Formation of different products during photo-catalytic reaction on TiO<Subscript>2</Subscript> suspension in water with and without 2-propanol under diverse ambient conditions

Studies on photo-catalytic reduction of CO₂ using TiO₂ photo-catalyst (0.1%, w/v) as a suspension in water was carried out at 350 nm light. CO₂ from both commercially available source, as well as generated in situ through 2-propanol oxidation, was used for this study. The photolytic products such as hydrogen (H₂), carbon monoxide (CO) andmethane (CH₄) generated were monitored in TiO₂ suspended aqueous solution with and without a hole scavenger, viz., 2-propanol. Similar photolytic experiments were also carried out with varying ambient such as air, O₂, N₂ and N₂O. The yields of CO and CH₄ in all these systems under the present experimental conditions were found to be increasing with light exposure time. H₂ yield in N₂-purged systems containing 2-propanol was found to be more as compared to the without 2-propanol system. The rate of H₂ production in N₂-purged aqueous solutions containing 0.1% TiO₂ suspension were evaluated to be 0.226 and 5.8 μl/h, without and with 0.5 M 2-propanol, respectively. This confirmed that 2-propanol was an efficient hole scavenger and it scavenged photo-generated holes (h⁺), allowing its counter ion, viz., e⁻, to react with water molecule/H⁺ to yield more H₂. The formation of both CO and CH₄ in the photolysis of CO₂-purged aqueous solutions containing suspended TiO₂ in absence of 2-propanol reveal that the generation of CH₄ is taking place mainly through CO intermediate. In presence of air/O₂, the yield of H₂ in the system without 2-propanol was observed to be negligible as compared to the system containing 2-propanol in which low yield of H₂ was obtained with a formation rate of approx. 0.5 μl/h.     

Photocatalytic Reduction of Greenhouse Gas CO2 to Fuel

Sun is the Earth’s ultimate and inexhaustible energy source. One of the best routes to remedy the CO₂ problem is to convert it to valuable hydrocarbons using solar energy. In this study, CO₂ was photocatalytically reduced to produce methanol, methane and ethylene in a steady-state optical-fiber reactor under artificial light and real sunlight irradiation. The photocatalyst was dip-coated on the optical fibers that enable the light to transmit and spread uniformly inside the reactor. The optical-fiber photoreactor, comprised of nearly 120 photocatalyst-coated fibers, was designed and assembled. The XRD spectra indicated the anatase phase for all photocatalysts. It is found that the methanol yield increased with UV light intensity. A maximum methanol yield of 4.12 μmole/g-cat h is obtained when 1.0 wt% Ag/TiO₂ photocatalyst was used under a light intensity of 10 W/cm². When mixed oxide, TiO₂–SiO₂, is doped with Cu and Fe metals, the resulting photocatalysts show substantial difference in hydrocarbon production as well as product selectivity. Methane and ethylene were produced on Cu–Fe loaded TiO₂–SiO₂ photocatalyst. Since dye-sensitized Cu–Fe/P25 photocatalyst can fully harvest the light energy of 400–800 nm from sunlight, its photoactivity was significantly enhanced. Finally, CO₂ photoreduction was studied by in situ IR spectroscopy and possible mechanism for the photoreaction was proposed.     

Effect of sodium cation on the electrochemical reduction of CO<Subscript>2</Subscript> at a copper electrode in methanol

The electrochemical reduction of CO₂ with a Cu electrode in methanol was investigated with sodium hydroxide supporting salt. A divided H-type cell was employed; the supporting electrolytes were 80 mmol dm⁻³ sodium hydroxide in methanol (catholyte) and 300 mmol dm⁻³ potassium hydroxide in methanol (anolyte). The main products from CO₂ were methane, ethylene, carbon monoxide, and formic acid. The maximum current efficiency for hydrocarbons (methane and ethylene) was 80.6%, at −4.0 V vs Ag/AgCl, saturated KCl. The ratio of current efficiency for methane/ethylene, r _f(CH₄)/r _f(C₂H₄), was similar to those obtained in LiOH/methanol-based electrolyte and larger relative to those in methanol using KOH, RbOH, and CsOH supporting salts. In NaOH/methanol-based electrolyte, the efficiency of hydrogen formation, a competing reaction of CO₂ reduction, was suppressed to below 4%. The electrochemical CO₂ reduction to methane may be able to proceed efficiently in a hydrophilic environment near the electrode surface provided by sodium cation.     

