CO Conversion Rate Research Articles

Construction of AgBr/BiOBr S-scheme heterojunction using ion exchange strategy for high-efficiency reduction of CO2 to CO under visible light

CO2 reduction via photocatalytic is regarded as the excellent strategy to resolve the severe environmental crisis and energy crisis caused by the accelerated utilization of fossil energy like natural gas, oil, and coal. The Ag ion and the Br ion in BiOBr are creatively used in the ion exchange strategy to form AgBr on the surface of BiOBr, and an S-scheme BiOBr/AgBr heterojunction with close interface contact is constructed. The visible light utilization rate and CO2 conversion rate of the obtained heterojunction are both remarkably improved. The reduction rate of CO2 over the catalyst was tested under visible light using pure water as the liquid environment. As obtained results displayed that the transformation efficiency of BA-1 to CO from CO2 in the visible light was 12.43 μ mol g-1h−1, which is about 3 times that the pristine BiOBr. The intermediates during the reaction were studied using in situ DRIFTS. The process by which CO2 was degraded was speculated based on in situ DRIFTS spectra. In addition, TPR, EIS, and PL measurements indicate that BA-1 has a high solar utilization rate and strong photo-generated carrier transfer and separation capability. This work showed a novel direction for preparation of efficient photocatalyst for CO2 reduction.

Study on CO2 absorption-mineralization characteristics of mixed amine solution coupled with CaO and key influencing factors in mineralization process

Amine CO2 capture is an effective post-combustion carbon capture (PCC) technology, while CO2 mineral carbonation is a safe and stable method for CO2 storage. In this paper, these two methods were combined, and the CO2 absorption-mineralization performance of mixed amine solution coupled with CaO under different ratios of mixed amine solution, temperature, reaction time and CaO addition ratio were studied by using MEA/MDEA mixed amine solution as the CO2 absorbent and using CaO as the CO2 mineralizing raw material. The results show that CaO could effectively mineralize the CO2 absorbed in MEA/MDEA solution, realizing the regeneration of MEA/MDEA solution simultaneously under normal temperature and pressure. Meanwhile, the MEA/MDEA solution can still maintain a high CO2 conversion rate (77.4%) and CO2 cycle loading (1.03 mol/L) after five cycles of absorption-mineralization experiments. The FT-IR and XRD analyses reveal that the addition of CaO makes a large amount of Ca2+ and OH− into the MEA/MDEA solution, which could react with and protonated amine in the solution to form calcium carbonate precipitate and free amine respectively, thus realizing the mineralization of CO2 and the regeneration of MEA/MDEA solution. The main component of solid products obtained is calcium carbonate, and calcite is its main crystal form.

Nature and Dynamic Evolution of Rh Single Atoms Trapped by CeO2 in CO Hydrogenation

Metal single-atom catalysts (SACs) have attracted extensive interest because of their maximum atom efficiency and potentially good performances. However, the understanding of the catalytic behavior and the stability of SACs in high-temperature catalytic reactions remains a major challenge, especially under reducing conditions. In this work, we investigated the nature and stability of Rh/CeO2 SACs with different Rh loadings (0.2–4 wt % Rh) during syngas conversion (260 °C, 2 MPa). Using CO-DRIFTS, we found that atomically dispersed Rh was dispersed on Rh/CeO2 catalysts with an Rh loading up to 3 wt %. The Rh/CeO2 catalysts were stable in H2 up to 350 °C, while Rh nanoclusters were formed in CO at 200 °C. During syngas conversion at 260 °C, the Rh single atoms (Rhiso) on a 0.5 wt % Rh/CeO2 SAC slowly agglomerated to form Rh nanoclusters (RhNC) and a Rhiso/RhNC ratio of ∼1:2.5 was obtained after ∼10 h time-on-stream run. Furthermore, the Rhiso/RhNC ratio did not change with further reaction, indicating that the reaction reached steady state after a 10 h run. After the catalysts reached steady state (∼10 h), the Rhiso/RhNC ratio on the spent Rh/CeO2 catalysts decreased with the increase in Rh loadings, while the reactivity increased first and then decreased. We observed an optimal value of Rhiso/RhNC ≈ 1:3 on the 1 wt % Rh/CeO2 catalyst, showing the maximum reaction rates of CO (rCO) and ethanol selectivity (SEtOH) of 85.8 μmol/s/gRh and 26.2%, respectively. This indicated that the combination of Rh single atoms and Rh nanoclusters is beneficial to the ethanol selectivity and reaction rate, which was confirmed by DFT simulations. Moreover, the ratios of Rhiso/RhNC on the spent catalysts under the steady state have good relationships with the CO conversion rate and product selectivity in the reaction.

