Performance For CO2 Conversion Research Articles

B-Doped and NH2-functionalized SBA-15 with hydrogen bond donor groups for effective catalysis of CO2 cycloaddition to epoxides

The novel B-SBA-15-NH2 catalyst with Lewis acid–base properties and hydrogen bond donor groups exhibited good catalytic performance for CO2 conversion under metal- and solvent-free conditions.

Reverse water-gas shift in a packed bed DBD reactor: Investigation of metal-support interface towards a better understanding of plasma catalysis

Palladium-loaded ZnO (Pd/ZnO) catalyst was synthesized by co-precipitation method and evaluated for plasma-catalytic reverse water-gas shift (RWGS) reaction. A CO2 conversion of 32.5 % was achieved on “Pd/ZnO + Plasma”, and was around two times higher than that of “ZnO + Plasma” (17.3 %). Catalyst characterization by X-ray diffraction, high-resolution transmission electron microscopy, temperature-programmed reduction and quasi in situ X-ray photoelectron spectroscopy revealed the possible formation of ZnOx@PdZn (ZnOx decorated PdZn alloy) at the interface of Pd active phase and ZnO support. The role of ZnOx@PdZn in plasma-catalytic CO2 conversion was systematically investigated by plasma-excited CO2 temperature-programmed desorption and in situ Fourier transform infrared spectroscopy. It was found that ZnOx@PdZn at Pd-ZnO interface improved significantly plasma-catalytic CO2 conversion by promoting the production of bidentate carbonate and bidentate formate species. In situ Raman spectroscopy studies proved that the ZnOx@PdZn remained largely intact during the RWGS process. Our in situ spectroscopic findings thus unveil that the ZnOx@PdZn at Pd-ZnO interface favors the activation of CO2, and, consequently, leads to a higher plasma-catalytic performance for CO2 conversion.

Carbon dioxide conversion in an atmospheric pressure microwave plasma reactor: Improving efficiencies by enhancing afterglow quenching

Microwave plasma is effective for decomposing CO2, which is a major contributor to global warming. Atmospheric pressure microwave plasma is of particular interest due to its vacuum-free configuration. Here, we investigated the CO2 conversion performance of a microwave plasma system operating at atmospheric pressure. CO2 conversion efficiency and energy efficiency were measured for various CO2 flow rates and input power levels. Lower CO2 flow and higher power yielded an enhanced CO2 conversion efficiency and lower energy efficiency. The afterglow temperature in the reactor was also measured. At a specific energy input (SEI) of 7.25 eV/molecule, a temperature of 1342 K was observed 12 cm below the gas injection nozzle. To improve the efficiencies of the plasma system, we propose an afterglow quenching method with enhanced heat transfer characteristics. This was achieved using a water-cooled quenching rod inserted into the plasma reactor to cool the afterglow gas stream, thus limiting the recombination reaction of CO to form CO2. At a SEI of 7.22 eV/molecule, CO2 conversion increased from 30.1% to 36.1% with the quenching rod; at 2.46 eV/molecule, the increment of CO2 conversion efficiency was 29 %. An energy efficiency of 28.9 % was achieved using an SEI of 1.19 eV/molecule. By tracking down the heat loss to cooling water flowing through the applicator, exhaust port, and quenching rod, we determined the energy distribution from the plasma plume to the exit gas stream. The quenching rod increased the chemical enthalpy of the product gas by reducing CO recombination.

NH2-UiO-66/g-C3N4/CdTe composites for photocatalytic CO2 reduction under visible light

To boost the photocatalytic activity of NH2-UiO-66 toward CO2 under visible light, CdTe quantum dots and g-C3N4 nanocrystals were introduced to form NH2-UiO-66/g-C3N4/CdTe composites via a two-step synthetic strategy. g-C3N4 and CdTe in different visible light ranges possessed a strong absorption ability, and, thereby, greatly extended the range of photoresponsive wavelength of the composites. Mott-Schottky analysis revealed that the energy level of the conduction band of g-C3N4 and CdTe was higher than the LUMO level of NH2-UiO-66, benefiting for the photogenerated carriers separation and electron injection from g-C3N4 and CdTe to NH2-UiO-66, leading to a high concentrated Zr (iii) formation. Finally, the NH2-UiO-66/g-C3N4/CdTe composites exhibited the superior photocatalytic performance for CO2 conversion in the acetonitrile/ethanol system upon visible light irradiation (≥400 nm) with a HCOOH generation rate of 24.6 µmol g−1 h−1 that was ∼7.5 times higher than that of NH2-UiO-66 alone.

