CO Conversion Rate Research Articles

Highly Selective Photoelectroreduction of Carbon Dioxide to Ethanol over Graphene/Silicon Carbide Composites.

Using sunlight to produce valuable chemicals and fuels from carbon dioxide (CO2 ), i.e., artificial photosynthesis (AP) is a promising strategy to achieve solar energy storage and a negative carbon cycle. However, selective synthesis of C2 compounds with a high CO2 conversion rate remains challenging for current AP technologies. We performed CO2 photoelectroreduction over a graphene/silicon carbide (SiC) catalyst under simulated solar irradiation with ethanol (C2 H5 OH) selectivity of>99 % and a CO2 conversion rate of up to 17.1 mmol gcat -1 h-1 with sustained performance. Experimental and theoretical investigations indicated an optimal interfacial layer to facilitate the transfer of photogenerated electrons from the SiC substrate to the few-layer graphene overlayer, which also favored an efficient CO2 to C2 H5 OH conversion pathway.

Analysis of dry reforming of methane under different fluidization regimes using a multiphase particle-in-cell approach

In the present study, the dry reforming of methane (DRM) has been simulated in fluidized-bed reactors using the multiphase particle-in-cell model. The model was meticulously built to investigate the effect of a wide range of superficial gas velocities covering particulate, aggregative, and lean-phase flow regimes on bed hydrodynamics, conversion, and yields of product gases. Constant values for catalyst loading, CH4:CO2:N2 ratio (1:1:1.3), and catalyst and gas properties were maintained in all simulations. The simulation results obtained are in good agreement with the experimental data reported in the literature. The results show that under different gas velocities, conversion is relatively indiscernible in the particulate regime. In contrast, for the inhomogeneous phases, the turbulent-fluidized bed had the best reactor performance with high CH4 and CO2 conversion rates, good CO + H2 productivity, and high CO/H2 molar ratio. This is due to the vigorous turbulent flow and relatively high gas–solid contact. Due to gas bypassing and backmixing triggered by bubbling, the bubbling-fluidized bed generally had the worst performance and below that of the fast-fluidized bed. The present study demonstrates that the performance of DRM reactions in fluidized-bed reactors is strongly related to the hydrodynamics. Moreover, it shows the significance of gas velocity on DRM conversion, yield, and overall reactor performance.

Technical analysis of the modified Fischer-Tropsch synthesis process for direct CO2 conversion into gasoline fuel: Performance improvement via ex-situ water removal

The modified Fischer-Tropsch synthesis (FTS) process is a promising technology for direct CO2 conversion into liquid fuels. However, the low yield of liquid fuels (below 29%) observed during CO2-FTS process is still of great concern for commercial deployment. Therefore, new strategies are needed to improve both CO2 conversion and liquid fuel yield during CO2-FTS process. A steady-state model based on first principles and a modified Anderson-Schulz-Flory (ASF) distribution was developed for the CO2-FTS process to predict gasoline range hydrocarbons (C5-C11). The model was implemented in Aspen Plus® using Fortran® routines and model validation was performed for different H2/CO2 feed ratios. Two process configurations (including a three-stage reactor in series and a single reactor with recycle) were considered for CO2-FTS performance analysis and improvement through ex-situ water removal. Both CO2-FTS process configurations showed significant improvements in CO2 conversion (from 34 to above 70%) with up to 61.0% gasoline yield. Though the single reactor with recycle achieved a higher CO2 conversion and gasoline production rate than the 3-stage reactor in series, the comparative analysis at the same CO2 conversion of 71.5% revealed that both process configurations have a similar process efficiency of roughly 66.4%.

