Highly-efficient and autocatalytic reduction of NaHCO_3 into formate by in situ hydrogen from water splitting with metal/metal oxide redox cycle

The Earth's sustainable development is threatened by the increasing atmospheric CO_2 level which can be attributed to the imbalance of CO_2 due to the rapid consumption of fossil fuels caused by human activities and the slow absorption and conversion of CO_2 by nature. One of the efficient methods for reconstructing the balance of CO_2 should involve the rapid conversion of CO_2 into fuels and chemicals.The hydrogenation of CO_2 with gaseous hydrogen is currently considered to be the most commercially feasible synthetic route, however, the supply of safe and economical hydrogen sources poses a significant challenge to up-scaling application. Direct utilization of hydrogen from dissociation of water, the most abundant, cheap and clean hydrogen resource, for the reduction of CO_2 would be one of the most promising approaches for CO_2 utilization. This paper provides an overview of the current advances in research on highly efficient reduction of CO_2 or NaHCO_3, a representative compound of CO_2, into formic acid/formate by in situ hydrogen from water dissociation with a metal/metal oxide redox cycle under mild hydrothermal conditions.     

MoS2/Zn3In2S6复合光催化剂构建:高效提升可见光驱动甲酸制氢

虽然传统的化石燃料依然能够满足当今快速工业化发展对能源的巨大需求,但其固有的不可再生性及其燃烧产物对环境的污染,严重阻碍了其在生产和生活中的广泛使用.因此,可持续清洁能源开发的研究已快速成为人类研究的热点.氢是一种具备高热值、可持续等优点的清洁能源,也兼备成本及污染低等优势.甲酸(FA)以其无毒、低成本、氢含量高等优点,是一种潜在的热门储氢材料,而可见光占太阳光谱的43%左右.因此,开发高效可见光催化剂驱动FA制氢将是一种应对能源危机的有效途径.许多传统光催化剂已被用于可见光催化FA制氢,但制备成本高、过程复杂、条件苛刻及可见光响应差、稳定性和选择性差、有毒气体释放等缺点严重限制了其光催化性能.光催化研究关键之一是实现光生电荷的高效率分离和转移,从而光催化剂光催化性能的提高.Zn3In2S6(ZIS6)因具有强可见光吸收、稳定性好及环保等特点正迅速成为光催化剂半导体的“明星”,常与助催化剂(如贵金属Pt、Au、Pd等)复合形成异质结以促进光生载流子分离和提高其光催化活性,但制备成本高等因素却严重限制其发展.将成本低、化学稳定性好的MoS2与其它半导体耦合也是提高半导体光催化剂性能的有效手段之一,但高温、热处理时间长及有毒气体释放等却成了制约因素.本文选用价格低廉的反应前驱体,采用简单的一锅法水将MoS2紧密地结合到ZIS6的表面,热制备了一系列含有不同质量百分比MoS2的MoS2/Zn3In2S6(MoS2/ZIS6)复合光催化剂,有效降低了制备成本和有毒气体(H2S)的释放.结果表明,可见光照射下(λ>400 nm),MoS2的引入可大大提高ZIS6光生电荷分离效率及制氢活性,尤其以0.5%MoS2/ZIS6性能最优,光催化制氢速率高达74.25μmol·h^-1(量子效率约2.9%),约ZIS6的4.3倍(17.47μmol·h^-1).XRD结果表明,MoS2/ZIS6样品中含有无定型MoS2紧密固定在晶型ZIS6片状结构表面,未影响ZIS6晶型,SEM表征也证实了此结果.随后的TEM、HRTEM及EDX结果也进一步确认了各组成元素的存在和分布.采用XPS对元素化学环境进行了分析,通过S和Mo元素的成键能变化证实了MoS2和ZIS6间的紧密接触.UV-Vis DRS测试表明,MoS2/ZIS6可以利用可见光在适当带隙的基础上进行光催化制氢.通过BET、PL和电化学技术研究了比表面积、光生电荷分离和传递速率等对光催化性能的影响.最终,结合上述表征结果成功阐述了可见光驱动FA制氢的反应机理.     

High-quality hydrogen from the catalyzed decomposition of formic acid by Pd-Au/C and Pd-Ag/C

Pd-Au/C and Pd-Ag/C were found to have a unique characteristic of evolving high-quality hydrogen dramatically and steadily from the catalyzed decomposition of liquid formic acid at convenient temperature, and further this was improved by the addition of CeO(2)(H(2)O)(x).     

