Theoretical study of vibration spectra of sensitizing dyes for photoelectrical converters based on ruthenium(II) and iridium(III) complexes

Quantum-chemical method of the density functional theory was employed to calculate, with the use of a B3LYP hybrid exchange-correlation functional, the IR absorption and Raman spectra of [Ru(bpy)₂(CN)₂] and [Ir(bpy)₂(CN)₂]⁺ complexes. All the normal vibrational frequencies were analyzed and new assignments of a number of bands in the IR absorption and Raman spectra were made. The role of vibrational motions of metal atoms and ligands in the vibronic deformation of electron shells in the course of electron transfer was discussed. This was done using data on surface-enhanced Raman spectra of [Fe(bpy)₂(CN)₂] and [Ru(bpy)₃]²⁺ complexes adsorbed on the surface of colloid silver.     

Fe/Zn double metal cyanide catalyzed ring-opening polymerization of propylene oxide: 2. Characterization of active structure of double metal cyanide catalysts

Double metal cyanide (DMC) complexes based on Zn₃[Fe(CN)₆]₂ were synthesized using different molar ratios of ZnCl₂ to K₃[Fe(CN)₆] and special complexing agents. IR spectroscopy, electron spectroscopy for chemical analysis, X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, and other analytical techniques were employed to characterize these catalysts. The morphology and structure of these DMC catalysts were attributed to the different complexing agents as well as to the different molar ratios of ZnCl₂ to K₃[Fe(CN)₆]. In addition, the catalytic activity was strongly correlated with the morphology and noncrystalline content of DMC catalysts. High-activity catalysts could be prepared by controlling the structure of DMC catalysts by incorporating complexing agents. The active species of DMC catalysts for ring-opening polymerization are Zn²⁺, [Fe(CN)₆]^3–, Cl^–, and the compound of their ligands.     

The state of metals in the Pt/Al2O3 and (Pt-Cu)/Al2O3 catalysts as indicated by IR spectroscopy with isotope dilution of 12C16O with 13C18O molecules

Adsorption of ¹³C¹⁸O+¹²C¹⁶O mixtures on the Pt(2.9%)/γ-Al₂O₃, (Pt(2.6%)+Cu(2.7%))/γ-Al₂O₃, and (Pt(2.6%)+Cu(5.1%))/γ-Al₂O₃ catalysts was studied by FTIR spectroscopy. On the metallic Pt surface at coverages close to saturation, CO is adsorbed both strongly and weakly to form linear species for which the vibrational frequencies of the isolated ¹³C¹⁸O molecules adsorbed on Pt are ∼1940 and ∼1970 cm⁻¹, respectively. The redistribution of intensities of the high-and low-frequency absorption bands in the spectra of adsorbed ¹³C¹⁸O indicates that these linear forms are present on the adjacent metal sites. The weak adsorption is responsible for the fast isotope exchange between the gaseous CO and CO molecules adsorbed on metal. The Pt-Cu alloys, in which the electronic state of the surface Pt atoms characteristic of monometallic Pt remains unchanged, are formed on the surface of the reduced Pt-Cu bimetallic catalysts. The decrease in the vibrational frequencies of the isolated C=O bonds in the isolated Pt-CO complexes suggests that the CO molecules adsorbed on the Cu atoms affect the electronic properties of Pt. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 831–836, May, 2007.     

Dehydration of Castor Oil over NaHSO4/MCM‐41 Catalyst Modified by n‐Dodecyltriethoxysilane

n‐Dodecyltriethoxysilane (DTEOS) modified NaHSO₄/MCM‐41 catalysts (silanized catalysts) were synthesized by different impregnation sequences and evaluated in the liquid‐phase dehydration of castor oil. The samples were evaluated by X‐ray diffraction, nitrogen adsorption‐desorption, SEM, TEM, FT‐IR spectroscopy, XPS, ²⁹Si MAS NMR spectroscopy, contact angle measurements, NH₃‐TPD, and pyridine‐FT‐IR spectroscopy. The analyses demonstrated that silanization enhanced the hydrophobicity of the catalysts, and the impregnation sequence of silanized catalysts had a significant effect on the NaHSO₄ dispersion, surface area, acid distribution, and hydrophobicity of the silanized catalysts. The catalytic activity of the silanized catalysts was much higher than that of NaHSO₄/MCM‐41. Among the silanized catalysts, the catalyst prepared by simultaneous impregnation with DTEOS and NaHSO₄ showed the highest iodine value of 141.8 [g(I₂) per 100 g] and lowest hydroxyl value of 11.3 [mg(KOH) · g^–1].     

