Bicarbonate Species Research Articles

Efficient nickel and copper-based catalysts supported on modified graphite materials for the hydrogen production from formic acid decomposition

Ni, Cu and Ni-Cu catalysts supported on high surface area graphite were synthesized by incipient wet impregnation. Also, the effect of doping the graphite support with alkali oxides (Li, Na and K) was studied. The catalysts were tested in the formic acid decomposition reaction to produce hydrogen. The bimetallic Ni-Cu catalyst doped with K showed the best catalytic performance with 100% conversion of formic acid at 130 °C and a 95% of selectivity to hydrogen. The turnover frequency (TOF) of the catalysts follows the order: Ni-Cu/K > NiCu/Na > Ni-Cu > Ni-Cu/Li. While the order for the apparent activation energy values is: Ni-Cu > Ni-Cu/Li > Ni-Cu/Na > Ni-Cu/K. The mechanism of the reaction is approached by programmed temperature surface reaction (TPSR) experiments and attenuated total reflectance (ATR). The greater catalytic activity of the Ni-Cu catalyst doped with potassium is ascribed to the lower stability of the formate, bicarbonate and carbonate species on its surface.

Theoretical Study of the Mechanism for the Reaction of Trimethylaluminum with Ozone.

The mechanism for the reaction of trimethylaluminum (TMA, Al(CH3)3) with ozone (O3) was investigated in detail using density functional theory calculations to understand the atomic layer deposition processes that form aluminum oxide surfaces. We examined the reactions of TMA and some possible intermediates with O3 and revealed plausible paths to form methoxy (−OCH3), formate (−OCHO), bicarbonate (−CO3H), and hydroxyl (−OH) species. These species have been observed in previous experimental studies. It was shown that TMA easily reacts with O3 to generate the Al(CH3)2(OCH3)(O2) intermediate. The subsequent reaction between the OCH3 and O2 groups finally generated an intermediate having a formate group. When all of the CH3 groups are converted into OCH3 or OCHO, O3 will react with these groups. In the latter reaction, bicarbonate was shown to be formed.

Unveiling the water-resistant mechanism of Cu(I)-O-Co interfaces for catalytic oxidation

The development of low-temperature and water-resistant heterogeneous catalysts without noble metals is vital in the effective treatment of atmospheric pollutants in practical application. Herein, we report that Cu(I)-O-Co interfaces of ultrafine CuOx on Co3O4 prepared by co-precipitation exhibit promising low-temperature activity and good water resistance. Experiment results together with density functional theory (DFT) calculations not only verify that Cu+ species are stabilized over Cu(I)-O-Co interfaces because of the strong interaction between Cu2O1 and Co3O4, but also demonstrate that the Cu(I)-O-Co interface facilitates oxygen species activation for promoting catalytic oxidation and reduces the accumulation of hydroxyl and bicarbonate species on the surface of CuOx/Co3O4. DFT calculations also reveal that the CO oxidation rate-limiting step via the dissociation pathway under dry conditions is the Co-OO-Cu species dissociation while the CO coupling with the adsorbed O2 becomes the rate determining step for CO oxidation through the direct pathway over Cu(I)-O-Co interface under humid conditions. Further, the CuOx/Co3O4 catalyst also exhibits superior and stable catalytic activity for toluene oxidation, comparable with partial supported noble metal catalysts (T90 = 190 °C). The present work gives a useful strategy for the rational design of low-temperature and water-resistant non-precious-based catalysts to be applicable in CO and toluene removal in practical applications.

Первичная продукция планктона озера Кенон (Забайкальский край, Россия)

Located in the Amur watershed, Lake Kenon is an urban reservoir that hosts recreational and commercial fishery activity. The current status of the lake is connected with the Chita Thermal Power Plant No 1, the basin’s human population, and the density of railways as well as highways within the basin. From the start of the thermal power plant’s operation, the reservoir’s ion composition significantly changed from largely sodium and bicarbonate species to sulfate, bicarbonate, chloride, sodium, calcium, and magnesium chemical species. Additionally, heavy metals have been accumulating in Kenon’s sediment. The results presented in this article are based on field measurements and comparative analysis with previous studies. Primary production was calculated using a light-dark bottle method. During the study period, current evidence corroborated previous investigations that respiration and decomposition rates generally tend to exceed photosynthesis rates. As noted in June 2015, in the cent of the lake where complete mixing occurs, primary production as well as respiration decreases with depth in the water column. With increased warming since August 2015, primary production exceeded respiration in upper layers. Considering the lake’s relatively small area for thermal fluxes (10% of the lake’s surface area), production-respiration processes are within Lake Kenon’s ecological capacities. The observed photosynthesis-respiration ratios from long-term study suggest that the system is resilient to the current anthropogenic load.

