NO与NO2在ZnO表面吸附的密度泛函理论研究

采用 DMol ³ 模块中广义梯度密度泛函理论(GGA)的Perdew-Burke-Ernzerh(PBE)方法研究含能材料分解气体产物NO, NO₂在ZnO(10 \bar{1} 0)表面的吸附和NO₂解离生成NO和O的过程. 结果表明, 优化后的吸附构型显示Zn顶位为稳定吸附位点, NO₂的吸附能大于NO. 态密度图分析结合差分电荷密度图表明, NO的N原子与表面Zn有相互作用, 电荷从NO转移到表面; NO₂的N_2p, O_2p轨道与表面Zn_3d轨道发生杂化, NO₂附近积累大量负电荷. 过渡态搜索显示NO₂的解离需跨过较高能垒, 不易进行.     

气体再燃低NOx燃烧中NO与NHi的反应机理研究

采用量子化学密度泛函理论(DFT)对NO与NH_i自由基的反应机理进行了研究,并结合经典过渡态理论对各反应速率常数进行了计算。结果表明,NO与NH₂自由基的反应体系可通过六个反应通道形成N₂+H₂O、N₂O+H₂和N₂H+OH。从能量变化和反应速率两方面考虑,产物N₂+H₂O最容易生成,其最佳反应通道为NO+NH₂→→N₂+H₂O;NO与NH自由基的反应体系可通过七个反应通道形成N₂+OH、N₂O+H和N₂H+O;其中,N₂+OH最容易生成,最佳反应通道为NO+NH→→N₂+OH。比较发现, NH比NH₂自由基更易与NO发生反应生成N₂。因此,在实际运行中改变操作条件,实现NH₂等向NH方向转化,有利于NO_x的还原。     

预吸附氧对NO在Pt(110)表面吸附和分解的影响

 利用程序升温反应谱、X射线光电子能谱和高分辨电子能量损失谱研究了NO在清洁和预吸附氧的Pt(110)表面的吸附和分解. 在清洁的Pt(110)表面,室温下低覆盖度时NO以桥式吸附为主,高覆盖度时NO以线式吸附为主. 加热过程中部分NO(主要是桥式吸附物种)分解,生成N2和N2O. 室温下O2在Pt(110)表面发生解离吸附. Pt(110)表面预吸附氧会抑制桥式吸附NO的生成,并导致其脱附温度降低40 K. 降低脱附温度有利于桥式吸附NO的分子脱附,从而抑制分解反应. 这些结果从表面化学的角度合理地解释了铂催化剂在富氧条件下对NO分解能力的降低.     

H原子在W低指数面上的吸附位和吸附态

应用原子和表面簇合物相互作用的5参数Morse 势及由5参数Morse势组装推广的LEPS方法对H-W低指数表面吸附体系进行了研究, 并获得了全部临界点特性. 计算结果表明, 低覆盖度下, H原子优先吸附在W(100)面的内层吸附位二层桥位B', 获得156 meV的垂直振动频率, 随着覆盖度的增加, H原子稳定吸附在表层的五重洞位(二层顶位)、桥位及顶位. 内层吸附位的优先吸附, 对与其邻近的表面吸附位的临界点性质有一定影响. 在W(110)面上只存在三重洞位的稳定吸附态, 垂直振动频率为151 meV. 在W(111)面上存在三种稳定吸附态, 子表面吸附位H₁, 桥位B'和顶位T, 分别获得104, 200, 259 meV的垂直振动频率. 在低覆盖度下, H原子优先吸附在子表面吸附位H₁.     

LaMnAl11O19催化剂上生物质气化气燃烧中NH3-NOx的转化特性

采用共沉淀法制备了LaMnAl₁₁O₁₉六铝酸盐催化剂,采用XRD、BET和XPS对样品结构进行了表征,并通过模拟生物质气化气的燃烧实验和NH₃单独氧化实验,分别考察了催化燃烧和均相燃烧过程中NH₃的转化特性。利用原位漫反射红外光谱（in-situ DRIFT）法在线研究了NH₃在催化剂表面的吸附和氧化信息。结果表明,焙烧后催化剂形成磁铅石（MP）结构的六铝酸盐晶体,且具有较大的比表面积,Mn以+2、+3价形式存在晶体中。均相燃烧下模拟气中的NH₃在500℃开始反应,随之就有NO生成。催化燃烧工况下NH₃氧化曲线和模拟气中NH₃的转化曲线相差不大,NH₃的起燃温度为310℃,反应后随之就有NO生成,NO在350℃~800℃保持一个较高的浓度。NO₂的生成温度较高,并仅在较窄的温度区间内出现,在整个燃烧过程中仅检测到几个10^-6的N₂O,反应过程中有40%以上的NH₃转化成NO。DRIFT结果表明,催化剂作用下NH₃的转化遵循 -NH反应机理,即催化剂表面吸附的NH₃分解产生 -NH,-NH与氧原子（O）反应生成HNO,再进一步反应生成N₂或N₂O,或是 -NH直接与氧分子（O₂）反应生成NO。     

