共查询到20条相似文献,搜索用时 31 毫秒
1.
《Catalysis communications》2005,6(6):399-403
Liquid phase Claisen–Schmidt condensation between 2′-hydroxyacetophenone and benzaldehyde to form 2′-hydroxychalcone, followed by intramolecular cyclisation to form flavanone was carried out over zinc oxide supported metal oxide catalysts under solvent free condition. The reaction was carried out over ZnO supported MgO, BaO, K2O and Na2O catalysts with 0.2 g of each catalyst at 140 °C for 3 h. Magnesium oxide impregnated zinc oxide was observed to offer higher conversion of 2′-hydroxyacetophenone than other catalysts. Further MgO impregnated with various other supports such as HZSM-5, Al2O3 and SiO2 were also used for the reaction to assess the suitability of the support. The order of activity of the support is ZnO > SiO2 > Al2O3 > HZSM-5. Various weight percentage of MgO was loaded on ZnO to optimize maximum efficiency of the catalyst system. The impregnation of MgO (wt%) in ZnO was optimized for better conversion of 2′-hydroxyacetophenone. The effect of temperature and catalyst loading was studied for the reaction. 相似文献
2.
Pt-based catalysts, supported on Al2O3, SiO2 and SiO2–Al2O3, were prepared by incipient wetness impregnation and tested in the gas phase hydrogenation of maleic anhydride at atmospheric pressure and 240 °C. In these conditions, the hydrogenolytic activity pattern was: Pt/SiO2 > Pt/Al2O3 > Pt/SiO2–Al2O3, which is just the opposite of the support acidity trend. These metal Pt-based catalysts showed high selectivity to propionic acid, which was always higher than 80%. The selectivity pattern to this product was: Pt/Al2O3 > Pt/SiO2 > Pt/SiO2–Al2O3. Both activity and selectivity patterns may be explained on the basis of metal-support interaction and support acidity. 相似文献
3.
Hydrodeoxygenation of phenol, as model compound of bio-oil, was investigated over Pd catalysts, using formic acid as a hydrogen donor. The order of activity for deoxygenation of phenol with Pd catalysts was found to be: Pd/SiO2 > Pd/MCM-41 > Pd/CA > Pd/Al2O3 > Pd/HY ≈ Pd/ZrO2 ≈ Pd/CW > Pd/HSAPO-34 > Pd/HZSM-5. The good performance of Pd/SiO2 is owing to its proper pore structure and large specific surface area. The high level of Brønsted acid sites in SiO2 also favors the deoxygenation of phenol. 相似文献
4.
《Catalysis communications》2011,12(15):1220-1223
Shape-selective amination of ethylene oxide over HZSM-5 was thoroughly investigated. TPD, FTIR and catalytic performance showed that HZSM-5 was more active than the sodium form. Relative selectivity of product was mainly controlled by the crystal size of ZSM-5. Surface modification such as silyation was effective for enhancing the shape selectivity. Among the catalysts tested in this study, HZSM-5 with SiO2/Al2O3 ratio being 76.7 exhibited the best performance. At 353 K and total pressure of 8.0 MPa the total selectivity of MEA and DEA was 97.6%, the yield reached 96.6%, the best performance achieved so far among EO amination. 相似文献
5.
Qingde Zhang Yisheng Tan Caihong Yang Hongjuan Xie Yizhuo Han 《Journal of Industrial and Engineering Chemistry》2013,19(3):975-980
The conversion of syngas to aromatics via dimethyl ether was investigated over MnCl2 modified HZSM-5 zeolites. The results demonstrated that 2%MnCl2 modified HZSM-5 (SiO2/Al2O3 = 38) exhibited higher p-xylene selectivity than other catalysts and further decreased 1,2,4,5-tetramethylbenzene selectivity. The CO conversion was obviously increased after 5%MnCl2 modification to HZSM-5. The catalysts were characterized by XRD, BET, XPS, FT-IR, NH3-TPD, SEM, element analysis and O2-TPO. The loading amount of MnCl2 affected the adsorption and reaction of DME molecules on zeolites. Appropriate amount of MnCl2 introduction could adjust the acidity and pore volume of HZSM-5 to increase p-xylene selectivity and CO conversion. 相似文献
6.
