Surface Of MnO Research Articles

Synergistic effects between Mn and Co species in CO2 hydrogenation over xCo/MnO catalysts

CO2 hydrogenation technology has great potential for mitigating the greenhouse effect and creating a green economy. The development of catalysts plays a key role in the progress of CO2 hydrogenation technology. In this study, the xCo/MnO catalysts for CO2 hydrogenation reaction were prepared by the impregnation method using MnOx as the catalyst support. And the effects of the Co loading on the CO2 hydrogenation performances of the prepared xCo/MnO catalysts were investigated. The active Co0 species on the xCo/MnO catalysts surface are the main active centers for the CO2 hydrogenation reaction, and the medium basic sites on the xCo/MnO catalysts are the main CO2 adsorption sites. The MnOx support possesses a large number of medium basic sites, which can enhance the CO2 molecules adsorption ability of the xCo/MnO catalysts. An effective regulation of the basic and hydrogenation active site numbers on the xCo/MnO catalysts surface can be achieved by changing the Co loading amount, which in turn can affect the CO2 molecules adsorption, activation and hydrogenation abilities of the xCo/MnO catalysts. Moreover, the Mn1-yCoyO solid solution was found to be formed in the prepared xCo/MnO catalysts, which is conducive to the dispersion of metal Co nanoparticles on the MnO surface and the generation of oxygen-deficient sites. The CO2 desorption amount on the 12Co/MnO catalyst reached 1.76 mmol/g, which provided the catalyst with strong CO2 adsorption and activation abilities, enabling it to exhibit great CO2 hydrogenation performance. Under the conditions of atmosphere and 420 °C, the CO2 conversion and CH4 selectivity on the prepared 12Co/MnO catalyst reached 57.5 % and 78.8 %, separately. Furthermore, the CO2 conversion was able to consistently remain at the initial 57.5 %, and the CH4 selectivity was maintained above 70.0 % in the 10 times CO2 hydrogenation cycle tests on the 12Co/MnO catalyst. Our study highlights the potential of using MnOx as catalyst support in the CO2 hydrogenation reaction, and the findings will provide convenient for the future studies.

MOF-derived core–shell MnO@Cu/C as high-efficiency catalyst for reduction of nitroarenes

The design of catalysts for competitive pricing and high-performance reduction reactions has attracted increasing attention. The low resistance to aggregation and sintering as well as the uneven size distribution during reaction and preparation of such catalysts, considerably limit their practical applications. This paper presents the preparation of highly stable copper nanoparticles (Cu-NPs) by coating MnO2 nanorods with Cu metal–organic frameworks (MOF) via simple layer-by-layer assembly. The high-temperature reduction of MnO2/Cu-MOF generates MnO/Cu-C as catalyst. The obtained Cu-NPs in a Cu/C@MnO catalyst, with partially uncovered free active surfaces, are encapsulated by a carbon-matrix. This unique structure, with homogeneously distributed Cu-NPs in the carbon matrix, significantly retards the sintering and oxidation of the Cu-NPs in solution. Excellent activity (100 % conversion in 90 s) and recyclability after six cycles [>98 % (conversion) in 120 s] in water are achieved for the reduction of 4-nitrophenol by sodium borohydride (NaBH4) under mild conditions. This high performance is attributed to the high adsorption ability of the carbon matrix and the high catalytic activity of Cu-NPs on the MnO surface. This study provides novel MOF-derived catalysts for use in various valuable applications.

Stability Mechanism of Low Temperature C2H4-SCR with Activated-Carbon-Supported MnO x -Based Catalyst.

Manganese-based catalysts have shown great potential for use as a hydrocarbon reductant for NOx reduction (HC-SCR) at low temperatures if their catalytic stability could be further maintained. The effect of CeO2 as a promoter and catalyst stability agent for activated carbon supported MnOx was investigated during low temperature deNOx based on a C2H4 reductant. The modern characterization technology could provide a clear understanding of the activity observed during the deNOx tests. When reaction temperatures were greater than 180 °C and with ceria concentrations more than 5%, the overall NO conversion became stable near 70% during long duration testing. In situ DRIFTS shows that C2H4 is adsorbed on the Mn3Ce3/NAC catalysts to generate hydrocarbon activated intermediates, R-COOH, and the reaction mechanism followed the E-R mechanism. The stability and the analytical data pointed to the formation of stable oxygen vacancies within Ce3+/Ce4+ redox couplets that prevented the reduction of MnO2 to crystalline Mn2O3 and promoted the chemisorption of oxygen on the surface of MnOx-CeOx structures. Based on the data, a synergetic mechanism model of the deNOx activity is proposed for the MnOx-CeOx catalysts.