Ring opening of epoxides with alcohols using Fe(Cp)2BF4 as catalyst

Fe(Cp)₂BF₄ is an efficient catalyst for the alcoholysis of aromatic, aliphatic, and cyclic epoxides giving excellent yields of the corresponding β-alkoxy alcohols under ambient conditions. The methanolysis of styrene oxide using Fe(Cp)₂BF₄ as a catalyst (5 mol %) gave excellent yield of 2-methoxy-2-phenylethanol with complete regio-selectivity. The ring opening of cyclic epoxides gave 77–97% yields of trans-β-methoxy alcohols, in 0.5–6 h. The use of 1,2-epoxyhexane and 1,2-epoxydodecane as substrates gave both regioisomers in excellent yields. The first order rate of reaction with respect to catalyst was observed for the kinetics of ring opening of 1,2-epoxyhexane with methanol.     

Monolayer oxide catalysts from alkoxide precursors, part IV. Vanadia, titania and stibia on SiO2, SnO2, and TiO2 in 2-propanol oxidation

Vanadia monolayer catalysts supported on SnO₂, ZrO₂, TiO₂, and SiO₂, similarly as titania and stibia monolayers deposited on SiO₂, have been synthesized by reacting the corresponding metal alkoxides with hydroxyls on the carrier surfaces. The metal ions loads in monolayer systems were determined. The catalysts activity was tested in 2-propanol transformations. The nature of carrier has a strong influence on the dehydrating to dehydrogenating activity ratio of vanadia monolayer.     

负载型CuO/TiO2催化剂催化CO2加氢制甲醇

采用浸渍法制备了CuO/TiO_2负载型催化剂,并将其用于CO2加氢制甲醇反应。重点考察了铜的负载量对催化剂性能的影响,并对其物化性能和催化性能之间的关系进行了讨论。结果发现,随着铜负载量的增加,催化剂中金属铜的比表面先增加后减小,当铜的负载量为10%(质量百分数)时达到最大值。催化剂的表面碱性位数量随铜含量的增加持续减小,中等碱位和强碱位的强度下降。当铜的负载量不高于10%时,CO2的转化率与铜的比表面积呈线性关系。甲醇选择性与催化剂的表面碱位性质有关,过强的碱性位会降低甲醇选择性。     

负载型CuO/TiO2催化剂催化CO2加氢制甲醇

采用浸渍法制备了CuO/TiO₂负载型催化剂,并将其用于CO₂加氢制甲醇反应。重点考察了铜的负载量对催化剂性能的影响,并对其物化性能和催化性能之间的关系进行了讨论。结果发现,随着铜负载量的增加,催化剂中金属铜的比表面先增加后减小,当铜的负载量为10%（质量百分数）时达到最大值。催化剂的表面碱性位数量随铜含量的增加持续减小,中等碱位和强碱位的强度下降。当铜的负载量不高于10%时,CO₂的转化率与铜的比表面积呈线性关系。甲醇选择性与催化剂的表面碱位性质有关,过强的碱性位会降低甲醇选择性。     

Titania supported copper catalysts for methanol synthesis from carbon dioxide

The effect of co-catalyst (ZnO or ZrO₂) has been tested for hydrogenation of CO₂ on CuO/TiO₂ and CuO/Al₂O₃. CuO−ZnO/TiO₂ catalyst showed the highest activity for methanol synthesis. Kinetic parameters were also determined.     

Effect of metal deposition on the photocatalytic activity of titania-silica for the removal of 2-propanol diluted in water

The influence of transition metals, such as Ag, Cr, and Co, on the photocatalytic properties of titania-silica (TiO₂-SiO₂) prepared via both impregnation (imp) and photo-assisted deposition (PAD) methods has been investigated. The decomposition of 2-propanol under UV-light irradiation was used to probe the effect of transition metals deposition on the activity of titania-silica. PAD-Ag/TiO₂-SiO₂ prepared by the PAD method was highly active compared to the original TiO₂-SiO₂, while imp-Cr/TiO₂-SiO₂ prepared by conventional impregnation method showed a weak tendency toward the decomposition of 2-propanol.     

