Showing papers in "Journal of CO 2 Utilization in 2019"
TL;DR: In this article, a review on inalienably associated methodologies is given and ongoing advancement on the improvement, designing, and comprehension of CO2 reduction using photochemical, biochemical and electrochemical is outlined.
Abstract: Carbon dioxide (CO2), a greenhouse gas is considered to contribute significantly to climate change and global warming. Environmental changes require to minimize the measure of CO2 in air. The capture, storage and utilization of carbon based on photochemical, biochemical and electrochemical processes are the innovative proposed methods to decrease utilization of nonrenewables such as coal and oil. CO2 can be reduced chemically through either homogeneous or heterogeneous pathway. In general, photochemical transformation of CO2 involves formation of carrier charges followed by its separation, transportation and finally reduction of CO2 using generated photoelectrons. Photocatalytic reduction of carbon dioxide is a rising territory of research. Beginning from the premise of photocatalytic reduction, the investigations about different semiconducting frameworks like oxides, sulfides, and phosphides are considered in this review. Biochemical transformation deals with enzymatic conversion of CO2 and electrochemical reduction uses electrical energy for converting CO2 into its reduced form. The enzyme catalytic carbon dioxide change gives an eco-accommodating approach to make carbon-based chemical products. A few favorable circumstances related with enzymatic change incorporate high selectivity, high return, less quantity of waste, less response conditions however certain downsides, for example, staggering expense of catalysts and cofactors, and longer response times as contrasted and normal strategies. Some products obtained as a result of CO2 reduction includes methanol, formic acid, CO, methane, ethylene and gasoline. In this review, a overview on inalienably associated methodologies is given and ongoing advancement on the improvement, designing, and comprehension of CO2 reduction using photochemical, biochemical and electrochemical is outlined.
258 citations
TL;DR: In this paper, a review of different technologies through which fly ash and materials derived from fly ash are applied in the CO2 capture, utilization, and storage technology while highlighting some challenges and opportunities for further research and development.
Abstract: Utilization is one of the prominent strategies for the management of hazardous industrial wastes like fly ash. As fossil-based power is expected to remain a major source of global electricity supply in the coming years, the absence of effective management strategies will exacerbate the problem of fly ash waste in the environment. Global fly ash utilization rates remain low due to limited utilization opportunities outside the construction industry. This necessitates the development of new pathways for its utilization as a means of diverting it from landfills where it poses a significant threat to the environment. Carbon capture, utilization, and storage presents opportunities to utilize fly ash in various ways; as a capture material, as a medium for permanent CO2 storage via mineralization, and as a catalyst or catalyst support for CO2 utilization processes. This study reviews the different technologies through which fly ash and materials derived from fly ash are applied in the CO2 capture, utilization, and storage technology while highlighting some challenges and opportunities for further research and development.
192 citations
TL;DR: In this article, the authors present state-of-the-art accomplishments in photocatalytic CO2 reduction through engineering approach towards reactor configuration and design aspects, and compare the performance of different types of photo-reactors.
Abstract: Photocatalytic conversion of CO2 to solar fuels, an artificial photosynthesis, is a promising solution to resolve the energy crisis and global warming issues. The overall efficiency of photo-reduction of CO2 to fuels can be improved through the development of highly efficient catalyst and suitable photoreactor configuration. Significant efforts have been devoted to the design and developments of photo-catalysts, but very little focus has been given towards photo-reactors development. In this perspective, this review presents state of the art accomplishments in photocatalytic CO2 reduction through engineering approach towards reactor configuration and design aspects. In the main stream, the perspectives of different types of photo-reactors employed for the photocatalytic conversion of CO2 has been discussed. Slurry, fixed bed and membrane photo-reactors have been identified as the main categories that are critically discussed based on their operational mode, type of bed, number of phases involved, membrane used and type of light source. Comparative analysis of photo-reactors is also being employed to improve selectivity and photo-conversion rates of these photo-reactors. The influence of the factors such as light position and distribution, material of construction, temperature and pressure on the production of fuels has also been explicated. Moreover, perspective gives an overview of basic principles, thermodynamics and mass transfer involved in photocatalytic conversion of CO2 to fuels. Finally, conclusions and future perspectives paves further improvements in the design of photo-reactors to be made to increase the efficiency of CO2 conversion to renewable fuels.
162 citations
TL;DR: In this paper, a review of the recent studies of activated biochars for CO2 adsorption, which were fabricated from various biomasses, was presented, and the effects of biochar properties on CO2 capture and separation was summarized with in-depth assessment of the activated biochar.
Abstract: Dramatic increase of CO2 emissions to sate the global carbon demand for chemicals, goods, and fuels has been regarded as one of the main contributors triggering global warming. Note that CO2 emissions are over the Earth’s full capacity to assimilate carbons via the natural carbon cycle. In these respects, CO2 capture and sequestration have been considered as one of the strategic principles to cancel out CO2 release from the anthropogenic activities in line with the use of fossil fuels. Thus, it is desirable to develop the efficient CO2 sorptive materials that are economically viable. Among CO2 sorptive materials, biochar (i.e., porous carbon-based materials) has been considered as one of the promising candidates. Indeed, a great deal of researches on biomass has been performed. Based on these rationales, this review laid great emphasis on informing the recent studies of activated biochars for CO2 adsorption, which were fabricated from various biomasses. Also, this review offered the up-to-date knowledge on the physicochemical properties of activated biochars in line with their synthesis procedures. Lastly, the effects of biochar properties on CO2 capture and separation was summarized with in-depth assessment of the activated biochars.
