Characterization of Hydrogen Adsorption on Palladium and Pd/c Using a Radiotracer

Hydrogen adsorption on palladium black and palladium supported on activated carbon was characterized by the Temperature Programmed Desorption technique (TPD) using the radiotracer tritium. It is shown that there are five energetic desorbed hydrogens with peak maxima at —50, 35, 115, 350, and 580°C. An additional peak at — 120°C hydrogen desorbed from activated carbon was observed on Pd/C. An isotopic hydrogen separation experiment was designed to demonstrate that hydrogen only dissociatively adsorbed on palladium surfaces whereas it was associatively adsorbed on activated carbon.     

原位程序升温脱附(TPD)方法的建立及其应用实例

介绍了在ＶＧＥＳＣＡＬＡＢ２１０电子能谱仪上自己研制组装的用于研究单晶金属表面吸附层的原位ＴＰＤ装置。研制的单晶样台采用钽丝加热，最高加热速度可达３０Ｋ／ｓ，线性升温范围－１００－１００℃，最高可达１０００℃以上。     

负载型纳米TiO2复合载体的制备及其酸性研究

采用溶胶-凝胶法在γ-Al2O3上制备出负载型纳为TiO2，并用XRD，TEM对TiO2的晶型及粒子大小进行了表征。结果表明，在550℃煅烧后，TiO2仍为锐钛矿结构，且通过控制制备条件，TiO2粒径可控制在5nm-10nm之间及15nm-20nm之间，TiO2都以纳米粒子的形式高分散负载在γ-Al2O3上。另外，还用NH3-TPD对复合载全进行酸性表征。实验发现，纳米TiO2对复合载体的酸量影响较大。复合载体的酸量并不是随TiO2含量的增加而一直下降，而是先降低，当TiO2含量达到30％后又开始增加。纳米TiO2对复合载体的酸强度和酸度分布影响较小。     

Studies of Acid Properties of FeSiMCM-41 and LaSiMCM-41 by NH3-microcalorimetric and NH3-TPD Measurements

The acidity of mesoporous materials FeSiMCM-41, LaSiMCM-41, SiMCM-41, AlSiMCM-41 and HAlSiMCM-41 has been investigated by microcalorimetric studies of the adsorption of ammonia and temperature programmed ammonia desorption method. In the initial stage, the acid strength sequence is SiMCM-41>HAlSiMCM-41>AlSiMCM-41>FeSiMCM-41>LaSiMCM-41, in agreement with that found for microporous molecular sieves materials. A small number of strong acid sites of SiMCM-41 may result from the aluminum impurity contained in the silica source material. The acid density sequence is HAlSiMCM-41>AlSiMCM-41>FeSiMCM-41>LaSiMCM-41SiMCM-41 and can be explained by the studies of existing states of trivalent atoms in these samples reported in previous work. Since some NH₃-TPD plots of these samples show the profiles that could not be back to baseline at elevated temperature, the technique of microcalorimetric adsorption is preferable in studying these samples.This revised version was published online in November 2005 with corrections to the Cover Date.     

碱性分子筛上不同吸附物的TPD研究

借助吸附不同酸性物的程序升温方法研究了碱金属交换的Ｘ型分子筛的碱性。发现吸附物对分子筛碱性的ＴＰＤ表征有很大影响。主要与吸附物的分子体积和酸强度两种因素有关，并对这些影响因素进行了分析。结果表明；甲醇做吸附物对用ＴＰＤ表征分子筛的碱性相对比较可靠。     

Interaction of Chlorine with Hydrogenated Diamond Surface

The interaction of chlorine with the hydrogenated diamond surface has been investigated by diffuse reflectance Fourier-transform Infrared (FTIR) spectroscopy, temperature-programmed desorption (TPD) spectroscopy, and X-ray photoelectron spectroscopy (XPS). The hydrogenated diamond surface is chlorinated by thermal reaction in chlorine. Hydrogen chemisorbed on the diamond surface is abstracted by chlorine and the chemisorption of chlorine is yielded. Hydroxyl groups are produced by treatment of the chlorinated diamond with water vapor at room temperature. Amino groups are produced by treatment of the chlorinated diamond with ammonia at 425 °C.     

