Temperature-programmed desorption and adsorption of hydrogen on Mo2N

Hydrogen adsorption-desorption over Mo₂N has been studied using a temperature-programmed technique. It is revealed that hydrogen on Mo₂N exhibits very high mobility leading to migration of the surface hydrogen into the sublayer and bulk of the sample or the reverse. The surface hydrogen species are preferentially formed when adsorption is carried out below 573 K. On increasing the adsorption temperature to above 573 K, the quantity of hydrogen species located in the sublayer or/and bulk of the Mo₂N sample increases significantly.     

Nitrogen Adsorption Study of MCM-41 Molecular Sieves Synthesized Using Hydrothermal Restructuring

Nitrogen desorption scanning hysteresis loops (DSHLs) for large-pore MCM-41 silicas (pore diameter from 4.0 to 6.5 nm) are reported for the first time. DSHLs for MCM-41 were compared with those of conventional mesoporous silicas and no appreciable differences were found, although hysteresis loops and DSHLs for the latter were usually broader. Since desorption behavior of conventional porous silicas is appreciably influenced by pore connectivity, the observed similarity in hysteresis behavior suggests single-pore blocking effects for MCM-41 due to variation of pore diameter along its nonintersecting channels. It was also shown that the steepness of nitrogen desorption branches at relative pressures close to 0.4 often results from proximity of the lower pressure limit of adsorption-desorption irreversibility and consequently it is not justified to consider it as an indication of narrow pore size distribution. Thus, application of desorption data in calculations of pore size distributions may be grossly misleading.     

Alkali metal cation doping of metal-organic framework for enhancing carbon dioxide adsorption capacity

Metal-organic frameworks （MOFs） have attracted much attention as adsorbents for the separation of CO2 from flue gas or natural gas. Here, a typical metal-organic framework HKUST-I（also named Cu-BTC or MOF-199） was chemically reduced by doping it with alkali metals （Li, Na and K） and they were further used to investigate their CO2 adsorption capacities. The structural information, surface chemistry and thermal behavior of the prepared adsorbent samples were characterized by X-ray powder diffraction （XRD）, thermo-gravimetric analysis （TGA） and nitrogen adsorption-desorption isotherm analysis. The results showed that the CO2 storage capacity of HKUST-1 doped with moderate quantities of Li＋, Na＋ and K＋, individually, was greater than that of unmodified HKUST-1. The highest CO2 adsorption uptake of 8.64 mmol/g was obtained with 1K-HKUST-1, and it was ca. 11% increase in adsorption capacity at 298 K and 18 bar as compared with HKUST- 1. Moreover, adsorption tests showed that HKUST-1 and 1K-HKUST-1 displayed much higher adsorption capacities of CO2 than those of N2. Finally, the adsorption/desorption cycle experiment revealed that the adsorption performance of 1K-HKUST-1 was fairly stable, without obvious deterioration in the adsorption capacity of CO2 after 10 cycles.     

Studies of physico-chemical properties and fractal dimensions of selected high-temperature superconductor surfaces

Properties relating to porosity of solids (fractal dimensions, surface roughness parameters) were evaluated from atomic force microscopy (AFM) and nitrogen adsorption-desorption isotherms measured at 77 K for selected high-temperature [(RE) Ba₂Cu₃O_7−x, RE=Y, Sm] superconductors. Adsorption capacity, specific surface area, fractal dimensions were determined from adsorption-desorption isotherms. The adsorption isotherms of all samples were S-shaped and belong to type II according to the IUPAC classification. A linear relationship was demonstrated between the fractal coefficients calculated by using the two methods and values of adsorption capacity of monolayer.     

担载的NaRuCo_3(CO)_(12)络合物及其分散型Ru-Co双金属催化剂

担载于Al_2O_3上的NaRuCO_3(CO)_(12)络合物在IR光谱上出现类似于Ru(CO)_2O_2络合物特征带的羰基带,在300～400℃左右变强,在CO中尤为明显。在以ZrO_2为载体时出现与原来络合物相近的弱羰基带。当CO吸附于以Al_2O_3为载体的脱羰基催化剂上时,发现在氧化态催化剂上也出现了与担载络合物相似的吸收带,在还原态催化剂上只出现线式带。吸附于以ZrO_2为载体的脱羰基催化剂上的CO不出现CO的IR吸收带,在He中亦无TPD脱附物,在H_2中却可发生加氢反应生成CH_4。从Na~+和ZrO_2协同效应角度,探讨了CO在上述两种分散型催化剂上吸脱附行为不同的原因。     