Measurement of the surface coverage of V/Al2O3 catalysts by infrared spectroscopy, CO2 chemisorption and ion scattering spectroscopy

Quantitative FTIR studies of alumina hydroxyl groups have been used to measure the surface coverage of V/Al₂O₃ catalysts. The IR spectra show a preferential consumption of the most basic hydroxyls (3769 cm^–1) with the initial V uptake. The integrated area of the hydroxyl region was used to calculate the surface coverage of the catalysts. The surface coverage increased to 0.63 as the V loading increased to 6.7 wt%. The surface coverage results obtained from IR were compared to those measured by ion scattering spectroscopy (ISS) and CO₂ chemisorption. The surface coverages measured by ISS were comparable to those obtained by IR. In contrast, CO₂ chemisorption appears to overestimate the surface coverage of the catalysts. The overestimation of the surface coverage by the CO₂ chemisorption method is attributed to the preferential adsorption of the V phase onto the most basic hydroxyls, the same sites which interact with CO₂.Dedicated to Professor Dr. Dieter Klockow on the occasion of his 60th birthday     

Sulfide Catalysts Supported on Al2O3: VI. Synthesis of Catalysts with the Use of Binuclear Molybdenum(V) Complexes with Sulfur-Containing Ligands

A new method was developed for the preparation of sulfide catalysts supported on aluminum oxide. The surface assembling of a direct precursor of the active component was used in this method. The method consists in the sequential immobilization of binuclear molybdenum complexes with S-containing ligands on the support surface followed by the immobilization of nickel (cobalt) compounds at the surface molybdenum complexes. The complexation and structure of the resulting complexes in solution and the structure of surface complexes were studied by ⁹⁵Mo and ¹⁷O NMR, IR, and EXAFS spectroscopy. The surface assembling of a direct precursor of the active component of sulfide hydrodesulfurization catalysts was demonstrated using IR and EXAFS spectroscopy. The activity of the resulting catalysts in a model reaction of thiophene hydrogenolysis was comparable to the activity of sulfide catalysts of the metal complex origin and was much higher than the activity of commercial catalysts and catalysts prepared by impregnation.     

Measurement of the surface coverage of V/Al2O3 catalysts by infrared spectroscopy,CO2 chemisorption and ion scattering spectroscopy

Quantitative FTIR studies of alumina hydroxyl groups have been used to measure the surface coverage of V/Al₂O₃ catalysts. The IR spectra show a preferential consumption of the most basic hydroxyls (3769 cm^?1) with the initial V uptake. The integrated area of the hydroxyl region was used to calculate the surface coverage of the catalysts. The surface coverage increased to 0.63 as the V loading increased to 6.7 wt%. The surface coverage results obtained from IR were compared to those measured by ion scattering spectroscopy (ISS) and CO₂ chemisorption. The surface coverages measured by ISS were comparable to those obtained by IR. In contrast, CO₂ chemisorption appears to overestimate the surface coverage of the catalysts. The overestimation of the surface coverage by the CO₂ chemisorption method is attributed to the preferential adsorption of the V phase onto the most basic hydroxyls, the same sites which interact with CO₂.     

