光还原催化剂Pt/TiO2富氢条件下CO优先氧化反应

用光还原法来提高富氢条件下CO优先氧化(PROX)催化活性和CO2选择性,分别对有无氢气时CO氧化反应参数进行了详尽研究.X射线光电子能谱(XPS)表征结果显示,在光还原催化剂表面产生了部分氧空穴,可为化学吸附H提供活性中心.针对光还原Pt/TiO2催化剂上CO优先氧化反应提出了一种可能的双功能反应机理.     

Supported Ru catalysts prepared by two sonication-assisted methods for preferential oxidation of CO in H2

The preferential oxidation (PROX) of CO in the presence of H(2) is an important step in the production of pure H(2) for industrial applications. In this report, two sonochemical methods (S1 and S2) were used to prepare highly dispersed Ru catalysts supported on mesoporous TiO(2) (TiO(2)(MSP)) for the PROX reaction, in which a reaction gas mixture containing 1% CO + 1% O(2) + 18% CO(2) + 78% H(2) was used. The supported Ru catalysts performed better than the supported Au and Pt catalysts, and the S1 and S2 methods are superior to the impregnation method. The Ru/TiO(2)(MSP) catalysts were active for the PROX reaction below 200 °C and good for the methanation reactions of CO and CO(2) above 200 °C. The presence of residual chlorine in the catalysts severely suppressed their PROX reaction activity, and a higher dispersion of Ru particles led to better catalytic performances. The addition of Au in the Ru/TiO(2)(MSP) catalyst also caused a poorer catalytic activity for both the PROX and the methanation reactions. TPR results showed that in the active catalysts prepared by the S1 and S2 methods, the well dispersed Ru particles, after calcination in air, had a stronger interaction with the support than those in the catalyst prepared by the impregnation method and in the Au-Ru/TiO(2)(MSP) catalyst. In situ CO absorption experiments performed with the diffusion reflectance Fourier transform infra red (DRIFT) method showed that the bridged adsorbed CO species on isolated Ru(0) sites correlated with the catalytic performances, indicating that these isolated Ru(0) sites are the most active sites of the Ru/TiO(2)(MSP) catalysts in the PROX reaction.     

甲醇在铂修饰的氧化钛电极上电催化氧化行为的研究

运用电化学方法评价了电化学阴极还原-阳极氧化两步法制得的以钛为基体的铂修饰的钛氧化物(Pt-TiO_x/Ti)电极对甲醇电催化氧化的性能,结果表明,制得的修饰电极对甲醇氧化呈现了很高的电催化活性和好的稳定性.通过X光电子能谱(XPS)、扫描隧道显微镜(STM)和现场傅立叶变换红外(FTIR)反射光谱等技术,发现修饰电极对甲醇氧化具有高的电催化性能,可归属于纳米级Pt粒子在TiO_x中的高度分散及由于Pt和TiO_x的相互作用,使电极表面对甲醇氧化中间产物CO的吸附量大大降低.     

TiO2负载Pt对光催化去除低浓度NO性能的影响

以溶胶-凝胶法以及湿式浸渍法制备了Pt/TiO2催化剂,采用了XRD、BET、UV-vis、TEM、XPS等方法进行表征,并进行了对NO的催化氧化性能测试.结果表明铂的负载能显著提高TiO2光催化剂对NO的氧化转化能力和去除率.0.5%Pt/TiO2对NO的氧化率与去除率分别为45.0%和38.1%,与纯锐钛矿TiO2(13.6%,10.7%)相比,氧化效率提高3.3倍,去除效率提高3.6倍.通过比较不同方法制备的负载Pt催化剂的活性,初步讨论了催化剂表面发生的反应机理:铂氧化物以及催化剂表面吸附的O2分子通过与光生电子和光生空穴结合,产生了强氧化性自由基,将NO氧化得到NO2.     

ZrO2改性对Pt/Al2O3催化剂上CO氧化性能的影响

用流动反应法、TPR和TPD－MS等技术研究了Pt／Al2O3催化剂掺杂ZrO2体系上CO的催化氧化反应、氧物种的还原及脱出－恢复行为．结果表明，掺杂ZrO2有利于催化剂上氧物种的脱出－恢复，从而促进CO氧化活性及表面活泼氧物种与氢的反应．并用催化剂集团结构适应理论对结果作出了解释．     

Low-temperature activation conditions for PAMAM dendrimer templated Pt nanoparticles

