未燃尽炭表面吸附汞的机理研究

本文应用量子化学密度泛函理论B3PW91方法,在lanl2dz基组水平上研究了飞灰中未燃尽炭表面对汞的微观吸附机理.建立了表征未燃尽炭的饱和簇模型,讨论了该簇模型在不同的情况下对汞的吸附作用,计算得出吸附能,并做出了相关的实验解释.结果表明量子化学的理论计算是揭示汞等痕量元素的吸附机理以及筛选合适吸附剂的一种有效方法.     

氢在A、X及ZSM-5型沸石上的高压物理吸附

采用常规体积吸附装置测定了77、195、293K和7MPa的条件下氢在A、X及ZSM-5沸石上的吸附特性和吸附容量．所有的氢吸附等温线基本符合Ⅰ型等温线,但在77K,压力为2-5MPa的等温线上观察到了超临界高压吸附所特有的最大吸附量．从等温线确定了等量吸附热并讨论了其影响因素．根据骨架结构和所含阳离子类型的差异,各种沸石表现出不同的氢吸附量．其中NaX沸石在77K/4MPa下的重量储氢分数为2．55％,是该实验中所测得的最高吸附量．CaA、NaX和ZSM-5沸石的氢吸附量与其比表面积成正比,这与沸石中的可用空穴容积有关．然而NaA和KA沸石不存在这种线性关系．实验中还观察到,NaA与KA沸石间出现氢吸附量的临界值是由KA沸石中较大的阳离子堵塞效应引起的．该实验将吸附质分了的动力学直径与沸石主晶孔的有效直径之比用于判断物理吸附中的堵塞效应．     

钴修饰单壁碳纳米管的贮氢性能

本文利用密度泛函理论中的广义梯度近似系统地研究了Co原子修饰的(5,5)单壁碳纳米管(SWCNT)的贮氢性能.结果表明:Co原子以桥位的形式吸附于(5,5)SWCNT表面能量最低,在Co原子周围可以吸附3个完整的氢分子,Co原子的修饰提高了(5,5)SWCNT对氢分子的吸附能力.态密度图显示(5,5)SWCNT具有金属性,磁矩为0,Co-SWCNT和Co-SWCNT·n H_2(n=1-3)的磁矩为1μB,氢分子的吸附未改变体系的磁性.Co-SWCNT·3H_2的氢分子平均吸附能为0.51 e V,适中的吸附能有利于常温常压下实现可逆贮氢.     

The dynamics of hydrogen adsorption on polycrystalline uranium

The dynamics of dissociative hydrogen adsorption on clean polycrystalline uranium has been studied using temperature programmed desorption and supersonic molecular beams. The initial sticking probability was measured as a function of incident kinetic energy between 3 and 255 meV. Two adsorption channels were observed; a non-activated direct channel was shown to be active over the entire energy range studied and a low energy indirect channel that was characterised by a decrease in sticking probability with increasing beam energy, and an insensitivity to both surface temperature and a range of hydrogen coverages. Together these results suggest the existence of an unaccommodated molecular precursor that has sufficient lifetime and mobility to locate favourable sites and dissociatively adsorb.     

碳纳米管在储氢上的应用

氢能是一种理想的能源载体,而经济有效的储氢手段是氢能实现规模应用急需解决的关键问题之一。碳纳米管在存储氢气上表现出来的独特性质,使其最有希望成为一种新的高效的储氢材料。从实验、理论研究两个方面总结了前人在碳纳米管储氢上的研究成果,并对碳纳米管储氢吸附方式,吸附量影响因素等方面做出分析。最后指出为实现碳纳米管储氢大规模应用仍需做的一些基础性研究工作。     

Hydrogen adsorption on the faujasite-type zeolite Mg-X: An IR spectroscopic and thermodynamic study

Hydrogen adsorption (physisorption) on the faujasite-type zeolite Mg-X was studied by means of variable-temperature (80-140 K) FT-IR spectroscopy. Perturbation of the adsorbed H₂ molecules by the cationic adsorbing centres of the zeolite renders the H-H stretching mode IR active, at 4065 cm⁻¹. Simultaneous measurement of IR absorbance and hydrogen equilibrium pressure, for a series of spectra recorded at the increasing temperature, allowed standard adsorption enthalpy and entropy to be determined. They resulted to be ΔH⁰ = −13 kJ mol⁻¹ and ΔS⁰ = −114 J mol⁻¹ K⁻¹, respectively. Both, spectroscopic and thermodynamic results are discussed in the broader context of corresponding data for hydrogen adsorption on other alkali and alkaline-earth cation exchanged zeolites, showing that, while an approximate correlation exists between ΔH⁰ and H-H stretching frequency, deviations can be expected for the case of zeolites containing small metal cations.     

