Au/CuMn催化剂对于C3H8还原NO催化性能的研究

以沉积-沉淀法制备了系列Au/CuMn催化剂,并对催化剂进行了XRD和XPS等表征,研究了Au负载量和催化剂焙烧温度对Au/CuMn催化剂性能的影响。实验结果显示,60℃烘干、Au理论负载量为3%的催化剂性能最佳,在50℃的反应条件下,NO的转化率达到72.4%,但催化剂失活较快。XPS分析显示,催化剂表面的Au3+与吸附氧物种Oads.是反应的活性中心,反应过程中催化剂表面氧化态Au3+与Oads.物种部分被还原,可能是催化剂失活的重要原因。另外,反应后在催化剂表面生成的亚硝酸盐、硝酸盐和碳酸盐等物种,覆盖了活性中心,也是导致催化剂失活的原因之一。     

Properties of TiO2 support and the performance of Au/TiO2 Catalyst for CO oxidation reaction

Gold catalysts were prepared on TiO₂ supports of different phase structures (i.e., anatase, rutile and biphasic), TiO₂ crystal size (i.e., 9–23 nm), surface and textural properties (i.e., hydration and surface area). The CO oxidation on the gold catalysts was carried out in an operando-DRIFTS set-up equipped with DRIFTS reactor cell connected on-line to CO gas analyser and gas chromatograph enabling real time monitoring of surface reaction and simultaneous reaction rate measurements. Gold catalysts supported on pure anatase TiO₂ were more resistant to sintering compared to catalysts supported on rutile and bi-phasic TiO₂. Besides catalyst sintering, deposition of surface carbonates is an important cause of catalyst deactivation. The best gold catalyst was prepared on 13 nm anatase TiO₂. It displays both increased activity and stability for CO oxidation reaction at room temperature. Surface and textural properties of TiO₂ also play a role on the performance of the Au/TiO₂ catalyst.     

Investigation of the active site and the mode of Au/TiO2 catalyst deactivation using Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS)

CO is a useful probe in the characterization of surface properties of both metal and metal oxide via adsorption. Adsorption of CO was used to monitor the possible active site of an Au/TiO₂ catalyst for the CO oxidation reaction. CO adsorption on the reduced catalyst results in the band at 2104 cm⁻¹ indicative of Au⁰. During the reaction (in the presence of both CO and O₂ present) the band is shifted to higher wave numbers indicating non-competitive adsorption on the surface of Au species. This study also reveals the relationship between the presence of CO (in the absence of oxygen) and the build-up of surface species such as bicarbonates, formates and carbonate species which decreases the activity of the catalyst. The presence of both the reduced and the cationic species of Au seem to be requirement for the activity of the catalyst.     

Support effects in the selective gas phase hydrogenation ofp-chloronitrobenzene over gold

The catalytic continuous gas phase hydrogenation of p-chloronitrobenzene (P=1 atm;T=423 K) has been investigated over a series of oxide (Al₂O₃, TiO₂, Fe₂O₃ and CeO₂) supported Au (1 mol %) catalysts. The application of two catalyst synthesis routes,i.e. impregnation (IMP) and deposition-precipitation (DP), has been considered where the DP route generated smaller mean Au particle sizes (1.5-2.8 nm) compared with the IMP preparation (3.5-9.0 nm). The catalysts have been characterised in terms H2 chemisorption and BET area measurements where the formation of metallic Au post-activation has been verified by diffuse reflectance UV-Vis, XRD and HRTEM analyses.p-Chloroaniline was generated as the sole reaction product over all the Au catalysts with no evidence of C-Cl and/or C-NO₂ bond scission and/or aromatic ring reduction. The specific hydrogenation rate increased with decreasing Au particle size (from 9 to 3 nm), regardless of the nature of the support. This response extends to a reference Au/TiO₂ catalyst provided by the World Gold Council. A decrease in specific rate is in evidence for smaller particles (< 2 nm) and can be attributed to a quantum size effect. The results presented establish the basis for the design and development of a versatile catalytic system for the clean continuous production of high value amino compounds under mild reaction conditions.     

Investigation of the active site and the mode of Au/TiO2 catalyst deactivation using Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS)

CO is a useful probe in the characterization of surface properties of both metal and metal oxide via adsorption. Adsorption of CO was used to monitor the possible active site of an Au/TiO₂ catalyst for the CO oxidation reaction. CO adsorption on the reduced catalyst results in the band at 2104 cm⁻¹ indicative of Au⁰. During the reaction (in the presence of both CO and O2 present) the band is shifted to higher wave numbers indicating non-competitive adsorption on the surface of Au species. This study also reveals the relationship between the presence of CO (in the absence of oxygen) and the build-up of surface species such as bicarbonates, formates and carbonate species which decreases the activity of the catalyst. The presence of both the reduced and the cationic species of Au seem to be requirement for the activity of the catalyst.     