Carbon dioxide hydrogenation to methanol: Process simulation and optimization studies

This work investigates process simulation and optimization as an efficient approach to mitigate global warming using carbon dioxide hydrogenation to methanol. Modeling and simulation of hydrogenation to methanol were studied using Aspen Plus V8. Cu/ZnO/Al2O3 catalyst is used to optimize parameters to enhance the reduction of CO2 to methanol. The effect of temperature, pressure, and the feed flow rate on CO2 conversion and CH3OH yield was reported. Response surface methodology (RSM) is used to analyze the chemical equilibrium of the CH3OH production process to obtain an optimal way of assuring a relatively higher CO2 conversion and CH3OH production rate. It helps to evaluate the optimum temperature, pressure, andH2/CO2 molar ratio to achieve maximum CO2 conversion and CH3OH yield. The impact of conversion and CH3OH yield was evaluated using surface plots. The RSM studies show optimized conditions for conversion and CH3OH yield at a temperature of 210 °C, a pressure of 55 bar, and a H2/CO2 concentration of 1:5. The anticipated CO2 conversion and CH3OH yield were 87.56% and 11.22%, respectively, whereas the simulation gave CO2 conversion of 87.65% and CH3OH yield of 11.39%. The generated quadratic model accurately predicts carbon dioxide conversion to methanol. The applicability of the model to forecast CO2 conversion and CH3OH yield is supported by the agreement between the simulated and expected results. This work can be considered a possible solution to overcome the thermodynamic difficulty by providing a higher CO2 conversion and would be beneficial for further investigation in industrial process.

ReaxFF reactive molecular dynamics study on electrochemistry of H2/CO hybrid fuel in Ni/YSZ anode

Fuel flexibility, e.g. using reformate or syngas fuel directly, is one of the most advantages of solid oxide fuel cells (SOFC). However, the electrochemical mechanism of the H2/CO mixture, which is common and key in hydrocarbon fuel-fed SOFC, is unclear and relatively rarely studied at present. This article makes Reactive Force-Field (ReaxFF) reactive molecular dynamics (RMD) simulations on the electrochemical co-oxidation of H2/CO hybrid fuel in Ni (nickel)/YSZ (yttria-stabilized zirconia) anode. The RMD simulations at different fuel gas components show that in the H2/CO/Ni/YSZ system the H2 conversion rate maintains the maximum (100%), and the conversion rate of CO improves compared with that of pure CO fuel in the case of 30%H2−70%CO. Two ways of CO2 generation are found: one is that the CO(Ni) species formed by the adsorption and activation of CO on the Ni surface is oxidized by the lattice oxygen; the other is the oxidation of CO(Ni) by spillover atomic oxygen, which is adsorbed on the Ni surface. It is worth noting that the effect of oxygen vacancies on the oxidation of CO is more significant than that of H2. A viewpoint is proposed to explain how H2 enhances the oxidation of CO. The results help understand the electrochemistry of H2/CO involved fuel in the context of SOFC operations.