Surface immobilized polyamidoamine (PAMAM) dendrimer templated Pt nanoparticles were employed as precursors to heterogeneous catalysts. CO oxidation catalysis and in situ infrared spectroscopy were used to evaluate conditions for dendrimer removal. Infrared spectroscopy showed that PAMAM dendrimer amide bonds begin decomposing at temperatures as low as 75 degrees C. Although the amide stretches are completely removed after 3 h of oxidation at 300 degrees C, 16 h were required to reach maximum catalytic activity. Further treatment under oxidizing or reducing atmospheres did not cause substantial changes in activity. Infrared spectroscopy of the activated materials indicated that organic residues, probably surface carboxylates, are formed during oxidation. These surface species passivate the Pt NPs, and their removal was required to fully activate the catalyst. Substantially less forcing activation conditions were possible by employing a CO/O(2)/He oxidation treatment. At appropriate temperatures, CO acts as a protecting group for the Pt surface, helping to prevent fouling of the nanoparticle by organic residues. CO oxidation catalysis and infrared spectroscopy of adsorbed CO indicated that the low temperature activation treatment yielded supported nanoparticles that were substantially similar to those prepared with more forcing conditions.     

Ce改性的Pt/γ-AlO3催化剂用于富氢气氛下CO选择氧化

研究了Ce改性的Pt/γ-AlO3对于富氢气氛下CO选择氧化反应的催化行为考察了制备条件（共沉积沉淀法、分步沉积沉淀法以及沉积沉淀温度）对催化活性的影响．结果表明，在80℃时用共沉积沉淀方法制备的催化剂Pt/γ-AlO3-CP-80对CO氧化反应表现出良好的活性和选择性，CO转化率在120℃时可以达到85％．利用氢气程序升温还原和原位漫反射红外光谱对不同条件下制备的催化剂进行了表征，分析了Cc的促进作用．     

Catalytic oxidation activity of Pt3O4 surfaces and thin films

The catalytic oxidation activity of platinum particles in automobile catalysts is thought to originate from the presence of highly reactive superficial oxide phases which form under oxygen-rich reaction conditions. Here we study the thermodynamic stability of platinum oxide surfaces and thin films and their reactivities toward oxidation of carbon compounds by means of first-principles atomistic thermodynamics calculations and molecular dynamics simulations based on density functional theory. On the Pt(111) surface the most stable superficial oxide phase is found to be a thin layer of alpha-PtO2, which appears not to be reactive toward either methane dissociation or carbon monoxide oxidation. A PtO-like structure is most stable on the Pt(100) surface at oxygen coverages of one monolayer, while the formation of a coherent and stress-free Pt3O4 film is favored at higher coverages. Bulk Pt3O4 is found to be thermodynamically stable in a region around 900 K at atmospheric pressure. The computed net driving force for the dissociation of methane on the Pt3O4(100) surface is much larger than that on all other metallic and oxide surfaces investigated. Moreover, the enthalpy barrier for the adsorption of CO molecules on oxygen atoms of this surface is as low as 0.34 eV, and desorption of CO2 is observed to occur without any appreciable energy barrier in molecular dynamics simulations. These results, combined, indicate a high catalytic oxidation activity of Pt3O4 phases that can be relevant in the contexts of Pt-based automobile catalysts and gas sensors.     

Improved CO oxidation activity in the presence and absence of hydrogen over cluster-derived PtFe/SiO2 catalysts

The catalytic performance of cluster-derived PtFe/SiO(2) bimetallic catalysts for the oxidation of CO has been examined in the absence and presence of H(2) (PROX) and compared to that of Pt/SiO(2). PtFe(2)/SiO(2) and Pt(5)Fe(2)/SiO(2) samples were prepared from PtFe(2)(COD)(CO)(8) and Pt(5)Fe(2)(COD)(2)(CO)(12) organometallic cluster precursors, respectively. FTIR data indicate that both clusters can be deposited intact on the SiO(2) support. The clusters remained weakly bonded to the SiO(2) surface and could be extracted with CH(2)Cl(2) without any significant changes in their structure. Subsequent heating in H(2) led to complete decarbonylation of the supported clusters at approximately 350 degrees C and the formation of Pt-Fe nanoparticles with sizes in the 1-2 nm range, as indicated by HRTEM imaging. A few larger nanoparticles enriched in Pt were also observed, indicating that a small fraction of the deposited clusters were segregated to the individual components following the hydrogen treatment. A higher degree of metal dispersion and more homogeneous mixing of the two metals were observed during HRTEM/XEDS analysis with the cluster-derived samples, as compared to a PtFe/SiO(2) catalyst prepared through a conventional impregnation route. Furthermore, the cluster-derived PtFe(2)/SiO(2) and Pt(5)Fe(2)/SiO(2) samples were more active than Pt/SiO(2) and the conventionally prepared PtFe/SiO(2) sample for the oxidation of CO in air. However, substantial deactivation was also observed, indicating that the properties of the Pt-Fe bimetallic sites in the cluster-derived samples were altered by exposure to the reactants. The Pt(5)Fe(2)/SiO(2) sample was also more active than Pt/SiO(2) for PROX with a selectivity of approximately 92% at 50 degrees C. In this case, the deactivation with time on stream was substantially slower, indicating that the highly reducing environment under the PROX conditions helps maintain the properties of the active Pt-Fe bimetallic sites.     

