Matrix infrared spectra and density functional calculations of TiO3 and TiO5 in solid argon

The reaction of titanium monoxide molecules and O2 was studied by using matrix isolation infrared spectroscopy as well as theoretical calculations. The titanium monoxide molecule reacts with O2 to form TiO 3 spontaneously on annealing. The TiO3 molecule is characterized to be a side-on bonded peroxo titanium monoxide complex, (eta(2)-O2)TiO, which has a nonplanar Cs symmetry with a 1A' ground state. The (eta(2)-O2)TiO complex can further coordinate another dioxygen to give TiO 5, a disuperoxo titanium monoxide complex, (eta(2)-O2)(2)TiO, which possesses a 3A' ground state and a nonplanar Cs geometry.     

Carbon dioxide coordination and activation by niobium oxide molecules

Carbon dioxide coordination and activation by niobium oxide molecules were studied by matrix isolation infrared spectroscopy. It was found that the niobium monoxide molecule reacted with carbon dioxide to form the niobium dioxide carbonyl complex NbO(2)(η(1)-CO) spontaneously on annealing in solid neon. The observation of the spontaneous reaction is consistent with theoretical predictions that this carbon dioxide activation process is both thermodynamically exothermic and kinetically facile. In contrast, four niobium dioxide-carbon dioxide complexes exhibiting three different coordination modes of CO(2) were formed from the reactions between niobium dioxide and carbon dioxide, which proceeded with the initial formation of the η(1)-O bound NbO(2)(η(1)-OCO) and NbO(2)(η(1)-OCO)(2) complexes on annealing. The NbO(2)(η(1)-OCO) complex rearranged to the η(2)-O,O bound NbO(2)(η(2)-O(2)C) isomer under visible light irradiation, while the NbO(2)(η(1)-OCO)(2) complex isomerized to the NbO(2)(η(1)-OCO)(η(2)-OC)O structure involving an η(2)-C,O ligand under IR excitation. In these niobium dioxide carbon dioxide complexes, the η(1)-O coordinated CO(2) ligand serves as an electron donor, whereas both the η(2)-C,O and η(2)-O,O coordinated CO(2) ligands act as electron acceptors.     

Methane activation by titanium monoxide molecules: a matrix isolation infrared spectroscopic and theoretical study

Reactions of titanium monoxides with methane have been investigated using matrix isolation infrared spectroscopy and theoretical calculations. Titanium derivatives of several simple oxyhydrocarbons have been prepared and identified. The titanium monoxide molecules prepared by laser evaporation of bulk TiO2 target reacted with methane to form the TiO(CH4) complex in solid argon, which was predicted to have C3v symmetry with the oxygen atom coordinated to one hydrogen atom of the methane molecule. The complex rearranged to the CH3Ti(O)H titano-acetaldehyde molecule upon visible (lambda > 500 nm) irradiation. The titano-acetaldehyde molecule sustained further photochemical rearrangement to the CH2Ti(H)OH titano-vinyl alcohol molecule, which was characterized to be a simple carbene complex involving agostic bonding. The CH2Ti(H)OH molecule reacted with a second methane to form the (CH3)2Ti(H)OH titano-isopropyl alcohol molecule spontaneously on annealing. The (CH3)2Ti(H)OH molecule also can be produced via UV photon-induced rearrangement of the CH3Ti(O)H(CH4) complex.     

Impact of defects on the surface chemistry of ZnO(0001 macro)-O

Scanning tunneling microscopy and core level photoelectron spectroscopy measurements have been used to investigate the morphology of ZnO(0001 macro)-O, and its reactivity with carbon monoxide and carbon dioxide, as a function of surface preparation. Real space images of the surface indicate that increasing the substrate anneal temperature during preparation significantly reduces the surface step density. Surface defect concentration is also monitored by employing formic acid as a chemical probe, which is shown to adsorb dissociatively (HCOOH --> [HCOO](-) + H(+)) only on zinc cations at step edges. Carbon 1s X-ray photoelectron spectra show that carbon monoxide and carbon dioxide both react to form surface carbonate species. Spectra, recorded both as a function of surface preparation and following coadsorption, demonstrate that the carbonate formed from either reactant molecule is located at oxygen vacancies at step edges, evidencing the significant role that defects can play in the surface chemistry of ZnO(0001 macro)-O.     