144 citations
TL;DR: In this paper, the performance of mixed metal-organic systems for the electroreduction of CO2 to alcohols in a filter-press electrochemical cell was evaluated, where bimetallic materials were supported onto porous carbon paper to form gas diffusion electrodes with a favorable continuous electrochemical conversion of CO 2 to methanol and ethanol, together with formic acid and gas-phase products.
Abstract: This work assesses the performance of Cu(II) and Bi(III)-based metal-organic framework (HKUST-1 and CAU-17, respectively) blends into the electroreduction of CO2 to alcohols in a filter-press electrochemical cell. The bimetallic materials are supported onto porous carbon paper to form gas diffusion electrodes with a favorable continuous electrochemical conversion of CO2 to methanol and ethanol, together with formic acid and gas-phase products (i.e. hydrogen, carbon monoxide and ethylene) in a 0.5 M KHCO3 aqueous solution. The maximum reaction rates and faradaic efficiencies for CO2 conversion to methanol and ethanol are rCH3OH=29.7 μmol·m−2·s-1 (FE = 8.6%) and rC2H5OH=48.8 μmol·m−2·s-1 (FE = 28.3%), respectively, at j = 20 mA·cm−2 which enhanced the values obtained at homometallic Cu and Bi-based materials independently. This denotes a synergic effect of Cu and Bi-based MOFs, associated with a favored interplay between the actives sites and reaction intermediates, prompting methanol formation and C C coupling reaction to ethanol. The results also show that reaction selectivity to produce alcohols can be controlled by Cu/Bi loading in the electrode surface and current density applied to the system. A 12% bismuth content seems to be the optimum for the production of alcohols (FEalcohols = 36.9%, Salcohols = 0.32). Regarding the current density, CO2 reduction is more selective to methanol with a j=10 mA·cm−2 (FECH3OH = 18.2%), while at j = 20 mA·cm−2, ethanol becomes the dominant CO2 reduction alcohol (FEC2H5OH = 28.3%). The performance of the Cu/Bi-MOFs remains also pseudo-stable after 5 h of operation denoting the potential of the mixed metal-organic systems for the utilization of CO2.
142 citations
TL;DR: In this article, microporous carbons were prepared from bee-collected pollens through carbonization and KOH activation, and various mass ratios of KOH/carbonized pollen from 1:3 to 3:1 were tested, and their effect on physicochemical properties and CO2 adsorption performance was analyzed.
Abstract: Novel microporous carbons were prepared from bee-collected pollens through carbonization and KOH activation. In the activation, various mass ratios of KOH/carbonized pollen from 1:3 to 3:1 were tested, and their effect on the physicochemical properties and CO2 adsorption performance was analyzed. As the KOH amount increased, the specific surface area and total pore volume increased because of the development of micropores during activation. Among the developed porous carbons, the sample activated with a high ratio (3:1) of KOH/carbonized pollen showed the highest CO2 adsorption uptake at 1 bar. However, the sample activated with a KOH/carbonized pollen mass ratio of 1:1 exhibited the highest CO2 adsorption uptake at 0.15 bar owing to different micropore distributions and nitrogen contents originating from the pollen precursor. Because narrower micropores are more important in the low-pressure region, cumulative pore volumes with pore sizes of less than 0.6 and 0.8 nm were well correlated with the CO2 adsorption uptake at 0.15 and 1 bar, respectively. Further, samples with residual nitrogen content showed high CO2/N2 selectivity. The developed microporous carbons also showed excellent adsorption–desorption cyclic stability during regeneration by simple N2 purging or by temperature-swing operation.
135 citations
TL;DR: In this article, a comprehensive review of all the recent studies conducted during the past decades is presented, where different aspects of the reaction system such as thermodynamic constrains, catalysts formulation, reactors aspects, reaction mechanism and influences of reaction conditions are discussed in detail.
Abstract: Catalytic reduction of carbon dioxide to methanol is an attractive option to reduce concentration of greenhouse gas and generation of renewable energy. Moreover, depletion of fossil fuel, global warming and steep hikes in the price of fuels are the key driving factor to investigate methanol synthesis by CO2 hydrogenation. In the last few decades, several investigations on catalytic CO2 hydrogenation to methanol have been reported in the literature. This article deals with a comprehensive review of all the recent studies conducted during the past decades. Furthermore, different aspects of the reaction system such as thermodynamic constrains, catalysts formulation, reactors aspects, reaction mechanism and influences of reaction conditions are discussed in detail. By now, such a discussion is still missing, and we intend to close this gap in this paper. The current scenario demonstrates the existence of immense prospects and opportunities to investigate further in this area.
