共查询到20条相似文献,搜索用时 93 毫秒
1.
Nicholas C. Nelson Linxiao Chen Debora Meira Libor Kovarik Jnos Szanyi 《Angewandte Chemie (International ed. in English)》2020,59(40):17657-17663
The application of single‐atom catalysts (SACs) to high‐temperature hydrogenation requires materials that thermodynamically favor metal atom isolation over cluster formation. We demonstrate that Pd can be predominantly dispersed as isolated atoms onto TiO2 during the reverse water–gas shift (rWGS) reaction at 400 °C. Achieving atomic dispersion requires an artificial increase of the absolute TiO2 surface area by an order of magnitude and can be accomplished by physically mixing a precatalyst (Pd/TiO2) with neat TiO2 prior to the rWGS reaction. The in situ dispersion of Pd was reflected through a continuous increase of rWGS activity over 92 h and supported by kinetic analysis, infrared and X‐ray absorption spectroscopies and scanning transmission electron microscopy. The thermodynamic stability of Pd under high‐temperature rWGS conditions is associated with Pd‐Ti coordination, which manifests upon O‐vacancy formation, and the artificial increase in TiO2 surface area. 相似文献
2.
Dr. Nicholas C. Nelson Dr. Linxiao Chen Dr. Debora Meira Dr. Libor Kovarik Dr. János Szanyi 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(40):17810-17816
The application of single-atom catalysts (SACs) to high-temperature hydrogenation requires materials that thermodynamically favor metal atom isolation over cluster formation. We demonstrate that Pd can be predominantly dispersed as isolated atoms onto TiO2 during the reverse water–gas shift (rWGS) reaction at 400 °C. Achieving atomic dispersion requires an artificial increase of the absolute TiO2 surface area by an order of magnitude and can be accomplished by physically mixing a precatalyst (Pd/TiO2) with neat TiO2 prior to the rWGS reaction. The in situ dispersion of Pd was reflected through a continuous increase of rWGS activity over 92 h and supported by kinetic analysis, infrared and X-ray absorption spectroscopies and scanning transmission electron microscopy. The thermodynamic stability of Pd under high-temperature rWGS conditions is associated with Pd-Ti coordination, which manifests upon O-vacancy formation, and the artificial increase in TiO2 surface area. 相似文献
3.
Yu Hang Li Wen Tao Yuan Prof. Ying Zhou Dr. Li Rong Zheng Prof. Hai Feng Wang Prof. P. Hu Prof. Yun Wang Prof. Hui Jun Zhao Prof. Yong Wang Prof. Hua Gui Yang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(8):2138-2144
The process of using solar energy to split water to produce hydrogen assisted by an inorganic semiconductor is crucial for solving our energy crisis and environmental problems in the future. However, most semiconductor photocatalysts would not exhibit excellent photocatalytic activity without loading suitable co‐catalysts. Generally, the noble metals have been widely applied as co‐catalysts, but always agglomerate during the loading process or photocatalytic reaction. Therefore, the utilization efficiency of the noble co‐catalysts is still very low on a per metal atom basis if no obvious size effect exists, because heterogeneous catalytic reactions occur on the surface active atoms. Here, for the first time, we have synthesized isolated metal atoms (Pt, Pd, Rh, or Ru) stably by anchoring on TiO2, a model photocatalystic system, by a facile one‐step method. The isolated metal atom based photocatalysts show excellent stability for H2 evolution and can lead to a 6–13‐fold increase in photocatalytic activity over the metal clusters loaded on TiO2 by the traditional method. Furthermore, the configurations of isolated atoms as well as the originality of their unusual stability were analyzed by a collaborative work from both experiments and theoretical calculations. 相似文献
4.
