CO Reactant Research Articles

Nickel supported on YSZ: The effect of Ni particle size on the catalytic activity for CO2 methanation

The catalytic conversion of carbon dioxide to synthetic CH4 was studied on five Ni/YSZ samples, with the same nickel loading (10 wt%) but different Ni particle size. The catalysts, prepared by different methods, were characterized combining morphological (BET, TEM), structural (XRD, in-operando XAS), electronic (XPS, in-operando XANES) analysis and H2-TPR experiments. The results showed that catalytic activity and CH4 selectivity depended on size and morphology of Ni particles, and that type and amount of deposited carbon strongly depended on Ni0 morphology. The kinetic measurements revealed that both H2 and CO2 reactants were activated on Ni sites, and that YSZ support was not directly involved in the reaction mechanism.The most efficient catalyst was that prepared by wet impregnation with Ni(EDTA)2− complex due to the high Ni0 dispersion.This catalyst showed low amount of carbon and remarkable stability over time on stream. In-operando XAS showed that it did not undergo deactivation by Ni0 → Ni2+ oxidation using high CO2 concentration, thus it is applicable in dynamic conditions like those typical in the energy storage from renewable sources process.

Activation of CO2 by Gadolinium Cation (Gd+): Energetics and Mechanism from Experiment and Theory

The exothermic and barrierless activation of CO2 by the lanthanide gadolinium cation (Gd+) to form GdO+ and CO is investigated in detail using guided ion beam tandem mass spectrometry (GIBMS) and theory. Kinetic energy dependent product ion cross sections from collision-induced dissociation (CID) experiments of GdCO2 + are measured to determine the energetics of OGd+(CO) and Gd+(OCO) intermediates. Modeling these cross sections yields bond dissociation energies (BDEs) for OGd+–CO and Gd+–OCO of 0.57 ± 0.05 and 0.38 ± 0.05 eV, respectively. The OGd+–CO BDE is similar to that previously measured for Gd+–CO, which can be attributed to the comparable electrostatic interaction with CO in both complexes. The Gd+(OCO) adduct is identified from calculations to correspond to an electronically excited state. The thermochemistry here and the recently measured GdO+ BDE allows for the potential energy surface (PES) of the Gd+ reaction with CO2 to be deduced from experiment in some detail. Theoretical calculations are performed for comparison with the experimental thermochemistry and for insight into the electronic states of the GdCO2 + intermediates, transition states, and the reaction mechanism. Although the reaction between ground state Gd+ (10D) and CO2 (1Σg +) reactants to form ground state GdO+ (8Σ−) and CO (1Σ+) products is formally spin-forbidden, calculations indicate that there are octet and dectet surfaces having a small energy gap in the entrance channel, such that they can readily mix. Thereby, the reaction can efficiently proceed along the lowest energy octet surface to yield ground state products, consistent with the experimental observations of an efficient, barrierless process. At high collision energies, the measured GdO+ cross section from the Gd+ reaction with CO2 exhibits a distinct feature, attributed to formation of electronically excited GdO+ products along a single dectet PES in a diabatic and spin-allowed process. Modeling this high-energy feature gives an excitation energy of 3.25 ± 0.16 eV relative to the GdO+ (8Σ−) ground state, in good agreement with calculated excitation energies for GdO+ (10Π, 10Σ−) electronic states. The reactivity of Gd+ with CO2 is compared with the group 3 transition metal cations and other lanthanide cations and periodic trends are discussed.

Carbon Nanotubes from the Sky to Mitigate Climate Change: Incentivized Greenhouse Gas Removal By Its Transformation to Valuable Commodities

