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《催化学报》2020,(1)
以半导体等为催化剂,在太阳能作用下将CO_2和H_2O转化为可再生燃料与氧气的"人工光合作用"有望同时解决目前面临的严峻能源和环境问题,因而备受关注.但半导体催化剂光谱响应范围较窄、表面反应动力学缓慢,从而导致目前仍无法获得可观的太阳能-燃料转换效率.已有很多研究采用了晶面调控、元素掺杂和异质结构建等方法,以提高半导体光催化剂的太阳能-燃料转换效率,但效果仍不令人满意,主要原因是半导体光催化剂很难在吸收带边-氧化还原能力和活性-稳定性这两种关系中取得较好的平衡.此外,光催化反应中的动力学也是主要问题之一,尤其在人工光合作用反应中, CO_2还原半反应和H_2O氧化半反应的动力学均较困难,这已成为共识,而解决这个问题,将有助于我们从一新的角度理解光催化过程,从而提升光催化反应性能.本文以AuNP/金红石为模型催化剂,纯金红石为参照,证明了存在太阳光中的红外光致热和可见光诱导的等离激元热效应等两类光致热效应,它们均可以促进人工光合作用反应.研究发现,人工光合作用反应与其他许多化学反应一样,表观活化能为正,从而表明动力学因素在该反应中起着重要作用.此外,根据不同反应温度下的结果,通过计算AuNP/金红石和纯金红石上生成CO和CH4的表观活化能,发现在这二种样品上CH4的表观活化能均高于CO,这就从动力学上解释了热力学上更容易得到的CH4在绝大多光催化CO_2还原反应中的产率均低于CO.此外,无论是对于CO还是CH4, AuNP/金红石的催化表观活化能均低于纯金红石的.因此,本文从实验上提供了贵金属纳米粒子改善人工光合作用动力学的实验证据,并从动力学角度解释了人工光合作用反应中的活性和选择性问题.本研究证明了动力学因素在光催化反应,尤其是人工光合作用反应中的重要性,并提出了从动力学角度提升人工光合作用反应的新方法,即利用太阳光的光致热效应加速反应,这不仅有助于提升太阳能转化效率,也有望减少反应设备成本,从而促进其大规模应用. 相似文献
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正化石燃料的不断消耗和温室气体CO_2的持续排放使温室效应和能源危机日益严峻。受自然界植物的光合作用的启发,光催化CO_2还原受到人们广泛关注,将大气中的CO_2还原成为高附加值碳氢化合物,成为有效缓解温室效应和能源危机的有效方式1。然而,一方面由于CO_2分子中C=O具有较大的键能(750 kJ·mol~(-1)),使其难以活化;另一方面,以水为还原剂的体系中,光激发所产生的质子 相似文献
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《催化学报》2016,(6)
研究表明,MgO能够活化吸附在其表面的CO_2分子,促进HCO_3~–的生成,而在H原子存在的条件下,HCO_3~–为CO_2光催化还原为碳氢化合物和CO的活性中间体.CO_2为对称的直线型分子,在化学反应中表现出极高的稳定性,成为阻碍人工光合作用发展的重要因素.在设计新型光催化剂时,复合MgO可能会有效提高催化剂的活性.绿色植物的叶片结构或茎中存在大量尺寸不一的多孔结构,以利于植物生命活动(包括光合作用和呼吸作用)过程中气体的有效扩散和水分、营养物质的运输.TiO_2因其良好的化学稳定性、无毒且成本低廉,在人工光合成领域得到广泛的研究.因此,本文以空心菜杆为模板,TiO_2为主体催化剂,应用溶胶-凝胶法,通过调节MgO的含量合成了一系列仿生多孔结构的MgO-TiO_2复合物.样品的X射线衍射、X射线光电子能谱和高分辨透射镜表征结果证明,生物模板空心菜杆在550℃下煅烧5 h之后可被完全移除,且MgNO_3分解为MgO,生成TiO_2-MgO复合物.从扫描电镜中可观察到,以空心菜杆为模板合成的MgO-TiO_2,模板的空心管状结构得以保持,在长度和宽度上有一定程度的皱缩.横截面和纵截面图说明样品很好地复制了空心菜杆的导管和筛管组成的多孔结构.同时N2吸附-脱附结果表明,样品中存在3–5 nm的介孔结构.同时我们发现,由于MgO的加入,0.05%MgO-TiO_2复合物的比表面积比TiO_2减少了18%,之后随着MgO含量的增加,MgO-TiO_2复合物的比表面积呈下降趋势.标准状况下,测试了样品对CO_2的吸附量.结果表明,随MgO含量的升高,吸附量先增加后减小,且MgO-TiO_2复合物的吸附量为TiO_2的1.3–1.8倍.结合样品比表面积及原位红外光谱测试结果,说明样品的CO_2吸附量受MgO的含量与样品的比表面积双重因素的影响.CO_2吸附包括物理吸附和化学吸附,而且对于同种样品,吸附量与样品比表面积正相关.当MgO-TiO_2复合物的比表面积随着MgO含量的增加而减小时,CO_2吸附量却先增加后减小,表明MgO的加入极大地促进了CO_2的化学吸附.以MgO-TiO_2复合物作为光催化剂将CO_2和H2O还原为CH_4.CH_4的总产量随着光照时间的增加而增加,10 h后的总产量随着MgO含量的升高先增加后减少,与样品的CO_2吸附量的变化趋势相似但不完全相同.与TiO_2(6.5μmol/g)相比,MgO-TiO_2复合物样品催化作用下的CH_4的最终产量均增大,活性最好的0.2%MgO-TiO_2(18.7μmol/g)的产量达到了它的2.88倍,说明MgO对CO_2具有活化作用,且活化后的CO_2更容易生成CH_4.综合结果表明,CO_2在催化剂表面的吸附量、电子的表面迁移、反应活性位点等因素共同决定了催化剂的光催化活性. 相似文献
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The acceleration of industrialization and the continuous upgradation of consumption structure has increased the atmospheric content of CO2 far beyond the past levels, leading to a serious global environmental problem. Photocatalytic reduction of CO2 is one of the most promising methods to solve the problem of rising atmospheric CO2 content. The core of this technology is to develop efficient, environment-friendly, and affordable photocatalysts. A photocatalyst is a semiconductor that can absorb photons from sunlight and produce electron-hole pairs to initiate a redox reaction. Owing to their low specific surface areas, significant electron-hole recombination, and less surface-active sites, bulk photocatalysts are not satisfactory. Ultrathin layered materials have shown great potential for photocatalytic CO2 reduction owing to their characteristics of large specific