Selective oxidation of butane on phosphorus-modified silica supported vanadia catalysts

Triethylphosphate impregnation of 2.8 wt% V/SiO₂ and subsequent controlled calcination produced phosphorus-modified supported vanadium catalysts. Phosphorus modification enhanced the yield of maleic anhydride in the partial oxidation of butane. Varying the phosphorus to vanadium atomic ratio from 0 to 2.8 increased the selectivity to maleic anhydride from 0 to approximately 48%. The selectivity was nearly constant up to 20% butane conversion and for different O₂/C₄H₁₀ ratios. The Raman spectra of the phosphorus-modified samples had bands at 1040 and 930 cm^–1, and broad unresolved bands between 580 and 540 cm^–1. It was concluded that the active phases in these samples were -VOPO₄.     

Partial oxidation of toluene to benzaldehyde and benzoic acid over model vanadia/titania catalysts: role of vanadia species

Pure and K-doped vanadia/titania prepared by different methods have been studied in order to elucidate the role of vanadia species (monomeric, polymeric, bulk) in catalytic toluene partial oxidation. The ratio of different vanadia species was controlled by treating the catalysts in diluted HNO₃, which removes bulk vanadia and polymeric vanadia species, but not the monomeric ones, as was shown by FT-Raman spectroscopy and TPR in H₂. Monolayer vanadia species (monomeric and polymeric) are responsible for the catalytic activity and selectivity to benzaldehyde and benzoic acid independently on the catalyst preparation method. Bulk V₂O₅ and TiO₂ are considerably less active. Therefore, an increase of the vanadium concentration in the samples above the monolayer coverage results in a decrease of the specific rate in toluene oxidation due to the partial blockage of active monolayer species by bulk crystalline V₂O₅. Potassium diminishes the catalyst acidity resulting in a decrease of the total rate of toluene oxidation and suppression of deactivation. Deactivation due to coking is probably related to the Brønsted acid sites associated with the bridging oxygen in the polymeric species and bulk V₂O₅. Doping by K diminishes the amount of active monolayer vanadia leading to the formation of non-active K-doped monomeric vanadia species and KVO₃.     

The adsorption of Sn on Pt(1 1 1) and its influence on CO adsorption as studied by XPS and FTIR

The coverage of Sn on Pt(1 1 1) which is obtained by electrochemical deposition from 5×10⁻⁵ M Sn²⁺ in 0.5 M H₂SO₄ has been determined by XPS for different deposition times. Complete suppression of hydrogen adsorption corresponds to a coverage of ?_max=0.35 (Sn to surface Pt atoms).Co-adsorption of CO with Sn on Pt(1 1 1) has been studied by FTIR spectroscopy. The IR spectra of the stretching vibration of CO can be interpreted in terms of the vibrational signature of the Pt(1 1 1)/CO system and no vibrational bands associated with CO on Sn are detected. At high Sn coverages, the 1840 cm⁻¹ band associated with bridge-bonded CO and the 2070 cm⁻¹ band assigned to on-top CO are present, however, no hollow site adsorption which is characterized by the 1780 cm⁻¹ band is revealed within the resolution of the experiment. This vibrational signature corresponds to a less compressed adlayer compared to the (2×2)-3CO saturation structure on Pt(1 1 1). At lower Sn coverages, signatures from both the compressed and the less compressed CO adlayer structures are seen in the spectra. From earlier structural and electrochemical studies it is known that Sn is adsorbed in 2D islands and influences CO molecules in its neighbourhood electronically. This leads to a disappearance of the IR band from CO adsorbed in the hollow site at high Sn coverages and to higher population of the weakly adsorbed state of CO for all Sn-modified surfaces, i.e. a relative increase of the amount of CO oxidised at low potentials. In addition to this electronic effect, Sn also exerts a co-catalytic effect at low Sn coverages on that part of CO which is adsorbed at a larger distance from Sn due to a bi-functional mechanism. The IR spectra shows for the Sn-modified Pt(1 1 1) surface that the transition from the compressed CO adlayer which is characterized by the hollow site adsorption of CO to the less compressed one which exhibits a characteristic band associated with bridge-bonded CO occurs already at 250 mV instead of 400 mV.     