CO2 Methanation of Biogas over Ni-Mg-Al: The Effects of Ni Content, Reduction Temperature, and Biogas Composition

Biogas is mainly composed of CH4 and CO2, so it is used as an alternative energy to CH4 with high energy density by separating and removing CO2 from biogas. In addition, it can be utilized by producing synthesis gas (CO and H2) through thermal decomposition of biogas or by synthesizing CH4 by methanation of CO2. The technique of CO2 methanation is a method that can improve the CH4 concentration without CO2 separation. This study aims to produce more efficient methane through CO2 methanation of biogas over Ni-Mg-Al catalyst. So, the effect of Ni contents in catalyst, catalyst reduction temperature, CO2 concentration in biogas, and the initial concentration of CH4 on CO2 conversion rate and CH4 selectivity was investigated. In addition, the effect of increasing CO2 concentration, H2/CO2 ratio, and GHSV (gas space velocity per hour) on H2 conversion, CH4 productivity, and product was investigated. In particular, the durability and stability of CO2 methanation was tested over 60 wt% Ni-Mg-Al catalyst at 350 °C and 30,000/h for 130 h. From the long-term test results, the catalyst shows stability by maintaining a constant CO2 conversion rate of 72% and a CH4 selectivity of 95%.

Highly Efficient ZIF-67-Derived PtCo Alloy–CN Interface for Low-Temperature Aqueous-Phase Fischer–Tropsch Synthesis

Designing new materials for selective Fischer–Tropsch synthesis (FTS) is an elegant way to enhance local feedstock utilization like biomass and waste. In this approach, we have designed a thermally and chemically stable bimetallic PtCo/NC hybrid nanocomposite catalyst derived from a zeolitic imidazolate framework (ZIF-67, which contains cobalt as a metal center) through carbonization for low-temperature (413–473 K) aqueous-phase Fischer–Tropsch synthesis (AFTS). The selectivity of the desired range of hydrocarbons is adjusted using a highly dispersed PtCo bimetallic alloy, which facilitates extraordinary reduction of a metal oxide to active species by the synergic effect under the AFTS reaction conditions. The ZIF-derived catalyst tested in this study exhibited the highest activity to date for very low temperatures (433 K) in aqueous-phase Fischer–Tropsch synthesis with CO conversion rates between 0.61 and 1.20 molCO·molCo–1·h–1. Insights of the remarkable catalyst activity were examined by in situ X-ray photoelectron spectroscopy (XPS) studies corroborated by density functional theory (DFT) calculation. The bimetallic Co3Pt (111) surface was found to be highly active for the C–C coupling reaction between surface-adsorbed C and CO, forming a CCO intermediate with a very low activation barrier (Ea = 0.37 eV), in comparison to the C–C coupling activation barrier obtained over the Co (111) surface (Ea = 0.87 eV). This unique approach and observations create a new path for developing next-generation advanced catalyst systems and processes for selective low-temperature FTS.

Single‐Atom Molybdenum‐N3 Sites for Selective Hydrogenation of CO2 to CO

AbstractThe design of efficient non‐noble metal catalysts for CO2 hydrogenation to fuels and chemicals is desired yet remains a challenge. Herein, we report that single Mo atoms with a MoN3 (pyrrolic) moiety enable remarkable CO2 adsorption and hydrogenation to CO, as predicted by density functional theory studies and evidenced by a high and stable conversion of CO2 reaching about 30.4 % with a CO selectivity of almost 100 % at 500 °C and very low H2 partial pressure. Atomically dispersed MoN3 is calculated to facilitate CO2 activation and reduces CO2 to CO* via the direct dissociation path. Furthermore, the highest transition state energy in CO formation is 0.82 eV, which is substantially lower than that of CH4 formation (2.16 eV) and accounts for the dominant yield of CO. The enhanced catalytic performances of Mo/NC originate from facile CO desorption with the help of dispersed Mo on nitrogen‐doped carbon (Mo/NC), and in the absence of Mo nanoparticles. The resulting catalyst preserves good stability without degradation of CO2 conversion rate even after 68 hours of continuous reaction. This finding provides a promising route for the construction of highly active, selective, and robust single‐atom non‐precious metal catalysts for reverse water–gas shift reaction.