(Invited) Catalyst Design and Development for Highly Selective Photocatalytic Conversion of CO2 By H2o As an Electron Donor

The reduction in human-induced emissions of CO2 from automobiles, factories, power stations etc., over the next 15 years is currently one of the most important issues facing the planet. We should therefore attempt to develop industrial processes using CO2 as a feedstock to build a sustainable society. Linear CO2 molecules adsorbed on the surface of the solid bases are converted into unique structures, such as bicarbonate and carbonate species possessing lattice oxygen atoms. We believe that the process involves the capture and distortion of CO2 upon adsorption on a solid base through activation by photoirradiation. These days, we succeeded in designing highly selective photocatalytic conversion of CO2 by H2O as the electron donor, by the simultaneous use of an inhibitor of the production of H2 and a material for CO2 capture and storage. An isotope experiment using 13CO2 and mass spectrometry clarified that the carbon source of the evolved CO is not the residual carbon species, but the CO2 introduced in the gas phase. In addition, stoichiometric amounts of O2 were generated together with CO.

Investigation of Gas Diffusion Electrode Systems for the Electrochemical CO2 Conversion

Electrochemical CO2 reduction is a promising carbon capture and utilisation technology. Herein, a continuous flow gas diffusion electrode (GDE)-cell configuration has been studied to convert CO2 via electrochemical reduction under atmospheric conditions. To this purpose, Cu-based electrocatalysts immobilised on a porous and conductive GDE have been tested. Many system variables have been evaluated to find the most promising conditions able to lead to increased production of CO2 reduction liquid products, specifically: applied potentials, catalyst loading, Nafion content, KHCO3 electrolyte concentration, and the presence of metal oxides, like ZnO or/and Al2O3. In particular, the CO productivity increased at the lowest Nafion content of 15%, leading to syngas with an H2/CO ratio of ~1. Meanwhile, at the highest Nafion content (45%), C2+ products formation has been increased, and the CO selectivity has been decreased by 80%. The reported results revealed that the liquid crossover through the GDE highly impacts CO2 diffusion to the catalyst active sites, thus reducing the CO2 conversion efficiency. Through mathematical modelling, it has been confirmed that the increase of the local pH, coupled to the electrode-wetting, promotes the formation of bicarbonate species that deactivate the catalysts surface, hindering the mechanisms for the C2+ liquid products generation. These results want to shine the spotlight on kinetics and transport limitations, shifting the focus from catalytic activity of materials to other involved factors.

Effect of CO2 on the selective catalytic reduction of NOx with NH3 of Fe0.4Ce0.6O2-δ catalyst: adsorption behavior

Besides of NOx, CO2 is always abundantly present in the exhaust gas stream, which is important for the investigation of de-NOx. The presence of CO2 has an inhibiting effect on the NH3-SCR activity at temperatures below 300°C for the Fe0.4Ce0.6O2-δ catalysts. To make clear this impact of CO2 for NH3-SCR reaction, we further investigate the changes of NH3 and NOx adsorption behaviors, using in situ TPD and in situ DRIFTS technologies. The DRIFT spectra of CO2 adsorption show that weakly adsorbed carbonate and bicarbonate species were formed, leading to the changes in adsorption and activation behaviors of NH3 and NOx. On the one hand, the formed carbonate and bicarbonate can act as new acid sites thereby improvement of NH3 adsorption. On the other hand, the adsorption of NOx on Fe-O-Ce is suppressed by CO2 results from its competitive adsorption. Especially, the formation path of monodentate nitrate may be blocked by CO2, which is usually active intermediate species for the NH3-SCR reaction, resulting in the deactivation of CO2.

