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1.
甘油是一种可由生物资源生产、可持续的、可降解的平台化学品,是生物柴油、肥皂化工等工业生产过程中的主要副产物.催化甘油脱水反应生产丙烯醛,有望能替代丙烯等石油裂解产物合成丙烯醛的传统工业路线.丙烯醛是一种重要的化工中间体,被用于合成蛋氨酸、丙烯酸、3-甲基吡啶和1,3-丙二醇,并被广泛地应用于农药、医药、高分子材料等领域.随着全球可持续能源发展,生物柴油生产迅速发展,将产生大量的副产物甘油.利用甘油为原料,通过合适的催化剂的催化脱水反应生成丙烯醛,是近十多年来国内外工业催化的研究热点之一.用于催化甘油脱水合成丙烯醛的酸催化剂有杂多酸、金属氧化物、沸石与酸性粘土矿物等.钨磷杂多酸(H3PW12O40)负载的催化剂虽然具有较强的酸性,有利于催化甘油脱水,但容易导致结焦,而且热稳定差,容易失活.钨磷杂多酸负载于SiO2,TiO2,Al2O3,SiO2-Al2O3,K-10蒙脱石上表现出不同的催化活性,表明催化剂和载体的表面酸性和孔结构影响催化性能.近来研究发现,负载于ZrO2,Al2O3的钨氧化物(WOx)催化剂热稳定性好、酸性高,在甘油脱水反应生成丙烯醛中表现出良好的催化性能.但有关钨氧化物(WOx)结构、催化活性受载体组成、酸性影响的本质和规律一直不清楚.本文采用20 wt%的硫酸、盐酸、磷酸和乙酸对蒙脱石进行酸改性,并在磷酸改性的蒙脱石上负载W含量为4–16 wt%的WOx作为催化剂,用于甘油气相脱水反应.X-射线衍射(XRD)、热重-差热法(TG-DTG)、氨程序升温脱附(NH3-TPD)、红外光谱(FT-IR)和紫外漫反射可见光谱(DR UV-vis)等表征,探讨了酸改性和负载WOx的蒙脱石对催化剂催化性能的影响.蒙脱石经过20wt%的硫酸、盐酸、磷酸和乙酸的活化,酸性增加.四种酸改性的蒙脱石对甘油气相脱水反应均有催化活性,这是因为在蒙脱石酸活化过程中,H+经过阳离子交换反应进入蒙脱石层间,同时蒙脱石八面体中的部分Al3+被浸出,使层板上出现不饱和Al3+,为催化剂提供了L酸位,蒙脱石硅氧四面体上的Si?OH以及[AlO4]上吸附的H3O+提供了B酸位.XRD分析表明,负载WOx的蒙脱石表面存在WO2.72,WO2.9和WO3三种不同类型的WOx,当钨负载量从12 wt%增至16 wt%,孤立的单斜晶系WO3晶粒增多.NH3-TPD和DR UV-vis结果表明,WOx负载在蒙脱石表面以[WO5/WO6](B酸位)、[WO4]和单斜晶系WO3相(L酸位)形式存在.蒙脱石上负载WOx能够调节催化剂的酸强度、酸量和酸位.随着钨负载量从4 wt%增至12 wt%,丙烯醛收率从40.9%增加到67.3%;进一步增加钨负载量到16 wt%,丙烯醛收率降为50.7%.结果发现,随着钨负载量的增加,催化活性组分含量增加,[WO5/WO6](B酸位)增加,使催化活性增加;当W负载量达到16 wt%时,WOx分散性降低,且在催化剂表面形成孤立的单斜晶系WO3相(L酸位),不利于提高丙烯醛选择性.当反应温度为320 oC,甘油水溶液浓度为15 wt%时,磷酸活化蒙脱石负载12 wt%W的催化剂上甘油转化率为89.6%,丙烯醛收率达到73.3%. 相似文献
2.