(Invited) Dilute Cu Alloying in Au Nanostructures for Highly Selective and Long-Term Stability of CO2 Reduction

Electrochemical CO2 reduction can produce value-added chemical or fuels in moderate reaction environment. For efficient CO2 reduction to a target product with high selectivity, vast research works have been carried out over a few decades. Particularly, CO2 conversion performance using Au and Ag based catalysts for CO production has reached to economically viable level according to recent techno-economic analysis [1]. In various routes to improve catalytic property, metal alloys are shown effective by tailoring intermediate binding energy of CO2 reduction reaction (CO2RR). For example, bimetallic AuCu alloys, such as AuCu, AuCu3 and Au3Cu, have shown synergetic effects which lead to higher catalytic activities (i.e. overpotential, stability) although CO selectivity is still lower than state-of-art records (over 95%) [2-4]. Herein, we demonstrate the dilute Cu alloying in Au nanostructure for highly selective CO production with long-term stability. To synthesize nanostructured Au with controlled Cu alloying, we firstly formed Cu/Au bilayers by employing the electrochemical deposition (ED) and underpotential deposition (UPD) of Cu on 200-nm-thick Au thin films on Si substrates. ED and UPD processes were conducted at applied potentials of –0.1 and 0.3 V (vs. Ag/AgCl), respectively, in 50 mM H2SO4 electrolyte with 50 mM CuSO4. We carried out electrodepositon for 10s and 60s while underpotentially deposited Cu sample were only prepared for 60s. The Cu-covered Au surfaces were then electrochemically treated for nanostructuring with the same method previously reported by our research group [5]. Specifically, we electrochemically oxidized the Cu/Au bilayers at 2.5 V (vs. RHE) for 40 minutes in 0.2 M KHCO3 solution (pH = 8.5). Then electro-reduction was sequentially followed under constant current density of –0.5 mA cm–2 for about 10 minutes in the same solution. We denote the prepared samples by Nano-ED-CuAu-10s, -60s and Nano-UPD-CuAu in accordance with the type of Cu deposition processes. Additionally, nanostructured Au without Cu was prepared for the comparison. As a result of the electrochemical treatment, nanoporous structures were formed for all samples. The heights of the nanostructures were 200, 215, 225 and 240 nm for Nano-Au, Nano-UPD-CuAu, Nano-ED-CuAu-10s and 60s. XPS investigations clearly show the appearance of Cu 2p peak and slight shift of Au 4f peak position to the higher binding energy (~0.1 eV) when Cu was incorporated in Au nanostructures. In addition, the surface concentration of Cu were found to be 2, 11 and 13% for Nano-UPD-CuAu, Nano-ED-CuAu-10s and 60s, respectively. Our nanostructured CuAu and Au exhibit low CO2RR overpotential and high selectivity for CO in CO2 saturated 0.2 M KHCO3. For instance, the selectivity of CO2RR for all electrodes is around 50 – 70% (Nano-Au : 47%, Nano-UPD-CuAu : 65% Nano-ED-CuAu-10s : 69%, Nano-ED-CuAu-60s : 57%) at low overpotential (–0.34 V (vs. RHE)). It is noted that bare Au thin film shows almost no CO production. At higher applied potential (–0.59 V), the CO selectivity increases over 90% and notably, Nano-UPD-CuAu shows almost unity CO production (~99.5%) with nearly completely suppressing H2 evolution. In addition, Cu-Au nanostructures show the remarkably improved durability as compared to nanostructured Au catalysts. Whereas the CO selectivity at –0.49 V for Nano-Au drops from 92% at 30 minutes to below 80% in about 4.5 hours, Nano-UPD-CuAu retains the same performance for about 7 hours. Surprisingly, Nano-ED-CuAu samples are stable for 12 hours showing the selective CO production over 80%. These results indicate that dilute Cu-Au alloy nanostructures can be effective to improve stability with highly selective CO production. Additionally, in the presentation, we will introduce an in-situ tailoring technique to re-active the degraded Au catalysts by utilizing Cu impurities in electrolyte during CO2 electroreduction process for robust and efficient CO2 reduction. [1] Jouny et al., Ind. Eng. Chem. Res. 57, 2165 (2018) [2] Kim et al., Nat. Commun. 5, 4948 (2014) [3] Kim et al., Appl. Catal. B, 213, 211 (2017) [4] Kim et al., ACS Energy Lett., 3, 2144 (2018) [5] Kim et al., J. Mater. Chem. A., 6, 5119 (2018)