Platinum catalysed nanoporous titanium dioxide electrodes in H2SO4 solutions

The preparation and electrochemistry of dispersed Pt metal on nanoporous titanium dioxide coatings is described. It is shown that photocatalytic deposition of Pt centres on a nanoporous titanium dioxide layer fabricated from TiO₂ nanoparticles leads to high surface area electrocatalysts. The reactions investigated are the evolution of hydrogen and the oxidation of carbon monoxide and methanol.     

Electron spin resonance analysis of paramagnetic Pd(I) species in Pd(II)-exchanged H-rho zeolite

Zeolite rho was synthesized and Pd(II) exchanged into it. Pd(II) was reduced to paramagnetic Pd(1) by a thermal activation process. The interactions of Pd(I) in zeolite H-rho with oxygen, water, methanol, ammonia, carbon monoxide and ethylene have been studied by electron spin resonance (ESR) and electron spin echo modulation (ESEM) spectroscopies. The ESR spectrum of an activated sample shows the formation of one Pd(I) species. Pd(I) interacts with water vapor or molecular oxygen to form Pd(II)–O₂, indicating decomposition of water. Equilibration with methanol results in a broad isotropic ESR signal which is attributed to the formation of small palladium clusters. ESEM shows that the Pd clusters coordinate one molecule of methanol. Adsorption of ammonia produces a Pd(I) complex containing four molecules of ammonia based upon resolved nitrogen superhyperfine coupling. Adsorption of carbon monoxide results in a Pd(I) complex containing two molecules of carbon monoxide based upon resolved¹³C superhyperfine coupling. ESR and ESEM results indicate that exposure to ethylene leads to two new Pd(I) species each of which coordinates one molecule of ethylene.     

Metal-Free Electrochemical Reduction of Carbon Dioxide Mediated by Cyclic(Alkyl)(Amino) Carbenes

Carbenes are known to activate carbon dioxide to form zwitterionic adducts. Their inherent metal-free redox activity remains understudied. Herein, we demonstrate that zwitterionic adducts of carbon dioxide formed with cyclic(alkyl)(amino) carbenes are not only redox active, but they can mediate the stoichiometric reductive disproportionation of carbon dioxide to carbon monoxide and carbonate. Infrared spectroelectrochemical experiments show that the reaction proceeds through an intermediate radical anion formed by one-electron reduction, ultimately generating a ketene product and carbonate in the absence of additional organic or inorganic reagents.     

Oxidation of formic acid and carbon monoxide on gold electrodes studied by surface-enhanced Raman spectroscopy and DFT.

The oxidation of formic acid and carbon monoxide was studied at a gold electrode by a combination of electrochemistry, in situ surface-enhanced Raman spectroscopy (SERS), differential electrochemical mass spectrometry, and first-principles DFT calculations. Comparison of the SERS results and the (field-dependent) DFT calculations strongly suggests that the relevant surface-bonded intermediate during oxidation of formic acid on gold is formate HCOO- ad*. Formate reacts to form carbon dioxide via two pathways: at low potentials, with a nearby water to produce carbon dioxide and a hydronium ion; at higher potentials, with surface-bonded hydroxyl (or oxide) to give carbon dioxide and water. In the former pathway, the rate-determining step is probably related to the reaction of surface-bonded formate with water, as measurements of the reaction order imply a surface almost completely saturated with adsorbate. The potential dependence of the rate of the low-potential pathway is presumably governed by the potential dependence of formate coverage. There is no evidence for CO formation on gold during oxidation of formic acid. The oxidation of carbon monoxide must involve the carboxyhydroxyl intermediate, but SERS measurements do not reveal this intermediate during CO oxidation, most likely because of its low surface coverage, as it is formed after the rate-determining step. Based on inconclusive spectroscopic evidence for the formation of surface-bonded OH at potentials substantially below the surface oxidation region, the question whether surface-bonded carbon monoxide reacts with surface hydroxyl or with water to form carboxyhydroxyl and carbon dioxide remains open. The SERS measurements show the existence of both atop and bridge-bonded CO on gold from two distinguishable low-frequency modes that agree very well with DFT calculations.     

