NO在Cu(111)表面吸附和分解的XPS和TPD研究：不同氧物种的影响

利用X射线光电子能谱和程序升温脱附谱研究了NO在清洁和预吸附氧的Cu(111)表面上的吸附和反应.通过改变NO的暴露量和退火温度,在Cu(111)表面可以制备出不同种类的化学吸附氧物种,其O 1s的结合能分别位于531.0 eV (O₅₃₁)和529.7 eV (O₅₂₉).表面O₅₃₁物种的存在对NO的不同吸附状态有着显著影响,同时使得大部分NO吸附分子(NO(a))在加热过程中发生分解并以N₂O和N₂形式脱附; 而表面O₅₂₉物种对NO(a)的解离脱附有着明显的抑制作用.相对于O₅₃₁物种来说,O₅₂₉物种对NO吸附表现出更强的位阻效应.上述结果表明,NO在Cu(111) 表面的吸附和分解行为与预吸附氧物种的种类和覆盖度密切相关.     

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.     

NH3-SCR反应过程中NH3和NOx在Cu/SAPO-34分子筛催化剂上的吸附特性和作用

通过离子交换法制得Cu/SAPO-34菱沸石分子筛催化剂, 同时研究了NH₃和NO_x (NO和NO₂)在该催化剂上的吸附位、吸附强度、吸附量和吸附速率, 得到了不同反应气氛在Cu/SAPO-34 上的吸附性能及其在NH₃选择性催化还原(NH₃-SCR)反应中的作用. 研究采用瞬态实验、程序升温脱附(TPD)和漫反射傅里叶变换红外光谱(DRIFTS)等方法进行表征实验. 瞬态实验结果表明NH₃是吸附性气体. 程序升温脱附实验和红外漫反射实验结果表明NH₃可以吸附在布朗斯特和路易斯酸性位上形成不同的NH₃物种, 它们显示不同的SCR活性. NH₃在Cu²⁺上的吸附速率最快, 且键强最强. NO_x可以氧化并以硝酸盐/亚硝酸盐的形式吸附在Cu物种上. 最后, 本文讨论了NH₃选择性催化还原反应过程中在Cu物种上的中间物种并推测反应机理.     

Au/α-Fe2O3 催化剂存贮失活环境因素及机理分析

 采用沉积沉淀法制备了 CO 低温氧化催化剂 Au/α-Fe₂O₃, 通过 X 射线衍射、X 射线光电子能谱、N₂ 吸附-脱附、傅里叶变换红外光谱、H₂ 程序升温还原和 CO₂ 程序升温脱附等手段对催化剂进行了表征, 探讨了在室温大气气氛下光线照射以及表面吸附等环境因素所导致的催化剂存贮失活及其作用机理. 结果表明, 经 110 ^oC 干燥的 Au/α-Fe₂O₃催化剂表面同时存在 Au³⁺和 Au^δ+ (0 ≤ δ ≤ 1) 物种, 且前者催化 CO 氧化的活性更高; 在室温大气气氛下, 紫外线照射会引起 Au³⁺的还原和 Au 颗粒的生长, 导致催化剂的不可逆失活. 此外, 空气中的 H₂O 和 CO₂ 可同时吸附在 α-Fe₂O₃的表面, 形成表面碳酸盐物种, 会引起催化剂的可逆失活.     

Pt/MOx(M=Ni,Fe,Co,Ce)催化剂上CO氧化反应中抗H2O与CO2的性能研究

我们研究了4种负载型Pt催化剂（1Pt/NiO、1Pt/FeO_x、1Pt/Co₃O₄和Pt/CeO₂）上不同反应条件下CO氧化活性及抗H₂O和CO₂性能.发现反应气氛中CO₂的加入与CO形成了竞争吸附,并在催化剂表面形成了碳酸盐物种堵塞了活性位,从而导致催化剂失活.反应气氛中H₂O的加入对1Pt/CeO₂催化剂的活性有所抑制,但对1Pt/FeO_x、1Pt/NiO和1Pt/Co₃O₄催化剂的活性却有促进作用.在1Pt/FeO_x和1Pt/CeO₂催化剂上的分步反应实验和动力学研究表明,尽管H₂O的加入在两种催化剂上均与CO形成了竞争吸附,但在1Pt/FeO_x催化剂上H₂O在载体表面解离形成的羟基更易与CO反应,开辟了新的反应途径,从而提高了反应性能.此外,H₂O的加入能有效分解该催化剂上的碳酸盐物种,从而保持了其稳定性.     