Simultaneous methanogenesis and acetogenesis from the greenhouse carbon dioxide by an enrichment culture supplemented with zero-valent iron

Abstract The microbial reduction of CO2 into value-added products is gaining considerable attention and can play a significant role in the field of environment and energy research. A novel strategy for biotransformation of CO2 was tested with zero valent iron (ZVI) and enrichment cultures for methane and acetate production under anaerobic conditions at room temperature. The favorable performance of CO2 conversion (81.67% of conversion rate) was achieved in ZVI-amended treatments by enhanced methanogenesis and acetogenesis simultaneously. The enrichment consortium of microorganisms containing Methanosarcina spp. and Clostridiaceae was responsible for methane and acetate production, and accounted for 25.89% and ∼4.83% of CO2 conversion, respectively. Scanning electron microscopy (SEM) observation and mass balance analysis of hydrogen detected in the headspace indicated that direct electron transfer and utilization possibly occurred with these microbes, especially methanogens. Interestingly, X-ray Photoelectron Spectroscopy (XPS) confirmed carbonation mineral (FeCO3) as the major strategy of CO2 consumption under the experimental conditions. These observations collectively revealed that supplementation of ZVI can be a favorable electron donor to stimulate and accelerate the biotransformation of CO2 into methane and acetate by the enrichment culture of microorganisms, and the information presents available alternative biochemical pathways for energy recovery from greenhouse gas under anaerobic conditions.

Z-scheme Photocatalytic CO2 Conversion on Three-Dimensional BiVO4/Carbon-Coated Cu2O Nanowire Arrays under Visible Light

Cuprous oxide (Cu2O) is one of the most promising materials for photoreduction of CO2 because of its high conduction band and small band gap, which enable the production of high-potential electrons under visible-light irradiation. However, it is difficult to reduce the CO2 using a Cu2O-based photocatalyst due to fast charge recombination and low photostability. In this work, we enhanced the photocatalytic CO2 conversion activity of Cu2O by hybridization of Cu2O NWAs, carbon layers, and BiVO4 nanoparticles. By construction of a Z-scheme charge flow on a 3-D NWA structure, the BiVO4/carbon-coated Cu2O (BVO/C/Cu2O) NWAs show significantly enhanced charge separation and light harvesting property. As a result, CO formation rate of BVO/C/Cu2O was 9.4 and 4.7 times those of Cu2O mesh and Cu2O NWAs, respectively, under visible light irradiation. In addition, the material retained 98% of its initial photocatalytic CO2 conversion performance after five reaction cycles (20 h) because of the protective carbon layer a...

Advances in state-of-art valorization technologies for captured CO2 toward sustainable carbon cycle

ABSTRACTValorization of captured CO2 is an important but challenging topic since CO2 is a stable and relatively inert compound. Nonetheless, CO2 valorization technologies should be sought after, because they can offer an opportunity for the sustainable carbon cycle towards a circular economy by creating value-added products and generate revenues from CO2. This paper provides an overview of state-of-the-art valorization technologies for captured CO2, including (1) supercritical CO2 as a reactive solvent, (2) mineralization of CO2 as inorganic carbonates, (3) catalytic reduction of CO2 into organic fuel for transport, (4) transformation of CO2 to value-added chemicals, and (5) biological CO2 utilization. The principles and application, in terms of CO2 conversion performance and environmental benefits of each technology, are reviewed in detail. In addition, the perspectives and prospects of CO2 valorization technologies as a portfolio solution are provided to achieve the effective CO2 reduction while minimizing social and economic costs in the near future.

Order engineering on the lattice of intermetallic PdCu co-catalysts for boosting the photocatalytic conversion of CO2 into CH4

Order engineering has been performed on PdCu co-catalysts for enhanced photocatalytic performance in conversion of CO2 to CH4 based on the disorder–order transformation from an A1 alloy phase to a B2 intermetallic phase.

Enhanced carbon dioxide conversion to formate on a multi-functional synergistic photoelectrocatalytic interface

