Ir0.08Ti0.92O2及其载Pt催化剂的制备与电催化性能

采用TiN浸渍热分解法制备了低铱含量Ir0.08Ti0.92O2纳米粉体,再通过微波辅助制备Pt/Ir0.08Ti0.92O2催化剂,并与采用传统亚当斯法制备的IrO2和商品化Pt/C进行对比研究.利用X射线衍射(XRD)、透射电子显微镜(SEM)、X射线能量散射谱(EDS)和X射线光电子能谱(XPS)对产物进行了分析.结果表明,Ir0.08Ti0.92O2是一种纳米棒状金红石相固溶体,直径约15 nm,担载Pt粒度5~7 nm,其中本体Ir/Ti原子比为0.084∶0.916,表面Ir/Ti原子比为0.296∶0.704,表明Ir在表面发生富集.经稳态极化曲线和线性扫描伏安测试得到析氧反应的本征催化活性由高到低为Ir0.08Ti0.92O2>Pt/Ir0.08Ti0.92O2>IrO2,前两者性能相近;Pt/Ir0.08Ti0.92O2的氧还原反应活性低于Pt/C,需进一步优化载Pt粒度.研究结果表明,Ir0.08Ti0.92O2既是高效、低成本的析氧反应催化剂,也是高性能载体材料,这使Pt/Ir0.08Ti0.92O2作为双效催化剂在成本、催化性能和稳定性上具有更大优势,也可作为优异的析氢反应催化剂.     

不同晶型TiO_2负载镍催化剂催化顺酐液相加氢

分别以锐钛矿相Ti O2和金红石相Ti O2为载体,采用等体积浸渍法制备了Ni/Ti O2催化剂,考察了其催化顺酐液相加氢性能.采用氮气吸附-脱附、氢气程序升温还原(H2-TPR)、X射线衍射(XRD)、氢气程序升温脱附(H2-TPD)及X射线光电子能谱(XPS)等技术对催化剂进行了表征.催化剂评价结果表明,以锐钛矿型Ti O2为载体催化剂的C O加氢活性明显高于以金红石型Ti O2为载体的催化剂.这主要是由于在还原过程中锐钛矿型Ti O2较易被还原,产生了较高浓度的氧缺陷位,该氧缺陷位可通过接受C O中O的孤对电子来活化C O,促使其与H2发生加氢反应,进而使催化剂表现出较高的C O加氢活性.     

富氧条件下Ir催化NO反应

用浸渍法制备了系列Ir催化剂, 研究了富氧条件下Ir催化NO的反应, 考察了催化剂的催化反应性能及负载量和载体对催化活性的影响. 结果表明, 在Ir催化剂上不仅发生了NO氧化反应, 同时也发生了NO还原反应; Ir催化剂对NO反应有催化作用, 催化活性随Ir负载量的增加而增强. 载体对催化剂活性有一定的影响, 负载量低于0.1%(w)时, 催化NO氧化的活性顺序为Ir/ZSM-5>Ir/γ-Al2O3>Ir/SiO2, 这主要受载体自身性质的影响; 负载量高于0.1%时, 催化NO氧化的活性顺序为Ir/ZSM-5>Ir/SiO2>Ir/γ的活性顺序为Ir/γ-Al2O3>Ir/SiO2>Ir/ZSM-5, 这主要由于载体吸附作用促进了NO2在Ir催化剂上吸附分解. 与Pt催化剂相比, Ir催化剂更有利于促进NO还原.     

贵金属铱对氨分解用镍基催化剂的促进作用研究

用湿式浸渍法制备了不同贵金属质量分数的镍-铱双金属催化剂,以氨分解为模型反应对其催化性能进行考察.结果表明,贵金属铱的添加提高了10%Ni/γ-Al2O3的低温活性.在铱的质量分数不高于1%时,氨分解反应活性随铱质量分数的增加出现最大值(相应的Ir质量分数为0.7%),对应的10%Ni-0.7%Ir/γ-Al2O3催化剂在400 ℃时,氨分解率为43.55%,较单组分的Ni催化剂高40.0%.用H2-TPR、H2-TPD 、BET和XRD表征方法对催化剂进行了表征.结果表明,Ir与活性组分Ni之间存在协同作用.铱的添加促进了活性组分的分散、减小了镍的晶粒尺寸,且增加了催化剂活性位的数量,从而提高了催化剂的氨分解性能.     

