Rate equations and isotherms for two adsorption models

The rate equations and isotherms for two adsorption models have been formulated and discussed. The rate equations obtained have been compared to those of pseudo-first-order model and pseudo-second-order model, respectively. Calculated results indicated that the rate equations of single site model and dual site model could be approximated by those of pseudo-first-order model and pseudo-second-order model, respectively, in a limited ranges of the values of , K*and t*. The adsorption isotherm of single site model has been found to be the same as that of Langmuir type.     

低碳烷烃选择性氧化高分散活性位催化剂的研究进展

石油资源的过渡消耗导致化工原料短缺危机,低碳烷烃选择性氧化可以有效缓解危机并降低化工原料成本。高分散活性位催化剂在低碳烷烃选择性氧化反应中具有特殊催化作用和广阔的应用前景,在石油化工行业发展中具有巨大的潜能。基于国内外研究者在高分散活性位催化剂用于低碳烷烃选择性氧化领域的研究工作,介绍高分散活性位催化剂的制备方法,总结低碳烷烃选择性氧化高分散活性位催化剂体系,分析低碳烷烃选择性氧化反应机理。重点评述钒基、钼基和铁基高分散活性位催化剂用于低碳烷烃选择性氧化反应的催化性能及反应机理。并对高分散活性位催化剂在低碳烷烃选择性氧化中存在的问题、发展趋势和应用前景进行总结和展望。     

Method for simultaneous determination of sorption isotherms and diffusivity of cement-based materials

A method for simultaneous determination of the diffusion and sorption properties of cement-based materials is presented. It is a gravimetric method where one small specimen is exposed to stepwise changes in relative humidity while its mass is being measured. As sorption in cement-based materials is slow, the change in relative humidity to the next level is made before final equilibrium has been reached on the previous level. Approximate final (equilibrium) levels are found by extrapolation using an exponential equation, and a factor is applied to correct for the fact that the sorption step does not start at equilibrium conditions. A correction for external mass transfer resistance is also included. The method can be used in desorption as well as absorption mode. Measurements of two materials are presented and compared with the results obtained using conventional methods.     

The determination of active filter aid adsorption sites by temperature-programmed desorption

Temperature programmed desorption (TPD) was used to evaluate the active sites of several filter aids that have been promoted for use by the deep-frying industry: activated carbon, aluminas, bleaching earths, diatomaceous earth, silica and synthetic magnesium silicate. TPD analysis determines both the total surface concentration of the active sites and the details of their intensity distribution. A correlation analysis was made between the adsorbents' oil treatment performance and the observed acidic/basic sites. For some of the adsorbents, the adsorption of free fatty acids and the percent change in the color of the oil was shown to relate to the total basic sites and acid sites, respectively. The study also showed that other factors might affect these adsorptivities.     

Mechanism of sulfur poisoning on supported noble metal catalyst — The adsorption and transformation of sulfur on palladium catalysts with different supports

A series of supported palladium catalysts (Pd/Al₂O₃, Pd/MgO and Pd/TiO₂) were prepared by the impregnating method and treated with H₂S, H₂ +O₂ or O₂, among which H₂S is used as a poison and H₂ +O₂ or O₂ are as purging atmospheres. The S^2– species in the supports was introduced by means of mechanically mixing Na₂S with the supports or catalysts. X-ray photoelectron spectroscopy (XPS) was employed to determine the changes in the chemical states of oxygen, palladium and sulfur in the catalysts before and after the treatment, while infrared (IR) spectroscopy was used to measure the SO^2– ₄ group produced in the catalysts and supports. The results show that on MgO and TiO₂ carriers whose acidities are weak, there exist two kinds of oxygen species, one is the lattice oxygen, the other one is the active species of oxygen. The latter can oxidize the S^2– into SO^2– ₄ even at room temperature in air. Because of the weak acidities and smaller specific surface area of MgO and TiO₂, the S^2– is liable to adsorb on the catalysts and to transform into SO^2– ₄. But for the case of Al₂O₃ support its acidity is rather strong, and its surface oxygen species under the experimental conditions is not so active as that in MgO and TiO₂ carries. The poison H₂S on the Al₂O₃ support only experiences a process of physical adsorption-desorption. In Pd/Al₂O₃ catalyst, the negatively charged sulfur ions are not so easily adsorbed and transformed as those in Pd/MgO and Pd/TiO₂. It is also implied that the properties of the carriers are related to the ability of self-regeneration of the corresponding catalysts. Pd/Al₂O₃ catalyst is more able to self-regenerate than Pd/MgO and Pd/TiO₂ catalyst.     