Carbon species on the surface of carbon-coated catalysts and their effects on Fischer-Tropsch synthesis products

Carbon coated cobalt core–shell catalysts with different coating thickness were prepared by acetylene dissociation at different temperatures, the carbon coating had significant cutting effects on the Fischer-Tropsch synthesis (FTS) products. Further, different carbon species remained on the surface of carbon coated catalysts with adjusting the hydrogenolysis temperature (250, 400, 600 and 700 °C, respectively). Accordingly, the catalyst structure was optimized, the selectivity of C1 ∼ C4 was reduced, while the CO conversion increased, the products in the range of C5 ∼ C12, C13 ∼ C20 and C5 ∼ C20 were obtained with high selectivity. The carbon species were discerned by elemental analysis, temperature programmed hydrogenation, Raman spectra, X-ray photoelectron spectroscopy, H2 temperature programmed reduction and H2 thermogravimetry. The roles of different carbon species in FTS were elucidated, and the relationships between carbon species and FTS products selectivity were studied in detail. The deposited carbon blocks the active center, while graphitic carbon does not block the active center, nor limit the conversion rate of CO, but only limits the diffusion of long chain products.

Hybrid Catalyst Coupling Zn Single Atoms and CuNx Clusters for Synergetic Catalytic Reduction of CO2

AbstractReverse water‐gas shift (RWGS) reaction is the initial and necessary step of CO2 hydrogenation to high value‐added products, and regulating the selectivity of CO is still a fundamental challenge. In the present study, an efficient catalyst (CuZnNx@C‐N) composed by Zn single atoms and Cu clusters stabilized by nitrogen sites is reported. It contains saturated four‐coordinate Zn‐N4 sites and low valence CuNx clusters. Monodisperse Zn induces the aggregation of pyridinic N to form Zn‐N4 and N4 structures, which show strong Lewis basicity and has strong adsorption for *CO2 and *COOH intermediates, but weak adsorption for *CO, thus greatly improves the CO2 conversion and CO selectivity. The catalyst calcined at 700 °C exhibits the highest CO2 conversion of 43.6% under atmospheric pressure, which is 18.33 times of Cu‐ZnO and close to the thermodynamic equilibrium conversion rate (49.9%) of CO2. In the catalytic process, CuNx not only adsorbs and activates H2, but also cooperates with the adjacent Zn‐N4 and N4 structures to jointly activate CO2 molecules and further promotes the hydrogenation of CO2. This synergistic mechanism will provide new insights for developing efficient hydrogenation catalysts.

Experimental study of the effect of dielectric materials on the decomposition of carbon dioxide in a dielectric barrier discharge

The low-temperature nonequilibrium characteristics of dielectric barrier discharge (DBD) make it an important candidate for the decomposition and conversion of CO2. In this study, quartz, alumina and zirconia are selected as the dielectrics to investigate the effect of dielectric materials of planar DBD reactor on the discharge and conversion characteristics of CO2. It is shown that under the same input power conditions, zirconia has the highest CO2 conversion rate when used as a dielectric, followed by alumina, and quartz has the lowest. Combined with the analysis of the measured electrical characteristics, it is shown that zirconia has the highest transferred charge, thus further increasing the discharge efficiency. Experimental results of the single dielectric barrier layer-metal mesh electrode reactor show that the CO2 discharge can operate in the lower power range and the CO2 conversion rate is higher than that of the double dielectric barrier layer reactor. Spectroscopic measurements show that the emission intensity of the discharge in the reactor with high relative permittivity materials is higher than that in the case of low relative permittivity materials, and the emission intensity of the single dielectric layer reactor is also higher than that in the case of the double dielectric layer reactor.

Significantly enhanced photothermal catalytic CO2 reduction over TiO2/g-C3N4 composite with full spectrum solar light

Using solar energy to drive catalytic conversion of CO2 into value-added chemicals has great potential to alleviate the global energy shortage and anthropogenic climate change. Herein, a “hitting three birds with one stone” strategy was reported to prepared boron-doped g-C3N4/TiO2-x composite (BCT) by a one-step thermal reduction process. A series of characterizations showed that the composite catalyst has extended full-spectrum absorption, rapid photogenerated charge separation, and outstanding CO2 photoreduction performance (265.2 μmol g-1h−1), which is 7.5 and 9.2 times higher than that of pure TiO2 and g-C3N4, respectively. In addition, the CO2 conversion rate can be further increased to 345.1 μmol g-1h−1 at 70 °C due to its excellent photothermal conversion. Mechanistic studies reveal that synergistic effects alter the charge density distribution, thereby lowering the energy barrier for CO2 conversion by adsorbing and activating CO2 molecules. This work provides a novel three-in-one integrated strategy for fabricating high-efficiency catalysts.

