From CO oxidation to CO2 activation: an unexpected catalytic activity of polymer-supported nanogold

A simple, clean, safe, and reproducible catalyst system, polymer-supported nanogold, was successfully developed for the fixation of CO2 to cyclic carbonate and for the carbonylation of amines to disubstituted ureas with unprecedented catalytic activity (TOF > 50 000 mol/mol/h and TOFP approximately 3000 mol/mol/h, respectively). To the best of our knowledge, it was the first to report that nanogold catalysts have exclusive catalytic activity for activation of carbon dioxide, and that the catalytic activity of the polymer-immobilized nanogold catalysts could be controlled by the particle size of the nanogold.     

Amide-bridged conjugated organic polymers: efficient metal-free catalysts for visible-light-driven CO2 reduction with H2O to CO

The visible-light-driven photoreduction of CO₂ to value-added chemicals over metal-free photocatalysts without sacrificial reagents is very interesting, but challenging. Herein, we present amide-bridged conjugated organic polymers (amide-COPs) prepared via self-condensation of amino nitriles in combination with hydrolysis, for the photoreduction of CO₂ with H₂O without any photosensitizers or sacrificial reagents under visible light irradiation. These catalysts can afford CO as the sole carbonaceous product without H₂ generation. Especially, amide-DAMN derived from diaminomaleonitrile exhibited the highest activity for the photoreduction of CO₂ to CO with a generation rate of 20.6 μmol g⁻¹ h⁻¹. Experiments and DFT calculations confirmed cyano/amide groups as active sites for CO₂ reduction and second amine groups for H₂O oxidation, and suggested that superior selectivity towards CO may be attributed to the adjacent redox sites. This work presents a new insight into designing photocatalysts for artificial photosynthesis.

Amino nitrile-derived conjugated organic polymers can realize the photoreduction of CO₂ with water to CO without H₂ generation efficiently.     

利用光热耦合下的光电导研究TiO2光热催化还原CO2（英文）

利用太阳能缓解能源危机和解决环境污染,是当前和未来的全球性课题.其中,光催化技术的研究步伐日渐加快.这不仅体现在光催化材料种类的增加,更体现在以光催化为基础的多场协同催化,特别是光热耦合作用成为增强光催化性能的一种高效、可靠的方法.氧空位的引入不仅可以拓宽催化剂对可见光的吸收、抑制载流子的复合、促进反应物的吸附以及降低反应的活化能,而且对于光热协同催化效率的提升有着重要的贡献.然而,目前光热协同催化的表征多局限于常规的光催化手段.开展光热耦合下的测量技术对深刻理解光热催化是十分必要的.本文研究温度、气氛、氧空位浓度对TiO2光电导的影响,构建光电导与光热催化活性之间的关系.我们将商用的ST-01 TiO2制成浆料,利用丝网印刷法将浆料覆盖在刻有沟槽的FTO上,并通过N2/H2混合气不同温度退火,得到不同氧空位含量的TiO2薄膜(Ov-TiO2).采用紫外-可见光谱(UV-Vis),拉曼光谱(Raman),电子顺磁共振(ESR)等手段对样品进行了表征.结果表明,N2/H2退火温度越高,氧空位浓度越高.我们对不同浓度氧空位的样品进行了光催化及光热协同催化CO2还原实验.结果表明,适量氧空位的样品(H2-150)光催化还原CO2性能最差,但光热协同催化还原CO2的性能最佳.我们对其光电导值的衰减情况进行了分析,看到H2-150样品在CO2气氛、光热条件下,电导衰减加快.由于光电导的衰减是由电荷复合和电荷参与的表面反应共同决定的,为确定是哪一因素决定了电导的衰减,我们进一步测试了H2-150样品在N2气氛下的电导衰减情况.结果发现,H2-150样品在N2气氛、光热条件下电导衰减反而变慢.这表明,造成H2-150样品在CO2气氛、光热条件下的电导衰减加快是光热条件下CO2还原速率加快,也验证了H2-150具有较好的光热催化CO2活性.与H2-150样品不同的是,大量氧空位样品(H2-350)在CO2气氛、光热条件下电导衰减反而变慢,我们认为这是由于H2-350存在深能级缺陷,在热的作用下会将捕获的电子释放,因此延缓了光电导的衰减.但由于深能级电子的还原能力较弱,所以H2-350样品的光热CO2还原活性稍逊于H2-150.综上所述,在光热电导与光热催化相关的研究中,我们证实了在Ov-TiO2中被捕获的电子在热激发下可再次向导带弛豫,从而解释了Ov-TiO2优异的光热催化性能.因此,光热电导的研究在理解光热催化方面具有重要的前景.     

