Metals Rb Research Articles

Characterization of Cabernet Sauvignon wines from California: determination of origin based on ICP-MS analysis and machine learning techniques

In this paper, samples of Cabernet Sauvignon wines produced in California have been analyzed on the basis of their elemental content and classified according to its geographical origin by the use of machine learning. Overall, 13 metals (Al, Cd, Co, Cr, Cu, Li, Mn, Ni, P, Pb, Rb, Sr, and Zn) were determined by inductively coupled plasma mass spectrometry (ICP-MS). We used two algorithms of variable selection in order to estimate the relevance of each metal to classification. Predictive models based on chemometric tools and machine learning algorithms were developed to differentiate origin of wine samples. Li and Sr were identified as the main responsible for the differentiation of samples. The application of Random Forest permitted to correctly classify all samples. A second analysis was performed by removing the variables Li and Sr to investigate the relevance of the others metals. We found that a group of seven variables (Cd, Ni, Mn, Pb, Rb, Co, Cu) which were able to discriminate the wines in 89% of accuracy by using Support Vector Machines. Results suggested that the developed methodology by advanced machine learning techniques is robust and reliable for the geographical classification of wine samples, and the study of the elements that characterize the regions.

Determination of Trace Metals in Garlic Bulbs (Allium sativum L.): A Variety Discrimination by Inductively Coupled Plasma Mass Spectrometry

Thirteen trace metals (Li, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Rb, Sr, Nb, and Mo) and two toxic metals (Cd and Pb) in two kinds of garlic bulbs have been quantified. Following the dehydration process, the garlic residues are digested using 10.0 mL of an acid mixture of HNO3:H2O2:HCl (3:1:1, v/v/v). The trace metal assay is accomplished by inductively coupled plasma mass spectrometry (ICP-MS). Results reveal that the metal levels for the garlic bulbs with purple skin in dry weight are 14.5, 1.32, 3.03, 3.88, 13.0, 2.50, 1.00, 64.1, 139.6, 13.6, 18.4, 0.29, 0.11, 1.60, and 0.52 mg/kg for Li, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Rb, Sr, Nb, Mo, Cd, and Pb, respectively, while the corresponding metal concentrations in the garlics with white skin are 22.9, 2.70, 3.95, 6.60, 19.7, 3.72, 1.16, 79.9, 149.8, 19.7, 24.0, 0.33, 0.43, 0.84, and 0.30 mg/kg, respectively. In general, the trace metals in both varieties are clearly under the FAO/WHO maximum permissible limits. However, it is observed that the garlics with white skin show higher quantities of essential/possible essential metals and lower levels of toxic metals, demonstrating the garlics with white skin exhibit a higher nutrition quality and are a better source of essential minerals.

ГОДОВЫЕ КОЛЬЦА СОСНЫ ОБЫКНОВЕННОЙ (PINUS SYLVESTRIS L.) – ИНДИКАТОР ГЕОХИМИЧЕСКОЙ ОБСТАНОВКИ И ХРОНОЛОГИЧЕСКОГО ИЗМЕНЕНИЯ ХИМИЧЕСКОГО ЭЛЕМЕНТНОГО СОСТАВА ОКРУЖАЮЩЕЙ СРЕДЫ