Lignin has been gasified with a Ni/Al2O3–SiO2 catalyst in sub/supercritical water (SCW) to produce gaseous fuels. XRD pattern at 6θ angle shows characteristic peaks of crystalline NiO, NiSi, and AlNi3, suggesting that Al2O3–SiO2 not only offers high surface area (122 m2 g) for Ni, but also changes the crystal morphology of the metal. 9 mmol/g of H2 and 3.5 mmol/g of CH4 were produced at the conditions that 5.0 wt% alkaline lignin plus 1 g/g Ni/Al2O3–SiO2 operating for 30 min at 550 °C. A kinetic model was also developed, and the activation energies of gas and char formation were calculated to be 36.68 ± 0.22 and 9.0 ± 2.4 kJ/mol, respectively. Although the loss of activity surface area during reuse caused slight activity reduction in Ni/Al2O3–SiO2, the catalyst system still possessed high catalytic activity in generating H2 and CH4. It is noted that sulfur linkage could be hydrolyzed to hydrogen sulfide in the gasification process of alkaline lignin. The stable chemical states of Ni/Al2O3–SiO2 grants its insensitivity to sulfur, suggesting that Ni/Al2O3–SiO2 should be economically promising for sub/supercritical water gasification of biomass in the presence of sulfur. 相似文献
7.
A bifunctional Pt–Pd catalyst supported on phosphorus-containing activated carbon has been prepared, characterized and tested in the hydrocracking of a hydrotreated tire pyrolysis oil. The product has a very interesting composition: 48–78 wt% naphtha and 19–42 wt% diesel fractions, with moderate amounts of aromatics (< 40 wt%) and sulfur (< 250 ppm). The challenge was to prepare a stable, porous, selective and acid carbonaceous catalyst from a waste (olive stone), which has been confirmed from the catalytic properties and product distribution point of view. In fact, phosphate groups in the activated carbon are stable hydrocracking sites, with comparable performance to that of the acid sites present in amorphous SiO2–Al2O3. 相似文献
8.
《Fuel》2005,84(2-3):135-142
Heteroatom containing molecules in South Banko coal liquid (SBCL) distillate were identified with a gas chromatograph equipped with an atomic emission detector (GC-AED). Thiophenes and benzothiophenes were found to be the major sulfur compounds. Pyridines, anilines, and phenols were the major nitrogen and oxygen compounds, respectively. Reactivities of heteroatom containing species in hydrotreatment over conventional NiMoS/Al2O3, NiMoS/Al2O3–SiO2 catalysts were very different according to their cyclic structure as well as the kind of heteroatom in the species. The sulfur species were completely desulfurized over the catalysts examined in the present study by 60 min at 360 °C under initial hydrogen pressure of 5 MPa. However, hydrodenitrogenation was more difficult than hydrodesulfurization even at 450 °C. Anilines were found the most refractory ones among the nitrogen species. Hydrodeoxygenation of SBCL was also difficult in the hydrotreatment conditions examined in the present study. Dibenzofuran was the most refractory molecule among the oxygen species. A two-stage reaction configuration at 340 and 360 °C improved HDN and HDO reactivities, although the conversions were still insufficient. Increasing the acidity of the support as well as the loading of the metals on the NiMoS/Al2O3 catalysts improved very much the heteroatom reduction to achieve complete removal of nitrogen by two-stage reaction configuration at 340–360 °C and oxygen at 360 °C, respectively. The addition of H2S in the reaction atmosphere inhibited the HDN reaction but increased markedly the HDO conversion. The acidic support increased the activity in hydrotreatment through enhancing the hydrogenation activity, while H2S maintained the catalyst in a sufficiently sulfided state. 相似文献
9.
