金属核及氧化铈的物理化学性质对一氧化碳氧化的影响

氧化铈独特的氧化还原性能使其适合用作氧化反应中的催化剂或载体.氧化铈负载的过渡金属纳米粒子或孤立的单原子提供了金属-载体界面,从而降低了去除界面氧原子的能耗,提供了可以参与ManVanKulvian氧化过程的活性氧物种.CO氧化是测试氧化铈负载催化剂还原性的主要探针反应,并且它常见于在相对低温下消除CO的各种应用中.在过量H2中优先氧化CO(PROX)反应可控制CO浓度达到超低水平,以防止氢氧化电催化剂中毒.催化剂在CO氧化反应中的活性和在PROX反应中对CO和H2的选择性取决于金属物种的种类和分散性、CeO2的结构和化学性质以及催化剂的合成方法.在这篇综述中,我们总结了最近发表的关于CeO2负载的金属纳米粒子和单原子催化CO氧化和PROX反应的相关工作;以及不同的负载金属和同种金属在普通CeO2表面上的反应性.我们还总结了密度泛函理论计算中提出的最可能的反应机理;并且讨论了各种负载型金属在PROX反应中影响CO氧化选择性的因素.

新型钯-铜纳米点析氢助催化剂: 优化界面氢脱附以实现高效光催化活性

助剂修饰是提高单相光催化剂催化制氢活性的有效策略之一.贵金属Pt是光催化制氢体系中较为理想的助催化剂,但价格高、储量少,严重限制了其广泛应用.在过去几十年中,研究者研发了一系列低成本的非Pt助催化剂,如金属氧化物、碳化物、氮化物、硫化物和磷化物等,并应用于光催化制氢,但其催化活性与Pt助催化剂相比有较大差距.近年来,与Pt具有相似的物化性质,但价格较低的其他铂族金属得到了广泛关注和研究.贵金属Pd不仅具有良好的导电性和稳定性,而且相对于Pt,Pd的储量更丰富且廉价(Pd:124.9元/克,Pt:224.8元/克),因而被认为是一种很有应用前景的析氢助催化剂.然而,Pd金属助剂在实际应用中的析氢活性并不理想,主要是因为Pd对氢原子(H)的吸附强度过高,严重限制了后续的氢脱附过程,导致材料整体的析氢反应速率较慢.因此,发展合适的方法来优化Pd的电子结构以弱化其对氢的吸附强度,对进一步提升Pd助剂的催化析氢活性具有重要意义.本文通过一种简易的NaH_(2)PO_(2)介导的共沉积策略,成功地将过渡金属Cu引入金属Pd的晶格中,并通过Pd-Cu合金化作用弱化了Pd对氢的吸附强度,进而有效提高界面H2释放速率.通过X射线衍射、高分辨率透射电镜、X射线光电子能谱和电感耦合等离子体等技术对Pd_(100-x)Cu_(x)合金的结构和形貌进行了分析.结果表明,Pd_(100-x)Cu_(x)合金纳米点(2-5 nm)成功修饰于TiO_(2)表面,所得的Pd_(100-x)Cux/TiO_(2)光催化剂表现出显著增强的光催化制氢性能.其中,Pd_(75)Cu_(25)/TiO_(2)样品的催化性能达到269.2μmol h^(-1),是纯TiO_(2)的90倍.此外,原位X射线光电子能谱和密度泛函理论的结果表明,所形成的Pd_(100-x)Cu_(x)合金纳米点因其自身优异的导电性可以有效促进光生电荷的分离;同时,Cu的成功引入弱化了Pd对氢的吸附强度,从而促进了Pd_(75)Cu_(25)合金上的氢解吸过程,最终有效提升了光催化剂的制氢活性.Pd_(75)Cu_(25)合金对H吸附强度降低的原因是:引入弱电负性的Cu元素后,Cu的部分电子转移至Pd上形成富电子的Pd,进而降低了Pd对H的吸附强度.本文通过优化电子结构以促进界面反应活性的策略为开发高效光催化剂提供了新的见解.