Activated Carbon Preparation from Sugarcane Leaf via a Low Temperature Hydrothermal Process for Aquaponic Treatment.

The effects of hydrothermal treatment, 0–5% KMnO4 content, and 300–400 °C pyrolysis temperature, were studied for activated carbon preparation from sugar cane leaves in comparison with non-hydrothermal treatment. The percent yield of activated carbon prepared by the hydrothermal method (20.33–36.23%) was higher than that prepared by the non-hydrothermal method (16.40–36.50%) and was higher with conditions employing the same content of KMnO4 (22.08–42.14%). The hydrothermal and pyrolysis temperatures have the effect of increasing the carbon content and aromatic nature of the synthesized activated carbons. In addition, KMnO4 utilization increased the O/C ratio and the content of C-O, Mn-OH, O-Mn-O, and Mn-O surface functional groups. KMnO4 also decreases zeta potential values throughout the pH range of 3 to 11 and the surface area and porosity of the pre-hydrothermal activated carbons. The use of the pre-hydrothermal activated carbon prepared with 3% KMnO4 and pyrolyzed at 350 °C as a filter in an aquaponic system could improve the quality of water with pH of 7.2–7.4, DO of 9.6–13.3 mg/L, and the turbidity of 2.35–2.90 NTU. It could also reduce the content of ammonia, nitrite, and phosphate with relative removal rates of 86.84%, 73.17%, and 53.33%, respectively. These results promoted a good growth of catfish and red oak lettuce.

In-situ electrochemical induced artificial solid electrolyte interphase for MnO@C nanocomposite enabling long-lived aqueous zinc-ion batteries

Rechargeable aqueous zinc-ion batteries (AZIBs) have attracted widespread attention as a sustainable energy storage system owing to the safe aqueous electrolyte. Manganese-based materials are potential cathodes for AZIBs, whereas, the dissolution of manganese would result in the significantly decline of capacity and unsatisfied lives. Herein, an in-situ electrochemical induced artificial solid electrolyte interphase (SEI), (Zn(OH)2)3(ZnSO4)(H2O)5 nanoflakes, is discovered to generate and coat on the surface of MnO@C in the initial charging process which could prevent the direct contact between the electrolyte and electrode with the result of inhibiting the excessive dissolution of manganese oxides. Benefiting from the artificial SEI, MnO@C exhibits an extremely excellent cycle performance with 0.003% capacity decay per cycle over 10,000 cycles without Mn2+ additive in electrolyte. Moreover, MnO@C is proved to demonstrate a (de)intercalation reaction mechanism after the electrochemical activation process in initial charging process. The strategy proposed in this study provides a new proposal to develop high stable manganes oxide cathodes for AZIBs.

Enhanced performance of carbon-coated manganese catalysts derived from metal-organic framework for rechargeable zinc-air batteries

The wide structural versatility of the Metal-Organic Framework (MOF) is considered to be potential catalysts. In this work, [Mn (BDC). nDMF]n was synthesized by the reaction of 1,4-benzene dicarboxylic acid (1,4-BDC) with Manganese (II) nitrate using a solvothermal method. The [Mn (BDC). nDMF]n crystals were calcined for 2 h to produce Mn-MOF derived catalysts ([email protected] catalysts). The formation of MnO crystals was investigated by the X-ray diffraction (XRD) and the Raman Spectroscopy analyzed the graphitization. The resulting catalysts, [email protected] are highly porous with a high specific surface area of 291.62 m2/g at 700 °C. After calcination, Ni deposition was performed, to produce [email protected]@MnO on which Ni-atoms are deposited on the surface of MnO. The surface area reduces to 214.09 m2/g at 700 °C and the structure is distorted due to deposition. Numerous characterization techniques, including XRD, SEM, EDS, TGA, and Raman, strongly support the effective incorporation of Mn and Ni into the material frameworks. When applied as a cathode for Zinc-air battery, the [email protected]@MnO electrode delivered a high current density of 0.206 Acm−2 for the OER. The cyclic test for charging-discharging was performed for 152 cycles revealing a potential catalyst, having splendid stability for the OER and ORR.