A series of CoMo catalysts were prepared by various methods with three different supports (Al2O3-1 of γ phase, Al2O3-2 containing γ and δ mixed phases, SiO2). And the effect of morphology of (Co)MoS2 phases on selective hydrodesulfurization was studied systematically. The TEM images showed, in general, the average slab length, the stacking number and the ratio of edge/corner of the sulfided catalysts increase remarkably in the order: SiO2 > Al2O3-2 > Al2O3-1, with the extent of metal–support interaction decreasing in the order: SiO2 < Al2O3-2 < Al2O3-1. And the hydrodesulfurization selectivity correlates linearly with the slab length (or the ratio of edge/corner) of (Co)MoS2 phases, the longer average slab length, the higher ratio of edge/corner, and then the better hydrodesulfurization selectivity. Among all the catalysts, sulfided CoMo/SiO2 of the longest average slab length and the highest edge/corner ratio exhibits the best hydrodesulfurization selectivity. 相似文献
10.
Chong Wang Xinping Wang Na Xing Qing Yu Yijing Wang 《Applied Catalysis A: General》2008,334(1-2):137-146
Zr-based zeolite catalysts were investigated for the first time in selective catalytic reduction of NO by hydrocarbon (HC-SCR). Highly dispersed zirconium species, especially the amorphous ultrafine zirconium oxide in the catalyst, considerably enhanced the activity for selective catalytic reduction of NO by acetylene (C2H2-SCR), both by accelerating the NO oxidation to NO2 and enlarging the NO2 adsorption capacity of the catalyst under the reaction conditions. Thus a durable and active Zr/HZSM-5 catalyst giving 89% of NO conversion to N2 at 350 °C in 1600 ppm NO, 800 ppm C2H2, and 9.95% O2 in helium was obtained. For the C2H2-SCR of NO, it was suggested that acidic sites with strong acidity on the Zr-based HZSM-5 catalysts are indispensable to initiate the aimed reaction via the route of NO oxidation to NO2, which explains the higher activity for the reaction obtained over the Zr/HZSM-5 catalyst sample with lower SiO2/Al2O3 ratio. The zirconium species could only functioned in the presence of protons in the C2H2-SCR of NO, so a synergistic effect between the zirconium species and protons of the Zr/HZSM-5 catalyst was proposed. 相似文献
11.
《Diamond and Related Materials》2007,16(8):1656-1664
Supported-NiO catalysts were tested in the synthesis of carbon nanotubes and carbon nanofibers by catalytic decomposition of methane at 550 °C and 700 °C. Catalytic activity was characterized by the conversion levels of methane and the amount of carbons accumulated on the catalysts. Selectivity of carbon nanotubes and carbon nanofiber formation were determined using transmission electron microscopy (TEM). The catalytic performance of the supported-NiO catalysts and the types of filamentous carbons produced were discussed based on the X-ray diffraction (XRD) results and the TEM images of the used catalysts. The experimental results show that the catalytic performance of supported-NiO catalysts decreased in the order of NiO/SiO2 > NiO/HZSM-5 > NiO/CeO2 > NiO/Al2O3 at both reaction temperatures. The structures of the carbons formed by decomposition of methane were dependent on the types of catalyst supports used and the reaction temperatures conducted. It was found that Al2O3 was crucial to the dispersion of smaller NiO crystallites, which gave rise to the formation of multi-walled carbon nanotubes at the reaction temperature of 550 °C and a mixture of multi-walled carbon nanotubes and single-walled carbon nanotubes at 700 °C. Other than NiO/Al2O3 catalyst, all the tested supported-NiO catalysts formed carbon nanofibers at 550 °C and multi-walled carbon nanotubes at 700 °C except for NiO/HZSM-5 catalyst, which grew carbon nanofibers at both 550 °C and 700 °C. 相似文献
12.
A series of nano-sized mesoporous Al2O3–B2O3 catalysts with different molar ratios of Al/B were prepared from aluminum isopropoxide and boric acid through an evaporation-induced self-assembly (EISA) process, and were characterized by ICP-AES, FTIR (pyridine adsorption), XRD, NH3-TPD, SEM, TEM, and N2 adsorption–desorption. These catalysts were further used as solid acids in the catalytic conversion of glucose to 5-hydroxymethylfurfural (HMF). An optimized HMF yield of 41.4% was obtained within 120 min at 140 °C over Al2O3–B2O3 (Al/B = 5:5). It was demonstrated that catalysts with the presence of Lewis acid sites were more favorable for the formation of HMF. 相似文献
13.