surface area, a large number of low-coordination surface atoms, short transfer distance from the inside to the catalyst surface, along with other advantages. Photoexcited electrons only need to cover a short distance to transfer to the nanowafer surface, and the speed of migrating electrons on the nanowafer surface is much higher than that in the layers or in the bulk catalyst. The ultrathin structure leads to significant coordinative unsaturation and even vacancy defects in the lattice structure of the atoms; while the former can be used as active sites for CO2 adsorption and reaction, the latter can improve the separation of the electron-hole pair. This review summarizes the latest developments in ultrathin layered photocatalysts for CO2 reduction. First, the photocatalytic reduction mechanism of CO2 is introduced briefly, and the factors governing product selectivity are explained. Second, the existing catalysts, such as g-C3N4, black phosphorus (BP), graphene oxide (GO), metal oxide, transition metal dichalcogenides (TMDCs), perovskite, BiOX (X = Cl, Br, I), layered double hydroxide (LDH), 2D-MOF, MXene, and two-dimensional honeycomb-like Ge―Si alloy compounds (gersiloxenes), are classified. In addition, the prevalent preparation methods are summarized, including mechanical stripping, gas stripping, liquid stripping, chemical etching, chemical vapor deposition (CVD), template method, self-assembly of surfactant, and the intermediate precursor method of lamellar Bi-oleate complex. Finally, we introduced the strategy of improving photocatalyst performance on the premise of maintaining its layered structure, including the factors of thickness adjustment, doping, structural defects, composite, etc. The future opportunities and challenges of ultrathin layered photocatalysts for the reduction of carbon dioxide have also been proposed. 相似文献
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Xuemei Zhou 《物理化学学报》1985,37(6):2008064-0
Titania (TiO2) has been among the most widely investigated and used metal oxides over the past years, as it has various functional applications. Extensive research into TiO2 and industrial interest in this material have been triggered by its high abundance, excellent corrosion resistance, and low cost. To improve the activity of TiO2 in heterogeneous catalytic reactions, noble metals are used to accelerate the reactions. However, in the case of nanoparticles supported on TiO2, the active sites are usually limited to the peripheral sites of the noble metal particles or at the interface between the particle and the support. Thus, highly dispersed single metal atoms are desired for the effective utilization of precious noble metals. The study of oxide-supported isolated atoms, the so-called single-atom catalysts (SACs), was pioneered by Zhang's group. The high dispersion of precious noble metals results helps reduce the cost associated with catalyst preparation. Because of the presence of active centers as single atoms, the deactivation of metal atoms during the reaction, e.g., by coking for large agglomerates, is retarded. The unique coordination environment of the noble metal center provides special sites for the reaction, consequently increasing the selectivity of the reaction, including the enantioselectivity and stereoselectivity. Hence, supported SACs can