Fine tuning of the catalytic effect of a metal-free porphyrin on the homogeneous oxygen reduction

The catalytic effect of tetraphenylporphyrin on the oxygen reduction with ferrocene in 1,2-dichloroethane can be finely tuned by varying the molar ratio of the acid to the catalyst present in the solution. The mechanism involves binding of molecular oxygen to the protonated free porphyrin base, in competition with ion pairing between the protonated base and the acid anion present.     

Advances in the electrochemical catalytic reduction of CO2 with metal complexes

Electrocatalytic CO₂ reduction has emerged as a promising strategy to effectively produce fuels and chemicals sustainably. In this regard, the study of electrochemical catalytic reduction of CO₂ with metal complexes is a powerful tool for both the development of catalysts that operated under desired conditions (low overpotentials, high catalytic rates and selectivity, and extended durability) and the understanding of basic principles in catalysis. To illustrate the state-of-the-art, this revision presents a selection of the most recent and remarkable findings reported in terms of key strategies to improve reaction rates, selectivity and mechanism understanding for the leading families of homogeneous catalysts.     

Recent advances in sulfoxidation reactions: a metal-free approach

Through the oxidation of sulfides useful elements of stereocontrol in asymmetric synthesis and important targets of pharmaceutical interest can be obtained. A number of metal-free methods have been developed over recent years for sulfoxidation reactions. The results published after 1998 through the beginning of 2010 have been reviewed with a focus being placed on sulfoxidations with hypervalent iodine compounds; iminium- and oxaziridinium derivatives; organic hydroperoxides and organocatalysts. In addition, autocatalytic and catalyst-free variants are discussed. Although, the asymmetric organocatalytic sulfoxidation is still in its infancy, the reported results show the high potential and versatility of this metal-free methodology.     

High catalytic activity of Ti-porphyrin for NO reduction by CO: a first-principles study

The present theoretical study was carried out to investigate the NO reduction by CO over a Ti-porphyrin catalyst. Thus, density functional theory with and without the van der Waals correction was employed. The calculated adsorption energies show that the Ti-porphyrin is active in bending the NO and CO molecules. So, we proposed two reaction mechanisms for the NO reduction by CO on Ti-porphyrin. The calculated activation energies show that both mechanisms are plausible and feasible at room temperature. The Ti-porphyrin shows a good catalytic activity to NO reduction by CO compared to conventional Rh⁷⁺ cluster catalyst. These results indicate that the Ti-porphyrin is a promising candidate for reducing NO and CO gases from our environment.     

A catalytic metal-free Ritter reaction to 3-substituted 3-aminooxindoles

The first Ritter reaction of 3-substituted 3-hydroxyoxindoles with nitriles, catalyzed by HClO(4), is developed, which enables the synthesis of 3-substituted 3-aminooxindoles in good to excellent yield with rich diversity.     

Efficient homogeneous catalysis in the reduction of CO2 to CO

The well-defined copper(I) boryl complex [(IPr)Cu(Bpin)] [where IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene, and pin = pinacolate: 2,3-dimethyl-2,3-butanediolate] deoxygenates CO2 rapidly and quantitatively, affording CO and the borate complex [(IPr)Cu(OBpin)]. The boryl may be regenerated by treatment with the diboron compound pinB-Bpin, giving the stable byproduct pinB-O-Bpin. The use of a copper(I) alkoxide precatalyst and stoichiometric diboron reagent results in catalytic reduction of CO2, with high turnover numbers (1000 per Cu) and frequencies (100 per Cu in 1 h) depending on supporting ligand and reaction conditions.     

Electrocatalytic reduction of CO2 to CO by polypyridyl ruthenium complexes

Electrocatalytic reduction of CO(2) by [Ru(tpy)(bpy)(solvent)](2+) (tpy = 2,2':6',2'-terpyridine, bpy = 2,2'-bipyridine) and its structural analogs is initiated by sequential 1e(-) reductions at the tpy and bpy ligands followed by rate limiting CO(2) addition to give a metallocarboxylate intermediate. It undergoes further reduction and loss of CO.     