Photocatalytic phosphine-mediated water activation generates hydrogen atom radicals for transfer hydrogenation of closed-shell π systems

Hydrogenation refers to the addition of hydrogen(H)atoms to unsaturated bonds.It is one of the most important transformation reactions in the organic synthesis of chemicals and pharmaceuticals[1].Based on different hydrogen sources,hydrogenation can be classified into direct hydrogenation(DH)and transfer hydrogenation(TH).

3D ordered macroporous sulfur-doped g-C_(3)N_(4)/TiO_(2)S-scheme photocatalysts for efficient H_(2)O_(2)production in pure water

Photocatalytic hydrogen peroxide(H_(2)O_(2))production offers a clean and cost-efficient alternative to the traditional anthraquinone oxidation approach.Herein,a step-scheme(S-scheme)heterojunction photocat-alyst is fabricated by coupling TiO_(2)with three dimensionally ordered macroporous sulfur-doped graphitic carbon nitride(3DOM SCN/T)by electrostatic self-assembly.The optimized photocatalyst achieved a high photocatalytic H_(2)O_(2)production activity with a yield of 2128μmol h^(−1)g^(−1)without the addition of hole scavengers.The remarkable performance was attributed to the synergy between the 3DOM framework and the S-scheme heterojunction.The former enhances light harvesting and provides abundant active sites for surface reactions,while the latter promotes the spatial separation of photogenerated carriers and enhances the redox power.Finally,the mechanism of photocatalytic H_(2)O_(2)production over the 3DOM SCN/T S-scheme composite is proposed.This work provides novel insights into the development of effi-cient photocatalysts for H_(2)O_(2)production from water and O_(2).

BiOBr/COF S-scheme photocatalyst for H_(2)O_(2) production via concerted two-electron pathway

Constructing step-scheme(S-scheme)heterojunctions has become a popular strategy for efficient pho-tocatalytic H_(2)O_(2) generation.Herein,we in situ grew BiOBr nanosheets(NSs)on a Schiff-base covalent organic framework(COF)with largeπ-conjugated structures to prepare S-scheme BiOBr/COF photocat-alysts for H_(2)O_(2) synthesis.The highest photocatalytic H_(2)O_(2) production performance of the composite sample constituting the S-scheme heterojunction is 3749μmol g−1 h−1,which was 1.85 and 27 times the rates of COF and BiOBr,respectively.The construction of S-scheme heterojunction contributed to ef-ficient carrier transfer and separation in space and enhanced redox power.Moreover,the lying-down O_(2)-adsorption configuration on the COF surface favors the concerted two-electron O_(2) reduction process,which greatly reduced the reduction potential requirement for O_(2)-to-H_(2)O_(2) conversion.The synergy be-tween the S-scheme heterojunction and the unique O_(2)-COF interaction boosted photocatalytic H_(2)O_(2) pro-duction activity.

TiO_(2)/In_(2)S_(3)S-scheme photocatalyst with enhanced H_(2)O_(2)-production activity

Photocatalytic production of hydrogen peroxide(H_(2)O_(2))is an ideal pathway for obtaining solar fuels.Herein,an S-scheme heterojunction is constructed in hybrid TiO_(2)/In_(2)S_(3)photocatalyst,which greatly promotes the separation of photogenerated carriers to foster efficient H_(2)O_(2)evolution.These composite photocatalysts show a high H_(2)O_(2)yield of 376μmol/(L·h).The mechanism of charge transfer and separation within the S-scheme heterojunction is well studied by computational methods and experiments.Density functional theory and in-situ irradiated X-ray photoelectron spectroscopy results reveal distinct features of the S-scheme heterojunction in the TiO_(2)/In_(2)S_(3)hybrids and demonstrate charge transfer mechanisms.The density functional theory calculation and electron paramagnetic resonance results suggest that O_(2)reduction to H_(2)O_(2)follows stepwise one-electron processes.In_(2)S_(3)shows a much stronger interaction with O_(2)than TiO_(2)as well as a higher reduction ability,serving as the active sites for H_(2)O_(2)generation.The work provides a novel design of S-scheme photocatalyst with high H_(2)O_(2)evolution efficiency and mechanistically demonstrates the improved separation of charge carriers.