Single-Atom Molybdenum-N3 Sites for Selective Hydrogenation of CO2 to CO.

The design of efficient non-noble metal catalysts for CO2 hydrogenation to fuels and chemicals is desired yet remains a challenge. Herein, we report that single Mo atoms with a MoN3 (pyrrolic) moiety enable remarkable CO2 adsorption and hydrogenation to CO, as predicted by density functional theory studies and evidenced by a high and stable conversion of CO2 reaching about 30.4 % with a CO selectivity of almost 100 % at 500 °C and very low H2 partial pressure. Atomically dispersed MoN3 is calculated to facilitate CO2 activation and reduces CO2 to CO* via the direct dissociation path. Furthermore, the highest transition state energy in CO formation is 0.82 eV, which is substantially lower than that of CH4 formation (2.16 eV) and accounts for the dominant yield of CO. The enhanced catalytic performances of Mo/NC originate from facile CO desorption with the help of dispersed Mo on nitrogen-doped carbon (Mo/NC), and in the absence of Mo nanoparticles. The resulting catalyst preserves good stability without degradation of CO2 conversion rate even after 68 hours of continuous reaction. This finding provides a promising route for the construction of highly active, selective, and robust single-atom non-precious metal catalysts for reverse water-gas shift reaction.

Heterogeneous Catalysis for CO2 Conversion into Chemicals and Fuels

Catalytic conversion of CO2 into chemicals and fuels is a viable method to reduce carbon emissions and achieve carbon neutrality. Through thermal catalysis, electrocatalysis, and photo(electro)catalysis, CO2 can be converted into a wide range of valuable products, including CO, formic acid, methanol, methane, ethanol, acetic acid, propanol, light olefins, aromatics, and gasoline, as well as fine chemicals. In this mini-review, we summarize the recent progress in heterogeneous catalysis for CO2 conversion into chemicals and fuels and highlight some representative studies of different conversion routes. The structure–performance correlations of typical catalytic materials used for the CO2 conversion reactions have been revealed by combining advanced in situ/operando spectroscopy and microscopy characterizations and density functional theory calculations. Catalytic selectivity toward a single CO2 reduction product/fraction should be further improved at an industrially relevant CO2 conversion rate with considerable stability in the future.Graphical

CO2 Activation and Hydrogenation on Cu-ZnO/Al2O3 Nanorod Catalysts: An In Situ FTIR Study

CuZnO/Al2O3 is the industrial catalyst used for methanol synthesis from syngas (CO + H2) and is also promising for the hydrogenation of CO2 to methanol. In this work, we synthesized Al2O3 nanorods (n-Al2O3) and impregnated them with the CuZnO component. The catalysts were evaluated for the hydrogenation of CO2 to methanol in a fixed-bed reactor. The support and the catalysts were characterized, including via in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The study of the CO2 adsorption, activation, and hydrogenation using in situ DRIFT spectroscopy revealed the different roles of the catalyst components. CO2 mainly adsorbed on the n-Al2O3 support, forming carbonate species. Cu was found to facilitate H2 dissociation and further reacted with the adsorbed carbonates on the n-Al2O3 support, transforming them to formate or additional intermediates. Like the n-Al2O3 support, the ZnO component contributed to improving the CO2 adsorption, facilitating the formation of more carbonate species on the catalyst surface and enhancing the efficiency of the CO2 activation and hydrogenation into methanol. The synergistic interaction between Cu and ZnO was found to be essential to increase the space–time yield (STY) of methanol but not to improve the selectivity. The 3% CuZnO/n-Al2O3 displayed improved catalytic performance compared to 3% Cu/n-Al2O3, reaching a CO2 conversion rate of 19.8% and methanol STY rate of 1.31 mmolgcat−1h−1 at 300 °C. This study provides fundamental and new insights into the distinctive roles of the different components of commercial methanol synthesis catalysts.