bridge homogenous and heterogeneous reactions in solution as they provide selective reaction sites and are recyclable. Moreover, owing to the high site homogeneity of the isolated metal atoms, SACs are ideal models for establishing the structure-activity relationships. The present review provides an overview of recent works on the synthesis, characterization, and photocatalytic applications of SACs (Pt1, Pd1, Ir1, Rh1, Cu1, Ru1) supported on TiO2. The preparation of single atoms on TiO2 includes the creation of surface defective sites, surface modification, stabilization by high-temperature shockwave treatment, and metal-ligand self-assembly. Conventional characterization methods are categorized as microscopic imaging and spectroscopic methods, such as aberration-corrected scanning transmission electron microscopy (STEM), scanning tunneling microscopy (STM), extended X-ray absorption fine structure analysis (EXAFS), and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). We attempted to address the critical factors that lead to the stabilization of single-metal atoms on TiO2, and elucidate the mechanism underlying the photocatalytic hydrogen evolution and CO2 reduction. Although many fascinating applications of TiO2-supported SACs in photocatalysis could only be addressed superficially and in a referencing manner, we hope to provide interested readers with guidelines based on the wide literature, and more specifically, to provide a comprehensive overview of TiO2-supported SACs. 相似文献
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Shufang Ji Prof. Yang Qu Dr. Tao Wang Yuanjun Chen Prof. Guofeng Wang Xue Li Dr. Juncai Dong QiuYu Chen Wanying Zhang Zedong Zhang Shiyou Liang Prof. Rong Yu Dr. Yu Wang Prof. Dingsheng Wang Prof. Yadong Li 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(26):10738-10744
The solar-driven photocatalytic reduction of CO2 (CO2RR) into chemical fuels is a promising route to enrich energy supplies and mitigate CO2 emissions. However, low catalytic efficiency and poor selectivity, especially in a pure-water system, hinder the development of photocatalytic CO2RR owing to the lack of effective catalysts. Herein, we report a novel atom-confinement and coordination (ACC) strategy to achieve the synthesis of rare-earth single erbium (Er) atoms supported on carbon nitride nanotubes (Er1/CN-NT) with a tunable dispersion density of single atoms. Er1/CN-NT is a highly efficient and robust photocatalyst that exhibits outstanding CO2RR performance in a pure-water system. Experimental results and density functional theory calculations reveal the crucial role of single Er atoms in promoting photocatalytic CO2RR. 相似文献
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Shufang Ji Yang Qu Tao Wang Yuanjun Chen Guofeng Wang Xue Li Juncai Dong QiuYu Chen Wanying Zhang Zedong Zhang Shiyou Liang Rong Yu Yu Wang Dingsheng Wang Yadong Li 《Angewandte Chemie (International ed. in English)》2020,59(26):10651-10657