《催化学报》2017,(6)
甘油是一种可由生物资源生产、可持续的、可降解的平台化学品,是生物柴油、肥皂化工等工业生产过程中的主要副产物.催化甘油脱水反应生产丙烯醛,有望能替代丙烯等石油裂解产物合成丙烯醛的传统工业路线.丙烯醛是一种重要的化工中间体,被用于合成蛋氨酸、丙烯酸、3-甲基吡啶和1,3-丙二醇,并被广泛地应用于农药、医药、高分子材料等领域.随着全球可持续能源发展,生物柴油生产迅速发展,将产生大量的副产物甘油.利用甘油为原料,通过合适的催化剂的催化脱水反应生成丙烯醛,是近十多年来国内外工业催化的研究热点之一.用于催化甘油脱水合成丙烯醛的酸催化剂有杂多酸、金属氧化物、沸石与酸性粘土矿物等.钨磷杂多酸(H_3PW_(12)O_(40))负载的催化剂虽然具有较强的酸性,有利于催化甘油脱水,但容易导致结焦,而且热稳定差,容易失活.钨磷杂多酸负载于SiO_2,TiO_2,Al_2O_3,SiO_2-Al_2O_3,K-10蒙脱石上表现出不同的催化活性,表明催化剂和载体的表面酸性和孔结构影响催化性能.近来研究发现,负载于ZrO_2,Al_2O_3的钨氧化物(WO_x)催化剂热稳定性好、酸性高,在甘油脱水反应生成丙烯醛中表现出良好的催化性能.但有关钨氧化物(WO_x)结构、催化活性受载体组成、酸性影响的本质和规律一直不清楚.本文采用20 wt%的硫酸、盐酸、磷酸和乙酸对蒙脱石进行酸改性,并在磷酸改性的蒙脱石上负载W含量为4–16 wt%的WO_x作为催化剂,用于甘油气相脱水反应.X-射线衍射(XRD)、热重-差热法(TG-DTG)、氨程序升温脱附(NH_(3~-)TPD)、红外光谱(FT-IR)和紫外漫反射可见光谱(DR UV-vis)等表征,探讨了酸改性和负载WO_x的蒙脱石对催化剂催化性能的影响.蒙脱石经过20wt%的硫酸、盐酸、磷酸和乙酸的活化,酸性增加.四种酸改性的蒙脱石对甘油气相脱水反应均有催化活性,这是因为在蒙脱石酸活化过程中,H~+经过阳离子交换反应进入蒙脱石层间,同时蒙脱石八面体中的部分Al~(3+)被浸出,使层板上出现不饱和Al~(3+),为催化剂提供了L酸位,蒙脱石硅氧四面体上的Si-OH以及[AlO_4]上吸附的H_3O~+提供了B酸位.XRD分析表明,负载WO_x的蒙脱石表面存在WO_(2.72),WO_(2.9)和WO_3三种不同类型的WO_x,当钨负载量从12 wt%增至16wt%,孤立的单斜晶系WO_3晶粒增多.NH_(3~-)TPD和DR UV-vis结果表明,WO_x负载在蒙脱石表面以[WO_5/WO_6](B酸位)、[WO_4]和单斜晶系WO3相(L酸位)形式存在.蒙脱石上负载WOx能够调节催化剂的酸强度、酸量和酸位.随着钨负载量从4wt%增至12 wt%,丙烯醛收率从40.9%增加到67.3%;进一步增加钨负载量到16 wt%,丙烯醛收率降为50.7%.结果发现,随着钨负载量的增加,催化活性组分含量增加,[WO_5/WO_6](B酸位)增加,使催化活性增加;当W负载量达到16 wt%时,WO_x分散性降低,且在催化剂表面形成孤立的单斜晶系WO_3相(L酸位),不利于提高丙烯醛选择性.当反应温度为320℃,甘油水溶液浓度为15 wt%时,磷酸活化蒙脱石负载12 wt%W的催化剂上甘油转化率为89.6%,丙烯醛收率达到73.3%. 相似文献
3.
磷酸锆催化甘油气相脱水制备丙烯醛 总被引:3,自引:0,他引:3
以沉淀法、水热合成法和浸渍法制备了磷酸锆催化剂,通过X射线衍射、热重分析、氮气物理吸附、红外光谱和Hammett指示剂法对催化剂进行了表征,并将该催化剂用于甘油气相脱水反应.研究表明,由沉淀法得到的磷酸锆经过400℃焙烧后能达到最佳催化活性,在温和条件下,甘油可完全转化,丙烯醛选择性为81%,反应24h内催化剂失活不明显.不同方法制备的磷酸锆其结构和表面酸性显著不同,催化剂表面酸性对催化剂活性、丙烯醛选择性和催化剂的寿命均有较大影响. 相似文献
4.