Study on activity, stability limit and reaction mechanism of CO self-sustained combustion over the LaMnO3, La0.9Ce0.1MnO3 and La0.9Sr0.1MnO3 perovskite catalysts using sugar agent

The LaMnO3, La0.9Ce0.1MnO3 and La0.9Sr0.1MnO3 catalysts are synthesized using sugar agent, and the CO self-sustained combustion is investigated, where the catalytic performance is decided by temperature with CO conversions of 10% (T10), 50% (T50), and 90% (T90). The results show that self-sustaining combustion is successfully realized on the catalyst, and the order of activity decrease is as follows: La0.9Ce0.1MnO3 (with sugar) > La0.9Sr0.1MnO3 (with sugar) > LaMnO3 (with sugar) > LaMnO3 (without sugar) > La0.9Sr0.1MnO3 (without sugar) > La0.9Ce0.1MnO3 (without sugar). Combined with the results of XPS, H2-TPR, O2-TPD and CO-TPD techniques, the excellent activity of La0.9Ce0.1MnO3 (with sugar) can be attributed to the high content of Mn4+ ions and reactive oxygen vacancies enriched on the catalyst surface, sound low-temperature reduction, and uniform dispersion. Besides, in situ IR spectroscopy results indicate that the catalytic combustion of CO over manganese-based perovskite catalysts follows the L-H mechanism: the chemisorption of CO and O2 takes place to produce monodentate carbonates and bicarbonate species, which then decompose to yield CO2 release. The high-temperature stability test provides evidence that the La0.9Ce0.1MnO3 (with sugar) gives 100% CO conversion and that the activities remain almost unchanged after reaction for 12 h, where the temperature of catalyst bed reaches about 717 °C. The results obtained are helpful to accept this technology on efficient and clean energy utilization in iron and steel industry.

Potential for uranium release under geologic CO2 storage conditions: The impact of Fe(III)

Saline aquifers are considered ideal subsurface sinks for large amounts of CO2 storage. It is common to have trace levels of uranium-bearing minerals (naturally occurring radioactive material, NORM) in sandstone saline aquifers and CO2 injection may cause uranium mobilization due to the coupled chemical and physical interactions at mineral-water interfaces. In this study, we developed a TOUGHREACT model to assess the uranium mobilization potential from uraninite (UO2) dissolution induced by CO2 injection into a hypothetical CO2 storage reservoir with Fe(III)-bearing hematite in a time scale of 30 years CO2 injection and 100 years after CO2 injection. Numerical simulation results show that injection of CO2 reduced pH and induced small amounts of hematite dissolution, which released Fe3+ into aqueous phase. Fe3+ together with dissolved bicarbonate species caused oxidative dissolution of UO2 (Fe3+ serving as an oxidant), resulting in an increase of dissolved uranium concentrations in the CO2 storage reservoir. However, the released uranium was limited to a small region close to Fe3+ supply source and the maximum concentration of released uranium was only 9.00 × 10−10 mol/kg in the CO2 storage reservoir at t = 30 years. The availability of Fe3+ is the main factor that limits mineralized uranium release because the pH drop induced by CO2 injection is not low enough to cause significant Fe3+ release. For sorbed uranium, the main factor that influences sorbed uranium release is pH because uranium sorption is amphoteric. Based on our simulation results, the pH range in the CO2 storage reservoir does not cause a substantial release of sorbed uranium. Also, the potential for released uranium to migrate through a permeable zone in the caprock to the layer above the caprock and cause groundwater contamination is negligible. In summary, results from this study imply a very low risk of environmental contamination by bicarbonate and Fe(III)-induced uranium mobilization.

Solubility product of amorphous magnesium carbonate

AbstractThe thermodynamic solubility product of amorphous magnesium carbonate (AMC) was studied at room temperature. The samples had been prepared at pH 8.78 and 9.37, where the particle size was 58 ± 11 nm and 49 ± 9 nm, respectively. Solid‐state NMR measurements showed that the former contained a minute amount of bicarbonate species, whereas we did not detect any for the latter. While the AMC sample prepared at higher pH exhibited a one‐step decomposition at 413°C, the one at lower pH decomposed in two steps at 425 and 510°C. The solubility products of AMC prepared at two pH are statistically identical and the average value is estimated to be 6.3 × 10−6.

