氢同位素在线分析用MnCl2\γ-Al2O3色谱填料的制备与性能

吸附活性太强的γ-Al2 O3将导致氢同位素各组分保留时间延长、色谱峰拖尾、选择性差异不明显,从而无法满足快速在线分析需求.为此,采用锰盐浸渍沉积法改性γ-Al2O3,制备了一种可在液氮温度下分析氢同位素的MnCl2\γ-Al2O3色谱填料,并对其形貌、比表面积、孔径、孔体积、吸附性能及氢氘分离性能进行研究.与改性前的...     

MnCl_2改性γ-Al_2O_3毛细管填充柱气相色谱分析氢同位素

针对常规气相色谱填充柱分析稳定氢同位素的柱效低、峰宽大、保留时间长等问题,采用MnCl_2改性γ-Al_2O_3填充的石英毛细管柱开展了系统性柱效分析及氢同位素分析技术研究。研究结果表明,使用MnCl_2对γ-Al_2O_3进行改性后,可大大改善单纯的γ-Al_2O_3表面有序度、孔结构和吸附性质,并将正氢(o-H_2)和仲氢(p-H_2)峰洗脱在单一谱峰区域内。制备的长1.0 m、内径0.53 mm的石英毛细填充柱与热导检测器(TCD)级联测试,在体积浓度1至10 m L/L范围内有较好的线性关系,对于低浓度样品检测的相对误差不大于5%。H_2、HD和D_2的保留时间可分别缩短至39、46和60 s,检出限可分别降低至0.046、0.067和0.072 m L/L。毛细管填充柱较常规填充柱具有峰形尖锐、相邻组分分离度高、保留时间短、检出限低等优点,可用于低浓度氢同位素快速测量及氢同位素在线分析。     

CeO2-MOx（M=La^3＋,Ca^2＋）改性Pd/γ-Al2O3催化甲烷燃烧性能

采用沉积-沉淀法制备了固溶体CeO2-MOx=(M=La3+,Ca2+)改性的Pd/γ-Al2O3催化剂,利用XRD、Raman和XPS对催化剂进行了表征.结果表明,金属(M)离子进入CeO2的晶格,形成CeO2-MOx固溶体,Raman谱上463cm-1处对应于Ce-O键的F2g对称伸缩振动强度降低.其中,样品Pd/γ-Al2O3CeO2-CaO在615 cm-1处出现一小峰,样品Pd/γ-Al2O3-CeO2-La2O3在320cm-1处出现的肩峰,都表明固溶体CeO2-MOx的形成使O2-亚晶格结构对称性降低.XPS分析表明,固溶体改性的Pd/γ-Al2O3催化剂中Pd的3d5/2结合能比正常价态的PdO的结合能高出0.5-0.6 eV,形成了一种高度离子化的.与载体具有强相互作用的Pd物种.催化甲烷燃烧实验证明,固溶体CeO2-MOx(M=La3+,Ca2+)改性的Pd/γ-Al2O3催化剂的低温活性和稳定性均高于未经改性的Pd/γ-Al2O3催化剂和仅用CeO2改性的Pd/γAl2O3催化剂,在空速为50000 h-1时,可使1%CH4-99%空气(体积分数)混合气中甲烷的10%转化温度降至254℃,转化率100%时的转化温度降至340℃.     