As the levels of carbon dioxide increase in the Earth’s atmosphere, this greenhouse gas’s effects on climate change including species extinction, flooding, draught, famine and economic disruption become increasingly apparent. An incentive to remove CO2 is provided by a low energy, low cost, high yield conversion to valuable products such as carbon nanotubes. Displaying superior strength, conductivity, flexibility and durability, carbon nanotube (CNT) applications had been limited due to the cost intensive complexities of their synthesis. An inexpensive source of CNTs made from carbon dioxide will facilitate the rate of its adoption as an important societal resource for the building, aerospace, transportation, renewable energy, sporting and consumer electronics industries, while concurrently consuming carbon dioxide. We present an inexpensive, high-yield and scale-able synthesis of CNTs. We show a new, unexpected chemistry for the effective capture of CO2 and its transformation at high yield and low energy, by dissolution in a molten carbonate electrolyte, and electrolysis splitting it to carbon nanotubes and oxygen.1-9 The CO2 reactant is directly absorbed from air (without the need for pre-concentration), or can be used and removed from industrial, home or transportation emissions. It is demonstrated that common metals act as CNT nucleation sites in molten media to efficiently drive the high yield electrolytic conversion of CO2 dissolved in molten carbonates to CNTs. We accomplish this by electrochemically reducing CO2 on steel electrodes in a molten carbonate electrolyte. The CNT structure is tuned by controlling the electrolysis conditions, such as the addition of trace common metals to act as CNF nucleation sites, the composition of the carbonate electrolyte, and the control of temperature and current density. Upward scalability of the process is demonstrated over several orders of magnitude. 1Ren, Li, Lau, Gonzalez-Urbina, Licht, One-pot synthesis of carbon nanofibers from CO2, Nano Letters , 15, 6142 (2015). 2Ren, Lau, Lefler, S. Licht, The minimum electrolytic energy needed to convert carbon dioxide by electrolysis in carbonate melts, J. Phys. Chem., C, 119, 23342 (2015). 3Licht, Douglas, Ren, Carter, Lefler, Pint, Carbon Nanotubes Produced from Ambient Carbon Dioxide for Environmentally Sustainable Lithium-Ion & Sodium-Ion Battery Anodes, ACS Central Science, 2, 162 (2015). 4Ren, Lau, Lefler, Licht, The minimum electrolytic energy needed to convert carbon dioxide by electrolysis in carbonate melts, J. Phys. Chem., C, 119, 23342 (2015). 5Lau, Dey, Licht, Thermodynamic assessment of CO2to carbon nanofiber transformation for carbon sequestration in a combined cycle gas or a coal power plant, Energy Conservation and Management, 122, 400 (2016). 6Wu, Li, Ji, Liu, Li, Yuan, Zhang, Ren, Lefler, Wang, Licht, One-Pot Synthesis of Nanostructured Carbon Material from Carbon Dioxide via Electrolysis in Molten Carbonate Salts, Carbon, 6, 27760 (2016). 7Ren, Licht, Tracking airborne CO2mitigation and low cost transformation into valuable carbon nanotubes, Scientific Reports , 106, 208 (2016). 8Ren, Wang, Johnson, Singhal, Licht, Transformation of the greenhouse gas CO2 by molten electrolysis into a wide controlled selection of carbon nanotubes, J. CO 2 Utilization ,18, 335 (2017). 9Licht, Co-Production of Cement and Carbon Nanotubes with a Carbon Negative Footprint, J. CO 2 Utilization ,18, 378 (2017). Figure: Molten carbonate electrolysis pathways transforming CO2 into a carbon nanotubes. Figure 1

CeCu composite catalyst for CO synthesis by reverse water–gas shift reaction: Effect of Ce/Cu mole ratio

In this study, CeCu composite catalysts with different Ce/Cu mole ratios were prepared by a hard-template, and their performances in the reverse water–gas shift (RWGS) reaction were investigated. The catalysts were characterized using H2-TPR, XRD, in-situ XPS, AAS, CO2-TPD, and H2-TPD. The characterizations showed that the oxygen vacancies and active Cu0 species as active sites were formed in the CeCu catalysts by the H2 reduction at 400°C. The synergistic effect of the surface oxygen vacancies and active Cu0 species enhanced catalytic activity of the studied CeCu composite catalysts. The electronic effect between Cu and Ce species boosted the adsorption and activation performances of the reactant CO2 and H2 molecules on the corresponding CeCu catalysts. The Ce1.1Cu1 catalyst demonstrated high stability and the highest CO2 conversion rate in the RWGS reaction, reaching 1.38mmolgcat−1min−1 at 400°C. Its excellent catalytic performance in the RWGS reaction was related to the complete synergistic interaction between the active species via Ce3+-□-Cu0 (□: oxygen vacancy). A CeCu composite material is a superior catalyst for the RWGS reaction because of its high CO2 conversion, 100% CO selectivity, and high stability.

