Maximum Turnover Frequency Research Articles

Rhodium Encapsulated within Silicalite‐1 Zeolite as Highly Efficient Catalyst for Nitrous Oxide Decomposition: From Single Atoms to Nanoclusters and Nanoparticles

AbstractThe size of metal species plays a pivotal role in governing catalytic performance of supported metal catalysts. In this work, a series of Rh encapsulated within silicalite‐1 catalysts with different sizes were prepared by one‐pot hydrothermal method and employed to catalyze the decomposition of N2O. Detailed structure determinations by HAADF‐STEM, XPS and CO‐DRIFTS demonstrate that subtle modulation of the encapsulated Rh species were achieved easily from single‐atom to nanoclusters and nanoparticles by controlling the loading and reduction conditions of Rh. The turnover frequency (TOF) of N2O decomposition showed a typical volcano‐type dependence on Rh size. Kinetic studies revealed that this structure‐sensitive catalysis was related to the difference in N2O and O2 adsorption/desorption for various Rh species. Furthermore, a Rh@S‐1 catalyst with a proper Rh size (ca. 1.6 nm) was identified as the best‐performing catalyst with a maximum TOF (ca. 95 h−1), showing much superior activity than other reported Rh‐based catalysts.

Efficient Electrochemical CO2/CO Interconversion by an Engineered Carbon Monoxide Dehydrogenase on a Gas-Diffusion Carbon Nanotube-Based Bioelectrode

Carbon monoxide dehydrogenase catalyzes the reversible oxidation of CO to CO2. The monofunctional enzyme from Rhodospirillum rubrum (RrCODH) has been extensively characterized in the past, although its use and investigation by bioelectrochemistry have been limited. Here, we developed a heterologous system yielding a highly stable and active recombinant RrCODH in one-step purification, with CO oxidation activity reaching a maximum of 26 500 U.mg(-1), making RrCODH the most active CODH under ambient conditions described so far. Electron paramagnetic resonance was used to precisely characterize the recombinant RrCODH, demonstrating the integrity of the active site. Selective CO2/CO interconversion with maximum turnover frequencies of 150 s(-1) for CO oxidation (1.5 mA cm(-2) at 250 mV overpotential) and 420 s(-1) for CO2 reduction (4.2 mA cm(-2) at 180 mV overpotential) is catalyzed by the recombinant RrCODH immobilized on MWCNT electrodes modified with 1-pyrenebutyric acid adamantyl amide (MWCNTADA), either in a classic three-electrode cell or in specifically designed CO2/CO-diffusing electrodes. This functional device is stable for hours with a turnover number of at least 800 000. The performances of recombinant RrCODH-modified MWCNTADA are close to the best metal-based and molecular-based catalysts. These results greatly increase the benchmark for bioelectrocatalysis of reversible CO2 conversion.

Homogeneous Electrocatalytic CO2Reduction Using a Porphyrin Complex with Flexible Triazole Units in the Second Coordination Sphere

The electrochemical reduction of carbon dioxide (CO2) to produce value-added chemicals is of great significance in mitigating environmental and energy concerns. In this work, an iron porphyrin catalyst, FePEG8T, with multiple triazole units tethered to a porphyrin ligand via flexible oxymethylene linkers, is reported for efficient electrocatalytic reduction of CO2 to afford carbon monoxide (CO). The electrocatalyst exhibits an excellent catalytic activity with a current density of −17.5 mA/cm2 and CO Faradaic efficiency of 95% at −2.5 V vs Fc/Fc+ in acetonitrile using water as the proton source. The maximum turnover frequency (TOFmax) was calculated to be 5.5 × 104 s–1 using foot-of-the-wave analysis, which is thirty times higher than the result from our previous zinc complex with the same triazole–porphyrin ligand. Control experiments on an iron porphyrin complex without triazole units confirm the contribution of triazole units on high catalytic activity. Long-term electrolysis of 40 h was also performed and demonstrated high catalyst stability. A normal KIE of 6.92 was obtained with H2O/D2O as the proton source at varying concentration ranges (0.5–5 M), suggesting that protonation of the catalyst–substrate intermediate is a rate-limiting step. Furthermore, the Tafel plot was generated for the catalyst FePEG8T for comparison with previously reported iron porphyrin catalysts. This work demonstrates an efficient CO2 reduction catalyst containing an iron metal center and a flexible triazole in the second coordination sphere toward CO formation with high stability, activity, and selectivity.