135 citations
TL;DR: In this article, the role of dopants on the catalytic activity for the dry reforming of methane (DRM) was investigated on nickel supported on metal doped ceria (Me-DC) catalysts, Ni/Me0.15Ce0.85O2-δ with Me = Zr4+, La3+ or Sm3+, prepared by citric acid synthetic route.
Abstract: The role of dopants on the catalytic activity for the dry reforming of methane (DRM) was investigated on nickel supported on metal doped ceria (Me-DC) catalysts, Ni/Me0.15Ce0.85O2-δ with Me = Zr4+, La3+ or Sm3+, prepared by citric acid synthetic route. The catalytic activity was in the order Ni/Zr-DC Zr-DC > CeO2. The extra oxygen vacancies introduced by La3+ and Sm3+ were not capable to split CO2. La-DC and Sm-DC showed significant differences in the numbers and strength of surface basic sites. Therefore, other phenomena rule the formation/removal of carbon on these catalysts. The nature of dopants influenced the Ni-supports interaction and the electronic state of the metal catalyst.
118 citations
TL;DR: In this article, the effects of pre-curing and carbonation duration on compressive strength and microstructure characteristics of Portland cement paste were investigated, and it was shown that 30-40% water loss of cement paste is ideal for CO2 uptake.
Abstract: This study aims to investigate the effects of pre-curing and carbonation duration on compressive strength and microstructure characteristics of Portland cement paste. Experimental results showed that 30–40% water loss of cement paste is ideal for CO2 uptake. The combination of appropriate pre-curing and carbonation duration could increase compressive strength of cement mortar effectively, especially at early age. The optimal pre-curing duration decreases as the carbonation duration increases. Thermogravimetric analysis indicated that carbonation could retard hydration of cement paste and higher concentration of CO2 increases crystallinity of carbonate. According to MIP results, the influence of hydration and carbonation on pore structure of cement paste is different. Carbonation could decrease large capillary porosity obviously while hydration fills small capillary first. In addition, it is observed from EDS point analysis that excessive carbonation lead to decalcification of C-S-H. Therefore, suitable pre-curing and carbonation duration is of significance to improve the strength and microstructure of cement pastes.
114 citations
TL;DR: In this paper, the authors highlight the recent progress in the pyrolysis of waste feedstocks in the presence of carbon dioxide (CO2) and discuss the points that should be considered for future research.
Abstract: Pyrolysis is a thermochemical conversion method for the production of energy and chemicals from carbonaceous substances. In this review, we emphasize the recent progress in the pyrolysis of waste feedstocks in the presence of carbon dioxide (CO2). CO2-assisted pyrolysis is compared to typical pyrolysis (i.e., pyrolysis under inert environment, such as nitrogen). It has been shown that CO2 plays a crucial role in increasing the yield of combustible permanent gas (e.g., carbon monoxide) while decreasing tar yield. CO2-assisted pyrolysis is also an attractive technique to treat waste (municipal solid waste, plastic waste, etc.) because CO2 enhances the thermal cracking of volatile species, thereby suppressing the formation of harmful chemical compounds, such as benzene derivatives and polycyclic aromatic hydrocarbons. In addition to highlighting the recent achievements in the CO2-assisted pyrolysis processes, we discuss the points that should be considered for future research.
112 citations
TL;DR: In this article, a series of α-Fe2O3/g-C3N4 photocatalysts for CO2 reduction at 0.6 MPa was synthesized via hydrothermal method.
Abstract: In this study, a series of α-Fe2O3/g-C3N4(FCN) photocatalysts for CO2 reduction at 0.6 MPa to produce CH3OH is synthesized via hydrothermal method and the FCN hybrid shows greater absorption of visible light than pure g-C3N4 due to the introduction of α-Fe2O3 (narrow bandgap). The Z-scheme heterojunction promotes photogenerated electron and hole separation and suppresses the recombination of photoexcited electron-hole pairs. Benefiting from this unique structure, the optimized FCN(40:60) hybrid shows a CH3OH evolution rate of 5.63 μmol g−1 h−1 without any sacrifice reagent and cocatalyst, which is 2.9 times higher than that of pure g-C3N4(1.94 μmol g−1 h−1). The excellent activity is ascribed to a Z-scheme transfer mechanism, which is proposed according to the band structure between g-C3N4 and α-Fe2O3. The results gained here may provide some illuminating insights for the design of new types of Z-scheme photocatalysts.
TL;DR: In this article, the performance of a variety of alkaline adsorbents and candidates for dual function materials (DFM) was evaluated and the strengths and weaknesses of candidate catalysts and adsorbent were evaluated.
