface acidity of the catalyst, while yield for middle distillate showed a volcano-shaped curve with respect
to surface acidity of the catalyst. Among the catalysts tested, Pd0.15Cs2.7PW12O40 catalyst with moderate surface acidity showed the best catalytic performance. 相似文献
3.
Hai Woong Park Sunyoung Park Dong Ryul Park Jung Ho Choi In Kyu Song 《Korean Journal of Chemical Engineering》2011,28(5):1177-1180
Cesium-exchanged Cs
x
H3.0−x
PW12O40 (X=2.0–3.0) heteropolyacid catalysts were prepared and applied to the decomposition of benzyl phenyl ether to aromatics.
Benzyl phenyl ether was chosen as a lignin model compound for representing α-O-4 bond in lignin. Phenol, benzene, and toluene were mainly produced by the decomposition of benzyl phenyl ether. Conversion
of benzyl phenyl ether and total yield for main products (phenol, benzene, and toluene) were closely related to the surface
acidity of Cs
x
H3.0−x
PW12O40 (X=2.0–3.0) heteropolyacid catalyst. Conversion of benzyl phenyl ether and total yield for main products increased with increasing
surface acidity of the catalyst. Among the catalysts tested, Cs2.5H0.5PW12O40 with the largest surface acidity showed the highest conversion of benzyl phenyl ether and total yield for main products. 相似文献
4.
Sunyoung Park Sang Hee Lee Sun Ho Song Dong Ryul Park Sung-Hyeon Baeck Tae Jin Kim Young-Min Chung Seung-Hoon Oh In Kyu Song 《Catalysis communications》2009,10(4):391-394
Palladium-exchanged insoluble heteropolyacid (Pd0.15CsxH2.7?xPW12O40) catalysts were prepared with a variation of cesium content (x = 2.0, 2.2, 2.5, and 2.7), and were applied to the direct synthesis of hydrogen peroxide from hydrogen and oxygen. Pd0.15CsxH2.7?xPW12O40 showed high catalytic performance even in the absence of H2SO4 additive, indicating that Pd0.15CsxH2.7?xPW12O40 acted as an efficient catalyst and served as an alternate acid source in the reaction. The catalytic performance of Pd0.15CsxH2.7?xPW12O40 increased with increasing surface acidity of the catalyst. Among the catalysts tested, Pd0.15Cs2.5H0.2PW12O40 catalyst with the largest surface acidity showed the highest yield for hydrogen peroxide. 相似文献
5.
The cesium salts Cs x H3?x PW12O40 of Cs content x = 2 up to x = 3 were tested as the catalysts in the gas and liquid phase reactions. Dehydration of ethanol and transesterification of triglycerides with methanol were selected as the catalytic reactions. Apart from the standard preparation, the catalysts were prepared by two-stage procedure with methanol or water as a solvent. The Cs-salts were characterized by FT-IR, XRD, scanning electron microscopy and energy dispersive X-ray techniques. In turn, the influence of Cs-salts composition on the pH and conductivity of their aqueous colloidal solutions was investigated. The results obtained by the latter techniques were also characteristic for acidity of surface layer of colloidal particles because of surface layer-solution equilibrium. It has been shown that the secondary structure of acidic cesium salts existing in crystalline samples (solid solution of H3PW12O40 in Cs3PW12O40) changes after contacting with polar medium to the system consisting most probably of Cs3PW12O40 core with epitaxial layer of heteropolyacid. This is result of the protons migration from bulk to surface layer of primary particles enhanced by polar medium. It strongly influences the surface acidity of primary particles as well as the activity of Cs-salts in transesterification of triglycerides with methanol. In such polar medium, Cs2HPW12O40 salt becomes the most active catalyst, more active than Cs2.5H0.5PW12O40. An accumulation of partial glycerides and in particular glycerol on the surface of primary particles of Cs-salts resulted in relatively low maximum conversion of triglycerides, most probably due to partial blockage of the catalytic centers. This effect and the almost constant activity of Cs-salts under recycling use in the transesterification experiments are considered to be experimental evidences that methanolysis over Cs-salts was accomplished with the participation of surface protons. 相似文献
6.
