Photocatalytic reaction of H2O+CO2 over pure and doped Rh/TiO2

In the photocatalytic reduction of carbon dioxide to formic acid, formaldehyde and methanol in aqueous suspensions of TiO₂ and Rh/TiO₂, the effects of doping the TiO₂ with W⁶⁺ were investigated.This laboratory is a part of the Center for Catalysis, Surface and Material Science at the University of Szeged.     

Rh single atoms embedded in CeO2 nanostructure boost CO2 hydrogenation to HCOOH

CO₂ hydrogenation to value-added chemicals is a promising pathway to solve CO₂-relevant environmental problems but still remains a great challenge. Herein, we report a CeO₂ nanostructure supported Rh single atoms (Rh-SAs/CeO₂) catalyst and was used for the efficient CO₂ hydrogenation to HCOOH. The Rh-SAs/CeO₂ exhibited high catalytic activity with turnover numbers (TON) up to 221 at 200 ℃, which was 4-fold to that of CeO₂ supported Rh nanoparticles (Rh-NPs/CeO₂). Moreover, HCOOH selectivity for Rh-SAs/CeO₂ reached 85%, much higher than that of Rh-NPs/CeO₂ (46%). Mechanism studies revealed that Rh single atoms in the Rh-SAs/CeO₂ with high metal atoms utilization efficiency not only provided abundant active sites to promote the catalytic activity, but also suppressed the decomposition of HCOOH to CO and benefited the formation of HCOOH.     

电泳披覆奈米二氧化钛薄膜之开发与特性研究

本研究将奈米二氧化钛粉体以电泳披覆法披覆于不锈钢电极基材表面,并进行后续热处理,以增加其附着强度.实验结果显示,奈米二氧化钛薄膜经600℃烧结处理后,结构上仍为锐钛矿相之二氧化钛,并未有明显变化,且能有效的增加薄膜与基材间之黏着性;然而经过800℃烧结处理后,薄膜结构由锐钛矿相之二氧化钛逐渐相变化为金红石相,应力变化引起裂缝产生,并导致奈米二氧化钛薄膜性质降低.     

A study on effect of Rh precursor and La addition on N2O decomposition over Rh catalyst

The decomposition of N₂O in the presence of oxygen was studied on Rh/CeO₂ and Rh/La₂O₃–CeO₂ catalysts prepared by wet impregnation method. The conversion of N₂O decomposition increased as the Rh loading increased, and the Rh-chloride catalyst showed a poor activity than the Rh-nitrate catalyst. XPS and IC/ICP analysis confirmed that the Rh-chloride catalyst's low activity caused since Rh-chloride catalyst had the some RhCl₃ species. N₂O decomposition rate over Rh/La₂O₃–CeO₂ catalysts decreased as the La loading increased due to the SMSI effect between Rh and CeO₂. H₂ TPR confirmed that the activity and reducibility of the catalyst were closely related.     

CO2 Hydrogenation on Rh/TiO2 Previously Reduced at Different Temperatures

Hydrogenation of CO₂ was studied on 1% Rh/TiO₂ reduced at different temperatures. The interaction of CO₂ with the catalyst and that of the CO₂+H₂ mixture was also studied. FTIR and TPD measurements revealed that CO₂ dissociation depends on the reduction temperature of the catalyst. In the surface reaction, besides Rh carbonyl hydride, formate groups and different carbonates and surface formyl species were also formed. The surface concentration of the formyl group depended on the reduction temperature. The initial rate of CO₂ hydrogenation significantly increased with increasing reduction temperature but after some time it drastically decreased. The promotion effect of the reduction temperature was explained by the formation of oxygen vacancies on the perimeter of the Rh/TiO₂ interface, which can be re-oxidized by the adsorption of CO₂ and H₂O.     

纯钛表面电沉积羟基磷灰石复合涂层组织及性能

采用水热电沉积法在纯钛基体表面制备前驱体,对其进行碱液处理和真空热处理后得到羟基磷灰石(HA)复合涂层.采用XRD、SEM和激光共聚焦显微镜分析涂层物相结构、组织形貌,利用热震法和模拟体液浸泡法表征涂层结合强度和生物活性.实验结果表明:前驱体主要成分为CaHPO4·2H2O、Ca3(PO4)2和CaTiO3,经室温碱液处理10 h后,涂层物相由Ca10(PO4)6(OH)2(简称:HA)、Ca3(PO4)2和CaTiO3组成,组织形貌由前驱体的块状转变为细针状HA晶体.当温度一定时,涂层厚度在4.5 V电压下达到最大值38μm,热震次数在4 V电压下达到最大值11次;当电压一定时,涂层厚度在40℃和50℃下均为最大值35μm,热震次数在40℃下达到最大值11次.沉积电压为4 V、水浴温度为40℃工艺条件下的涂层经体外生物活性测试表明:HA复合涂层表面可在模拟体液中形成新的HA晶核,并不断长大.     