直接甲酸燃料电池氧还原碳载Au-Ir催化剂的电催化性能

用四氢呋喃(THF)络合还原法分别合成并比较了碳载金(Au/C)、碳载铱(Ir/C)、碳载金-铱(Au-Ir/C)催化剂对氧气还原和甲酸氧化的电催化活性.发现3种催化剂对甲酸氧化都没有电催化活性;Au-Ir/C催化剂对氧还原的电催化活性要远好于Au/C和Ir/C催化剂.表明Au-Ir/C催化剂适合作为直接甲酸燃料电池(DFAFC)的阴极催化剂.     

不同沉淀剂对Co_3O_4催化剂结构及催化分解N_2O活性的影响

采用了不同沉淀剂(K_2CO_3、Na_2CO_3、NaOH、NaHCO_3)制备了一系列Co_3O_4氧化物催化剂.通过XRD、XPS、BET、H2-TPR、O_2-TPD表征手段,探究了催化剂物相结构和氧化还原性能对N_2O催化分解性能的影响.研究表明,以K_2CO_3为沉淀剂制备的Co_3O_4催化剂具有优越的氧化还原性能.此外,较低结晶度有助于提高催化剂的催化性能,催化剂表面物种与其沉淀剂相关:丰富的表面Co物种促进催化活性,较多氧空位有利于催化剂表面的电子传递和氧气的脱附.以K_2CO_3为沉淀剂制备的Co_3O_4催化剂表现出最佳的N_2O催化分解活性,在450℃达到90%以上的转化率.     

煅烧温度对Mn/TiO_2催化剂催化NO氧化活性的影响

以浸渍在二氧化钛上的锰基催化剂为对象,研究了制备过程中煅烧温度对锰基催化剂催化NO氧化活性的影响。结果表明,较低的煅烧温度有利于提高Mn/TiO2催化剂对于NO氧化的催化效率。利用X射线粉末衍射(XRD)、场发射扫描电子显微镜(FESEM)、X射线光电子能谱(XPS)、H2程序升温还原(H2-TPR)和O2程序升温脱附(O2-TPD)等表征手段研究了煅烧温度影响Mn/TiO2催化剂催化活性的作用机理。结果表明,在NO氧化过程中发挥主要作用的是Mn2O3,较低的煅烧温度有利于提高Mn2O3在锰氧化物中所占的比例,同时增加锰氧化物在载体表面的分散度,从而改善催化剂活性;当煅烧温度超过500℃时,催化剂会发生烧结,载体TiO2的晶形开始由锐钛型向金红石型转变,Mn2O3也从非晶相向晶相转变。H2-TPR和O2-TPD测试结果表明,低温煅烧有利于提高催化剂的还原性能和表面化学吸附态O2-的脱附性能,良好的还原性能和脱附性能的相互作用使催化剂表面的氧有较好的移动能力,从而促进催化剂的活性。     

钡修饰Ir/SiO2催化剂对氨分解促进作用的研究

研究了浸渍法制备的Ba修饰S iO2担载型铱(Ir)基催化剂(Ba-Ir/S iO2)在氨催化分解模型反应的作用。结果表明Ba的添加显著提高了催化剂的活性和稳定性。采用H2-TPR和H2-TPD对Ba-Ir/SiO2进行分析和研究,结果显示助催化剂Ba和活性催化组分Ir之间发生了强相互作用。Ba-Ir/SiO2在氨催化分解模型反应中的主要活性物种是零价态的Ir。     

室温条件下硝酸羟胺的催化分解

 采用等体积浸渍法制备了一系列以Al2O3和SiO2为载体的负载型贵金属催化剂. 用热重法考察了催化剂对80%硝酸羟胺推进剂的分解活性. 结果表明, Ir/SiO2催化剂能够在室温以下(20.7 ℃)催化分解80%硝酸羟胺,显示出该催化体系在环境友好的单组元推进器上具有很大的应用潜力. H2化学吸附实验表明, Ir/SiO2 具有比 Ir/Al2O3更大的Ir颗粒,这可能是造成前者活性比后者高的原因之一.     