Pore Structure and Shape Selectivity of Platinum-Promoted Cesium Salts of 12-Tungstophosphoric Acid 总被引:1,自引:0,他引:1
Yoshinaga Yusuke Suzuki Tetsuo Yoshimune Miki Okuhara Toshio 《Topics in Catalysis》2002,19(2):179-185
Pore-widths and pore-size distributions of 0.5 wt% Pt-CsxH3-xPW12O40 have been studied by means of adsorption of various molecules. For the distributions of micropore and mesopore, isotherms of Ar and N2 adsorption were analyzed, respectively. Pt-Cs2.1H0.9PW12O40 possessed only ultramicropores. On the other hand, the pores of Pt-CsxH3-xPW12O40 (x = 2.3, 2.5, 2.8 and 3.0) showed bimodal distributions in the range from micropore to mesopore, and the widths of both pores tended to increase as the Cs content increased. From the amounts and rates of adsorption for n-butane and isobutane, the pore width of Pt-Cs2.1H0.9PW12O40 was determined to be close to the molecular size of n-butane, that is, 0.43 nm. The fraction of external surface area in the total surface area of Pt-Cs2.1H0.9PW12O40 was estimated to be only 0.06 from the adsorption of 1,3,5-trimethylbenzene and t-plot of N2 adsorption. Pt- Cs2.1H0.9PW12O40 exhibited a shape selectivity due to the uniform ultramicropores and small external surface area; it catalyzed the oxidation of n-butane but not that of isobutane. SEM and TEM measurements revealed the primary crystallites and their aggregated states. 相似文献
7.
The heteropolyacid H3PW12O40 and its cesium salts CsxH3-x
PW12O40 (x = 1, 2, 2.5, 3) were synthesized, characterized and tested as catalysts for hydrocarbon reactions. All samples were characterized
by a variety of techniques including elemental analysis, X-ray diffraction, dinitrogen adsorption, thermal gravimetric analysis
and ammonia sorption. Results from these methods confirmed that pure cesium salts were prepared without significant contamination
by amorphous oxide phases. Incorporation of cesium into the heteropolyacid decreased the acidic protons available for catalysis,
increased the specific surface area, and increased the thermal stability. The heteropolyacids were tested as catalysts for
butane skeletal isomerization, pentane skeletal isomerization and 1-butene double bond isomerization. For comparison, the
activity of sulfated zirconia, a well-studied strong acid catalyst, was also evaluated for the three probe reactions. On a
per gram basis, the Cs2HPW12O40 sample was the most active heteropolyacid, presumably due to its high surface area. This sample was more active than sulfated
zirconia for pentane skeletal isomerization and 1-butene double bond isomerization. However, sulfated zirconia was more effective
for butane skeletal isomerization. Since the pentane and 1-butene reactions were monomolecular in nature, whereas butane isomerization
was bimolecular, restrictions inside the micropores of the heteropolyacid may inhibit the formation of long chain intermediates.
Interestingly, trace butenes were required to initiate butane isomerization reactions on sulfated zirconia, whereas heteropolyacids
catalyzed the reaction in the absence of butenes.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
8.
Ruihua Gao Hui Chen Yingyi Le Wei-Lin Dai Kangnian Fan 《Applied Catalysis A: General》2009,352(1-2):61-65
In the present work, for the first time the Cs2.5H0.5PW12O40/SBA-15 catalysts were prepared as highly efficient catalysts for the direct production of glutaric acid (GAC) via selective oxidation of cyclopentane-1,2-diol by using aqueous hydrogen peroxide as the green oxidant. The yield of GAC is higher than 88%. The fresh catalyst and the recovered ones were all characterized by XRD, FT-IR, Raman and 31P MAS NMR to reveal the structure change during the reaction. XRD results revealed that the Cs2.5H0.5PW12O40/SBA-15 catalysts keep the crystalline structure of the as-prepared Cs2.5H0.5PW12O40. And it is found that the structure of the Cs2.5H0.5PW12O40/SBA-15 catalysts was retained after the reaction, as determined by Raman, FT-IR and 31P MAS NMR. The new Cs2.5H0.5PW12O40/SBA-15 catalyst can be easily recycled after reaction and can be reused six times, indicating its excellent stability. 相似文献
9.
制备了负载型磷钨酸铯(Cs2.5H0.5PW12O40)催化剂,考察了载体种类、载体性质、制备方法和制备条件对催化剂性能的影响,对制备的催化剂进行了表征,并考察了负载型Cs2.5H 0.5PW12O40作为醚化催化剂的催化活性.结果表明,大孔硅胶是Cs2.5H0.5PW12O40的适宜载体,硅胶的钠含量越低制备的Cs2.5H0.5PW12O40/SiO2催化剂的活性越高.采用一步法和二步法制备的Cs2.5H0.5PW12O40/SiO2催化剂均具有较强的酸性、催化活性以及良好的稳定性,可以替代液体酸和阳离子交换树脂,成为一种环境友好的固体酸催化剂. 相似文献
10.