Electrochemical CO2 Conversion Using Skeleton (Sponge) Type of Cu Catalysts

Highly porous 3D Cu skeletons (sponges) modified by electropolishing, thermal annealing, and foam electrodeposition have been studied as catalysts for the electrochemical conversion of CO2 with a particular emphasis on C2 products formation. These catalyst materials appear to be promising for future applications where gaseous CO2 reactants can be transported through the 3D catalyst thereby tuning the mean residence time of reaction intermediates inside the catalyst, which crucially influences the final product distribution. In particular, the annealed skeleton (300 °C, 12 h) and the one modified by Cu foam electrodeposition show profound activities toward C2 product formation (C2H4, C2H6) with faradaic efficiencies reaching FEC2 = 32.3% (annealed skeleton sample, −1.1 V vs RHE) and FEC2 = 29.1% (electrodeposited sample, −1.1 V vs RHE), whereas the electropolished Cu skeleton remains largely inactive for both the C1 and the C2 pathway of hydrocarbon formation. This effect is discussed on the basis of resid...

Photocatalytic reduction of CO2 to CO by diamond nanoparticles

Recent studies have shown that optically excited diamond can act as a solid-state source of solvated electrons in aqueous media, leading to novel reduction reactions such as the one-electron activation pathway (CO2+e−→−CO2−, E°=−1.9V vs SHE) for reduction of CO2 to CO. However, an understanding of the valence band reactions is also essential, especially since CO can also be produced in the absence of CO2 by oxidation of diamond via C+H2O→CO+2H++2e− (E°=0.52V). Here, we demonstrate that H-terminated diamond nanoparticles with a median diameter of 125nm can initiate selective photochemical reduction of CO2 to CO, and that argon-purged control samples show no production of CO production in the absence of intentional CO2 reactant as long as a sacrificial electron donor (here, Na2SO3) is present. However, in the absence of an electron donor clear signs of diamond oxidation and aggregation are observed. In contrast, experiments with detonation nanodiamond show rapid changes upon illumination consistent with oxidation of the samples. Our results indicate that crystallinity and absence of high-energy defect sites is important to stability of nanodiamond-based photocatalysts.

The role of emerging grain boundary at iron surface, temperature and hydrogen on metal dusting initiation

We conduct a multiscale modeling of different iron systems exposed to carbon-rich atmospheres by means of density functional theory and reactive molecular dynamics in order to evaluate the effects of temperature, gas content and surface defects such as emerging grain boundaries and grooves on CO dissociation rate. Comparative density functional theory calculations of carbon adsorption energies on clean surface and the groove area show that grooves have preferential binding sites, explaining why emerging grain boundaries are more severely attacked by metal dusting corrosion. Molecular dynamical simulations using a ReaxFF potential on iron Σ3 and Σ5 emerging grain boundaries on (111) and (210) surfaces, respectively, also demonstrate the enhanced CO dissociation rate within the grooves area. Analysis of CO dissociation and recombination events on these systems demonstrates quantitatively the dual role of hydrogen as a CO dissociation enhancer and reactant with dissociated carbon atoms. By carefully characterizing reaction mechanisms as a function of reactant content, we provide a linear correspondence between CO dissociation variation as function of temperature and the experimental measurement of metal dusting corrosion rate.

Effect of Pt:Pd ratio on CO and hydrocarbon oxidation

For several reasons, typical diesel oxidation catalysts (DOCs) contain a mixture of Pt and Pd and in this study, the effect of the Pt:Pd ratio on a DOC’s ability to oxidize CO and different hydrocarbon types was investigated. The concentrations and types of pollutant species were used to simulate those found in low temperature combustion (LTC) engine exhaust. Representative hydrocarbon species were selected; C2H4 (short-chain alkene), C2H6 (short-chain alkane), C6H14 (long-chain alkane) and C7H8 (aromatic). Two types of experiments were performed, one in which the oxidation of each hydrocarbon or CO reactant was examined individually (simple feed conditions), and the second in which all reactants were added together (full feed conditions). Under the simple feed conditions, CO and C2H6 oxidation increased with increasing Pd content, while C2H4 and C6H14 oxidation improved with higher Pt content. When the full mixture of CO and hydrocarbons was used, hydrocarbon oxidation light off consistently followed that of CO, regardless of the Pt:Pd ratio, due to strong inhibition by CO. The best CO oxidation activity was observed over the Pd-only catalyst, and performance over the bimetallic samples was a function of both CO inhibition and Pt:Pd ratio. More specifically, as Pd content increased, CO inhibition was dampened, and as Pt content increased its inherent activity toward alkene oxidation became significant. Since inhibition is a function of the Pt/Pd content and the individual metals have different inherent activities toward the oxidation of different hydrocarbons, results obtained from the experiments with the simple feed could not be directly correlated to those from the experiments with the mixture of hydrocarbons.

