共查询到18条相似文献,搜索用时 218 毫秒
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考察在不同相对压力范围应用BET公式计算中孔材料、含少量微孔材料及纯微孔材料的表面积,结果表明,应用BET公式计算微孔材料的表面积时,相对压力取值0.01~0.10,BET线性关系较为合理.多数微孔材料相对压力取值在0.05~0.20计算出的表面积比0.01~0.10小.有少量的分子筛样品经水热老化处理后,其等温线产生低压滞后环,这类微孔材料在相对压力取值为0.05~0.20计算的表面积比0.01~0.10大.催化剂中微孔材料含量越多,两个相对压力范围内计算出的结果差别越大,对于纯分子筛样品二者差值可达15%左右. 相似文献
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采用分子模拟的方法模拟77 K下N2在沸石咪唑骨架材料(ZIFs)上的吸附等温线,并与实验结果比较,确定合适的力场参数,提供用BET方法分析ZIFs材料比表面积的吸附等温线。通过BET吸附方程中的参数c与单层吸附压力(p/p0)m之间的关系为(p/p0)m=(槡c+1)-1,确定应用BET方程分析时的压力区间。采用这样的方法计算5种ZIF材料的比表面积并与根据一致性原则(Rouquerol,2007)的结果进行比较,结果表明方法是可靠的,这说明采用合适的压力区间时,BET方法同样适用于分析微孔ZIF材料的比表面积。计算得到的5种ZIF材料比表面积均在1 000 m2/g以上,说明ZIF材料是一种具有高比表面积、有应用前景的吸附材料。 相似文献
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应用BET、XRD和IR等技术研究了磷和水蒸汽联合改性的Hβ分子筛的物化性能。系统考察了FCC汽油在Hβ为基质的改性沸石分子筛上的烯烃转化反应。BET结果表明,磷改性引起分子筛比表面积由417 m2·g-1减小到401 m2·g-1,单独经过水蒸汽处理的分子筛的比表面积随处理温度的升高也明显下降。XRD和IR研究表明,磷与水蒸汽改性前后没有新的晶相出现,并且联合改性后Hβ沸石保留了合适的酸含量,总酸量均保持在038 mmol·g-1以上。改性前后样品的活性评价在微型反应装置上进行,结果表明,联合改性样品在973 K的高温条件下,烯烃转化率仍可达到42%,远高于仅仅由水蒸汽改性分子筛的催化活性(后者烯烃转化率仅为33%),显示出磷物种对沸石分子筛高温水蒸汽脱铝的抑制作用。 相似文献
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以硅藻土为原料,以氢氧化钠或氨水为碱源,分别水热合成出具有较高相对结晶度的钠型ZSM-5分子筛和氢型ZSM-5分子筛。采用X射线衍射仪(XRD)、扫描电子显微镜(SEM)、吡啶吸附红外光谱(Py-IR)和N2-吸附脱附等手段,对所合成的样品进行了表征。结果表明,合成的Na ZSM-5分子筛和HZSM-5分子筛均具有较高的结晶度,但有不同的酸性、孔结构、形貌和粒径,粒径分别约为500 nm或7μm。相比硅藻土,晶化产物的比表面积、微孔表面积和微孔孔容均明显增大。用Na OH合成样品的比表面积、孔容大于用NH3?H2O合成的样品。采用氨水合成的ZSM-5分子筛经焙烧后可直接转化成氢型分子筛。 相似文献
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为快速测量煤基活性炭比表面积和孔隙结构等性能指标,通过分析活性炭的碘吸附值与比表面积、孔结构之间的关系,明确BET与碘吸附值之间的相关性。结果表明,碘吸附值在50~800 mg/g时,碘吸附值与比表面积之间具有良好的线性关系,拟合度达0.933,利用碘吸附值可快速高效估算比表面积和微孔结构,还可用来预测BET,但相对吸附压力(P/P0)和常数C选择不当,将导致比表面积测量不准确;碘吸附值的大小主要表征了活性炭微孔0.8~1.2 nm孔隙的发达程度;碘分子在微孔中进行单层吸附符合由致密堆积的六方晶格组成的表面覆盖模型。碘吸附值能够实现煤基活性炭比表面积和孔结构的快速分析。 相似文献
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A good correlation was found between apparent BET surface area and total pore volume determined for a number of active charcoals by measurement of the nitrogen adsorption isotherms at 77 K. A similar correlation is also illustrated in which apparent BET surface area is calculated from the uptake of nitrogen at relative pressure . This method is suggested as a rapid means of estimating pore volume in predominantly microporous carbons. 相似文献
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《分离科学与技术》2012,47(7):931-945
Abstract Adsorption isotherms for acetaldehyde, propionaldehyde, and butyraldehyde on Davison molecular sieve 13X were determined gravimetrically at three temperatures. The isoteric heat of adsorption of acetaldehyde and propionaldehyde decreased initially with the increase in loading, then increased up to a certain point after which it decreased again. For butyraldehyde the heat of adsorption initially increased and then decreased with increased loading. The equilibrium adsorption data reduce to a single characteristic curve when correlated according to Polanyi's potential theory. Recently proposed isotherm equations for heterogeneous surfaces by Sircar and Hines et al. were used to correlate the isotherm data. The BET equation gave a good correlation of the data for a relative pressure range of 0.05 ≤ P/P, ≤ 0.25. The monolayer surface coverage and surface area were calculated by the Langmuir and the BET equations. The Langmuir equation consistently provided a larger estimate of the surface area than did the BET equation. 相似文献
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N. Passe-Coutrin S. Altenor D. Cossement C. Jean-Marius S. Gaspard 《Microporous and mesoporous materials》2008,111(1-3):517-522