Cs exchanged phosphotungstic acid is a highly efficient and environmentally benign solid acid catalyst for the liquid-phase Beckmann rearrangement of ketoximes to the corresponding amides. The catalysts CsxH3−xPW12O40 (x = 1.5, 2, 2.5 and 3) were prepared by a titration method. The characterization results indicated that the primary Keggin structure remained intact after exchanging the protons with Cs ions. Moreover, the Cs exchanged catalysts were insoluble and exhibited larger BET surface area than the parent acid. The catalysts exhibited high reactivity and selectivity for the formation of -caprolactam, the precursor of Nylon 6, from cyclohexanone oxime. The catalyst can be recovered after reaction without any structural transformation. 相似文献
11.
Catalytic synthesis of N-adamantylacrylamide from acrylonitrile and 1-adamantanol has been studied over various solid and
liquid acids. Solid acids such as Cs2.5H0.5PW12O40, Amberlyst 15, Nafion, and Nafion–SiO2 composite gave yields higher than 97% at 373 K, and were superior in yield to liquid acids like p-toluenesulfonic acid, H3PW12O40, and H2SO4. It was further demonstrated that Cs2.5H0.5PW12O40 exhibited the highest catalytic performance for this reaction in the presence of excess water.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
12.
12-Phosphotungstic acid and its cesium salts supported on a dealuminated ultra-stable Y zeolite were prepared, and showed the high catalytic activity in the liquid-phase esterification of acetic acid with n-butanol. The supported Cs2.5H0.5PW12O40 catalyst gave a high conversion of n-butanol of 94.6% and a selectivity for n-butyl acetate of 100%, accompanying the high water-tolerance and catalytic reusability without regeneration. 相似文献
13.
Xiaoxiang Han Yingying Kuang Chunhua Xiong Xiujuan Tang Qing Chen Chin-Te Hung Li-Li Liu Shang-Bin Liu 《Korean Journal of Chemical Engineering》2017,34(7):1914-1923
A series of organic-inorganic composite catalysts, prepared by modifying tungstophosphoric acid (TPA; H3PW12O40) with different amino acids such as phenylalanine (Phe), alanine (Ala), and glycine (Gly) were synthesized. The physicochemical and acidic properties of these (MH) x H3?x PW12O40 (M=Phe, Ala, and Gly; x=1–3) composite materials were characterized by a variety of different analytical and spectroscopic techniques, namely TGA, XRD, FT-IR, XPS, and NMR, and exploited as heterogeneous catalysts for selective oxidation of benzyl alcohol (BzOH) with hydrogen peroxide (H2O2). Among them, the [PheH]H2PW12O40 catalyst exhibited the best oxidative activity with an excellent BzOH conversion of 99.0% and a desirable benzaldehyde (BzH) selectivity of 99.6%. Further kinetic studies and model analysis by response surface methodology (RSM) revealed that the oxidation of BzOH with H2O2 follows a second-order reaction with an activation energy of 56.7 kJ·mol?1 under optimized experimental variables: BzOH/H2O2 molar ratio=1 : 1.5 mol/mol, amount of catalyst=6.1 wt%, reaction time (x3)=3.8 h, and amount of water (x4)=30.2 mL. 相似文献
14.
Yihang Guo Kexin Li Xiaodan Yu James H. Clark 《Applied catalysis. B, Environmental》2008,81(3-4):182-191
Mesoporous H3PW12O40-silica composite catalysts with controllable H3PW12O40 loadings (4.0–65.1%) were prepared by a direct sol–gel–hydrothermal technique in the presence of triblock poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) copolymer. Powder X-ray diffraction (XRD) patterns and nitrogen sorption analysis indicate the formation of well-defined mesoporous materials. With H3PW12O40 loading lower than 20%, the materials exhibit larger BET surface area (604.5–753.0 m2 g−1), larger and well-distributed pore size (6.1–8.6 nm), larger pore volume (0.75–1.2 cm3 g−1), and highly dispersed Keggin unit throughout the materials. Raman scattering spectroscopy studies confirm that the primary Keggin structure remained intact after formation of the composites. As a novel kind of reusable solid acid catalyst, as-prepared H3PW12O40-silica composite was applied for the synthesis of diphenolic acid (DPA) from biomass platform molecule, levulinic acid (LA), under solvent-free condition, and remarkably high catalytic activity and stability were observed. 相似文献
15.