Synthesis of porous MnO@C nanocomposite via controlled heat-treatment of malonate precursor for the potential remediation of dye-contaminated water

Remediation of the dye-contaminated water has received a broad interest due to the health problems and defects in the ecological system originating from the presence of such toxic materials in water. Herein, MnO@C nanocomposites as efficient adsorbent/photocatalyst materials for the removal of cationic and anionic dyes were synthesized via a simple and new precursor-assisted method. Manganese malonate was prepared and calcined at 350 °C for 1 h under air, argon, and H2 atmospheres. Pristine MnO was obtained under argon and H2. The obtained nanocomposites are highly crystalline and have sphere-like shapes as evidenced by TEM, HRTEM, and SAED. EDX analysis demonstrated the presence of C in the prepared samples. The study of the surface texture via the BJH method and Va-t plots has revealed the presence of both microporous and mesoporous pores. BET surface areas of 22.7 and 50.1 m2/g were found for MnO@C nanocomposites prepared under Ar and H2, respectively. Removal of MB as a cationic dye from water was explored via adsorption of the dye over the surface of MnO@C nanocomposites. The MnO@C sample prepared under H2 exhibited the largest removal efficacy, removal of 97% of the dye occurs in 6 h. Furthermore, the MnO@C nanocomposite was utilized as a photocatalyst for removal of the anionic dye, eosin Y. Complete removal of eosin Y color was achieved after exposure to sunlight for 2 h. The mechanism of the photocatalytic degradation of eosin Y was investigated. The possible degradation products were detected through HPLC-UV analysis. The prepared nanocomposite showed good recyclability and even preserving its structure after 4 cycles.

Thermodynamic and Kinetic Analysis for Transformation of Oxide Inclusions in Solid 304 Stainless Steels

Inclusions in 304 stainless steels are transformed from manganese silicate to manganese chromite (spinel) upon heating in the range of 1000–1350 °C, while this transformation is not observed when heating temperature is 1400 °C. Thermodynamic analysis with software FactSage™ is applied in interpreting the transformation. Manganese chromite spinel, with light color under SEM, is deemed to be formed on the surface of MnO–SiO2 inclusions by the reaction between Cr in steel matrix and MnO–SiO2 in inclusions. Heating experiments with different time at 1235 °C (rolling insulation temperature) are carried out to confirm the kinetics of the transformation reaction. Mass transfer coefficients of inclusions’ composition, SiO2, MnO, and Cr2O3 are ranging from 5 × 10−7 to 9 × 10−7 m s−1, depending on diameters and components of inclusions.

Hybrid-DFT Modeling of Lattice and Surface Vacancies in MnO

We have investigated the properties of defects in MnO bulk and at (100) surfaces, as used in catalytic applications, using hybrid-level density functional theory (i.e., inclusion of exact exchange within the exchange-correlation evaluation) in a hybrid QM/MM embedded-cluster approach. Initially, we calculate the formation energy for bulk Mn and O vacancies, comparing charged-defect compensation with charge carriers at the Fermi Level (ϵf) and through Schottky defect formation. Oxygen vacancies were also investigated at the (100) surface, where the vacancy formation energy is very similar to the bulk. Defect levels associated with the most stable vacancies are calculated using the ΔSCF method: all are positioned mid band gap, with surface environments failing to alter strongly the overall nature of the defect relative to bulk. Chemical activity of the (100) MnO surface was considered through the adsorption of a probe CO2 molecule, which is considered the initial step in the transformation of CO2 into hydro...

Author Correction: Decoupling electron and ion storage and the path from interfacial storage to artificial electrodes

In the version of this Perspective originally published, in the sentence “It is worthy of note that the final LiF-free situation characterized by MnO taking up the holes and the (F– containing) MnO surface taking up the lithium ions is also a subcase of the job-sharing concept23.”, the word ‘holes’ should have been ‘electrons’. This has now been corrected.

Ab initio study of magnetism and interaction of graphene with the polar MnO(111) surface

Simulation of graphene adsorption onto the oxygen-terminated polar manganese monoxide surface (111) was performed as a function of the hydrogen coverage based on the density functional theory. Local atomic reconstructions of the SLG/H:MnO(111) interface, and their thermodynamic, electronic and magnetic properties were methodically analyzed for different adsorption models. The bond lengths and the adsorption energy values were found for different reconstructions of the surface atomic structure in the SLG/H:MnO(111) systems, and the effects of graphene adsorption on the electronic spectrum of the SLG/H:MnO(111) interface were studied for its different reconstructions. The effective charges and the local magnetic moments on the carbon atoms and on the nearest-neighbor atoms were determined for the considered adsorption models. Charge transfer from the carbon atom to the nearest-neighbor atoms was found due to reconstruction of the local atomic and electronic structures, correlating with the interface hydrogenation rate. Hydrogenation of the interface surface provides for the p-n junction, turning graphene into an n-type semiconductor. The latter opens the way for creation of n-type graphene field-effect transistors. This paper predicts magnetism for zero-defect graphene adsorbed on the hydrogenated surface of MnO(111) magnetic insulator, and discusses the nature of such magnetism.

