常规二脉冲叠加四阶跃微分伏安法研究─准可逆电极过程的理论和验证

推导并验证了新型阶跃伏安技术─常规二脉冲叠加四阶跃微分伏安法准可逆电极过程的理论电流方程式,同时研究了各项参数如扫描增量(E_s)、脉冲高度(△E)、传递系数(α)对峰电流函数(ψ_p)、峰电流(i_p)、峰电位(E_p)和半峰宽(W_1/2)的影响。运用理论ψ_p-lgk_s图和单纯形优化计算测量了及Zn(Ⅱ)/Zn(Hg)-NaNO3体系的K_s及α值,结果与文献值一致。     

用热脱附方法测定氧气、乙醇在Porapak样品上的脱附级数和脱附活化能

本文采用热脱附(TDS的实验方法,以多孔性Porapak微球为样品,测定了氧气、乙醇分子在PorapakQ、N两种样品上的脱附级数n和脱附活化能E_d,并与气相色谱法测定的吸附热作了比较。得出E_d≥ΔH令人满意的结果。     

CO2在Cu/ZnO/Al2O3型低变催化剂上的TPD研究

本文采用程序升温脱附(TPD)法研究了CO₂在Cu/ZnO/Al₂O₃型低变催化剂上的吸、脱附行为。结果表明:在350℃以内,该催化剂对于CO₂显示出一种能量分布的活泼部位,且其主要是由催化剂中的游离ZnO所提供。以T_f法结合脱附速率等温线法进行了TPD谱图的定量解析,求出了脱附动力学参数,并发现Cu/ZnO/Al₂O₃对CO₂的有效表面为非理想表面,CO₂在Cu/ZnO/Al₂O₃上的脱附近似地服从一级过程。最后针对得到的Arrhenius图进行了有关的讨论。     

最小二乘法计算苯、噻吩和正辛烷在NaY上程序升温脱附活化能

采用程序升温脱附(TPD)技术测定了苯、噻吩和正辛烷在NaY上以不同升温速率升温时的TPD谱图. 利用TPD谱图的峰形和其微分曲线判断了程序升温脱附过程中的脱附级数. 提出了一种利用最小二乘法计算吸附剂/催化剂的脱附活化能及其动力学参数的方法. 以这些TPD谱图为基础, 分别采用传统TPD计算模型、最小二乘法以及一阶微分曲线法计算了苯、噻吩和正辛烷在NaY上的脱附活化能和动力学参数. 结果表明, 最小二乘法对在不同线性升温速率时的程序升温脱附活化能的计算结果是一致的.     

聚-4-乙基苯酚抗氧剂对聚丙烯结晶行为的影响

通过差示扫描量热仪(DSC)和X射线粉末衍射仪(XRD)研究了聚-4-乙基苯酚抗氧剂对聚丙烯结晶行为的影响。 分别用Jeziorny法和Mo法处理非等温结晶动力学。 同时用Friedman法和Kissinger法计算其结晶活化能。 最后由结晶活化能与结晶温度的变化曲线求得Hoffman-Lauritzen参数成核速率常数(K_g)和迁移活化能(U^*)值,进而求得折叠链端表面自由能(σ_e)和分子链段折叠功(q)。 结果表明,抗氧剂的加入,使聚丙烯的结晶峰温度向低温区移动,结晶半峰宽变大,半结晶时间(t_1/2)增大,Jeziorny法所得的结晶速率常数(Z)降低,Mo法所得反映结晶速率快慢的参数F(T)提高,在相同结晶转化率下,结晶活化能负值变小。 Hoffman-Lauritzen参数K_g、U^*、σ_e和q值均增大。 所有变化均表明聚-4-乙基苯酚抗氧剂对PP的结晶有抑制作用。     

二氧化钛系列光催化剂的拉曼光谱

采用溶胶-凝胶法制备了TiO₂粉体和薄膜光催化剂.使用FT-Raman光谱和激光共聚焦拉曼光谱研究了粉体和薄膜的拉曼光谱,探讨了热处理条件、Fe³⁺掺杂和以硅胶为载体的薄膜化所引起的TiO₂结构变化.结果表明,TiO₂在350℃存在由无定形向锐钛矿相的转变,600℃下存在锐钛矿相向金红石相的转变,750℃下完全转变为金红石相;掺杂会引起TiO₂的晶格畸变,导致拉曼谱峰宽化;以硅胶为载体的TiO₂负载薄膜的部分拉曼谱峰与粉体相比,有一定的位移和宽化.     