Nadine Essayem Gisèle Coudurier Michel Fournier Jacques C. Védrine 《Catalysis Letters》1995,34(1-2):223-235
The heteropolyacid of Keggin structure (H3PW12O40) and several of its cesium salts have been synthesized and characterized for their acidic properties. Chemical analysis, TGA, NH3 adsorption-desorption and31P MAS-NMR techniques permit the characterization of the Brønsted acidity. The catalytic properties were studied forn-butane isomerization and for methanol conversion to dimethyl ether at 200 and 180°C, respectively. Our conclusion is that, in term of conversion, the more acidic catalysts are in the range Cs2/2.7 if considering a wide range of acid strengths evidenced by methanol conversion. The range is Cs2/Cs2.1 if one considers only very strong acidity as evidenced byn-butane isomerization. 相似文献
16.
Influence of the nature and porosity of different supports on the acidic and catalytic properties of H3PW12O40 总被引:3,自引:0,他引:3
In order to obtain highly dispersed heteropolyacid (HPA) species, H3PW12O40 was supported on various supports exhibiting different porosities and surface chemical properties. Amorphous and monoclinic amphoteric zirconias, activated montmorillonite (AC) and hexagonal silica (HMS) were chosen as supports. It was observed that the zirconia support partly decomposed HPA at low coverage, giving the lacunary anion PW11O39
7–, due to the reaction with basic hydroxyl groups, whereas montmorillonite and HMS did not. Catalytic properties for n-butane to isobutane isomerisation at 473 K and propan-2-ol decomposition at 353 K were compared for all samples as a function of HPA loadings and compared to data already published on bulk H3PW12O40 and Cs1.9H1.1PW12O40 samples. It was found for HPA/AC samples that, although their activity for propan-2-ol decomposition varied linearly with HPA loading, their activity for n-butane isomerisation was very weak, which indicates a weaker acid strength by supporting the HPA. This is probably due to the exchange of protons from the HPA by the exchangeable cations of the montmorillonite, the new protons associated with the clay being much less acidic. It also appeared, when comparing with catalytic data already published on for HPA/HMS, that HMS was the best support for HPA without modifying appreciably its catalytic and thus their acid properties, the HPA being certainly bonded to the HMS walls by hydrogen bonding. Assuming a diameter of 1.2 nm for each Keggin anion, the turnover frequency (TOF) values for n-butane isomerisation at 473 K were calculated per surface Keggin species for HPA/HMS, bulk H3PW12O40 and Cs1.9H1.1PW12O40, and were found to be equal to 155, 113 and 100×10–5 s–1, respectively, and thus to be very close, showing that the acid strength of the three samples was comparable. It was found to equal only 3.4×10–5 s–1 for the HPA/AC sample, in agreement with a weaker acid strength. At last, mesoporosity of the support was found to favour n-butane isomerisation reaction. 相似文献
17.
Micropore size distributions of Cs2.1H0.9PW12O40 and 0.5 wt% Pt-Cs2.1H0.9PW12O40 as well as H-ZSM-5, H-Y and AlPO4-5 as standard porous materials were analyzed by Ar porosimetry, assuming cylindrical pores consisting of oxide ions. The calculated pore-widths of H-ZSM-5, HY and AlPO4-5 were in agreement with the pore-opening sizes determined by XRD. The Ar porosimetry demonstrated that Cs2.1H0.9PW12O40 and 0.5 wt% Pt-Cs2.1H0.9PW12O40 possess only ultramicropores having widths of about 0.5 nm. Adsorption of various molecules revealed that the pore widths of these heteropoly compounds were in the range 0.43–0.59 nm, which is consistent with the results of the Ar porosimetry. In conclusion, nearly uniformly sized micropores are formed on both Cs2.1H0.9PW12O40 and 0.5 wt% Pt-Cs2.1H0.9PW12O40. 相似文献
18.