Remarks on catalytic reduction of CO2, H+ and H2 by monovalent Ni

Prompted by catalysis of CO2 electroreduction by a tetraazamacrocyclic Ni(i)(cyclam) complex (cyclam = 1,4,8,11-tetraazacyclotetradecane), we examine theoretically the possibility of H2 reduction by this molecule. We show that the process 2 Ni(i) + H2 --> 2 [Ni(ii)(H-)] is thermodynamically facile, and that H2 could be reduced by a binuclear Ni(i) complex in two concerted 1e- processes. Our calculations also indicate that hydride complexes of Ni(iii)(cyclam) are significantly unstable thermodynamically and therefore they are unlikely to serve as intermediates in process of H2 evolution from water.     

Hantzsch ester triggered metal-free cascade approach to isoindolinones

Disclosed herein is an expedient synthesis of biologically important isoindolinone derivatives from reactions of 2-formylbenzoic acids with various amines. This method operates via a deliberately designed catalyst-free tandem reductive amination/cyclization cascade event triggered by a transfer hydrogenation process with easily available Hantzsch ester as the organic hydride source. The ease of operation, mild reaction conditions, facile accessibility of the starting materials, and easy scalability of the current method distinguish it from the other precedent protocols, thus enable it a practical approach to the syntheses of valuable isoindolinone-incorporated drugs.     

(2-Pyridyl)phenyl methanol: a new reagent for metal-free reduction of nitro aromatic compounds

As previously reported for 1-(2-pyridyl)-2-propen-1-ol, (2-pyridyl)phenyl methanol is able to react as hydrogen donor towards nitro aromatic and heteroaromatic compounds. Operating in the presence of methyl acrylate as an aza-Michael acceptor, a domino process involving reduction and conjugate addition steps allows the one pot formation of β-amino esters. The crucial role of the pyridine nucleus in making this purely thermal reactivity of carbinols possible has been shown.     

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.     

Synchronous activation of Ag nanoparticles and BiOBr for boosting solar-driven CO2 reduction

Artificial photosynthesis of valuable chemicals from CO₂ is a potential way to achieve sustainable carbon cycle. The CO₂ conversion activity is still inhibited by the sluggish charge kinetics and poor CO₂ activation. Herein, Ag nanoparticles coupled BiOBr have been constructed by in-situ photoreduction strategy. The crafting of interface between Ag nanoparticles and BiOBr nanosheets, achieving an ultra-fast charge transfer. The BiOBr semiconductor excited electrons and plasmonic Ag nanoparticles generated high-energy hot electrons synchronous accelerates the C=O double bond activation. Thus, the optimized Ag/BiOBr-2 heterostructure shows excellent CO₂ photoreduction activity with CO production of 133.75 and 6.83 µmol/g under 5 h of 300 W Xe lamp and visible light (λ > 400 nm) irradiation, which is 1.51 and 2.81 folds versus the pristine BiOBr, respectively. The mechanism of CO₂ photoreduction was in-depth understood through in-situ FT-IR spectrum and density functional theory calculations. This study provides some new perspectives into efficient photocatalytic CO₂ reduction.     

钙钛矿材料光催化还原CO2综述

利用半导体材料光催化还原CO2合成可燃物是目前解决能源危机和缓解温室效应的理想途径.本文对几种钙钛矿型材料,包括纯无机卤化物钙钛矿材料、金属有机钙钛矿材料、氧化物型钙钛矿材料和复合型钙钛矿材料在光催化还原CO2领域的应用进行了简单的归纳与总结.     

Covalent attachment of a rhenium bipyridyl CO2 reduction catalyst to Rutile TiO2

We have characterized the covalent binding of the CO(2) reduction electrocatalyst ReC0A (Re(CO)(3)Cl(dcbpy) (dcbpy =4,4'-dicarboxy-2,2'-bipyridine)) to the TiO(2) rutile (001) surface. The analysis based on sum frequency generation (SFG) spectroscopy and density functional theory (DFT) calculations indicates that ReC0A binds to TiO(2) through the carboxylate groups in bidentate or tridentate linkage motifs. The adsorbed complex has the dcbpy moiety nearly perpendicular to the TiO(2) surface and the Re exposed to the solution in a configuration suitable for catalysis.     

From amines to diketopiperazines: a one-pot approach

An efficient one-pot synthesis is described for the preparation of 1,4-disubstituted piperazine-2,5-diones starting from a suitable amine and chloroacetyl chloride in the presence of an aqueous base. The resulting chloroacetamide is cyclised in situ by employing the phase-transfer (PT) catalyst, benzyltriethylammonium chloride (TEBA). The products are isolated in excellent yields of up to 90%.