2,4，6-三硝基甲苯的光催化降解

在模拟日光下利用Pt／TiO2光催化剂对水中2,4,6-三硝基甲苯（TNT,梯恩梯）进行了光催化降解,在有催化剂存在时,TNT的破坏更快更彻底,其降解遵循一级反应动力学．TNT分子上的硝基部分转化为硝酸根离子和亚硝酸根离子．Pt／TiO2光催化剂加速了亚硝酸根离子向硝酸根离子的氧化,在2．5h内,终产物硝酸根离子的含量比没有催化剂时提高了32.3倍．     

光照和加热条件下Pt/TiO_2催化二氧化碳加氢(英文)

浸渍法制备了Pt负载量为0.5 to 2%的Pt/TiO2催化剂,考察它们在光照和加热条件下二氧化碳催化加氢性能.结果表明,二氧化碳加氢反应均可在Pt/TiO2的催化下进行,但在不同反应条件下加氢反应通过不同方式进行.在加热条件下,二氧化碳可转化为一氧化碳和甲烷,且在低温加热条件下一氧化碳是主产物(CO选择性为100%,250℃,0.5%Pt/TiO2).在1.5%Pt/TiO2催化剂上,当反应温度从250℃升高到450℃时,CH4的选择性由0增加到60.94%.同时,增加Pt的负载量也会导致CH4的选择性的增加.然而,在光照条件下,产物只有甲烷.CO2-TPD结果表明,二氧化碳通过羰基基团与作为吸附中心的Pt相连接.结合催化活性与表征结果,提出在光照条件下,反应可能以二氧化碳和氢气分别被光生电子活化反应生成甲酸中间体,随后经由甲酸加氢和脱水生成甲烷的机理进行.而在加热条件下,反应可能以二氧化碳首先吸附在催化剂表面形成羰基Pt物种,随后加氢生成一氧化碳,一氧化碳继续加氢生成甲烷的机理进行.     

The photocatalytic and thermal catalytic reduction of CO2 with H2 over Pt/TiO2 catalysts

浸渍法制备了Pt负载量为0.5 to 2%的Pt/TiO2催化剂,考察它们在光照和加热条件下二氧化碳催化加氢性能.结果表明,二氧化碳加氢反应均可在Pt/TiO2的催化下进行,但在不同反应条件下加氢反应通过不同方式进行.在加热条件下,二氧化碳可转化为一氧化碳和甲烷,且在低温加热条件下一氧化碳是主产物(CO选择性为100%,250℃,0.5%Pt/TiO2).在1.5%Pt/TiO2催化剂上,当反应温度从250℃升高到450℃时,CH4的选择性由0增加到60.94%.同时,增加Pt的负载量也会导致CH4的选择性的增加.然而,在光照条件下,产物只有甲烷.CO2-TPD结果表明,二氧化碳通过羰基基团与作为吸附中心的Pt相连接.结合催化活性与表征结果,提出在光照条件下,反应可能以二氧化碳和氢气分别被光生电子活化反应生成甲酸中间体,随后经由甲酸加氢和脱水生成甲烷的机理进行.而在加热条件下,反应可能以二氧化碳首先吸附在催化剂表面形成羰基Pt物种,随后加氢生成一氧化碳,一氧化碳继续加氢生成甲烷的机理进行.     

光催化降解污染物制氢反应与原位红外表征

研究了在Pt/TiO2悬浮体系中单组分和双组分污染物为电子给体光催化分解水制氢反应. 比较了污染物甲醛、甲酸和草酸为电子给体光催化放氢反应效率，发现其活性为：草酸 >甲酸 >甲醛.原位ATR（衰减全反射）红外研究结果表明，光催化放氢活性与污染物吸附特性有关.还研究了草酸与甲酸双组分污染物体系的光解水放氢和污染物降解动力学，发现总的放氢和污染物降解速率与污染物组分在TiO2表面的吸附强度和溶液浓度有关.污染物在TiO2表面的竞争吸附决定了反应动力学.原位ATR-IR方法研究双组分混合物体系的吸附，直观地证实了上述结果.     