Abstract: Dual Function Materials (DFM) capture CO2 from flue gas followed by catalytic conversion to methane all at 320 °C using renewable H2. DFM is composed of a catalytic metal intimately in contact with alkaline metal oxides supported on high surface area carriers. The catalyst is required to methanate the adsorbed CO2 after the capture step is carried out in an O2-and steam-containing flue gas. Ruthenium, Rhodium and Nickel are known CO2 methanation catalysts provided they are in the reduced state. Ni is a preferred methanation catalyst based on price and activity, however, its inability to be reduced to its active state during the DFM process (capture and hydrogenation at 320 °C) was compared with Ru and Rh as methanation candidates. The performance of a variety of alkaline adsorbents was also studied and the strengths and weaknesses of candidate catalysts and adsorbents were evaluated. All samples were tested in a fixed bed reactor to quantify the extent and rate of methane generation. Complementing fixed bed testing, thermogravimetric analysis (TGA) was used to evaluate the extent of CO2 adsorption and rate of catalytic methanation. Pre-reduced (at 650 °C) Ni-containing DFM is highly active for CO2 methanation. However, the hydrogenation with 15% H2/N2 is completely inactive after exposure to O2 and steam, in a flue gas simulation, during the CO2 capture step at 320 °C. Rh and Ru DFMs were effective methanation catalysts with Ru being superior based on capture capacity, hydrogenation rate and price. In contrast to Ni – containing DFM, Ru remained active towards methanation even after exposure to flue gas simulation. Alkaline adsorbents (“Na2O”, CaO, “K2O” and MgO) in combination with reduced Ru were tested for adsorption and methanation. Ru – “Na2O”/Al2O3 DFMs showed the highest rates for methanation although CaO is also a reasonable candidate. To date, we have demonstrated that γ-Al2O3 is the most suitable carrier for DFM application relative to other materials studied.
TL;DR: In this paper, Ni-15CaO/Al2O3 and Ni-10Na2CO3/Al 2O3 catalyst have been synthesized varying the Ni loading, i.e. 5, 10 and 15 wt., and the impregnation methodology of the adsorbent and the metallic phase.
Abstract: Anthropogenic CO2 emissions are one of the main causes of global warming. One alternative is the CO2 capture and valorization through catalytic processes to produce CH4 using dual function materials. In this work, Ni-15CaO/Al2O3 and Ni-10Na2CO3/Al2O3 catalyst have been synthesized varying the Ni loading, i.e. 5, 10 and 15 wt.%, and the impregnation methodology of the adsorbent and the metallic phase. All prepared samples have been physically and chemically characterized by adsorption-desorption of N2, XRD, TEM, H2 chemisorption, XPS, H2-TPR, CO2-TPD and TPSR with H2. The presence of CaO or Na2CO3 provides the catalyst with basic sites with different strength for the adsorption of CO2. Specifically, carbonates with lower stability are formed onto Na2CO3 in comparison to CaO. Besides, increasing Ni loadings slightly promote the decomposition of CO2 adsorbed species. The reducibility of Ni species is enhanced in the presence of the adsorbent and for increasing Ni loadings. CH4 formation during TPSR experiments is observed between 200–600 °C for CaO containing samples, whereas CH4 formation is observed in a narrower temperature range of 200–400 °C for Na2CO3 containing samples. A reaction scheme is proposed which describes the temporal evolution of reactants and products during the CO2 storage and hydrogenation cycles. The formation of CH4 increases with Ni loading. Maximum CH4 formation (142 μmol g−1) is observed for 15Ni15Ca sample at 520 °C. On the other hand, the formation of CH4 is higher (185 μmol g−1) operating at lower temperature, i.e. 400 °C, with 10Ni10Na sample containing a lower amount of nickel.
TL;DR: In this paper, the strategy of adding large amount of metal oxide promoters (15wt%) to nickel supported on micro-size catalysts (dp"="400-500"μm") is presented.
Abstract: The Power-to-Gas concept has the challenge to convert the excess of renewable electricity to synthetic natural gas, composed mainly by methane, through CO2 methanation. The superior heat transfer capacity of micro-structured reactors offers a suitable alternative for an efficient control of the reaction temperature. In the present work, the strategy of adding large amount of metal oxide promoters (15 wt.%) to nickel supported on micro-size catalysts (dp = 400–500 μm) is presented. The addition of CeO2, La2O3, Sm2O3, Y2O3 and ZrO2 was clearly beneficial, as the corresponding metal-oxide promoted catalysts exhibited higher catalytic performance than Ni/Al2O3 and the commercial reference Meth® 134 (T = 200–300 °C, P = 5 bar·g). This increase of catalytic activity is attributed to the higher amount of CO2 adsorbed on the catalyst. Among the selected promoters, La2O3 showed the highest catalytic activity (XCO2=+20% at 300 °C) due to the enhancement of nickel reducibility, nickel dispersion and the presence of moderate basic sites. In addition, Ni-La2O3/Al2O3 was stable for one week, while the unpromoted catalyst exhibited a slight decline in its activity. Accordingly, the technical catalyst proposed in this study could be used directly in compact reactors for CO2 methanation with much higher activity than the commercial reference.
TL;DR: In this article, a review of recent advances of graphene-based catalysts in electrocatalytic CO2 reduction is presented, where the relationship between structure and property with regard to CO2 electroreduction is highlighted.