Pulsed electrolysis of carbon dioxide by large‐scale solid oxide electrolytic cells for intermittent renewable energy storage

AbstractCO2 electrolysis with solid oxide electrolytic cells (SOECs) using intermittently available renewable energy has potential applications for carbon neutrality and energy storage. In this study, a pulsed current strategy is used to replicate intermittent energy availability, and the stability and conversion rate of the cyclic operation by a large‐scale flat‐tube SOEC are studied. One hundred cycles under pulsed current ranging from −100 to −300 mA/cm2 with a total operating time of about 800 h were carried out. The results show that after 100 cycles, the cell voltage attenuates by 0.041%/cycle in the high current stage of −300 mA/cm2, indicating that the lifetime of the cell can reach up to about 500 cycles. The total CO2 conversion rate reached 52%, which is close to the theoretical value of 54.3% at −300 mA/cm2, and the calculated efficiency approached 98.2%, assuming heat recycling. This study illustrates the significant advantages of SOEC in efficient electrochemical energy conversion, carbon emission mitigation, and seasonal energy storage.

Precise Modulation of Triple‐Phase Boundaries towards a Highly Functional Exsolved Catalyst for Dry Reforming of Methane under a Dilution‐Free System

AbstractDry reforming of methane (DRM) has been emerging as a viable solution to achieving carbon neutrality enhanced by the Paris Agreement as it converts the greenhouse gases of CO2 and CH4 into industrially useful syngas. However, there have been limited studies on the DRM catalyst under mild operating conditions with a high dilution gas ratio due to their deactivation from carbon coking and metal sintering. Herein, we apply the triple‐phase boundary (TPB) concept to DRM catalyst via exsolution phenomenon that can secure elongated TPB by controlling the Fe‐doping ratio in perovskite oxide. Remarkably, the exsolved catalyst with prolongated TPB shows exceptional CO2 and CH4 conversion rates of 95.9 % and 91.6 %, respectively, stable for 1000 hours under a dilution‐free system. DFT calculations confirm that the Lewis acid of support and Lewis base of metal at the TPB promote the adsorption of reactants, resulting in lowering the overall CO2 dissociation and CH4 dehydrogenation energy.

Investigation of La0.6Sr0.4Co1-xNixO3-δ (x=0, 0.2, 0.4, 0.6, 0.8) catalysts on solid oxide fuel cells anode for biogas dry reforming

The introduction of catalyst on anode of solid oxide fuel cell (SOFC) has been an effective way to alleviate the carbon deposition when utilizing biogas as the fuel. A series of La0.6Sr0.4Co1-xNixO3-δ (x = 0, 0.2, 0.4, 0.6, 0.8) oxides are synthesized by sol-gel method and used as catalysts precursors for biogas dry reforming. The phase structure of La0.6Sr0.4Co1-xNixO3-δ oxides before and after reduction are characterized by X-ray diffraction (XRD). The texture properties, carbon deposition, CH4 and CO2 conversion rate of La0.6Sr0.4Co1-xNixO3-δ catalysts are evaluated and compared. The peak power density of 739 mW cm−2 is obtained by a commercial SOFC with La0.6Sr0.4Co0.4Ni0.6O3-δ catalyst at 850 °C when using a mixture of CH4: CO2 = 2:1 as fuel. This shows a great improvement from the cell without catalyst for internal dry reforming, which is attributed to the formation of NiCo alloy active species after reduction in H2 atmosphere. The results indicate the benefits of inhibiting the carbon deposition on Ni-based anode through introducing the La0.6Sr0.4Co0.4Ni0.6O3-δ catalyst precursor. Additionally, the dry reforming technology will also help to convert part of the exhaust heat into chemical energy and improve the efficiency of SOFC system with biogas fuel.