Bi/UiO-66-derived electrocatalysts for high CO2-to-formate conversion rate

In the CO2 electrocatalytic reduction reaction (CO2RR) technology, high CO2 conversion rate is highly required for efficient CO2 utilization from the CO2 resource. In this study, we propose the strategy of combining UiO-66 metal organic framework (MOF) structure with Bi electrocatalyst for highly active CO2RR with selective formic acid production. The synthesized Bi/UiO-66 catalyst shows superior CO2 reduction property, 4.6 times higher current density at −0.7 V vs. reversible hydrogen electrode (RHE) than bare Bi without UiO-66 despite of low electrochemical surface area. Also, NH2 functionalized UiO-66 shows almost no effect on CO2RR as compared to without NH2 probably due to disassembled linkers during CO2RR. Various characterizations such as Fourier transform infrared (FTIR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) indicate carbonate species captured form of CO2 at Zr-MOF site should contribute the high CO2 conversion rate. Our findings demonstrate the feasibility of Zr-MOF as a Supporting material to achieve efficient CO2 reduction.

EDTA impregnation assisted synthesis of nickel nanoparticles embedded in activated carbon and its application for dry reforming of methane

In this paper, the catalysts with nanoscale nickel particles embedded in activated carbon were synthesized by Ethylenediaminetetraacetic acid (EDTA) assisted impregnation method. The experimental results revealed that EDTA addition could promote Ni particle dispersion and decrease Ni particle size. Ni particle size was significantly decreased from 18.23 to 4.57 nm when Ni/EDTA ratio was increased from 1:0 to 1:3. Catalytic performance of Ni15-AC-E3 demonstrated that CH4 and CO2 conversion rate under 850 °C were 90.05% and 96.28%, which were decreased by 1.08% and 1.27% after 72 h dry reforming methane (DRM) reaction. Moreover, the characteristic of the used catalyst showed that Ni particle size was only increased from 4.57 to 5.94 nm after the stability test, and NiO was not appeared. Meanwhile, the deposited carbon in the used catalyst was 5.02%. The above results meant that the catalyst prepared by EDTA assisted impregnation method had the ability of suppressing carbon deposition, Ni particle sintering and oxidation during DRM reaction.

Conversion mechanism of thermal plasma-enhanced CH4-CO2 reforming system to syngas under the non-catalytic conditions

Thermal plasma activation of CH4-CO2 reforming (CRM) to syngas under non-catalytic conditions is an efficient and clean technology for the large-scale utilization of hydrocarbon resources and the conversion of greenhouse gases. This study investigates the equilibrium state and transformation mechanism of a CRM reaction system activated by thermal plasma through experimental, thermodynamic, and kinetic analyses. The experimental results illustrated that the CO2 conversion rate and H2 selectivity showed a downward trend with an increase in the CO2/CH4 molar ratio, whereas the CH4 conversion rate and CO selectivity showed the opposite trend. When CO2/CH4 molar ratio was 6/4, the selectivity for CO and H2 increased to 87.0 % and 80.8 %, respectively. Excess CO2 promotes the partial oxidation of CH4 to eliminate carbon deposition, resulting in an H2/CO molar ratio value closer to 1. Thermodynamic results show that the thermal-plasma-initiated CRM reaction can reach thermodynamic equilibrium more easily than the conventional catalyzed reactions, achieving much higher feedstock gas conversion without carbon deposition. The kinetic results obtained from the PSR model revealed that CH4 and CO2 were cleaved to form free radicals at the instant of contact with the plasma flame. O, H, and other particles generated in the form of free radicals rapidly collided with each other and transformed into CO and H2, accelerating the reaction process. The results presented in this study will help reveal the transformation mechanism of the CRM reaction activated by thermal plasma under non-catalytic conditions and provide a new perspective for studying CRM reactions.