Ce和Mg改性的γ-Al2O3负载Pt催化剂催化乙二醇水相重整制氢

 采用浸渍法制备了Ce和Mg改性的 γ-Al2O3 负载Pt乙二醇水相重整制氢催化剂. 采用催化活性评价、N2物理吸附、CO化学吸附、X射线衍射(XRD)和程序升温还原(TPR)等手段系统研究了催化剂的活性、选择性及物化性质. 实验结果表明, Ce和Mg改性的 γ-Al2O3 负载Pt催化剂的活性明显高于Pt/γ-Al2O3 催化剂. 在498 K和2.58 MPa条件下,乙二醇的转化率由72.3%提高到100%, 氢的选择性接近100%. 在Pt/(Ce)γ-Al2O3 和Pt/(Mg)γ-Al2O3 催化剂的XRD谱中,除了 γ-Al2O3 特征峰外,还分别出现了CeO2和Mg-Al层状化合物及微弱的Mg-Al尖晶石结构化合物的特征峰. Ce的存在促进了Pt对乙二醇的吸附-裂解作用和CO水煤气变换反应; Mg的存在中和了 γ-Al2O3 表面的酸性,增加了载体的碱性中心,影响了PtCl2-6的分散,抑制了乙二醇的脱水反应.     

γ-Al2O3改性对AlCl3/γ-Al2O3催化剂性能的影响

采用HCl和NaOH改性γ-Al2O3载体制备AlCl3/γ-Al2O3固载催化剂,用吡啶-FTIR和吡啶-TPD技术分析了催化剂的表面酸性(酸中心类型、酸强度和酸量),并以1-癸烯齐聚作为探针反应,研究了催化剂的稳定性以及催化剂对聚合反应的影响.结果表明,催化剂含有两种酸类型,即Lewis酸和Br(o)nsted酸,与未改性的催化剂相比,氢氧化钠改性载体制备的催化剂,酸量增大了47％,催化剂催化1-癸烯的齐聚反应活性增加了11.4％;而经盐酸改性制备的催化剂酸量增大112％,催化剂的活性增加了33.6％.酸强度依AlCl3/γ-Al2O3,AlCl3/γ-Al2O3(NaOH),AlCl3/γ-Al2O3 (HCl)的顺序增强.     

MO(M=Cu和Ni)/TiO2/-Al2O3催化剂在CO+O2反应中的活性

采用X射线衍射(XRD),程序升温还原(TPR)等表征手段考察了TiO2改性对CuO(或NiO)在γ-Al2O3表面上分散以及还原性能的影响,同时检测了这些改性的催化剂在CO+O2反应中的活性.结果表明:TiO2的改性使得CuO和NiO在γ-Al2O3载体上的分散复杂化,产生了多种状态的氧化铜(氧化镍)物种.当负载量低于其在γ-Al2O3上的分散容量(0.56 mmol Ti4+/100 m2γ-Al2O3)时,TiO2的加入主要是抑制了CuO和NiO在γ-Al2O3载体上的分散;而当负载量远大于其分散容量时,出现了CuO和NiO在晶相TiO2(锐钛矿)上的分散.无论其负载量如何,TiO2的加入促进了CuO的还原.因此,在250℃的CO+O2反应中,改性的催化剂中具有更多的活性位,因而显示出更高的活性;相反,TiO2的改性则抑制了NiO的还原.因此,在350℃的CO+O2反应中,可还原的氧化镍的量明显少于未经改性的催化剂,导致改性催化剂的活性降低.     

NiO在γ-Al_2O_3及 TiO_2/γ-Al_2O_3载体上的表面存在状态

本文采用 LRS, XRD, UV-DRS, TPR考查了γ-Al2O3上 TiO2的分散容量,分散态 Ti4＋离子的配位环境; NiO在经 TiO2改性后的γ-Al2O3载体上的分散容量。结果表明：（ 1） TiO2在γ-Al2O3表面的分散容量约为 0.62 mmol/100m2γ-Al2O3,当 TiO2含量低于该分散容量时 Ti4＋在γ-Al2O3载体表面以嵌入形式呈离子态分布;而含量高于分散容量时还有结晶态的 TiO2出现。（ 2） NiO在 TiO2/γ-Al2O3载体表面的分散容量约为 1.1 mmol/100m2γ-Al2O3,比之在γ-Al2O3载体表面的分散容量 (1.5mmol/100m2γ-Al2O3)要低,这是由于γ-Al2O3表面上部分空位被 Ti4＋离子占据。用表面相互作用的“嵌入模型” (Incorporation Model）讨论了这些结果。     