Актуальность исследования обусловлена необходимостью поиска или изобретения точного и информативного индикатора для проведения экологического мониторинга окружающей среды. Цель: изучить особенности накопления 28 химических элементов в годовых кольцах сосны обыкновенной (Pinus sylvestris L.) различных территорий. Объект: годовые кольца сосны обыкновенной (Pinus sylvestris L). Методы: отбор кернов сосны обыкновенной; высушивание и разделение проб на временные интервалы, измельчение кернов; определение содержания 28 химических элементов методом количественного инструментального нейтронно-активационного анализа; обработка данных статистическими методами. Результаты. Определен химический элементный состав образцов годовых колец сосны обыкновенной (Pinus sylvestris L.), отобранных на территориях трех регионов России: Томской области, Кемеровской области и Республики Бурятия. Сравнение химического элементного состава годовых колец деревьев разных регионов помогло увидеть геохимические особенности каждой территории в отдельности. Специфичными для дерева Томской области являются элементы Ba (3 мг/кг), Rb (0,5 мг/кг), Ce (0,02 мг/кг), Cs (0,01 мг/кг) и другие. Для дерева Кемеровской области: Cr (1 мг/кг), Fe (34 мг/кг), As (0,01 мг/кг), Sb (0,002 мг/кг), La (0,01 мг/кг), U (0,004 мг/кг) и другие. Для дерева из Республики Бурятия: Br (1 мг/кг), Sr (7 мг/кг), Ag (0,04 мг/кг), Au (0,001 мг/кг), Th (0,001 мг/кг) и другие. Таким образом, дендрогеохимический метод исследования может быть использован для оценки геохимической обстановки территории по уровню накопления химических элементов в годовых кольцах дерева. Динамики поступления химических элементов в годовые кольца позволяют изучать историю трансформации химического элементного состава окружающей среды. Так, тренды железа и хрома для Pinus sylvestris Кемеровской области ярко отражают развитие черной металлургии, а тренды As, Ag, Cs, Sb, U, Sm, Th и Br – развитие угольной промышленности региона. Тренды щелочных металлов Rb, Cs, радиоактивного U и редкоземельных элементов Nd, Sm, Eu показали интенсивность воздействия в разные промежутки времени предприятий ядерно-топливного цикла и других предполагаемых источников на окружающую среду Томского района Томской области. Сделан вывод, что дендрогеохимический мониторинг может быть использован в целях исследования локальных и глобальных изменений окружающей среды и позволяет восстанавливать историю прошлого загрязнения.

Segregation of Na, K, Rb and Cs into the cores of Earth, Mars and Vesta constrained with partitioning experiments

Alkali metals Na, K, Rb and Cs are depleted in planetary mantles and their depletion is commonly attributed to the effect of volatility during the condensation of the first solids in the solar nebula or the high temperatures involved during planetary growth. Most models of planetary differentiation assume that alkalis behave entirely as lithophile elements and do not participate in core segregation. Here, we tested this hypothesis by determining experimentally the partitioning of Na, Cs and Rb between iron sulfide and silicate (Dsulf/sil) and combining it with available data from the literature on K, Na and Cs partitioning. Our experiments were conducted at 1–3.5 GPa, with an additional one at 8 GPa, 1600–1900 °C, and varying FeO contents, which lead to a relatively large range of O content in the sulfide phases (up to 13 wt%). We found maximum Dsulf/sil of 0.8, 0.4, and 0.36 for Na, Cs and Rb respectively. In addition, Dsulf/sil for Na, K, Cs and Rb increases with temperature and O content in the sulfide and decreases with FeO content in the silicate. The degree of polymerization of the silicate melt and the S content of the sulfide additionally increase Dsulf/sil for Na, K and Cs. Since the solubility of O in sulfides is correlated with the FeO content of the silicate and both have opposite effects on Dsulf/sil, varying the oxidation state of equilibrating material does not significantly affect Dsulf/sil, which is more controlled by the temperature of equilibration. We modeled core formation for Earth, Mars and asteroid Vesta, assuming that some of the accreted embryos contained immiscible sulfides, that segregated into planetary cores. Our results show that with such a scenario, significant amounts of Na, K, Cs and Rb were sequestered in planetary cores, leading to core/mantle distribution of alkalis between 4·10−5 and 0.15. The depletion of alkalis in the mantles of Earth, Mars and Vesta could have resulted from combined effects of volatility and core segregation, but are largely due to volatile depletion in the accreting materials.

Synthesis and structural characterization of the type-I clathrates K8AlxSn46-x and Rb8AlxSn46-x (x ≃ 6.4-9.7).