Xiaoxiao Ge Peng Zhou Qinghua Zhang Zhonghong Xia Shulin Chen Peng Gao Zhe Zhang Lin Gu Shaojun Guo 《Angewandte Chemie (International ed. in English)》2020,59(1):232-236
Traditional methods for analyzing organophosphorus pesticide chlorpyrifos, usually require the tedious sample pretreatment and sophisticated bio‐interfaces, leading to the difficulty for real‐time analysis. Herein, we use palladium single‐atom (PdSA)/TiO2 as a photocatalytic sensing platform to directly detect chlorpyrifos with high sensitivity and selectivity. PdSA/TiO2, prepared by an in situ photocatalytic reduction of PdCl42? on the TiO2, shows much higher photocatalytic activity (10 mol g?1 h?1) for hydrogen evolution reaction than Pd nanoparticles (1.95 mol g?1 h?1), and excellent stability. In the presence of chlorpyrifos, the photocatalytic activity of PdSA/TiO2 decreases. Through this inhibition effect the platform can realize a detection limit for chlorpyrifos of 0.01 ng mL?1, much lower than the maximum residue limit (10 ppb) permitted by the U.S. Environmental Protection Agency. 相似文献
5.
Quan Zuo Tingting Liu Chuanshuang Chen Yi Ji Xueqing Gong Yiyong Mai Yongfeng Zhou 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(30):10304-10309
A surfactant‐stabilized coordination strategy is used to make two‐dimensional (2D) single‐atom catalysts (SACs) with an ultrahigh Pt loading of 12.0 wt %, by assembly of pre‐formed single Pt atom coordinated porphyrin precursors into free‐standing metal–organic framework (MOF) nanosheets with an ultrathin thickness of 2.4±0.9 nm. This is the first example of 2D MOF‐based SACs. Remarkably, the 2D SACs exhibit a record‐high photocatalytic H2 evolution rate of 11 320 μmol g?1 h?1 via water splitting under visible light irradiation (λ>420 nm) compared with those of reported MOF‐based photocatalysts. Moreover, the MOF nanosheets can be readily drop‐casted onto solid substrates, forming thin films while still retaining their photocatalytic activity, which is highly desirable for practical solar H2 production. 相似文献
6.
A large variety of reduced titanium dioxide (TiO2-x) materials have been reported recently. Reduced TiO2, usually resulting from the removal of oxygen atoms or hydrogen incorporation, is proved to be efficient for achieving highly photocatalytic performance including photodegradation of organic compounds, hydrogen generation from water splitting, CO2 reduction for CH4 evolution, solar cells, etc. To further improve the properties and activities of TiO2-x, a combination of the Ti3+ self-doping and other traditional modifications like nonmetals doping has been proposed in the past decades. This paper provides a general and critical review on the further modifications on reduced TiO2 samples, including non-metal elements (N, B, S, F and I) doping, noble-metal (Au, Pt, Pd and Ag) and iron-group metal (Fe, Co and Ni) grafting, metal oxide compositing, carbon (nanotubes and graphene) and carbon-based-material compositing, special facets exposure (mainly dual {001}-{101} and {111}-{110} facets) of TiO2-x and ordered structure controlling of TiO2-x. These modifications enhance the physical and/or chemical properties of the reduced TiO2, or create new features for the modified TiO2-x samples, which finally leads to the enhancement of photocatalytic performance. Key examples such as N-doping, Au grafting and graphene-based compositing are discussed carefully, and the mechanisms for solar light enhancement, electron transfer and charge separation are also investigated. Finally, some challenging issues on TiO2-x catalysts are also proposed to encourage new approaches for preparation of TiO2-x catalysts with efficiently photocatalytic performance. 相似文献
7.
Pd particles loading on TiO2-embedded multi-walled carbon nanotubes (MWCNTs), MWCNTs, and TiO2 particles were prepared via an impregnation method with palladium(II) chlorate solution followed by heat treatment at high temperature. To characterize the catalysts, BET surface area, scanning electron microscopy, transmission electron microscopy, X-ray diffraction, energy dispersive X-ray, Fourier transform infrared spectroscopy and ultraviolet-visible spectroscopy were employed. The prepared catalysts were tested in degradation of methyl orange under visible light. Pd/TiO2-MWCNTs catalyst demonstrates the highest photocatalytic activity, and the phase transformation from PdO to Pd0 phase takes place at heat treatment of embedded TiO2. The nanoparticles size of TiO2 can be decreased by introduction of MWCNTs species. Combining structural characterization with kinetic study results we could conclude that the superior catalytic performance could arise due to the Pd/TiO2-MWCNTs catalyst’s structure. 相似文献
8.