焙烧温度对CeO2改性Pd/Al2O3甲醇分解催化剂性能的影响

考察了焙烧温度对Pd/Al2O3和CeO2改性Pd/Al2O3甲醇分解催化剂反应性能的影响.在300℃～700℃范围内焙烧,Pd/Al2O3和Pd/CeO2/Al2O3催化剂的活性都呈现出先升高后降低的趋势.XRD结果表明高温焙烧时活性组分Pd在γ-Al2O3载体表面发生聚集是Pd/Al2O3催化剂活性降低的原因,而XPS结果却表明,Pd在CeO2改性γ-Al2O3载体表面的浓度与Pd/CeO2/Al2O3催化剂的活性变化并非呈现一致关系,TPR表明活性组分Pd和助剂CeO2在γ-Al2O3上产生了一定的相互作用.从而认为Pd的分散度以及Pd和CeO2之间的相互作用共同决定催化剂的甲醇分解性能.     

Pt/γ-Al2O3/CexZr1-xO2催化剂低温催化燃烧去除饮食油烟

以CexZr1-xO2固溶体做载体,制备了系列Pt/γ-Al2O3/CexZr1-xO2催化剂(x=1,0.75,0.5,0.25,0).应用Brunauer-Emmet-Teller(BET)比表面积分析、X射线衍射(XRD)和H2程序升温还原(H2-TPR)等手段对催化剂进行相关表征,并系统研究了催化剂在饮食油烟催化燃烧中的催化活性.BET结果表叫催化剂的比表面积随Ce/Zr摩尔比的减小而减小.XRD结果表明贵金属Pt很好地分散在氧化铝和CexZr1-xO2固溶体上.H2-TPR结果发现催化剂Pt/γ-Al2O3/Ce0.5Zr0.5O2的还原峰面积最大且氧离子的流动性最好.催化活性研究结果表明Pt负载在CexZr1-xO2固溶体上有利于油烟的催化燃烧,降低了反应温度.随着CexZr1-xO2固溶体中Ce/Zr摩尔比的变化,催化剂的活性顺序为Pt/γ-Al2O3/Ce0.5Zr0.5O2＞Pt/γ-Al2O3/Ce0.25Zr0.75O2＞Pt/γ-Al2O3/Ce0.75Zr0.25O2＞Pt/γ-Al2O3/CeO2＞Pt/γ-Al2O3/ZrO2.     

CuO/TiO2/γ-Al2O3催化剂表征及对NO＋CO反应性能研究

采用色谱-微反流动法反应装置考察了w%CuO/15%TiO2/γ-Al2O3催化剂对NO＋CO的反应活性;催化剂经空气氛或氢气氛预处理后,NO转化率达100%的反应温度分别是325和275℃;XRD仅能检测到γ-Al2O3晶相,负载15%CuO后可以检测到微弱的CuO晶相;H2-TPR能检测到2个CuO的还原峰（α和β峰）,将其归属于高度分散的CuO分别在裸露的γ-Al2O3和TiO2/γ-Al2O3载体上的还原;原位红外分析结果表明催化剂经空气氛或氢气氛预处理后,吸附NO＋CO反应气后,反应的中间产物N2O出现的温度分别为200和150℃。     

Experimental studies on the hydrogen isotope recovery using low-pressure palladium membrane diffuser

In this paper, we introduce a set of low-pressure palladium membrane diffuser designed to recover hydrogen isotopes from inert mixture gases. Several gaseous mixtures (D₂/Ar and D₂/He) with different deuterium concentration have been used for cleanup test of the low-pressure palladium membrane diffuser at 723 K. Effect of the composition of feed gas on the pressure of permeate side has been observed by gas chromatography (GC) and pressure sensor. With the feed flow rate of the mixture gases increasing, the D₂ permeate pressure is increasing as well. Decontamination factor (DF) of more than 1000 and recovery efficiency greater than 99.9% have been obtained by controlling the feed gas flow rate. The same palladium membrane diffuser was used to process helium-3 gas with more than 10% hydrogen isotope and about 0.3% tritium gas. The pure helium-3 (above 99.4%) with low content of hydrogen isotopes (about 0.084%) has been obtained. Recovery efficiency of all hydrogen isotopes is 99.5% above.     