定量解析程序升温脱附谱图的新方法

能量分布不均匀表面的TPD谱图,常常出现拖尾、峰重叠等复杂情况,难以定量解析。本文提出的T_f法,解决了这类TPD谱图的覆盖度θ的求值问题。并以CO,CO,H_2在Cu/ZnO/Al_2O_3型低变催化剂上的TPD谱图为例,证明了T_f法在实际应用中的可行性和可靠性。     

程序升温脱附法对低变反应体系的吸-脱附研究

本文采用程序升温脱附法(TPD)研究了低变反应各组分CO、H₂O、CO₂和H₂在Cu/ZnO/A1₂O₃型低变催化剂上的吸-脱附行为,并对与Cu/ZnO/A1₂O₃具有可此相对组成的六种样品进行了类似的讨论,通过对所得TPD谱图的定性分析发现:构成Cu/ZnO/A1₂O₃型低变催化剂的各个组元对低变反应各组分的吸-脱附作用互不相同,且不同的组元具有各自的吸-脱附特征。     

(Fe,Cr)3O4催化剂表面酸性的研究

本文研究了(Fe,Cr)₃O₄催化剂的表面酸性,发现其表面结构具有可变性,表面主要存在Fe²⁺(α位)和Fe³⁺(β位)两种酸中心,β位上吸附吡啶的E_d=278.8±13.8kJ/mol。     

高稳定度CH4/CO2重整Ni/MgO催化剂的研究

用TPR,TPD,TPO,TPMC(程序升温CH₄解离积炭)和活性评价等手段研究了普通浸渍法与载体盐助分散浸渍法制得的CH₄/CO₂重整制合成气Ni基催化剂的性能.结果表明,用载体盐助分散浸渍制备的催化剂Ni-O-Mg间作用较强,吸附CO₂能力较大,CH₄解离积炭量少,因此其稳定性及寿命较好.     

n-alkanes on MgO(100). I. Coverage-dependent desorption kinetics of n-butane

High-quality temperature-programmed desorption (TPD) measurements of n-butane from MgO(100) have been made for a large number of initial butane coverages (0-3.70 ML, ML-monolayers) and a wide range of heating ramp rates (0.3-10 K/s). We present a TPD analysis technique which allows the coverage-dependent desorption energy to be accurately determined by mathematical inversion of a TPD spectrum, assuming only that the preexponential factor (prefactor) is coverage independent. A variational method is used to determine the prefactor that minimizes the difference between a set of simulated TPD spectra and corresponding experimental data. The best fit for butane desorption from MgO is obtained with a prefactor of 10(15.7+/-1.6) s(-1). The desorption energy is 34.9+/-3.4 kJ/mol at 0.5-ML coverage, and varies with coverage approximately as Ed(theta)=34.5+0.566theta+8.37 exp(-theta/0.101). Simulations based on these results can accurately reproduce TPD experiments for submonolayer initial coverages over a wide range of heating ramp rates (0.3-10 K/s). Advantages and limitations of this method are discussed.     

线性分析法来解热脱附动力学参数

TPD方法是研究表面常规手段之一.对于如何从实验结果获得正确的脱附动力学参数,已有不少工作发表。然而,现有方法均存在一定的适用范围,尤其是重叠谱解叠,仍然没有很好地解决。本文介绍的线性分析法,不仅适用于简单的一级和二级脱附TPD谱的解析,而且也适用于重叠谱解叠,从而为实验上确定动力学级数和复杂谱解叠提供了依据。     

Thermal decomposition kinetics of titanium hydride and Al alloy melt foaming process

Metal foams, now one of research foci, are a newclass of materials with low densities and novel physi-cal, mechanical, thermal, electrical and acoustic prop-erties[1—8]. Demands from high-tech make Al alloyfoam, which has much higher specific strength than ofpure Al foam, the new development focus[9—11]. Melt foaming process is one of the approaches tofabricate Al foam and Al alloy foam and their porestructure (pore diameter and porosity) has close rela-tionship with the thermal decompo…     

Controlled-Rate Thermal Desorptton

A new way of conducting thermal desorption experiments is described. The method consists in maintaining the desorption rate constant by a rigorous control of temperature. The equations for two models of constant rate desorption are described: from a surface with only one type of adsorption site, and with two different types. The technique is applied to two real systems and the kinetic parameters are determined. The results are compared with those obtained by using TPD. The main advantages are discussed and the methodology and modifications required for a TPD set-up to work at a constant desorption rate are described.     