Light-enhanced metal-support interaction for synergetic photo/thermal catalytic formaldehyde oxidation

The strong metal-support interaction(SMSI)plays a pivotal role in regulating electronic properties and activating surface oxygen species.In this work,we report light-irradiation-modulated SMSI for enhanced formaldehyde(HCHO)oxidation.Specifically,the SMSI between Pt nanoparticles(NPs)and Bi_(2)MoO_(6)cre-ated surface-active oxygen at Pt-Bi_(2)MoO_(6)interfaces to activate HCHO to dioxymethylene(DOM).Notably,light irradiation boosted the SMSI and catalytic activity.Moreover,photogenerated holes in Bi_(2)MoO 6 im-proved HCHO adsorption and activation,while photogenerated electrons migrated from Bi_(2)MoO_(6)to Pt NPs to promote O_(2)adsorption and activation,accelerating the oxidation of DOM to CO_(2)and H_(2)O.The light-modulated SMSI and the synergy between photocatalysis and thermocatalysis lead to enhanced cat-alytic oxidation activity,providing a practical strategy for indoor volatile organic compound(VOC)de-composition under ambient conditions.

Electron transfer dynamics in Schottky junction photocatalyst during electron donor-assisted hydrogen production

Electron donors(EDs)are widely used to improve the H 2 production performance of Schottky junction photocatalysts,but the functions of EDs are still unknown from the perspective of electron transfer dy-namics.Herein,Pt nanocluster-decorated CdS nanorod is successfully prepared to construct a typical CdS/Pt Schottky junction.Pt nanoclusters with a diameter of∼2 nm are deposited on the surface of CdS nanorods by in situ photoreduction at sub-zero temperature.The CdS/Pt photocatalyst using lactic acid shows a higher H_(2)production rate of 4762μmol g^(-1)h^(-1)compared to that using methanol,tri-ethanolamine,and glycerol.To understand the cause,the dynamics of photogenerated carriers in CdS/Pt photocatalysts during ED-assisted H_(2)production are revealed by femtosecond transient absorption spec-troscopy.Among the four organic EDs,lactic acid enables the fastest electron transfer rate of 1.8×10^(9)s^(-1)and the highest electron transfer efficiency of 76%at the CdS/Pt interface due to the most efficient hole consumption.This work sheds light on the importance of efficient interfacial electron transfer for im-proving the photocatalytic performance of Schottky junction photocatalysts.

Review on g-C_(3)N_(4)-based S-scheme heterojunction photocatalysts

With the rapid development of economy and modern industry,serious environmental pollution and energy shortage have become major urgent challenges to the human society.Photocatalysis is a promising technology to provide green energy.As a typical metal-free polymer photocatalyst,g-C_(3)N_(4) has attracted more and more attention due to its excellent performance.Unfortunately,the fast recombination of photo-induced charges,limited light response range as well as weak oxidation ability are still the key drawback that restrict the photocatalytic performance of g-C_(3)N_(4).These problems can be effectively addressed by constructing g-C_(3)N_(4)-based heterojunctions with two or more semiconductor materials,during which the respective advantages can be integrated.Up to now,the various oxidation semiconductor photocatalysts have been tried to construct the novel S-scheme heterojunction photocatalysts with g-C_(3)N_(4).Thus,this review provides a comprehensive introduction of g-C_(3)N_(4)-based S-scheme heterojunctions,including the main characteristics of the S-scheme heterojunction,photocatalytic mechanisms,design rules and preparation methods of g-C_(3)N_(4)-based S-scheme heterojunction photocatalysts.Moreover,this review summarizes recently reported works on the potential applications of g-C_(3)N_(4)-based S-scheme photocatalysts in various important photocatalytic reactions,including photocatalytic hydrogen production,photocatalytic degradation of contaminants,photo-reduction of CO_(2) into fuels,and photocatalytic sterilization.Finally,based on the current research progress,we propose some shortages in the preparation methods and applications of g-C_(3)N_(4)-based S-scheme heterojunctions,which are to be further investigated and resolved in this promising and creative research field.