Gas chromatographic separation of hydrogen isotopes on columns packed with alumina,modified alumina and sol–gel alumina

The stationary phase of alumina adsorbents, prepared by different chemical processes, was used to study the separation behaviour of hydrogen isotopes. Three types of alumina, obtained by conventional hydroxide route alumina coated with silicon oxide and alumina prepared by internal gelation process (IGP), were used as packing material to study the separation of HT and T₂ in a mixture at various temperatures. The conventional alumina and silicon oxide coated alumina resolved HT and T₂ at 77 K temperature with different retention times. The retention times on SiO₂ coated columns were found to be higher than those of other adsorbents. However, the column filled with IGP alumina was found to be ideal for the separation of HT and T₂ at 240 K. The peaks were well resolved in less than 5 min on this column.     

金属有机框架CPL-1填充柱气相色谱分析氢同位素

金属有机框架(MOFs)材料CPL-1的比表面积大、孔径均一,在低温条件下对氢同位素具有良好的量子筛分效应,是气相色谱固定相潜在的应用材料。采用CPL-1填充制备了长0.5 m、内径1 mm的微孔填充柱,借助单晶Al_2O_3颗粒间隙构建了色谱载气流通路径,在低温条件下探索研究了CPL-1填充柱的氢同位素分析性能。结果表明,在77 K时CPL-1对H_2和D_2的吸附量接近4 mmol/g,优于MnCl2/γ-Al_2O_3和γ-Al_2O_3,CPL-1填充柱在取样量0.25~2 mL范围内对低浓度氢同位素样品的检测具有良好的线性关系,检测的相对误差小于4%。CPL-1填充柱具有线性范围宽、重复性好、准确度高等优点,在氢同位素色谱分析中具有潜在的应用价值。     

Fundamental study on decontamination of tritium from gaseous phases by copper oxide

Some fundamental studies on removal of tritium from gaseous streams by a small column of copper oxide were carried out. An about 10 cm length of column packed with 100 g of copper oxide was examined on the conversion ratios of hydrogen and tritium into water. The experiment with hydrogen of 0.1% in argon showed that the logarithmic plot of remaining ratio of hydrogen by passing through the column is proportional to the reciprocal of gas flow rate and to the length of oxide column. The oxide column was also used for treating tritium-bearing waste gas from an evacuating system of alpha D-T neutron generator. It was observed that at column temperatures lower than 450 degrees C the conversion ratio of tritium in the waste gas into water is considerably smaller than that of hydrogen of 0.1% in argon.     

Analysis of trace levels of impurities and hydrogen isotopes in helium purge gas using gas chromatography for tritium extraction system of an Indian lead lithium ceramic breeder test blanket module

In the fusion fuel cycle, the accurate analysis and understanding of the chemical composition of any gas mixture is of great importance for the efficient design of a tritium extraction and purification system or any tritium handling system. Methods like laser Raman spectroscopy and gas chromatography with thermal conductivity detector have been considered for hydrogen isotopes analyses in fuel cycles. Gas chromatography with a cryogenic separation column has been used for the analysis of hydrogen isotopes gas mixtures in general due to its high reliability and ease of operation. Hydrogen isotopes gas mixture analysis with cryogenic columns has been reported earlier using different column materials for percentage level composition. In the present work, trace levels of hydrogen isotopes (∼100 ppm of H₂ and D₂) have been analyzed with a Zeolite 5A and a modified γ‐Al₂O₃ column. Impurities in He gas (∼10 ppm of H₂, O₂, and N₂) have been analyzed using a Zeolite 13‐X column. Gas chromatography with discharge ionization detection has been utilized for this purpose. The results of these experiments suggest that the columns developed were able to separate ppm levels of the desired components with a small response time (<6 min) and good resolution in both cases.     