Rationalizing Photo-Triggered Hydrogen Evolution Using Polypyridine Cobalt Complexes: Substituent Effects on Hexadentate Chelating Ligands.

Four novel polypyridine cobalt(II) complexes were developed based on a hexadentate ligand scaffold bearing either electron-withdrawing (-CF3 ) or electron-donating (-OCH3 ) groups in different positions of the ligand. Experiments and theoretical calculations were combined to perform a systematic investigation of the effect of the ligand modification on the hydrogen evolution reaction. The results indicated that the position, rather than the type of substituent, was the dominating factor in promoting catalysis. The best performances were observed upon introduction of substituents on the pyridine moiety of the hexadentate ligand, which promoted the formation of the Co(II)H intermediate via intramolecular proton transfer reactions with low activation energy. Quantum yields of 11.3 and 10.1 %, maximum turnover frequencies of 86.1 and 76.6 min-1 , and maximum turnover numbers of 5520 and 4043 were obtained, respectively, with a -OCH3 and a -CF3 substituent.

Effects of Appended Poly(ethylene glycol) on Electrochemical CO2 Reduction by an Iron Porphyrin Complex

Electrochemical carbon dioxide (CO2) reduction is a sustainable approach for transforming atmospheric CO2 into chemical feedstocks and fuels. To overcome the kinetic barriers of electrocatalytic CO2 reduction, catalysts with high selectivity, activity, and stability are needed. Here, we report an iron porphyrin complex, FePEGP, with a poly(ethylene glycol) unit in the second coordination sphere, as a highly selective and active electrocatalyst for the electrochemical reduction of CO2 to carbon monoxide (CO). Controlled-potential electrolysis using FePEGP showed a Faradaic efficiency of 98% and a current density of -7.8 mA/cm2 at -2.2 V versus Fc/Fc+ in acetonitrile using water as the proton source. The maximum turnover frequency was calculated to be 1.4 × 105 s-1 using foot-of-the-wave analysis. Distinct from most other catalysts, the kinetic isotope effect (KIE) study revealed that the protonation step of the Fe-CO2 adduct is not involved in the rate-limiting step. This model shows that the PEG unit as the secondary coordination sphere enhances the catalytic kinetics and thus is an effective design for electrocatalytic CO2 reduction.

Monodisperse-porous cerium oxide microspheres carrying iridium oxide nanoparticles as a heterogeneous catalyst for water oxidation

Iridium oxide nanoparticle (IrO2 NP) decorated-monodisperse, porous CeO2 (IrO2@CeO2) microspheres were synthesized as a heterogeneous catalyst for chemical water oxidation with cerium ammonium nitrate (CAN) or sodium periodate (NaIO4) as the sacrificial agent. Before synthesis of the proposed catalyst, considerable oxygen evolution was observed using only plain CeO2 microspheres as the catalyst. Individual catalytic activity of plain CeO2 microspheres was explained by the formation of oxidative oxygen species due to the coexistence of Ce(III) and Ce(IV) ions on the surface as demonstrated by deconvoluted XPS analysis. Hence, CeO2 component of IrO2@CeO2 microspheres acted either support or active center. In other words, another active center, IrO2 NPs, was immobilized on the satisfactorily high surface area of porous CeO2 microspheres acted a support. IrO2@CeO2 microspheres with double catalytic active centers exhibited superior catalytic activity with respect to IrO2 NP decorated-porous SiO2 (IrO2@SiO2) microspheres due to the contribution coming from CeO2 microspheres. The maximum turnover number (TON) and turnover frequency (TOF) were obtained as 483 and 724 h−1 using CAN. By using IrO2@CeO2 microspheres as the catalyst, no significant decrease occurred in the oxygen evolution in the repeated runs with NaIO4 as the oxidant while the oxygen evolution apparently decreased using CAN.

Carbon monoxide powered fuel cell towards H2-onboard purification

Proton exchange membrane fuel cells (PEMFCs) suffer extreme CO poisoning even at PPM level (<10 ppm), owning to the preferential CO adsorption and the consequential blockage of the catalyst surface. Herein, however, we report that CO itself can become an easily convertible fuel in PEMFC using atomically dispersed Rh catalysts (Rh-N-C). With CO to CO2 conversion initiates at 0 V, pure CO powered fuel cell attains unprecedented power density at 236 mW cm−2, with maximum CO turnover frequency (64.65 s−1, 363 K) far exceeding any chemical or electrochemical catalysts reported. Moreover, this feature enables efficient CO selective removal from H2 gas stream through the PEMFC technique, with CO concentration reduced by one order of magnitude through running only one single cell, while simultaneously harvesting electricity. We attribute such catalytic behavior to the weak CO adsorption and the co-activation of H2O due to the interplay between two adjacent Rh sites.