Ni/support-CaO bifunctional combined materials for integrated CO2 capture and reverse water-gas shift reaction: Influence of different supports

Integrated CO2 capture and utilisation (ICCU) is a promising strategy for restricting carbon emissions and achieving carbon neutrality. Bifunctional combined materials (BCMs), containing adsorbents and active catalysts, are widely applied in this process. Producing syngas via reverse water–gas shift reaction (RWGS) and integrating with Fischer-Tropsch (F-T) synthesis is an attractive and valuable CO2 utilisation route. This work investigated a series of Ni/support-CaO BCMs (supports = ZrO2, TiO2, CeO2 and Al2O3) for the integrated CO2 capture and RWGS (ICCU-RWGS) process. The Ni/support-CaO BCMs were prepared by physically mixing various metal oxide supports loaded Ni with sol–gel derived CaO. The ICCU-RWGS performance (CO2 conversion, CO yield and CO generation rate) of these BCMs followed the order during tested conditions (550–750 °C): Ni/CeO2-CaO > Ni/TiO2-CaO > Ni/ZrO2-CaO > Ni/Al2O3-CaO. A comprehensive characterisation of Ni/support materials showed that Ni/CeO2 had the characteristics of stronger basicity, optimal Ni dispersion and improved NiO reducibility, which led to the outperforming ICCU-RWGS activity over Ni/CeO2-CaO (e.g. 56.1% CO2 conversion, 2.68 mmol g−1 CO yield and ∼100% CO selectivity at 650 °C). Furthermore, the Ni/CeO2-CaO BCM showed a stable, yet, self-optimising catalytic performance during the cyclic ICCU-RWGS reaction over 20 cycles. The TEM characterisation suggested that was ascribed to the volume expansion and shrinkage of CaO in the cyclic adsorption–desorption altering the distance between the adsorbent and Ni/CeO2, resulting in an enhanced CO2 conversion during the cycle.

Effective CO2 methanation at ambient pressure over Lanthanides (La/Ce/Pr/Sm) modified cobalt-palygorskite composites

Hear a series of Lanthanide-modified cobalt-palygorskite composite (LnCoPal, LnLa/Ce/Pr/Sm) for CO2 methanation reaction under atmospheric pressure were prepared by a simple impregnation method. The results showed that the PrCoPal catalyst showed fairly good activity for CO2 methanation, the CO2 conversion rate was 68.05% and the CH4 selectivity was 95.0% at 425 °C and atmospheric pressure (GHSV=15,000). The improved catalytic performance for the PrCoPal composite materials, compared to the other elements doped samples, was attributed to the incorporation of the Pr elements into the Co/Pal system, which enhanced the metal-support interaction between Co and palygorskite (Pal), improved the dispersibility of Co particles on Pal, refined Co particles, and increased catalytically active sites on the surface of the catalyst. The surface modification with a small amount of lanthanides slightly increased the surface alkalinity, enhanced the adsorption of CO2, and improved the overall catalytic performance.

Dopant induced modification of support-surface structure for high throughput conversion of CO in aqueous media

The paper addresses the structural and catalytic influence of different modifiers on mesoporous TiO2 loaded with Co, Mn, and Pt for aqueous phase Fischer-Tropsch synthesis (AFTS). The catalysts were synthesized in a two-step method; first, the modified TiO2 was prepared by the revised sol–gel method using different precursors of metal oxide. Then the metal precursors were loaded on the modified support using a mechanochemical procedure, a top-down approach. The quick high yield at room temperature without using any organic or inorganic solvent makes this synthesis procedure efficient. The synthesized catalysts were characterized with different techniques, including XRD, BET, XPS, TEM, HRTEM, H2, CO, CO2, NH3-TPD, etc. Under the identical reaction conditions, the rate of CO conversion under aqueous reaction medium follows the trend SiO2 > ZrO2 > TiO2 > Al2O3 > ZnO > MgO for modified TiO2, whereas the selectivity of C5+ hydrocarbons follow SiO2 > ZnO > MgO > TiO2 > Al2O3 > ZrO2 trend at 453 K and 3 MPa pressure. Based on the results obtained, we found that a balanced surface acidity to basicity ratio plays an important role in the activation of CO, followed by its hydrogenation. Moreover, the DFT results show that the CO conversion and hydrogenation are linearly correlated to the CO* + H* adsorption energy over the catalyst surface. Despite the aqueous phase, the rate of CO conversion for Si-Ti catalyst is kinetically determined using different Fischer-Tropsch empirical kinetic models, with negligible dependency on the partial water pressure term.