The role of local structure on formic acid decomposition in supercritical water: A hybrid quantum mechanics/Monte Carlo study

We explored water-assisted decompositions of formic acid in supercritical water in terms of local structure near reactant. A hybrid quantum mechanics/molecular mechanics (QM/MM) simulation used in this paper includes QM part as first solvation shell members around the reactant. A present QM/MM approach can simulate supercritical water solution with a reasonable computational load while keeping the simulation preciseness because a density functional theory of B3LYP/6-31+G(d) level was iterated at every 1000 Monte Carlo solute moves. The formic acid converts mainly decarboxylation by water-assisted mechanism, and the coordinated water molecules play an important role for understanding supercritical water density dependence of the reaction. We analyzed a contour map based on the solute–solvent interaction energy along with the reaction pathway. Coordinated water molecule restricted the dehydration pathway by means of hydrogen bond with formic acid, however, the coordinated water promotes the decarboxylation pathway by means of stabilization of the transition state structure with one catalytic water molecule. The contour map of the pair interaction energy along the reaction path elucidates the role of local structure on reactions in supercritical water.     

高能Zn离子注入CaF2基质形成ZnO纳米粒子的机制、构型及电子结构

将高能Zn2+注入到CaF2介电基质中,在CaF2的表面下注入Zn2+浓度呈近似高斯分布,通过氧气氛后经热退火形成ZnO量子点.采用MaterialsStudio和Gaussian98W程序,结合实验结果计算分析了CaF2基质中ZnO纳米粒子的电子结构和光学性质.选取由4个ZnO原胞组成的超晶胞模型计算了ZnO纳米粒子的吸收光谱,理论结果与实验结果相符.对ZnO纳米粒子电子结构的研究结果表明,ZnO纳米粒子与CaF2基质的相互作用主要是ZnO表面的O与基质中Ca之间的作用,这种作用使ZnO纳米晶体的Fermi能级变窄,带隙相应减小;ZnO纳米粒子表面构型的变化对其本征吸收光谱没有影响,理论计算结果与实验值一致.     

Direct generation of hydrogen peroxide from formic acid and O2 using heterogeneous Pd/gamma-Al2O3 catalysts

Hydrogen peroxide formation is achieved with remarkable productivity at ambient conditions (25 degrees C and atmospheric pressure) in aqueous medium using a heterogeneous catalytic system; formic acid is decomposed in the presence of a continuous flow of O(2) over Pd/gamma-Al(2)O(3) catalyst leading to the generation of hydrogen peroxide; the addition of a negligible amount of bromide ion improves the selectivity of the reaction.     

微球形CdIn2S4/ZnO复合材料的多模式光降解与光解水制氢

本文通过水热辅助水浴法制备了CdIn₂S₄/ZnO复合材料,并采用XRD、XPS、UV-Vis/DRS、SEM、N₂吸附-脱附等测试技术对复合材料的晶形结构和表面物理化学性质进行了表征。结果表明,相比于单体ZnO,微球形复合材料CdIn₂S₄/ZnO晶型结构更加优异,孔径分布更加均匀,比表面积明显增大,其光吸收范围拓展至可见光区。多模式光催化降解染料亚甲基蓝的实验结果显示,微球形复合材料CdIn₂S₄/ZnO的光催化活性优于单体ZnO和CdIn₂S₄,其中CdIn₂S₄与ZnO的比例为1：5时活性最好,其对不同有机污染物均具有光降解能力;另外,光解水制氢实验结果显示,在8 h内产氢量达到310.2 μmol/g,表明该复合材料具有优异的光解水制氢性能。     

Enhanced effect of plasma on catalytic reduction of CO_2 to CO with hydrogen over Au/CeO_2 at low temperature