Electrocatalytic and Photocatalytic Hydrogen Evolution by Ni(II) and Cu(II) Schiff Base Complexes

AbstractHomogeneous catalytic hydrogen evolution reaction (HER) by five‐coordinate Schiff base complexes with first‐row transition metals (Ni(II), Cu(II) and Zn(II)) were firstly investigated in organic medium. Both nickel and copper complexes revealed efficient electrocatalytic and photocatalytic HER activities. Cyclic voltammetry experiments and foot of wave analysis (FOWA) were applied to assess the electrocatalytic performance and to probe the catalytic mechanism. The Cu(II) and Ni(II) catalysts achieved maximum electrocatalytic HER turnover frequencies (TOFmax) of 70139.5 and 63827.5 s−1, respectively, in MeCN using acetic acid as a proton source. Photocatalytic HER investigation suggested a superior activity of the Cu(II) complex to the Ni(II) counterpart. In an aqueous three‐component system consisting of organic Eosin Y (EY2−) photosensitizer, trimethylamine (TEA) sacrificial donor, and the Cu(II) catalyst, a photocatalytic HER turnover number (TON) of 21 was obtained after 4 h irradiation under white LED light. Employing triethanolamine (TEOA) instead of TEA as a sacrificial donor substantially enhanced stability of the photocatalytic HER system, of which deactivation was not observed after 6 h photocatalysis. The photocatalytic HER reaction was monitored by time‐resolved UV‐vis spectra which suggested faster decomposition of EY2− in the presence of TEA than TEOA.

Amino-group and space-confinement assisted synthesis of small and well-defined Rh nanoparticles as efficient catalysts toward ammonia borane hydrolysis

Hydrogen evolution from ammonia borane (AB) hydrolysis is of great importance considering the ever-increasing demand for green and sustainable energy. However, the development of a facile and efficient strategy to construct high-performance catalysts remains a grand challenge. Herein, we report an amino-group and space-confinement assisted strategy to fabricate Rh nanoparticles (NPs) using amino-functionalized metal-organic-frameworks (UiO-66-NH2) as a NP matrix (Rh/UiO-66-NH2). Owing to the coordination effect of amino-group and space-confinement of UiO-66-NH2, small and well-distributed Rh NPs with a diameter of 3.38 nm are successfully achieved, which can be served as efficient catalysts for AB hydrolysis at room temperature. The maximum turnover frequency of 876.7 min−1 is obtained by using the Rh/UiO-66-NH2 with an optimal Rh loading of 4.38 wt% and AB concentration of 0.2 M at 25 °C, outperforming most of the previously developed Rh-based catalysts. The catalyst is also stable in repetitive cycles for five times. The high performance of this catalyst must be ascribed to the structural properties of UiO-66-NH2, which enable the formation of small and well-dispersed Rh NPs with abundant accessible active sites. This study provides a simple and efficient method to significantly enhance the catalytic performance of Rh for AB hydrolysis.

Atropisomeric Effects of Second Coordination Spheres on Electrocatalytic CO2 Reduction

AbstractControl of the second coordination spheres of molecular catalytic systems has enhanced the catalytic efficiencies and facilitated the elucidation of catalytic mechanisms. Herein, we present the evaluation of stereoisomeric effects of a set of metal redox‐innocent zinc porphyrin complexes on CO2 reduction, including complexes containing four (ZnP4T) and one (ZnP1T) triazole units, and two atropisomers with two triazole units positioned at the same (ZnP2T‐αα) and different (ZnP2T‐αβ) sides of the zinc porphyrin framework. Kinetic study and foot‐of‐the‐wave analysis indicated that complexes with more than one triazole unit on the same side of the porphyrin framework (ZnP4T and ZnP2T‐αα) display at least double maximum turnover frequency than the counterparts with a single triazole unit on the same side (ZnP1T and ZnP2T‐αβ). These results suggest the formation of a hydrogen‐bonding network in the second coordination sphere that facilitates proton transfer from the hydrophilic network to the catalyst‐CO2 intermediate.