Exploratory studies in the systems A-Al-Sn (A = K and Rb) yielded the clathrates K8AlxSn46-x (potassium aluminium stannide) and Rb8AlxSn46-x (rubidium aluminium stannide), both with the cubic type-I structure (space group Pm-3n, No. 223; a ≃ 12.0 Å). The Al:Sn ratio is close to the idealized A8Al8Sn38 composition and it is shown that it can be varied slightly, in the range of ca ±1.5, depending on the experimental conditions. Both the (Sn,Al)20 and the (Sn,Al)24 cages in the structure are fully occupied by the guest alkali metal atoms, i.e. K or Rb. The A8Al8Sn38 formula has a valence electron count that obeys the valence rules and represents an intrinsic semiconductor, while the experimentally determined compositions A8Al8±xSn38∓x suggest the synthesized materials to be nearly charge-balanced Zintl phases, i.e. they are likely to behave as heavily doped p- or n-type semiconductors.

First-Principles Computational Screening of Perovskite Hydrides for Hydrogen Release.

This study investigates perovskite hydrides (ABH3) comprising alkali metals of A, where A is Li, Na, K, Rb, or Cs, and alkaline-earth metals of B, where B is Be, Mg, Ca, Sr, or Ba, to screen the highest potential hydrides for hydrogen release. Herein, we investigated the most favorable dehydrogenation pathway for each ABH3 system and found that NaCaH3 was the most attractive ABH3 system. Analysis was performed to determine the influence of the alkali dopants (at the A-site) and alkaline-earth dopants (at the B-site) on hydrogen release from NaCaH3. For this analysis, we calculated the reaction enthalpies of a NaCaH3 system for hydrogen release with different dopants and pathways. Cs was the best dopant for improving hydrogen release with the lowest reaction enthalpy. However, no clear effect from B-site doping on the dehydrogenation was found.

First principles study of alkali and alkaline earth metal ions adsorption and diffusion on penta-graphene

Developing carbon based anode materials for alkali and alkaline earth metal ion batteries is important for the development of non-Li metal ion batteries. From density functional theory calculations, we studied alkali metal (Li, Na, K, and Rb) and alkaline earth metal (Be, Mg, Ca, Sr, and Ba) ions adsorption on penta-graphene (PG), which is a novel two dimensional (2D) carbon isomer composed of both sp2 and sp3 hybridized C-atoms. Strong correlations are observed between the adsorption energy and the electronegativity of the M-atoms, namely, smaller electronegativity corresponds to lower adsorption energy. The suitable Ca-ion intercalation potential (~117 mV), metallic electronic structures of Ca-ion adsorbed PG, low Ca-ion diffusion energy barriers (0.36 eV to 0.51 eV), and high specific capacity (1487.6 mAh/g) suggest that PG can be applied as an excellent anode material for Ca-ion batteries.

All-electron product basis set: Application to plasmon anisotropy in simple metals

An efficient basis set for products of all-electron wave functions is proposed, which comprises plane waves defined over the entire unit cell and orbitals confined to small nonoverlapping spheres. The size of the set and the basis functions are, in principle, independent of the computational parameters of the band-structure method. The approach is implemented in the extended linearized augmented plane wave method, and its properties and accuracy are discussed. The method is applied to analyze the dielectric response of the simple metals Al, Na, Li, K, Rb, and Cs with a focus on the origin of the anisotropy of the plasmon dispersion in Al and Na. The anisotropy is traced to tiny structures of the one-particle excitation spectra of Al and Na, and relevant experimental observations are explained.