镁铁和镁铁铝催化剂氢还原过程的研究

以水滑石为前体 ,制备了镁铁和镁铁铝复合氧化物催化剂 ,运用原位穆斯堡尔谱研究了催化剂在H2 气氛中的还原行为。结果表明 :由于Mg、Al的加入和固溶体的形成 ,相对地稳定了FeO物相 ,阻碍了H2 对铁离子的还原 ,使得Fe2 进一步还原为金属Fe0 的能力减弱 ;在还原过程中催化剂首先生成含Fe2 的固溶体FeO MgO或FeO MgO Al2O3,然后再完全还原成金属Fe0。     

Superacid polymers from sulfonated poly(styrene-divinylbenzene): Preparation and characterization

Superacid polymers were prepared by bringing metal halides (AlCl₃, SnCl₄, TiCl₄, BF₃, or SbF₅) in contact with macroporous sulfonic acid resins [sulfonated, crosslinked poly(styrene-divinylbenzene)]. The resulting solids were characterized by chemical analysis, temperature-programmed desorption, transmission electron microscopy, and X-ray photoelectron spectroscopy. They were also tested as catalysts for n-butane isomerization at 0.5 bar and 60 to 120°C. The polymers consist of supported metal oxyhalide particles, complexes of metal oxyhalides and sulfonate groups, and the remaining unreacted sulfonic acid groups. In the presence of HCl, these polymers were highly active catalysts for the butane isomerization reaction, the activity being a consequence of a high proton-donor strength inferred to be associated with H₂Cl⁺ groups stabilized on the polymer surface by negative charge delocalization over sulfonate–metal oxyhalide sulfonate groups.     

Alkali metal intercalated titanate nanotubes: A vibrational spectroscopy study

Alkali metal (Li⁺, Na⁺, K⁺) intercalated titanate nanotubes have been studied by vibrational spectroscopy (Raman and FT-infrared), X-ray diffraction, and electron microscopy. The vibrational spectroscopic data shown that the most affected vibrational mode is that related to Ti-O bond whose oxygen is not shared among the TiO₆ units of the framework structure. A correlation between vibrational frequency shifts and intercalated metal was found, thus showing that vibrational spectroscopy is very useful for probing metal intercalated titanate nanotubes. Our results provide good evidences that the structure of titanate layers in titanate nanotube, a subject of long debate in the literature, is similar to trititanates (like Na₂Ti₃O₇).     

Catalytic properties of transition metal salts immobilized on nanoporous silica polyamine composites II: hydrogenation

The transition metal compounds Pd(OAc)₂, RhCl₃·4H₂O and RuCl₃ · nH₂O were adsorbed onto the nanoporous silica polyamine composite (SPC) particles (150–250 µm), WP‐1 [poly(ethyleneimine) on amorphous silica], BP‐1 [poly(allylamine) on amorphous silica], WP‐2 (WP‐1 modified with chloroacetic acid) and BP‐2 (BP‐1 modified with chloroacetic acid). Inductively coupled plasma‐atomic emission spectrometry analysis of the dried samples after digestion indicated metal loadings of 0.4–1.2 mmol g^?1 except for RhCl₃·4H₂O on BP‐2 which showed a metal loading of only 0.1 mmol g^?1. The metal loaded composites were then screened as hydrogenation catalysts for the reduction of 1‐octene, 1‐decene, 1‐hexene and 1, 3‐cyclohexadiene at a hydrogen pressure of 5 atm in the temperature range of 50–90 °C. All 12 combinations of SPC and transition metal compound proved active for the reduction of the terminal olefins, but isomerization to internal alkenes was competitive in all cases. Under these conditions, selective hydrogenation of 1,3‐cyclohexadiene to cyclohexene was observed with some of the catalysts. Turnover frequencies were estimated for the hydrogenation reactions based on the metal loading and were in some cases comparable to more conventional heterogeneous hydrogenation catalysts. Examination of the catalysts before and after reaction with X‐ray photoelectron spectroscopy and transmission electron microscopy revealed that, in the cases of Pd(OAc)₂ on WP‐2, BP‐1 and BP‐2, conversion of the surface‐ligand bound metal ions to metal nano‐particles occurs. This was not the case for Pd(OAc)₂ on WP‐1 or for RuCl₃ · nH₂O and RhCl₃· 4H₂O on all four composites. The overall results are discussed in terms of differences in metal ion coordination modes for the composite transition‐metal combinations. Suggested ligand interactions are supported by solid state CPMAS ¹³C NMR analyses and by analogy with previous structural investigations of metal binding modes on these composite materials. Copyright © 2011 John Wiley & Sons, Ltd.     