Underway Measurement of Dissolved Inorganic Carbon (DIC) in Estuarine Waters

Dissolved inorganic carbon (DIC) is an important parameter of the marine carbonate system. Underway analyses of DIC are required to describe spatial and temporal changes of DIC in marine systems. In this study, we developed a microvolume flow detection method for the underway determination of DIC in marine waters, using gas-diffusion flow analysis in conjunction with electrical conductivity (EC) measurement. Only an acid carrier reagent (0.2 mol.L−1) and an ultrapure water acceptor are required for the DIC monitoring system. In this system, a sampling loop (100 µL) is used to quantify the injection sample volume, allowing micro-sample volume detection. The water sample reacts with the acid reagent to convert carbonate and bicarbonate species into CO2. The water sample is then carried into a gas-diffusion assembly, where the CO2 diffuses from the sampling stream into the acceptor stream. CO2 in the acceptor is detected subsequently by an electrical conductivity. The limit of DIC detection using ultrapure water is 0.16 mM. A good repeatability is obtained, with a relative standard deviation (RSD) of 0.56% (1 mM, n = 21). The time interval for detecting one sample is 5 min. During the observation period, measurements can be switched between standard solutions and water samples automatically. Accuracy and precision of the instrument is sufficient for the underway observation of marine DIC in estuarine waters.

Atomic-Scale Studies of Fe3 O4 (001) and TiO2 (110) Surfaces Following Immersion in CO2 -Acidified Water.

Difficulties associated with the integration of liquids into a UHV environment make surface‐science style studies of mineral dissolution particularly challenging. Recently, we developed a novel experimental setup for the UHV‐compatible dosing of ultrapure liquid water and studied its interaction with TiO2 and Fe3O4 surfaces. Herein, we describe a simple approach to vary the pH through the partial pressure of CO2 (pCO2 ) in the surrounding vacuum chamber and use this to study how these surfaces react to an acidic solution. The TiO2(110) surface is unaffected by the acidic solution, except for a small amount of carbonaceous contamination. The Fe3O4(001)‐(2 ×2 )R45° surface begins to dissolve at a pH 4.0–3.9 (pCO2 =0.8–1 bar) and, although it is significantly roughened, the atomic‐scale structure of the Fe3O4(001) surface layer remains visible in scanning tunneling microscopy (STM) images. X‐ray photoelectron spectroscopy (XPS) reveals that the surface is chemically reduced and contains a significant accumulation of bicarbonate (HCO3 −) species. These observations are consistent with Fe(II) being extracted by bicarbonate ions, leading to dissolved iron bicarbonate complexes (Fe(HCO3)2), which precipitate onto the surface when the water evaporates.

CO2 methanation on Ni-Ce0.8M0.2O2 (M=Zr, Sn or Ti) catalyst: Suppression of CO via formation of bridging carbonyls on nickel

The effect of different cations (M=Zr, Sn or Ti) doping on ceria supported nickel (Ni-Ce0.8M0.2O2) catalysts and their performance in the CO2 methanation reaction has been investigated. Among the prepared catalysts, the Ni-CeO2 (CN) catalyst exhibited the best catalytic performance with a CO2 conversion of 62.9% at 400 °C. The selectivity on Ni-Ce0.8Zr0.2O2 (CZN) remained above 98.4% from 200 to 400 °C. As confirmed by in-situ DRIFTS, the dissociative adsorption of H2 mainly proceeds on Ni, by-product CO is mainly assigned to the releasing of weak-binding linearly adsorbed CO on nickel, which is from the hydrogenation of formates with adsorbed H. The CO-suppressing effect is attributed to the strong adsorption of carbon monoxide on nickel via the forming of bridging carbonyls. It was found that CO2 is adsorbed on the catalysts to form carbonate, bicarbonate and formate species. The formate species could be further hydrogenated by dissociated H and then finally release methane.