Vapor-phase low-temperature methanol synthesis from CO2-containing syngas via self-catalysis of methanol and Cu/ZnO catalysts prepared by solid-state method

Binary Cu/ZnO catalysts were prepared by solid-state method and tested for vapor-phase low-temperature methanol synthesis from CO2-containing syngas. The influence of H2C2O4/(Cu + Zn) molar ratio on the physicochemical properties and the corresponding catalytic activity was systematically studied. The space time yield (STY) of methanol exhibited a linear relationship with the Cu0 surface area, and increased linearly by enhancing the number of strongly acidic sites or moderately basic sites. The effects of various parameters on the methanol synthesis reaction were also investigated. C4-Red catalyst (H2C2O4/(Cu + Zn) = 4/1) exhibited the maximum turnover frequency (TOF, 11.4 × 10−3 s−1) and STY values (456.3 g/kg h−1), due to the larger Cu0 surface area, greater specific surface area, more strongly acidic sites and moderately basic sites. The strengthened Cu-ZnO interaction, superior CO and H2 adsorption capability as well as higher adsorbed CO and H2 amount also contributed to increasing the catalytic performance of C4-Red catalyst.

Synergistic catalysis of Pd–Ni(OH)2 hybrid anchored on porous carbon for hydrogen evolution from the dehydrogenation of formic acid

The development of a facile yet efficient strategy to boost the catalytic performance of supported Pd nanoparticles (NPs) toward the dehydrogenation of formic acid (FA) is essential but remains challenging. Here, a novel hybrid nanocatalyst comprising Pd and Ni(OH)2 supported on porous carbon (PC) is developed. The obtained Pd–Ni(OH)2/PC nanocatalyst exhibits an excellent catalytic performance for FA dehydrogenation to produce hydrogen. The introduction of Ni(OH)2 in PC support can significantly promote the catalytic activity of Pd NPs toward FA dehydrogenation. Additionally, the catalytic property of Pd–Ni(OH)2/PC is correlated with the Pd/Ni ratio. The 2Pd–1Ni(OH)2/PC with the optimum Pd/Ni ratio of 2/1 exhibits the maximum turnover frequency (TOF) of 3409 h−1 at 60 °C for FA dehydrogenation. The highly dispersed ultrafine Pd–Ni(OH)2 hybrid NPs with numerous accessible active sites and Ni(OH)2−induced positive synergetic effects with Pd NPs considerably boost the catalytic performance for FA dehydrogenation.

Asymmetric transfer hydrogenation of acetophenone using bis-imine rhodium complexes: Kinetic study and modeling

Asymmetric transfer hydrogenation of acetophenone (APh) to (R)-1-phenylethanol (PhE) was studied in 2-propanol solution in the presence of Rh(1,5-COD)(μ-Cl)]2+L, where COD = cyclooctadiene and L is a bis-aldimine ligand based on (R,R)-1,2-cyclohexanediamine and pyridinecarboxaldehyde. This rhodium (I) complex bearing optically active ligands achieved a maximum turnover frequency (TOF) of 268 h−1 at 78 °C and a moderate maximum enantioselectivity (ee) of 55 % for (R)-1-PhE. A formal kinetic study of the process was carried out using the Rh(1,5-COD)(N,N'-(R,R)-1,2-cyclohexane-1,2-diyl-bis-(1-(pyridine-2-yl)-methanimine)-Cl complex. The induction period for catalyst activation is proposed to involve the rapid reaction of the pre-catalyst with excess iso-propoxide to give the catalytically active Rh(1,5-COD)(N,N'-(R,R)-1,2-cyclohexane-1,2-diyl-bis-(1-(pyridine-2-yl)-methanimine)-OiPr, which leads to the transfer hydrogenation of 1,5-COD. Reaction profiles were obtained by varying the initial concentrations of APh, pre-catalyst, base, acetone, and the temperature. These data were fitted to a kinetic model for the proposed mechanism, and numerical simulation led to a set of rate constants and thermodynamic parameters.

Second Coordination Sphere Effects in an Evolved Ru Complex Based on Highly Adaptable Ligand Results in Rapid Water Oxidation Catalysis.