Electrochemical Carbon Dioxide Reduction on Cu-Zn Bimetallic Catalysts with Enhanced Ethanol Selectivity

The electrochemical carbon dioxide (CO2) reduction to ethylene (C2H4) and ethanol (C2H5OH) using renewable energy is a viable method for the production of these commercially vital chemicals. Copper (Cu) based materials are by far the most promising electrocatalysts for this purpose. However, the formation of ethanol using Cu and its oxides is generally less favored as compared to that of ethylene. Here, we demonstrate that the selectivity of CO2 reduction towards ethanol could be systematically tuned by introducing a co-catalyst to generate an in situ source of mobile CO reactant. Cu-based oxides with different amount of Zn dopants (Cu, Cu10Zn, Cu4Zn and Cu2Zn) were prepared via electrodeposition and used as catalysts under ambient pressure in aqueous 0.1 M KHCO3 electrolyte. By varying the concentration of Zn in the bimetallic catalysts, we found that the selectivity of ethanol versus ethylene formation, defined by the ratio of their faradaic efficiencies (FEethanol/FEethylene), could be tuned by a factor of up to ~12.5. Ethanol selectivity was maximized on Cu4Zn at -1.05 V vs. RHE, with a remarkable faradaic efficiency and current density of 29.1% and -8.2 mA/cm2 respectively. The Cu4Zn catalyst was also catalytically stable towards ethanol formation for at least 5 hrs. Operando Raman spectroscopy revealed that the as-deposited oxides were reduced to the metallic Cu/Zn during CO2 reduction, after which only signals belonging to CO adsorbed on Cu sites were recorded. This indicated that the reduction of CO2 might preferably occur on metallic sites rather than on metal oxides. The importance of Zn as a CO producing site was also demonstrated by performing CO2 reduction on Cu-Ni and Cu-Ag bimetallic catalysts. Thus, the mechanism of ethanol formation was proposed as following: Incoming CO2 molecules could first bind to either Cu or Zn sites, and be reduced to CO. On the Cu sites, CO could be reduced further to CHO or CHx (x=1,2,3) intermediates, while CO adsorbs weakly on Zn sites and is likely to desorb. The desorbed CO could diffuse and spill over onto the Cu sites. The spilled-over CO may then insert itself into the bond between the Cu surface and *CH2, to form *COCH2. Further reduction of *COCH2 will produce acetaldehyde and finally ethanol. 1) Ren, D.; Ang, B. S. H.; Yeo, B. S. ACS Catal. 2016, 8239-8247. 2) Ren, D.; Deng, Y.; Handoko, A. D.; Chen, C. S.; Malkhandi, S.; Yeo, B. S. ACS Catal. 2015, 5, 2814-2821. 3) Hori, Y.; Murata, A.; Takahashi, R. J. Chem. Soc., Faraday Trans. 1 1989, 85, 2309-2326. 4) Calle-Vallejo, F.; Koper, M. T. M. Angew. Chem. Int. Ed. 2013, 52, 7282-7285.

Na–CO batteries: devices to trap CO

Metal-gas batteries that remove CO gases would provide enormous environmental benefits. We report here Na-CO batteries using the combination of a sodium anode and a binder-free multiwall carbon nanotube cathode with a CO reactant. The constructed Na-CO batteries show a high discharge capacity of 8000 mA h g-1 based on the mass of carbon nanotubes (corresponding to ∼865.9 W h kg-1 based on the mass of total active materials) and a stable cycling of 70 cycles with an increased gap of only 3.7 mV. This work offers a promising strategy for efficient utilization of CO to generate electricity through an electrochemical conversion method.