Ag-ZSM-5催化剂上CH4选择催化还原NOx的研究

摘要研究Ag-ZSM-5催化剂上CH₄选择性催化还原NO_x的反应性能,采用TPD和TPSR技术研究NO和O₂共吸附于Ag-ZSM-5催化剂表面形成的吸附物种及其和CH₄之间的反应。结果表明,Ag-ZSM-5催化剂上CH₄选择性还原NO_x活性和选择性较高。NO和O₂共吸附在Ag-ZSM-5催化剂上形成的NO₃(s)吸附物种能被CH₄还原生成N₂.在NO₃(s)和O₂共存的体系中,CH₄能优先并选择性还原NO₃(s)生成N₂.     

CO2在α-U(001)表面的吸附和解离

采用广义梯度密度泛函理论研究了0.25ML覆盖度下CO₂在α-U（001）表面上的吸附和解离,得到了CO₂的稳定吸附构型和吸附能,确定了CO₂的解离过渡态和解离能垒,探讨了CO₂与表面U原子的相互作用本质.结果表明CO₂趋向以C（O）-U多键结合方式在α-U（001）面发生强化学吸附,吸附能为1.24-1.67 eV;C-O键的活化程度依赖于表面电子向CO₂发生转移的程度.CO₂与表面U原子的相互作用主要来自于U原子电子向CO₂最低空轨道（LUMO）2π_u转移,以及CO₂π_u/1π_g/3σ_u-U 6d轨道间杂化而生成新的化学键.以形成3个C-U键和6个O-U键模式在穴位1和穴位2上发生吸附的CO₂（H1-C₃O₆和H2-C₃O₆）的解离吸附能分别为3.15和3.13 eV,解离能垒分别为0.26和0.36 eV,预示着吸附CO₂分于易于解离形成CO分子和O原子.     

N2O在焦炭表面异相生成和分解机理的密度泛函理论研究

选用合理简化的焦炭模型,对煤焦燃烧过程中N₂O的异相生成和分解机理进行了分子水平上的研究。采用UB3LYP/6-31G(d)密度泛函理论方法优化得到了反应路径上反应物、产物、中间体和过渡态的几何构型和各中间反应的活化能和反应焓变。NO与其预先吸附在焦炭表面解离生成的表面氮组分反应生成N₂O的路径有两个,需要克服的势垒分别为69.3kJ/mol和200.0kJ/mol;NO亦可直接与焦炭中的吡啶氮结合释放出N₂O,该反应路径所需克服的最大势垒为418.0kJ/mol。N₂O可在焦炭表面分解释放出N₂,异相分解反应为一步反应,计算所得活化能为100.8kJ/mol。N₂O的异相生成和异相分解反应均为放热反应。采用经典过渡态理论计算得到了各路径中速率控制步骤的反应速率常数。低温条件下,N₂O的异相分解反应速率略低于其异相生成速率,随着温度的升高,两者逐渐接近,说明高温条件有利于N₂O的异相分解。     

纳米团簇Au19Pd和Au19Pt催化解离N2O

采用密度泛函理论研究Au-Pd和Au-Pt 纳米团簇催化解离N₂O. 首先根据计算得到Au₁₉Pd和Au₁₉Pt 团簇的最优构型(杂原子均位于团簇的表面). 以Au₁₉Pd催化解离N₂O为例研究催化解离的反应机理. 对此主要考虑两个反应机理, 分别是Eley-Rideal (ER)和Langmuir-Hinshelwood (LH). 第一个机理中N₂O解离的能垒是1.118 eV, 并且放热0.371 eV. N₂分子脱附后, 表面剩余的氧原子沿着ER路径消除需要克服的能垒是1.920eV, 这比反应沿着LH路径的能垒高0.251 eV. 此外根据LH机理, 氧原子在表面的吸附能是-3.203 eV, 而氧原子在表面转移所需的能垒是0.113 eV, 这表明氧原子十分容易在团簇表面转移, 从而促进氧气分子的生成. 因此, LH为最优反应路径. 为了比较Au₁₉Pd和Au₁₉Pt 对N₂O解离的活性, 根据最优的反应路径来研究Au₁₉Pt 催化解离N₂O, 得到作为铂族元素的铂和钯对N₂O的解离有催化活性, 尤其是钯. 同时, 将团簇与文献中的Au-Pd合金相比较, 得到这两种团簇对N₂O 解离有较高的活性, 尤其是Au₁₉Pd团簇. 再者, O₂的脱附不再是影响反应的主要原因, 这可以进一步提高团簇解离N₂O的活性.     