Reductive disproportionation of carbon dioxide by a sm(II) complex: unprecedented f-block element reactivity giving a carbonate complex

A macrocyclic organosamarium(II) complex has been shown to provide the first example of the reductive disproportionation of carbon dioxide, giving a bimetallic carbonate complex and carbon monoxide in a facile reaction under ambient conditions.     

Spectrophotometric determination of carbon monoxide with ruthenium(II) octaethylporphyrin

A novel spectrophotometric method for the estimation of carbon monoxide at levels from 2 to 250 ppm is presented. The method is empirical and based on formation of a carbonyl complex of ruthenium(II) octaethylporphyrin and measurement of the difference in absorbance at 393.5 nm between this complex and the porphyrin reagent. Oxygen and nitrogen do not interfere and up to 300 ppm of sulphur dioxide and about 1500 ppm of carbon dioxide can be tolerated in determination of carbon monoxide at the 4 and 10 ppm levels. Hydrogen sulphide interferes and must be removed before the determination. The method has been tested over the range 2-45 ppm of carbon monoxide with 16 synthetic and 2 commercial standard air samples. The average error was +/- 3%. Application to urban-air samples and car-exhaust gases yielded acceptable results. The main disadvantages are the tedious preparation of the initial ruthenium(III)-porphyrin compound and the decomposition of the reagent in the presence of hydrazine.     

Formation of carbon oxides during tobacco combustion: Pyrolysis studies in the presence of isotopic gases to elucidate reaction sequence

During the combustion of tobacco, carbon monoxide is formed by the thermal decomposition of tobacco with primary products such as carbon dioxide and water. These three processes occur in parallel and are interdependent. The temperature ranges over which each process occurs, and their relative importance have been assessed by pyrolysing tobacco in the presence of various isotopically labelled gases. Non-isothermal pyrolyses were conducted at a heating rate of 1.6 K s^?1 up to 1000°C, with the products analysed by mass spectrometer.Pyrolysis in the presence of oxygen-18 indicates that combustion of tobacco starts at 180°C. Carbon dioxide and water are formed by combustion at 180°C, while carbon monoxide is not formed as a combustion product until 460°C. The quantities of carbon monoxide and dioxide formed by thermal decomposition of tobacco above 400°C are significantly reduced by the occurrence of combustion.Pyrolysis in the presence of carbon-13 dioxide or carbon dioxide-18 shows that its major reaction, endothermic reduction to form carbon monoxide begins at 450°C. Pyrolysis in an oxygen-18/carbon-13 dioxide atmosphere has shown that this endothermic reduction of carbon dioxide occurs in parallel with the strongly exothermic oxidising reactions. 30% of the total carbon monoxide formed was produced by thermal decomposition of the tobacco. 36% was produced by combustion of the tobacco, and at least 23% was produced via carbon dioxide. The remainder was produced by an interaction of the carbon dioxide reduction and the oxidation. Similar proportion would be expected inside the reaction zone of a burning cigarette.Pyrolysis in the presence of heavy water has shown that the major reaction of the water is to quantitatively produce carbon monoxide and hydrogen above 600°C. Considerable isotopic exchange reactions also occur. Pyrolysis in the presence of carbon monoxide-18 has shown that carbon monoxide reacts with tobacco to a small extent at temperatures above 220°C mainly to abstract oxygen combined in the tobacco and produce carbon dioxide.A sequence of general chemical steps for the production of the carbon oxides and water during tobacco combustion has been deduced. This is based on the present work together with considerations of previously published studies on graphite and coal reactions.     