Effects of Au nanoparticles on TiO2 in the photocatalytic degradation of an azo dye

The photocatalytic activity of Au modified titanium dioxide was evaluated in the photodegradation of the azo dye Acid Red 1 (AR1) under 254 nm irradiation. Noble metal nanoparticles were deposited on TiO₂ either through depositionprecipitation (DP), or by immobilisation of preformed metallic sols (polyvinylalcohol (PVA)/NaBH₄ or tetrakis(hydroxymethyl)phosphonium chloride (THPC)/NaOH systems). Gold nanoparticles on the photocatalyst surface had dimensions of around 3–4 nm in diameter, as determined by HRTEM analysis, and exhibited visible light plasmon absorption. THPC Au/TiO₂ appears to be the most photoactive amongst the photocatalysts with a 1 wt.% Au loading, while among THPC samples with different Au loadings (0.5–20.0 wt.%) the maximum photoactivity was attained with 5 wt.% Au/TiO₂. The higher AR1 photodegradation rate observed on Au/TiO₂ at basic pH can be related to the higher concentration of hydroxyl anions at the interface: these are able to effectively scavenge photoproduced valence band holes, possibly in competition with Au⁰ oxidation to Au⁺.     

PAN/PANI/rGO/Au复合纤维的制备及其催化、原位SERS监测性能研究

负载型贵金属纳米催化剂是提高贵金属催化剂利用率,降低经济成本的一种有效途径,也是一种新型的有潜力的表面增强拉曼光谱(SERS)的基底材料。本文首先利用静电纺丝技术构建了还原的氧化石墨烯(rGO)增强的聚丙烯腈/聚苯胺复合纤维(PAN/PANI/rGO),然后采用原位还原的方法在其表面生长金纳米颗粒得到了PAN/PANI/rGO/Au复合纤维,通过SEM, FTIR, XRD, XPS, Raman和UV-Vis光谱等手段对复合纤维进行了结构和形貌表征,最后以NaBH₄还原四硝基苯酚(4-NP)为模型,研究了复合纤维的催化性能和原位SERS检测该催化还原反应的过程,并将其与同种方法制备的PAN/PANI/GO/Au和PAN/PANI/Au复合纤维进行比较。结果表明,rGO增强的PAN/PANI/rGO/Au复合纤维具有优于PAN/PANI/GO/Au和PAN/PANI/Au复合纤维的催化活性、原位增强拉曼检测的能力和循环性能。     

Thermal treatment effect on structure, electrical conductivity and transient photoconductivity behavior of thiourea modified TiO2 sol-gel thin films

Thiourea modified nanocrystalline titanium dioxide (TiO₂) thin films were prepared by sol-gel route and were thermally treated at five different temperatures (400, 500, 600, 800 and 1000 °C). The films were studied using GIXRD, PIGE and UV-vis spectroscopy. It was observed that the anatase to rutile phase transformation of TiO₂ was inhibited by the thiourea modification. The transmittance of the modified films appeared reduced which was attributed both to the modification of TiO₂ with thiourea and the light scattering in the films. The dark conductivity and the transient photoconductivity of the modified TiO₂ sol-gel thin films were studied in vacuum and in air. The environment does not influence significantly the dark conductivity, because of the almost equivalent competition between oxygen and water adsorption. The photoconductivity reaches high values for all samples in both environments, with the sample treated at 500 °C to present the highest value. The larger values in vacuum can be attributed to the reduced amount of adsorbed oxygen at the surface, which acts as electron scavenger.     

Effect of the oxidation state of gold on the complete oxidation of isobutane on Au/CeO2 catalysts

Catalysts of highly dispersed gold supported on ceria were prepared by deposition precipitation method. Au is dispersed as Au⁰, Au⁺ and Au³⁺ species on ceria. The content of Au⁺ and Au³⁺ was highest on catalyst prepared on uncalcined ceria, which possess least ordered surface. It is inferred that oxygen vacancy on disordered ceria surface is essential for the preparation of highly dispersed gold catalysts and in stabilizing monolayer surface Au⁺ clusters while cationic vacancies are sites for substitutional Au³⁺. Au/CeO₂ catalysts showed low-temperature isobutane oxidation activity with maximum conversion at 150–180°C. Ex-situ XPS results demonstrated that the low temperature isobutane oxidation activity was closely related to the content of Au⁺ which we interpreted as surface gold oxide formed under reaction conditions. Isobutane oxidation activity associated with ceria at temperature above 300°C was enhanced by substitutional Au³⁺.     