Tuning the Selectivity of Carbon Dioxide Electroreduction toward Ethanol on Oxide-Derived CuxZn Catalysts

The electrochemical reduction of carbon dioxide (CO2) to ethanol (C2H5OH) and ethylene (C2H4) using renewable electricity is a viable method for the production of these commercially vital chemicals. Copper (Cu) and its oxides are by far the most effective electrocatalysts for this purpose. However, the formation of ethanol using these catalysts is generally less favored in comparison to that of ethylene. In this work, we demonstrate that the selectivity of CO2 reduction toward ethanol could be tuned by introducing a cocatalyst to generate an in situ source of mobile CO reactant. Cu-based oxides with different amounts of Zn dopants (Cu, Cu10Zn, Cu4Zn, and Cu2Zn) were prepared and used as catalysts under ambient pressure in aqueous 0.1 M KHCO3 electrolyte. By varying the amount of Zn in the bimetallic catalysts, we found that the selectivity of ethanol versus ethylene production, defined by the ratio of their Faradaic efficiencies (FEethanol/FEethylene), could be tuned by a factor of up to ∼12.5. Ethanol fo...

Effect of magnetic field on CO2 conversion over Cu-ZnO/ZrO2 catalyst in hydrogenation reaction

Based on green and sustainable innovation with efficient utilization concepts for enhancement of catalyst performance and energy conservation, an external magnetic field has been applied in CO2 hydrogenation reaction in order to improve catalytic activity and reduce the energy consumption. In this research, the performances of Cu-ZnO/ZrO2 catalyst under magnetic field with different magnetic field intensities (0, 20.8, and 27.7mT) and orientations (north-to-south (N-S) and south-to-north (S-N) directions) in CO2 hydrogenation were investigated. Cu-ZnO/ZrO2 catalysts operated under magnetic field gave higher CO2 conversions, compared to that of without magnetic field at all reaction temperatures. The highest CO2 conversions were obtained under the magnetic field condition at 20.8mT in S-N direction which was 1.8–3.0 times higher than that of without magnetic field. Accordingly, the operating temperatures were significantly lower than those of without magnetic field at the same reaction rate. This outstanding performance could be attributed to the fact that the external magnetic field facilitated adsorption of CO2 reactant gas molecules over the surface of magnetized catalysts. Accordingly, the challenge in application of magnetic field in CO2 hydrogenation process help reduce CO2 emission into the atmosphere compared to the convention reactor, and therefore led to the carbon-neutral CO2 conversion process.

A high performance dual electrolyte microfluidic reactor for the utilization of CO2

The pH-differential membraneless architecture could enhance the thermodynamic property and raise the electrochemical performance of a dual electrolyte microfluidic reactor (DEMR) for electrochemical conversion of CO2. Freed from hindrances of membrane structure and thermodynamic limitation, DEMR demonstrates the possibility of altering anolyte and catholyte pHs to achieve higher reactivity rates and efficiencies. Different operation condition parameters of a microfluidic network would affect the reactor performance to a certain extents, constraining further improvement. Therefore, we conducted experimental analysis to study the mechanisms and intrinsic correlations of catalyst to Nafion ratio, microchannel thickness, electrolyte flow rate and CO2 supply for an optimized outcome. A comprehensive investigation on the cell durability was also carried out in the way of repetitiveness and long period operation, regarding both reactivity and efficiency. It was found that the catalyst to Nafion ratio affects the performance in a parabolic relation and there exists optimal values of electrolyte flow rate and microfluidic channel thickness for maximized cell performance. The influence of the reactant CO2 supply rate is not significant above a certain level where kinetics limitation is not dominant. The parametric study provides an operational point of view on the dual electrolyte microfluidic reactor and serves as a tool for DEMR optimization design.

Effects of temperature and rich-phase composition on the performance of a commercial NOx-Storage-Reduction material