Enhancement of Fischer-Tropsch Synthesis by Periodical Draining of the Wax-Filled Pores of a Cobalt Catalyst by Hydrogenolysis

Fischer-Tropsch reactors operated in a steady state suffer from a low pore effectiveness factor and a high methane selectivity caused by internal mass transfer limitations due to the accumulation of long-chain hydrocarbons inside the catalyst pores. Therefore, an alternating process switching between Fischer-Tropsch synthesis (FTS) and drainage of the pores by hydrogenolysis is proposed. The periodical cracking of the accumulated waxes within the (partially) filled pores, realized by a switch from syngas (H<sub>2</sub>, CO) to pure hydrogen, results in a higher overall catalyst productivity and a more favorable product distribution. The influence of temperature and time of FTS on drainage time and product distribution was experimentally investigated at typical temperatures of FT fixed bed processes in a range of 210 to 240°C. Alternating drainage of the pores by hydrogenolysis at a hydrogen partial pressure of just 1 bar leads to an improvement of the rate of CO conversion by up to 90% (240°C, 2 h FTS) and an improvement of even 120% concerning the rate of production of non-methane hydrocarbons (240°C, 2 h FTS).

Effect of reduction pretreatment on the structure and catalytic performance of Ir-In2O3 catalysts for CO2 hydrogenation to methanol

In2O3 has been found a promising application in CO2 hydrogenation to methanol, which is beneficial to the utilization of CO2. The oxygen vacancy (Ov) site is identified as the catalytic active center of this reaction. However, there remains a great challenge to understand the relations between the state of oxygen species in In2O3 and the catalytic performance for CO2 hydrogenation to methanol. In the present work, we compare the properties of multiple In2O3 and Ir-promoted In2O3 (Ir-In2O3) catalysts with different Ir loadings and after being pretreated under different reduction temperatures. The CO2 conversion rate of Ir-In2O3 is more promoted than that of pure In2O3. With only a small amount of Ir loading, the highly dispersed Ir species on In2O3 increase the concentration of Ov sites and enhance the activity. By finely tuning the catalyst structure, Ir-In2O3 with an Ir loading of 0.16 wt.% and pre-reduction treatment under 300°C exhibits the highest methanol yield of 146 mgCH3OH/(gcat·hr). Characterizations of Raman, electron paramagnetic resonance, X-ray photoelectron spectroscopy, CO2-temperature programmed desorption and CO2-pulse adsorption for the catalysts confirm that more Ov sites can be generated under higher reduction temperature, which will induce a facile CO2 adsorption and desorption cycle. Higher performance for methanol production requires an adequate dynamic balance among the surface oxygen atoms and vacancies, which guides us to find more suitable conditions for catalyst pretreatment and reaction.

Integration of Materials and Process Informatics: Metal Oxide and Process Design for CO2 Reduction.

In materials informatics, a mathematical model constructed between the synthesis conditions of materials and their properties and activities is used to design synthesis conditions in which the properties and activities have the desired values. In process informatics, a mathematical model constructed between the process conditions for devices and industrial plants and product quality and cost is used to design process conditions that can produce the desired products. In this study, we propose a method to simultaneously design the synthesis conditions of materials and the process conditions of products by integrating materials and process informatics in the reverse water-gas shift chemical looping (RWGS-CL) reaction, which produces CO from CO2 using metal oxides via the RWGS-CL process. Four methods: Gaussian process regression-Bayesian optimization (GPR-BO), Gaussian mixture regression-Bayesian optimization (GMR-BO), GMR-BO-multiple, and GPR-GMR-BO were investigated for the optimization. All four proposed methods outperformed the results of a random search. GPR-BO achieved the highest performance and proposed 27 promising candidates for the synthesis conditions and metal oxides. The selected metals did not include Cu and Ga, which tended to have high predicted CO2 and H2 conversion rates, but Fe and La, which had slightly lower predicted CO2 and H2 conversion rates. These results indicate that a combination of metal oxides with lower predicted CO2 and H2 conversion rates and optimized process conditions was important for the optimization of both materials and processes, which was achieved by integrating materials and process informatics via the proposed method. Thus, we confirmed that it is possible to simultaneously optimize the combination of metals, composition ratios, synthesis conditions of the material or the metal oxide, and the process conditions using experimental datasets, process simulations, and machine learning, such as GPR, GMR, BO, and multiobjective optimization with a genetic algorithm.