凹凸棒石负载锰氧化物低温选择性催化还原催化剂的表征及对氨的吸脱附

 以非均相沉淀法制备了凹凸棒石 (PG) 载体上负载锰氧化物催化剂 Mn/PG, 并用于低温选择性催化还原法 (SCR) 脱硝反应. 采用 X 射线衍射、透射电子显微镜和 H2-程序升温还原方法对催化剂进行了表征; 通过 NH3 吸脱附实验考察了催化剂的锰负载量和煅烧温度对 NH3 吸附和脱附量及吸附位的影响. 结果表明, 锰氧化物高度分散于 PG 晶体表面, 其存在状态取决于催化剂煅烧温度. 煅烧温度低于 550 oC, 锰氧化物为 Mn2O3 和 Mn3O4, 煅烧温度为 550 oC 时, 锰氧化物为 Mn3O4. NH3 主要吸附在 PG 载体上, 锰氧化物的担载基本不影响催化剂吸附 NH3 的能力, 但促进了吸附 NH3 的活化, 这是催化剂 SCR 活性显著增加的直接原因.     

Influence of Adsorption and Desorption of Gas Micronuclei on the Nature of the Flow of a Gassy Liquid through a Porous Medium

The problem of gassy liquid flow through a porous medium is considered theoretically. Periodic oscillations of the liquid and gas flow rate observed experimentally are attributable to the processes of sorption and desorption of gas micronuclei on the walls of the pore space and their diffusion. In the kinetic equation employed the desorption rate is directly proportional to the adsorbed micronucleus concentration and the seepage rate, and the adsorption rate is directly proportional to the product of the mobile micronucleus concentration and the free site concentration on the pore surfaces. Steady-state solutions of this equation are investigated. It is shown that periodic oscillations of the flow rate can manifest themselves only when the processes of micronuclei adsorption predominate over the desorption processes.     

柠檬酸溶胶-凝胶法制备的纳米Ce1－xMnxO2: 织构与晶相结构

采用N2-吸附/脱附、XRD、Raman光谱和TEM等表征技术研究了柠檬酸溶胶-凝胶法制备的Ce1－xMnxO2 (0≤x≤1) 样品的织构及晶相结构.结果表明, Ce1－xMnxO2 样品的N2吸附等温线为IV型, 滞后环为H1型, 最可几孔径处在2.5~3.7 nm范围.由XRD测得的样品晶粒大小与由TEM测定的颗粒尺寸相近, 表明制备的样品具有较好的分散性, 但是样品的组成对颗粒大小有明显的影响, Mn浓度适中样品(x=0.3~0.7)的颗粒(1~5 nm)明显小于低Mn浓度样品(x<0.3)和高Mn浓度样品(x>0.7)的颗粒(10~50 nm).尽管在x>0.7时, XRD未能检测到样品中有α-Mn2O3晶粒存在, 但Raman光谱结果表明, 所有Ce1－xMnxO2混合氧化物均以α-Mn2O3相和立方CeO2相Ce-Mn-O固溶体形式存在.     

稀土元素替代Y对YBa_2Cu_3O_(7-δ)氧吸附性能的影响

用热重法研究了RBa2Cu3O7-δ(R=Gd、Er、Eu、Dy、Sm、Ho和Nd)及Y1-xLaxBa2Cu3O7-δ(x=0.1,0.5和1.0)共10种材料在高温下的氧吸附—脱附性能。结果表明,随着温度的升降循环,仅NdBa2Cu3O7-δ(R=Gd)和Y1-xLaxBa2Cu3O7-δ的氧吸附—脱附性能有较好的重复性,其余的6个样品的重复性都很差;并且这10种样品的质量变化率都没有YBCO的大。     

限域于SBA-15孔道内的活性相聚集形态

针对Pd/SBA-15和MoO3/SBA-15两类催化剂样品,使用N2物理吸附手段对比研究了限域于介孔SBA-15分子筛孔道内活性相Pd与MoO3的聚集形态.结果表明,金属Pd以颗粒状形态分布在SBA-15分子筛孔道内,氧化物MoO3则以层状形态存在.并用高分辨透射电镜验证了此分析结果.