用分子轨道理论研究NO气体在TiO2表面吸附

根据一氧化氮(NO)气体在二氧化钛(TiO₂)表面吸附和脱附的实验结果, 揭示了气体脱附量的变化规律. 利用MOPAC 和GAUSSIAN分子轨道理论计算了在TiO₂(110)表面上吸附NO分子的原子簇模型, 电荷分布以及原子簇的能级, 推断了NO在TiO₂(110)表面吸附的稳定性.     

Ni-Ti-O混合氧化物的制备、表征及其富氧选择性催化还原NO

采用均匀共沉淀法制备了不同Ni/Ti摩尔比的Ni-Ti-O混合氧化物,考察了它们在富氧条件下丙烯选择性催化还原NO反应中的催化性能,并运用X射线衍射,N₂吸附-脱附、吡啶吸附、程序升温脱附和原位红外光谱对催化剂进行了表征.结果表明,Ni/Ti摩尔比为1的催化剂表现出最佳催化活性,430℃时NO_x转化率达68%.该催化剂具有锐钛矿结构,比表面积较高(149m²/g),有利于提高催化活性;其表面Lewis酸性位有利于硝酸盐物种的吸附,而硝酸盐物种是该反应的重要中间体.     

氧分子在Pt低指数面上的吸附和解离

应用原子和表面簇合物相互作用的5参数Morse势方法(简称5-MP)构造推广的LEPS势对O₂-Pt分子体系进行了系统的研究, 获得了O₂分子在Pt的2个低指数面(111)和(110)重构面上的吸附几何、结合能和振动频率等临界点性质; 计算结果显示O₂在Pt(111)面上难解离, 且存在超氧化吸附态, 同时, 应用表面分子解离限和晶面解离距的概念分析了(111)面上的解离机理; 并根据分子指纹性质, 将O₂在Pt(110)缺行重构面上出现的振动频率860, 930, 1250 cm^－1进行了合理的指派.     

H2在K0-MWCNTs上储存和吸附/脱附特性研究

利用高压容积法辅以卸压升温脱附排水法, 测定金属K修饰多壁碳纳米管对H₂的吸附储存容量. 结果表明, 在室温(25 ℃), 7.25 MPa实验条件下, x%K⁰-MWCNTs (x%＝30%～35%, 质量百分数)对H₂的吸附储存容量可达3.80 wt%(质量百分数), 是相同条件下单纯MWCNTs氢吸附储量的2.5倍; 室温下卸至常压的脱附氢量为3.36 wt%(占总吸附氢量的～88%), 后续升温至673 K的脱附氢量为0.41 wt%(占总吸附氢量的～11%). 利用LRS和H₂-TPD-GC/MS等谱学方法对H₂/K⁰-MWCNTs吸附体系的表征研究表明, H₂在K⁰-MWCNTs上吸附存在非解离 (即分子态)和解离(即原子态)两种吸附态; 在≤723 K温度下, H₂/K⁰-MWCNTs体系的脱附产物几乎全为H₂气; 723 K以上高温脱附产物不仅含H₂, 也含有CH₄, C₂H₄和C₂H₂等C₁/C₂-烃.     

负载金属对WO3-TiO2光催化剂结构与催化性能的影响

用溶胶-凝胶和浸渍-还原相结合的方法制得M/WO₃-TiO₂ (M＝Pd, Cu, Ni, Ag)光催化剂. 利用X射线衍射(XRD)、程序升温还原(TPR)、红外(IR)、程序升温脱附(TPD)、紫外-可见漫反射光谱(UV-Vis-DRS)和光反应器等技术研究了复合半导体负载金属的物相结构、光吸收性能和光催化反应性能. 结果表明: 金属负载在复合半导体上延迟了TiO₂由锐钛矿向金红石相转化, 增强W与载体TiO₂的相互作用, 使TiO₂光吸收限发生蓝移, 对可见光部分的吸收明显增加; 固体材料吸光性能强弱顺序Pd/WO₃-TiO₂＞Cu/WO₃-TiO₂＞Ag/WO₃-TiO₂＞Ni/WO₃-TiO₂; 金属Pd对CO₂吸附能力过强, 卧式吸附态脱附温度高, 光催化效率不高; 金属Cu对CO₂吸附能力适中, CO₂与C₃H₆脱附温度较接近, 实现了“光-表面-热”协同作用, 光量子效率最高, 达到19.7%.     