CO在轻微氧化的Mo(100)表面上的吸附和反应

应用HREELS和TDS研究了120K时CO在轻微氧化的Mo(100)上的吸附和脱附状况.120K时,CO在轻微氧化的Mo(100)上存在顶位垂直吸附(ν_CO=2016～2050cm^-1)、四重空位倾斜吸附(ν_CO=1088cm^-1)和通过π键与表面发生作用的倾斜吸附(ν_CO=1600cm^-1).当表面温度升高时,顶位吸附的CO在低覆盖度下发生解离,但在较高覆盖度下,可以同时发生脱附(T_p=319K)和解离;而后两种吸附态在温度升高时只发生解离.CO解离产生的C原子和O原子在930K和1320K时可重新结合成CO脱附.     

Adsorption and dissociation of NO on Ir(100): a first-principles study

Density functional theory (DFT) and periodic slab model have been used to systemically study the adsorption and dissociation of NO and the formation of N(2) on the Ir(100) surface. The results show that NO prefers the bridge site with the N-end down and NO bond-axis perpendicular to the Ir surface, and adsorption to the top site is only 0.05 eV less favorable, whereas the hollow adsorption is the least stable. Two dissociation pathways for the adsorbed NO on bridge or top site are located: One is a direct decomposition of NO and the other is diffusion of NO from the initial state to the hollow site followed by dissociation into N and O atoms. The latter pathway is more favorable than the former one due to the lower energy barrier and is the primary pathway for NO dissociation. Based on the DFT results, microkinetic analysis suggests that the recombination of two N adatoms on the di-bridge sites is the predominant pathway for N(2) formation, whereas the formation of N(2)O or NO(2) is unlikely to occur during NO reduction. The high selectivity of Ir(100) toward N(2) is in good agreement with the experimental observations.     

Theoretical Study of NO Dimer Adsorption and Dissociation on the CuCr2O4 （100） Surface

Theoretical simulation of the adsorption and dissociation of two NO molecules at the Cu^2＋, Cr^3＋ and bridge Cr^3＋ sites （b-Cr^3＋） on the normal spinel CuCr2O4 （100） surface has been carried out by density functional theory calculations. The results show that the formed N-down and O-down NO dimers are negatively charged. The formation of stable O-down dimers on the surface leads to the great elongation of N-O bond, which contributes to the NO reduction. The transition-state calculations indicate that the decomposition of O-down NO dimer at the b-Cr^3＋ site is most favorable and N2O is the major reduction product.     

Theoretical Study of NO Dimer Adsorption and Dissociation on the CuCr204 (100) Surface

Theoretical simulation of the adsorption and dissociation of two NO molecules at the Cu2 , Cr3 and bridge Cr3 sites (b-Cr3 ) on the normal spinel CuCr2O4 (100) surface has been carded out by density functional theory calculations. The results show that the formed N-down and O-down NO dimers are negatively charged. The formation of stable O-down dimers on the surface leads to the great elongation of N-O bond, which contributes to the NO reduction. The transition-state calculations indicate that the decomposition of O-down NO dimer at the b-Cr3~ site is most favorable and N2O is the major reduction product.     

Nb(110)表面氧原子覆盖度对氧分子解离的影响

用基于密度泛函理论的第一性原理方法研究了Nb(110)表面氧原子覆盖度分别为0.25、0.50、0.75 和1.00单层时对氧分子解离的影响. 结果表明, 在氧原子覆盖度不大于0.50单层时, 由于氧分子和表面铌原子的较强相互作用, 使它们能够自发解离. 然而在氧原子覆盖度为0.75单层时, 氧分子只能够在未占据的洞位附近解离, 同时发生严重的晶格畸变. 在形成一个氧原子单层后(1.00 单层), 氧分子只能弱吸附在Nb(100)表面上,此时氧原子向内扩散成为氧分子继续解离的速率决定步骤. 这些结果从理论上解释了在形成一个氧原子单层后, Nb(110)表面氧分子吸收速率迅速下降的原因.     