负载TiO2杏仁壳活性炭对亚甲基蓝的光解研究

研究了负载TiO2杏仁壳活性炭对亚甲基蓝的光解催化效果。结果表明,在室温下、pH值5.0亚甲基蓝初始浓度10.0 mg/L 50.0 mL溶液,加入负载TiO2杏仁壳活性炭100.0 g/L和30%H2O220.0 mL/L,用24 W紫外灯光照射60 min,亚甲基蓝降解率96.75%。对于光解亚甲基蓝负载TiO2杏仁壳活性炭具有与商业纳米TiO2P25近似效果。     

Photocatalytic oxidation of ethane over TiO2

The photocatalytic oxidation of ethane has been studied at room temperature using a specially designed stirred reactor. The effect on the rate of ethane oxidation, of the partial pressure of reactants, the UV light intensity, the amount of catalyst and the residence time has been evaluated. Running the experiments according to a factorial plan permitted to deduce from a limited amount of experimental data the complete kinetic model corresponding to the steady state adsorption mechanism. On the basis of the experimental critical mass of the catalyst (1.5 g), an expression permitting calculation of the critical mass of the catalyst (TiO₂) for any type of photocatalytic reactor has been derived.     

Benzaldehyde synthesis via styrene oxidation by O2 over TiO2 and TiO2/SiO2

Styrene was oxidized by molecular oxygen over TiO₂ and TiO₂/SiO₂ for the formation of benzaldehyde. In the absence of catalyst at 100 °C and 10 atm O₂, polystyrene is the major product. Over the catalysts, the oxidation of styrene is enhanced with benzaldehyde and formaldehyde being the major whereas phenylacetaldehyde, acetophenone, styrene oxide, benzoic acid, and polymer being the minor products. The polymerization of styrene was initiated by the radicals formed in the oxidation reaction. The addition of radical inhibitor nitrobenzene and/or the employment of a catalyst of high specific surface area can promote the termination of the radicals, and hence improve the selectivity of benzaldehyde.     

Low-temperature steam reforming ofn-butane over Rh and Ru catalysts supported on ZrO2

In the 500 ° C steam reforming reaction ofn-butane, Rh and Ru catalysts supported on ZrO₂ exhibited high catalytic activities for hydrogen production at a low steam-to-carbon ratio with little activity decline.     

Optical and Structural Properties of TiO2 Thin Films Deposited by RF Magnetron Sputtering

Silicon - Titanium dioxide thin films were grown by RF magnetron sputtering. After that, deposited TiO2 films were annealed at 300 °C for 2 h. Having used different oxygen flow rates as a...     

Mechanism of degradation of nitrilotriacetic acid by heterogeneous photocatalysis over TiO2 and platinized TiO2

TiO₂-heterogeneous photocatalysis of nitrilotriacetic acid (NTA) at pH 2.5 was studied to establish the kinetic regime and the reaction mechanism. Pure Degussa P-25 and Hombikat UV100 commercial samples were compared. A Langmuirian behavior was observed over P-25. Platinization of the Hombikat sample (0.5 wt.%) caused an important increase on the photocatalytic rate with a change in the kinetics from zero order in the pure precursors to first order in the platinized sample. The nature of the intermediates and their evolution with time were compared on all systems. Glycine, iminodiacetic and oxamic acids have been identified in different proportions, together with ammonium and glycolic acid, depending on the catalyst used. The rapid depletion of NTA was not accompanied by a corresponding total organic carbon (TOC) reduction, but 84% of TOC decrease was obtained on P25 after 24 h, a very reasonable result for refractory compounds. A detailed mechanism is proposed for the photocatalytic reaction, suggested to be the same over the three catalysts here tested.     

