共查询到19条相似文献,搜索用时 171 毫秒
1.
从TPD谱图求解Ed、ko的等脱附速率法 总被引:2,自引:1,他引:2
提出了一种简便的TPD谱图处理法——等脱附速率法。此法与查表法相结合, 有助于确定脱附反应动力学级数。实验证明, 该法适用于从一级或二级脱附反应TPD谱求解脱附活化能E_d和指前因子k_o值。 相似文献
2.
以Polangi—Wagner模型为基础、谱峰高的方差为目标函数,用单纯形加速法对TPD谱图进行定量解析,求算脱附活化能和指前因子,计算值与理论值一致,对重叠峰的解析结果更为理想. 相似文献
3.
本文以程序升温脱附(TPD)为主要实验手段,对环己胺在5种不同沸石分子筛上的吸脱附行为进行了研究。结果表明,沸石分子筛对环己胺有着较强的吸附作用,不同的沸石分子筛对环己胺的吸附能力受其结构和表面酸性特征的影响而异。有效吸附部位为与沸石分子筛表面酸性有关的弱化学吸附位;环己胺从不同沸石分子筛表面脱附的动力学与晶内扩散有关,其表观脱附活化能分别为:63.6kJ/mol(5A),68.6kJ/mol(13X),20.1kJ/mol(菱沸石),46.9kJ/mol(NaY)和47.3KJ/mol(ZSM-5)。 相似文献
4.
提出了一种简便的TPD谱图处理法——等脱附速率法。此法与查表法相结合,有助于确定脱附反应动力学级数。实验证明,该法适用于从一级或二级脱附反应TPD谱求解脱附活化能E_d和指前因子k_o值。 相似文献
5.
烷基化催化剂表面酸性及催化性能的动力学研究 总被引:2,自引:0,他引:2
在确定关联升温速率、脱附峰温和脱附峰覆盖率的程序升温脱附动力学模型的基础上,通过TPD实验和模型参数估值,建立了表征催化剂酸密度、酸强度及强度分布情况的方法。研究表明,随着活化温度的提高,固体酸催化剂表面酸中心强度分布先变宽后趋于均匀,350?℃活化催化剂的强度分布最宽;催化剂表面酸强度和酸密度随活化温度提高均呈先增大后降低、分别在350 ℃和250 ℃活化温度达到极大值的变化规律。催化剂酸性与催化性能关联的结果表明,随着活化温度的提高,烷基化反应速率常数与总脱附量的变化趋势相同,而催化剂失活速率常数与脱附活化能变化趋势相同;催化剂活性稳定性随其酸强度的增大而变差,催化剂活性与催化剂酸量和酸强度有关。 相似文献
6.
7.
本文以H_2在Cu/ZnO/Al_2O_2型低变催化剂上的程序升温脱附为例,解析了其TPD谱图。提出了T_f法及曲线拟合法。与其它几种方法计算结果的对比表明,该方法具有一定的可靠性及可行性。由分析计算得到的动力学参数可知,同一催化剂,不同的活泼部位具有相同形式的脱附动力学方程,而只是动力学参数不同。计算结果还表明,Cu/ZnO/Al_2O_3型低变催化剂对H_2的有效表面为非理想表面,并求出脱附过程中的频率因子γ_d、活化能E_d与表面复盖度θ的函数关系分别为指数函数和对数函数。从脱附级数推测出,H_2在Cu/ZnO/Al_2O_3型低变催化剂上的吸附为分解二位吸附。 相似文献
8.
龚健 《高等学校化学学报》1990,11(9):1025-1027
TPD技术[1]已成为研究固体表面性质的重要手段,本文在总结前人工作的基础上考察了TPD谱峰峰宽和相应参数与脱附活化能(Ed)之间的变化规律,证明用任意峰宽法或半峰宽法测定Ed值有很好的实用性,该法直接运用TPD谱图参数,无需另外作图,故十分快速、简便,与其它方法比较,结果吻合。 相似文献
9.
10.
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。/ 相似文献
11.