Preparation of Vermiculite‐based Molecular Sieve‐Supported Ni‐Co Alloy Catalyst Assisted by Oleic Acid and Application in Dry Reforming of Methane

AbstractIn this work, microporous vermiculite‐based molecular sieves were etched into mesoporous vermiculite‐based molecular sieves by alkaline solution, and the mesoporous vermiculite‐based molecular sieves were supported by Ni or Ni‐Co alloy active components by oleic acid‐assisted method and impregnation method, respectively. And prepared catalysts were applied to the dry reforming of methane (DRM) reaction. Under the reaction conditions of T=750 °C and GHSV=30000 mL/(h gcat), the conversion rate of CO2 and CH4 of the Ni‐Co‐oa/VSiO2 bimetallic catalyst reached 84.7 % and 71.9 %, respectively. According to the analysis of the relevant characterization results, the Ni‐Co‐oa/VSiO2 catalyst has more nickel active sites and stronger interaction between metal and support due to the addition of oleic acid. Therefore, Ni‐Co‐oa/VSiO2 has better catalytic reactivity and stability.

Numerical study and field synergy analysis on CO selective methanation packed-bed reactor

Carbon monoxide selective methanation (CO-SMET) is one of the most efficient technologies for hydrogen purification and CO deep removal. This paper applies the field synergy principle for a deep understanding on the chemically reactive flow in a CO-SMET tubular reactor. The variation of CO conversion rate under different operating conditions is interpreted, at the first time, as relevant to the variation of the synergy angle between temperature and gas concentration fields. Sensitive analyses of the bed pressure, CO/CO2 ratio, heat exchange modes, etc., are studied to obtain the profile of field synergy angle in the inlet gas temperature range of 373 K – 873 K. It is found that the region with synergy angles between 0° and 70° enhances the heat transfer between mass transfer and contributes the main output of CO conversion. This work provides a fundamental basis on the future optimal design of CO–SMET reactors.

Simulation of Biogas Conversion Using Porous Solid Oxide Electrochemical Cells: Virtual Prototyping

The computer-aided engineering approach has made it possible to achieve virtual prototypes and to describe expected performances of new apparatuses. In this study, a direct production of syngas with biogas using the configuration of the cascade conversion cell in the supply feed direction of the system was exhibited. Momentum, heat, mass and charge balances were solved using COMSOL Multiphysics® commercial software. These simulations allowed calculation of distributions of partial pressures for all gas species within the anode (CH4, H2, CO, CO2, H2O, N2), as well as velocity field and temperature. The conversion process included methane reforming (steam and dry) associated with the water–gas shift reaction. The computing results showed that the configuration of three porous oxide solid cells based on a solid oxide fuel cell (SOFC) system conferred a larger active surface area and limited thermal stress in oxide materials. In addition, depending on the production process of the biogas, feeding composition strongly influences the conversion rate of CO2 and CH4. We observed that production of syngas was optimal for a CO2/CH4 ratio = 1.

Comment on "CO2 Footprint of Thermal Versus Photothermal CO2 Catalysis".

The previously published report by Wang et al. provides universal equations for evaluating the net CO2 emission via photothermal/thermal CO2 hydrogenation reactions in batch and flow reactors, respectively. However, it remains to be discussed whether the original feed amount or feed rate of H2 should be changed accordingly when the CO2 reduction rate is selected as the variable to investigate the net CO2 emission rate of the system. If not, the reaction would not be in accordance with the stoichiometric ratio, which is inconsistent with reality, bringing about the optimistic scenario in the assessment of CO2 footprint. This work has taken the potential relationship between the original feed amount or feed rate of H2 and CO2 conversion rate into account. The effects of CO2 conversion rate on the net CO2 emission rate in the photothermal catalytic system are re-examined, the obtained trends exhibit more challenging preconditions to achieve net-zero carbon emission than those in the work by Wang etal. The quantitative results indicate that green hydrogen source is indeed vital for carbon neutrality in photothermal CO2 catalysis. Here, the viewpoints will be worth considering and be seen as complementary to the proposed carbon emission assessment equations.