Abstract: Electrocatalytic CO2 reduction (ECR) using renewable electricity provides an alternative strategy for alleviating energy shortage and global warming issues. To facilitate this kinetically sluggish process, the design of highly selective, energy-efficient, and cost-effective electrocatalysts is key. Graphene-based materials have features of relatively low cost, excellent electrical conductivity, tunability in structure and surface chemistry, and renewability, rendering them competitive for CO2 electroreduction. In particular, by doping with heteroatoms, it’s possible to create unique active sites on graphene for CO2 adsorption and activation. Besides, integration of graphene with other materials enables creation of a synergistic effect, thereby boosting CO2 conversion. This review focuses on recent advances of graphene-based catalysts in ECR. The relationship between structure and property with regard to CO2 electroreduction is highlighted. Leading electrocatalysts are discussed and compared with some metal benchmark materials to provide an evolutionary perspective of performance progress. Development opportunities and challenges in the field are also summarized.
TL;DR: In this article, the application of Cu oxides/ZnO-based electrocatalytic surfaces for the continuous and selective gas-phase electroreduction of CO2 to ethylene in a filter-press type electrochemical cell is studied.
Abstract: In this work, the application of Cu oxides/ZnO-based electrocatalytic surfaces for the continuous and selective gas-phase electroreduction of CO2 to ethylene in a filter-press type electrochemical cell is studied. The prepared catalytic materials are characterized by transmission electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. Then, the Cu oxides/ZnO-based gas diffusion electrodes are electrochemically characterized by cyclic voltammetry and Tafel plot analyses. The ethylene formation rate and Faradaic efficiency are as high as 487.9 μmol m−2s−1 and 91.1% when a current density of 7.5 mAcm−2 (-2.5 V vs. Ag/AgCl) is applied to the system, with an ethylene/methane production ratio of 139, showing a better performance than previous electrocatalytic systems for the production of ethylene from CO2 conversion. Consequently, the use of Cu oxides/ZnO-based electrocatalysts for gas-phase CO2 reduction is a step forward in the production of C2 products, such as ethylene.
TL;DR: In this paper, the reduced oxide graphene (RGO) supported Ni-based catalysts were modified with ceria (Ni-Ce/RGO), which achieved the highest CO2 conversion of 84.5% and the highest methane yield of 83.0% at 350°C with atmospheric pressure.
Abstract: The reduced oxide graphene (RGO) supported Ni-based catalysts is prepared and modified with ceria (Ni-Ce/RGO) for CO2 methanation for the first time in the present work, and compared with the active carbon (AC) and γ-Al2O3 supported samples. The results show that the catalytic activity of the samples without ceria follow the order Ni/RGO > Ni/γ-Al2O3 > Ni/AC, vs. samples with ceria Ni-Ce/RGO > Ni-Ce/γ-Al2O3 > Ni-Ce/AC. The activities of all samples were greatly improved after ceria modification. The Ni-Ce/RGO works the best for CO2 methanation, which could reach the highest CO2 conversion of 84.5% and the highest methane yield of 83.0% at 350 °C with atmospheric pressure. The excellent catalytic performance of Ni-Ce/RGO could be attributed to the special support effect of RGO and the ceria promotion effect. The support effect of RGO could be attributed to its large surface area and surface oxygen-containing functional groups, which results in stable anchoring of the active metal. The addition of ceria promotes the Ni dispersion on the supports as well as to accelerate the positive reaction due to the oxygen vacancies of ceria.
TL;DR: In this paper, three approaches for mitigating CO2 including hydrogenation, bi-and tri-reforming are investigated for methanol production at three different capacities (300, 1500, and 3500 ton/day).
Abstract: Minimizing CO2 emission into the atmosphere to prevent climate change has required immense efforts from us. Flue gases from fossil fuel-based power plants and many heavy industries are considered main anthropogenic sources of releasing CO2. Although there is a popular solution to mitigate CO2 through CO2 capture and storage, its cost is still quite significant, and this prevents broad application. A newly proposed process to convert flue gases into methanol has grabbed a headline because it offers an opportunity to alleviate CO2 emissions and delivers a way to produce methanol (MeOH) from recycling feedstock. In this work, three approaches for mitigating CO2 including hydrogenation, bi- and tri-reforming are investigated for methanol production at three different capacities (300, 1500, and 3500 ton/day). The environmental and economic consequences are evaluated as a primary implementation for green process design. These evaluations pointed out that the processes based on reforming are the most appropriate direction for employment during the transition step of producing methanol from a carbon-based- to carbon-free program whereas the hydrogenation-based processes with hydrogen from renewable sources could be the proper implementation scenarios for a long-term plan to obtain near-zero emissions.
TL;DR: In this paper, a tandem catalyst comprising of ZnO/ZrO2 and ZSM-5 zeolite was proposed for one-pass CO2 conversion to aromatics with a selectivity of 70%.
Abstract: In the past decades, considerable achievements have been made in CO2 hydrogenation to various C1 chemicals, lower olefins, and gasoline. However, the synthesis of aromatics from one-pass CO2 hydrogenation is still a great challenge owing to the extreme inertness of CO2 and the high aromatization barrier. Here we present a tandem catalyst comprising of ZnO/ZrO2 and ZSM-5 zeolite for one-pass CO2 conversion to aromatics with a selectivity of 70%, and the selectivity of undesirable methane is greatly suppressed to lower than 1%. A pathway of CO2 → CH3OH → aromatics over the tandem catalyst was demonstrated. This work offers a viable alternative for CO2 emission abatement through its valorization as a low or even negative-cost feedstock.