The solar‐driven photocatalytic reduction of CO2 (CO2RR) into chemical fuels is a promising route to enrich energy supplies and mitigate CO2 emissions. However, low catalytic efficiency and poor selectivity, especially in a pure‐water system, hinder the development of photocatalytic CO2RR owing to the lack of effective catalysts. Herein, we report a novel atom‐confinement and coordination (ACC) strategy to achieve the synthesis of rare‐earth single erbium (Er) atoms supported on carbon nitride nanotubes (Er1/CN‐NT) with a tunable dispersion density of single atoms. Er1/CN‐NT is a highly efficient and robust photocatalyst that exhibits outstanding CO2RR performance in a pure‐water system. Experimental results and density functional theory calculations reveal the crucial role of single Er atoms in promoting photocatalytic CO2RR. 相似文献
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Dr. Shan Hu Dr. Panzhe Qiao Dr. Xinli Yi Yiming Lei Huilin Hu Prof. Jinhua Ye Prof. Defa Wang 《Angewandte Chemie (International ed. in English)》2023,62(26):e202304585
Artificial photosynthesis is a promising strategy for converting carbon dioxide (CO2) and water (H2O) into fuels and value-added chemical products. However, photocatalysts usually suffered from low activity and product selectivity due to the sluggish dynamic transfer of photoexcited charge carriers. Herein, we describe anchoring of Ag single atoms on hollow porous polygonal C3N4 nanotubes (PCN) to form the photocatalyst Ag1@PCN with Ag−N3 coordination for CO2 photoreduction using H2O as the reductant. The as-synthesized Ag1@PCN exhibits a high CO production rate of 0.32 μmol h−1 (mass of catalyst: 2 mg), a high selectivity (>94 %), and an excellent stability in the long term. Experiments and density functional theory (DFT) reveal that the strong metal–support interactions (Ag−N3) favor *CO2 adsorption, *COOH generation and desorption, and accelerate dynamic transfer of photoexcited charge carriers between C3N4 and Ag single atoms, thereby accounting for the enhanced CO2 photoreduction activity with a high CO selectivity. This work provides a deep insight into the important role of strong metal–support interactions in enhancing the photoactivity and CO selectivity of CO2 photoreduction. 相似文献
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Zhiming Pan Minghui Liu Pingping Niu Fangsong Guo Xianzhi Fu Xinchen Wang 《物理化学学报》2020,36(1):1906014-0
Artificial photosynthesis is an ideal method for solar-to-chemical energy conversion, wherein solar energy is stored in the form of chemical bonds of solar fuels. In particular, the photocatalytic reduction of CO2 has attracted considerable attention due to its dual benefits of fossil fuel production and CO2 pollution reduction. However, CO2 is a comparatively stable molecule and its photoreduction is thermodynamically and kinetically challenging. Thus, the photocatalytic efficiency of CO2 reduction is far below the level of industrial applications. Therefore, development of low-cost cocatalysts is crucial for significantly decreasing the activation energy of CO2 to achieving efficient photocatalytic CO2 reduction. Herein, we have reported the use of a Ni2P material that can serve as a robust cocatalyst by cooperating with a photosensitizer for the photoconversion of CO2. An effective strategy for engineering Ni2P in an ultrathin layered structure has been proposed to improve the CO2 adsorption capability and decrease the CO2 activation energy, resulting in efficient CO2 reduction. A series of physicochemical characterizations including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and atomic force microscopy (AFM) were used to demonstrate the successful