Simultaneous CO2 Reduction Research Articles

Enhanced activity of Ag[sbnd]MgO[sbnd]TiO2 catalyst for photocatalytic conversion of CO2 and H2O into CH4

Using solar energy to recycle carbon dioxide (CO2) offers a brand new opportunity for simultaneous mitigation of the global climate change effect and production of energy-bearing compounds. Silver (Ag) and magnesium oxide (MgO) co-modified titania (TiO2) (AgMgTi) synthesized through a combined impregnation and photo-deposition process. The catalysts were characterized through surface area analysis, X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), ultraviolet-visible (UV–vis) diffuse reflectance spectroscopy, and photoluminescence spectrum (PL). The TEM and XPS analysis demonstrated the presence of Ag nanoparticles (NPs) on the AgMgTi catalyst. The synergistic activities of Ag NPs and MgO significantly contributed to CO2 photoreduction to methane (CH4). CH4 yield over the AgMgTi catalyst was 20 times higher than over P25 TiO2, and was higher than over single modified catalysts (MgOTiO2 or AgTiO2) under either ultraviolet (UV) or UV–vis irradiation. MgO on the surface of TiO2 enhanced the chemisorption of CO2 and/or initiated the CO2 reduction process, and hence facilitated the conversion of CO2 to CH4. Under UV light excitation, the deposited Ag NPs facilitated the separation of electron–hole due to the formation of Schottky barriers on the metal-semiconductor interface. Visible light in the solar spectrum improved the energy of trapped electrons on Ag NPs through enhanced localized electric field attributed to the Ag surface plasmon resonance (SPR) effect. Abundant electrons with higher energy facilitated CH4 formation. Therefore, more CH4 was obtained under UV–vis irradiation comparing to that under UV irradiation. This study demonstrated that the AgMgTi catalyst can effectively utilize full spectrum solar energy for simultaneous reduction of CO2 and production of energy-bearing compounds.

Simultaneous CO2 Reduction and Dye (Crystal Violet) Removal Electrochemically on Sn and Zn Electrocatalysts Using Co3O4 Anode

The simultaneous reduction of CO2 to product electrochemically (RCPE) was studied on Sn and Zn electrocatalysts and oxidation of dye (crystal violet (CV)) at Co3O4 electrocatalyst. The electrodes for anode and cathode were prepared by coating the electrocatalysts on the graphite surface. The experimental studies were done in aqueous 0.5 M NaHCO3 and KHCO3 electrolyte solutions with CV (10 ppm) at different applied voltages (2–3.8 V). The results in forming product and CV dye removal were shown in time intervals of 5, 10, 15, 20, and 25 min, respectively. However, HCOOH was the only reduced product formed from RCPE, along with removal of CV observed for the applied experimental conditions. High Faradaic efficiency of 45.33% for HCOOH at Zn electrocatalyst in KHCO3 solution was observed in reaction time of 5 min. Maximum dye removals for Sn and Zn electrocatalyst are reported to be 64.3 and 61% in NaHCO3 electrolyte solution, and similarly dye removals of 71.5 and 60.9% were obtained in KHCO3 electrolyte at...

Facile synthesis of Co/RGO nanocomposite for methylene blue dye removal

In the present study, we report a facile and efficient method for the anchoring of cobalt nanoparticles (Co NPs) on reduced graphene oxide (RGO) sheets in presence of cationic surfactant cetyltrimethyl ammonium bromide (CTAB) and dispersing agent polyvinylpyrrolidone (PVP). Co NPs were decorated on RGO by the simultaneous reduction of Co2+ ions and graphene oxide (GO) under reducing condition of sodium borohydride (NaBH4) at room temperature (RT). The formation Co NPs and the reduction of GO sheets was confirmed by the X-ray diffraction (XRD) technique. The surface morphology was characterized by scanning electron microscopy (SEM) technique. The catalytic activity of Co/RGO nanocomposites was investigated for removal of methylene blue (MB) dye from water. Moreover, I/V characteristics of Co/RGO showed remarkable increment in current value compare to GO under applied bias range of -10 to + 10 V at RT (with typical on/off the resistive current), suggests their use for nanoelectronic device fabrication also.

Copper-doped titania photocatalysts for simultaneous reduction of CO2 and production of H2 from aqueous sulfide

Copper-doped titanium dioxide materials with anatase phase (Cu-TiO2, atomic Cu contents ranging from 0 to 3% relative to the sum of Cu and Ti), and particle sizes of 12–15nm, were synthesised by a solvo-thermal method using ethanol as the solvent and small amounts of water to promote the hydrolysis-condensation processes. Diffuse reflectance UV–vis spectroscopy show that the edges of absorption of the titania materials are somewhat shifted to higher wavelengths due to the presence of Cu. X-ray photoelectron spectroscopy (XPS) indicate that Cu(II) is predominant. Photocatalytic CO2 reduction experiments were performed in aqueous Cu-TiO2 suspensions under UV-rich light and in the presence of different solutes. Sulfide was found to promote the efficient production of H2 from water and formic acid from CO2. The effect of the Cu content on the photoactivity of Cu-TiO2 was also studied, showing that copper plays a role on the photocatalytic reduction of CO2.