铂负载二氧化钛光催化剂在单波长下苯乙炔高选择性加氢（英文）

苯乙烯是一种非常重要的化工原料,它是工业上生产聚苯乙烯、树脂和丁苯橡胶的重要单体,而苯乙烯单体中经常含有苯乙炔杂质,影响苯乙烯的聚合性能,因此研究苯乙炔选择性加氢生成苯乙烯具有十分重要的工业意义.传统的热催化苯乙炔加氢反应会用到易燃易爆的氢气,引起操作的危险性,因此,开发具有环境友好型的加氢反应体系具有很重要的意义.光催化加氢反应利用光生电子强的还原能力,还原质子产生活性的氢物种加氢,相较于传统的热催化使用氢气作为加氢源加氢,能够在温和的条件下实现高选择性加氢.基于此,本文利用Pt/TiO2作为光催化剂,甲醇作为加氢源实现了在385 nm单波长光照下苯乙炔的高选择性加氢.首先,我们利用光沉积的方法将Pt负载在TiO2的表面,通过透射电子显微镜图像和紫外可见吸收光谱表征了负载在TiO2表面Pt的颗粒分布和光学性质.结果表明负载的Pt的颗粒大约在5 nm左右,Pt的负载改变了TiO2在可见光区的吸收性能.XPS结果显示,通过光沉积得到的Pt的价态为金属态和氧化态共存.光催化苯乙炔加氢实验表明,Pt/TiO2催化剂在室温常压条件下不仅具有高的苯乙炔光催化转化率,当光照达8 h后,苯乙炔完全转化,而且在6 h之内苯乙烯选择性保持在91.3%,具有高的苯乙烯选择性.通过对负载的Pt的含量进行了优化,筛选出当Pt的负载量为1 wt%时,苯乙炔的转化率最高.为了对比,利用传统热催化的方法氢气作为加氢源进行了苯乙炔加氢实验,结果发现,使用氢气作为加氢源时,虽然苯乙炔的转化率为100%,但产物是过加氢的产物乙苯.这主要是因为在光催化反应过程中,TiO2导带上的电子迁移至Pt颗粒上,导致Pt的电子密度增加,Pt颗粒表面高的电子密度有利于加氢中间产物苯乙烯的脱附,因此,在光催化加氢过程中不会发生过加氢反应,具有高的苯乙烯选择性.同时,扩展实验表明,Pt/TiO2光催化剂对其他类型的炔烃加氢也具有高的选择性,表明Pt/TiO2光催化炔烃加氢具有普适性.由此可见,光催化炔烃加氢未来将成为一种环境友好而高效的方法.     

纳米Pt/TiO2催化剂上气相CH3OH光催化分解制氢反应的研究

利用不同还原方法制备了不同纳米粒度的Pt/tiO2光催化剂,并且用脉冲氢氧滴定法测定了TiO2表面Pt的分散度.在气相连续流动装置中利用纳米Pt/tiO2作为光催化剂,对气相甲醇的脱氢反应进行了研究.研究了添加Pt和不添加Pt的纳米TiO2,Pt负载量、铂的不同还原方法、不同TiO2纳米粒度对气相甲醇光催化分解反应的影响,并对反应气的空速、光照时间、添加水蒸汽、改变甲醇浓度等与光催化分解甲醇制氢的关系进行了研究,在最佳反应条件下,产氢速率达到5.808 mmol/(g·h).研究了反应的动力学,得到该反应为一级反应,求得了该反应的活化能为8.53 kJ/mol,并讨论了反应机理.     