A new Ru complex containing the deprotonated 2,2':6',2''-terpyridine-6,6''-diphosphonic acid (H4tPa) and pyridine (py) of general formula [RuII(H3tPa-κ-N3O)(py)2]+, 2+, has been prepared and thoroughly characterized by means of spectroscopic and electrochemical techniques, X-ray diffraction analysis, and density functional theory (DFT) calculations. Complex 2+ presents a dynamic behavior in the solution that involves the synchronous coordination and the decoordination of the dangling phosphonic groups of the tPa4- ligand. However, at oxidation state IV, complex 2+ becomes seven coordinated with the two phosphonic groups now bonded to the metal center. Further, at this oxidation state at neutral and basic pH, the Ru complex undergoes the coordination of an exogenous OH- group from the solvent that leads to an intramolecular aromatic O atom insertion into the CH bond of one of the pyridyl groups, forming the corresponding phenoxo-phosphonate Ru complex [RuIII(tPaO-κ-N2OPOC)(py)2]2-, 42-, where tPaO5- is the 3-(hydroxo-[2,2':6',2''-terpyridine]-6,6''-diyl)bis(phosphonate) ligand. This new in situ generated Ru complex, 42-, has been isolated and spectroscopically and electrochemically characterized. In addition, a crystal structure has been also obtained using single-crystal X-ray diffraction techniques. Complex 42- turns out to be an exceptional water oxidation catalyst achieving record maximum turnover frequencies (TOFmax) on the order of 16 000 s-1. A mechanistic analysis complemented with DFT calculations has also been carried out, showing the critical role of intramolecular second coordination sphere effects exerted by the phosphonate groups in lowering the activation energy at the rate-determining step.

Ligand-Controlled Product Selectivity in Electrochemical Carbon Dioxide Reduction Using Manganese Bipyridine Catalysts.

Electrocatalysis is a promising tool for utilizing carbon dioxide as a feedstock in the chemical industry. However, controlling the selectivity for different CO2 reduction products remains a major challenge. We report a series of manganese carbonyl complexes with elaborated bipyridine or phenanthroline ligands that can reduce CO2 to either formic acid, if the ligand structure contains strategically positioned tertiary amines, or CO, if the amine groups are absent in the ligand or are placed far from the metal center. The amine-modified complexes are benchmarked to be among the most active catalysts for reducing CO2 to formic acid, with a maximum turnover frequency of up to 5500 s-1 at an overpotential of 630 mV. The conversion even works at overpotentials as low as 300 mV, although through an alternative mechanism. Mechanistically, the formation of a Mn-hydride species aided by in situ protonated amine groups was determined to be a key intermediate by cyclic voltammetry, 1H NMR, DFT calculations, and infrared spectroelectrochemistry.

Oxygen Functionalized Copper Nanoparticles for Solar-Driven Conversion of Carbon Dioxide to Methane.

Solar conversion of carbon dioxide (CO2) into hydrocarbon fuels offers a promising approach to fulfill the world's ever-increasing energy demands in a sustainable way. However, a highly active catalyst that can also tune the selectivity toward desired products must be developed for an effective process. Here, we present oxygen functionalized copper (OFn-Cu) nanoparticles as a highly active and methane (CH4) selective catalyst for the electrocatalytic CO2 reduction reaction. Our electrochemical results indicate that OFn-Cu (5 nm) nanoparticles with an oxidized layer at the surface reach a maximum CH4 formation current density and turnover frequency of 36.24 mA/cm2 and of 0.17 s-1 at the potential of -1.05 V vs RHE, respectively, exceeding the performance of existing Cu and Cu-based catalysts. Characterization results indicate that the surface of the OFn-Cu nanoparticles consists of an oxygen functionalized layer in the form of Cu2+ (CuO) separated from the underneath elemental Cu by a Cu+ (Cu2O) sublayer. Density functional theory calculations also confirm that presence of the O site at the CuO (101) surface is the main reason for the enhanced activity and selectivity. Using this catalyst, we have demonstrated a flow cell with an active area of 25 cm2 that utilizes solar energy to produce 7.24 L of CH4 after 10 h of continuous process at a cell power density of 30 mW/cm2.