In situ FTIR and ex situ XPS/HS-LEIS study of supported Cu/Al2O3 and Cu/ZnO catalysts for CO2 hydrogenation

Cu-based catalysts are commonly used in industry for methanol synthesis. In this study, supported catalysts of 5 wt% Cu/Al2O3 and 5 wt% Cu/ZnO were prepared, and their surface characteristics during H2 reduction and CO2 hydrogenation were investigated using in situ Fourier transform infrared spectroscopy (FTIR), ex situ X-ray photoelectron spectroscopy, and high sensitivity low energy ion scattering spectroscopy. During the H2 reduction and CO2 hydrogenation processes, it was found that Al2O3 can stabilize Cu+. In situ FTIR spectra indicated that the 5 wt% Cu/Al2O3 can adsorb large amounts of bicarbonate and carbonate species, which then convert into formate during CO2 hydrogenation. For the 5 wt% Cu/ZnO, it was found that Cu nanoparticles were gradually covered by a highly defective ZnOx overlayer during H2 reduction, which can effectively dissociate H2. During CO2 hydrogenation, the adsorbed bicarbonate or carbonate species can convert into formate and then into a methoxy species. Using these surface sensitive methods, a more in-depth understanding of the synergistic effect among the Cu, Al2O3, and ZnO components of Cu-based catalysts was achieved.

Photocatalytic Oxidation of Propane Using Hydrothermally Prepared Anatase-Brookite-Rutile TiO2 Samples. An In Situ DRIFTS Study.

Photocatalytic oxidation of propane using hydrothermally synthesized TiO2 samples with similar primary crystal size containing different ratios of anatase, brookite and rutile phases has been studied by measuring light-induced propane conversion and in situ DRIFTS (diffuse reflectance Fourier transform infrared spectroscopy). Propane was found to adsorb on the photocatalysts, both in the absence and presence of light. The extent of adsorption depends on the phase composition of synthesized titania powders and, in general, it decreases with increasing rutile and brookite content. Still, the intrinsic activity for photocatalytic decomposition of propane is higher for photocatalysts with lower ability for propane adsorption, suggesting this is not the rate-limiting step. In situ DRIFTS analysis shows that bands related to adsorbed acetone, formate and bicarbonate species appear on the surface of the photocatalysts during illumination. Correlation of propane conversion and infrared (IR) data shows that the presence of formate and bicarbonate species, in excess with respect to acetone, is composition dependent, and results in relatively low activity of the respective TiO2. This study highlights the need for precise control of the phase composition to optimize rates in the photocatalytic oxidation of propane and a high rutile content seems to be favorable.

Impacts of metal loading in Ni/attapulgite on distribution of the alkalinity sites and reaction intermediates in CO2 methanation reaction

Both metal sites and alkaline sites are essential parameters for a catalyst used in methanation of CO2. This study investigated the impacts of the relative abundance of metal sites and alkaline sites on the catalytic performances of nickel-based catalyst with attapulgite, a natural mineral, as the support. The results showed that the increase of nickel loading to attapulgite significantly decreased the abundance of alkaline sites, remarkably enhanced the catalytic activity, and suppressed the formation of CO. The in situ DRIFTS characterization of the CO2 methanation indicated that the alkaline sites favored formation of the oxygen-containing reaction intermediates such as CO∗, –OH, ∗CO2, formate, carbonate and bicarbonate species. In comparison, metallic nickel species promoted their further hydrogenation to form CH4. Besides the absorption/activation of ∗CO2 was more preferable on surface of metallic nickel, but not on the alkaline sites. The availability of the alkaline sites was not as important as the metallic nickel species for preparation of an efficient catalyst for CO2 methanation.

(Invited) Efficient CO Production from CO2 and H2o By the Aid of Artificial Photosynthesis

The reduction in human-induced emissions of CO2 from automobiles, factories, power stations etc., over the next 15 years is currently one of the most important issues facing the planet. We should therefore attempt to develop industrial processes using CO2 as a feedstock to build a sustainable society. Linear CO2 molecules adsorbed on the surface of the solid bases are converted into unique structures, such as bicarbonate and carbonate species possessing lattice oxygen atoms. We believe that the process involves the capture and distortion of CO2 upon adsorption on a solid base through activation by photoirradiation. These days, we succeeded in designing highly selective photocatalytic conversion of CO2 by H2O as the electron donor, by the simultaneous use of an inhibitor of the production of H2 and a material for CO2 capture and storage. An isotope experiment using 13CO2 and mass spectrometry clarified that the carbon source of the evolved CO is not the residual carbon species, but the CO2 introduced in the gas phase. In addition, stoichiometric amounts of O2 were generated together with CO.