Propane combustion over supported Pd catalysts

We prepared Pd catalysts supported on various metal oxides, viz. γ-Al₂O₃, α-Al₂O₃, SiO₂–Al₂O₃, SiO₂, CeO₂ and TiO₂ by an incipient wetness method and applied them to propane combustion. Several techniques: N₂ physisorption, inductively coupled plasma-atomic emission spectroscopy (ICP-AES), CO chemisorption, temperature-programmed reduction (TPR) and temperature-programmed oxidation (TPO) were employed to characterize the catalysts. Pd/SiO₂–Al₂O₃ showed the least catalytic activity at high temperatures among Pd catalysts supported on irreducible metal oxides, viz. SiO₂, Al₂O₃ and SiO₂–Al₂O₃. Pd/γ-Al₂O₃ was much superior for this reaction to Pd/α-Al₂O₃. The Pd catalyst supported on reducible metal oxides (CeO₂ and TiO₂) with a less specific surface area showed the higher catalytic activity compared with that supported on reducible metal oxides with a higher specific surface area, even though the former had a less Pd dispersion than the latter. In the case of Pd/SiO₂–Al₂O₃, the initially reduced Pd catalyst was superior to the fully oxidized one. The oxidation of metallic Pd occurred in the presence of O₂ with increasing reaction temperature, which resulted in the change in the catalytic activity.     

Hydrogenation of aromatic hydrocarbons in a mixture with thiophene on sulfided Pd/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts

The activity and stability of aluminum-palladium catalysts in the hydrogenation of aromatic hydrocarbons mixed with thiophene were studied. The catalysts were obtained by impregnation of γ-A₂O₃ with aqueous solutions of salts of palladium complexes. Preliminary sulfiding followed by oxidative activation of Pd/Al₂O₃ catalysts were found to favor the formation of such palladium state on the surface at which the hydrogenation of aromatic hydrocarbons in the presence of sulfur-containing impurities proceeds without a noticeable change in the activity with time. IR spectroscopy showed that the palladium metal surface fragments forming CO complexes with a characteristic absorption band at 1998 cm^–1 are resistant to poisoning with sulfur-containing compounds in the hydrogenation of aromatic hydrocarbons.     

Synthesis new Co–Mn mixed oxide catalyst for the production of light olefins by tuning the catalyst structure

In order to increase the catalyst activity for Fischer–Tropsch synthesis (FTS), the preparation methods of two new catalysts were studied. The chemically identical bimetallic Co–Mn/Al₂O₃ catalysts were synthesized by different synthetic methods: (a) via thermal decomposition of the complex [Co_1.33Mn_0.667(C₇H₃NO₄)₂(H₂O)₅].2H₂O ( 1 ) and (b) by the impregnation technique. The complex was characterized by the single‐crystal analysis, elemental analysis, and Fourier‐transform infrared (FT‐IR) spectroscopy. Both catalysts were characterized by powder X‐ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X‐ray spectrometry (EDS), Brunauer–Emmett–Teller (BET) specific surface area, hydrogen temperature‐programmed reduction (H₂‐TPR), and H₂‐chemisorption. The catalysts' activity was investigated for the Fischer–Tropsch synthesis in a fixed bed microreactor. Higher activity was obtained for the catalyst prepared by thermal decomposition of the inorganic precursor due to its small particle size, superior dispersion, and higher surface area. The results show that the catalyst prepared thermal decomposition has 21% ethylene, 10% propylene, and 50% C₅⁺ selectivity, while methane selectivity of this catalyst is 11% at 250°C. On the other hand, the catalyst obtained by the impregnation method displays 15% ethylene, 8% propylene, 29% C₅⁺_, and 29% methane selectivity at the same temperature.     