A thin self-supported wafer of a commercial NOx-Storage-Reduction (NSR) material was investigated by operando transmission FT-IR to assess the effects of the operating temperature and the composition of the rich period (in particular with respect to H2, CH4, CO, CO2 and C3H6 reactants) on the deNOx activity. The DeNOx activity was high at 300°C under the simulated exhaust gas composition, but dropped sharply at 200°C and 100°C, primarily due to a loss of the NOx storage ability. The origin of the trapping loss depended on the temperature. Pt-bound CO(ads) were observed at 200°C, pointing to a significant poisoning of metallic Pt sites by strongly bound carbon monoxide, hindering NOx decomposition and reduction. Surprisingly, no Pt-CO was observed at 100°C, revealing the absence of accessible metallic Pt at this temperature, most likely due to the presence of a fully oxidized (or nitrated) Pt surface. In contrast, an important NSR activity could be obtained at 200°C and even at 100°C when H2 was used as the only reducing agent in a C-free feed. Propene had a similar detrimental effect as that of CO, while methane only induced a minor loss of trapping efficiency. The presence of a large concentration of CO2 also induced a trapping loss, albeit significantly less marked than those due to propene and CO. The combination of all the C-containing compounds (i.e. CO, CO2, C3H6, CH4) led to an almost complete inhibition of the NSR activity at temperatures equal to or lower than 200°C. The operando analysis also revealed that the nature of the NOx species trapped varied with the temperature; nitrates were the dominant species at 300°C, while nitrites were more prominent at 200°C and 100°C.

Development of a stable MnCo2O4 cocatalyst for photocatalytic CO2 reduction with visible light.

The synthesis of uniform MnCo2O4 microspheres and their cooperation with a visible light harvester to achieve efficient photocatalytic CO2 reduction under ambient conditions are reported here. The MnCo2O4 materials were prepared by a facile two-step solvothermal-calcination method and were characterized by XRD, SEM, TEM, EDX, XPS, elemental mapping, and N2 adsorption measurements. By using the MnCo2O4 microspheres as a heterogeneous cocatalyst, the photocatalytic performance of the CO2-to-CO conversion catalysis was remarkably enhanced, and no decrease in the promotional effect of the cocatalyst was observed after repeatedly operating the reaction for six cycles. (13)CO2 isotope tracer experiments verified that the CO product originated from the CO2 reactant. The effect of synthetic conditions and various reaction parameters on the photocatalytic activity of the system were investigated and optimized. The stability of the MnCo2O4 cocatalyst in the CO2 reduction system was confirmed by several techniques. Moreover, a possible mechanism for MnCo2O4-cocatalyzed CO2 photoreduction catalysis is proposed.

Influence of Ionization Degrees on Conversion of CO and CO2 in Atmospheric Plasma near the Ground

A zero-dimensional model is used to study the processes of physical and chemical reactions in atmospheric plasma with different ionization degrees near the ground (0 km). The temporal evolutions of CO, CO2 and other main reactants (namely OH and O2), which affect the conversion of CO and CO2, are obtained for afterglow plasma with different initial values. The results show that the consumption rate of CO is largest when the initial electron number density ne0=1012 cm−3, i.e. the ionization degree is 0.000004%. The number density of CO2 is relatively small when ne0=1016 cm−3, i.e. the ionization degree is 0.04%, whereas they are very close under the condition of other ionization degrees. Considering the total number densities of CO and CO2 and the consumption rate of CO comprehensively, the best condition is ne0=1013 cm−3, i.e. the ionization degree is 0.00004% for reducing the densities of CO and CO2 in the atmospheric plasma. The temporal evolutions of N+, Ar+, CO+ and CO2+ are also shown, and the influences on the temporal evolutions of CO and CO2 are analyzed with increasing ionization degree.

Kinetic fractionation of carbon and oxygen isotopes during hydration of carbon dioxide

Kinetic isotope effects (KIEs) during the inorganic hydration of carbon dioxide (CO2) in aqueous solution cause reduced stable carbon and oxygen isotope ratios (13C/12C and 18O/16O) in the reaction product carbonic acid (H2CO3) or bicarbonate ion (HCO3-), relative to CO2. While such KIEs are of importance in various physicochemical, geochemical, and biological systems, very few experimental and theoretical studies have attempted to determine the magnitude of the carbon and oxygen kinetic isotope fractionation (KIF) during hydration of CO2. Here I use transition state theory (TST) and quantum chemistry calculations to investigate the reaction rates of isotopic reactants CO2+nH2O (n=1–8) along the hydration pathway to H2CO3 or HCO3-. Locating transition states is difficult and the quantum chemistry calculations time-consuming at large n. My results suggest that the hydration mechanism for n=1–3 is unlikely to be the dominant pathway producing KIFs during CO2 hydration in aqueous solution; hydration mechanisms for n⩾4 appear more likely. For n=4–8, the predicted KIF based on MP2/aug-cc-pVDZ calculations at 25°C is ∼1.023–1.033 and ∼1.013–1.015, for carbon and oxygen, respectively. However, these values are uncertain and the results of the present study suggest that new experimental work is required to accurately determine the KIF of carbon and oxygen during CO2 hydration.