Dr. Xujun Ma Donghui Wang Jianan Wu Dr. Bin Zhao Prof. Feng Chen 《Chemphyschem》2023,24(7):e202200505
Single atomic site catalysts display the maximal atom-utilization efficiency, unique structural properties, and remarkable enhancements on catalytic activity. Herein, single Pt atoms loaded Fe−TiO2 catalysts were prepared. Fe3+ doping leads to the formation of oxygen vacancies and improve the interaction between TiO2 and Pt. Single Pt atoms are thus anchored and effectively modify the local energy band structure of TiO2. The optimized local band structures improve the intrinsic photoexcitation of Pt/Fe−TiO2, promote the separation of photogenerated carriers, and extend the lifetime of photogenerated carriers. Meanwhile, the electrons transfer from the excited dyes to the conduction band edge of Pt/Fe−TiO2 is also facilitated due to the shift-down of the conduction band edge. Therefore, with the increase of the Pt content (till up to 0.6 wt%), the photocatalytic performance of Pt/ Fe−TiO2 with the confined single Pt atoms is significantly boosted in either the intrinsic or the sensitized photocatalytic process. 相似文献
9.
Ying Ma Dr. Yujing Ren Dr. Yanan Zhou Dr. Wei Liu Dr. Walid Baaziz Prof. Dr. Ovidiu Ersen Dr. Cuong Pham-Huu Dr. Mark Greiner Prof. Dr. Wei Chu Prof. Dr. Aiqin Wang Prof. Dr. Tao Zhang Prof. Dr. Yuefeng Liu 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(48):21797-21803
Single-atom catalysts (SACs) have shown superior activity and/or selectivity for many energy- and environment-related reactions, but their stability at high site density and under reducing atmosphere remains unresolved. Herein, we elucidate the intrinsic driving force of a Pd single atom with high site density (up to 5 wt %) under reducing atmosphere, and its unique catalytic performance for hydrogenation reactions. In situ experiments and calculations reveal that Pd atoms tend to migrate into the surface vacancy-enriched MoC surface during the carburization process by transferring oxide crystals to carbide crystals, leading to the surface enrichment of atomic Pd instead of formation of particles. The Pd1/α-MoC catalyst exhibits high activity and excellent selectivity for liquid-phase hydrogenation of substituted nitroaromatics (>99 %) and gas-phase hydrogenation of CO2 to CO (>98 %). The Pd1/α-MoC catalyst could endure up to 400 °C without any observable aggregation of single atoms. 相似文献
10.
Feilong Gong Yuheng Liu Yang Zhao Prof. Wei Liu Prof. Guang Zeng Prof. Guoqing Wang Prof. Yonghui Zhang Lihua Gong Prof. Jian Liu 《Angewandte Chemie (International ed. in English)》2023,62(40):e202308091
The coordination structure determines the electrocatalytic performances of single atom catalysts (SACs), while it remains a challenge to precisely regulate their spatial location and coordination environment. Herein, we report a universal sub-nanoreactor strategy for synthesis of yolk-shell MoS2 supported single atom electrocatalysts with dual-anchored microenvironment of vacancy-enriched MoS2 and intercalation carbon toward robust hydrogen-evolution reaction. Theoretical calculations reveal that the “E-Lock” and “E-Channel” are conducive to stabilize and activate metal single atoms. A group of SACs is subsequently produced with the assistance of sulfur vacancy and intercalation carbon in the yolk-shell sub-nanoreactor. The optimized C−Co−MoS2 yields the lowest overpotential (η10=17 mV) compared with previously reported MoS2-based electrocatalysts to date, and also affords a 5–9 fold improvement in activity even comparing with those as-prepared single-anchored analogues. Theoretical results and in situ characterizations unveil its active center and durability. This work provides a universal pathway to design efficient catalysts for electro-refinery. 相似文献
11.