Nature of the Ftir Band in Acidic Zeolites

The nature of a FTIR band (1490 cm ^-1 ) in the spectrum of zeolite HZSM-5 after pyridine adsorption was investigated. It is shown that the source of this band is not a combined contribution from Brönsted and Lewis acidic sites as widely believed.     

Site-blocking effects of preadsorbed H on Pt(1 1 1) probed by 1,3-butadiene adsorption and reaction

The influence of hydrogen coadsorption on hydrocarbon chemistry on transition metal surfaces is a key aspect to an improved understanding of catalytic selective hydrogenation. We have investigated the effects of H preadsorption on adsorption and reaction of 1,3-butadiene (H₂CCHCHCH₂, C₄H₆) on Pt(1 1 1) surfaces by using temperature-programmed desorption (TPD) and Auger electron spectroscopy (AES). Preadsorbed hydrogen adatoms decrease the amount of 1,3-butadiene chemisorbed on the surface and chemisorption is completely blocked by the hydrogen monolayer (saturation) coverage (θ_H = 0.92 ML). No hydrogenation products of reactions between coadsorbed H adatoms and 1,3-butadiene were observed to desorb in TPD experiments over the range of θ_H investigated (θ_H = 0.6-0.9 ML). This is in strong contrast to the copious evolution of ethane (CH₃CH₃, C₂H₆) from coadsorbed hydrogen and ethylene (CH₂CH₂, C₂H₄) on Pt(1 1 1). Hydrogen adatoms effectively (in a 1:1 stoichiometry) remove sites from interaction with chemisorbed 1,3-butadiene, but do not affect adjacent sites. The adsorption energy of coadsorbed 1,3-butadiene is not affected by the presence of hydrogen on Pt(1 1 1). The chemisorbed 1,3-butadiene on hydrogen preadsorbed Pt(1 1 1) completely dehydrogenates to H₂ and surface carbon upon heating without any molecular desorption detected, which is identical to that observed on clean Pt(1 1 1). In addition to revealing aspects of site blocking that should have broad implications for hydrogen coadsorption with hydrocarbon molecules on transition metal surfaces in general, these results also provide additional basic information on the surface science of selective catalytic hydrogenation of butadiene in butadiene-butene mixtures.     

Au/TiO2/Ru(0 0 0 1) model catalysts and their interaction with CO

Au/TiO₂/Ru(0 0 0 1) model catalysts and their interaction with CO were investigated by scanning tunneling microscopy and different surface spectroscopies. Thin titanium oxide films were prepared by Ti deposition on Ru(0 0 0 1) in an O₂ atmosphere and subsequent annealing in O₂. By optimizing the conditions for deposition and post-treatment, smooth films were obtained either as fully oxidized TiO₂ or as partly reduced TiO_x, depending on the preparation conditions. CO adsorbed molecularly on both oxidized and reduced TiO₂, with slightly stronger bonding on the reduced films. Model catalyst surfaces were prepared by depositing submonolayer quantities of Au on the films and characterized by X-ray photoelectron spectroscopy and scanning tunneling microscopy. From X-ray photoelectron spectroscopy, a weak interaction between the Au and the TiO₂ substrate was found. At 100 K CO adsorption occurred on both the TiO₂ film and on the Au nanoparticles. CO desorbed from the Au particles with activation energies between 53 and 65 kJ/mol, depending on the Au coverage. If the Au deposit was annealed to 770 K prior to CO exposure, the CO adsorption energy decreased significantly. STM measurements revealed that the Au particles grow upon annealing, but are not encapsulated by TiO_x suboxides. The higher CO adsorption energy observed for smaller Au coverages and before annealing is attributed to a significantly stronger interaction of CO with mono- and bilayer Au islands, while for higher particles, the adsorption energy becomes more bulk-like. The implications of these effects on the known particle size effects in CO oxidation over supported Au/TiO₂ catalysts are discussed.