铬助剂对Cu/ZrO_2/CNTs-NH_2催化剂催化CO_2加氢合成甲醇性能的影响

采用并流共沉淀方法制备了一系列不同铬含量的Cu/ZrO2/CNTs-NH2催化剂,在固定床反应器上考察铬对催化剂催化CO2加氢合成甲醇反应性能的影响.当铬含量为1%(w),反应温度为260°C,压力为3.0MPa,原料气组成为V(H2):V(CO2):V(N2)=69:23:8,空速为3600 mL·h-1·g-1时,催化剂的促进效果最显著,甲醇收率达7.78%.氮吸附、粉末X射线衍射(XRD)、氢气程序升温脱附(H2-TPR)、X射线光电子能谱(XPS)、二氧化碳程序升温脱附(CO2-TPD)、差热分析(DTA)以及扫描电子显微镜(SEM)等表征结果表明,随着铬含量的增加,铜颗粒的粒径减小,催化剂的比表面积增大.铬的加入一方面提高了铜的分散性,抑制了ZrO2的相变和活性组分的烧结;另一方面提高了CO2的吸附量并促进CO2由弱吸附向强吸附转化,从而提高甲醇的收率;但是当铬含量大于1%时,催化剂表面Cu、Zr的总含量明显下降,降低了CO2的吸附量并且形成了超强CO2吸附物种,抑制了CO2及其中间产物的转化,从而降低了甲醇收率.     

Significant roles of oxygen and unbound <Superscript>•</Superscript>OH radical in phenol formation during photo-catalytic degradation of benzene on TiO<Subscript>2</Subscript> suspension in aqueous system

Studies on photo-catalytic degradation of benzene using TiO₂ photo-catalyst as a suspension in water is reported. Degradation studies have been carried out using 350 nm UV light. Phenol, a photo-catalytic product of benzene, was monitored under varying experimental conditions such as amount of TiO₂, concentration of benzene, photolysis time, ambient (air, O₂, Ar, N₂O and N₂O–O₂ mixture), etc. The phenol yields in both aerated and O₂-purged systems increased with the photolysis time. In contrast to oxygenated systems, the yields of phenol in deoxygenated (viz. Ar-purged and N₂O-purged) systems were quite low (~30 μM) and remained steady. H₂O₂ yields in all these systems were also monitored, and found lower than an order of magnitude as compared to phenol yields for the respective systems. The rate of phenol production in aerated 1 mM benzene solution containing 0.05% TiO₂ suspension was evaluated at 12.3 μM min⁻¹ which is lower than the rate obtained in an O₂-saturated system (22.4 μM min⁻¹). The low yields of phenol in both Ar- and N₂O-purged systems, and also the increasing trends in oxygenated systems, together reveal that, for the phenol formation with an enhanced rate, oxygen is essential. In the present study, it is implied that the photo-generated hole, which is mainly an ^•OH radical, is either freely available in the aqueous phase or migrates to the aqueous phase from the catalyst surface, to react with benzene to produce HO-adduct radical. Later, following reaction with oxygen, the adduct produces phenol. On the other hand, h⁺ and surface adsorbed ^•OH radical, being trapped/bonded due to rigid association with the catalyst surface, were not able to generate phenol under similar experimental conditions. The mechanism of phenol formation with TiO₂ photolysis in an aqueous system is rechecked, on the basis of present results on h⁺/surface adsorbed ^•OH radical/unbound ^•OH radical scavenging by benzene, collectively with previous reports on various systems.     