As one of the main greenhouse gases, the conversion of CO2 into useful chemicals is of great significance to global warming, climate change and energy supply. Herein, a multi-functional synergistic photoelectrocatalytic (PEC) interface is employed to realize enhanced PEC CO2 reduction by using intrinsic Au doped TiO2 as the light harvester, nanotube photonic crystal (NTPC) as optical channels and Cu nanoparticles (NPs) as CO2 electrocatalyst. Formic acid is produced as the main product with a selectivity of 98% and a Faraday efficiency of 82.6% under simulated sunlight illumination and an applied potential of −1.0V vs. Ag/AgCl. Its yield ratio is up to 1019.3μmolL−1cm−2 after an 8h reduction, nearly 6.3 times higher than that on the traditional TiO2 NTs. Such enhanced PEC CO2 conversion performance is due to a synergistic catalytic effect on this multi-functional interface. The extraordinary localized surface plasmon resonance sensitized by the intrinsic Au NPs expands the light absorption region to the visible region. The photonic crystal layer structure raises the multi-reflection of incident light. The electrocatalyst of Cu NPs synergistically promotes PEC activity toward CO2 reduction. The calculated enhancement factors of photonic crystal layer, intrinsic Au NPs, and Cu NPs are 813%, 91%, and 2028%, respectively. This work provides an effective approach for photocathode design to promote the efficiency of PEC CO2 conversion.

Heterojunction p-n-p Cu2O/S-TiO2/CuO: Synthesis and application to photocatalytic conversion of CO2 to methane

Photocatalytic conversion of CO2 to fuel is a topic of great current interest. The problem is a challenging one, requiring a photocorrosion-stable, industrially-scalable, broad-spectrum light absorbing semiconductor, the energy bands of which align with the CO/CO2 and H2O/O2 potentials. Herein we report the synthesis of a unique p-n-p heterojunction material architecture, Cu2O/S-doped TiO2 micro-blocks covered with CuO nanowires, using anodization and annealing processes. The photocatalytic material shows excellent performance in the photocatalytic conversion of CO2 and water vapor to methane under AM 1.5G illumination. The heterojunction material architecture exhibits a methane yield of 2.31μmolm−2h−1, a rate approximately ten times higher than TiO2 nanotube array films synthesized using similar anodization conditions. The improved performance of the heterojunctioned material architecture appears due to improved light absorption and efficient separation of the photogenerated charge.

Enriching CO2 Activation Sites on Graphitic Carbon Nitride with Simultaneous Introduction of Electron‐Transfer Promoters for Superior Photocatalytic CO2‐to‐Fuel Conversion

Limited CO2 adsorption and inefficient charge transfer of graphitic carbon nitride (g‐C3N4) have been the two major obstacles for its application in photocatalytic CO2 reduction. In this work, a new type of carbon nitride photocatalyst (K‐incorporated amino‐rich carbon nitride, K‐AUCN) is designed and prepared by a facile posttreatment of urea‐polymerized g‐C3N4 (UCN) using KOH as a chemical activation agent. The resultant K‐AUCN has not only enriched intrinsic amino groups for superior CO2 adsorption, but also incorporated potassium and carbon defects as electron promoters for efficient photocatalytic reduction of CO2 in the presence of water vapor. Compared to UCN, the photocatalytic CO2 conversion performance on K‐AUCN is drastically promoted by five folds with 7.7‐time increase in CO2 adsorption. This work not only presents a simple design of low‐cost photocatalyst for CO2 reduction with enhanced performance, but shall also inspire more rational design of efficient catalysts for photocatalytic reduction of CO2 and other specific photocatalytic reactions.

Photoelectrocatalytic reduction of CO2 to methanol over a photosystem II-enhanced Cu foam/Si-nanowire system

A solar-light double illumination photoelectrocatalytic cell (SLDIPEC) was fabricated for autonomous CO2 reduction and O2 evolution with the aid of photosystem II (PS-II, an efficient light-driven water-oxidized enzyme from nature) and utilized in a photoanode solution. The proposed SLPEC system was composed of Cu foam as the photoanode and p-Si nanowires (Si-NW) as the photocathode. Under solar irradiation, it exhibited a super-photoelectrocatalytic performance for CO2 conversion to methanol, with a high evolution rate (41.94mmol/hr), owing to fast electron transfer from PS-II to Cu foam. Electrons were subsequently trapped by Si-NW through an external circuit via bias voltage (0.5V), and a suitable conduction band potential of Si (−0.6eV) allowed CO2 to be easily reduced to CH3OH at the photocathode. The constructed Z-scheme between Cu foam and Si-NW can allow the SLDIPEC system to reduce CO2 (8.03mmol/hr) in the absence of bias voltage. This approach makes full use of the energy band mismatch of the photoanode and photocathode to design a highly efficient device for solving environmental issues and producing clean energy.

