Effect of preparation method on the acidities of Al-B-O x mixed oxides

A series of Al-B-O _x metal oxides with various Al/B ratios were prepared with impregnation and coprecipitation methods. The surface acidic properties of these catalysts were examined by temperature-programmed desorption (TPD) of ammonia and the dehydration reaction of isopropanol. The dehydration reaction was carried out in a continuous-flow microreactor at 130–260 °C under atmospheric pressure. The results of TPD of ammonia indicated that the surface acidity of Al-B-O _x material is medium-strong. The acidic strengths are approximately the same for all the Al-B-O _x samples, regardless of its preparation method. In addition, their acid strengths are much stronger than that of pure alumina. However, the acid concentration is increased with decreasing the Al/B atomic ratio of the catalyst. The dehydration activities of these catalysts are increased with decreasing the Al/B atomic ratios of the samples. The results also indicated that the addition of boron on alumina, no matter what preparation method is used, could significantly enhance the acidities of the catalysts. A compensation effect was observed in isopropanol dehydration reaction over these catalysts. The preexponential factor decreases and activation energy increases with increasing Al/B ratio of the catalyst. The results can be interpreted in terms of the acidity of the catalyst.     

Effect of preparation conditions on the characteristics of exfoliated graphite

Exfoliated graphite (EG) was prepared from graphite intercalation compounds (GICs) synthesized electrochemically with different electricity consumption from 10.83 to 40.00 A h/kg. Effects of electricity consumption on the synthesis of GICs and of exfoliation temperature on different parameters of EG, i.e. exfoliation volume, volatile content, specific surface area and pore volume measured by mercury porosimetry, length and width of worm-like particles, and distance between neighboring balloons based on the zigzag model for worm-like particles of EG, were studied. These parameters were found to depend strongly on the electricity consumption and also on exfoliation temperature. Exfoliation volume, volatile content, specific surface area and pore volume on EG prepared at 1000 °C increased with increasing electricity consumption, but the distance between neighboring balloons was found to decrease. These results reveal marked development of pores in EG samples. Raising exfoliation temperature increased exfoliation volume, specific surface area and pore volume up to 800 °C. Above this temperature these parameters tended to be stable.     

制备条件对ZrO_2结构的影响

本文对以工业ZrOCl2为原料,NH3·H2O为沉淀剂合成ZrO2进行了研究,重点考察了ZrOCl2溶液浓度、NH3·H2O浓度、沉淀pH值、沉淀及老化温度等因素对所制备的ZrO2表面积和孔容的影响,从而得出了一定的规律。     

制备条件对氧化锆表面酸性的影响

采用Hamm ett指示剂法,研究了制备条件对ZrO2催化剂的表面酸性的影响。结果表明,焙烧条件对氧化锆表面酸强度影响不大,但总酸量随着焙烧温度和时间的增加而减小;降低表面活性剂的用量,氧化锆表面酸强度及总酸量均随之减小。适宜的催化剂制备条件是:Zr与十六烷基三甲基溴化铵(CTAB)的摩尔比为2,焙烧温度450℃,焙烧时间6 h。     

乳化条件对正十八烷微胶囊制备的影响

以正十八烷为囊芯,密胺树脂(MF)为高分子囊壁材料,采用原位聚合法制备了相变材料微胶囊。利用光学显微镜、激光粒度分布仪、差示扫描量热仪和傅立叶变换红外光谱仪分别研究了微胶囊的表面形貌、粒径分布、相变性能和化学结构等。讨论了乳化方式和乳化剂种类对微胶囊性质的影响。结果表明:当采用十二烷基苯磺酸钠为乳化剂,将预聚物与熔融的正十八烷混合后再乳化时,所得微胶囊结构完好,粒径分布均匀,体积平均粒径约为150μm,囊芯含量高达67.3(wt)%。     

制备条件对吸附剂脱硫性能的影响

制备了FCC汽油脱硫吸附剂.考察了吸附剂制备条件对吸附剂脱硫性能的影响,确定了适宜的吸附剂制备条件.     

制备工艺对中间相沥青基泡沫炭结构的影响

以煤沥青基中间相沥青为前驱体制备泡沫炭生料,经850℃和2300℃热处理分别得到炭化和石墨化泡沫炭,研究了发泡工艺参数和热处理温度对泡沫炭微观结构的影响。结果表明,较快的升温速率使泡沫炭易形成开孔型结构;随着压力的增大,泡沫炭的孔径减小、密度增大、孔隙率降低;经炭化和石墨化后泡沫炭孔径有所收缩,孔间的连通性增强;泡沫炭石墨化后孔壁及其韧带大部分转化成为高取向度的石墨晶体结构,微晶层间距和石墨化度分别为0.3376nm和0.733。     

Effect of the preparation conditions of carbon-supported Pt catalyst on PEMFC performance

