11C]Formaldehyde revisited: considerable concurrent [ 11C]formic acid formation in the low-temperature conversion of [ 11C]carbon dioxide into [ 11C]formaldehyde

The processing of cryogenic ices consisting of water and carbon monoxide by different types of radiation is known to lead to the formation of carbon dioxide, formic acid, formaldehyde, and also methanol. In this study, we have investigated these reactions upon electron irradiation with energies between 2 and 20 eV, an energy range typically found in secondary electrons. This is the first time that the reactions have been monitored with a sufficiently fine step width in energy to resolve and identify the primary electron–molecule interactions leading to the specific products. This enables us to elucidate reaction mechanisms by linking these primary electron–molecule interactions to final products. In these reactions, HCO• and HOCO• radicals are key intermediates. Our results show that the HCO• intermediate predominantly leads to formaldehyde, while HOCO• is intermediate to the formation of formic acid. Noticeably, the formation of both formaldehyde and formic acid is enhanced within characteristic energy ranges by resonant electron attachment processes. In contrast, the reactions leading to carbon dioxide show no resonant energy dependence but can be traced back to nonresonant neutral dissociation processes. This reveals that carbon dioxide is linked to neither of these two intermediates. This is in contrast to prior experimental studies, which have proposed that carbon dioxide is formed by loss of a H• radical from HOCO•. However, our results confirm theoretical studies that have predicted that carbon dioxide formation from HOCO• is not very efficient, because HOCO• presents an energetic well and quickly loses any excess energy it might have in an ice matrix. Instead, we provide evidence that the primary electron–molecule interaction leading to the formation of carbon dioxide in cryogenic ices of water and carbon monoxide is the neutral dissociation of water into O atoms and H2. The so-formed O atoms then react directly with carbon monoxide to yield carbon dioxide.

The reduction of carbon dioxide employing 1,4,7,10-tetramethyl-1,4,7,10 tetraazacyclododecane nickel(II) as a electron relay catalyst

Reduction of CO 2 by molecular hydrogen to formic acid and formaldehyde and their decomposition to CO and H 2O

The photocatalytic reduction of CO2 using copper-loaded silicate rocks has been reported. The Cu-silicate rock powders suspended in the solution were illuminated with sunlight. Amphibolite, gneiss, granite, granodiorite, phyllite, quartzdiorite, and shale, which are quite ordinary rocks, were tested as substrates (silicate rock) of the catalyst. These catalysts were specific for the formation of formic acid. The effects of amounts of copper, illumination time, and temperature were investigated on photoreduction of CO2. The 30% Cu-loaded quartzdiorite (0.3 g/g) in these Cu rocks was the best catalyst. The formation of formic acid on the Cu-silicate rock increased with time up to 10 h after which the formation decreased, and then became constant. The formic acid formation decreased with temperature for 10 h sunlight illumination. For the photochemical reduction of CO2, a relatively low temperature was suitable. With photochemical reduction, the maximum yield of formic acid was 54 nmol/g under optimum experimental conditions. The carbon dioxide reduction system developed might well become of practical interest for the photochemical production of raw materials for the photochemical industry.Key words: photocatalytic reduction of carbon dioxide, formic acid, copper-loaded silicate rocks, temperature effect, illumination time.

A conversion of stearic acid into hydrocarbons in the presence of palladium on alumina has been studied. It has been shown that heptadecane and carbon monoxide are formed as the main products, diheptadecylketone is formed as a by-product, and the contribution of the decarbonylation reaction increases as compared to decarboxylation in the presence of hydrogen with an increase in its pressure. The formation of heptadecene and formic acid as intermediate products has allowed the conclusion that the cleavage of the carbon-carbon bond in the stearic acid molecule R-COOH takes place in the Pd coordination sphere, resulting in the formation of formic acid (or its fragment associated with palladium) and the corresponding olefinic product. Depending on the reaction conditions, formic acid and/or its fragment decompose, yielding CO and H2O or CO2 and H2. The main routes of the reaction have been simulated using quantum-chemical methods, and it has been shown that the reaction rate-limiting stage is the cleavage of C-C bond in the acid molecule.