还原-氧化预处理对Co_3O_4催化分解N_2O性能的影响

采用液相沉淀法制备了Co_3O_4催化剂,并对其进行还原-氧化预处理制得Co_3O_4-RO。通过XRD、N_2-physisorption、Raman、H_2-TPR、XPS和O_2-TPD等技术对催化剂进行表征,在连续流动微反应装置上考察了催化剂催化分解N_2O性能。结果表明,经过还原-氧化预处理,与Co_3O_4催化剂相比,Co_3O_4-RO结晶度变差,晶粒粒径减小,尤其是尖晶石结构重构过程削弱了Co-O键,增强了催化剂表面的氧物种脱附能力,降低了催化分解N_2O反应的活化能,因而显著提高了催化剂的催化活性。同时,Co_3O_4-RO对原料气中的O_22%(体积分数)和H_2O 2. 3%(体积分数)表现出较强的耐受性。     

NO在氧预吸附Ir(100)表面吸附和解离的第一性原理研究

采用第一性原理密度泛函理论和周期性平板模型研究了NO在O预吸附Ir(100)表面的吸附和解离, 并考察了预吸附的O对可能产物N₂, N₂O和NO₂的选择性的影响. 优化得到反应过程中初态、 过渡态和末态的吸附构型, 并获得反应的势能面信息. 计算结果表明, NO在O预吸附表面最稳定的吸附位是桥位, 其次是顶位. 桥位和顶位的NO在表面存在两条解离通道, 即直接解离通道和由桥位和顶位扩散到平行空位, 继而发生N-O键断裂生成N原子和O原子的解离通道. 此分离机理与洁净表面上NO解离机理相同, 但后一种解离方式优于前一种, 是NO在表面上解离的主要通道. 预吸附的O原子在不同程度上抑制了NO的解离, 导致桥位和顶位NO解离互相竞争. 在O预吸附Ir(100)表面, N₂气是唯一的产物, 不会有副产物N₂O和NO₂的生成, 与实验结果一致. 预吸附的O在N/O低覆盖度下几乎不影响N₂气的生成, 但在较高覆盖度下则促进了N₂气的生成.     

Zr掺杂对La（Ba）ZrxCo1-xO3-δ钙钛矿催化N2O分解性能的影响（英文）

采用溶胶凝胶法制备了Zr掺杂的钴基钙钛矿La(Ba)ZrxCo1-xO3-δ,并将其用于航天推进剂领域的高浓度N2O催化分解反应.发现Zr的引入明显提高了钙钛矿La(Ba)ZrxCo1-xO3-δ的催化活性,尤其是当Zr掺杂量分别为0.05和0.2时,LaZrxCo1-xO3-δ和BaZrxCo1-xO3-δ催化剂性能较为优异.应用N2物理吸附、X射线衍射、H2程序升温还原、O2程序升温脱附和氧脉冲吸附技术表征了Zr掺杂对La(Ba)ZrxCo1-xO3-δ催化剂的物化性质的影响.结果表明,Zr掺杂增大了钴基钙钛矿的比表面积,改善了晶格结构,从而提高了钴物种的还原及氧吸附脱附能力,因而催化剂上N2O分解活性增加.     

Conversion of N2O to N2 on MgO （001） Surface with Vacancy： A DFT Study

The adsorption and decomposition of NzO at regular and defect sites of MgO (001) surface have been studied using cluster models embedded in a large array of point charges (PCs) by DFT/B3LYP method. The results indicate that the MgO (001)surface with oxygen vacancies exhibits high catalytic reactivity toward N2O adsorptive-decomposition. It is different from the regular MgO surface or the surface with magnesium vacancies.Much elongation of O—N bond of N2O after adsorption at oxy-gen vacancy site with O end down shows that O—N bond has been broken with concurrent production of N2, leaving a regu-lar site instead of the original oxygen vacancy site (F center ).The MgO (001) surface with magnesium vacancies hardly ex-hibits catalytic reactivity. It can be concluded that N2O dissoci-ation likely occurs at oxygen vacancy sites of MgO (001) sur-face, which is consistent with the generally accepted viewpoint in the experiments. The potential energy surface (PES) reflects that the dissociation process of N2O does not virtually need to surmount a given energy barrier.     