TL;DR: In this article, a simple, environmentally friendly, and low-cost method to prepare N-doped adsorbents with outstanding CO2 adsorption property under 1 bar was proposed.
Abstract: This study offers a simple, environmentally friendly, and low-cost method to prepare N-doped adsorbents with outstanding CO2 adsorption property under 1 bar. Utilizing waste walnut shell as adsorbents precursor and NaNH2 as chemical activator and nitrogen source, porous adsorbents containing nitrogen are prepared at low temperature zone 400–500 °C. Also, by adjusting the activation temperature of the adsorbent and the ratio of NaNH2/AC, the pore structure and nitrogen content of the adsorbent are regulated to affect CO2 adsorption performance. The specific surface area of the prepared series of nitrogen-containing porous adsorbents is from70 m2/g to 419–1721 m2/g. The result indicates that the optimal adsorbent has the highest 5.22 mmol/g of CO2 adsorption capacity. A systematic study on the prepared series of adsorbents demonstrates that the narrow pore volume, pore structure and nitrogen content of the adsorbent jointly affected adsorption performance of CO2. Besides, these walnut shell-derived N-doped adsorbents show appropriate CO2/N2 selectivity and Qst. The numerous advantages of the cheap waste walnut shell adsorbents enjoy simple and low-temperature synthesis process indicating that they are outstanding substitution to CO2 adsorbents. The study hopes to further understand the synthesis of N-doped carbon and its carbon dioxide adsorption mechanism.
TL;DR: Dimethyl ether (DME) is the cleanest high-efficiency compression ignition fuel as a substitute for diesel and also LPG as a cooking fuel as mentioned in this paper, which can be synthesized from different routes such as coal, petroleum and biomass including various greenhouse gases.
Abstract: Dimethyl ether (DME) is heralded as the cleanest high-efficiency compression ignition fuel as a substitute for diesel. DME's autoignition property and high octane number are favorable to use it as a substitute for diesel and also LPG as a cooking fuel. DME can be synthesized from different routes such as coal, petroleum and biomass including various greenhouse gases. Huge amounts of greenhouse gases (CO and CO2) are generated in coal or petroleum operated thermal power plants and released in the atmosphere. Roughly 5–10% of total CO2 emission can be utilized for fuel and chemical production. CO2 capture and sequestering (CCS) plants only can be sustainable if supported by DME synthesis plant with a capacity of 3000–7500 TPD. DME can be produced from CO2 using innovative catalysts, reactors and separators. Part I of this review is a representation of the innovative strategies which have been reported for the production of DME from different sources of raw materials, catalysts and influence of operational parameters on DME selectivity and yield. The critical gaps are identified and further, research potentials are given in Part I. However, the industrial processes using a variety of reactor configurations affect the overall capex and opex. The production of syngas, irrespective of the source, is the first step in DME synthesis, which is then followed by conversion into DME using a battery of reactors and separators. A critical analysis is presented and future scope is outlined in Part II.
TL;DR: In this article, high-resolution transmission electron microscopy, 13C magic angle spinning nuclear magnetic resonance spectroscopy, the Rietveld method, and thermogravimetric analysis confirmed that amorphous and/or poorly-crystalline calcium carbonates were produced during carbonation.
Abstract: Larnite (β-C2S) is a low-calcium mineral with a low rate of early hydration which has a high CO2 sequestration potential. Synthetic β-C2S was exposed to pure CO2 for gas–solid carbonation for varied time periods to investigate changes in mineral composition, calcite crystal growth, and the development of physico-chemical properties. Results show that the ultimate degree of carbonation reached 61.5% and the ultimate CO2 sequestration capacity was 314.7 g/kg raw β-C2S. High-resolution transmission electron microscopy, 13C magic angle spinning nuclear magnetic resonance spectroscopy, the Rietveld method, and thermogravimetric analysis confirmed that amorphous and/or poorly-crystalline calcium carbonates were produced during carbonation. Well-crystalline calcite with a single crystal structure was formed, having a crystallite size of 107 nm and an average particle size of 1.8 μm after 168 h of carbonation. The compact stack and the strong mechanical bond between well-crystalline calcite particles were observed in scanning electron microscopy images, and they are thought to contribute to a strong micro level force, thereby leading to the good macro level performance of carbonation products which reached 127 MPa after 168 h of carbonation. This study contributes to a more insightful understanding of the vital role of calcite in promoting the mechanical and physico-chemical properties of β-C2S-containing wastes and cements produced by carbonation. A further investigation into the micro level mechanical properties of calcite is required to understand the relation between carbonation and increased strength.
TL;DR: In this paper, a membrane electrode assembly that consists of gas diffusion electrode (GDE) and anion exchange membrane (AEM) was used to reduce CO2 using renewable electricity.