Novel mechanistic view of catalytic ozonation of gaseous toluene by dual-site kinetic modelling

Abstract The catalytic ozonation of VOCs is a promising approach for degradation of indoor VOCs, such as gaseous toluene. However, the mechanism and relevant kinetic steps involved in this reaction remain unclear. In this study, the catalytic ozonation of toluene over MnO 2 /graphene was investigated using the empirical power law model and classic Langmuir-Hinshelwood single-site (denoted as L-H s ) mechanism. The apparent activation energy determined using the power law model was 29.3 ± 2.5 kJ mol −1 . This finding indicated that the catalytic ozonation of toluene over MnO 2 /graphene was a heterogeneous reaction, and the Langmuir-Hinshelwood mechanism was applicable. However, the L-H s mechanism did not fit the experimental data, suggesting that the reaction was non-single-site governed. A novel Langmuir-Hinshelwood dual-site (denoted as L-H d ) mechanism was then proposed to explain the experimental observations of the catalytic ozonation of toluene over MnO 2 /graphene through a steady-state kinetic study. This mechanism was based on the hypothesis that MnO 2 was responsible for ozone decomposition and toluene adsorption on graphene; these two types of adsorption were coupled by an adjacent attack. Furthermore, XPS results confirmed the presence of a strong connection between MnO 2 and graphene sites on the surface of MnO 2 /graphene. This connection allowed the adjacent attack and validated the dual-site mechanism. The L-H d model was consistent with the predicted reaction rate of toluene removal with a correlation coefficient near unity (r 2 = 0.9165). Moreover, the physical criterion was in accordance with both enthalpy and entropy of toluene adsorption constraints. Fulfillment of mathematical and physical criteria indicated the catalytic ozonation of toluene over MnO 2 /graphene can be well described by the L-H d mechanism. This study helps understand the catalytic ozonation of toluene over MnO 2 /graphene in a closely mechanistic view.

Surface activity of antiperovskite manganese nitrides

Abstract

MnO Nanoparticle@Mesoporous Carbon Composites Grown on Conducting Substrates Featuring High-performance Lithium-ion Battery, Supercapacitor and Sensor

We demonstrate a facile, two-step coating/calcination approach to grow a uniform MnO nanoparticle@mesoporous carbon (MnO@C) composite on conducting substrates, by direct coating of the Mn-oleate precursor solution without any conducting/binding reagents, and subsequent thermal calcination. The monodispersed, sub-10 nm MnO nanoparticles offer high theoretical energy storage capacities and catalytic properties, and the mesoporous carbon coating allows for enhanced electrolyte transport and charge transfer towards/from MnO surface. In addition, the direct growth and attachment of the MnO@C nanocomposite in the supporting conductive substrates provide much reduced contact resistances and efficient charge transfer. These excellent features allow the use of MnO@C nanocomposites as lithium-ion battery and supercapacitor electrodes for energy storage, with high reversible capacity at large current densities, as well as excellent cycling and mechanical stabilities. Moreover, this MnO@C nanocomposite has also demonstrated a high sensitivity for H2O2 detection, and also exhibited attractive potential for the tumor cell analysis.

Selective Oxidation of TWIP Steel During Continuous Annealing

AbstractThe selective oxidation of Al‐free and Al‐added TWIP steel after full austenitic annealing at 800°C in a N2 + 10%H2 gas atmosphere with a dew point of −17°C was investigated by means of transmission electron microscopy. A thick MnO layer was formed at the surface of Al‐free TWIP steel after the recrystallization annealing. Small crystalline c‐xMnO · SiO2 (x > 2) particles and amorphous a‐xMnO · SiO2 (x < 0.9) particles were found at the MnO/steel interface. In the subsurface, the Mn depletion resulted in the formation of a narrow ferrite layer. The annealing of the Al‐added TWIP steel also resulted in the formation of a thick MnO surface layer. At the MnO/steel interface, Kirkendall voids were formed between the amorphous a‐xMnO · SiO2 (x < 0.9) oxide and crystalline c‐xMnO · Al2O3 oxide in the case of Al‐added TWIP steel. In the subsurface, a thin layer was depleted of Mn and the original austenite had transformed into ferrite. Internal oxidation of Al to Al2O3 and the formation of crystalline c‐xMnO · Al2O3 (x > 1) compound oxide particles were found to occur at the grain boundaries of the Mn‐depleted ferritic zone. The present contribution highlights the implications of the selective oxidation of TWIP steels for their processing in continuous annealing and continuous hot dip galvanizing lines.