Statistical condensation adsorption isotherms of gas molecules adsorbed on porous adsorbents, surface monolayer adsorption isotherms and hysteresis phenomena

Condensation adsorption isotherms of type IV (or V) according to BDDT classification on porous adsorbents composed of one or two groups of adsorption sites are derived statistically. When Β_c1 (or Β_c2) is less than unity, the isotherm becomes type IV, and when it is greater than unity, the isotherm becomes type V. It is understood that the negative sign(-) of the additional adsorption energy, q, in the nth layer in deriving those theoretical isotherms plays a decisive role on the horizontally flat approach to the axis of the isotherm near the saturation vapor pressure. The values of the surface area can be calculated easily. The pore radii of all the adsorbents which we have obtained by using the derived isotherms with respect to the appropriately selected experimental data agree with those obtained by using the Kelvin equation. Many surface mono-layer adsorption isotherms are obtained in the process of deriving the various adsorption isotherms. From them we can learn that the surface sites are not adsorbed completely even near the saturated vapor pressure, and we can find the range of error by comparing them with v_ms of the BET equation. We could mention through judging the results of a great deal of the experimental isotherm data of types IV and V that “the cause of hysteresis phenomena of the condensation adsorption-desorption of gases is originated from the deviation from the thermodynamically reversible adsorption-desorption process in the condensation adsorption-desorption of gases”.     

二氧化钛基催化剂催化氧化甲醛的研究进展

甲醛（HCHO）是一种主要的室内空气污染物,具有高致癌性和致突变性,催化氧化是一种理想而有效的室内消除甲醛的方法。二氧化钛作为载体负载贵金属催化剂在甲醛催化氧化反应中表现出优良的催化性能。本文综述了近年来二氧化钛基催化剂催化氧化甲醛的研究进展,主要总结了二氧化钛的吸附机理,二氧化钛晶体结构、表面形貌及微观结构、表面活性氧物种和还原性等对二氧化钛基负载贵金属催化剂催化氧化甲醛性能的影响,重点关注了催化剂的化学结构性质与甲醛氧化活性的关系,并归纳了一部分甲醛催化氧化反应机理。最后指出二氧化钛基催化剂在甲醛催化氧化反应中未来研究方向为：合理设计TiO₂各种缺陷和晶面暴露,同时提高贵金属的分散性和原子利用效率,继而进一步提高催化剂的性能;在保持催化剂高活性、高稳定性的同时,推进设计实际应用整体式催化剂的研究进程。     

VOCs在MAC上吸附等温线的测定与拟合

大气中挥发性有机物（VOCs）所造成的污染严重地危害人体健康,引起了社会公众和政府的高度重视,研究高效的VOCs治理技术已是一个刻不容缓的课题.本文主要研究用微电磁天平在线测定20、60、90、140℃时甲苯、丁醇和乙酸乙酯在蜂窝状活性炭MAC上的吸附等温线,并用Langmuir、Freundlich、Langmuir-Freundlich、DR和Toth方程对吸附实验等温线进行了拟合.结果表明,MAC对3种VOCs都有比较大的吸附容量,是一种有效的治理VOCs的方法;无论在低浓度下还是在高浓度下,Toth方程都能够很好地拟合甲苯、丁醇和乙酸乙酯在MAC上的吸附等温线,相对误差不超过±6％.     

Fischer-Tropsch synthesis on ruthenium supported ETS-10 titanium silicate catalysts

Titanium silicate ETS-10 was found to be a suitable metal catalyst support, having high surface area, high ion exchange capacity and no acidic functions. In this work, ETS-10 was used as a support in preparing ruthenium supported catalyst for Fischer-Tropsch synthesis. Ru/METS-10 catalytic systems (M standing for Na or K) showed some important characteristics, as good metal dispersion and shape selectivity. Moreover, no side reactions due to acidic functions were evidenced; indeed readsorption of olefins on active metal centers was found to control the activity of the catalysts.In part presented at 10th IZC, Garmisch-Partenkirchen, July 1994.     