Study of the Surface Charge of a Porous Clay Heterostructure (PCH) and Its Adsorption Capacity of Alkaline Metals

A Porous Clay Heterostructure (PCH) was prepared by chemical modification of a natural clay, by intercalation of a cationic surfactant. Its surface charge properties as well as its adsorption capacity for alkali metals were studied using a potentiometric titration method. The PCH developed a pH-dependent charge (sH), probably due to the presence of amphoteric silanol groups (SiO2) coming from the pillars of silica interlayered during the pillared process. The PCH presented a region of zero charge in the range of pH of 4.0 to 7.7. The sH acquired by the PCH was adjusted with good correlation to the electric double layer model of Gouy-Chapman (r2 = 0.9925). The surface charge conferred the PCH ion exchange capacity for the studied metals (Li, Na, K, Rb and Cs) at high pH values (10 < pH), in comparable quantities (3.5 to 6 meq/g) to some Dowex resins. The results of this study suggest that PCH could have applications in the recovery of toxic metals from waste waters.

Fibroscan® and ELF score in the study of fibrosis in obese patients with chronic liver disease: A preliminary study

Developing carbon based anode materials for alkali and alkaline earth metal ion batteries is important for the development of non-Li metal ion batteries. From density functional theory calculations, we studied alkali metal (Li, Na, K, and Rb) and alkaline earth metal (Be, Mg, Ca, Sr, and Ba) ions adsorption on penta-graphene (PG), which is a novel two dimensional (2D) carbon isomer composed of both sp2 and sp3 hybridized C-atoms. Strong correlations are observed between the adsorption energy and the electronegativity of the M-atoms, namely, smaller electronegativity corresponds to lower adsorption energy. The suitable Ca-ion intercalation potential (~117 mV), metallic electronic structures of Ca-ion adsorbed PG, low Ca-ion diffusion energy barriers (0.36 eV to 0.51 eV), and high specific capacity (1487.6 mAh/g) suggest that PG can be applied as an excellent anode material for Ca-ion batteries.

First-principles calculation study of electronic structures of alkali metals (Li, K, Na and Rb)-incorporated formamidinium lead halide perovskite compounds

Electronic structures of alkali metals (Li, Na, K or Rb)-incorporated formamidinium lead halide perovskite compounds were investigated by first-principles calculation. The conduction band were supplied with electrons from energy levels at 2s, 3s, 4s and 5s orbital of alkali metal to energy levels at 6p orbital of Pb atom in the perovskite crystal. Deviation of charge distribution in the perovskite crystal promoted the photo-induced charge generation, electron correlation and electron-lattice interaction as phonon effectiveness. The chemical shifts of 127I-NMR in the perovskite crystal were originated in a slight perturbation of the coordination structure with nuclear quadruple interaction based on the electric field gradient. The slight incorporation of alkali metal near the ligand structure decreased the enthalpy with the Gibbs free-energy by contribution of the entropy due to the PI stretching vibration.

Fluid-melt trace-element partitioning behaviour between evolved melts and aqueous fluids: Experimental constraints on the magmatic-hydrothermal transport of metals