Ruthenium as oxidation catalyst: bridging the pressure and material gaps between ideal and real systems in heterogeneous catalysis by applying DRIFT spectroscopy and the TAP reactor

Two supported Ru catalysts were prepared by the chemical vapor deposition of Ru₃(CO)₁₂ on MgO and SiO₂ (MOCVD). TEM, XRD, and static H₂ chemisorption measurements confirmed that the Ru particle size was about 2 nm on both supports. Using in situ DRIFT (diffuse reflectance infrared Fourier transform) spectroscopy at atmospheric pressure it was found that the adsorption of CO on the reduced samples is clearly influenced by the supports whereas the adsorption of CO on the oxidized Ru catalysts is essentially independent of the support. O₂ chemisorption measurements showed that a thin RuO₂ surface layer was formed on both catalysts under oxidizing conditions at room temperature. The observed C–O stretching frequencies were found to be in good agreement with HREELS and LEED data reported for the RuO₂(1 1 0) single crystal surface. The catalytic activity was assessed under high-vacuum conditions using the TAP (temporal analysis of products) reactor by co-feeding CO and O₂. These conditions ensured that heat and mass transfer limitations were absent. Both supported Ru catalysts were found to be highly active and stable under the CO oxidation conditions even down to room temperature. The deactivation of the catalysts observed at room temperature was reversible and independent of the support. The turnover frequencies (number of CO₂ molecules per metal surface site per second) derived from steady-state measurements are in good agreement with data reported for the RuO₂(1 1 0) single crystal surface under UHV conditions. Based on the results of the DRIFTS (diffuse reflectance infrared Fourier transform spectroscopy) and the kinetic measurements supported RuO₂ is identified as the catalytically active phase. In addition, the turnover frequencies are in good agreement with data reported for Ru/SiO₂ at atmospheric pressure. Thus, both the materials and the pressure gap were bridged successfully.     

In situ FTIR Study of Cobalt Oxides for the Oxidation of Carbon Monoxide

A high-valance cobalt oxide, CoO _x , was prepared from cobalt nitrate aqueous solution through precipitation with sodium hydroxide and oxidation by hydrogen peroxide. Further, other pure cobalt oxide species were refined from the CoO _x by temperature-programmed reduction (TPR) to 170, 230 and 300 °C. They were characterized by TPR and X-ray diffraction (XRD). Adsorption of CO and the co-adsorption of CO/O₂ over the cobalt oxides were further tested by in situ FTIR. It was shown that Co₃O₄ is quite active for the oxidation of CO at room temperature in the presence of oxygen, leading to the formation of CO₂. The variation in the oxidation of CO was interpreted with a mechanism involving two kinds of oxygen species, i.e., *-O₂ on the CoO _x surface and *-O_L on the surface of Co₃O₄ spinel structure.     

Possible effects of site isolation in antimony oxide-modified vanadia/titania catalysts for selective oxidation of o-xylene

Titania-supported vanadia catalysts were modified by addition of antimony oxide for application in o-xylene selective oxidation to phthalic anhydride. It was shown that active and selective catalysts can be prepared by ball-milling mixtures of powders of TiO₂, V₂O₅and Sb₂O₃followed by calcination. X-ray photoelectron spectroscopy proves the formation of highly dispersed overlayers of vanadium oxide and antimony oxide, in which V⁵⁺is partially reduced to lower oxidation states and Sb³⁺is partially oxidized to Sb⁵⁺. Antimony oxide segregated into the outermost surface layers. It is therefore inferred that the presence of the antimony oxide modifier spatially separates V–O species and leads to site isolation which may be responsible for the positive effect of the modifier for the catalyst's selectivity.     

Effect of calcination temperature on the catalytic activity of Au colloids mechanically mixed with TiO2 powder for CO oxidation

In order to elucidate the role of the contact structure between gold and metal oxide support in low-temperature CO oxidation, a mechanical mixture of colloidal gold with TiO₂ powder was prepared and calcined at different temperatures. The sample calcined at 473 K, which is composed of spherical gold particles with a mean diameter of 5.1 nm and TiO₂ powder, is poorly active for CO oxidation at temperatures up to 473 K. The catalytic activity appreciably increases with an increase in calcination temperature up to 873 K even though gold particles grow to larger ones, reaching a level with almost the same turnover frequency as that of Au/TiO₂ prepared by a deposition–precipitation method. This revised version was published online in July 2006 with corrections to the Cover Date.     