Comparison of CO2 Reduction Performance with NH3 and H2O between Cu/TiO2 and Pd/TiO2

The aim of this study is to clarify the effect of doped metal type on CO₂ reduction characteristics of TiO₂ with NH₃ and H₂O. Cu and Pd have been selected as dopants for TiO₂. In addition, the impact of molar ratio of CO₂ to reductants NH₃ and H₂O has been investigated. A TiO₂ photocatalyst was prepared by a sol-gel and dip-coating process, and then doped with Cu or Pd fine particles by using the pulse arc plasma gun method. The prepared Cu/TiO₂ film and Pd/TiO₂ film were characterized by SEM, EPMA, TEM, STEM, EDX, EDS and EELS. This study also has investigated the performance of CO₂ reduction under the illumination condition of Xe lamp with or without ultraviolet (UV) light. As a result, it is revealed that the CO₂ reduction performance with Cu/TiO₂ under the illumination condition of Xe lamp with UV light is the highest when the molar ratio of CO₂/NH₃/H₂O = 1:1:1 while that without UV light is the highest when the molar ratio of CO₂/NH₃/H₂O = 1:0.5:0.5. It is revealed that the CO₂ reduction performance of Pd/TiO₂ is the highest for the molar ratio of CO₂/NH₃/H₂O = 1:1:1 no matter the used Xe lamp was with or without UV light. The molar quantity of CO per unit weight of photocatalyst for Cu/TiO₂ produced under the illumination condition of Xe lamp with UV light was 10.2 μmol/g, while that for Pd/TiO₂ was 5.5 μmol/g. Meanwhile, the molar quantity of CO per unit weight of photocatalyst for Cu/TiO₂ produced under the illumination condition of Xe lamp without UV light was 2.5 μmol/g, while that for Pd/TiO₂ was 3.5 μmol/g. This study has concluded that Cu/TiO₂ is superior to Pd/TiO₂ from the viewpoint of the molar quantity of CO per unit weight of photocatalyst as well as the quantum efficiency.     

Effect of PEG with different <Emphasis Type="Italic">M</Emphasis><Subscript>W</Subscript> as template direction reagent on preparation of porous TiO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript> with assistance of supercritical CO<Subscript>2</Subscript>

Titania–silica composite have been prepared using polyethylene glycol (PEG) with different molecular weights (M _w), PEG20000, PEG10000, and PEG2000, as template in supercritical carbon dioxide (SC CO₂). The composite precursors were dissolved in SC CO₂ and impregnated into PEG templates using SC CO₂ as swelling agent and carrier. After removing the template by calcination at suitable temperature, the titania–silica composite were obtained. The composite were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, and nitrogen sorption–desorption experiment. Photocatalytic activity of the samples has been investigated by photodegradation of methyl orange. Results indicate that there are many Si–O–Ti linkages in the TiO₂/SiO₂ composite; the PEG template has a significant influence on the structure of TiO₂/SiO₂. In addition, the TiO₂/SiO₂ prepared with PEG10000 exhibited high photocatalytic efficiency. So this work supplies a clue to control and obtain the TiO₂/SiO₂ composite with different photocatalytic reactivity with the aid of suitable PEG template in supercritical CO₂.     

Evaluation of polymeric nanocomposites for the detection of toxic gas analytes

Four different metal oxide nanoparticles, copper oxide (CuO), aluminum oxide (Al₂O₃), nickel oxide (NiO), and titanium dioxide (TiO₂), were added to poly (2,5-dimethyl aniline) (P25DMA) during synthesis to create different polymer nanocomposites. These polymer nanocomposites were evaluated as potential sensing materials for six different gas analytes (acetaldehyde, acetone, benzene, ethanol, formaldehyde, and methanol). It was found that CuO did not incorporate into the P25DMA and only a small percentage of Al₂O₃ was incorporated. However, both NiO and TiO₂ were incorporated into the P25DMA at the same concentration as during the synthesis step. Overall, the type of metal oxide significantly affected the morphology of the sensing material and the amount of each analyte sorbed. For example, P25DMA doped with 5 wt% Al₂O₃ had high selectivity towards ethanol, whereas P25DMA doped with 20 wt% TiO₂ sorbed the most ethanol. However, P25DMA doped with 20 wt% TiO₂ also sorbed a high amount of formaldehyde, making P25DMA doped with 20 wt% TiO₂ less selective than P25DMA doped with 5 wt% Al₂O₃ towards ethanol with respect to formaldehyde.     