Carbon-supported Pt catalysts were prepared using NaBH₄ as a reducing agent in either ethylene glycol or water for use as a cathode catalyst in PEMFCs (polymer electrolyte membrane fuel cells). Aqueous NaBH₄ solution was used to reduce Pt precursor and to produce the Pt-W catalyst, while Pt-E and Pt-E-base catalysts were synthesized using NaBH₄ in ethylene glycol for the reduction of Pt. Compared to Pt-W catalyst, Pt-E and Pt-E-base catalysts have higher Pt dispersion and larger EAS (electrochemically active surface area) due to the stabilizing effect of ethylene glycolic NaBH₄ solution on Pt particles. In addition, increasing pH of the preparation solution improved the Pt dispersion (Pt-E-base). In unit cell tests the performance of Pt catalysts decreased in the following order: Pt-E-base > Pt-E > Pt-commercial > Pt-W. Higher metal dispersion and larger EAS are believed to be responsible for the superior performance of Pt-E catalysts, particularly Pt-E-base, compared to other catalysts.     

制备工艺条件对硅胶孔性质的影响

研究了在茂金属催化剂体系所用硅胶的制备过程中,反应体系中二氧化硅的浓度和溶胶-凝胶的反应温度对硅胶孔容及孔径的影响.结果表明,当SiO2的质量分数为9.2%、溶胶-凝胶反应温度为75℃时,可制得孔容和孔径较为理想的催化剂载体用硅胶.     

Effect of iron oxides on mullite-corundum refractories under the conditions of oxidizing and reducing media

The interaction of mullite-corundum refractories with iron oxides in an oxidizing medium results in the formation of solid solutions in mullite and corundum. When fired in a reducing medium the solid solutions decompose with disruption of the structure and loosening of the refractory. Repeated heat cycles in different gaseous media lead to a periodic change in the phase composition of the refractory and worsen its quality and hence its stability in service.Translated from Ogneupory, No. 5, pp. 22 – 24, May, 1995.     

The effect of preparation conditions on the photoelectrochemical properties of polybithiophene based photoelectrodes

The effect of the preparation and treatment conditions on the photoefficiency of electropolymerized polybithiophene (PBT) was studied. It was found that, after initial discharging, further electrochemical undoping of the polymer in dark had no effect on the photocurrents. However, illuminating the polymer films in solutions containing Li⁺ ions resulted in a five-fold increase in the photocurrent. This fact was attributed to photoelectrochemical removal of the trapped charge that was present in the as-grown polymer films. This conclusion was confirmed by local conductivity measurements using current-sensing atomic force microscopy (CS-AFM). The as-grown polymer films showed a high degree of microscopic heterogeneity and well-pronounced conducting domains of submicrometer dimensions embedded into a nominally undoped polymer phase. Further, electrochemical undoping in dark failed to produce any noticeable change in the trapped charge content. The photoelectrochemical treatment, however, drastically improved the microscopic homogeneity of the polymer and its semiconductor properties, as indicated by CS-AFM images and current-voltage characteristics. The maximum steady-state photocurrent obtained in LiPF₆ was 1.4 mA cm⁻² under 20 mW 405 nm monochromatic laser illumination, which corresponded to an external quantum efficiency of 1.5%. This result indicates that, upon necessary optimization, single-layer polymer photoelectrodes can produce relatively high photocurrents without employing the donor-acceptor architectures.     

白炭黑制备工艺条件对其脱水性能的影响

采用工业固体垃圾——煤矸石为生产原料制备白炭黑,通过改变制备过程中的通气速度、CO2质量分数及后处理工艺,研究工艺参数对白炭黑脱水性能的影响。结果表明,在制备白炭黑过程中,可以通过改变制备工艺条件来控制白炭黑的粒度,以致生成粒度较大、形态为絮状的白炭黑沉淀。同时,在洗涤中也应适当搅拌,从而提高其脱水性能。这样,既可以节约成本,也可以提高产品的纯度。     

Kinetics and preparation of amine oxides

A kinetic model for the oxidation of dimethyllaurylamine to its amine oxide with hydrogen peroxide was developed. It is a second-order reaction where k=.0250, .0079 and .0037 kg per mol/min at 75, 60 and 50°C, respectively. Amine oxides ofN-lauryl morpholine, piperidine and 3-methyl piperidine were synthesized, and their rates of formation were determined. Compared to dimethyllaurylamine, the piperidines react slower, while the morpholine reaction is much faster.     