通过添加亮氨酸/谷氨酸制备了MoVOx复合金属氧化物,考察了亮氨酸/谷氨酸添加浓度对MoVOx晶相组成及含量的影响。将制备的MoVOx用于催化甘油选择性氧化性能研究。研究表明,添加亮氨酸/谷氨酸能够抑制产物中V2O5的生成。与谷氨酸相比,添加亮氨酸可以进一步减少产物中MoO3的含量。此外,当添加谷氨酸摩尔比为Mo:V:Glu=1:1:0.5时制备的MoVOx呈现出特殊的多层片状结构,该样品(Mo/V/Glu-0.5)在催化甘油选择性氧化反应中表现出优异的性能,当催化反应温度为340 ℃时,甘油的转化率为98.17%,丙烯醛和丙酮选择性分别为45.96%和34.84%。此时,体系中MoV2O8和MoO3的含量分别为65.56%和34.44%,表明MoVOx催化甘油选择性氧化反应中MoV2O8和MoO3具有明显的协同效应。 相似文献
5.
6.
7.
磷酸铋纳米棒的可控合成及其光催化性能 总被引:4,自引:0,他引:4
采用水热法合成了形貌可控的磷酸铋纳米棒光催化剂,并以亚甲基蓝(MB)为探针研究了其光催化活性.利用粉末X射线衍射(XRD),透射电镜(TEM)和紫外-可见漫反射光谱(UV-VisDRS)对产物进行了表征.研究发现甘油含量、水热时间、水热温度及前驱体浓度会影响磷酸铋纳米棒的形貌及结构.甘油含量和前驱体浓度主要影响产物形貌.随着甘油含量的增加,产物的长径比先增大后减小.前驱体浓度越低,所得BiPO4纳米棒的尺寸越小,长径比越大.水热时间短时,产物结晶度差,且为六方相,时间延长后转化为单斜相.水热温度过低或过高均不利于完美晶体的形成,160°C时产物的结晶度最高.实验结果表明:BiPO4纳米棒在紫外光下具有良好的光催化性能,其光催化活性受长径比和尺寸大小影响的总体趋势是长径比越大,尺寸越小,其光催化活性越强.结晶度对BiPO4的光催化性能影响较大,结晶度越高,其光催化活性越好.单斜相BiPO4的光催化活性较六方相的强. 相似文献
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9.
利用水热反应模拟原始地球的水热环境,以甘油和磷酸二氢铵为原料,采用非生物手段合成了sn-甘油-1(3)-磷酸和甘油-2-磷酸2种磷酸酯类物质.通过此反应,无机磷进入生物分子形成了在生物体中起重要作用C—O—P键.研究了反应温度、反应时间及矿物催化剂对反应的影响.在蒙脱土的催化下,C—O—P键的产率最大可达到1.15%(摩尔分数). 相似文献
10.
利用水热反应模拟原始地球的水热环境, 以甘油和磷酸二氢铵为原料, 采用非生物手段合成了sn-甘油-1(3)-磷酸和甘油-2-磷酸2种磷酸酯类物质. 通过此反应, 无机磷进入生物分子形成了在生物体中起重要作用C—O—P键. 研究了反应温度、 反应时间及矿物催化剂对反应的影响. 在蒙脱土的催化下, C—O—P键的产率最大可达到1.15%(摩尔分数). 相似文献
11.
Cesium is a member of the Group I alkali metals, very reactive earth metals that react vigorously with both air and water.
The chemistry of cesium is much like the chemistry of neighboring elements on the periodic table, potassium and rubidium.
This close relation creates many problems in plant-life exposed to cesium because it is so easily confused for potassium,
an essential nutrient to plants. Radioactive 134Cs and 137Cs are also chemically akin to potassium and stable cesium. Uptake of these radioactive isotopes from groundwater by plant-life
destroys the plant-life and can potentially expose humans to the radioactive affects of 134Cs and 137Cs. Much experimental work has been focused on the separation of 137Cs from uranium fission products. In previous experimental work performed a column consisting of Kel-F supporting tetraphenylboron
(TPB) was utilized to separate 137Cs from uranium fission products. It is of interest at this time to attempt the separation of 134Cs from 0.01M EDTA using the same method and Neoflon in the place of Kel-F as the inert support. The results of this experiment
give a separation efficiency of 88% and show a linear relationship between the column bed length and the separation efficiency
obtained. 相似文献
12.