On the mechanism of CO adsorption on a silica‐supported ruthenium catalyst

The adsorption of CO at room temperature on a Ru/SiO₂ catalyst has been studied by means of FTIR spectroscopy. Spectral evidence for formation of water molecules and a quantity of very dispersed ruthenium on the catalyst surface during CO adsorption was found. On the basis of these experimental results a new reaction scheme for the interaction of CO with a silica‐supported ruthenium catalyst is proposed. This revised version was published online in July 2006 with corrections to the Cover Date.     

IR characterization of sulfated zirconia derived from zirconium sulfate

Surface characterization of a sulfate-derived zirconia sample containing approximately 1 wt% S was performed by IR spectroscopy. Several types of sulfate groups were detected which are resistant to heating in vacuo up to 973 K. By using CO as a spectroscopic probe, two kinds of Lewis acid sites were identified which were assigned to surface Zr⁴⁺ ions in different environments. Comparison with corresponding data for a nearly sulfate-free zirconia sample showed that sulfated zirconia has an enhanced Lewis acidity.     

Fischer-Tropsch合成中的CO活化机理

Fischer—Tropsch(F—T)合成是将煤炭、天然气和生物质等含碳资源间接转化为液体燃料的关键工艺步骤,深入了解其反应机理,对于完善F-T合成催化剂设计以及优化其工业操作条件具有重要的理论价值．对近年来有关F—T合成中关键的CO活化机理研究进行了总结和评述,着重介绍了不同过渡金属元素对CO的吸附和活化性质,并就金属晶面与CO的相互作用、催化助剂的影响以及F—T合成反应中与H2的共吸附作用等方面进行分析,为进一步的研究工作提供理     

焙烧温度对CuO/Co_3O_4-CeO_2催化剂CO优先氧化性能的影响

采用浸渍法制备了Cu O/Co3O4-Ce O2(Cu Co Ce10)催化剂,考察了在不同温度(250、300、350、400和450℃)焙烧后的样品在富氢气氛中对CO优先氧化反应的催化性能。应用BET、XRD、H2-TPR及XAFS技术详细表征了催化剂的结构与性能。结果表明,不同温度焙烧的催化剂中,铜物种均主要以Cu O相存在;350℃焙烧的Cu Co Ce10催化剂具有最大的比表面积和最好的氧化还原性能,在98~173℃的温度范围内能够将CO完全转化为CO2,呈现出最宽的CO优先氧化可操作温度窗口,以及良好的催化活性稳定性。     

In situ FT-IR Spectroscopic Studies on the Mechanism of the Catalytic Oxidation of Carbon Monoxide over Supported Cobalt Catalysts

Three types of supported cobalt catalysts (5% as metal Co loading on SiO₂, Al₂O₃ and TiO₂) were prepared by incipient wetness impregnation with aqueous Co(NO₃)₂·6H₂O solution. Then, all catalysts were calcined in air at 400 °C (assigned as 5Co/Si C400, 5Co/Al C400 and 5Co/Ti C400). Their catalytic activities towards the CO oxidation were studied in a continuous flow micro-reactor. Adsorption of carbon monoxide (CO) and the co-adsorption of CO/O₂ over cobalt oxide were further tested under in situ FT-IR. The results showed that both 5Co/Si C400 and 5Co/Al C400 had higher activity than 5Co/Ti C400. The T₅₀ (50% conversion) for both 5Co/Si C400 and 5Co/Al C400 was reached at temperatures as low as ambient temperature. According to the in situ FT-IR analysis, the variation in oxidation of CO was interpreted with different mechanisms, i.e., the reaction between adsorbed CO and lattice oxygen of cobalt oxide, and part of CO₂ formation via carbonates on 5Co/Si C400; both types of carbonates are formed on 5Co/Al C400 to promote the CO oxidation; while both strong adsorption of CO on TiO₂ and CO₂ on cobalt oxide for 5Co/Ti C400 leads to affect the activity.     