CO2 reforming of methane over vanadia-promoted Rh/SiO2 catalysts

The reforming of methane with carbon dioxide over rhodium dispersed on silica, Rh/SiO₂, and vanadia-promoted silica, Rh/VO_x/SiO₂, was studied by kinetic test reactions under differential conditions in a temperature range from 723 to 773 K. Transmission infrared spectroscopy was applied to observe the interaction of CO₂ with the catalysts and the formation of surface intermediates during the CO₂–CH₄ reforming reaction. To analyze carbon deposition XP spectroscopy and TPO was carried out. It has been shown that the promotion of Rh/SiO₂ catalysts with vanadium oxide enhances the catalytic activity for CO₂ reforming of methane and decreases the deactivation by carbon deposition. This is attributed to the formation of a partial VO_x overlayer on the Rh surface, which reduces the size of accessible ensembles of Rh atoms required for coke formation and creates new sites at the Rh–VO_x interfacial region that are considered to be active sites for the activation/dissociation of carbon dioxide. This revised version was published online in June 2006 with corrections to the Cover Date.     

TiO2/SiO2的制备及其对茜素红溶液的降解动力学

以钛酸四丁酯和正硅酸乙酯为前驱体，冰醋酸为水解抑制剂，采用溶胶-凝胶法制备了TiO₂/SiO₂复合物。X射线衍射和红外光谱等表征结果表明，纳米TiO₂/SiO₂粒子焙烧后主要以锐钛型存在，有Ti—O—Si键产生。在实验浓度范围，光催化降解茜素红反应符合一级动力学规律，采用半衰期法确定反应级数为0.82。     

The non-linear behaviour of the NO-H2 reaction over Rh surfaces

In this paper we describe the non-linearity of the NO-H₂ reaction over Rh surfaces. Rate oscillations have been observed over a stepped (111) surface with (100) steps, (Rh(533) at low pressures (10^?4 Pa) below 500 K, while no oscillations could be observed under these conditions over a Rh(100) surface and a stepped (100) surface with (111) steps, Rh(711). The thermal stability of the N atoms formed during the reaction explains the observed structure sensitivity. Moreover, the results suggest that diffusion of N atoms is needed to synchronise the rate oscillations, a process that is absent on Rh(100) and Rh(711).     

Photodegradation of o‐Cresol with Ag Deposited on TiO2 under Visible and UV Light Irradiation

This study investigated the effect of dosage of Ag on the characteristics of TiO₂, quantum yield, and temporal decomposition behavior of o‐cresol in an annular reactor under ultraviolet (UV) and visible light irradiation. In order to extend light absorption and minimize the rapid recombination during photoreaction, the Ag deposited on TiO₂ photocatalysts was prepared by a photodeposition process. The results of diffuse reflectance spectra (DRS) indicated that Ag deposited on TiO₂ promoted the optical absorption in the visible region and made it possible for it to be excited by visible light. The degradation rate of o‐cresol with 0.50 wt % Ag/TiO₂ under visible light irradiation was 2.0 times that with pure TiO₂.     

Catalytic decomposition of N2O over supported Rh catalysts: effects of supports and Rh dispersion

The study of catalytic decomposition of nitrous oxide to nitrogen and oxygen over Rh catalysts supported on various supports (USY, NaY, Al₂O₃, ZrO₂, FSM-16, CeO₂, La₂O₃) showed that the activities of Rh/Al₂O₃ and Rh/USY (ultrastable Y zeolite) catalysts were comparable to or higher than the other catalysts reported in the literatures. The catalytic activity of N₂O decomposition was sensitive not only to the Rh dispersion but also to the preparation variables such as the Rh precursors and the supports used. A pulsed N₂O experiment over a Rh/USY catalyst suggested that the catalytic N₂O decomposition occurs on oxygen-covered surface and that O₂ may be freed on collision of N₂O molecules with the adsorbed oxygen atoms.     

Photocatalytic nitrate reduction over metal modified TiO2

Photocatalytic removal of nitrates from water was examined using Cu, Fe and Ag containing titania based materials, and using a range of hole scavengers. In the presence of formic acid, complete nitrate removal was possible with all catalysts. All catalysts presented high activities and overall selectivites, with Ag containing catalysts in particular reaching residual levels of nitrite and ammonium below the EU guideline levels for drinking water. Some titania samples exhibited an induction period prior to the onset of nitrate removal and the size of the titania particles was found to influence the photocatalytic performance. An extended induction period for iron containing catalysts, which was absent during second and subsequent reaction tests, was attributed to a leaching of part of the Fe from the catalysts to reveal active sites of the titania support.