The fluid-melt partition coefficients of ten trace metals (Li, Mn, Cu, Zn, Rb, Sr, Mo, W, and Pb, along with K) between hydrous evolved melts and coexisting Cl-bearing fluid(s) have been experimentally determined at 850–1050 °C, 0.6–2.2 kbar, and ƒO2 ≈ NNO –0.5 to NNO +2 log units. The measured compositions of the quenched fluid phases vary from low salinity (~2 wt% Cl−) to >19 wt% Cl−, with maximum starting fluid concentrations of >21 wt% Cl. The results of 15 partitioning experiments confirm that Dmetalfluid/melt values depend strongly on the melt and fluid composition, with the greatest metal affinities for the fluid phase shown in the experiments with high-Cl fluids, and the most fractionated melts. Five experiments conducted in Au96Cu4 capsule alloy show DCufluid/melt values ranging from ~40 to >80, and a strong correlation with melt FeO wt% contents at equivalent fluid Cl− contents. In contrast, Li shows only weak partitioning in favour of coexisting fluids across all melt compositions, with DLifluid/melt ranging from 0.16 in low salinity fluids to 1.17 in the highest Cl fluid (19.15 wt% Cl−).A procedure was employed to redissolve and analyse the aluminosilicate precipitates that form during quenching of the experiments. This procedure allows for metal contents of the final quench fluids to be constrained by both mass balance and direct measurement by solution ICP-MS analysis. A comparison of the mass balance calculated vs. directly measured fluid-melt partition coefficients generally gives good agreement, within an order of magnitude for most trace elements. However, discrepancies between these methods arise due to errors inherent in the mass balance calculations for metals with low abundances in the fluids (e.g. Sr), and especially those showing affinities to alloy with the experiment capsule material (e.g. Mo). These discrepancies in constraining experimental fluid trace element budgets also suggest that the precious metal capsule alloys cannot always be considered completely inert containers in experimental investigations, and semi-quantitative LA-ICP-MS analysis of the raw capsule alloys confirms the detectable presence of several of the trace elements investigated here.Integrating these new partitioning data with previous experimental and natural studies confirms that aqueous Cl-bearing fluids exsolved by hydrous calc-alkaline melts stored at mid- to upper-crustal conditions are capable of efficiently sequestering and transporting some economically important trace metals (e.g. Mn, Cu, Zn). However, the new fluid/melt Li partitioning data, in conjunction with evidence of very late (post-eruptive) Li modification, suggests that Li is moderately-strongly fluid-immobile at depth and suffers from significant post-eruptive re-equilibration. This has implications for deciphering the signatures of ‘volatile fluxing’ in arc magmas that are preserved in mineral and melt inclusion trace element concentrations, and the development of mineralised stockwork regions in porphyry-style metal deposits.

ASbF3Cl (A = Rb, Cs): Structural Evolution from Centrosymmetry to Noncentrosymmetry

The alkali metals Rb+ and Cs+ involving structural evolution from centrosymmetric (CS) to noncentrosymmetric (NCS) is investigated in the ASbF3Cl compounds. RbSbF3Cl crystallizes in the orthorhombi...

Crystal chemistry and physical properties of the A2M3(H2O)2[B4P6O24(OH)2] (A = Cs, Rb; M = Ni, Cu, (Ni, Fe)) borophosphate family.

Three new transition metal borophosphates, Cs2Cu3(H2O)2[B4P6O24(OH)2] (denoted (I)), Cs2Ni3(H2O)2[B4P6O24(OH)2] (II) and mixed Rb2Ni2.5Fe0.5(H2O)2[B4P6O24(OH)2] (III), were synthesized by a boric acid flux method at 473-493 K. X-ray single-crystal diffraction study confirms their isotipy with (Cs/Rb)2Co3(H2O)2[B4P6O24(OH)2] borophosphates crystallizing in the orthorhombic space group Pbca. The crystal structures of all compounds are based on 3D frameworks made from corrugating borophosphate layers [B4P6O24(OH)2] and trimers of MO4(H2O)2 and two MO6 edge-sharing octahedra. The negative charge of the framework is compensated by alkali metal cations, Rb+ or Cs+. Structural analysis reveals the flexibility of mixed anionic frameworks of the described structural type. The Cu-member demonstrates a strong distortion of the unit cell due to the Jahn-Teller effect of the d9 configuration of the Cu2+ cation. The possibility of a solid solution between different transition metals (Fe and Ni) with the formation of crystals with mixed structural positions is confirmed by an example of the (III) phase. It is shown that Fe2+ cations prefer to occupy the M2 position with more distorted oxygen environment, as compared to the M1O6 octahedra. Magnetic studies of (I), (II) and (III) prove that all compounds are paramagnets down to the lowest temperatures of measurements, 2 K. (I) and (II) compounds are thermally stable up to 500 °C. Different mechanisms of their thermal decomposition are discussed. The possibility of a wide isomorphous substitution at the transition metal sites of the title structure type opens the way to the modification of the properties in the discussed series of borophosphates.