Specific Metal Nanostructures toward Electrochemical CO2 Reduction: Recent Advances and Perspectives

AbstractElectrochemically converting CO2 (CO2 reduction reaction(CO2RR)) to value‐added fuels is an advanced technology to effectively alleviate global warming and the energy crisis. However, thermodynamically high energy barriers, sluggish reaction kinetics, and inadequate CO2 conversion rate as well as poor selectivity of target products and rapid materials degradation severely limit its further large‐scale application, which highlights the importance of high‐performance electrocatalysts. Metal nanomaterials, due to their intrinsically high but still insufficient reactivity, selectivity, and stability, have been brought to the forefront and have lead to many reviews from various points of view. However, reviews which comprehensively unravel the importance and excellence of specific metal nanostructures and their associated properties for CO2RR are quite limited. To bridge this gap, various specific monometal and bimetal nanostructures are summarized, with an emphasis on the deep understanding of crystal orientation, surface structure, surface crystallography, surface modification, and many associated effects benefiting from the constructed specific metal nanostructures as well as the intrinsic relationships of specific metal nanostructure‐property‐CO2RR activities. Finally, the challenges and the perspectives to advance CO2RR are proposed to pay particularly more attention to architecture evolution during CO2RR with in situ/operando techniques, high‐throughput theoretical computations, and facile synthetic strategies with high yield and production for scale‐up applications.

In situ generated oxygen vacancy on Nb2O5 for boosted catalytic activities of M/Nb2O5 in photothermal CO2 reforming of CH4

Photothermal synergistic CO2 reforming of CH4 (CRM) is a promising avenue to convert the greenhouse gases (CO2 and CH4) into valuable chemicals and store the abundant clean solar energy into chemical energy simultaneously. Developing photothermal catalysts that could drive CRM efficiently at low temperatures remains as a challenge. In the present study, Nb2O5 supported group VIII metal catalysts (M/Nb2O5) were synthesized, with the typical catalyst Rh/Nb2O5 recording a CO2 conversion rate of 50.6 mmol gRh−1 min−1 in CRM at 500 °C under visible light irradiation, about double fold higher than that achieved under the thermal-driven reaction condition. Mechanism study disclosed that oxygen vacancy was generated in situ over M/Nb2O5 under the CRM reaction atmosphere. The oxygen vacancy promoted CO2 adsorption and enhanced the light harvesting capacities of M/Nb2O5 catalysts, which ultimately boosted their activities in photothermal CRM. This study provides a promising pathway for the rational design of efficient catalysts by tailoring the properties of the catalysts under the reaction atmosphere.

Hierarchically Structured CA@ZIF-8 Biohybrids for Carbon Dioxide Mineralization.

Carbonic anhydrase (CA) is a powerful biocatalyst for carbon dioxide (CO2) mineralization, of which immobilization is usually used for maintaining its catalytic activity against harsh external stimuli. However, the incorporated materials for CA immobilization would commonly increase the internal diffusion resistance during the catalytic process, thereby decreasing the catalytic efficiency. In our study, poly-L-glutamic acid (PLGA) as the structure regulator was used to induce the synthesis of CA@zeolitic imidazolate framework-8 (CA@ZIF-8) biohybrids. The introduction of PLGA that could coordinate with Zn2+ interfered the crystallization of ZIF-8, thereby changing the morphological structure of CA@ZIF-8 biohybrids. With the increase of PLGA amount from 0 to 60mg, PLGA(x)-CA@ZIF-8 biohybrids were gradually transformed from a dodecahedron structure to a 3D lamellar nano-flower structure, which caused elevated exposed surface area. Accordingly, the loading ratio was increased from 34.6 to 49.8mg gcat-1, while the catalytic activity was elevated from 20.6 to 23.4%. The CO2 conversion rate was enhanced by nearly two folds compared to PLGA(0)-CA@ZIF-8 under the optimized condition. The final CaCO3 yield could reach 5.6mg mgcat-1, whereas the reaction system could remain above 80% of the initial reaction activity after 8 cycles.