Dr. Mahnaz Najafi Dr. Sara Abednatanzi Abbas Yousefi Prof. Mehrorang Ghaedi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(72):17999-18014
Photocatalysis has been known as one of the promising technologies due to its eco-friendly nature. However, the potential application of many photocatalysts is limited owing to their large bandgaps and inefficient use of the solar spectrum. One strategy to overcome this problem is to combine the advantages of heteroatom-containing supports with active metal centers to accurately adjust the structural parameters. Metal nanoparticles (MNPs) and single atom catalysts (SACs) are excellent candidates due to their distinctive coordination environment which enhances photocatalytic activity. Metal-organic frameworks (MOFs), covalent organic frameworks (COFs) and carbon nitride (g-C3N4) have shown great potential as catalyst support for SACs and MNPs. The numerous combinations of organic linkers with various heteroatoms and metal ions provide unique structural characteristics to achieve advanced materials. This review describes the recent advancement of the modified MOFs, COFs and g-C3N4 with SACs and NPs for enhanced photocatalytic applications with emphasis on environmental remediation. 相似文献
12.
Dr. Weijia Zhou Yu Guan Dongzhou Wang Prof. Xinhai Zhang Prof. Duo Liu Prof. Huaidong Jiang Prof. Jiyang Wang Prof. Xiaogang Liu Prof. Hong Liu Prof. Shaowei Chen 《化学:亚洲杂志》2014,9(6):1648-1654
Heterostructures play an important role not only in the manufacture of semiconductor devices, but also in the field of catalysis. Herein, we report the synthesis of PdO/TiO2 and Pd/TiO2 heterostructured nanobelts by means of a simple co‐precipitation method, followed by a reduction process using surface‐modified TiO2 nanobelts as templates. The as‐obtained heterostructures were characterized by transmission electron microscopy, X‐ray photoelectron spectroscopy, and UV/Vis diffuse reflectance spectroscopy. PdO and Pd nanoparticles with a size of about 1.3 and 1.6 nm were assembled uniformly on the surface of TiO2 nanobelts, respectively. Compared with TiO2 nanobelts, PdO/TiO2 and Pd/TiO2 hybrid nanobelts exhibit enhanced photocatalytic activity upon UV and visible‐light irradiation. Photoelectrochemical technology was used to study the heterostructure effect on enhanced photocatalytic activity. Our mechanistic investigation revealed that energy‐band matching is the major factor in the observed enhancement of photocatalytic activity. 相似文献
13.
Yun‐Nan Gong Long Jiao Yunyang Qian Chun‐Yang Pan Lirong Zheng Xuechao Cai Bo Liu Shu‐Hong Yu Hai‐Long Jiang 《Angewandte Chemie (International ed. in English)》2020,59(7):2705-2709
The general synthesis and control of the coordination environment of single‐atom catalysts (SACs) remains a great challenge. Herein, a general host–guest cooperative protection strategy has been developed to construct SACs by introducing polypyrrole (PPy) into a bimetallic metal–organic framework. As an example, the introduction of Mg2+ in MgNi‐MOF‐74 extends the distance between adjacent Ni atoms; the PPy guests serve as N source to stabilize the isolated Ni atoms during pyrolysis. As a result, a series of single‐atom Ni catalysts (named NiSA‐Nx‐C) with different N coordination numbers have been fabricated by controlling the pyrolysis temperature. Significantly, the NiSA‐N2‐C catalyst, with the lowest N coordination number, achieves high CO Faradaic efficiency (98 %) and turnover frequency (1622 h?1), far superior to those of NiSA‐N3‐C and NiSA‐N4‐C, in electrocatalytic CO2 reduction. Theoretical calculations reveal that the low N coordination number of single‐atom Ni sites in NiSA‐N2‐C is favorable to the formation of COOH* intermediate and thus accounts for its superior activity. 相似文献
14.