Catalytic hydrogen transfer over magnesia, IXa. reduction of long chain aliphatic ketones by 2-propanol

A series of symmetrical long chain aliphatic ketones of general formula CH₃−(CH₂)_n-CO-(CH₂)₂−CH₃, where n=4,5,6,7 and 8, has been used as hydrogen acceptors from 2-propanol at 573–723 K in the presence of MgO catalyst under flow conditions. The yeilds of the appropriate alcohols exceeded 50%. Above 623 K the consecutive dehydration of the alcohols formed took place with moderate yields leading to internal alkenes. The direct one-step synthesis of C₁₃ alkene from 7-tridecanone has been realized under catalytic transfer reduction (CTR) conditions with high yield (>90%) over a MgO catalyst of enhanced acidity. Part VIII: Appl. Catal. A.:General,150, 77 (1997)     

1-丁基-3-甲基咪唑六氟磷酸盐+水+醇体系的相行为

在298.15 K, 常压下研究了1-丁基-3-甲基咪唑六氟磷酸盐([bmim][PF₆])+水+甲醇、[bmim][PF₆]+水+乙醇、[bmim][PF₆]+水+2-丙醇、[bmim][PF₆]+水+1-丙醇三元体系的相行为. 结果表明, 对于含甲醇、乙醇和2-丙醇的体系, 醇在水+醇溶液中摩尔分数分别为0.55-1.00、0.40-0.75 和0.35-0.50 时, 醇的水溶液与[bmim][PF₆]可以互溶. 而水+1-丙醇体系没有此类现象. 这说明, 这类三元系的相行为不但取决于醇分子的大小, 而且取决于其结构.     

A New Type of Photocatalysis Initiated by Photoexcitation of Adsorbed Carbon Dioxide on ZrO2

ZrO₂ has been found to be an effective photocatalyst for reduction of CO₂ by hydrogen or methane at room temperature. The effective photon energy is less than the band gap energy of ZrO₂ (5.0 eV), indicating that photoexcitation of bulk ZrO₂ is not involved. The reaction is initiated by photoexcitation of surface carbonates derived from adsorption of CO₂ to convert it to a CO₂ ^– radical, which in turn reacts with hydrogen or methane to form surface formate. The formate is stable at temperatures below 573 K, but works as a reductant of CO₂ under photoirradiation. A new type of reaction mechanism is proposed.     

Preparation of TiO2 nanocrystalline films controlled by acetylacetone/polyethylene glycol and their photoelectric properties

TiO₂ nanocrystalline films were prepared from titanium tetra-n-butoxide modified with double hydrolysis inhibitors, acetylacetone and polyethylene glycol (PEG), in mixture of methanol and ethanol. The correlation among surface structure of the TiO₂ films, preparation conditions, and photovoltaic properties of the solar cells using the TiO₂ films was investigated. The particle size of the obtained TiO₂ films was decreased as the PEG content increased. The nanostructured films with the narrow distribution of particle size could be prepared. The amounts of adsorbed dyes for these TiO₂ films were larger than that without PEG. The performance of the solar cell fabricated using the TiO₂ film improved as the amount of the PEG increased, and the solar cell using the TiO₂ film prepared from the solution with 30 wt% PEG exhibited the highest performance.     

Chloride-catalyzed oxidation of phenol in pulsed-laser irradiation titanium dioxide sols

The kinetics of photolysis of phenol in presence of two kinds of TiO₂ colloid in acid aqueous solution medium was studied by transient absorption spectroscopy. The absorbance and quantum yield of the phenoxyl radicals is strongly influenced by the chloride ions. The process of laser flash photolysis of phenol in the presence of chloride has been discussed.     

Microwve induced catalytic reactions of carbon dioxide and water: mimicry of photosynthesis

In an attempt to emulate the highly successful photosynthetic recycling of CO₂ to form energetically useful fuels in nature this study investigates the microwave induced reaction of carbon dioxide and water in a continuous flow system using a supported nickel catalyst and 2.45 GHz microwave radiation with an average incident power of 2.2 kW. The major reaction products were methane, ethane, methanol, acetone, C₃ and C₄ alcohols. The yields of methane, C₃ and C₄ alcohols reached maximum values after 30 s of irradiation, while the yields of ethane, methanol and acetone were proportional to the irradiation time within the investigated range.