NO Adsorption on Ag/Pt(110)-(1×2) Bimetallic Surfaces: Unexpected Formation of Nitrite/nitrate Surface Species

NO adsorption on Ag/Pt(110)-(1×2) bimetallic surfaces at room temperature was inves-tigated by means of Auger electron spectroscopy, X-ray photoelectron spectroscopy and thermal desorption spectroscopy. An unexpected formation of nitrite/nitrate surface species on Ag/Pt(110)-(1×2) bimetallic surfaces is observed, then decompose at elevated tempera-tures to form N₂. However, such nitrite/nitrate surface species do not form on clean Pt(110) and Ag-Pt alloy surfaces upon NO exposure at room temperature. The formation of ni-trite/nitrate surface species on Ag/Pt(110)-(1×2) bimetallic surfaces is attributed to highreactivity of highly coordination-unsaturated Ag clusters and the synergetic effect between Ag clusters and Pt substrate.     

Chemical Reconstruction of Pt-Rh(100) Alloy and Pt/Rh(100), Rh/Pt(100) Bimetallic Surfaces

When Cu(110), Ni(l 10), Ag(110) surfaces are exposed to O₂ at room temperature, one dimensional metal-oxygen strings grow in the < 001 > direction of the (110) surfaces. A similar phenomenon occurs in the adsorption of H₂ on Ni( 110) surface at room temperature, where the one dimensional strings grow along the < 110 > direction. These phenomena are undoubtedly different from the adsorption induced reconstruction but are explained by the chemical reconstruction involving the formation of quasi-compounds and their self-ordering on the metal surfaces. The chemical reconstruction is indispensablly important to understand the structure and catalysis of alloy and bimetallic surfaces. Pt_0.25Rh_0.75(100) alloy surface being active for the reaction of NO with H₂ is an interesting example. When the Pt-Rh(100) alloy surface is exposed to NO or O₂ at arround 500 K, a p(3 × 1) ordered Rh-O over-layer is obtained on a Pt-enriched 2nd layer by the chemical reconstruction. Ordering of Rh-0 in the p(3 × 1) structure on the Pt(100) surface was reproduced by heating a Rh/Pt(100) bimetallic surface in O₂, and the chemical reconstruction making the p(3 × 1) Rh-O overlayer on a Pt enriched 2nd layer was also proved by heating a Pt/Rh(100) bimetallic surface in O₂ or NO. The activation mechanism of the Pt-Rh alloy and the Pt/Rh bimetallic surfaces by the chemical reconstruction was evidently shown by using a Pt deposited Rh(100), Pt/Rh(100), surface. That is, the Pt/Rh(100) is not so active for the reaction of NO with H₂, but the reconstructed p(3 × 1)Rh-O/Pt-layer/Rh(100) surface is very active for the reaction. Therefore, it was concluded that the chemical reconstruction of the Pt-Rh catalyst makes the active surface which is composed of Rh-O and a Pt layer.     

水在HfO2(111)和(110)表面的吸附与解离

运用广义梯度近似密度泛函理论方法(GGA-PW91)结合周期平板模型, 研究水分子在二氧化铪(111)和(110)表面不同吸附位置在不同覆盖度下的吸附行为. 通过比较不同吸附位的吸附能和几何构型参数发现:(111)和(110)表面铪原子(top 位)是活性吸附位. 水分子与表面的吸附能值随覆盖度的变化影响较小. 在(111)和(110)表面, 水分子都倾向以氧端与表面铪原子相互作用. 同时也计算了羟基、氧和氢在表面的吸附, Mulliken 电荷布居, 态密度及部分频率. 结果表明, 在两种表面羟基以氧端与表面铪相互作用, 氧原子与表面铪和氧原子同时成键, 而氢原子直接与表面氧原子相互作用形成羟基. 通过过渡态搜索, 水分子在(111)和(110)表面发生解离, 反应能垒分别为9.7和17.3 kJ·mol^-1, 且放热为59.9和47.6 kJ·mol^-1.     

Ag on Pt(111): Changes in Electronic and CO Adsorption Properties upon PtAg/Pt(111) Monolayer Surface Alloy Formation

The electronic and chemical (adsorption) properties of bimetallic Ag/Pt(111) surfaces and their modification upon surface alloy formation, that is, during intermixing of Ag and Pt atoms in the top atomic layer upon annealing, were studied by X‐ray photoelectron spectroscopy (XPS) and, using CO as probe molecule, by temperature‐programmed desorption (TPD) and infrared reflection absorption spectroscopy (IRRAS), respectively. The surface alloys are prepared by deposition of sub‐monolayer Ag amounts on a Pt(111) surface at room temperature, leading to extended Ag monolayer islands on the substrate, and subsequent annealing of these surfaces. Surface alloy formation starts at ≈600–650 K, which is evidenced by core‐level shifts (CLSs) of the Ag(3d_5/2) signal. A distinct change of the CO adsorption properties is observed when going to the intermixed PtAg surface alloys. Most prominently, we find the growth of a new desorption feature at higher temperature (≈550 K) in the TPD spectra upon surface alloy formation. This goes along with a shift of the CO_ad‐related IR bands to lower wave number. Surface alloy formation is almost completed after heating to 700 K.     