First-principles study of magnetic properties of alkali metals and alkaline earth metals doped two-dimensional GaN materials

We systematically study the electronic structure and magnetic properties of alkali metals (Li, Na, K and Rb) and alkaline earth metals (Be, Mg and Sr) doped two-dimensional GaN monolayers using the first-principles calculations based on density functional theory. The results show that Be atom is located in the plane of the GaN monolayer, and the other doped atoms reside slightly above the plane. It is found that doping is easier to achieve under the N-rich condition. The total magnetic moment of the alkali metals doped system and the alkaline earth metals doped system are 2μB and 1μB, respectively, which are presented mainly by the spin-polarized holes of the nearest N atoms of the impurity atoms. The band structures indicate that the four alkali metal atoms doped systems are magnetic semiconductors, and the three alkaline earth metal doped systems are all semi-metallic. For a double M-doped GaN monolayer system, there is a long-range ferromagnetic coupling in the seven elements doped systems, which are realized by the hole-mediated p-p hybrid interaction. The Heisenberg mean field model is used to estimate the Curie temperature. It is found that the long-range ferromagnetic coupling states of Li, Be, Mg and Sr are existent at higher than room temperature, indicating that the four atom-doped two-dimensional GaN monolayers are very good candidates for the room temperature ferromagnetic candidate materials. The alkali metals and alkaline earth metals doped two-dimensional GaN monolayers are expected to play an important role in the studying of spintronics.

Trace Element Analysis by ICP-MS and Chemometric Approach in Some Euphorbia Species: Potential to become a Biomonitor.

In this study, the branch, leaves, flowers, roots and mixed parts of different nine Euphorbia species were analyzed for their trace element contents by using ICP-MS. The samples were digested by concentrated nitric acid and hydrogen peroxide in a microwave by ICP-MS before the analysis. The accuracy and precision of the method was evaluated by CRM 1573a Tomato Leaves. Trace element contents accumulated in different parts of each sample were contrasted. Minitab Statistical Software Inc., programme was used for the multivariate analysis of 12 toxic metals of seeds, roots, branches, leaves, flowers, and mixed parts of Euphorbia species collected from Diyarbakir, Kayseri, Malatya, Mardin, Trabzon, and Van cities.When the studied Euphorbia species are compared in terms of their metal contents; V, Tl, Cr, and Ni metals in E. eriophora, Ba in E. aleppica, As and Co metals in E. segıieriana, Ag and Se metals in E. craspedia, Cu and Cd metals in E. fistulosa, Cs and Pb metals in E. grisophylla, Zn in E. macroclada and also Rb and Sr metals in E. denticulata were determined higher. It was determined that the studied species accumulated some metals at highly amounts especially in the root and leaf parts. In general, it can be said that Euphorbia species have high potential to become a biomonitor. For this reason, it can be predicted that these species will be used as ornamental plants in landscape architecture due to both their toxic metals retention properties and their beautiful appearance.

Antioxidant Activities and Heavy Metal Contents of Castanea Sativa Honey

<p>Honey is one of the most valuable foods in terms of its antioxidant nature and antioxidant activity. In this study, their botanic origins, total flavonoid content, total phenol content, the hydrogen peroxide scavenging activity (HPSA) (in terms of SC50 (µg mL-1)), ferric reducing antioxidant power capacity (FRAP), 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity (in terms of SC50), metal-chelating activity (MCA) (%) and heavy metal amounts were examined to determine the qualities of honey samples that gathered from Giresun city of Black Sea region in Turkey. According to the melissopalynological analysis, the botanic origins of the samples are Castanea sativa (Chestnut) Miller and uni-floral. The HPSA, FRAP, DPPH, MCA (%), total phenol content (TPC), and total flavonoid content (TFC) were found between 251.99±0.48-258.64±1.22 µg mL-1, 71.34±0.09-73.71±0.20 %, 584.86±0.06-595.04±0.29 µg mL-1, 36.73±0.00-36.86±0.09 %, 93.82±1.05-173.15±2.46 mg GAE 100 g-1 and 5.51±0.19-8.29±0.05 mg CAE/100 g, respectively. For comparison of these results, Butylated Hydroxy Anisole (BHA), Butylated Hydroxy Toluene (BHT) and α-Tocopherol (TOC) were used as standard antioxidant compounds. In addition, it was observed that honey samples were been contaminated with most of the heavy metals (Al, Ca, Cr, Cu, Fe, Li, Mg, Mn, Ni, Rb, and Zn) to a lesser or greater extent, whereas others (Te, Tl, and U) were never detected in these samples. However, Cd and Cs were detected only in one sample and Pb in another sample Finally, the results indicate that although honey is an important source of nutrients, nevertheless it could be affected by environmental pollution.</p>