Oxidation of As(III) by MnO 2 in the absence and presence of Fe(II) under acidic conditions

Oxidation of As(III) by natural manganese (hydr)oxides is an important geochemical reaction mediating the transformation of highly concentrated As(III) in the acidic environment such as acid mine drainage (AMD) and industrial As-contaminated wastewater, however, little is known regarding the presence of dissolved Fe(II) on the oxidation process. In this study, oxidation of As(III) in the absence and presence of Fe(II) by MnO 2 under acidic conditions was investigated. Kinetic results showed that the presence of Fe(II) significantly inhibited the removal of As(III) (including oxidation and sorption) by MnO 2 in As(III)–Fe(II) simultaneous oxidation system even at the molar ratio of Fe(II):As(III) = 1/64:1, and the inhibitory effects increased with the increasing ratios of Fe(II):As(III). Such an inhibition could be attributed to the formation of Fe(III) compounds covering the surface of MnO 2 and thus preventing the oxidizing sites available to As(III). On the other hand, the produced Fe(III) compounds adsorbed more As(III) and the oxidized As(V) on the MnO 2 surface with an increasing ratio of Fe(II):As(III) as demonstrated in kinetic and XPS results. TEM and EDX results confirmed the formation of Fe compounds around MnO 2 particles or separated in solution in Fe(II) individual oxidation system, Fe(II) pre-treated and simultaneous oxidation processes, and schwertmannite was detected in Fe(II) individual and Fe pre-treated oxidation processes, while a new kind of mineral, probably amorphous FeOHAs or FeAsO 4 particles were detected in Fe(II)–As(III) simultaneous oxidation process. This suggests that the mechanisms are different in Fe pre-treated and simultaneous oxidation processes. In the Fe pre-treated and MnO 2-mediated oxidation pathway, As(III) diffused through a schwertmannite coating formed around MnO 2 particles to be oxidized. The newly formed As(V) was adsorbed onto the schwertmannite coating until its sorption capacity was exceeded. Arsenic(V) then diffused out of the coating and was released into the bulk solution. The diffusion into the schwertmannite coating and the oxidation of As(III) and sorption of both As(V) and As(III) onto the coating contributed to the removal of total As from the solution phase. In the simultaneous oxidation pathway, the competitive oxidation of Fe(II) and As(III) on MnO 2 occurred first, followed by the formation of FeOHAs or FeAsO 4 around MnO 2 particles, and these poorly crystalline particles of FeOHAs and FeAsO 4 remained suspended in the bulk solution to adsorb As(III) and As(V). The present study reveals that the formation of Fe(III) compounds on mineral surfaces play an important role in the sorption and oxidation of As(III) by MnO 2 under acidic conditions in natural environments, and the mechanisms involved in the oxidation of As(III) depend upon how Fe(II) is introduced into the As(III)–MnO 2 system.

Kirkendall Void Formation During Selective Oxidation

The selective oxidation of high Mn austenitic steel was investigated by transmission electron microscopy. The annealing resulted in a MnO surface layer and a Mn-depleted ferritic layer. At the MnO/steel interface, voids were formed between the a-xMnO.SiO2 and c-MnO.Al2O3 layers. This is the first time that void formation is observed during selective oxidation of steel. The Kirkendall voids grow and develop characteristic void surfaces because of the fast diffusion of MnO on the void surface.

Solvent-free selective oxidation of alcohols by molecular oxygen over gold nanoparticles supported on β-MnO2 nanorods

Abstract The performances of a series of MnO 2 -supported gold nanocatalysts with varying gold loading were studied in the solvent-free selective oxidation of alcohols by molecular oxygen. The gold was deposited onto the β-MnO 2 support, featuring one dimensional rod-like morphology, by means of homogeneous deposition–precipitation. The catalytic activity of the catalyst for the solvent-free aerobic oxidation of benzyl alcohol was found to increase with increasing gold loading, with the highest specific activity in terms of turnover frequencies (TOF) being achieved over the catalyst with 5 wt.% gold loading. Both XRD and TEM results showed that the majority of Au particles of various catalysts have diameters in the range of 2–6 nm. Temperature-programmed reduction (TPR) results indicated that the reducibility of MnO 2 was significantly enhanced with the surface-deposited gold nanoparticles. X-ray photoelectron spectroscopy (XPS) revealed the coexistence of both oxidized and metallic gold species on the surface of MnO 2 , the composition of which depends critically on the gold loading. The superior specific activity of the catalyst with 5% gold loading was attributed to the presence of higher amounts of positive gold species and more surface oxygen vacancy sites resulting from stronger metal–support interactions as compared to other catalysts.