Thermal degradation of polymers with phenylene units in the chain. IV. Aromatic polyamides and polyimides

The breakdown mechanism of an aromatic polyamide and four polyimides has been studied under vacuum in the temperature range of 375–620°C, by using techniques described earlier, involving collection and analysis of volatile products as well as analyses of residues at different temperatures. The decomposition of the polyamide up to 375°C yielded predominantly carbon dioxide, while between 375 and 450°C about equal amounts of carbon dioxide and carbon monoxide formed. Hydrogen is the major product between 450 and 550°C, along with hydrogen cyanide, methane, and carbon monoxide. The major reaction at the lower temperatures seems to be the cleavage of the linkage between the carbonyl group and the ring, with subsequent formation of a carbodiimide linkage via isocyanate intermediates, and liberation of carbon dioxide. Alternatively, cleavage between the carboxyl and the NH-group leads to the formation of carbon monoxide. Carbon dioxide and carbon monoxide are also the major volatile decomposition products of the polyimides at the lower temperatures. The primary cleavage reaction is believed to be the rupture of the imide ring between a carbonyl and nitrogen, with subsequent formation of isocyanate groups. The latter react with each other to form carbodiimide linkages and carbon dioxide, while the remaining benzoyl radical is the source for carbon monoxide.     

Macromolecule-Metal Complexes for Gas Separation

Macromolecule-copper(I) chloride complexes have been prepared for the separation of carbon monoxide and ethylene from gas mixtures with hydrogen, nitrogen, carbon dioxide, methane, and water. A toluene solution of a polystyrene-aluminum copper(I) chloride complex can separate carbon monoxide selectively and retains this function even on contact with gas containing water. Strong charge-transfer absorption bands have been found in the 380-500 nm region for the toluene solution of polystyrene-aluminum copper(I) chloride complex. A solution of 1, 3-diphenylpropane-aluminum copper(I) chloride complex also exhibits similar absorption bands. A continuous variation plot using the chemical shift change in ¹³C-NMR shows a 1:1 interaction between 1,3-diphenylpropane and aluminum copper(I) chloride. These results suggest a two-way interaction between the adjacent phenyl groups of polystyrene and aluminum copper(I) chloride. A resin bead of crosslinked polystyrene-aluminum copper(I) chloride complex has been prepared as a solid adsorbent. The water resistance of the solid macromolecular complex depends on the nature of the solvent used in the preparation of the solid adsorbent. Carbon disulfide is a suitable solvent. A selective adsorbent of ethylene has been prepared from a macroreticular polystyrene resin with primary and secondary amino groups and copper(I) chloride. The selectivity of ethylene against ethane and that of carbon monoxide against carbon dioxide increase with an increasing amount of supported copper(I) chloride.     

Contribution of the ligand to the electroreduction of CO2 catalyzed by a cobalt(II) macrocyclic complex

The electrochemical reduction of carbon dioxide using hexa-aza-macrocycles derived from the condensation of 1,10-phenanthroline and its Co(II) complex as an electrocatalyst dissolved in dimethylformamide has been studied by cyclic voltammetry and UV-visible spectroscopy. The ligand does not show catalytic activity and only generates hydrogen when it is reduced under carbon dioxide. The cobalt complex shows electrocatalytic activity toward the reduction of carbon dioxide, generating carbon monoxide and formic acid. Cyclic voltammetry and UV-visible spectroscopy show that the active site for the reduction is the metal center in oxidation state (I), although the reduced cobalt center alone is not enough to promote reduction of the carbon dioxide. Electrolysis at controlled potential shows that only at potentials corresponding to reduction of the ligand (second reduction) does carbon dioxide reduction occur. Cobalt(I) probably reacts with CO₂ forming a non-isolated intermediate which, when reduced, gives CO and formic acid. The second reduction that takes place on the ligand regenerates the catalyst and gives products, thus becoming the rate-determining step of the reaction.     

Self-assembly of a tripodal pseudorotaxane on the surface of a titanium dioxide nanoparticle

This paper describes the self-assembly of a heterosupramolecular system consisting of a tripodal viologen, adsorbed at the surface of a titanium dioxide nanoparticle, that threads a crown ether to form a pseudorotaxane. The viologen, a 1,1'-disubstituted-4,4'-bipyridinium salt with a rigid tripodal anchor group, has been synthesized. This viologen is adsorbed at the surface of a titanium dioxide nanoparticle in solution. As intended, this tripodal viologen is both oriented normal to and displaced from the surface of the nanoparticle and threads a crown ether to form the heterosupramolecular complex. The threading of the crown ether by the tripodal viologen to form the above pseudorotaxane complex at the surface of a titanium dioxide nanoparticle has been studied by (1)H NMR, optical absorption spectroscopy, and cyclic voltammetry.     