Self-activation of catalyst and functionalization of metal surfaces

Why can solid surfaces promote a variety of chemical reactions? We supposed that active sites or active compounds are formed over the catalyst surface during catalysis or in pretreatment. Three topics are discussed from this viewpoint in this review. The first topic is an activation of inactive MoO_x film to super-active olefin metathesis catalyst, where Mo=CHR sites are prepared on MoO_x. A total mechanism for the productive and the cross metathesis of propene was firstly established on an activated catalyst by using deuterium labeled olefins. In the second topic, a new concept of quasi-compounds is discussed by using scanning tunneling microscopy (STM), and it is shown that the reaction of quasi-compounds yields (Cu)₆ cluster and (–Cu–O–) strings on Ag(110). In the third topic, a self-activation of Pt–Rh alloy and Pt/Rh bimetallic surfaces during the reaction of NO + H₂ is discussed by using single crystal surfaces. STM image showed that a Pt–Rh(100) surface is activated by reacting with oxygen where a specific array of Pt and Rh atoms is established. Formation of similar active sites on the other crystallographic surfaces is responsible for structure insensitive catalysis of Pt/Rh bimetallic surfaces.     

Effect of conversion of NO2 into no on the catalytic reduction of NO2 with C3H6 in excess O2

During the reduction of NO₂ by C₃H₆ in O₂ over alumina-supported Au, Rh and Pt it was found that three parallel reactions take place,i.e., reduction of NO₂ to N₂ and N₂O, partial decomposition of NO₂ to NO and oxidation of C₃H₆ to CO and CO₂. In the absence of C₃H₆, the NO₂→NO+O₂ reaction reaches a fast equilibrium on Rh and Pt but not on Au and γ-Al₂O₃. Addition of C₃H₆ to the NO₂+O₂ mixture leads to the formation of NO above equilibrium conversion levels.     

Conversion of NO in NO/N2, NO/O2/N2, NO/C2H4/N2 and NO/C2H4/O2/N2 Systems by Dielectric Barrier Discharge Plasmas

An experimental study on the conversion of NO in the NO/N₂, NO/O₂/N₂, NO/C₂H₄/N₂ and NO/C₂H₄/O₂/N₂ systems has been carried out using dielectric barrier discharge (DBD) plasmas at atmospheric pressure. In the NO/N₂ system, NO decomposition to N₂ and O₂ is the dominating reaction; NO conversion to NO₂ is less significant. O₂ produced from NO decomposition was detected by an on-line mass spectrometer. With the increase of NO initial concentration, the concentration of O₂ produced decreases at 298 K, but slightly increases at 523 K. In the NO/O₂/N₂ system, NO is mainly oxidized to NO₂, but NO conversion becomes very low at 523 K and over 1.6% of O₂. In the NO/C₂H₄/N₂ system, NO is reduced to N₂ with about the same NO conversion as that in the NO/N₂ system but without NO₂ formation. In the NO/C₂H₄/O₂/N₂ system, the oxidation of NO to NO₂ is dramatically promoted. At 523 K, with the increase of the energy density, NO conversion increases rapidly first, and then almost stabilizes at 93–91% of NO conversion with 61–55% of NO₂ selectivity in the energy density range of 317–550 J L⁻¹. It finally decreases gradually at high energy density. A negligible amount of N₂O is formed in the above four systems. Of the four systems studied, NO conversion and NO₂ selectivity of the NO/C₂H₄/O₂/N₂ system are the highest, and NO/O₂/C₂H₄/N₂ system has the lowest electrical energy consumption per NO molecule converted.     

Theoretical study of CO and H2O interaction on (110) and (101) Zirconia surfaces

Theoretical calculations of CO and H₂O adsorption on (110) and (101) tetragonal Zirconia surfaces were carried out using ONIOM2 methodology. The calculations showed that the adsorption processes are exothermic reactions with energy values of −28.4 kcal/mol for H₂O on the (110) surface, −51.0 kcal/mol for H₂O on the (101) surface, −21.7 kcal/mol for CO on (110) surface and −23.4 kcal/mol for CO on (101) surface. Analysis of the results suggest that different kinds of basic sites can be found on the (110) and (101) surfaces. In both (110) and (101) surfaces, CO adsorption is on bridged (bonded to two Zr atoms on the (110) surface, bonded to one Zr and O atoms on the (101) surface). The calculations showed that ONIOM can be a powerful tool to study structural and thermodynamics properties of solid surfaces.     

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.