污染物甲醛为电子给体Pt/TiO2光催化制氢

研究了甲醛为电子给体在Pt/TiO2上光催化生成氢的反应。甲醛经光催化降解产生CO2和甲酸，甲酸可进一步被氧化；甲醛的光催化降解与放氢同时发生，催化剂的最佳Pt负载量为0．5％，甲醛浓度对反应的影响，表观上符合Langmuir-Hinshelwood关系式；碱性条件有利于该反应；在甲醛浓度较低时，甲醇的存在能部分地提高放氢速率，并讨论了可能的反应机理。     

采用CO吸附原位红外光谱研究Pt/TiO_2光催化体系中助催化剂作用

采用CO作为探针分子,将原位透射红外光谱应用于研究助催化剂Pt在Pt/TiO2光催化体系中的作用.实验发现,光照条件下,CO的覆盖度及样品温度没有明显变化,CO在Pt/TiO2上的吸附峰红移11 cm–1,在Pt/Al2O3上的吸附峰没有位移,表明CO在Pt/TiO2上的红移来源于TiO2上的光生电子转移到Pt上,这解释了为什么加入Pt助催化剂可提高光催化产氢活性.     

采用CO吸附原位红外光谱研究Pt/TiO2光催化体系中助催化剂作用

采用CO作为探针分子,将原位透射红外光谱应用于研究助催化剂Pt在Pt/TiO2光催化体系中的作用.实验发现,光照条件下,CO的覆盖度及样品温度没有明显变化,CO在Pt/TiO2上的吸附峰红移11 cm–1,在Pt/Al2O3上的吸附峰没有位移,表明CO在Pt/TiO2上的红移来源于TiO2上的光生电子转移到Pt上,这解释了为什么加入Pt助催化剂可提高光催化产氢活性.     

Ag改性提高TiO2对Cr(Ⅵ)的光催化还原活性机理

在消除了质子缺乏、光生电子-空穴复合对Cr6+光催化还原负效应影响下,比较了TiO2和Ag/TiO2(Ag质量分数1.0%)光催化还原活性.结果表明,相同条件下Ag/TiO2表现出比TiO2更高的催化活性.EPR分析表明,对于Ag/TiO2,UV照射后Ag表面有活性物种O-2生成,在TiO2上有活性中心表相Ti3+生成.光生电子通过表相Ti3+向Cr6+传递电子是Cr6+光催化还原的速度控制步骤.较多的表相Ti3+参与还原反应是Ag/TiO2表现出较高催化活性的主要原因,担载Ag上积聚光生电子的较强流动性对反应也起到一定促进作用.     

甲酸存在下硝酸根在二氧化钛表面光催化还原成氨

用甲酸作空穴清除剂,研究了ＴｉＯ２水悬浮体系中硝酸根光催化还原氨的反应。与草酸作空穴清除剂相比,甲酸加速硝酸根的还原更显著。研究了硝酸根和甲酸根的浓度效应及ｐＨ效应。实验结果表明,硝酸根在ＴｉＯ２表面的吸附是加附是加速该光催化还原反应的重要因素。     

Gas-chromatographic determination of carboxylic acid anhydrides in oxidation products of alcohols and other organic compounds

A procedure was developed for the gas-chromatographic determination of carboxylic acid anhydrides in the composition of oxidation products of organic compounds after their conversion into alkyl formate by formic acid and benzyl alcohol or other primary alcohol introduced into the reaction medium. The reaction proceeds through the mixed anhydride, which is formed in situ from formic acid and the determined anhydride and is predominantly transformed into the corresponding alkyl formate in alcoholysis with alcohol. The potentialities of the procedure were illustrated by the determination of anhydrides in oxidation products of cyclohexane, cyclohexanone, and cyclohexanol.     

Photochemistry of the indoor air pollutant acetone on Degussa P25 TiO2 studied by chemical ionization mass spectrometry

We have used chemical ionization mass spectrometry (CIMS) to study the adsorption and photochemistry of several oxygenated organic species adsorbed to Degussa P25 TiO2, an inexpensive catalyst that can be used to mineralize volatile organic compounds. The molecules examined in this work include the common indoor air pollutant acetone and several of its homologs and possible oxidation and condensation products that may be formed during the adsorption and/or photocatalytic degradation of acetone on titanium dioxide catalysts. We report nonreactive uptake coefficients for acetone, formic acid, acetic acid, mesityl oxide, and diacetone alcohol, and results from photochemical studies that quantify, on a per-molecule basis, the room-temperature photocatalytic conversion of the species under investigation to CO2 and related oxidation products. The data presented here imply that catalytic surfaces that enhance formate and acetate production from acetone precursors will facilitate the photocatalytic remediation of acetone in indoor environments, even at room temperature.     