Degradation and deactivation of Sn catalyst used for CO2 reduction as function of overpotential

Degradation and deactivation mechanisms of an Sn catalyst used for CO2 reduction to formate in 2M KCl solution was investigated at various potentials by using a rotating disk electrode. Surface degradation was studied by SEM/EDS and chemical analysis was performed by XPS. The results indicated that the optimum potential for CO2 reduction on Sn electrode was ∼ −1.8 VSCE where maximum faradaic efficiency and minimum degradation were obtained. Two types of degradation were observed after cathodic polarization: cathodic corrosion resulting in the potential loss of catalyst and formation of alkali metal deposits resulting in deactivation of the catalyst. The former type gave a crystallographic type of etching morphology near and at the grain boundaries after polarization in the potential range of −1.8 to −2.2 VSCE. The number of attacked areas increased at more negative potentials and with increasing electrode rotation rate. Corrosion did not cause electrode deactivation as indicated by a relatively stable faradaic efficiency. Moreover, the material loss was insignificant because only small areas were affected. Corrosion was attributed to the formation of tin hydride. Meanwhile, formation of intermetallic compound (KSn), which occurred during simultaneous CO2 reduction reaction at all potentials tested in this work, led to both cathodic deactivation and material loss. The existence of KSn deposits on the electrode surface was detected by EDS. The formation of intermetallic compound was always accompanied by an increase in current output possibly due to hydrogen evolution. Heavy colloidal deposits of KSn were found. For use of an Sn catalyst in a device, it is necessary to develop a technique to avoid or remove the alkali metal deposit.

Low-voltage electrochemical CO2 reduction by bacterial voltage-multiplier circuits

Using the voltage-multiplying circuits of chemolitho-autotrophic Fe-oxidizing bacteria (Mariprofundus ferrooxydans), we describe an integrated bioelectrochemical system that affords simultaneous CO2 reduction and H2O oxidation at an external voltage of less than 1.24 V.

Solar Syngas Production from H2O and CO2 via Two-Step Thermochemical Cycles Based on Zn/ZnO and FeO/Fe3O4 Redox Reactions: Kinetic Analysis

Syngas production via a two-step H2O/CO2-splitting thermochemical cycle based on Zn/ZnO and FeO/Fe3O4 redox reactions is considered using highly concentrated solar process heat. The closed cycle consists of: (1) the solar-driven endothermic dissociation of ZnO to Zn or Fe3O4 to FeO; (2) the nonsolar exothermic simultaneous reduction of CO2 and H2O with Zn or FeO to CO and H2 and the initial metal oxide; the latter is recycled to the first step. The second step was experimentally investigated by thermogravimetry for reactions with Zn in the range 673−748 K and CO2/H2O concentrations of 2.5−15% in Ar, and for reactions with FeO in the range 973−1273 K and CO2/H2O concentrations of 15−75% in Ar. The reaction mechanism was characterized by an initial fast interface-controlled regime followed by a slower diffusion-controlled regime. A rate law of Langmuir−Hinshelwood type was formulated to describe the competitiveness of the reactions based on atomic oxygen exchange on active sites, and the corresponding Arrhenius kinetic parameters were determined by applying a shrinking core model.

The comparison study on the operating condition of gasification power plant with various feedstocks

Gasification technology, which converts fossil fuels into either combustible gas or synthesis gas (syngas) for subsequent utilization, offers the potential of both clean power and chemicals. Especially, IGCC is recognized as next power generation technology which can replace conventional coal power plants in the near future. It produces not only power but also chemical energy sources such as H2, DME and other chemicals with simultaneous reduction of CO2. This study is focused on the determination of operating conditions for a 300 MW scale IGCC plant with various feedstocks through ASPEN plus simulator. The input materials of gasification are chosen as 4 representative cases of pulverized dry coal (Illinois#6), coal water slurry, bunker-C and naphtha. The gasifier model reflects on the reactivity among the components of syngas in the gasification process through the comparison of syngas composition from a real gasifier. For evaluating the performance of a gasification plant from developed models, simulation results were compared with a real commercial plant through approximation of relative error between real operating data and simulation results. The results were then checked for operating characteristics of each unit process such as gasification, ash removal, acid gas (CO2, H2S) removal and power islands. To evaluate the performance of the developed model, evaluated parameters are chosen as cold gas efficiency and carbon conversion for the gasifier, power output and efficiency of combined cycle. According to simulation results, pulverized dry coal which has 40.93% of plant net efficiency has relatively superiority over the other cases such as 33.45% of coal water slurry, 35.43% of bunker-C and 30.81% of naphtha for generating power in the range of equivalent 300 MW.

Electrochemical synthesis of urea at gas-diffusion electrodes

Abstract Simultaneous reduction of CO2 and nitrite ions was examined by using the gas-diffusion electrodes with Cu, Ag and Au catalysts. The formation of urea, CO, formic acid and ammonia was found in the simultaneous reduction. The maximum current efficiencies of urea formation at Cu, Ag and Au catalysts are 37%, 38% and 26% in the range of −0.75 to −3.0 V (SHE), respectively. Urea is supposed to be formed from both an ammonia precursor and CO precursor on the catalysts.