Fabrication of Heterostructured g-C3N4/Ag-TiO2 Hybrid Photocatalyst with Enhanced Performance in Photocatalytic Conversion of CO2 Under Simulated Sunlight Irradiation

Heterostructured g-C3N4/Ag-TiO2 (CN/AgTi) hybrid catalysts were fabricated through a facile solvent evaporation followed by a calcination process, using graphitic carbon nitride (g-C3N4) and Ag-TiO2 (AgTi) as precursors. The phase compositions, optical properties, and morphologies of the catalysts were systematically characterized. The heterostructured combination of g-C3N4, titania (TiO2) and silver nanoparticles (Ag NPs) resulted in significant synergy for catalytic conversion of CO2 in the presence of water vapor under simulated sunlight irradiation. The optimal CN/AgTi composite with a g-C3N4 to AgTi mass ratio of 8% exhibited the maximum CO2 photoreduction activity, achieving a CO2 conversion of 47μmol, CH4 yield of 28μmol, and CO yield of 19μmol per gram of catalyst during a 3h simulated sunlight irradiation. Under the experimental conditions, the rate of electron consumption was calculated to be 87.3μmol/g·h, which was 12.7 times, 7.9 times, and 2.0 times higher than those for TiO2, g-C3N4 and AgTi, respectively. The combination of g-C3N4 and AgTi resulted in more sunlight harvesting for electron and hole generations. Photoinduced electrons transferred through the heterjunction between g-C3N4 and TiO2, and further from TiO2 to Ag NPs with lower Fermi level greatly suppressed the recombination of electron-hole pairs, and hence resulted in electron accumulation on Ag NPs deposited on the TiO2 surface in the CN/AgTi. Abundant electrons accumulated on the Ag NPs were further energized by the surface plasmon resonance effect with the aid of visible light. Therefore, the CN/AgTi catalysts exhibited superior catalytic performance in CO2 reduction by water vapor under simulated sunlight irradiation.

Nanostructured Graphene-Titanium Dioxide Composites Synthesized by a Single-Step Aerosol Process for Photoreduction of Carbon Dioxide.

Photocatalytic reduction of carbon dioxide (CO2) to hydrocarbons by using nanostructured materials activated by solar energy is a promising approach to recycling CO2 as a fuel feedstock. CO2 photoreduction, however, suffers from low efficiency mainly due to the inherent drawback of fast electron-hole recombination in photocatalysts. This work reports the synthesis of nanostructured composites of titania (TiO2) nanoparticles (NPs) encapsulated by reduced graphene oxide (rGO) nanosheets via an aerosol approach. The role of synthesis temperature and TiO2/GO ratio in CO2 photoreduction was investigated. As-prepared nanocomposites demonstrated enhanced CO2 conversion performance as compared with that of pristine TiO2 NPs due to the strong electron trapping capability of the rGO nanosheets.

Performance of power generation extension system based on solid-oxide electrolyzer cells under various design conditions

Parametric study of a power plant extension system based on solid-oxide electrolyzer cell (SOEC) system was conducted. Parameters involved in the analysis include temperature, amount of exhaust gas recirculation (EGR) and mole flux.Three limiting steps for reactant gases conversion were identified. An attempt has been made to explain the twin effects of EGR on the system performance. Increased performance of CO2 conversion at lower temperatures has been observed. Significant effects of mole flux and temperature on CO2 and H2O conversion have been confirmed.For the system configuration under study, 46.2% of electricity-to-syngas efficiency has been achieved. Maximum CO2 removal performance of ∼2.57 mol CO2/kWh was predicted at the temperature of 500 °C. Conversion ratio of 50–100% of CO2 is achievable depending on the operating conditions.Recommendations have been made for incorporating SOEC system into a power plant to mitigate CO2 and improve efficiency and flexibility of electricity production.

An anion-controlled crystal growth route to Zn2GeO4 nanorods for efficient photocatalytic conversion of CO2 into CH4

For photoreduction of CO2 into solar fuels driven by photocatalysis, a means to convert solar energy into chemical energy, a semiconductor photocatalyst with a specific crystal surface and high chemical stability is expected to achieve high activity and selectivity. Here, (110) facets exposed Zn2GeO4 nanorods with different aspect ratios were prepared by the ion exchange reaction between Na2GeO3 colloidal solution and various zinc salt solutions. The aspect ratio of Zn2GeO4 can be adjusted in the wide range from 2.5:1 to 20:1, depending on the acid radical. In this synthetic route, the Na2GeO3 precursor is a strong base, but strong acids such as HCl, HNO3 and H2SO4 as by-products were formed, meaning that the Zn2GeO4 single-crystal nanorods have good chemical stability in acid as well as in base. The excellent hydrothermal stability for the Zn2GeO4 nanorods in NaOH solution provides a simple method to obtain a hydroxylated surface for high performance in the photocatalytic conversion of CO2 and H2O to hydrocarbons fuels.