Nagaoka S Matsumoto T Okada E Mitsui M Nakajima A 《The journal of physical chemistry. B》2006,110(32):16008-16017
The adsorption state and thermal stability of V(benzene)2 sandwich clusters soft-landed onto a self-assembled monolayer of different chain-length n-alkanethiols (Cn-SAM, n = 8, 12, 16, 18, and 22) were studied by means of infrared reflection absorption spectroscopy (IRAS) and temperature-programmed desorption (TPD). The IRAS measurement confirmed that V(benzene)2 clusters are molecularly adsorbed and maintain a sandwich structure on all of the SAM substrates. In addition, the clusters supported on the SAM substrates are oriented with their molecular axes tilted 70-80 degrees off the surface normal. An Arrhenius analysis of the TPD spectra reveals that the activation energy for the desorption of the supported clusters increases linearly with the chain length of the SAMs. For the longest chain C22-SAM, the activation energy reaches approximately 150 kJ/mol, and the thermal desorption of the supported clusters can be considerably suppressed near room temperature. The clear chain-length-dependent thermal stability of the supported clusters observed here can be explained well in terms of the cluster penetration into the SAM matrixes. 相似文献
12.
Temperature-programmed desorption (TPD) and reflection absorption infrared spectroscopy (RAIRS) are used to investigate the crystallization kinetics and measure the excess free energy of metastable amorphous solid water films (ASW) of H(2)O and D(2)O grown using molecular beams. The desorption rates from the amorphous and crystalline phases of ASW are distinct, and as such, crystallization manifests can be observed in the TPD spectrum. The crystallization kinetics were studied by varying the TPD heating rate from 0.001 to 3 K/s. A coupled desorption-crystallization kinetic model accurately simulates the desorption spectra and accurately predicts the observed temperature shifts in the crystallization. Isothermal crystallization studies using RAIRS are in agreement with the TPD results. Furthermore, highly sensitive measurements of the desorption rates were used to determine the excess free energy of ASW near 150 K. The excess entropy obtained from these data is consistent with there being a thermodynamic continuity between ASW and supercooled liquid water. 相似文献
13.
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. 相似文献
14.
The bilayer of benzene on Cu(110) was studied with temperature-programmed desorption (TPD), time-of-flight electron stimulated desorption ion angular distribution (TOF-ESDIAD), and scanning tunneling microscopy (STM). TPD spectra show that three well-defined adsorption states exist. The alpha layer corresponds to the first layer containing flat-lying benzene molecules. As coverage increases, the beta layer forms on top of the alpha layer, and eventually, a multilayer, gamma, forms. TPD measurements show that the number of benzene molecules in the beta layer is equal to the number of benzene molecules in the alpha layer. ESDIAD measurements establish that the orientation of the benzene molecules in the beta layer is edge-on, with two C-H bonds directed toward the surface. STM images of the beta layer reveal closely spaced edge-on benzene molecules arranged in repeating hexagons, as well as loosely spaced benzene molecules with greater apparent height, which are also edge-on species. Correlation between the different measurements suggests a structural model for the benzene bilayer. 相似文献
15.
Equilibrium adsorption isotherms for low-volatile compounds are extremely difficult to measure. A simple technique using temperature programmed desorption (TPD) is proposed. It is demonstrated that the two parameters needed for constructing the Langmuir isotherm can be derived with data from the TPD technique alone. Thus, the Langmuir isotherms of iodine on AX-21 super-activated carbon were obtained with this technique. A series of TPD experiments for samples with different initial loadings of iodine were carried out by varying the heating rates which resulted in different peak desorption temperatures. The peak desorption temperature decreased as the initial loading was increased because of the re-adsorption effect. The Langmuir constant was derived from kinetic theory with the activation energy for desorption obtained from the experiment. The activation energy for desorption was 12.3 kcal/mol. The Langmuir constants determined by this technique were in comparable order of magnitude to the reported values for iodine on activated carbon. The saturation capacity of AX-21 for iodine could also be determined from the TPD data obtained from samples with different initial loadings. The estimated saturation capacity from the TPD experiment was 2.96 g I(2)/g AX-21, which was close to the experimentally measured saturation capacity of 3.25 g I(2)/g AX-21 for the same system. 相似文献
16.