Abstract: Electrochemical CO2 reduction reaction (CO2RR) has received much attention as a promising technology to reduce CO2 using renewable electricity, but it typically suffers from low CO2 solubility in aqueous phase and a high cell resistance of a conventional liquid phase reactor. Here, we report the CO2RR using a membrane electrode assembly that consists of gas diffusion electrode (GDE) and anion exchange membrane (AEM). The GDE enabled facile mass transfer of gaseous CO2 directly to the catalyst and the AEM could suppress hydrogen evolution reaction (HER) by increasing local pH at the catalyst. Various metal powders of Pd, Ag, Zn, Cu, Sn, Ru, Pt, Ni were tested as cathode catalysts. Pd and Ag showed high current density of >200 mA cm−2 at -3.0 V and faradaic efficiency >95% for CO production with a low cell resistance of
TL;DR: In this paper, a series of CuO/ZnO photocatalysts were developed by varying the Cu contents, which provided solar driven CO2 reduction efficiencies comparable to those obtained for water splitting in similar devices without using reductant and Pt as co-catalyst.
Abstract: Construction of hierarchical CuO/ZnO p-n heterojunction was envisaged between CuO and ZnO nanospheres via following the cost effective, simple and facile hydrothermal treatment for the photocatalytic reduction of CO2 to methanol under visible light irradiation. In this report, a series of CuO/ZnO photocatalysts were developed by varying the Cu contents. The developed photocatalysts provided solar driven CO2 reduction efficiencies comparable to those obtained for water splitting in similar devices without using reductant and Pt as co-catalyst. The as-prepared photocatalysts are found to be highly efficient, robust for the photoreduction of CO2 to methanol in aqueous solution containing dimethylformamide (DMF) and triethylamine (TEA) as electron donor under visible light irradiation. The synthesized p-CuO/n-ZnO heterojunction nanospheres having CuO concentration of 0.1, 0.2, 0.4 and 0.5 mmol were denoted as ZC1, ZC2, ZC3 and ZC4 respectively. Among them, ZC3 photocatalyst showed relatively higher activity for methanol formation than that of ZnO, ZC1, ZC2 and ZC4. The yield of methanol for photocatalysts is in the order of ZC3 > ZC4> ZC2 > ZC1 > ZnO as 3855.36, 3020.76, 2464.3, 1788.6 and 1190.5 μmol g−1 cat, respectively. This CuO/ZnO heterojunction photocatalysts shows enhanced separation of the electron and hole to the surface and reduce the recombination.
TL;DR: In this article, the authors developed a model that takes into account all the major contributing mechanisms in shale gas dynamics including viscous flow, gas slippage, Knudsen diffusion, competitive adsorption of different components, pore size variation and real gas effect.
Abstract: Carbon capture and storage in depleted shale gas reservoirs offers an opportunity to utilize CO2 for enhanced gas recovery while providing access to fossil fuels. To evaluate CO2 sequestration coupled with enhanced gas recovery (CO2-EGR), we have developed a model that takes into account all the major contributing mechanisms in shale gas dynamics including viscous flow, gas slippage, Knudsen diffusion, competitive adsorption of different components, pore size variation and real gas effect. The CO2-EGR process is divided into periods of primary production, CO2 injection, soaking and secondary simultaneous production of CO2 along with other natural gas components. Numerical simulations are conducted to study the feasibility of CO2 sequestration and enhanced gas recovery and analyze the response of the shale gas reservoir to input variables including reservoir pressure, temperature and intrinsic permeability. The results show that the stronger adsorption of CO2 over CH4 molecules to shale surface is the main influencing mechanism on CO2 sequestration. It is shown that 30–55% percent of the injected CO2 can be trapped as adsorbed phase in shale while providing 8–16% incremental gas recovery. Comparing trapping efficiency of CO2-EGR with other methods of accelerating CO2 dissolution in deep saline aquifers, adsorbed phase trapping is promising.
TL;DR: The performance analyses showed that RBFNN-ABC model exhibits the higher accuracy in the prediction of CO2 solubility in brine compared with the other proposed smart approaches and the existing well-known models.
Abstract: Carbon dioxide (CO2) capture and sequestration in saline aquifers have turned into a key focus as it becomes an effective way to reduce CO2 in the atmosphere. The solubility of CO2 in brine is of vital role in monitoring CO2 sequestration. In this study, based on molality of NaCl, pressure and temperature, modeling of CO2 solubility in brine has been carried out utilizing multilayer perceptron (MLP) and radial basis function neural network (RBFNN). Levenberg-Marquardt (LM) algorithm was implemented to optimize the MLP model, while genetic algorithm (GA), particle swarm optimization (PSO) and artificial bee colony (ABC), were applied to optimize the RBFNN model. To this end, a widespread experimental databank including 570 data sets gathered from literature was considered to implement the proposed models. Graphical and statistical assessment criteria were considered to investigate the performances of these models. The obtained results revealed that all the proposed techniques are in excellent correspondence with experimental data. In addition, the performance analyses showed that RBFNN-ABC model exhibits the higher accuracy in the prediction of CO2 solubility in brine compared with the other proposed smart approaches and the existing well-known models. The RBFNN-ABC model yields a root mean square error (RMSE) value of 0.0289 and an R2 of 0.9967. Finally, the RBFNN-ABC model validity was confirmed and a small number of probable doubtful data was detected.