Catalytic effect of Ni nanoparticles on the desorption kinetics of MgH2 nanoparticles

Mg and Ni nanoparticles were prepared by hydrogen plasma-metal reaction (HPMR). MgH₂ nanoparticles were obtained by hydriding the Mg nanoparticles. Hydrogen storage kinetics of the MgH₂ nanoparticles doped with different amount of Ni nanoparticles was investigated by differential scanning calorimetry (DSC) and hydrogen desorption rate measurements. The obtained samples show superior hydrogen storage kinetics. 6.1 wt% hydrogen is desorbed in 10 min at 523 K under an initial pressure of 0.01 bar of H₂ when the proportion of Ni nanoparticles is 10 wt%. The desorption rate increases when enhancing the amount of catalyst. However, the activation energy of desorption does not decrease any more when the amount of Ni exceeds a value. The enhanced desorption kinetics are mainly attributed to the accelerated combination process of hydrogen atoms by the Ni nanoparticles on the surface of MgH₂.     

Photodegradation of methyl orange by BiOI-sensitized TiO2

BiOI-sensitized titanium dioxide (TiO2) photocatalysts were prepared by a deposition method at room temperature and characterized by X-ray diffraction, X-ray photoelectron spectroscopy, and Brunauer-Emmett-Teller surface area measurements. The photocatalytic activities of the catalysts were evaluated for the degradation of methyl orange (MO) solution under UV and visible light irradiation. The effects of catalyst amount, initial pH value, initial concentration of MO, as well as KI amount were investigated. ...     

Calcination/acid-activation treatment of an anodic oxidation TiO<Subscript>2</Subscript>/Ti film catalyst

The aim of this work was to investigate the effects of calcination/acid-activation on the composition, structure, and photocatalytic (PC) reduction property of an anodic oxidation TiO₂/Ti film catalyst. The surface morphology and phase composition were examined by scanning electron microscopy and X-ray diffraction. The catalytic property of the film catalysts was evaluated through the removal rate of potassium chromate during the PC reduction process. The results showed that the film catalysts were composed of anatase and rutile TiO₂ with a micro-porous surface structure. The calcination treatment increased the content of TiO₂ in the film, changed the relative ratio of anatase and rutile TiO₂, and decreased the size of the micro pores of the film catalysts. The removal rate of potassium chromate was related to the technique parameters of calcination/acid-activation treatment. When the anodic oxidation TiO₂/Ti film catalyst was calcined at 873 K for 30 min and then acid-activated in the concentrated H₂SO₄ for 60 min, it presented the highest catalytic property, with the removal rate of potassium chromate of 96.3% during the PC reduction process under the experimental conditions.     

The role of nanosized gold particles in adsorption and oxidation of carbon monoxide over Au/Fe2O3 Catalyst

The presence of gold is found to promote the development of weakly bonded (CO)_ad species over the surface of Au/Fe₂O₃ catalyst during interaction with carbon monoxide (CO) or a mixture of carbon monoxide and oxygen. The concentration of these species and the nature of the bonding depend on the gold particle size. No such species are formed for gold particles larger than ∼11 nm or over gold-free iron oxide. The bulk carbonate-like species, formed in the process with the involvement of the hydroxy groups of the support, are merely side products not responsible for the low temperature activity of this catalyst.     

制备条件对Au/AC催化分解臭氧性能的影响

研究了活性炭负载的金催化剂(Au/AC)对低浓度臭氧的催化分解性能,考察了前驱体溶液pH值、干燥方式、焙烧温度等制备条件对催化剂活性的影响,以及空速对臭氧分解率的影响。结果表明,在金前驱体溶液pH值为10、经微波辐射干燥、200℃氢气还原制备的催化剂,金颗粒在活性炭表面的分布更加均匀,尺寸更小,具有更高的催化活性。在室温、相对湿度45%和空速72000h-1时,对浓度为50mg/m3臭氧的分解率保持在90%以上(在2400min内)。N2吸附-脱附和XPS表征结果表明,活性炭载金催化剂在催化分解臭氧后,比表面积和孔体积略有下降;Au4f的XPS峰虽稍向高能方向移动,但仍保持催化活性;活性炭表面碳含量显著下降而氧含量大幅增加,说明活性炭上负载的Au在自身催化分解臭氧的同时,还起到了促进臭氧与单质碳反应的作用。     

Aqueous phase epoxidation of 1-butene catalyzed by suspension of Au/TiO2 +TS-1

A combination of two catalysts, Au/TiO₂ and TS-1 were used to catalyze the demanding reaction of butene epoxidation in an aqueous solution using molecular oxygen under very mild reaction conditions. Peroxy initiator was not necessary but carbon monoxide as a sacrificial reductant was needed. Carbon monoxide conversions increase with time on stream suggesting the generation of a highly active aqueous phase CO oxidation catalyst.     