Isomerization of n-hexane and n-heptane was carried out over Cs2.5H0.5PW12O40 (denoted by Cs2.5) promoted by Pt which was introduced by either impregnation of H2PtCl6 or mechanical mixing of Pt/Al2O3 and over non-promoted Cs2.5H0.5PW12O40 in the presence of hydrogen at atmospheric pressure. The reaction temperature studied was relatively low (typically 453 and
423 K for n-hexane and n-heptane, respectively) and the hydrogen pressure was also rather low (standard conditions: feed = n-alkane 0.05 atm, H2 0.20 atm, N2 balance; W/F = 40 g h mol−1). Results were compared with those obtained under the same conditions for other Pt-promoted solid acids, where particular
attention was paid to the time courses of the reaction (initial vs. stationary performance). Both the activity and selectivity
of Cs2.5 at the initial stage (after 5 min) increased by the addition of the Pt component. Pressure dependencies of the rate
at the initial stage were approximately first and −0.5th orders in alkane and hydrogen, respectively. Most remarkable was
the suppression of the deactivation during the reaction in the presence of both Pt and hydrogen. For example, the mechanical
mixture of Pt/Al2O3 and Cs2.5 (abbreviated as Pt+Cs2.5) showed little deactivation and much improved selectivity; resulting in high stationary
conversion and selectivity; e.g., 98.4 and 92.1% selectivities for n-hexane and n-heptane at the conversions of 58.6 and 39.4%, respectively. Most of the results were well explained by a classical bifunctional
mechanism, although other mechanisms are not all excluded. As for the other solid acids, the initial activity of Pt-promoted
SO4/ZrO2 was high, but decreased rapidly. The deactivation was small with Pt-promoted H-ZSM-5, but the activity was low. The stationary
yields of isomerized products were higher for Pt-promoted beta zeolite and Al-pillared saponite (tested only for n-heptane), although higher reaction temperatures were necessary.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
19.
Composites based on polydiphenylamine (PDPA) doped with heteropolyanions of H3PW12O40 and single-walled carbon nanotubes (SWNTs) were prepared by electrochemical polymerization of diphenylamine (DPA) on carbon nanotube films deposited onto Pt electrodes. HRTEM studies reveal that the electrochemical polymerization leads to the filling the spaces between tubes which compose the bundles, creating a monolithic film on the Pt electrode. The resulting composites were tested as active materials in supercapacitors. Resonant Raman scattering studies showed that the electropolymerization of DPA in the presence of H3PW12O40 and SWNTs leads to the covalent functionalization of SWNTs with doped PDPA. The covalent functionalization of SWNTs with PDPA doped with H3PW12O40 heteropolyanions was revealed by FTIR spectroscopy, based on the changes in the vibrational features of PDPA and H3PW12O40. These changes included i) a down-shift of the PDPA IR bands, which was attributed to the C–H bending vibrational mode of benzene (B), Caromatic–N, C–C stretching (B) + C–H bending (B) and C–C stretching vibrations of the B ring, from 1174, 1321, 1495 and 1603 cm− 1 to 1165, 1313, 1487 and 1599 cm− 1, respectively; ii) a change in the peak positions of IR bands associated with the W = O and P-O-W vibration modes of H3PW12O40; and iii) a down-shift of the IR band situated in the spectral range 650–725 cm− 1, which was assigned to the inter-ring deformation vibration mode.The characterization of symmetric solid-state supercapacitors was performed for electrodes prepared from i) SWNTs functionalized with PDPA doped with H3PW12O40 heteropolyanions, ii) SWNTs electrochemically decorated with H3PW12O40 heteropolyanions, and iii) PDPA doped with H3PW12O40 heteropolyanions. Preliminary results indicate high discharge capacitance values of up to 157.2 mF/cm2 for SWNTs functionalized with PDPA doped with H3PW12O40 heteropolyanions. The discharge capacitance of this material is superior to those recorded for SWNTs electrochemically decorated with H3PW12O40 heteropolyanions (~ 18.2 mF/cm2) and PDPA doped with H3PW12O40 heteropolyanions (~ 62.1 mF/cm2). 相似文献
20.
A series of Pd/XCs2.5H0.5PW12O40/OMC (ordered mesoporous carbon) (X = 10, 15, 20, 25, and 30 wt.%) catalysts with different Cs2.5H0.5PW12O40 contents (X, wt%) were prepared by a sequential incipient wetness impregnation method for use in the catalytic decomposition of 2,3-dihydrobenzofuran to monomeric cyclic compounds. 2,3-Dihydrobenzofuran was used as a lignin model compound for representing β-5 linkage of lignin. Acidity of Pd/XCs2.5H0.5PW12O40/OMC catalysts served as an important factor determining the catalytic performance in the reaction. Conversion of 2,3-dihydrobenzofuran and total yield for main products (2-ethylphenol and ethylcyclohexane) increased with increasing acidity of Pd/XCs2.5H0.5PW12O40/OMC catalysts. 相似文献