The formation of 2-furaldehyde and formic acid from pentoses in slightly acidic deuterium oxide studied by 1H NMR spectroscopy

Effect of co-adsorbed water on electrochemical CO2 reduction reaction on transition metal oxide catalysts

The development of sustainable catalysts to get methanol from CO2 under milder conditions and without any additives is still considered an arduous task. In many instances, transition-metal-catalyzed carbon dioxide to formic acid formation is more facile than methanol formation. This article provides comprehensive density functional theoretic investigations of six new Mn(I)PNN complexes, which are designed to perform CO2 to methanol conversion under milder reaction conditions. All these six catalysts have similar structural features except at terminal nitrogen, -N (1), where adenine-inspired nitrogen heterocycles containing pyridine and pyrimidine moieties are attached to instill an electron withdrawing effect on the central metal and thus to facilitate dihydrogen polarization during the catalyst regeneration. All these computationally modeled Mn(I)PNN complexes demonstrate the promising catalytic activity to get methanol through cascade catalytic cycles at 298.15 K. The metal-ligand cooperative (MLC) as well as noncooperative (NC) pathways are investigated for each catalytic cycle. The NC pathway is the preferred pathway for formic acid and formaldehyde formation, whereas methanol formation proceeds through only the MLC pathway. Different nitrogen heterocycles attached to the -N (1) terminal manifested a considerable amount of impact on the Gibbs free energies, overall activation energies, and computed turnover frequencies (TOFs). Among all the catalysts, SPCAT02 provides excellent TOFs for HCO2H (500 151 h-1), HCHO (11 912 h-1), and CH3OH (2 372 400 h-1) formation at 50 °C. SPCAT04 is found to be a better catalyst for the selective formation of formic acid formation at room temperature than the rest of the catalysts. The computed TOF results are found reliable upon comparison with experimentally established catalysts. To establish the structure-activity relationship, the activation strain model and Fukui function calculations are performed on all the catalysts. Both these studies provide complementary results. The present study revealed a very important finding that a more electrophilic metal center could facilitate the CO2 hydrogenation reaction robustly. All computationally designed catalysts could be cheaper and better alternatives to convert CO2 to methanol under mild reaction conditions in an aqueous medium.

Formation of formic acid from renewable biomass resources is of great interest since formic acid is a widely used platform chemical and has recently been regarded as an important liquid hydrogen carrier. Herein, a novel approach is reported for the conversion of glucose, the constituent carbohydrate from the cellulose fraction of biomass, to formic acid under mild hydrothermal conditions with simultaneous reduction of Ag2O to Ag. Results showed that glucose was selectively converted to formic acid with an optimum yield of 40.7% and glycolic acid with a yield of 6.1% with 53.2% glucose converting to carbon dioxide (CO2) immediately at a mild reaction temperature of 135 °C for 30 min. In addition, Ag2O was used as a solid oxidant for glucose oxidation, which avoids the use of traditionally dangerous liquid oxidant H2O2. Furthermore, complete conversion of Ag2O to Ag can be achieved. This study not only developed a new method for value-added chemical production from renewable biomass but also explored an alternative low-carbon and energy-saving route for silver extraction and recovery.

The electro-oxidation of glycerol on Au and Pt was studied in acid and alkaline media. The reaction intermediates and products formed were determined by in situ Fourier transform infrared (FTIR) spectroscopy. The experimental FTIR spectra measured on Au and Pt in acid and alkaline media were compared with the standard ones for the identification of the oxidation products. For Au, the oxidation reaction is highly dependent on the solution pH. In alkaline medium, dihydroxyacetone, tartronic acid, mesoxalic acid, glyoxylic acid, and carbon dioxide are formed while in acidic medium tartronic acid, formic acid, and carbon dioxide are formed. However, the oxidation of glycerol on Pt leads to the formation of tartronic acid, glycolic acid, glyoxylic acid, formic acid, and carbon dioxide, independent of the solution pH. For both electrode materials, Pt and Au, carbon dioxide is detected indicating the possible breaking of the C–C–C bonds. Clearly, the glycerol oxidation pathways can be controlled by the nature of the electrode material and solution pH. Furthermore, glycerol is a typical compound that has potentiality to produce electricity when feed a fuel cell while many chemicals with commercial interest are concomitantly formed.