Influence of structural heterogeneity of nanoporous sorbent walls on hydrogen storage

Heterogeneity is an ubiquitous aspect of adsorption, often modifying substantially the observed behaviour of the adsorbate-adsorbent system. In this paper, the influence of heterogeneity is explicitly analyzed for the case of the adsorption of molecular hydrogen onto nanoporous carbon. Grand Canonical Monte Carlo simulations were used to study the mechanism of adsorption in the models of the adsorbate that include both energetic and structural modifications of graphene-based slit pores. In particular, a partial substitution of carbons by boron modifies both the symmetry of the energy landscape and the strength of hydrogen physisorption; which results in considerable increases of the amount of adsorbed gas without major modification of the mechanism of adsorption. Additional heterogeneity arises from structural modifications of the adsorbent by neutron irradiation of boron-doped samples, where the boron fission products generate additional surface area for adsorption. Simulations of adsorption in such pores show that hydrogen uptake is strongly dependent on the chemical nature of the modified pore walls.     

Variable temperature FT-IR studies on hydrogen adsorption on the zeolite (Mg,Na)-Y

Variable-temperature infrared spectroscopy was used for the thermodynamic studies on the adsorption of hydrogen on the zeolite (Mg,Na)-Y. Adsorption renders the HH stretching mode infrared active, and simultaneous measurement of IR absorbance and hydrogen equilibrium pressure, over a range of temperature, allowed adsorption enthalpy and entropy to be determined. The standard adsorption enthalpy and entropy resulted to be ΔH° = −18.2(±0.8) kJ mol⁻¹ and ΔS° = −136(±10) J mol⁻¹ K⁻¹, respectively. The adsorption enthalpy is substantially higher than the hydrogen liquefaction heat, which suggests that magnesium-containing porous materials are potential candidates in the search for suitable adsorbents for reversible hydrogen storage.     

YK-1活性炭平衡储氢特性分析

文中基于氢在椰壳活性炭YK-1上的平衡吸附数据,以探寻氢在碳基材料上适宜存储条件为目的,研究吸附氢分子间相互作用能随储存系统温度、压力、表面遮盖率的变化规律。首先,依据容积法的原理,在温度区间113K—293K、压力范围0—13MPa测试氢在YK-1椰壳活性炭上的吸附等温线。其次,应用格子理论推导通用吸附等温方程,通过等温方程的线性标绘确定氢分子在吸附表面的最大浓度,并由氢分子在活性炭典型吸附空间内受到的壁面作用势函数迭代求解氢分子受到的壁面作用势,进而获得与各吸附平衡态对应的氢分子间相互作用能。最后,根据氢分子间作用能随温度、表面遮盖率等的变化关系,分析氢分子在此活性炭上吸附的特点。     

H_2在Al_nCr(n=1-7)团簇上吸附和解离的密度泛函研究

采用密度泛函理论中的B3LYP方法研究了H2在AlnCr(n=1-7)团簇上的吸附和解离.结果表明:AlnCr团簇结构与Aln+1团簇结构相似;物理吸附是H2以侧向的形式吸附在Cr原子上,H-H键长略微增长,H2的振动频率发生了红移;除了n=5外,其它AlnCr H2团簇的最稳定结构均是AlnCr团簇的最稳定结构与两个氢原子成键而成;AlnCr团簇向H原子转移了电荷;AlnCr H2团簇的平均结合能,垂直电离势和能隙均大于AlnCr团簇的,即AlnCr H2团簇比AlnCr团簇更稳定;Al7Cr对H2的化学吸附表现出较强的惰性,而AlnCr H2(n=1,2,6)则表现出较强的化学活性;由化学反应路径跟踪可知,通过改变AlnCr团簇中Al原子的个数可以调节H2的物理化学吸附行为.     

H2在AlnCr(n=1-7)团簇上吸附和解离的密度泛函研究

采用用密度泛函理论中的B3LYP方法研究了H2在AlnCr(n=1-7)团簇上的吸附和解离。结果表明：AlnCr团簇结构与Aln+1团簇结构相似;物理吸附是H2是以侧向的形式吸附在Cr原子上,H-H键长略微增长,H2的振动频率发生了红移;除了n=5外,其它AlnCrH2团簇的最稳定结构均是AlnCr团簇的最稳定结构与两个氢原子成键而成;AlnCr团簇向H原子转移了电荷;AlnCrH2团簇的平均结合能,垂直电离势和能隙均大于AlnCr团簇的,即AlnCrH2团簇比AlnCr团簇更稳定;Al7Cr对H2的化学吸附表现出较强的惰性,而AlnCrH2(n=1,2,6)则表现出较强的化学活性;由化学反应路径跟踪可知,通过改变AlnCr团簇中Al原子的个数可以调节H2的物理化学吸附行为。