铜系催化剂上甲醇蒸气转化制氢过程的原位红外研究

 用原位红外光谱法跟踪研究了不同条件下铜系催化剂上甲醇蒸气转化制氢反应的初始开车过程．结果表明，反应过程中二氧化碳不是在一氧化碳之后产生的．可以推断，铜系催化剂上的甲醇蒸气转化制氢过程不是先进行甲醇分解为一氧化碳和氢气，然后一氧化碳和水蒸气发生变换反应生成二氧化碳和氢气．甲醇蒸气转化反应的主要过程是甲醇和水直接生成二氧化碳和氢气．     

Titanium oxide complexes with dinitrogen. Formation and characterization of the side-on and end-on bonded titanium oxide-dinitrogen complexes in solid neon

The reactions of titanium oxide molecules with dinitrogen have been studied by matrix isolation infrared spectroscopy. The titanium monoxide molecule reacts with dinitrogen to form the TiO(N(2))(x) (x = 1-4) complexes spontaneously on annealing in solid neon. The TiO(η(1)-NN) complex is end-on bonded and was predicted to have a (3)A' ground state arising from the (3)Δ ground state of TiO. Argon doping experiments indicate that TiO(η(1)-NN) is able to form complexes with one or more argon atoms. Argon atom coordination induces a large red-shift of the N-N stretching frequency. The TiO(η(2)-N(2))(2) complex was characterized to have C(2v) symmetry, in which both the N(2) ligands are side-on bonded to the titanium metal center. The tridinitrogen complex TiO(η(1)-NN)(3) most likely has C(3v) symmetry with three end-on bonded N(2) ligands. The TiO(η(1)-NN)(4) complex was determined to have a C(4v) structure with four equivalent end-on bonded N(2) ligands. In addition, evidence is also presented for the formation of the TiO(2)(η(1)-NN)(x) (x = 1-4) complexes, which were predicted to be end-on bonded.     

Thermal degradation of polymers with phenylene units in the chain. I. Polyphenylenes and poly(phenylene oxides)

The thermal degradation of polyphenylenes and poly(phenylene oxides) was studied under vacuum at temperatures between 350 and 620°C. The volatile and solid degradation products were analyzed by mass spectroscopy, infrared spectroscopy, and elemental analysis. Overall mechanisms for the thermal breakdown have been proposed. Polyphenylene decomposes to form polymer carbon, while hydrogen is the major volatile product. Some ring breakdown occurs with evolution of methane. Poly(phenylene oxide) forms mainly low molecular weight chain fragments, partially with hydroxyl endgroups. Some of the ether linkages decompose with ring breakdown, yielding carbon monoxide, water, and some carbon dioxide. Pendent groups on polyphenylenes and poly(phenylene oxides) are removed at the lower temperatures. The hydroxyl group yields essentially carbon monoxide and dioxide (the carbon being supplied by the rings), the methyl group methane, and the methoxy group methane and some methanol.     

Reactions of water with carbon and ethylene over illuminated pt/tio2

The room temperature reaction between gas phase water and active carbon to form carbon dioxide and hydrogen on a platinized titanium dioxide catalyst, illuminated with band gap radiation, is reported. Using the same catalyst system, ethylene is converted to ethane, carbon dioxide, hydrogen and a small amount of methane.     

Matrix isolation infrared spectroscopic and theoretical study of the reactions of tantalum oxide molecules with methanol

The reactions of tantalum monoxide (TaO) and dioxide (TaO(2)) molecules with methanol in solid neon were investigated by infrared absorption spectroscopy. The ground-state TaO molecule reacted with CH(3)OH in forming the CH(3)OTa(O)H molecule via the hydroxylic hydrogen atom transfer from methanol to the metal center spontaneously on annealing. The observation of the spontaneous reaction is consistent with theoretical predictions that the OH bond activation process is both thermodynamically exothermic and kinetically facile. In contrast, the TaO(2) molecule reacted with CH(3)OH to give primarily the TaO(2)(CH(3)OH) complex, which further rearranged to the CH(3)OTa(O)OH isomer via the hydroxylic hydrogen atom transfer from methanol to one of oxygen atom of metal dioxide upon visible light excitation.