掺杂ZrO＿2的Pt／Al＿2O＿3表面氧性质及一氧化碳氧化性能研究

用ＴＰＤ－ＭＳ、ＴＰＳＲ－ＭＳ及ＣＯ氧化活性测定等方法研究了Ｐｔ／Ａｌ２Ｏ３和掺杂超细ＺｒＯ２的样品的表面氧脱出－恢复性能、ＣＯ表面氧化性能及催化氧化性能．结果表明，在Ｐｔ／Ａｌ２Ｏ３中掺杂ＺｒＯ２后，样品表面上的氧物种脱出和氧化恢复性能明显提高，脱氧量也明显增大；并发现在ＣＯ－ＴＰＳＲ过程中程脱物ＣＯ２的脱附量大小及峰顶温度次序与对ＣＯ的催化氧化活性也有一致的关系     

Continuous hot electron generation in Pt/TiO2, Pd/TiO2, and Pt/GaN catalytic nanodiodes from oxidation of carbon monoxide

Thin films (<10 nm) of platinum or palladium were deposited on TiO2 or GaN to form Schottky diodes. We detected and monitored the continuous electron flow across the metal-oxide interfaces of Pt/TiO2, Pd/TiO2, and Pt/GaN during the catalytic oxidation of carbon monoxide. The electron excitation and flow in the metals were due to conversion of energy released by the oxidation of carbon monoxide into the kinetic energy of free electrons in platinum and palladium. The best conversion of three electrons per four CO2 molecules was observed from 5 nm Pt/TiO2.     

Modulating the reactivity of Ni-containing Pt(111)-skin catalysts by density functional theory calculations

We present here a first principles density functional theory investigation of the reactivity of Pt(111)-skin catalysts, which are varied from surface alloys with Ni to bulk PtxNi 1-x (x=0.25,0.50,0.75) alloys. Molecule (CO, O, and H) adsorption and oxidation of CO+O and H+O reactions were studied and analyzed in detail. Independent of the adsorbates, the interaction between adsorbates and substrates becomes weakened with increase in Ni, due to the downshift of d-band center of surface Pt atoms. Moreover, activation barriers of CO and H oxidation toward atomic oxygen gradually decrease. In term of CO preferential oxidation (PROX) in excess of hydrogen, it turns out that the overall reactivity and selectivity rely on the optimum of various elementary steps involved such as competitive molecular (dissociative) adsorption and oxidation reaction. The present calculations show that Pt3Ni(111) with Pt overlayer is an optimum catalyst for CO PROX in excess of hydrogen.     

DRIFTS investigation and DFT calculation of the adsorption of CO on Pt/TiO2, Pt/CeO2 and FeOx/Pt/CeO2

Molecular structures and vibrational spectra of the CO species adsorbed on the Pt/TiO2, Pt/CeO2 and FeOx/Pt/CeO2 have been investigated by means of density functional theory (DFT) calculation and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The geometrical structures and vibrational frequencies were obtained at the MPW1PW91/SDD level. Theoretical calculation shows that the calculated IR spectra were in good agreement with the experimental results. The calculated results clarify the assignment of the adsorbed CO species on the surface of Pt/TiO2, Pt/CeO2 and FeOx/Pt/CeO2.     

Au/TiO2催化剂上非催化CO氧化反应中活性氧物种的生成和消除

在定量的瞬时产物分析(TAP)反应器中,于80 oC下采用CO脉冲和O2脉冲补充等方法,研究了高温(400 oC)焙烧的Au/TiO2催化剂上活性氧物种的移除反应活性,特别是活性氧物种的性质。以往的研究大多关注的是CO催化氧化反应中活性氧物种及其性质,在典型的反应条件下该物种的形成和消除是可逆的;而本研究表明,催化剂直接焙烧后就存在额外的氧物种;该物种对CO氧化反应也具有活性,但其在典型的反应条件下不生成或生成很少。基于此,讨论了Au/TiO2催化剂上CO氧化反应的机理,特别是不同活性氧物种的作用。     

Pt／Al_2O_3，Pd／Al_2O_3催化剂上CO氧化与表面氧脱出－恢复性能

Ｐｔ／Ａｌ_２Ｏ_３，Ｐｄ／Ａｌ_２Ｏ_３催化剂上ＣＯ氧化与表面氧脱出－恢复性能周仁贤，郑小明（杭州大学催化研究所，杭州３１００２８）关键词铂，钯，氧化铝，氧化锆，负载型催化剂，一氧化碳，氧化，氧脱附ＡＩ。Ｏ。负载的贵金属（Ｐｔ，Ｐｄ或Ｒｈ等）催化剂对有...     