A Revisit to the Role of Bridge-adsorbed Formate in the Electrocatalytic Oxidation of Formic Acid at Pt Electrodes (cited: 2)

The mechanism and kinetics of electrocatalytic oxidation of formic acid at Pt electrodes is discussed in detail based on previous electrochemical in-situ ATR-FTIRS data [Langmuir 22, 10399 (2006) and Angewa. Chem. Int. Ed. 50, 1159 (2011)]. A kinetic model withformic acid adsorption (and probably the simultaneous C-H bond activation) as the rate determining step, which contributes to the majority of reaction current for formic acid oxi-dation, was proposed for the direct pathway. The model simulates well the IR spectroscopic results obtained under conditions where the poisoning effect of carbon monoxide (CO) is negligible and formic acid concentration is below 0.1 mol/L. The kinetic simulation predicts that in the direct pathway formic acid oxidation probably only needs one Pt atom as active site, formate is the site blocking species instead of being the active intermediate. We review in detail the conclusion that formate pathway (with either 1st or 2nd order reaction kinetics) is the direct pathway, possible origins for the discrepancies are pointed out.     

In situ FTIR Study of the Adsorption of Formaldehyde, Formic Acid, and Methyl Formiate at the Surface of TiO2 (Anatase)

The catalytic properties of TiO₂ (anatase) in the reactions of formaldehyde oxidation and formic acid decomposition are examined. At 100–150°C, formaldehyde is converted into methyl formate with high selectivity regardless of the presence of oxygen in the reaction mixture. Formic acid is decomposed to CO and water. Surface compounds formed in the reactions of formaldehyde, formic acid, and methyl formate with TiO₂ (anatase) are identified by in situ FTIR spectroscopy. In a flow of a formaldehyde-containing mixture at 100°C, H-bonded HCHO, dioxymethylene species, bidentate formate, and coordinatively bonded HCHO are observed on the TiO₂ surface. In the adsorption of formic acid, H-bonded HCOOH and two types of formates (bidentate and unsymmetrical formates) are formed. In the adsorption of methyl formate, H-bonded HCOOCH₃, HCOOCH₃ coordinatively bonded via the carbonyl oxygen, and bidentate formate are identified.     

Mechanistic study of electrocatalytic oxidation of formic acid at platinum in acidic solution by time-resolved surface-enhanced infrared absorption spectroscopy

Surface-enhanced infrared absorption spectroscopy (SEIRAS) combined with cyclic voltammetry or chronoamperometry has been utilized to examine kinetic and mechanistic aspects of the electrocatalytic oxidation of formic acid on a polycrystalline Pt surface at the molecular scale. Formate is adsorbed on the electrode in a bridge configuration in parallel to the adsorption of linear and bridge CO produced by dehydration of formic acid. A solution-exchange experiment using isotope-labeled formic acids (H(12)COOH and H(13)COOH) reveals that formic acid is oxidized to CO(2) via adsorbed formate and the decomposition (oxidation) of formate to CO(2) is the rate-determining step of the reaction. The adsorption/oxidation of CO and the oxidation/reduction of the electrode surface strongly affect the formic acid oxidation by blocking active sites for formate adsorption and also by retarding the decomposition of adsorbed formate. The interplay of the involved processes also affects the kinetics and complicates the cyclic voltammograms of formic acid oxidation. The complex voltammetric behavior is comprehensively explained at the molecular scale by taking all these effects into account.     

Bridge-bonded formate: active intermediate or spectator species in formic acid oxidation on a Pt film electrode?