Low-temperature growth of AlN on nearly lattice-matched MnO substrates

We have investigated low-temperature epitaxial growths of AlN on nearly lattice-matched MnO(1 1 1) with pulsed laser deposition (PLD). Coaxial impact collision ion scattering spectroscopy (CAICISS) analysis has revealed that the surface of MnO(1 1 1) just before the growth consists of both the Mn-plane and the O-plane with a coverage ratio of 1:1. We have confirmed that the epitaxial growth temperature for AlN on MnO can be reduced down to 400 °C by the use of PLD. The roughness of the AlN/MnO interface decreased from 1.3 to 2.1 nm by the reduction of the growth temperature, which is probably due to the suppression of the intermixing reactions at the interface. On the contrary, the surface morphology of the AlN films was degraded by the reduction of the growth temperature probably due to the stress buildup caused by the suppression of the interface reactions.

Global occurrence of tellurium-rich ferromanganese crusts and a model for the enrichment of tellurium

Hydrogenetic ferromanganese oxyhydroxide crusts (Fe-Mn crusts) precipitate out of cold ambient ocean water onto hard-rock surfaces (seamounts, plateaus, ridges) at water depths of about 400 to 4000 m throughout the ocean basins. The slow-growing (mm/Ma) Fe-Mn crusts concentrate most elements above their mean concentration in the Earth’s crust. Tellurium is enriched more than any other element (up to about 50,000 times) relative to its Earth’s crustal mean of about 1 ppb, compared with 250 times for the next most enriched element. We analyzed the Te contents for a suite of 105 bulk hydrogenetic crusts and 140 individual crust layers from the global ocean. For comparison, we analyzed 10 hydrothermal stratabound Mn-oxide samples collected from a variety of tectonic environments in the Pacific. In the Fe-Mn crust samples, Te varies from 3 to 205 ppm, with mean contents for Pacific and Atlantic samples of about 50 ppm and a mean of 39 ppm for Indian crust samples. Hydrothermal Mn samples have Te contents that range from 0.06 to 1 ppm. Continental margin Fe-Mn crusts have lower Te contents than open-ocean crusts, which is the result of dilution by detrital phases and differences in growth rates of the hydrogenetic phases. Correlation coefficient matrices show that for hydrothermal deposits, Te has positive correlations with elements characteristic of detrital minerals. In contrast, Te in open-ocean Fe-Mn crusts usually correlates with elements characteristic of the MnO 2, carbonate fluorapatite, and residual biogenic phases. In continental margin crusts, Te also correlates with FeOOH associated elements. In addition, Te is negatively correlated with water depth of occurrence and positively correlated with crust thickness. Q-mode factor analyses support these relationships. However, sequential leaching results show that most of the Te is associated with FeOOH in Fe-Mn crusts and ≤10% is leached with the MnO 2. Thermodynamic calculations indicate that Te occurs predominantly as H 5TeO 6 − in ocean water. The speciation of Te in ocean water and charge balance considerations indicate that Te should be scavenged by FeOOH, which is in agreement with our leaching results. The thermodynamically more stable Te(IV) is less abundant by factors of 2 to 3.5 than Te(VI) in ocean water. This can be explained by preferential (not exclusive) scavenging of Te(IV) by FeOOH at the Fe-Mn crust surface and by Fe-Mn colloids in the water column. We propose a model in which the extreme enrichment of Te in Fe-Mn crusts is likely the result of an oxidation reaction on the surface of FeOOH. A similar oxidation process has been confirmed for Co, Ce, and Tl at the surface of MnO 2 in crusts, but has not been suggested previously to occur in association with FeOOH in Fe-Mn crusts. Mass-balance considerations indicate that ocean floor Fe-Mn deposits are the major sink for Te in the oceans. The concentration and redox chemistry of Te in the global ocean are likely controlled by scavenging on Fe-Mn colloids in the water column and Fe-Mn deposits on the ocean floor, as is also the case for Ce.