preparation of ultrathin Ni2P nanosheets. The XRD and XPS results confirm the successful synthesis of Ni2P from Ni(OH)2 by a low temperature phosphidation process. According to the TEM images, the prepared Ni2P nanosheets exhibit a 2D and near-transparent sheet-like structure, suggesting their ultrathin thickness. The AFM images further demonstrated this result and also showed that the height of the Ni2P nanosheets is ca 1.5 nm. The photoluminescence (PL) spectroscopy results revealed that the Ni2P material could efficiently promote the separation of the photogenerated electrons and holes in [Ru(bpy)3]Cl2·6H2O. More importantly, the Ni2P nanosheets could more efficiently promote the charge transfer and charge separation rate of [Ru(bpy)3]Cl2·6H2O compared with the Ni2P particles. In addition, the electrochemical experiments revealed that the Ni2P nanosheets, with their high active surface area and charge conductivity, can provide more active centers for CO2 conversion and accelerate the interfacial reaction dynamics. These results strongly suggest that the Ni2P nanosheets are a promising material for photocatalytic CO2 reduction, and can achieve a CO generation rate of 64.8 μmol·h-1, which is 4.4 times higher than that of the Ni2P particles. In addition, the XRD and XPS measurements of the used Ni2P nanosheets after the six cycles of the photocatalytic CO2 reduction reaction demonstrated their high stability. Overall, this study offers a new function for the 2D transition-metal phosphide catalysts in photocatalytic CO2 reduction. 相似文献
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杂原子掺杂的Fe-NC催化剂在氧还原反应中表现出优异的性能.本工作采用密度泛函理论研究了S原子掺杂对Fe-NC单原子催化剂电子结构的调控及促进氧还原反应的作用机理,分析了硫原子掺杂后Fe-NC催化剂的稳定构型, S原子对FeN4活性位点电子结构的调控,以及氧气的吸附和氧还原反应作用机理.研究结果表明,在FeN4活性位点周围掺杂少量S原子,可以提高催化剂的稳定性. S原子掺杂提高氧还原性能的机理为:(1) S原子的掺杂降低了催化剂的带隙,提高催化剂导电性,有利于电催化氧还原反应;(2) S原子的掺杂可以提高催化剂吸附氧气的能力,有利于氧还原反应;(3)体系中引入四个S原子可以降低氧还原反应的过电位,提高FeN4位点催化氧还原反应的活性.这项工作可能为基于碳材料的单原子催化剂上杂原子掺杂的调控提供新的思路. 相似文献
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Prof. Dr. Yasuhiro Arikawa Itoe Tabata Yukari Miura Hiroki Tajiri Yudai Seto Dr. Shinnosuke Horiuchi Prof. Dr. Eri Sakuda Prof. Dr. Keisuke Umakoshi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(25):5603-5606
Photocatalytic CO2 reduction using a ruthenium photosensitizer, a sacrificial reagent 1,3-dimethyl-2-(o-hydroxyphenyl)-2,3-dihydro-1H-benzo[d]imidazole (BI(OH)H), and a ruthenium catalyst were carried out. The catalysts contain a pincer ligand, 2,6-bis(alkylimidazol-2-ylidene)pyridine (CNC) and a bipyridine (bpy). The photocatalytic reaction system resulted in HCOOH as a main product (selectivity 70–80 %), with a small amount of CO, and H2. Comparative experiments (a coordinated ligand (NCMe vs. CO) and substituents (tBu vs. Me) of the CNC ligand in the catalyst) were performed. The turnover number (TONHCOOH) of carbonyl-ligated catalysts are higher than those of acetonitrile-ligated catalysts, and the carbonyl catalyst with the smaller substituents (Me) reached TONHCOOH=5634 (24 h), which is the best performance among the experiments. 相似文献
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Photocatalytic Reduction of Greenhouse Gas CO2 to Fuel 总被引:1,自引:0,他引:1
Jeffrey C. S. Wu 《Catalysis Surveys from Asia》2009,13(1):30-40
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. 相似文献