Gas chromatography flow rates for determining deuterium/hydrogen ratios of natural gas by gas chromatography/high-temperature conversion/isotope ratio mass spectrometry

The effects of the gas chromatography flow rate on the determination of the deuterium/hydrogen (D/H) ratios of natural gas utilising gas chromatography/high-temperature conversion/isotope ratio mass spectrometry (GC/TC/IRMS) have been evaluated. In general, the measured deltaD values of methane, ethane and propane decrease with increase in column flow rate. When the column flow rate is 1 mL/min or higher, which is commonly used for the determination of D/H ratios of natural gas, the organic H in gas compounds may not be completely converted into hydrogen gas. Based on the results of experiments conducted on a GC column with an i.d. of 0.32 mm, a GC flow rate of 0.6 mL/min is proposed for determining the D/H ratios of natural gas by GC/TC/IRMS. Although this value may be dependent on the instrument conditions used in this work, we believe that correct deltaD values of organic compounds with a few carbon atoms are obtained only when relatively low GC flow rates are used for D/H analysis by GC/TC/IRMS. Moreover, as the presence of trace water could significantly affect the determination of D/H ratios, a newly designed inlet liner was used to remove trace water contained in some gas samples.     

Effect of chemical modification on the adsorption and chromatographic properties of aluminas

The effect of chemical modification by sodium hydrogen carbonate on the adsorption and chromatographic properties of aluminas was studied by low-temperature nitrogen adsorption followed by thermal desorption, IR spectrometry, and gas chromatography. It was found that, at a decrease in the volume of micropores, adsorption and desorption proceed in mesopores. It was shown that, at the higher chemical homogeneity of the alumina surface, the symmetry of the chromatographic peaks and the efficiency of the column are considerably improved.     

A novel sorbent tube for ambient hydrogen sulfide determination

A novel tubular device has been developed for hydrogen sulfide determination in air. Several substrates such as commercial silica gel and alumina TLC plates, silica gel powder, alumina, CaSO(4), CaCO(3), BaSO(4), MgO, chalk, alpha-cellulose and ethyl cellulose were tested as solid substrates. 30-70-mesh silica gel was finally employed in glass tubes of 4.0 mm internal diameter. Silica gel is treated with 0.5 M aqueous CdCl(2) solution, dried, filled into the glass tube and sample gas is passed through the device using nitrogen as the carrier gas where 70% relative humidity is employed. The analyte reacts with the solid substrate to form a luminescent spot whose length in the tube is measured and correlated to concentration. The flow rate was 68 ml min(-1). The analytical system is linear in the range of 0.2-1.3 ppm H(2)S for the specified conditions. The prepared devices are stable at least for 3 months prior to sampling; and after sampling, the luminescing spot is stable also at least for 3 months.     

Effect of H2 Flow Rate on High-Rate Etching of Si by Narrow-Gap Microwave Hydrogen Plasma

For the purpose of realizing a low-cost production process of silane (SiH₄) gas, we have proposed the high-rate etching of metallurgical-grade Si by narrow-gap microwave hydrogen plasma. In this paper, effect of hydrogen gas flow rate (0–10 L/min) on the etch rate has been investigated and correlated with the relative variation of hydrogen-atom density estimated by actinometry. By decreasing hydrogen gas flow rate, the etch rate gradually increases up to the maximum value of 11 μm/min at 2 L/min. This increase is well correlated with the increase of hydrogen-atom density due to the longer residence time of hydrogen molecules in the plasma. On the other hand, when the gas flow rate is lower than 2 L/min, the etch rate abruptly decreases with decreasing gas flow rate in spite of the increase of hydrogen-atom density. From the surface observations and Raman measurements, it is found that the decrease in etch rate in the lower flow rate range is attributed to the formation of microcrystalline Si particles due to the decomposition of generated-SiH₄ molecules in the plasma.