We present and discuss the results of an in situ IR study on the mechanism and kinetics of formic acid oxidation on a Pt film/Si electrode, performed in an attenuated total reflection (ATR) flow cell configuration under controlled mass transport conditions, which specifically aimed at elucidating the role of the adsorbed bridge-bonded formates in this reaction. Potentiodynamic measurements show a complex interplay between formation and desorption/oxidation of COad and formate species and the total Faradaic current. The notably faster increase of the Faradaic current compared to the coverage of bridge-bonded formate in transient measurements at constant potential, but with different formic acid concentrations, reveals that adsorbed formate decomposition is not rate-limiting in the dominant reaction pathway. If being reactive intermediate at all, the contribution of formate adsorption/decomposition to the reaction current decreases with increasing formic acid concentration, accounting for at most 15% for 0.2 M DCOOH at 0.7 VRHE. The rapid build-up/removal of the formate adlayer and its similarity with acetate or (bi-)sulfate adsorption/desorption indicate that the formate adlayer coverage is dominated by a fast dynamic adsorption-desorption equilibrium with the electrolyte, and that formate desorption is much faster than its decomposition. The results corroborate the proposal of a triple pathway reaction mechanism including an indirect pathway, a formate pathway, and a dominant direct pathway, as presented previously (Chen, Y. X.; et al. Angew. Chem. Int. Ed. 2006, 45, 981), in which adsorbed formates act as a site-blocking spectator in the dominant pathway rather than as an active intermediate.     

Oxygen vacancy promoting catalytic dehydration of formic acid on TiO2(110) by in situ scanning tunneling microscopic observation

The catalytic dehydration reaction processes of formic acid on a TiO2(110) surface at 350 K have been studied to visualize reaction intermediates and their dynamic behaviors by scanning tunneling microscopy. Three types of configurations of adsorbed formates on the surface were identified by their shapes and positions in STM images. Successive STM observations revealed transformations among the three configurations, i.e., bridge formate on a 5-fold coordinated Ti4+ row, bridge formate on an oxygen vacancy site with an oxygen atom of formate and on a 5-fold coordinated Ti4+ ion and with the other formate oxygen atom, and a monodentate formate on an oxygen vacancy site with an oxygen atom of formate. The decomposition of the monodentate formate to carbon monoxide and hydroxyl was also imaged, which is a rate-determining step in the catalytic dehydration of formic acid. Combined with first-principle DFT calculations, the overall reaction processes of the catalytic dehydration of formic acid on the surface have been elucidated. Oxygen vacancies on the surface that can be produced by dehydration of two hydroxyls in situ under the catalytic reaction conditions are essential for the reaction.     

Improved hydrogen production from formic acid on a Pd/C catalyst doped by potassium

The rate of hydrogen production from vapour-phase formic acid decomposition can be increased by 1-2 orders of magnitude by doping a Pd/C catalyst with potassium ions. Surface potassium formate and/or bicarbonate species could be involved in the rate-determining step of this reaction.     

Heterogeneous uptake and reactivity of formic acid on calcium carbonate particles: a Knudsen cell reactor, FTIR and SEM study

The heterogeneous uptake and reactivity of formic acid (HCOOH), a common gas-phase organic acid found in the environment, on calcium carbonate (CaCO(3)) particles have been investigated using a Knudsen cell reactor, Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). FTIR measurements show that the adsorption of formic acid on the surface of calcium carbonate results in the formation of calcium formate. Besides calcium formate, carbonic acid is also a reaction product under dry conditions (<1% RH). Under dry conditions and at low pressures, the initial uptake coefficient of formic acid on CaCO(3) particles is measured to be 3 +/- 1 x 10(-3) and decreases as the surface saturates with adsorbed products. The maximum surface coverage of formic acid under dry conditions is determined to be (3 +/- 1)x 10(14) molecules cm(-2). Under humidified conditions (RH >10%), adsorbed water on the surface of the carbonate particles participates in the surface reactivity of these particles, which results in the enhanced uptake kinetics and extent of reaction of this organic acid on CaCO(3) as well as opens up several new reaction pathways. These reaction pathways include: (i) the water-assisted dissociation of carbonic acid to CO(2) and H(2)O and (ii) the formation of calcium formate islands and crystallites, as evident by SEM images. The results presented here show that adsorbed water plays a potentially important role in the surface chemistry of gas-phase organic acids on calcium carbonate particles.