SINGLET AND TRIPLET ENERGY TRANSFER IN α-DIKETONE DERIVATIVES OF URACIL and THYMINE

Irradiation of 1-(3,4-dioxopentyl)uracil (UPD) and 1-(3.4-dioxopentyl)thymine (TPD) in acetonitrile solution at 25°C, at the wavelength (280 nm) where only the pyrimidine absorbs the light, sensitizes both fluorescence and phosphorescence of the diketone chromophore in the sidechain. From comparison of the intensity in the corrected excitation spectra with the absorption spectra in acetonitrile solution, it was estimated that the yield of singlet energy transfer in UPD was 0.17 and in TPD was 0.44. It was also observed that the ratio of phosphorescence to fluorescence was greater in the sensitized emission than in that from direct excitation of the diketone chromophore. The yield of triplet energy transfer thus measured corresponds to minimum values for the yields of intersystem crossing from singlet excited state to triplet excited state of 0.075 in the uracil chromophore of UPD and of 0.14 in the thymine chromophore of TPD. These are in agreement with other recent values for these quantities. The value of this type of system as an intramolecular triplet counter is discussed.     

沸石分子筛上程序升温脱附谱的Monte Carlo模拟研究 Ⅰ．模型的建立

沸石分子筛因其特殊的孔道结构而致使其ＴＰＤ谱图的分析比其它催化剂更为困难，目前尚无一种切实可行的理论分析方法。本文发展了一种较为简单的模拟分子筛上ＴＰＤ谱图的ＭｏｎｔｅＣａｒｌｏ方法，模拟结果表明，在同一组脱附动力学参数下，沸石分子筛上的峰形和峰位置与其它催化剂都有明显的差异，并且峰温的差别与脱附活化能和指前因子有关。同时表明，对于普通催化剂可以根据峰最大时的覆盖度θ＿Ｍ来判断脱附级数，而对于沸石分子筛，θ＿Ｍ却随Ｅ＿ｄ线性变化。     

Analysis of molecular hydrogen formation on low-temperature surfaces in temperature programmed desorption experiments

The study of the formation of molecular hydrogen on low-temperature surfaces is of interest both because it enables the exploration of elementary steps in the heterogeneous catalysis of a simple molecule and because of its applications in astrochemistry. Here, we report results of experiments of molecular hydrogen formation on amorphous silicate surfaces using temperature-programmed desorption (TPD). In these experiments, beams of H and D atoms are irradiated on the surface of an amorphous silicate sample. The desorption rate of HD molecules is monitored using a mass spectrometer during a subsequent TPD run. The results are analyzed using rate equations, and the energy barriers of the processes leading to molecular hydrogen formation are obtained from the TPD data. We show that a model based on a single isotope provides the correct results for the activation energies for diffusion and desorption of H atoms. These results are used in order to evaluate the formation rate of H2 on dust grains under the actual conditions present in interstellar clouds. It is found that, under typical conditions in diffuse interstellar clouds, amorphous silicate grains are efficient catalysts of H2 formation when the grain temperatures are between 9 and 14 K. This temperature window is within the typical range of grain temperatures in diffuse clouds. It is thus concluded that amorphous silicates are good candidates to be efficient catalysts of H2 formation in diffuse clouds.     

程序升温脱附导数谱

提出了TPD导数谱，并以理论TPD导数谱图为对象，讨论了TPD导数谱在提高分辨率，消除口音干扰及确定脱附级数等方面的特点，推导了由TPD一阶、二阶导数谱求算脱附活化能和指标因子和的数学方程式，并对其进行了验证。／