Stabilizing Sulfur Sites in Tetraoxygen Tetrahedral Coordination Structure for Efficient Electrochemical Water Oxidation

Ion regulation strategy is regarded as a promising pathway for designing transition metal oxide-based electrocatalysts for oxygen evolution reaction (OER) with improved activity and stability. Precise anion conditioning can accurately change the anionic environment so that the acid radical ions (SO₄²⁻, PO₃²⁻, SeO₄²⁻, etc.), regardless of their state (inside the catalyst, on the catalyst surface, or in the electrolyte), can optimize the electronic structure of the cationic active site and further increase the catalytic activity. Herein, we report a new approach to encapsulate S atoms at the tetrahedral sites of the NaCl-type oxide NiO to form a tetraoxo-tetrahedral coordination structure (S-O₄) inside the NiO (S-NiO -I). Density functional theory (DFT) calculations and operando vibrational spectroscopy proves that this kind of unique structure could achieve the S-O₄ and Ni-S stable structure in S-NiO-I. Combining mass spectroscopy characterization, it could be confirmed that the S-O₄ structure is the key factor for triggering the lattice oxygen exchange to participate in the OER process. This work demonstrates that the formation of tetraoxygen tetrahedral structure is a generalized key for boosting the OER performances of transition metal oxides.     

Solvent Migration in Microhydrated Aromatic Aggregates: Ionization‐Induced Site Switching in the 4‐Aminobenzonitrile–Water Cluster

The dependence of the preferred microhydration sites of 4‐aminobenzonitrile (4ABN) on electronic excitation and ionization is determined through IR spectroscopy of its clusters with water (W) in a supersonic expansion and through quantum chemical calculations. IR spectra of neutral 4ABN and two isomers of its hydrogen‐bonded (H‐bonded) 4ABN–W complexes are obtained in the ground and first excited singlet states (S₀, S₁) through IR depletion spectroscopy associated with resonance‐enhanced multiphoton ionization. Spectral analysis reveals that electronic excitation does not change the H‐bonding motif of each isomer, that is, H₂O binding either to the CN or the NH site of 4ABN, denoted as 4ABN–W(CN) and 4ABN–W(NH), respectively. The IR spectra of 4ABN⁺–W in the doublet cation ground electronic state (D₀) are measured by generating them either in an electron ionization source (EI‐IR) or through resonant multiphoton ionization (REMPI‐IR). The EI‐IR spectrum shows only transitions of the most stable isomer of the cation, which is assigned to 4ABN⁺–W(NH). The REMPI‐IR spectrum obtained through isomer‐selective resonant photoionization of 4ABN–W(NH) is essentially the same as the EI‐IR spectrum. The REMPI‐IR spectrum obtained by ionizing 4ABN–W(CN) is also similar to that of the 4ABN⁺–W(NH) isomer, but differs from that calculated for 4ABN⁺–W(CN), indicating that the H₂O ligand migrates from the CN to the NH site upon ionization with a yield of 100 %. The mechanism of this CN→NH site‐switching reaction is discussed in the light of the calculated potential energy surface and the role of intracluster vibrational energy redistribution.     

Synthesis, thermal and other studies of 2,4'-bipyridine-dichloroacetato complexes of Mn(II), Co(II), Ni(II) and Cu(II)

Four new mixed ligand complexes were prepared by the reaction of title metal dichloroacetates and 2,4'-bipyridine. The general formulae of synthesized compounds are M(2,4'-bpy)₂(CCl₂HCOO)₂·nH₂O (where M(II)=Mn, Co, Ni, Cu; 2,4'-bpy=2,4'-bipyridine, n=2 or 4). The complexes have been isolated from aqueous media and characterized by chemical analysis, molar conductance (in MeOH, DMSO and DMF), magnetic, IR and VIS spectral studies. The nature of metal(II)-ligand coordination is discussed. The thermal behaviour of obtained complexes was studied by thermal analysis and TG-MS techniques in air. IR, X-ray powder diffraction and thermoanalytical data were used for the determination of solid intermediate products of the thermal decomposition. The principal volatile products of thermal decomposition of complexes were proved by mass spectroscopy: H₂O⁺, CO⁺ ₂, HCl⁺ ₂, Cl⁺ ₂, NO⁺ and other. This revised version was published online in July 2006 with corrections to the Cover Date.     