掺杂Sn对V/UiO-66催化剂抗碱金属性能的影响

采用浸渍法,以UiO-66为载体,制备了V/UiO-66及改性Sn-V/UiO-66催化剂,并对催化剂的碱金属钾中毒进行了模拟,探讨了钒钛催化剂的反应机理和失活机理。结果表明,K负载后催化剂的晶型变化不大并且催化剂比表面积的变化呈现不规律波动。负载了碱金属以后,催化剂的金属氧化还原性能和表面酸量迅速降低,这是催化剂活性降低的主要原因。添加Sn能够增强VO_x与其他组分的相互作用,进而提高VO_x的可还原性及V⁵⁺的占比,使Sn-V/UiO-66催化剂表面的VO_x提供更多的酸性位点。中毒后的K-Sn-V/UiO-66催化剂仍然具有较高的总酸量和较强的氧化还原性,表明Sn-V/UiO-66催化剂具有优异的抗碱金属中毒能力。     

简单一步法合成Co9S8氧还原反应电催化剂

采用低温回流技术,以Co₄(CO)₁₂和S粉为原料,在1, 6-己二醇溶剂中一步合成了钴硫化物催化剂。用X射线衍射仪和扫描电子显微镜对合成的化合物进行了表征。XRD分析表明合成样品为立方结构的Co₉S₈化合物,其SEM图片显示了花椰菜状的表面形貌。Co₉S₈化合物表现出良好的氧还原催化活性,开路电位为0.75 V(vs. NHE)。在电荷转移控制电位区,电极反应传递系数和塔菲尔斜率分别为0.50和119 mV。同时,将催化剂的催化活性和电化学稳定性与商业铂催化剂进行了比较。     

Influence of substrate temperature on the preparation of GaP thin films

Gallium phosphide (GaP) was prepared by treating specpure gallium with AnalaR grade Zn₃P₂ in an argon atmosphere. Thin films of GaP were evaporated onto glass substrates at various substrate temperatures under vacuum. Films evaporated onto substrates at and above 250°C were polycrystalline in nature. Films of various thicknesses were grown. The conductivity of these films in the dark and in white light is presented for the temperature range 100–300 K. Optical absorption spectra for films grown at substrate temperatures T_s = 90, 180 and 250°C were also recorded in the range 0.5–2.5 eV. All the features are attributed to the structural disorder which probably occurs during evaporation onto the glass substrates.     

Catalytic performance and kinetics of Au/γ-Al_2O_3 catalysts for low-temperature combustion of light alcohols

Au/γ-Al2O3 catalysts were prepared by deposition-precipitation method for the catalytic combustion of low concentration alcohol streams(methanol,ethanol,iso-propanol and n-propanol).The catalysts were characterized by X-ray photoelectron spectroscopy(XPS),X-ray diffractometry(XRD) and energy dispersive X-ray micro analysis(EDS) techniques.The XPS results showed that there was only Au0 on the surface of catalysts.The XRD patterns showed that Au was presumably highly dispersed over γ-Al2O3.The temperatures for complete conversion of methanol,ethanol,iso-propanol and n-propanol with concentration of 2.0 g/m3 were 60,155,170 and 137 ℃,respectively,but they were completely mineralized into CO2 and H2O at 60,220,260 and 217 ℃ respectively over the optimized catalyst.The activity of the catalyst was stable in 130 h.The kinetics for the catalytic methanol elimination followed quasi-first order reaction expressed as r=0.652 8c0+0.084 2.The value of apparent activation energy is 54.7 kJ/mol in the range of reaction temperature.     

Enhanced hydrogen sorption properties in the LiBH4-MgH2 system catalysed by Ru nanoparticles supported on multiwalled carbon nanotubes

The LiBH₄-MgH₂ system has a high reversible hydrogen storage capacity. However, the hydrogen de/absorption kinetics has to be further enhanced for its practical application. Motivated by the possibility that the metal catalysts facilitating the dissociation and combination of hydrogen molecules and activating Mg-H and B-H bonds, a novel catalyst, ruthenium nanoparticles supported on multiwalled carbon nanotubes (Ru/C) is prepared and its effect on the hydrogen sorption properties of LiBH₄-MgH₂ systems is investigated. The experimental results show that the Ru/C catalyst is active in reducing the dehydrogenation temperature and enhancing the dehydrogenation kinetics. Furthermore, the reversible capacity is also markedly enhanced under moderate conditions, and the catalytically enhanced hydrogen absorption capacity persists well during three de/rehydrogenation cycles.