《Journal of the European Ceramic Society》2006,26(8):1447-1454
The crystallisation of amorphous precursors has been studied in the whole range of composition in the Al2O3–SiO2 system. The amorphous precursors have been obtained by hydrolysing TEOS directly in a diluted aqueous solution of aluminium nitrate, spray drying the clear solution and heating the resulting powder. Up to 70 mol % Al2O3, only mullite crystallises around 980–1000 °C; between 70 and 80 mol % Al2O3 mullite and spinel crystallise together; and for more than 80 mol % Al2O3 only spinel is formed. In the 70–80 mol % Al2O3 range of composition, when both mullite and spinel crystallise, low heating favours the crystallisation of mullite and it is nearly possible to crystallise only mullite from a 75 mol % Al2O3 sample. By rapid heating it is also possible to crystallise only spinel from the same 75 mol % Al2O3 precursor. The enthalpy and the activation energy for crystallisation are maximum for 60–80 mol % Al2O3. Heating the samples up to 1700 °C for 1 h, the phase equilibrium is not reached, particularly when both mullite and spinel crystallise together, and θ-Al2O3 is still present. 相似文献
14.
《Fuel》2006,85(10-11):1329-1334
Using the amorphous aluminosilicate in coal fly ash (FA), a single phase Na–A zeolite was synthesized from FA by dialysis. The FA and NaOH solution added into the tube made by semipermeable membrane were pretreated in the same NaOH solution at 85 °C for 24 h. After the pretreatment, the tube was removed and NaOH–NaAlO2 solution was added into the residual solution to control SiO2/Al2O3 molar ratio of the solutions from 0.9 to 4.3. The precipitates thus formed were aged for 24 h at 85 °C. The amorphous aluminosilicate in FA was dissolved during the pretreatment. When the NaOH–NaAlO2 solution was added into the solution after the pretreatment and then aged, white precipitates were yielded over the whole SiO2/Al2O3 range. At SiO2/Al2O3=0.9, the material formed was identified as a single phase Na–A zeolite. The Na–X zeolite was slightly produced at SiO2/Al2O3≥1.7. 相似文献
15.
《Journal of the European Ceramic Society》2014,34(5):1329-1340
This new and economic approach to fabricate resistant porous membrane supports consists of Algerian kaolin and calcite (CaCO3) instead of Al2O3. The porous mullite (3Al2O3·2SiO2) and anorthite (CaO·Al2O3·2SiO2) based ceramics were obtained by solid state reaction. Different calcite amounts (10–28 wt%) have been added into kaolin halloysite type (Al2O3·2SiO2·4H2O) in order to control pores forming with appropriate distribution and sizes. Based on a pore distribution and formed phases, a kaolin + 15 wt% calcite (K15C) mixture was selected for flat and tubular configurations. A porosity of 45–52% was also obtained when K15C compacts were sintered at 1100–1250 °C. For example, porosity, average pore size (APS) and 3 point flexural strength were 49%, 3 μm and 87 MPa (same as Al2O3 value), respectively when K15C compacts were sintered at 1250 °C for 1 h. Finally, a correlation between microstructure and mechanical properties of elaborated supports has been discussed. 相似文献
16.
Yun Hoe Kim Dong Wook Shin Jin Sang Kim Jong-Han Song Seok-Jin Yoon Kyung Bong Park Ji-Won Choi 《Ceramics International》2012
The dielectric properties of composition spread SiO2–Al2O3 thin films deposited by off-axis radio-frequency magnetron sputtering at room temperature were explored to obtain optimized compositions, which have low dielectric constants and losses. The specific points (compositions) showing superior dielectric properties of low dielectric constants (8.13 and 9.12) and losses (tanδ ~0.02) at 1 MHz were found in area of the distance of 25.0 mm (Al2Si3O8) and 42 mm (Al2.4Si3O8) apart from SiO2 target side in 75 mm × 25 mm sized Pt/Ti/SiO2/Si(1 0 0) substrates, respectively. The specific thin films were amorphous phase and the compositions were Al2Si3O8 (k ~8.13) and Al2.4Si3O8 (k ~9.12). 相似文献
17.