Low temperature methanation of CO2 over an amorphous cobalt-based catalyst

CO₂ methanation is an important reaction in CO₂ valorization. Because of the high kinetic barriers, the reaction usually needs to proceed at higher temperature (>300 °C). High-efficiency CO₂ methanation at low temperature (<200 °C) is an interesting topic, and only several noble metal catalysts were reported to achieve this goal. Currently, design of cheap metal catalysts that can effectively accelerate this reaction at low temperature is still a challenge. In this work, we found that the amorphous Co–Zr_0.1–B–O catalyst could catalyze the reaction at above 140 °C. The activity of the catalyst at 180 °C reached 10.7 mmol_CO2 g_cat⁻¹ h⁻¹, which is comparable to or even higher than that of some noble metal catalysts under similar conditions. The Zr promoter in this work had the highest promoting factor to date among the catalysts for CO₂ methanation. As far as we know, this is the first report of an amorphous transition metal catalyst that could effectively accelerate CO₂ methanation. The outstanding performance of the catalyst could be ascribed to two aspects. The amorphous nature of the catalyst offered abundant surface defects and intrinsic active sites. On the other hand, the Zr promoter could enlarge the surface area of the catalyst, enrich the Co atoms on the catalyst surface, and tune the valence state of the atoms at the catalyst surface. The reaction mechanism was proposed based on the control experiments.

It is discovered that an amorphous transition metal catalyst Co–Zr0.1–B–O could effectively accelerate CO2 methanation, at a rate that is comparable to or even higher than that of some noble metal catalysts under similar conditions.     

Ammoxidation of ethylene to acetonitrile over chromium or cobalt alumina catalysts prepared by sol–gel method

A series of Cr/Al₂O₃ and Co/Al₂O₃ catalysts were tested in the selective ammoxidation of ethylene to acetonitrile. Catalysts were prepared either by sol–gel method or by impregnation with chromium or cobalt acetylacetonate salts. Physicochemical properties of catalysts were accomplished by several techniques such as chemical analysis, physisorption of N₂, X-ray diffraction (XRD), ²⁷Al MAS NMR, UV–Visible diffuse reflectance (DRS) and Raman spectroscopy and temperature programmed reduction of H₂ (H₂–TPR). Textural analysis reveals that mesoporous materials with pronounced surface areas were obtained using sol–gel procedure while impregnation of the support produces a moderate decrease of its surface area and pore volume. XRD analysis confirms the presence of highly dispersed metal species which reside essentially on the surface and measure less than 4 nm. Furthermore, ²⁷Al MAS NMR shows that for xerogels, part of metal species occupies sites on/in A1₂O₃ in close vicinity of octahedral ²⁷Al. This, apparently, is not the case for aerogels. For Cr/Al₂O₃ catalysts, isolated Cr⁶⁺, mono and polychromate species were identified using DRS, Raman Spectroscopy and H₂–TPR which seem to play a key role in the ammoxidation of ethylene. Furthermore, for cobalt doped catalysts, CoAl₂O₄ was identified as active phase on the basis of DRS and H₂–TPR results. From the supercritical drying, it results generally better catalysts than catalysts calcined by ordinary procedure which leads to inactive agglomerated Co₃O₄ and CoO–Al₂O₃ phase.     

Amino-substituted gem-diphosphonic acids: structures of complexes with divalent metal cations in aqueous solutions

A comparative study of complexation of acids R₂N(CH₂)_nCR"(PO₃H₂)₂ (R = H or Me; R" = OH or H; n = 1 or 2) with the Ca²⁺, Mg²⁺, Zn²⁺, and Cu²⁺ cations in aqueous solutions was carried out by vibrational (IR and Raman) and electronic spectroscopy using the data of ESR spectroscopy and conformational analysis (molecular mechanics). The MOPCPO chelate ring is formed in all ML and MHL complexes. The involvement of the N atom in coordination was found only in the Cu²⁺ complexes and is determined by the structure of the ligand. The relationship between the stability constants and the structures of the complexes in aqueous solutions is analyzed.