Kinetics and isotherm studies for the adsorption of boron from water using titanium dioxide

Boron is a necessary element for plants that are generally found in the ground and seawater, but it can also be poisonous in large doses. Contamination of water with boric acid or borate ions is a global concern. Due to the absence of the chemical charge that boron possesses, its removal is often difficult. To investigate boron's adsorption characteristics, kinetic, isotherm, and isothermal studies were performed. The adsorption of boron was shown to be a pH-dependent mechanism, with the best results at around pH 9.0. About 47% of the boron from a solution of 50 mg L⁻¹ was removed using 5 g titanium dioxide in 30 min. It was also demonstrated that boron adsorption kinetics increased with temperature, which is best described by the pseudo-second-order kinetic model (R² > 0.98) and also fits well with Elovich and pseudo-first-order models (R² > 0.94) at pH 9.0. Equilibrium was reached in about 40 min for all the samples. The film boundary layer diffusion step limits the rate. Experimental results correspond well to the Freundlich isotherm (R² = 0.95–0.99). Langmuir and Temkin's isotherms also fitted reasonably well (R² = 0.94–0.98). The Freundlich and Langmuir constants indicate favourable adsorption. The Gibbs free energy (ΔG) values increased negatively (from −11.47 to −15.63 kJ mol⁻¹) with increasing temperature, signifying a feasible and spontaneous process. The enthalpy change (ΔH) value of about 30.35 kJ mol⁻¹ indicated endothermic physical adsorption. The results indicate that titanium dioxide is an excellent and safe adsorbent for the removal of boron from water.     

基于模式搜索加速遗传算法的逆向法确定竞争吸附等温线

基于局部优化算法的逆向法,被广泛应用于确定吸竞争附等温线模型,但其存在的主要问题是:不能保证结果的广义收敛性和低下的计算效率.本文提出了一种基于模式搜索加速遗传算法的反晨向法.并将该算法成功应用于柠檬酸/葡萄糖的竞争吸附等温线的确定,在保证了计算结果的广义收敛性的前提下,算法执行效率相对传统遗传算法提高了一倍以上.     

Supported hybrid catalysts based on zirconocene and tris(pyrazolyl)borate titanium derivatives

A series of hybrid supported catalysts were prepared by combining (iBuCp)₂ZrCl₂ and {Tp^Ms*}TiCl₃ complex (Tp^Ms* = HB(3‐mesityl‐pyrazolyl)₂(5‐mesityl‐pyrazolyl)^?) sequentially grafted onto MAO (methylaluminoxane)‐modified silica according to a Plackett Burmann 2³ design. Supported catalysts were prepared taking into account the immobilization order, silica pretreatment temperature, and grafting temperature. Grafted metal content was comparatively determined by Rutherford backscattering spectrometry (RBS), X‐ray photoelectronic spectroscopy (XPS), and inductively coupled plasma–optical emission spectroscopy (ICP–OES). The resulting catalysts were evaluated in terms of catalyst activity and polymer properties. According to RBS measurements, grafted metal content remained comprised between 0.1 and 0.5 wt % Zr/SiO₂ and 0.1 and 0.3 wt % Ti/SiO₂ depending on the immobilization order and on silica pretreatment temperature. All the systems were shown to be active in ethylene polymerization having external MAO as cocatalyst. Catalyst activity seemed to be governed by the zirconocene species, influenced slightly by Ti ones. Resulting polymers were characterized by DSC and GPC. The polyethylenes mostly presented higher molecular weight than those produced by homogeneous catalysts or by zirconocene grafted on bare or on MAO‐modified silica. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

The determination of adsorption isotherms by XPS and ToF-SIMS: their role in adhesion science

The study of the adsorption of characteristic ions or molecules from liquid solutions by XPS or ToF-SIMS is shown to be an important experimental method in adhesion science. The theoretical background to adsorption and experimental procedures necessary to yield high-quality results are described. It is shown that in most cases adsorption data conforms to the Langmuir equation, which enables a parameter to be defined which is proportional to the interaction energy between absorbate and adsorbent. A series of examples of the approach are given involving the adsorption of macromolecules, organosilane adhesion promoters, and other organic molecules on oxidised metal and carbon fibre substrates. The estimation of the surface acidity of carbon fibres by measuring the capacity of the surface for derivatising ions is shown to improve the accuracy of the determination.     

超声法制备纳米有机膨润土及其吸附性能研究

在超声作用下,以十四烷基三甲基溴化铵对膨润土进行改性,制备了纳米有机膨润土。通过红外光谱（FTIR）、X-射线衍射（XRD）对纳米有机膨润土进行表征。结果表明有机改性剂进入膨润土层间,层间距由L38nm增大为2．10nm。实验测试了该材料对品绿的吸附性能,结果显示在25℃,对品绿的最大理论吸附量为333．97mg／g,高于原土的最大理论吸附量243．21mg／g。用不同模型对吸附等温线及动力学数据进行了拟合,结果表明准二级动力学方程所得参数更为合理,更符合实验数据,等温吸附平衡更符合Langmuir模型。     