The glass structure, wetting behavior and crystallization of BaO–Al2O3–B2O3–SiO2 system glass containing 2–10 mol% Al2O3 were investigated. The introduction of Al2O3 caused the conversion of [BO3] units and [BO4] units to each other and it played as glass network former when the content was up to 10 mol%, accompanied by [BO4] → [BO3]. The stability of the glass improved first and then decreased as Al2O3 increased from 2 to 10 mol%, the glass with 5 mol% Al2O3 being the most stable one. The wetting behavior of the glasses indicates that excess Al2O3 leads to high sealing temperature. The glass containing 5 mol% Al2O3 characterized by a lower sealing temperature is suitable for SOFC sealing. Al2O3 improves the crystallization temperature of the glass. The crystal phases in the reheated glasses are mainly composed of Ba2Si3O8, BaSiO3, BaB2O4 and BaAl2Si2O8. Al2O3 helps the crystallization of BaSiO3 and BaAl2Si2O8. 相似文献
18.
《Catalysis communications》2004,5(10):557-561
Identifying the preferentially coking sites of Mo2C/HZSM-5 catalyst in the CH4 dehydroaromatization at non-oxidative conditions was attempted by employing a physically separable Mo2C/α-Al2O3 + HZSM-5 mixture instead of Mo2C/HZSM-5 as catalyst. Photographic observation on the spent Mo2C/α-Al2O3 and HZSM-5 components separated from the deactivated mixture and their thermogravimetric analysis clearly revealed that coke accumulation occurred predominantly on the HZSM-5. Then, the comparative activity tests with the physical blends of the deactivated Mo2C/α-Al2O3 + HZSM-5 mixture sample with fresh Mo2C/α-Al2O3 or HZSM-5 further confirmed that the coked HZSM-5 component in the deactivated mixture definitely deactivated while that un-coked Mo2C constituent remained highly active. 相似文献
19.
Production of porous anorthite ceramics from mixtures of paper processing residues and three different clays are investigated. Suitability of three different clays such as enriched clay, commercial clay and fireclay for manufacturing of anorthite based lightweight refractory bricks was studied. Porous character to the ceramic was provided by addition of paper processing residues (PPR). Samples with 30–40 wt% PPR fired at 1200–1400 °C contained anorthite (CaO·Al2O3·2SiO2) as major phase and some minor secondary phases such as mullite (3Al2O3·2SiO2) or gehlenite (2CaO·Al2O3·SiO2), depending on the calcite to clay ratio. Anorthite formation for all clay types was quite successful in samples with 30–40 wt% of paper residues fired at 1300 °C. A higher firing temperature of 1400 °C was needed for the fireclay added samples to produce a well sintered product with large pores. Gehlenite phase occurred mostly at lower temperatures and in samples containing higher amount of calcium (50 wt% PPR). Compressive strength of compacted and fired pellets consisting of mainly anorthite ranged from 8 to 43 MPa. 相似文献
20.
In this paper, SO42 −/Al2O3-SiO2 (SAS) was prepared and used for the esterification of octanoic acid with methanol. The effect of introduction of SiO2 was characterized by nitrogen sorption, ICP-AES, XRD, NH3-TPD, TG, FTIR and FTIR-pyridine adsorption. The results demonstrated that the doping of SiO2 resulted in the increase of BET surface areas and amount of surface sulfur species which led to an increase of acid sites especially Brönsted acid sites, which consequently boosted the catalytic esterification activity. In addition, the introduction of SiO2 can also increase the thermal stability of SO42 − and its interaction with Al2O3 support which resulted in the alleviation of catalyst deactivation. 相似文献