Gu Z Ma Y Zhai T Gao B Yang W Yao J 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(29):7717-7723
The large-scale synthesis of single-crystal K(x)WO(3) tungsten bronze nanowires has been successfully realized by a hydrothermal method under mild conditions. Uniform K(0.33)WO(3) nanowires with diameters of 5-25 nm and lengths of up to several micrometers are obtained. It is found that the morphology and crystallographic forms of the final products are strongly dependent on the sulfate and citric acid, which may act as structure-directing and soft-reducing agent, respectively. Some other influential factors on the growth of tungsten bronze nanowires, such as temperature and reaction time, are also discussed. It is worth noting that other alkali metal tungsten bronzes such as (NH(4))(x)WO(3), Rb(x)WO(3), and Cs(x)WO(3) could also be selectively synthesized by a similar route. Thus, this novel and efficient method could provide a potential mild route to selectively synthesize various tungsten bronze on-dimensional nanomaterials. 相似文献
13.
A Novel Synthetic Access to the Tungsten Bronze Cs0.29WO3 and its Crystal Structure The hexagonal tungsten bronze Cs0.29WO3 was obtained in form of black, prismatic crystal by the reduction of WO3 with molten cesium iodide at 700°C. Its crystal structure was determined by X-ray diffraction (399 unique observed reflexions, R = 0.058). Crystal data: a = 741.2(3), c = 760.0(5) pm, space group P6322, Z = 6. It corresponds to the known structure of hexagonal tungsten bronzes, having tungsten atoms displaced from the octahedra centres by 11.9 pm and with three different W? O bond lengths (198, 191, 187 pm). The WO6 octahedra are slightly titled mutually. 相似文献
14.
Alimonti A Forte G Spezia S Gatti A Mincione G Ronchi A Bavazzano P Bocca B Minoia C 《Rapid communications in mass spectrometry : RCM》2005,19(21):3131-3138
The wide use of barium (Ba), cesium (Cs), antimony (Sb) and tungsten (W) in many industrial and agricultural fields causes the increased release of these metals into the environment, laying the basis for health risk. To assess the exposure for the general population, the development of adequate and reliable analytical techniques becomes compulsory. This study refers to the quantification of urinary Ba, Cs, Sb and W levels by both quadrupole (Q) and sector field (SF) inductively coupled plasma mass spectrometry (ICP-MS). The two procedures were compared for their performances and their measurement uncertainties. The limits of detection were (Q and SF) 23.0 and 5.21 ng L(-1) for Ba; 21.1 and 7.52 ng L(-1) for Cs; 1.09 and 0.43 ng L(-1) for Sb; and 0.36 and 0.49 ng L(-1) for W. The trueness was better than 93.3% and the precision less than 12% for both techniques. Relative expanded uncertainties of the analytical procedures, at the median levels found in the general population, were below 5% for all the elements with both ICP-MS techniques. The uncertainties related to the calibration and repeatability were the parameters most influencing the final analytical performance. The urinary median values observed in healthy subjects from central Italy were 1146, 4301, 60.8 and 48.5 ng L(-1) for Ba, Cs, Sb and W, respectively. 相似文献
15.
Kongpatpanich K Nanok T Boekfa B Probst M Limtrakul J 《Physical chemistry chemical physics : PCCP》2011,13(14):6462-6470
The initial stage of glycerol conversion over H-ZSM-5 zeolite has been investigated using density functional theory (DFT) calculations on an embedded cluster model consisting of 128 tetrahedrally coordinated atoms. It is found that glycerol dehydration to acrolein and acetol proceeds favourably via a stepwise mechanism. The formation of an alkoxide species upon the first dehydration requires the highest activation energy (42.5 kcal mol(-1)) and can be considered as the rate determining step of the reaction. The intrinsic activation energies for the first dehydration are virtually the same for both acrolein and acetol formation, respectively, suggesting the competitive removal of the primary and secondary OH groups. A high selectivity to acrolein at moderate temperatures can be attributed to the selective activation of the stronger adsorption mode of glycerol through the secondary OH group and the kinetically favoured subsequent consecutive steps. In addition, the less reactive nature of acrolein relative to acetol precludes it from being converted to other products upon conversion to glycerol. In accordance with typical endothermic reactions, the forward rate constant for glycerol dehydration significantly increases with increasing reaction temperature. 相似文献
16.