Improved Photocatalytic Activities of g-C3N4 Nanosheets by B Doping and Ru-Oxo Cluster Modification for CO2 Conversion

g-C3N4 is a promising photocatalyst for CO2 conversion owing to its outstanding reduction potential. However, its shallow valence band position and sluggish water oxidation reaction restrict the overall CO2 photoreduction process. Herein, g-C3N4 nanosheets are first doped with B through thermal treatment of mixed NaBH4 and subsequently modified with highly dispersed Ru-oxo clusters by using tailored chitosan oligomers. The optimal Ru-oxo modified B-doped g-C3N4 exhibits an exceptional photocatalytic CO2 conversion rate with 22-fold improvement compared with pristine CN. Based on the results of electron paramagnetic resonance, atmosphere-controlled surface photovoltage spectroscopy, in situ diffuse reflectance infrared Fourier transform spectroscopy, etc., it is confirmed that the improved photoactivities are attributed to the downward shift of the valence band to obtain the strong driving force for water oxidation along with extension of the visible light response region by B doping and to the capture of photogenerated holes to enhance charge separation and then to accelerate the water oxidation process from the modified Ru-oxo clusters.

Data Analysis in Green Industrial Processes with Modified Chemical Efficiency and Environmental Impact: Smart Urea Production and CO2 Removal

Agriculture can benefit from urea fertilizer because it contains a lot of nitrogen at a reasonable cost. Urea fertilizer can be stored easily and does not pose a fire hazard over time. Due to its acidifying properties, urea fertilizer is an ideal fertilizer for many plants. Input and feed of the urea unit are taken from the output of the ammonia unit (CO2 and NH3). Hence, in this study, two methods of CO2 recovery from combustion gases and CO2 recycling in ammonia units will be used to increase urea production to realize low-carbon and industrial systems (including green agriculture). CO2 recovery also reduces environmental pollution, which is a very important factor in sustainable cities and societies. The results showed that CO reduction increases the overall efficiency compared to the data reported in the world for the same process, which is due to the reduction of CO input to methanize. Collecting information around the globe for constructing the same green system considering various conditions in each environment makes complicated situations in terms of how to design the process and the observed outcomes. However, we could find a new smart design to build the green system in our case study where it is completely acceptable compared to the same systems’ outputs. The obtained results indicate that the temperature of the shift reactor can be brought closer to 365°C without reducing the selectivity of the catalysts, which in turn would increase the CO conversion rate, the CO2 output, and the overall efficiency of the unit. Finally, it is shown that the rate of CO escape from shift reactors is decreased.

Hydrotalcite-derived Ni-LDO catalysts via new approach for enhanced performances in CO2 catalytic reduction

In this work, hydrotalcite-derived new Ni-LDO catalysts were synthesized via sequenced precipitation, for CO2 catalytic reduction to synthetic natural gas (SNG) with high performances, while the traditional sample via coprecipitation was prepared and measured as the comparison. By regulating precipitation procedure, a significant performance enhancement was attained, in which the CO2 conversion rate per gram nickel was 7-times higher than that of the conventional comparison, at the temperature of 573 K and atmospheric pressure. In addition, the desired product selectivity is up to 99%. Structural characterizations proved that the as-synthesized catalysts showed layered meso-porous properties. An increasing Ni particle size and higher coverage of medium-strong basic sites was observed over the optimized catalyst sample prepared when part of Mg2+ and Al3+ were precipitated at first step. Catalyst surface nickel enrichment and promoted reducibility were also achieved when using sequenced precipitation. This work achievements provided a new route for surface nickel enrichment of much more active hydrotalcite-derived Ni-LDO layered catalysts for enhanced performances.