氮掺杂生物炭材料的制备及其在环境中的应用

由生物质转化得到的生物炭材料因其成本低且环境友好被广泛用于环境领域,且对我国实现碳达峰与碳中和有积极的促进作用。非金属氮掺杂生物炭由于氮元素的引入,呈现表面碱度以及多吸附位点的特性,提高了其对污染物的去除性能,然而对氮掺杂生物炭材料的绿色可控合成及掺杂机理的关注不够。本文综述了近几年来国内外氮掺杂生物炭材料的制备及其在环境中的研究应用,梳理了氮掺杂生物炭材料中含氮官能团的类型和不同制备方法,含氮官能团包括吡啶N、吡咯N和石墨N等,其含量和类型受氮源、热解温度和时间的影响,阐明了其中的氮掺杂机理由氮源分解的中间产物、生物炭表面官能团和掺杂过程中的活化剂等因素决定。最后,对氮掺杂生物炭在环境方面的应用及作用机理进行探讨,并在此基础上提出未来研究高效氮掺杂生物炭的重点和研究方向,以期为氮掺杂生物炭在环境中的实际应用提供参考。     

Influence of the calcination temperature on the Au/FeOx/Al2O3 catalyst

The effect of calcination temperature on the electronic structure of gold catalyst was investigated in this paper. CO oxidation was employed as a test reaction to correlate the phase changes to the catalytic activity. The TPR, XPS and XRD characterization showed that the highly active Au/FeO_x/Al₂O₃ catalyst contained both gold atoms and ions. The catalytic performance of gold catalyst may depend on the Au⁰/Au³⁺ ratio. The best activity in the present work was obtained when the Au⁰/Au³⁺ ratio was about 0.89. Copyright © 2006 Society of Chemical Industry     

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.     

Performance of CO preferential oxidation reactor with noble-metal catalyst coated on ceramic monolith for on-board fuel processing applications

On-board fuel processors are being developed to provide hydrogen-rich gas to the polymer electrolyte fuel cell automotive propulsion systems. Whereas the anode catalyst in the fuel cell has low tolerance for carbon monoxide, 10–100 ppm, reforming of gasoline and other hydrocarbon fuels generally produces 1–2% of CO. Of the many methods of removing CO from the reformer gas, preferential oxidation (PrOx) of CO over noble-metal catalysts is practiced most frequently. In this paper, we present experimental data for CO conversion on a Pt-based catalyst that is active at room temperature and was coated on a ceramic monolith. The data is used to develop an empirical correlation for selectivity for CO oxidation as a function of CO concentration and oxygen stoichiometry at 30,000–80,000/h space velocity. The selectivity correlation is used in a model to analyze the performance of multi-stage, adiabatic PrOx reactors with heat exchange between the stages to cool the reformate to 100 °C. An optimization algorithm is used to determine the operating conditions that can reduce CO concentration to 10 ppm while minimizing parasitic loss of H₂ in the reformate stream. It is found that the 10 ppm constraint limits the maximum inlet CO concentration to 1.05% in a single-stage reactor and to 3.1% in a two-stage reactor. The results clearly show the incremental reduction in parasitic H₂ loss by addition of second and third stages.     

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     

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。     

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。     

Esthetic performance of thermochromic pigments in cataphoretic and sprayed coatings for outdoor applications

This study aims to assess the aesthetical performances of thermochromic coatings for outdoor applications. In details, this work focuses on the efficiency of thermochromic pigments inside cataphoretic and sprayed primers, evaluating the possible synergic effect of a protective transparent topcoat. The structure of thermochromic pigments is examined by optical microscope, and their color-changing behavior is evaluated by colourimetric measurements. Colourimetric analyses are also carried out to monitor the thermochromic performances of the coatings during exposure to an aggressive NaCl solution and UV-B radiations, and to assess the protective role of the top-coat. In addition to that, wet- and dry-abrasion tests are carried out to define the suitability of these coatings for outdoor applications where good resistance to mechanical damage is required. Thus, this work evidences the better aesthetical features of the cataphoretic primer, which, however, particularly suffers from chemical–physical degradation processes. Nevertheless, the application of the transparent topcoat allows to maintain the integrity of the cataphoretic primer. The double-layer coating exhibits a remarkable color-changing behavior even when subjected to degradation phenomena due to exposure to aggressive environments.     

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.     

生物炭基光催化剂的制备、性能及环境应用研究进展

生物炭因具有独特的表面性质、易修饰的官能团、良好的导电性和化学稳定性常被用作光催化剂的载体。将光催化剂与生物炭复合制备得到生物炭基光催化剂,不仅将二者的优势有效结合起来,同时得到的复合材料在官能团、孔性能、表面活性位点、催化降解能力等方面均有显著改善。生物炭良好的导电性提高了光催化过程中电子-空穴对分离的效率,丰富的表面官能团能够吸附固定不同的污染物,便于其光催化去除。本文综述了生物炭基光催化剂的各种制备工艺、催化性能及其对废水处理的影响,详细地介绍了溶胶-凝胶、超声、水热/溶剂热、水解、焙烧、沉淀和热缩聚等生物炭基光催化剂的制备方法。此外,还通过深入的机理分析,探讨了生物炭基光催化剂对污染物的吸附和光催化降解的协同效应。最后,归纳了生物炭基光催化剂在不同污染物去除方面的应用并展望了未来的发展前景和潜力。