Jingkun Chen Yuetan Su Qingjie Meng Hehe Qian Le Shi Prof. Jawwad A. Darr Prof. Zhongbiao Wu Prof. Xiaole Weng 《Angewandte Chemie (International ed. in English)》2023,62(49):e202310191
The development of oxidation catalysts that are resistant to sulfur poisoning is crucial for extending the lifespan of catalysts in real-working conditions. Herein, we describe the design and synthesis of oxide-metal interaction (OMI) catalyst under oxidative atmospheres. By using organic coated TiO2, an oxide/metal inverse catalyst with non-classical oxygen-saturated TiO2 overlayers were obtained at relatively low temperature. These catalysts were found to incorporate ultra-small Pd metal and support particles with exceptional reactivity and stability for CO oxidation (under 21 vol % O2 and 10 vol % H2O). In particular, the core (Pd)-shell (TiO2) structured OMI catalyst exhibited excellent resistance to SO2 poisoning, yielding robust CO oxidation performance at 120 °C for 240 h (at 100 ppm SO2 and 10 vol % H2O). The stability of this new OMI catalyst was explained through density functional theory (DFT) calculations that interfacial oxygen atoms at Pd−O−Ti sites (of oxygen-saturated overlayers) serve as non-metal active sites for low-temperature CO oxidation, and change the SO2 adsorption from metal(d)-to-SO2(π*) back-bonding to much weaker σ(Ti−S) bonding. 相似文献
15.
Selective hydrogenation of citral over Au-based bimetallic catalysts in supercritical carbon dioxide
Selective hydrogenation of citral was investigated over Au-based bimetallic catalysts in the environmentally benign supercritical carbon dioxide (scCO2) medium. The catalytic performances were different in citral hydrogenation when Pd or Ru was mixed (physically and chemically) with Au. Compared with the corresponding monometallic catalyst, the total conversion and the selectivity to citronellal (CAL) were significantly enhanced over TiO2 supported Pd and Au bimetallic catalysts (physically and chemically mixed); however, the conversion and selectivity did not change when Ru was physically mixed with Au catalyst compared to the monometallic Ru/TiO2, and the chemically mixed Ru-Au/TiO2 catalyst did not show any activity. The effect of CO2 pressure on the conversion of citral and product selectivity was significantly different over the Au/TiO2, Pd-Au/TiO2, and Pd/TiO2 catalysts. It was assumed to be ascribed to the difference in the interactions between Au, Pd nanoparticles and CO2 under different CO2 pressures. 相似文献
16.
The Ni/TiO2 nanoparticles with different Ni dopant content were prepared by a modified sol–gel method. The structure and photoinduced
charge properties of the as-prepared catalysts were determined using X-ray diffraction, transmission electron microscopy,
UV–vis diffuse reflectance spectroscopy and surface photovoltage spectroscopy techniques, and the photocatalytic efficiency
of these catalysts was tested using an organic dye. It was shown that Ni modification could greatly enhance the photocatalytic
efficiency of these nanocomposite catalysts by taking the photodegradation of methyl orange as a model reaction. With appropriate
ratio of Ni and TiO2, Ni/TiO2 nanocomposites showed the superior photocatalytic activity than the single TiO2 nanoparticles. Surface photovoltage spectra demonstrated that Ni modification could effectively inhibit the recombination
of the photoinduced electron and holes of TiO2. This electron–hole pair separation conditions are responsible for the higher photocatalytic performance of Ni/TiO2 nanocomposites in the visible region of electromagnetic spectrum. 相似文献
17.
Xinjiang Hu Daixi Zhou Hui Wang Wenlong Zhang Haoxiang Zhong Yongsheng Chen 《中国化学快报》2023,34(8):108050-167
Single atom catalysts(SACs) have become the frontier research fields in catalysis. The M1-Nx-Cybased SACs, wherein single metal atoms(M1) are stabilized by N-doped carbonaceous materials, have provided new opportunities for catalysis due to their high reactivity, maximized atomic utilization, and high selectivity. In this review, the fabrication methods of M1-Nx-Cybased SACs via support anchoring strategy and coordination design strategy are summarized to help the readers understand the interact... 相似文献
18.