Molybdenum-Doped Manganese Oxide as a Highly Efficient and Economical Water Oxidation Catalyst

The development of efficient and noble-metal-free electrocatalysts for the challenging oxygen evolution reaction (OER) is crucial for sustainable energy solutions. In this work, a facile co-precipitation method, followed by thermal postsynthetic treatment in N2/air, was developed to synthesize molybdenum-doped α-Mn2O3 materials (Mn2O3:1.72%Mo, Mn2O3:2.64%Mo, Mn2O3:32.23%Mo, and Mn2O3:49.67%Mo) as low-cost water-oxidizing electrocatalysts. Powder X-ray diffraction (PXRD), extended X-ray absorption fine structure (EXAFS), X-ray photoelectron spectroscopy (XPS), and high-resolution transmission electron microscopy (HRTEM) investigations showed the presence of strong distortions in the molybdenum-doped α-Mn2O3 host lattice (Mn2O3:2.64%Mo) and an average oxidation state of Mn2.8+. Several test assays demonstrated that these structural features significantly promote the OER activity. Mn2O3:2.64%Mo was found to exhibit very good activity among the series in cerium ammonium nitrate (CAN)-assisted water oxidation with a maximum turnover frequency (TOF) of 585 μmol O2 m–2 h–1, which is a 15-fold improvement of the pure α-Mn2O3 activity and higher than the value of the previously reported benchmark Mn-based catalyst, birnessite. The optimized catalyst (Mn2O3:2.64%Mo) excelled through a low onset potential (300 mV) and a promising overpotential of 570 mV for OER at a current density of 10 mA cm–2, which is only 20 mV above that of the noble metal benchmark RuO2 electrode and competitive with that of the most active Mn-based OER catalysts reported to date. Electrochemical impedance spectroscopy (EIS) studies demonstrated that the catalytically active surface area of Mn2O3:2.64%Mo is much higher than that of α-Mn2O3 for the OER at the applied potential. In addition, stability during 30 h without degradation was achieved, which exceeds that of a wide range of current noble-metal-free electrocatalysts. Our study provides a facile and effective approach for the preparation of economical and high-performance manganese-based electrocatalysts for water oxidation.

Ligand-based electronic effects on the electrocatalytic hydrogen production by thiosemicarbazone nickel complexes.

This work reports on the synthesis and characterization of a series of mononuclear thiosemicarbazone nickel complexes that display significant catalytic activity for hydrogen production in DMF using trifluoroacetic acid as the proton source. The ligand framework was chemically modified by varying the electron-donating abilities of the para substituents on the phenyl rings, which was expected to impact the capability of the resulting complexes to reduce protons into hydrogen. Over the four nickel complexes that were obtained, the one with the thiomethyl substituent, NiSCH3, was found to overtake the catalytic performances of the parent complex NiOCH3 featuring lower overpotential values and similar maximum turnover frequencies. These results confirm the electronic effects of the ligand on HER when using thiosemicarbazone nickel complexes and support that chemical modifications can tune the catalytic performances of such systems.

Toward glucuronic acid through oxidation of methyl-glucoside using PdAu catalysts

The production of glucuronic acid via enzyme catalysis from biomass is slow. Here we studied the oxidation of methoxy-protected glucose (MG) using Pd-on-Au nanoparticle model catalysts to generate methoxy-protected glucuronic acid (MGA), a precursor to glucuronic acid. Pd-on-Au showed volcano-shape activity dependence on calculated Pd surface coverage (sc). The 80 sc% Pd-on-Au catalyst composition showed maximum initial turnover frequency (413 mol-MG mol-surface-atom−1 h−1) that was 5× higher than that of Au/C, while Pd/C was inactive. This Pd-on-Au composition gave the highest MGA yield (46%), supporting a bimetallic approach to glucuronic acid production.

Mesoporous Co3O4 catalysts for VOC elimination: Oxidation of 2-propanol

Mesoporous cobalt oxides were prepared by an inverse micelle method and calcined at different temperatures. These materials exhibited superior activity for oxidation of 2-propanol as the model substrate for VOC elimination. Highest active Co3O4-350 material showed a maximum turnover frequency of 25.8 h−1 at 160 °C at a weight hourly space velocity of 60 L g-1 h−1. The apparent activation energies of mesoporous cobalt oxides ranged from 69.7 kJ/mol to 115.6 kJ/mol. In situ Diffuse Reflectance Infrared spectroscopy (DRIFTS) revealed that the reaction involves formation of carbonyl and carbonate species on the surface of the catalyst before complete oxidation to CO2 and H2O. The activities of the materials were correlated to better low temperature reducibility, large pore volumes, higher Co3+/ Co2+ ratios, and higher number of surface-active oxygen species.