Oxidative CO2Reforming of Methane in La0.6Sr0.4Co0.8Ga0.2O3-δ(LSCG) Hollow Fiber Membrane Reactor

CO2 utilization in catalytic membrane reactors for syngas production is an environmentally benign solution to counter the escalating global CO2 concerns. In this study, integration of a La0.6Sr0.4Co0.8Ga0.2O3-δ (LSCG) hollow fiber membrane reactor with Ni/LaAlO3-Al2O3 catalyst for the oxidative CO2 reforming of methane (OCRM) reaction was successfully tested for 160 h of reaction. High CH4 and CO2 conversions of ca. 94% and 73% were obtained with O2 flux ca. 1 mL·min(-1)·cm(-2) at 725 °C for the 160-h stability test. Surface temperature programmed desorption studies of the membrane were conducted with H2, CO, and CO2 as probe gases to facilitate understanding on the effect of H2 and CO product gases as well as CO2 reactant gases on the membrane surface. Scanning electron microscopy-energy dispersive X-ray (SEM-EDX), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FTIR) analysis of the postreacted membrane after 160-h stability tests suggests Sr-enriched phases with the presence of adsorbed carbonate and hydrogenated carbon. This shows the subsequent reactant spillover on the membrane surface from the catalyst bed took place due to the reaction occurring on the catalyst. However, XRD analysis of the bulk structure does not show any phase impurities, thus confirming the structural integrity of the LSCG hollow fiber membrane.

Thermal and adsorbate effects on the activity and morphology of size-selected Pdn/TiO2 model catalysts

Model catalysts containing size-selected Pdn (n=1,2,4,7,10,16,20,25) deposited on rutile TiO2(110) deactivate during repeated CO oxidation temperature-programmed reaction (TPR) cycles, and the deactivation process has been probed using a combination of X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), low-energy ion scattering (ISS), temperature-dependent ion scattering (TD-ISS), annealing experiments, and temperature-programmed desorption following exposure to CO and O2 reactants. Results from such experiments suggest the cluster deactivation proceeds via an alloy-like, strong metal-support interaction (SMSI) effect that chemically modifies the clusters via electronic interactions between the supported metal atoms and Ti from the support. Threshold measurements show that this effect detrimentally affects CO-oxidation activity prior to the formation of an encapsulating overlayer by severely weakening the COPd bond strengths for binding configurations on top of the clusters. Oxidation appears to provide means of partially restoring the clusters to their initial state, but after sufficient exposure to reducing environments and elevated temperatures, all Pdn become covered by an overlayer and begin to electronically and chemically resemble freshly deposited atoms, which are completely inactive towards the probe reaction. In addition, we find evidence of oxygen spillover induced by co-adsorbed CO during TPRs for all active Pdn clusters.

Visible light plasmonic heating of Au–ZnO for the catalytic reduction of CO2

Plasmonic excitation of Au nanoparticles attached to the surface of ZnO catalysts using low power 532 nm laser illumination leads to significant heating of the catalyst and the conversion of CO2 and H2 reactants to CH4 and CO products. Temperature-calibrated Raman spectra of ZnO phonons show that intensity-dependent plasmonic excitation can controllably heat Au-ZnO from 30 to ~600 °C and simultaneously tune the CH4 : CO product ratio. The laser induced heating and resulting CH4 : CO product distribution agrees well with predictions from thermodynamic models and temperature-programmed reaction experiments indicating that the reaction is a thermally driven process resulting from the plasmonic heating of the Au-ZnO. The apparent quantum yield for CO2 conversion under continuous wave (cw) 532 nm laser illumination is 0.030%. The Au-ZnO catalysts are robust and remain active after repeated laser exposure and cycling. The light intensity required to initiate CO2 reduction is low (~2.5 × 10(5) W m(-2)) and achievable with solar concentrators. Our results illustrate the viability of plasmonic heating approaches for CO2 utilization and other practical thermal catalytic applications.