Breanna M. Wong Greg Collinge Alyssa J.R. Hensley Yong Wang Jean-Sabin McEwen 《Progress in Surface Science》2019,94(2):100538
Bimetallic catalysts have demonstrated properties favorable for upgrading biofuel through catalytic hydrodeoxygenation. However, the design and optimization of such bimetallic catalysts requires the ability to construct accurate, predictive models of these systems. To generate a model that predicts the kinetic behavior of benzene adsorbed on Pt (1 1 1) and a Pt3Sn (1 1 1) surface alloy (Pt3Sn (1 1 1)), the adsorption of benzene was studied for a wide range of benzene coverages on both surfaces using density functional theory (DFT) calculations. The adsorption energy of benzene was found to correlate linearly with benzene coverage on Pt (1 1 1) and Pt3Sn (1 1 1); both surfaces exhibited net repulsive lateral interactions. Through an analysis of the d-band properties of the metal surface, it was determined that the coverage dependence is a consequence of the electronic interactions between benzene and the surface. The linear coverage dependence of the adsorption energy allowed us to quantify the influence of the lateral interactions on the heat of adsorption and temperature programmed desorption (TPD) spectra using a mean-field model. A comparison of our simulated TPD to experiment showed that this mean-field model adequately reproduces the desorption behavior of benzene on Pt (1 1 1) and Pt3Sn (1 1 1). In particular, the TPD correctly exhibits a broadening desorption peak as the initial coverage of benzene increases on Pt (1 1 1) and a low temperature desorption peak on Pt3Sn (1 1 1). However, due to the sensitivity of the TPD peak temperature to the desorption energy, precise alignment of experimental and theoretical TPD spectra demands an accurate calculation of the adsorption energy. Therefore, an analysis of the effect of the exchange-correlation functional on TPD modeling is presented. Through this work, we show the necessity of incorporating lateral interactions into theoretical models in order to correctly predict experimental behavior. 相似文献
17.
The adsorption of monolayer and multilayer benzene on the Ag(111) surface was characterized using temperature programmed desorption (TPD). TPD spectra revealed two broad peaks at approximately 205 and approximately 150 K at submonolayer coverage and a sharper, multilayer peak at 140 K. Analysis of the coverage-dependent shape and shift of the two submonolayer peaks has resulted in their assignment to desorption from two different binding geometries on threefold-hollow sites with symmetries C(3v)(sigma d) and C(3v)(sigma v). The TPD peak analysis incorporated inter-adsorbate repulsive interaction that resulted from the local dipole moment at the adsorption site induced by the adsorbate-surface charge transfer bonding. The analysis has yielded desorption energies of 54.9 +/- 0.8 and 50.4 +/- 0.4 kJ/mol for the C(3v)(sigma d) and C(3v)(sigma v) configurations, respectively. The interface dipole and polarizability of the benzene-silver complex have been determined to be 5.4 +/- 1.8 D and 14 +/- 10 A3, respectively. Repulsive interactions in the monolayer were found to lower the desorption energy from the zero-coverage value by 14.8 kJ/mol. Leading edge analysis of the multilayer peak yielded a desorption energy of 40.9 +/- 0.7 kJ/mol. 相似文献
18.
We have investigated the temperature-programmed desorption (TPD) of ammonia during the activation of NH4Na-mordenites of different
exchange degrees. Using a regularization method, desorption energy distribution functions have been calculated. The obtained
results indicate the heterogeneity of the bridging Si-OH-Al groups in HNa-mordenites. This was concluded from the width of
the distribution functions and from the presence of submaxima. For HNa-mordenites of exchange degrees below 50%, containing
only hydroxyls in the broad channels, two distinct submaxima are present, thus suggesting the presence of at least two kinds
of bridging hydroxyls of various acid strengths. In HNa-mordenites of exchange degrees above 50%, the hydroxyls appear in
narrow channels and the distribution of ammonia desorption energy broadens on the side of higher energies. This may be related
to a strong stabilization of ammonium ions inside narrow channels. The maximum concentrations of hydroxyls of desorption energies
between 95 and 135 kJ mol-1 and between 135 and 165 kJ mol-1 calculated from TPD data were 3.9 and 3.3 OH per unit cell (u.c.). These values agree well with our previous IR results of
concentrations of hydroxyls in broad and in narrow channels (3.7 and 2.8 OH per u.c.). The TPD data obtained for the heterogeneity
of OH groups in HNa-mordenites are in accordance with the IR data concerning ammonia desorption. The IR band of OH groups
restoring upon saturation of all the hydroxyls with ammonia and subsequent step-by-step desorption at increasing temperatures
shifts to lower frequencies indicating that there are hydroxyls of various acid strengths and the less acidic hydroxyls restore
first at lower desorption temperatures.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献