In terms of the reaction of CO_2 reduction to CO with hydrogen, CO_2 conversion is very low at low temperature due to the limitation of thermodynamic equilibrium(TE). To overcome this limitation, plasma catalytic reduction of CO_2 to CO in a catalyst-filled dielectric barrier discharge(DBD) reactor is studied. An enhanced effect of plasma on the reaction over Au/CeO_2 catalysts is observed. For both the conventionally catalytic(CC) and plasma catalytic(PC, Pin= 15 W) reactions under conditions of 400 °C, H_2/CO_2= 1,200 SCCM, GHSV = 12,000 mL·g~(-1)cat·h~(-1), CO_2 conversions over Au/CeO_2 reach 15.4% and 25.5% due to the presence of Au, respectively, however, those over CeO_2 are extremely low and negligible. Moreover,CO_2 conversion over Au/CeO_2 in the PC reaction exceeds 22.4% of the TE conversion. Surface intermediate species formed on the catalyst samples during the reactions are determined by in-situ temperatureprogrammed decomposition(TPD) technique. Interestingly, it disclosed that in the PC reaction, the formation of formate intermediate is enhanced by plasma, and the acceleration by plasma in the decomposition of formate species is much greater than that in the formation of formate species on Au/CeO_2. Enhancement factor is introduced to quantify the enhanced effect of plasma. Lower reactor temperature, higher gas hourly space velocity(GHSV), and lower molar ratio of H_2/CO_2 would be associated with larger enhancement factor.     

Kinetic study on disproportionations of C1 aldehydes in supercritical water: methanol from formaldehyde and formic acid

The reaction pathways and kinetics of C1 aldehydes, formaldehyde (HCHO) and formic acid (HCOOH=HOCHO), are studied at 400 degrees C in neat condition and in supercritical water over a wide range of water density, 0.1-0.6 g/cm3. Formaldehyde exhibits four reactions: (i) the self-disproportionation of formaldehyde generating methanol and formic acid, (ii) the cross-disproportionation between formaldehyde and formic acid generating methanol and carbon dioxide, (iii) the water-independent self-disproportionation of formaldehyde generating methanol and carbon monoxide, and (iv) the decarbonylation of formaldehyde generating hydrogen and carbon monoxide. The self- and cross-disproportionations overwhelm the water-independent self-disproportionation and the formaldehyde decarbonylation. The rate constants of the self- and cross-disproportionations are determined in the water density range of 0.1-0.6 g/cm3. The rate constant of the cross-disproportionation is 2-3 orders of magnitude larger than that of the self-disproportionation, which indicates that formic acid is a stronger reductant than formaldehyde. Combining the kinetic results with our former computational study on the equilibrium constants of the self- and cross-disproportionations, the reaction mechanisms of these disproportionations are discussed within the framework of transition-state theory. The reaction path for methanol production can be controlled by tuning the water density and reactant concentrations. The methanol yield of approximately 80% is achieved by mixing formaldehyde with formic acid in the ratio of 1:2 at the water density of 0.4 g/cm3.     

FTIR study of hydrogen bonding of stearic acid with ethanol, dimethyl sulfoxide,and acetonitrile in supercritical CO_2

FTIR spectroscopy was used to study the hydrogen bonding of stearic acid with ethanol, dimethyl sulfoxide (DMSO),and acetonitrile in supercritical CO_2 at 318.15 K, and 12.5 and 16.5 MPa. The concentrations of the cosolvents range from 0—0.6 mol·L~(-1). The area percentage of absorption bands for hydrogen-bonded and nonhydrogen-bonded species was obtained from the IR spectra. The acid and the cosolvents can form hydrogen bond even when their concentrations are very low. At fixed solute concentration, the extent of hydrogenbonding increases with cosolvent concentration. At higher ethanol concentrations, it seems that one stearic acid molecule can hydrogen bond with more than one ethanol molecules simultaneously. It is seen that the strength of the hydrogen bond formed by the acid and the cosolvents is in the order: DMSO>ethanol>acetonitrile.     

Anodic oxidation of formic acid on PdAuIr /C-Sb_2O_5·SnO_2 electrocatalysts prepared by borohydride reduction