Alkali Metals‐Based Energetic Coordination Polymers as Promising Primary Explosives: Crystal Structures, Energetic Properties, and Environmental Impact

Coordination polymers (CPs) consisting of alkali metals (Na, K, Rb, and Cs) and a powerful nitrogen- and oxygen-rich energetic ligand (4,4'-bis(dinitromethyl)-3,3'-bisnitramide-methylene-furazanate, DBMF2- ) were developed. Molecular structures of these CPs, confirmed by single-crystal X-ray diffraction analysis, indicated that the same ligand takes on a U-shaped state for Na and an N-shaped state for K, Rb, and Cs. Explosion tests demonstrated that both Na2 DBMF and K2 DBMF efficiently detonated the secondary explosive RDX. This indicates that they are both effective primary explosives. K2 DBMF exhibits better calculated detonation performance (D: 8227 m s-1 ; P: 32.5 GPa) than the primary explosive Pb(N3 )2 . In addition, toxicity tests and evaluation of their decomposition products reveal their low impact on the environment. Both experimental results and theoretical analyses indicate that the combination of alkali metals and a powerful energetic ligand can stimulate the development of primary explosives.

Hydrogenation of carbon dioxide over iron carbide prepared from alkali metal promoted iron oxalate

Iron carbide was prepared by the carburization of iron oxalate doped with various alkali metals in flowing CO at 400 °C. The addition of alkali metal (Li, Na, K, Rb or Cs) to iron oxalate was found to decrease the bulk iron carbides formation. However, the amount of carbon deposited on Fe as inferred from temperature programmed hydrogenation and high-resolution transmission electron microscopic studies show an increasing trend with the increase of the basicity of alkali added. The CO2 and H2 conversions of all alkali doped iron catalysts were initially higher but they declined over time irrespective of alkali. The benefits of addition of alkali to iron without any structural and reduction promoters, such as copper, is found to lower the selectivity for methane, higher olefins and oxygenates formation for CO2 hydrogenation.

Effect of alkali metals on the performance of CoCu/TiO2 catalysts for CO2 hydrogenation to long-chain hydrocarbons

CoCu/TiO2 catalysts promoted using alkali metals (Li, Na, K, Rb, and Cs) were prepared by the homogeneous deposition-precipitation method followed by the incipient wetness impregnation method. The influences of the alkali metals on the physicochemical properties of the CoCu/TiO2 catalysts and the catalytic performance for CO2 hydrogenation to long-chain hydrocarbons (C5+) were investigated in this work. According to the characterization of the catalysts based on X-ray photoelectron spectroscopy, X-ray diffraction, CO2 temperature-programmed desorption (TPD), and H2-TPD, the introduction of alkali metals could increase the CO2 adsorption and decrease the H2 chemisorption, which could suppress the formation of CH4, enhance the production of C5+, and decrease the hydrogenation activity. Among all the promoters, the Na-modified CoCu/TiO2 catalyst provided the maximum C5+ yield of 5.4%, with a CO2 conversion of 18.4% and C5+ selectivity of 42.1%, because it showed the strongest basicity and a slight decrease in the amount of H2 desorption; it also exhibited excellent catalytic stability of more than 200 h.