Effect of membrane preparation conditions on solute permeability in chitosan membrane

Chitosan membrane was prepared in various conditions and diffusive permeabilities of theophylline and vitamin B₁₂ were investigated. The membrane preparation procedure consists of dissolving chitosan in acid solution, cast on the glass plate, drying the dope solution, and immersion of the plate in the gelating agent. Effects of the kinds of acids to dissolve chitosan, chitosan concentration, drying time of the dope solution, and the kinds of the gelating agent on the membrane structure and performance were studied in detail. With increasing the chitosan concentration, the solute permeability decreased, while the selectivity of theophylline to vitamin B₁₂ increased. The membrane changed from the wholly porous structure to the asymmetric structure by the increase of the chitosan concentration. Furthermore, the use of ethanol as the gelating agent brought about the wholly porous structure with the high permeability and the low selectivity. The asymmetric structure and the wholly dense structure were obtained in the cases of the gelating agents, such as aqueous NaOH solution and dimethyl sulfoxide (DMSO), respectively. Thus, the membrane structure can be controlled by the kinds of gelating agent. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2715–2725, 1999     

The chemistry of catalysts based on vanadium-phosphorous oxides: Note II The role of the method of preparation

Vanadium-phosphorous mixed oxides, specific catalysts for C₄. oxidation to maleic anhydride, were prepared using two methods as follows; i) method A, by reduction of V₂O₅ with HCl after addition of H₃PO₄ and ii) method B, by addition of NH₄VO₃ to a solution containing H₃PO₄ and oxalic acid as reducing agents. It was observed that, with both procedures, H₃PO₄ in excess to that for a ratio of P/V = 1.1 serves to stabilize the tetravalent form of vanadium in calcination at high temperatures. The nature of the compounds formed was different for the two methods. For P/V less than 1.1, βVOPO₄ was formed with method A and amorphous αVOPO₄ was formed with method B. For P/V greater than 1.1, method A gave the β-phase, described in the literature as the active phase, while method B gave other crystalline and amorphous compounds. It is suggested that the β-phase formed as a polyphosphate of V(IV) containing excess phosphorous. The differences observed with the two preparation procedures are related to the different precursors which formed after the drying stage at 125°C. Method A gave (VO)₂P₂O₇,2H₂O and method B VO(NH₄)P0₄,4H₂O.     

Effect of preparation conditions on the properties of a coal-derived activated carbon honeycomb monolith

Activated carbon honeycomb (ACH) monoliths were prepared by extruding of a mixture of bituminous coal and organic additives and subsequent carbonization and steam activation. Preparation parameters that were varied were carbonization temperature and activation time. The carbonization conditions were 500, 650 and 800 °C for 1 h and the steam activation conditions were 850 °C for 2, 4 and 6 h. The monoliths at various states were characterized by SEM, XRD, nitrogen adsorption and compression test. It was found that carbonization temperature has significant effects on pore size distribution and mechanical strength of ACH monoliths. The ACH monoliths prepared from high carbonization temperatures exhibited lower values of the BET surface area and total pore volume and higher value of the mechanical strength than those of the ACH monoliths prepared from low carbonization temperatures. This was attributed to the effect of high temperature carbonization that results in the formation of relatively less defective structures.     

Effect of preparation conditions on diamond cluster formation in bulk nanoporous carbon

The structure of bulk nanoporous carbon chemically prepared from SiC powders is studied by TEM microdiffraction and HRTEM techniques. The conditions for the formation of diamond and graphite clusters in the carbonization process are analyzed. The experimental data suggest that diamond clusters can be produced near carbonization reaction front in the case of its quick propagation into the precursor. The slower the reaction front, the greater is the chance that graphite or quasi-graphite clusters are formed.     

Effect of preparation conditions on the properties of microspheres prepared using an emulsion-solvent extraction process

Methylaluminoxane microspheres were prepared using a hydrocarbon-in-perfluorocarbon-emulsion solvent extraction process. The effect of the preparation conditions on the size of the microspheres was investigated. As expected, the size of the microspheres decreased with increasing stirring speed. At low surfactant concentrations the size of the microspheres was independent of the surfactant concentration. However, the size of the microspheres decreased as the surfactant concentration was further increased. The size of the microspheres was not only affected by the surfactant concentration but also by the volume ratio of the dispersed phase to the continuous phase. At a low volume ratio of the phases the effect of the surfactant on the size of the microspheres was larger than the effect of the increased volume ratio of the phases. At high volume ratios of the phases the effect of the volume ratio of phases on the size of the microspheres became more significant than the effect of the surfactant. A slow solidification increased the formation of non-spherical microspheres.     

制备条件对超高比表面积活性炭结构的影响

以石油焦为炭前驱材料、用不同试剂作为活化剂,讨论了不同活化剂对石油焦的活化作用。在以KOH为活化剂时,研究了活化条件对活性炭孔结构的影响。结果表明,强碱具有明显的活化作用,盐类试荆的活化作用很差,且KOH的活化作用远优于NaOH。在碱与碳质量比为4、800℃下活化60min制得了BET比表面积为3422m^2／g的超高比表面积活性炭(SBET≥2500m^2／g)。且碱与碳质量比越大、活化温度越高及活化时间越长,所制得活性炭中大于2nm的孔所占的比例越大。