Coverage dependence of neopentane trapping dynamics on Pt(111)

Adsorption probabilities for neopentane on Pt(111) were measured directly using supersonic molecular-beam techniques at coverages ranging from zero to monolayer saturation, incident translational energies between 18 and 110 kJ mol⁻¹ and incident angles between 0° and 60° at a surface temperature of 105 K. The adsorption probability was found to increase with coverage up to near monolayer saturation at all incident translational energies and incident angles. The coverage dependence of the adsorption probability predicted by a modified Kisliuk model with enhanced trapping into the second layer exhibits good quantitative agreement with the experimental values. The angular dependence of the adsorption probability decreases with increasing coverage, suggesting that the effective corrugation of the gas–surface interaction potential increases with the adsorbate coverage. The initial adsorption probability into the second layer onto the covered surface decreases from 0.95 to 0.75 with increasing energy over the energy range studied, and exhibits total energy scaling. A comparison with second-layer trapping data of simpler molecules onto covered Pt(111) indicates that the structural complexity of adsorbed neopentane molecules facilitates collisional energy transfer during adsorption.     

沸石的骨架结构与酸强度

沸石分子筛是应用广泛的固体酸催化剂，其催化性能与沸石质子酸的强度和密度密切有关，对沸石酸性的研究是沸石催化领域内一个永恒的课题，国内外许多学者对此进行了长期工作，然而至今仍有许多问题认识不一致，关于沸石骨架结构与酸性的关系也是其中争议较多的问题之一．Sohn等N曾经根据脱铝Y沸石和ZSM－5沸石上正己烷反应结果，笼统地认为Si／Al比超过一定值以后，不同骨架结构的沸石的酸强度相同，催化活性只与酸位密度有关．Barthomeuf[2]则从沸石的结构参数出发，提出了一种较为精确的说法，即沸石的酸强度与骨架中铝的拓扑密度有…