Oxidation of CO by NO on planar and faceted Ir(210)

Oxidation of CO by pre-adsorbed NO has been studied on planar Ir(210) and nanofaceted Ir(210) with average facet sizes of 5 nm and 14 nm by temperature programmed desorption (TPD). Both surfaces favor oxidation of CO to CO(2), which is accompanied by simultaneous reduction of NO with high selectivity to N(2). At low NO pre-coverage, the temperature (T(i)) for the onset of CO(2) desorption as well as CO(2) desorption peak temperature (T(p)) decreases with increasing CO exposure, and NO dissociation is affected by co-adsorbed CO. At high NO pre-coverage, T(i) and T(p) are independent of CO exposure, and co-adsorbed CO has no influence on dissociation of NO. Moreover, at low NO pre-coverage, planar Ir(210) is more active than faceted Ir(210) for oxidation of CO to CO(2): T(i) and T(p) are much lower on planar Ir(210) than that on faceted Ir(210). In addition, faceted Ir(210) with an average facet size of 5 nm is more active for oxidation of CO to CO(2) than faceted Ir(210) with an average facet size of 14 nm, i.e., oxidation of CO by pre-adsorbed NO on faceted Ir(210) exhibits size effects on the nanometer scale. In comparison, at low O pre-coverage planar Ir(210) is more active than faceted Ir(210) for oxidation of CO to CO(2) but no evidence has been found for size effects in oxidation of CO by pre-adsorbed oxygen on faceted Ir(210) for average facet sizes of 5 nm and 14 nm. The TPD data indicate the same reaction pathway for CO(2) formation from CO + NO and CO + O reactions on planar Ir(210). The adsorption sites of CO, NO, O, CO + O, and CO + NO on Ir are characterized by density functional theory.     

氧气的体积分数对N2O热分解的影响

N2O是大气中不可忽视的污染物.目前,世界上所排放的N2O主要有三个来源:一是硝酸工业等化工生产;二是流化床锅炉等煤燃烧设备;三是汽车发动机.由于N2O会导致温室效应和破坏臭氧层,而近年来大气层中N2O的氧气体积分数逐年上升,N2O排放的控制技术受到越来越多的关注[1～4].……     

Cyclometalated iridium and platinum complexes as singlet oxygen photosensitizers: quantum yields, quenching rates and correlation with electronic structures

Photophysical properties are reported for a series of cyclometalated platinum and iridium complexes that can serve as photosensitizers for singlet oxygen. The complexes have the formula (C;N)(2)Ir(O;O) or (C;N)Pt(O;O) where C;N is a monoanionic cyclometalating ligand such as 2-(phenyl)pyridyl and 2-(phenyl)quinolyl, and O;O is the ancillary ligand acetylacetonate (acac) or dipivaloylmethane (dpm). Also examined were a series of (N;N)PtMe(2) complexes where N;N is a diimine such as 2,2'-bipyridyl. In general, the cyclometalated complexes are excellent photosensitizers for the production of singlet oxygen, while the (N;N)PtMe(2) complexes were ineffective at this reaction. Quantum yields of singlet oxygen production range from 0.9-1.0 for the cyclometalated Pt complexes and 0.5-0.9 for Ir complexes. Luminescence quenching and singlet oxygen formation of the Ir complexes occurs from a combination of electron and energy transfer processes, whereas the Pt complexes only react by energy transfer. For Ir complexes with low emission energy, physical deactivation of the triplet excited state becomes competitive with energy transfer to ground state dioxygen. The rates of singlet oxygen quenching for the complexes presented here are in the range 6 x 10(6)-2 x 10(7) M(-1) s(-1) for Pt complexes and 2 x 10(5)-2 x 10(7) M(-1) s(-1) for Ir complexes, respectively. Differences in the efficiency of both forming and quenching singlet oxygen between the Ir and Pt cyclometalates are believed to come about from the more exposed coordination geometry in the latter species.     