TL;DR: In this article, the authors summarized the research progress of photocatalytic conversion of CO2 from the product selectivity point of view, including surface modification of catalyst, the control of reaction conditions, the selection of incident light source, and the challenges and prospects in achieving efficient, stable and selective CO2 photoconversion.
Abstract: The emissions of carbon dioxide (CO2) from the combustion of hydrocarbon fuels have brought increasingly serious global warming. Photocatalytic conversion of CO2 to the renewable fuels or valuable chemicals is proposed as an effective solution to simultaneously achieve the reduction of CO2 emission, the use of sustainable solar energy and the harvest of products with high added-value. Various products such as methane (CH4), methanol (CH3OH), carbon monoxide (CO) have been gained through the photocatalytic conversion of CO2. This review systematically summarized the research progress of photocatalytic conversion of CO2 from the product selectivity point of view. Particularly, the common strategies to covert CO2 into the desired target products, including the surface modification of catalyst, the control of reaction conditions, the selection of incident light source, are completely discusses. Finally, the challenges and prospects in achieving efficient, stable and selective CO2 photoconversion are pointed out.
TL;DR: In this paper, a layered double hydroxide (Mg-Al LDH) was used as a carrier for Cu-ZnO-ZrO2 to produce a catalyst by co-precipitation.
Abstract: Methanol synthesis via CO2 hydrogenation is an important part of the strategy for generating clean energy as we attempt to reduce our dependency on fossil fuels. Conventional catalysts for this reaction need improvement in their methanol selectivity. In this work, a layered double hydroxide (Mg-Al LDH) was used as a carrier for Cu-ZnO-ZrO2 to produce a catalyst by co-precipitation. From characterization results, CuO-ZnO-ZrO2 nanoparticles were formed and were uniformly dispersed and attached to the surface of LDH. BET surface area and copper dispersion of the catalysts were significantly improved by 4.3 times and 2.9 times, respectively, compared with a reference catalyst without the support. In a catalytic reaction, the catalyst showed dramatic methanol selectivity of 78.3% at 523 K and 3.0 MPa, which is 14.4% higher than the commercial catalyst measured in this investigation and about 50% higher than conventional copper-based catalysts in literatures. It also showed over twice the space time yield based on active metal sites compared to a commercial catalyst in the temperature range 473 K–573 K. Therefore, the prepared catalyst can be efficiently applied at relatively mild reaction temperatures and pressures.
TL;DR: In this paper, the authors reported the highly efficient electrochemical reduction of CO2 to ethanol by using Cu nanoparticles decorated on pyridoxine modification graphene oxide sheets (GO-VB6-Cu) as robust electrocatalysts.
Abstract: Efficient electrochemical reduction of CO2 to ethanol is a promising approach for obtaining high-density renewable energy storage and relieving environment stress. In this paper, we report the highly efficient electrochemical reduction of CO2 to ethanol by using Cu nanoparticles decorated on pyridoxine modification graphene oxide sheets (GO-VB6-Cu) as robust electrocatalysts. CO2 was efficiently reduced to ethanol in 0.1 M KHCO3 solution by using GO-VB6-Cu-2 catalyst at an overpotential as low as 0.140 V. The maximum Faradaic efficiency for ethanol formation of 56.3% was obtained at the potential of −0.250 V vs. the reversible hydrogen electrode. The resultant nanocomposite presented no degradation after approximately 24 h of continuous operation, demonstrating the pronounced stability of the electrode. The notable reactivity toward CO2 reduction achieved here can be ascribed to large electrochemically active surface area, enhanced CO2 adsorption, and low electron transfer resistance.
TL;DR: In this paper, a series of CO2 core flooding tests was carried out on a high-rank bituminous coal core with CO2 injection pressures from 6 to 10 MPa.
Abstract: Enhanced coalbed methane (ECBM) recovery performed by injecting CO2 into coal reservoirs has been found to be a viable option for methane recovery, while CO2 injection into coal seams, especially unmineable ones, has great potential to sequestrate large volumes of CO2 to mitigate greenhouse gas accumulation in the atmosphere. This study was therefore initiated to investigate the effect of CO2 flooding on ECBM recovery and CO2 storage in coal. A series of CO2 core flooding tests was carried out on a high rank bituminous coal core with CO2 injection pressures from 6 to 10 MPa. CO2 injection rate, methane and CO2 production rates, methane displacement efficiency and the volumetric strains of the core were calculated and recorded to enable interpretation of the results. It was observed that, compared with natural methane production in which only around 51.73% of methane is recovered, CO2 injection provides excellent methane displacement efficiency (over 90%), especially for high injection pressures (greater than 8 MPa), which drive methane completely out of the coal sample. Although higher CO2 flooding pressure favours greater CO2 injection rates and methane production rates for any coal types, high rank coal shows faster and greater methane production and CO2 storage capacity. The observed rapid breakthrough of CO2 in the gas produced by elevated CO2 injection, especially for high injection pressures, may complicate the gas separation process. Adsorption-induced volumetric strain is approximately proportional to the CO2 storage capacity in coal which increases with CO2 pressure, and the strain reduces coal permeability and therefore CO2 injectivity and methane production.