合成气制低碳烯烃铁催化剂活性相的研究进展

近年来,合成气制低碳烯烃铁基催化剂的研究备受广大研究者关注,但催化剂的活性相备受争议。大多数研究者认为碳化铁是合成气制低碳烯烃的活性相。本文归纳总结了近些年研究者对活性相碳化铁的研究,重点阐述了催化剂及其活性相的制备方法、还原气体、渗碳温度等因素对形成碳化铁的影响以及活性相碳化铁及暴露于催化剂表面的碳化铁晶面对合成气制低碳烯烃催化性能及产物分布的影响。今后工作的重点是进一步制备和研究不同结构的碳化铁活性相对目标产物的调控。此外,碳化铁的晶面对产物分布的影响也是未来的研究方向。     

纳米尺度高配位活性钛TS-1的制备及性能评价

采用低成本模板剂和硅源（四丙基溴化铵和硅溶胶）,利用蒸汽辅助干胶晶化法,通过添加晶种的方式合成出纳米级TS-1分子筛。再经二次水热晶化,采用乙胺和四丙基溴化铵的混合溶液对其进行处理,制备出了含有六配位钛的高活性TS-1分子筛。采用X射线衍射、紫外漫反射可见光谱、紫外拉曼光谱、傅里叶变换红外光谱、固体核磁共振、N2物理吸附-脱附等手段对其物理化学性质等进行表征,并考察其对丙烯环氧化反应的催化性能。结果表明,纳米级TS-1分子筛后处理生成了活性更为优异的六配位钛物种,且其孔道结构得到了改善,比表面积明显增大;其催化丙烯环氧化反应的活性明显提高,双氧水转化率由47.59%增至85.79%,有了明显的提升。     

NHPI/SMA-Co多活性位点催化氧气氧化环己烷的工艺研究

研究了NHPI/SMA-Co多活性位点催化氧气氧化环己烷的反应。得出该反应的最佳反应条件为：5mL环己烷,10mL乙腈,NHPI/SMA-Co摩尔配比为10:3,0.04g NHPI/SMA-Co复合催化剂用量,反应温度120℃,初始氧压1.0MPa。在此条件下反应6h,环己烷转化率为19.84%,环己醇选择性22.23%,环己酮选择性38.65%,KA油选择性达60.88%。经过对催化剂进行多次重复使用实验,表明催化剂的活性在反应过程中无明显降低,可以循环使用。     

Protein adsorption on titanium dioxide: Effects on double layer and semiconductor space charge region studied by EIS

The semiconductor properties of an n-type TiO₂ oxide surface and its modification by protein adsorption using electrochemical impedance spectroscopy (EIS) were studied. Impedance spectra under steady state conditions were obtained as a function of electrode potential and human serum albumin (HSA) concentration in solution. The effect of the adsorption potential on the EIS response was also analyzed (E_ads −0.70, −0.50 and −0.080 V vs. saturated calomel electrode). The impedance spectra were modeled using different equivalent circuits, and data analysis were performed by data fitting in the whole frequency range, as well as in the low and high frequency ranges. The electric representation that better fit experimental data consisted of two equivalent subcircuits composed by a combination of constant phase elements (cpe₁ and cpe₂) and resistances (R_s and R₁). The cpe₁ element represented the distributed capacity in the semiconductor oxide. The cpe₂ element was associated with diffusional processes. We have analyzed EIS data based on a theoretical calculation of interface apparent capacitance (C_app) from the cpe₁ parameters (Q₁ and ?₁) and resistance elements. The changes in capacitance, produced by the presence of HSA, were associated to changes in the space charge layer capacitance of the semiconductor, as a result of the energy band bending near the surface. The values obtained for the R₁ element from the theoretical fitting procedures (in the high and whole frequency range) were correlated to the electric resistance inherent to the semiconductor properties having a value of 6.10³ Ω cm².     

The importance of site isolation and phase cooperation in propane ammoxidation on rutile-type vanadia catalysts

Propane ammoxidation to acrylonitrile over rutile-type vanadia catalysts is discussed regarding phase cooperation and site isolation effects. Compared with the pure phases, biphasic catalysts with both SbVO₄and -Sb₂O₄are considerably more selective to the formation of acrylonitrile. It is demonstrated that cooperation between the phases during the calcination of the catalyst and the use in propane ammoxidation results in spreading of antimony species from free antimony oxide to the surface of SbVO₄, forming Sb⁵⁺–V³⁺/V⁴⁺supra-surface sites being involved in the formation of acrylonitrile. Dilution and isolation of the vanadium centers in SbVO₄through the partial replacement with, e.g., Al, Ti and W improves the catalytic properties. Structure–reactivity correlations using data for a nominal Sb_0.9V_0.9-x Ti _x O _y series indicate that the activation of propane occurs on a V³⁺site and the activation of ammonia requires an Sb⁵⁺site.