State‐sensitive XAFS was enabled combined with high‐energy‐resolution (ΔE = 0.3 eV@5.5 keV) X‐ray fluorescence spectrometry and applied to Au sites of An/TiO2 and Sn promoter sites of Pt‐Sn/SiO2. Each state of interfacial Au sites located on Ti/O atoms and negatively/positively charged Aun clusters was discriminated. Feasibility of more direct information of on‐site catalysis via frontier orbital‐sensitive XAFS was demonstrated.
X-ray absorption fine structure combined with fluorescence spectrometry was used for the speciation of trace amounts of lead and arsenic adsorbed. The Pb2+ species were effectively adsorbed on a layered material Mg6Fe2(OH)16(CO3)·3H2O from 100 ppb–1.0 ppm test aqueous solutions. A eutectic mixture of PbCO3 and Pb(OH)2 coagulated in the case of a 1.0 ppm Pb2+ solution, and in contrast, the major species was ion-exchanged Pb2+ in the case of the adsorption from the 100 ppb aqueous solution. The arsenic species were effectively adsorbed on intercalated Fe-montmorillonite from 50 ppb–16 ppm test aqueous solutions. In this concentration range, As3+ in the solution was oxidized upon adsorption. The adsorbed structure was suggested to be [AsV(OH)2(μ-OFe)2] both in the cases of adsorption of As3+ and As5+.
The local structure of trace amounts of lead in an adsorbent matrix that contains a high concentration of iron and magnesium (Mg6Fe2(OH)16(CO3)·3H2O) was successfully monitored by means of X-ray absorption fine structure spectroscopy combined with fluorescence spectrometry. A eutectic mixture of PbCO3 and Pb(OH)2 coagulated when Pb2+ was adsorbed from a 1.0 ppm aqueous solution, and in contrast, the major species was ion-exchanged Pb2+ in the case of adsorption from a 100 ppb aqueous solution. The difference was ascribed to the balance between the precipitation equilibrium for coagulation and the rate of the ion exchange reaction with surface hydroxyl groups.
Photocatalytic reduction of CO2 into C2,3 hydrocarbons completes a C‐neutral cycle. The reaction pathways of photocatalytic generation of C2,3 paraffin and C2H4 from CO2 are mostly unclear. Herein, a Co0–ZrO2 photocatalyst converted CO2 into C1–3 paraffin, while selectively converting CO into C2H4 and C3H6 (6.0 ± 0.6 μmol h−1 gcat−1, 70 mol%) only under UV–visible light. The photocatalytic cycle was conducted under 13CO and H2, with subsequent evacuation and flushing with CO. This iterative process led to an increase in the population of C2H4 and C3H6 increased up to 61–87 mol%, attributed to the accumulation of CH2 species at the interface between Co0 nanoparticles and the ZrO2 surface. CO2 adsorbed onto the O vacancies of the ZrO2 surface, with resulting COH species undergoing hydrogenation on the Co0 surface to yield C1–3 paraffin using either H2 or H2O (g, l) as the reductant. In contrast, CO adsorbed on the Co0 surface, converted to HCOH species, and then split into CH and OH species at the Co and O vacancy sites on ZrO2, respectively. This comprehensive study elucidates intricate photocatalytic pathways governing the transformation of CO2 into paraffin and CO to olefins.
In this chapter, recent advances in photocatalytic CO2 conversion with water and/or other reductants are reviewed for the publications between 2012 and 2015. Quantitative comparisons were made for the reaction rates in μmol h−1 gcat −1 to acertain the progress of this field although the rates depends on photocatalyst conditions and reaction conditions (temperature, pressure, and photon wavelength and flux). TiO2 photoproduced methane or CO from CO2 and water at rates of 0.1–17 μmol h−1 gcat −1 depending on the crystalline phase, crystalline face, and the defects. By depositing as minimal thin TiO2 film, the rates increased to 50–240 μmol h−1 gcat −1. Gaseous water was preferred rather than liquid water for methane/CO formation as compared to water photoreduction to H2. Pt, Pd, Au, Rh, Ag, Ni, Cu, Au3Cu alloy, I, MgO, RuO2, graphene, g-C3N4, Cu-containing dyes, and Cu-containing metal-organic frameworks (MOFs) were effective to assist the CO2 photoreduction using TiO2 to methane (or CO, methanol, ethane) at rates of 1.4–160 μmol h−1 gcat −1. Metals of greater work function were preferred. By depositing as minimal thin photocatalyst film, the rates increased to 32–2200 μmol h−1 gcat −1. The importance of crystal face of TiO2 nanofiber was suggested. As for semiconductors other than TiO2, ZnO, Zn6Ti layered double hydroxide (LDH), Mg3In LDH, KTaO3, In(OH)3, graphene, graphene oxide, g-C3N4, CoTe, ZnO, ZnTe, SrTiO3, ZnGa2O4, Zn2GeO4, Zr–Co–Ir oxides, Nb2O5, HNbO3, NaNbO3, InNbO4, NiO, Co3O4, Cu2O, AgBr, carbon nanotube, and the composites of these were reported to form methane, CO, methanol, acetaldehyde from CO2 and water at rates of 0.15–300 μmol h−1 gcat −1 that were comparable to rates using promoted TiO2. The band energy designs comprising appropriate conduction band for CO2 reduction and valence band for water oxidation were made progresses in these semiconductors and semiconductor junctions in the three years. If H2 was used as a reductant, Ni/SiO2-Al2O3 formed methane at 423 K under pressurized CO2 + H2 at a rate of 55 mmol h−1 gcat −1. This rate was not enabled by heating the system under dark, suggesting photoactivated reaction followed by thermally-assisted reaction(s) via Ni–H species. As pure photocatalytic reactions from CO2 + H2, methanol formation rates were improved up to 0.30 μmol h−1 gcat −1 by the doping of Ag/Au nanoparticles, [Cu(OH)4]2− anions, and Cu-containing dyes to Zn–Ga LDH. Furthermore, sacrificial reductants, e.g. hydrazine, Na2SO3, methanol, triethanol amine, and triethyamine, were also utilized to form CO, formate, and methanol at rates of 20–2400 μmol h−1 gcat −1 using semiconductor or MOF photocatalysts. Finally, similar to the integrated system of semiconductor photocatalyst for water oxidation and metal complex/enzyme catalyst for CO2 (photo)reduction, two semiconductors (WO3, Zn–Cu–Ga LDH) were combined on both side of proton-conducting polymer to form methanol at a rate of 0.05 μmol h−1 gcat −1 from CO2 and moisture. These promotion of photoconversion rates of CO2 and new photocatalysts found in these three years have indicated the way beyond for a new energy.