(Invited) Catalyst Design and Development for Highly Selective Photocatalytic Conversion of CO2 By H2o As an Electron Donor

The reduction in human-induced emissions of CO2 from automobiles, factories, power stations etc., over the next 15 years is currently one of the most important issues facing the planet. We should therefore attempt to develop industrial processes using CO2 as a feedstock to build a sustainable society. Linear CO2 molecules adsorbed on the surface of the solid bases are converted into unique structures, such as bicarbonate and carbonate species possessing lattice oxygen atoms. We believe that the process involves the capture and distortion of CO2 upon adsorption on a solid base through activation by photoirradiation. These days, we succeeded in designing highly selective photocatalytic conversion of CO2 by H2O as the electron donor, by the simultaneous use of an inhibitor of the production of H2 and a material for CO2 capture and storage. An isotope experiment using 13CO2 and mass spectrometry clarified that the carbon source of the evolved CO is not the residual carbon species, but the CO2 introduced in the gas phase. In addition, stoichiometric amounts of O2 were generated together with CO.

Second Dissociation Constant of Carbonic Acid in H2O and D2O from 150 to 325 °C at p = 21 MPa Using Raman Spectroscopy and a Sapphire-Windowed Flow Cell.

Solvent-corrected reduced isotropic spectra of carbonate and bicarbonate in light and heavy water have been measured from 150 to 325 °C at 21 MPa using a confocal Raman microscope and a custom-built titanium flow cell with sapphire windows. The positions of the symmetric vibrational modes of CO32- and HCO3-/DCO3- were compared to density functional theory (DFT) calculations with a polarizable continuum model in light and heavy water. The experimental Raman peak positions shifted linearly toward lower wavenumbers with increasing temperatures. Raman scattering coefficients, measured relative to a perchlorate internal standard, were used to determine equilibrium molalities of the carbonate and bicarbonate species. These yielded quantitative thermodynamic equilibrium quotients for the reaction CO32- + H2O ⇌ HCO3- + OH- and its deuterium counterpart. Ionization constants for HCO3- and DCO3-, K2a,H,m and K2a,D,m, calculated in their standard states using the Meissner-Tester activity coefficient model, were combined with critically evaluated literature data to derive expressions for their dependence on temperature and pressure, expressed as solvent molar volume, over the range 25 to 325 °C from psat to 21 MPa. These are the first experimental values to be reported for this reaction in light water above 250 °C and in heavy water above 25 °C. The value of the deuterium isotope effect on the chemical equilibrium constant, ΔpK2a,m = pK2a,D,m - pK2a,H,m, decreased from ΔpK2a,m = 0.67 ± 0.07 at 25 °C to ΔpK2a,m = 0.17 ± 0.13 at 325 °C and psat.

Vibrational properties of CO2 adsorbed on the Fe3O4 (111) surface: Insights gained from DFT.

By virtue of density functional theory calculations, this work discusses several carbonate, carboxylate, and bicarbonate species on two thermodynamically relevant metal terminations of the (111) surface of magnetite, Fe3O4. We present adsorption energies and vibrational wavenumbers and conclude in assigning the observed infrared reflection-absorption spectroscopy bands. CO2 prefers to adsorb molecularly on the Fetet1 terminated Fe3O4(111) surface, a finding consistent with observation. Calculations compared with the experiment lead to interpreting results in favor of the Fetet1 (single metal) terminated Fe3O4(111) surface as the regular surface termination. Formation of carbonate and bicarbonate requires metal impurities on that surface. Such impurities exist, for instance, on the Feoct2 (double metal) termination, which can thus be used as a model for "metal-rich terminations" of more complex surfaces.