The products distribution of glycerol hydrogenolysis over supported Co catalysts was evaluated in a liquid phase system. The effects of support type, temperature, pressure and reaction time on the conversion of glycerol as well as yield of desired products were investigated. The preliminary results indicated that various added compounds were generated in the presence of supported Co catalysts. The type of support and the reaction temperature, pressure and time significantly affected either the glycerol conversion or the product yield. The acidity of catalyst played a more important role in the glycerol hydrogenolysis over supported Co catalysts than the specific surface and pore volume. Among the utilized supported Co catalysts, Co/γ-Al2O3 exhibited the highest acrolein yield of about 31.1% at 70.5% conversion at 200°C, 8 MPa H2 pressure and 6 h reaction time. 相似文献
17.
Mohapatra PK Ansari SA Sarkar A Bhattacharyya A Manchanda VK 《Analytica chimica acta》2006,571(2):308-314
Extraction of Cs-137 from nitric acid was carried out using nitrobenzene solutions of calix-crowns such as calix[4]arene-bis(crown-6) (CC-A), calix[4]arene-bis(benzo crown-6) (CC-B) and calix[4]arene-bis(napthocrown-6) (CC-C). CC-C was found to be superior extractant for Cs(I) as compared to the other two calix-crown ligands used in the present study. The effect of diluent on the extraction of Cs(I) indicated the trend: nitrobenzene>dichloroethane>chloroform>decanol>carbon tetrachloride approximately n-hexane approximately toluene. Subsequently, the studies were carried out with nitrobenzene solutions of the calix-crown ligands (mainly CC-C) on the effects of (a) aqueous phase acidity, (b) ligand concentration, and (c) cesium concentration on Cs extraction from nitric acid media. Conditions for quantitative extraction and stripping were optimized and the extracted species conformed to {[CsL]+.[NO3]-.nH2O}. Selectivity studies were carried out using an irradiated natural U target involving tracer amount of fission products activities. Extraction of Cs(I) from a synthetic high level waste solution was also carried out. The promising results obtained in the present studies indicate possible use of the calix-crown ligand for Cs(I) recovery from the acidic high level waste. 相似文献
18.
M. Koyama T. Mitsuji O. Tochiyama T. Fujinaga 《Journal of Radioanalytical and Nuclear Chemistry》1969,3(5-6):413-420
A rapid separation of radioactive cesium by the solvent extraction method was investigated. Cesium ions are quantitatively
extracted with [Cr(NH2C6H5)2(NCS)4]− into nitrobenzene. EDTA is an effective masking agent for other polyvalent cations. The extracted cesium can be back-extracted
into the aqueous phase by shaking with 6N HCl. The method was applied to samples of a natural mixture of fission products and a reactor coolant. The decontamination
factors for other predominant isotopes in fission products were 102∼104. The separation of137m
Ba from a mixture of137Cs and137m
Ba is also described. 相似文献
19.
T. Ekström M. Parmentier K.A. Watts R.J.D. Tilley 《Journal of solid state chemistry》1984,54(3):365-377
Attempts have been made to prepare tungsten bronze phases from the Group IIIA metals, Al, Ga, and In. Of these, only In seems to from bronzes with any facility and three distinct compounds were characterized. Two of these were perovskite-type phases, one of tetragonal symmetry, with lattice parameters a = 0.3714 nm, c = 0.3870 nm, which forms below 1173 K and one of orthorhombic (pseudotetragonal) symmetry, with lattice parameters a = 0.3696 nm, b = 0.3722 nm, and c = 0.3859 nm, which forms above 1173 K. Both of these have a composition of approximately In0.02WO3. The third phase which formed in this system was a hexagonal tungsten bronze which has been characterized already. In neither the AlWO or the GaWO systems were stable bronzes formed, but some evidence suggested that metastable perovskite bronzes may form in the GaWO system in some circumstances. The formation of these phases is discussed and related to the formation of tungsten bronzes in general. 相似文献