Effects of preparation conditions of Au/FeO_x /Al_2O_3 catalysts prepared by a modified two-step method on the stability for CO oxidation

Composite oxide FeO x /Al 2 O 3 -supported gold catalysts were prepared by a modified two-step method. The effects of preparation conditions on the initial catalytic activity and long-time stability were studied for CO oxidation. XRD, XPS and in situ FTIR were employed to investigate the state of FeO x and the species on the catalyst surface. The results showed that Au/FeO x /Al 2 O 3 catalysts prepared by this method exhibited high activity and high stability in a wide pH value range. Calcination pretreatm...     

Effects of preparation conditions of Au/FeOx/Al203 catalysts prepared by a modified two-step method on the stability for CO oxidation

Composite oxide FeO x /Al 2 O 3 -supported gold catalysts were prepared by a modified two-step method. The effects of preparation conditions on the initial catalytic activity and long-time stability were studied for CO oxidation. XRD, XPS and in situ FTIR were employed to investigate the state of FeO x and the species on the catalyst surface. The results showed that Au/FeO x /Al 2 O 3 catalysts prepared by this method exhibited high activity and high stability in a wide pH value range. Calcination pretreatment was proved to be beneficial to improving the activity and stability. The beneficial effects of FeO x acting as a structural promoter could be ascribed to the ability to supply active oxygen species. As the precursor of FeO x , Fe(NO 3 ) 3 is superior to FeCl 3 for obtaining higher stability.     

Preferential oxidation of carbon monoxide catalyzed by platinum nanoparticles in mesoporous silica

Preferential oxidation (PROX) of CO is an important practical process to purify H2 for use in polymer electrolyte fuel cells. Although many supported noble metal catalysts have been reported so far, their catalytic performances remain insufficient for operation at low temperature. We found that Pt nanoparticles in mesoporous silica give unprecedented activity, selectivity, and durability in the PROX reaction below 353 K. We also studied the promotional effect of mesoporous silica in the Pt-catalyzed PROX reaction by infrared spectroscopy using the isotopic tracer technique. Gas-phase O2 is not directly used for CO oxidation, but the oxygen of mesoporous silica is incorporated into CO2. These results suggest that CO oxidation is promoted by the attack of the surface OH groups to CO on Pt without forming water.     

Intrinsic catalytic role of mesoporous silica in preferential oxidation of carbon monoxide in excess hydrogen

We have studied the intrinsic catalytic role of MCM-41 mesoporous silica in preferential oxidation of CO in excess H(2) (PROX). Two types of MCM-41 supports (MCM-41A and MCM-41B) were obtained from the same pristine as-synthesized materials by using different procedures for surfactant removal: one-step calcination or two-step extraction-calcination. Although two kinds of Pt catalysts prepared from the MCM-41 supports exhibit high similarity in apparent physicochemical parameters such as Pt morphology, particle-size distribution, electronic states, support architecture, and pore-size distribution, they show a dramatic difference in catalytic activity (ca. 100?% versus 10?% CO conversions at 298?K). This feature motivated us to investigate the catalytic role of MCM-41 in the PROX reaction. By means of infrared experiments with the isotope tracer technique, it was revealed that the reactive microenvironment at the interface between Pt and the MCM-41A support is the origin of the high activity. On the highly active Pt/MCM-41A catalyst, interfacial silanols play a decisive role in the ignition of CO oxidation, and gaseous O(2) and H(2) are dissociated on CO-free Pt sites created by the interfacial reaction. The dissociated oxygen and hydrogen are proposed to sustain the catalytic cycle in the form of regenerated silanols on the support, which is catalyzed by the Pt surface in the presence of H(2).     

La2O3助剂对Au/TiO2催化氧化CO性能的影响

采用溶胶-凝胶法制备了TiO2以及La2O3-TiO2载体, 再用沉积沉淀法制备Au/TiO2和Au/La2O3-TiO2催化剂, 并对催化剂的CO氧化反应活性进行测试. 结果表明, La2O3助剂可以显著提高催化剂催化氧化CO的活性. X射线衍射(XRD)、程序升温脱附(TPD)、N2吸附-脱附(BET)表征结果表明, La2O3助剂不仅提高了催化剂比表面积, 抑制了TiO2晶粒尺寸的长大, 并且增强了TiO2的晶格应变, 在O2气氛吸附过程中主要在TiO2表面形成O-物种. 原位傅立叶变换红外(FT-IR)结果进一步表明, La的掺杂不仅提高了吸附在Au活性位CO的氧化速率, 还使TiO2表面形成第二种活性位, 从而显著提高了催化活性.