The role of Oad in the decomposition of NH3 adsorbed on Ir(110): a combined TPD and high-energy resolution fast XPS study

High energy resolution fast XPS combined with TPD experiments were used to study the effect of chemisorbed oxygen on the adsorption and dissociation of NH(3) on Ir(110). Below 250 K the presence of O(ad) does not influence NH(3) decomposition. Above 250 K O(ad) enhances NH(3) dissociation, which results in three times as much N(2) formation and less molecular NH(3) desorption compared to the experiments without O(ad). The effect of O(ad) can be attributed to destabilization of NH(ad) on the surface, resulting in a further dehydrogenation towards N(ad). The presence of O(ad) on the surface lowers the temperature at which the N(ad) combination reaction takes place by as much as 200 K, due to repulsive interaction between N(ad) and O(ad). NO is formed above 450 K if both N(ad) and O(ad) are present on the surface.     

二维M-Co3O4负载Ir对香草醛加氢脱氧性能研究

以二维金属-有机框架M-Co₃O₄为载体制备了具有高活性的Ir/M-Co₃O₄催化剂.采用X射线粉末衍射(XRD)、X射线光电子能谱(XPS)、透射电子显微镜(TEM)、电感耦合等离子体发射光谱仪(ICP-OES)、 N₂物理吸/脱附等方法对催化剂进行了表征,并研究了催化剂、温度、时间、溶剂等因素对香草醛加氢脱氧反应的影响.结果表明, Ir/M-Co₃O₄催化剂具有较好的普适性和稳定性,在香草醛加氢脱氧制备4-甲基愈创木酚(MMP)反应中表现出较高的活性和选择性,香草醛的转化率达100%, MMP的选择性不低于99%.     

Hydrazine decomposition over Irn/Al2O3 model catalysts prepared by size-selected cluster deposition

Hydrazine decomposition chemistry was probed over a temperature range from 100 to 800 K for a series of model catalysts prepared by mass-selected Ir(n)(+) deposition on planar Al(2)O(3)/NiAl(110). Two sets of experiments are reported. Temperature-programmed desorption (TPD) was used to study hydrazine desorption and decomposition on Al(2)O(3)/NiAl(110) and on a model catalyst prepared by deposition of Ir(+) on Al(2)O(3)/NiAl(110) at a density large enough (5 x 10(14) cm(-2)) that formation of a distribution of small Ir(n) clusters on the surface is expected. This model catalyst was found to have hydrazine decomposition properties qualitatively similar to those observed on single-crystal Ir and polycrystalline Rh. This catalyst was also studied by X-ray photoelectron spectroscopy (XPS), to probe TPD-induced changes in the samples. A substantial decrease in the Ir XPS intensity suggests that considerable sintering takes place when the samples are heated to 800 K. In addition, a significant fraction of the nitrogen contained in the hydrazine is converted to an aluminum nitride (or mixed Al(x)O(y)N(z)) compound. Continuous flow experiments were used to probe relative reactivity at 300 and 400 K of samples prepared by depositing differently sized Ir(n)(+) clusters. At 300 K, samples prepared with preformed Ir(n)(+) (n = 5, 7, 10) are about twice as active, per Ir atom, as samples prepared with Ir(+) deposition, and there is a weaker trend to higher activity with increasing cluster size. At 400 K the trends are similar, but weaker, suggesting that thermal modification of the samples is already significant.     

有氧气氛中碱金属改性CuAl复合氧化物催化分解N2O的活性

合成了Cu/Al原子比分别为2.0、3.1、4.1的CuAl类水滑石样品,焙烧得到CuAl复合氧化物。在Cu/Al原子比为3.1的CuAl氧化物表面浸渍碱金属盐溶液,制备改性CuAl复合氧化物,用AES、XRD、FT-IR、BET、H₂-TPR、XPS等技术对催化剂进行了结构表征,考察了CuAl复合氧化物组成、碱金属助剂类型和K的前驱物对改性催化剂在有氧气氛中催化分解N₂O活性的影响。结果表明,Na、K、Cs改性CuAl复合氧化物均提高了催化剂活性,但K助剂的增强效应最显著;钾的不同前驱物改性CuAl复合氧化物的催化活性有显著差异,加入碳酸钾、草酸钾提高了催化剂的活性,而加入醋酸钾、硝酸钾反而降低了催化剂活性。优化出的K改性CuAl复合氧化物催化剂在含氧含水气氛的N₂O分解反应中表现出了较高的活性。