The empirical linear relationship between the BET surface area SBET and the Freundlich constant KF, calculated from nitrogen adsorption isotherms of activated carbons, SBET = a0KF is mathematically demonstrated. This correlation exists in the relative pressure domain in which the BET equation is valid, whatever the value of c for the BET equation and for values of the Freundlich exponent, , between 0 and 0.2. This study allows to determine the correlation factor a0 = 1/a with . From this result, a new expression, depending of and KF, can be deduced for calculating the specific surface area. 相似文献
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以Y分子筛和HZSM-5分子筛为前驱体,以纯氨为氮源,在800 ℃焙烧制备了氮化微孔分子筛。采用元素分析、氮气吸附-脱附、X射线衍射(XRD)、原位漫反射红外光谱等技术对材料的结构与酸碱性能进行了研究。结果表明,NaY分子筛是可获得高比表面积和完整结构掺氮分子筛理想的前驱体。原位漫反射红外光谱证实了氮原子主要以-NH2-或-NH-形式进入各分子筛骨架。原位探针分子吸附漫反射红外光谱实验表明两种分子筛均含B酸位与L酸位,经高温氨处理掺氮后B酸位显著减少、L酸位变化不明显,碱性变强。 相似文献
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New microporous hybrid organic/inorganic materials were obtained by modification of zeolites using chlorination of their surface,
followed by treatment with a Grignard reagent. Loading of butyl groups and retained crystallinity of ZSM-5 type zeolites was
higher than for zeolites Y. In contrast to zeolites Y, the lattice parameters of zeolites ZSM-5 increased after surface modification.
The obtained hybrid materials on the basis of high-silica zeolites possess a high degree of crystallinity at increased hydrophobicity. 相似文献
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以国产聚丙烯腈(PAN)基碳纤维为原料,采用KOH为活化剂制备PAN基活性碳纤维。测定了不同ACF样品的CO2吸附量,并通过氮气吸附、碘吸附以及红外光谱对所得活性碳纤维的比表面积、孔结构及表面官能团进行表征。研究了活化温度、活化时间和表面改性对活性碳纤维CO2吸附量的影响。结果表明,活化温度是影响活性碳纤维CO2吸附量的主要因素。当活化温度为850℃时,所得活性碳纤维BET比表面积为1235m2/g,微孔比表面积为745 m2/g,在吸附温度为273 K、吸附相对压力P/P0为1时,CO2的吸附量达到87.29 mL/g。 相似文献
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SBA-15 carbon replicas were synthesized with a sucrose solution as carbon source, carrying out carbonization at two different temperatures (800 and 1000 °C). Carbon pyrolised at 800 °C showed higher BET surface area and was chosen for further post-synthesis activation treatments (physical via CO2 or chemical via KOH), with the aim of improving hydrogen adsorption capacity. For comparison, an amorphous carbon was also synthesized, by direct carbonization of the carbon source, without any inorganic template: on this material a chemical activation was also performed. H2 adsorption isotherms at the temperature of liquid nitrogen and sub-atmospheric pressure were measured. A linear correlation was found between hydrogen uptake and microporous volume of the different carbons, rather than with BET specific surface area. Surprisingly, the sample prepared in the absence of inorganic template resulted the most effective one. 相似文献
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Om Parkash Hari Shanker Tewari Lakshman Pandey Ravindra Kumar Devendra Kumar 《Journal of the American Ceramic Society》1989,72(8):1520-1522
Attempts have been made to synthesize the compositions with x = 0.01, 0.05, 0.10, 0.20, 0.30, 0.40, and 0.50 in the valence-compensated solid-solution Ba1–x Lax Ti1–x Nix O3 by ceramic methods. Solid solutions formed in the compositions with x0.10. The structure of the composition with x = 0.01 is tetragonal, whereas samples with x = 0.05 and 0.10 are cubic. A ferroelectric-paraelectric transition is observed only in the composition with x = 0.01 at ∼ 350 K. 相似文献