A DFT study of H2O dissociation on metal‐precovered Fe (100) surface

The H₂O adsorption and dissociation on the Fe (100) surface with different precovered metals are studied by density functional theory. On both kinds of metal‐precovered surface, H₂O molecules prefer adsorb on hollow sites than bridge and top sites. The impurity energy difference is proportional to the adsorption energy, but the adsorbates are not sensitive to the adsorption orientation and height relative to the surface. The Hirshfeld charge analysis shows that water molecules act as an electron donor while the surface Fe atoms act as an electron acceptor. The rotation and dissociation of H₂O molecule occur on the Co‐ and Mn‐precovered surfaces. Some H₂O molecules are dissociated into OH and H groups. The energy barriers are about 0.5 to 1.0 eV, whose are consistence with the experimental data. H₂O molecules can be dissociated more easily at the top site on Co‐precovered surface 1 than that at bridge site on Mn‐precovered surface 2 because of the lower reaction barrier. The dispersion correction effects on the energies and adsorption configurations on Co‐precovered surface 1 were calculated by OBS + PW91. The dispersion contributions can improve a bit of the bond energy of adsorbates and weaken the hydrogen bond effect between adsorption molecules a little.     

周期性密度泛函理论研究氯气在CuCl(111)表面上的吸附与解离

运用广义梯度密度泛函理论(Generalized Gradient Approximation，GGA)的PBE(Perdew-Burke-Ernzerh)方法结合周期性平板模型，研究了氯气分子和氯原子在CuCl(111)表面上的吸附。通过对不同吸附位和不同单层覆盖度下的吸附能和几何构型参数的计算和比较发现：氯气分子在CuCl(111)表面的吸附为解离吸附；单层覆盖度为0.50时的吸附构型为稳定的吸附构型；氯气分子平行吸附在CuCl(111)表面时最稳定，吸附能最大，达364.5 kJ·mol^-1；伸缩振动频率的计算结果表明，吸附后的氯气分子的伸缩振动频率与自由氯气分子的伸缩振动频率相比，都发生了红移；布居分析结果表明整个吸附体系发生了由Cu原子向氯气分子的电荷转移。氯原子吸附的计算结果显示氯原子以穴位稳定的吸附在CuCl(111)表面。     

Dissociative adsorption of carbon monoxide on Mo(110): first-principles theory

The adsorption and dissociation of carbon monoxide on Mo (110) surface is studied with density functional theory. The results at different sites (atop, short bridge, long bridge, and hollow) are presented. The hollow site is found to be the most stable adsorption site for CO. The CO molecule is found to adsorb in end-on configurations (alpha states) at high coverage and inclined configurations (beta states) at low coverage. The dissociation activation energy from beta states is found to be approximately 1 eV lower than from alpha state. The adsorption of dissociation products, C and O, on Mo(110) has also been studied. The most stable adsorption site for C and O is long bridge and hollow site, respectively. The adsorption of C and O at low coverage is, in general, stronger than at high coverage, which is partly responsible for the high reactivity of CO dissociation at low coverage, since the binding energy of CO is not very sensitive to the coverage.     

Theoretical study of NO adsorption/dissociation on Pd (100) and (111) surfaces

Both adsorption and dissociation of the diatomic molecular NO on Pd (100) and (111) surfaces are studied using the extended London‐Eyring‐Polyani‐Sato (LEPS) method constructed by means of 5‐MP (the 5‐parameter Morse potential). All critical characteristics of the system that we obtain, such as adsorption geometry, binding energy, eigenvalues for vibration, are in good agreement with the experimental results. On Pd (100) surface, NO prefers to adsorb in fourfold hollow site (H) uprightly at low coverage. With increase in the coverage NO gradually tilts in fourfold hollow and bridge sites. For NO? Pd (111) system, two adsorption states are found at low coverage, of which one adsorption state is the B(tilt) state that the centroid of NO projects at bridge site, another (H? B? H state) that NO almost parallels to the (111) surface with the vibration frequency of 610 cm^?1, but the frequency is near to that of the atoms, which is easy to be ignored in experiments. At high coverage, two transitional states (BH and HT) are found. NO is difficult to dissociate on Pd (100) and (111) surfaces. Especially for NO? Pd (111) system, the three‐well‐potential dissociation mode is initially put forward to show the remarkable dissociation process with two dissociation transitional states of NO on Pd (111). Copyright © 2008 John Wiley & Sons, Ltd.     

H2S在立方ZrO2(110)面的吸附与解离

采用量子化学的密度泛甬理论方法,探讨了H2S、HS和S在立方ZrO2(110)面上不同吸附位的吸附情况.构型优化的结果表明:在bridge位H2S以垂直底物平面H原子向上、垂直底物平面H原子向下、平行底物平面和hollow位H2S平行底物平面模式吸附在ZrO2(110)面发生解离吸附.SH和S的最佳吸附位分别为桥位和顶位.Mulliken布局和态密度分析显示S原子的p轨道与Zr原子的d轨道发生相互作用.通过计算解离反应的能垒,表明H2S分子在立方ZrO2(110)面发生两步解离.