Peng Zhou Ning Li Yuguang Chao Weiyu Zhang Fan Lv Kai Wang Wenxiu Yang Peng Gao Shaojun Guo 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(40):14322-14326
Noble metal single atoms coordinated with highly electronegative atoms, especially N and O, often suffer from an electron‐deficient state or poor stability, greatly limiting their wide application in the field of catalysis. Herein we demonstrate a new PH3‐promoted strategy for the effective transformation of noble metal nanoparticles (MNPs, M=Ru, Rh, Pd) at a low temperature (400 °C) into a class of thermally stabilized phosphorus‐coordinated metal single atoms (MPSAs) on g‐C3N4 nanosheets via the strong Lewis acid–base interaction between PH3 and the noble metal. Experimental work along with theoretical simulations confirm that the obtained Pd single atoms supported on g‐C3N4 nanosheets exist in the form of PdP2 with a novel electron‐rich feature, conceptionally different from the well‐known single atoms with an electron‐deficient state. As a result of this new electronic property, PdP2‐loaded g‐C3N4 nanosheets exhibit 4 times higher photocatalytic H2 production activity than the state‐of‐art N‐coordinated PdSAs supported on g‐C3N4 nanosheets. This enhanced photocatalytic activity of phosphorus‐coordinated metal single atoms with an electron‐rich state was quite general, and also observed for other active noble metal single atom catalysts, such as Ru and Rh. 相似文献
19.
Hojin Jeong Dongjae Shin Beom-Sik Kim Junemin Bae Sangyong Shin Chanyeong Choe Prof. Jeong Woo Han Prof. Hyunjoo Lee 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(46):20872-20877
Single-atom catalysts (SACs) have emerged as promising materials in heterogeneous catalysis. Previous studies reported controversial results about the relative level in activity for SACs and nanoparticles (NPs). These works have focused on the effect of metal atom arrangement, without considering the oxidation state of the SACs. Here, we immobilized Pt single atoms on defective ceria and controlled the oxidation state of Pt SACs, from highly oxidized (Pt0: 16.6 at %) to highly metallic states (Pt0: 83.8 at %). The Pt SACs with controlled oxidation states were then employed for oxidation of CO, CH4, or NO, and their activities compared with those of Pt NPs. The highly oxidized Pt SACs presented poorer activities than Pt NPs, whereas metallic Pt SACs showed higher activities. The Pt SAC reduced at 300 °C showed the highest activity for all the oxidations. The Pt SACs with controlled oxidation states revealed a crucial missing link between activity and SACs. 相似文献
20.
采用改进的sol-gel法和浸渍法制备了TiO2掺杂稀土离子La3+、Y3+、Gd3+、Er3+、Nd3+、Pr3+的RE/TiO2光催化剂,运用FTIR、XRD、TEM、低温氮吸附/脱附、TG/DTA、UV-Vis DRS、表面光电压谱(SPS)等进行表征,以气相光催化降解乙烯、溴代甲烷作为探针反应,阐明了RE/TiO2光催化剂的谱学特性与气相光催化性能的关系。结果显示,稀土离子掺杂后,TiO2的锐钛矿含量增加,比表面积增大,粒径变小,吸收边发生蓝移,表面光电压的响应阈值增大,此外,Pr3+除外的其它稀土离子掺杂的TiO2的表面光电压信号增强;光催化降解实验表明,与纯TiO2相比,La3+、Y3+、Gd3+、Er3+、Nd3+掺杂TiO2样品上乙烯、溴代甲烷的光催化活性均有不同程度的增强,而且表现出较强的矿化能力。但是,掺杂Pr3+的TiO2的光催化性能降低恰好对应较弱的表面光电压信号。所以,本文认为提高光生电子-空穴对的分离效率是改善光催化性能的关键因素。 相似文献