Photodeposition of CoOx and MoS2 on CdS as dual cocatalysts for photocatalytic H2 production

Photocatalytic Hproduction from water splitting has a promising prospect for alleviating energy and environmental issues.However,the fast recombination of photogenerated charge carriers limits the photocatalytic efficiency and its practical application.Cocatalyst engineering is an effective strategy to spatially separate photogenerated charge carriers.In this work,noble-metal-free MoSand CoOcocatalysts are loaded on CdS nanorods by a two-step photodeposition method.The MoSfunctions as the reduction cocatalyst to trap electrons and Co Oas the oxidation cocatalyst to trap holes.Transmission electron microscopy(TEM),inductively coupled plasma(ICP),X-ray photoelectron spectroscopy(XPS)and MottSchottky results demonstrate the effectiveness of photodeposition for loading MoSand CoOdual cocatalysts on CdS and their impact on the photochemical properties.The optimized CdS-MoS-CoOcomposite exhibits a high photocatalytic H-production rate of 7.4 mmol g^(-1)h^(-1)and an apparent quantum efficiency(QE)of 7.6%at 420 nm.Further analysis on time-resolved photoluminescence(TRPL)indicates that the introduction of dual cocatalysts greatly prolongs the lifetime of photogenerated charge carriers and deceases the charge recombination rates,consequently leading to superior photocatalytic H-production performance.This work provides a facile and effective strategy for the construction of highly efficient dual-cocatalyst-modified CdS photocatalyst for high-performance photocatalytic Hproduction.

S-scheme ZnO/WO3 heterojunction photocatalyst for efficient H2O2 production

Designing highly efficient photocatalyst for hydrogen peroxide(HO)production is an ideal strategy to avoid the shortcomings of traditional HOproduction and to realize the conversion of solar energy to chemical energy.In this work,a step-scheme(S-scheme)heterojunction photocatalyst composed of Zn O and WOis carefully prepared by hydrothermal and calcination method for efficient photocatalytic HOproduction.The ZW30 composite photocatalysts exhibit enhanced activity with the highest HO-production rate of 6788μmol Lh.The results show that the photocatalytic HOproduction process is dominated by a direct two-electron Oreduction pathway.The enhanced photocatalytic HO-production activity is attributed to the formation of interfacial internal electric field(IEF)in the S-scheme heterojunction,which boosts the spatial separation of charge carriers and enables electrons with the strongest reduction power to participate in HOproduction.This work provides an in-depth insight of the great advantages of S-scheme heterojunction in photocatalytic HOproduction.

Molecular-level Engineering of S-scheme Heterojunction:the Site-specific Role for Directional Charge Transfer

The promising S-scheme heterojunction photocatalysts are considered as a novel frontier due to their superiority in various solar-driven energy-related applications.Recently,a novel atom-specific tailoring strategy has been introduced on the construction of S-scheme het-erojunction for promoting the electronic transferability.The S-scheme heterojunction is regulated by integrating high-crystalline carbon nitride with Co-doped CeO_(2).Specifically,this atom-specific regulation of S-scheme heterojunction boosts directional electron-driving effect towards functionalized Co sites,benefit-ing for effective photogenerated charge carrier transferability.Moreover,a series of tracking characterizations show that Co-embedded modification promotes CO_(2)photoreduction into hydrogenation steps,resulting in high performance towards CO_(2)-to-CH_(4)photoreduction,which provides new opportunities for the development of multifunctional cooperation in heterogeneous photocatalysis.