The electrochemical reduction of CO2 in a KOH/methanol-based electrolyte was investigated with an indium (In) wire electrode at ambient temperature and pressure. Formic acid, carbon monoxide, and methane were the main products from the CO2. The formation of formic acid from the CO2 predominated in all the potential ranges studied. Under the optimum experimental conditions, 76.0% Faradaic efficiency formic acid, 41.4% CO, and 0.2% methane were produced from CO2 by the electrochemical reduction. Hydrogen evolution, in competition with CO2 reduction, was observed at only 0.2% Faradaic efficiency. The partial current density for CO2 reduction was more than 429 times larger than that for hydrogen evolution. This research can contribute to the application in the conversion of CO2-saturated methanol into useful products and the large-scale removal of CO2 from the atmosphere. Key words: Electrochemical reduction; carbon dioxide; indium wire electrode; KOH/methanol-based electrolyte; global warming

The homogeneously catalyzed hydrogenation of carbon dioxide to formic acid is a promising route for carbon dioxide utilization and power‐to‐X concepts. Separation of the product and the catalyst under retention of the performance of the catalyst remains a major challenge, however. Herein, we present a Ru‐phosphine catalyzed reaction system comprising only a hydrophobic solvent as the catalyst phase and N‐methyldiethanolamine as a base. The formation of formic acid causes a spontaneous separation of the monophasic reaction mixture into a pure formic acid/amine product and a recyclable catalyst phase. By optimizing the reaction conditions, a turnover number of 1590 in a single reaction and a total turnover number of 5590 after four recycling runs were achieved.

Formation of formic acid from renewable biomass resources is of great interest since formic acid is a widely used platform chemical and has recently been regarded as an important liquid hydrogen carrier. Herein, a novel approach is reported for the conversion of glucose, the constituent carbohydrate from cellulose fraction of biomass, to formic acid under mild hydrothermal conditions with simultaneous reduction of Ag2O to Ag. Results showed that glucose was selectively converted to formic acid with an optimum yield of 40.7% at a mild reaction temperature of 135 for 30 min. In addition, Ag2O was used as a solid oxidant for the glucose oxidation, which avoids the use of traditionally dangerous liquid oxidant H2O2. Furthermore, complete conversion of Ag2O to Ag can be achieved. This study not only developed a new method for value-added chemical production from renewable biomass but also explored an alternative low-carbon and energy-saving route for silver extraction and recovery.

Pd is one of the most promising catalysts for carbon dioxide electroreduction (CO2RR) to formate (HCOO-). However, the lack of understanding of the active phase remains remains obscure with the role of different crystal facets in the formation of formic acid. Herein, Pd nanocubes and nanooctahedra particles with Pd (100) and (111) facets were, respectively, prepared. Compared with ordinary Pd nanoparticles and Pd octahedra, Pd nanocubes exhibited the most excellent electrocatalytic performance of carbon dioxide reduction, achieving a Faraday efficiency of 96% for formate production at a low applied potential of-0.20 V (vs RHE) in 0.5 M KHCO3. At the same time, first-principles theoretical calculations also showed that the Pd (100) surface is more conducive to the conversion of CO2 to HCOO* intermediates, thereby promoting the formation of formic acid. This result indicates that the Pd (100) crystal plane is more conducive to the reduction of CO2 to formate. This research has important guiding significance for exploring the efficient reduction of carbon dioxide to formic acid catalyst.

Effects of isolated soybean protein (ISP) and ascorbic acid on volatiles formed from fructose solution were investigated by selected ion flow tube-mass spectrometry (SIFT-MS). Model system were prepared by 5% fructose solution with pH 6 phosphate buffer and heated at 100°C for 2 h. The results show that fructose forms furan (114 PPB), ormic acid (59 PPB), and acetic acid (40 PPB) in the headspace of 500ml bottle containing 80 mL solution. 0.5% ascorbic solution also form furan, formic and acetic acid which are less than the yields of 5% fructose does. ISP stimulates the formation of furan from fructose. Fructose and ascorbic acid form formic and acetic compounds independently, but form the furan dependently. It could be concluded that the degradation mechanism is multiple and complicated for the formation of furan, formic and acetic acids from ISP, fructose and ascorbic acid, which need further researching.