沸石形貌调控及相关应用的研究进展

综述了沸石形貌调控及相关应用的最新研究进展,着重介绍了沸石形貌调控合成中的几种热门合成方法及其机理,包括可脱除颗粒模板、生物模板法、催化剂小球上的分子筛涂层、限制空间合成(反胶团、微乳和凝胶)、结构导向剂法晶体形貌修饰。同时把沸石的形貌、存在的多级孔道同改善的性能(比如催化活性和选择性)联系起来,并分析了它们的优势与缺陷。     

Spatially resolved infrared spectroscopy: a novel technique for in situ study of spatial surface coverage during CO oxidation on supported catalysts

A spatially resolved infrared (IR) imaging technique to monitor the linear adsorbed CO coverage on supported catalyst surface combining an IR bandpass filter and an IR thermography camera has been developed. Images acquired during the CO adsorption/desorption and ignition indicate that the technique provides an excellent method to image the change of surface coverage with a spatial resolution. It is expected that the combination of infrared thermography with spatially resolved imaging of surface coverage will provide a deeper insight in the dynamics of spatio-temporal patterns on heterogeneous catalysts.     

高级氧化技术降解水中环境激素的研究进展

环境激素是一类像激素一样影响人类和动物内分泌功能的物质.介绍了废水中环境激素类物质的高级氧化降解技术的机理、特点、应用以及局限性,主要介绍了03/H2/O2、O3/金属催化剂、光催化降解以及核辐射法等高级氧化技术在降解此类废水中的应用.高级氧化技术与其他廉价水处理技术的联合应用将是此类废水处理技术的发展方向之一.     

综述高级氧化技术在废水处理中的应用

高级氧化技术以产生具有强氧化能力的羟基自由基（·oH）为特点,该技术用于有效去除和降解有毒污染物,或者作为预处理将污染物转化为可生物降解化合物,然后通过传统的生物处理方法处理。该文总结了·OH的形成以及污染物的降解机制,同时阐述了高级氧化法的研究方向。     

The oxidation and scrambling of CO with oxygen at room temperature on Au/ZnO

An FTIR and quadrupole mass study of CO adsorption and oxidation with¹⁶O₂ and¹⁸O₂ on Au/ZnO catalysts is presented. The experimental results indicate that: (i) CO is activated by gold in two molecular forms, a linear carbonyl species bonded at terrace Au sites and a carbonyl species bonded to Au peripheral sites; (ii) a band related to CO adsorbed on Au oxidized sites and a scrambling reaction between CO and¹⁸O₂ indicate that oxygen is also activated on gold sites. The oxygen adsorbed on gold is probably strongly basic, as is the oxygen adsorbed on silver and on copper, and it can easily oxidize CO to CO₂.     

Interface species and effect of hydrogen on their amount in the CO oxidation on Au/ZnO

A FTIR study of the CO oxidation on Au/ZnO from 90 to 300 K in the absence and in the presence of hydrogen has been performed. An insight on the origin of deactivation during CO oxidation at room temperature and on the regeneration effect of hydrogen is given. FTIR spectra show that at 90 K only carbonylic species on the metallic particles and on the support cations are produced. Carbonates and/or carbonyls at the interface between the metal and the oxide are produced by increasing the temperature from 90 to 300 K. The presence of hydrogen in the mixture inhibits in some extent the formation of transient intermediates and of stable carbonates adsorbed on the support. The amount of stable species at the interface is reduced as a consequence of the lowered basicity of the reactive oxygen species at the borderline between the metal and the oxide.     

Effect of protonation media on chemically and electrochemically synthesized polyaniline

Polyaniline films have been prepared both chemically and electrochemically using formic (‘Pani‐Formic’), boric (‘Pani‐Boric’) or acetic acid (‘Pani‐Acetic’) as protonation media. Among the three, formic acid seems to be a better protonating medium because it selectively yields the conducting phase of polyaniline. The variation of potential with the amount of oxidizing agent suggests one dimensional growth of polymer chain, which proceeds through a PG/EM mechanism as indicated by spectral data. The Pani‐Boric and Pani‐Acetic acid demonstrate three‐ and four‐step decomposition patterns, respectively, with complete decomposition at about 760 °C. Pani‐Formic acid, in contrast, reveals a three‐step decomposition pattern with 90% weight loss at about 900 °C and shows a tendency to react with the Pt sample holder. The films of polyaniline generated electrochemically also suggest formic acid to be a better protonating medium for achieving a relatively greater fraction of conducting emeraldine salt. However, boric acid produces excellent quality adherent films with very high deposition rate. Morphological features give strong support to this observation. The films of Pani‐Formic and Pani‐Acetic acids show a spongy network and globular morphology, respectively, while Pani‐Boric acid yields an extremely uniform surface coating. Furthermore, cyclic voltammetry reveals different patterns depending upon the formation of different oxidation states and the results are in accordance with optical absorption studies. © 2000 Society of Chemical Industry