PdAuIr/C-Sb2O5·SnO2electrocatalysts with Pd∶Au∶Ir molar ratios of 90∶5∶5,70∶20∶10 and 50∶45∶5 were prepared by borohydride reduction method.These electrocatalysts were characterized by EDX,X-ray diffraction,transmission electron microscopy and the catalytic activity toward formic acid electro-oxidation in acid medium investigated by cyclic voltammetry(CV),chroamperometry(CA)and tests on direct formic acid fuel cell(DFAFC)at 100℃.X-ray diffractograms of PdAuIr/C-Sb2O5·SnO2electrocatalysts showed the presence of Pd fcc phase,Pd-Au fcc alloys,carbon and ATO phases,while Ir phases were not observed.TEM micrographs and histograms indicated that the nanoparticles were not well dispersed on the support and some agglomerates.The cyclic voltammetry and chroamperometry studies showed that PdAuIr/C-Sb2O5·SnO2(50∶45∶5)had superior performance toward formic acid electro-oxidation at 25℃compared to PdAuIr/C-Sb2O5·SnO2(70∶20∶10),PdAuIr/C-Sb2O5·SnO2(90∶5∶5)and Pd/C-Sb2O5·SnO2electrocatalysts.The experiments in a single DFAFC also showed that all PdAuIr/C-Sb2O5·SnO2electrocatalysts exhibited higher performance for formic acid oxidation in comparison with Pd/C-Sb2O5·SnO2electrocatalysts,however PdAuIr/C-Sb2O5·SnO2(90∶5∶5)had superior performance.These results indicated that the addition of Au and Ir to Pd favor the electro-oxidation of formic acid,which could be attributed to the bifunctional mechanism(the presence of ATO,Au and Ir oxides species)associated to the electronic effect(Pd-Au fcc alloys).     

Synthesis of perovskite BaTaO2N with low defect by Zn doping for boosted photocatalytic water reduction

Perovskite BaTaO2N (BTON) is one of the most promising photocatalysts for solar water splitting due to its wide visible-light absorption and suitable conduction...     

Selective hydrogen transfer from formic acid to α,β-unsaturated ketones by polystyrene-bound IrCl(CO)(PPh3)2

Polytyrene-anchored chlorocarbonylbis(triphenylphosphine)iridium has been shown to be a highly stable and active catalyst for the selective transfer hydrogenation of α,β-unsaturated ketones by formic acid.     

Preparation of hydrogen from water by reduction with lithium aluminium hydride for the analysis of delta(2)H by isotope ratio mass spectrometry

An off-line technique is described for the preparation of H(2) from water prior to analysis of delta(2)H by dual-inlet isotope ratio mass spectrometry. H(2) is produced from sample water by reaction with LiAlH(4). This provides a rapid and inexpensive method for the analysis of delta(2)H in small (10 microL) samples of water. Precision was +/- 4.2 to 8.0 (1sigma(n), n = 8) delta(2)H(VSMOW) for samples between 428 and 1500 delta(2)H(VSMOW), +/- 14.5 delta(2)H(VSMOW) for water enriched to 3750 delta(2)H(VSMOW) and +/- 26.0 delta(2)H(VSMOW) for water enriched to 6100 delta(2)H(VSMOW). Accuracy was +/- 1.1 to 4.2 delta(2)H(VSMOW) for water standards from natural abundance to 1000 delta(2)H(VSMOW) (the highest enrichment at which water of accepted delta(2)H is currently available). This method for delta(2)H determination is most appropriate for use with small (<50 microL) samples of high delta(2)H enrichment such as those produced from doubly labelled water studies of small animals. The levels of measurement precision of delta(2)H would contribute 2.6-3.8% to the precision error in estimates of small animal energy expenditure made using the doubly labelled water technique when duplicate analyses are performed.     

Characterization and performance of Cu/ZnO/Al_2O_3 catalysts prepared via decomposition of M(Cu,Zn)-ammonia complexes under sub-atmospheric pressure for methanol synthesis from H_2 and CO_2

Methanol synthesis from hydrogenation of CO2 is investigated over Cu/ZnO/Al2O3 catalysts prepared by decomposition of M(Cu,Zn)-ammonia complexes (DMAC) at various temperatures.The catalysts were characterized in detail,including X-ray diffraction,N2 adsorption-desorption,N2O chemisorption,temperature-programmed reduction and evolved gas analyses.The influences of DMAC temperature,reaction temperature and specific Cu surface area on catalytic performance are investigated.It is considered that the aurichalcite phase in the precursor plays a key role in improving the physiochemical properties and activities of the final catalysts.The catalyst from rich-aurichalcite precursor exhibits large specific Cu surface area and high space time yield of methanol (212 g/(Lcat·h);T=513 K,p=3MPa,SV=12000 h-1).     

A comparative study of electrocatalytic hydrogen evolution by iron complexes of corrole and porphyrin from acetic acid and water

Transition Metal Chemistry - Iron complexes of corrole and porphyrin bearing electron-withdrawing meso-C6F5 groups had been used for the electrocatalytic evolution of hydrogen. In neutral buffer...