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTStudy of stereochemical properties of molecular orbitals by Penning ionization electron spectroscopy. Effects of through-space/through-bond interactions on electron distributionsKoichi Ohno, Toshimasa Ishida, Yukito Naitoh, and Yasuo IzumiCite this: J. Am. Chem. Soc. 1985, 107, 26, 8082–8086Publication Date (Print):December 1, 1985Publication History Published online1 May 2002Published inissue 1 December 1985https://pubs.acs.org/doi/10.1021/ja00312a048https://doi.org/10.1021/ja00312a048research-articleACS PublicationsRequest reuse permissionsArticle Views261Altmetric-Citations33LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts
Photocatalytic conversion of CO2 into fuels is an attractive option in terms of both reducing the increased concentration of atmospheric CO2 as well as generating renewable hydrocarbon fuels. It is necessary to investigate good catalysts for CO2 conversion and to clarify the mechanism irradiated by natural light. Layered Double Hydroxides (LDH) have been attracting attention for CO2 photoreduction with the expectation of sorption capacity for CO2 in the layered space and tunable semiconductor properties as a result of the choice of metal cations. This study first clarifies the effects of Cu doping to LDH comprising Zn and Al or Ga. Cu could be incorporated in the cationic layers of LDH as divalent metal cations and/or interlayer anions as Cu(OH)42−. The formation rates of methanol and CO were optimized for [Zn1.5Cu1.5Ga(OH)8]+2Cu(OH)42−·mH2O at a total rate of 560 nmol h−1 gcat−1 irradiated by UV–visible light. Cu phthalocyanine tetrasulfonate hydrate (CuPcTs4−) and silver were effective as promoters of LDH for CO2 photoreduction. Especially, the total formation rate using CuPcTs-[Zn3Ga(OH)8]+2CO32−·mH2O irradiated by visible light was 73% of that irradiated by UV–visible light. The promotion was based on HOMO–LUMO excitation of CuPcTs4− by visible light. The LUMO was distributed on N atoms of pyrrole rings bound to central Cu2+ ions. The photogenerated electrons diffused to the Cu site would photoreduce CO2 progressively in a similar way to inlayer and interlayer Cu sites in the LDH in this study.
Both the metallurgical and electrochemical studies were simultaneously performed in order to understand the mechanism of stress corrosion cracking (SC cracking) in Al-Zn-Mg alloys. The intergranular corrosion occurred preferentially in the low temperature aged specimens. Its ageing condition resulted in the high SC susceptibility and the pH dependence of the corrosive solution, where the SC cracking life was suggested to be controlled by the nucleation process of the SC crack at the grain boundary. On the other hand, general corrosion progressed in the two-step aged specimens. The alloy containing a small amount of the Cu element had a tendency toward general corrosion regardless of the heat treatment. The general corrosion was very effective in decreasing the SC susceptibility and the pH dependence. For the long life of SC cracking, the propagation of SC cracking exerted a dominant role. The propagation was modulated by some profitable microstructural factors as the region denuded of grain boundary precipitates and the precipitated free zones.
Abstract Site-selective XAFS spectra were measured by tuning the Rowland-type fluorescence spectrometer to each site of Cu/ZnO and Cr/SiO2 catalysts. The chemical shifts between Cu0 and CuI sites and between CrIII and CrVI sites were relatively large for model compounds (ΔE = 1.6 eV), and were utilized as the tune energies of site-selective XAFS. Site-selective XANES tuned to Cu0, CuI, and CrIII sites were successfully obtained. Based on the correlation between the chemical shift and the peak width (energy resolution of the fluorescence spectrometer), site-selective XANES spectra were analyzed. The population ratio of Cu metal, Cu2O, and CuI atomically dispersed on ZnO was estimated to be 70(±23) : 22(±14) : 8(±5). The contribution of the CrIII site to site-selective XANES tuned to the CrIII site was 94(±3)%.
