C2 Yield Research Articles

Intrinsic reactivity of stoichiometric IrO2(1 1 0) surface toward oxidative coupling of methane

This study investigates the oxidative coupling of methane on the IrO2(110) surface using TPRS simulations informed by DFT-derived data. We discover that the efficiency of the IrO2(110) surface in generating ethylene is strongly influenced by methane surface coverage. Our simulations reveal that the presence of surface hydroxyl group enhances the yield of C2+ species from methane oxidation, but this effect is counteracted at high methane coverages due to the accelerated formation of CH2OH. In addition, the study reveals that slight modifications in energy barriers at the branching point (C2H4 formation vs. CH2OH formation) significantly affect C2H4(g) production from the simulation, underscoring the importance of precise energetic data for accurate catalytic reaction predictions. The results have broader implications for reactions and catalysts where branching point selectivity determines high-value product yields. Thus, combining surface science with computational analysis is crucial for accurately determining energy profiles of key steps at the branching points.

Effective enhancement of the ability of Monascus pilosus to produce lipid-lowering compound Monacolin K via perturbation of metabolic flux and histone acetylation modification

Monacolin K (MK), also known as lovastatin, is a polyketide compound with the ability to reduce plasma cholesterol levels and many other bio-activities. Red yeast rice (also named Hongqu) rich in MK derived from Monascus fermentation has attracted widespread attention due to its excellent performance in reducing blood lipids. However, industrial Monascus fermentation suffers from the limitations such as low yield of MK, long fermentation period, and susceptibility to contamination. In this study, we firstly blocked the competitive pathway of MK biosynthesis to create polyketide synthase gene pigA (the key gene responsible for the biosynthesis of Monascus azaphilone pigments) deficient strain A1. Then, based on the strategies to increase precursor supply for MK biosynthesis, acetyl-CoA carboxylase gene acc overexpression strains C1 and C2 were constructed with WT and A1 as the parent, respectively. Finally, histone deacetylase gene hos2 overexpression strain H1 was constructed by perturbation of histone acetylation modification. HPLC detection revealed all these four strains significantly increased their abilities to produce MK. After 14 days of solid-state fermentation, the MK yields of strains A1, C1, C2, and H1 reached 2.03 g/100 g, 1.81 g/100 g, 2.45 g/100 g and 2.52 g/100 g, which increased by 28.5 %, 14.7 %, 43.9 % and 36.1 % compared to WT, respectively. RT-qPCR results showed that overexpression of hos2 significantly increased the expression level of almost all genes responsible for MK biosynthesis after 5-day growth. Overall, the abilities of these strains to produce MK has been greatly improved, and MK production period has been shortened to 14 days from 20 days, providing new approaches for efficient production of Hongqu rich in MK.

Breakthrough in CO2 Electroreduction to Multi‐Carbon Products at Ampere‐Level Enabled by Active Sites Engineering

AbstractEfficient production of value‐added chemicals with high selectivity from CO2 electroreduction at industrial‐level current density is highly demanded, yet remains a big challenge. In a recent issue of Angewandte Chemie, Han and colleagues have elegantly increased the Faradaic efficiency (FE) of multi‐carbon (C2+) products to over 70 % at amperes level (1.4 A cm−2) by engineering the active sites for the key reactions involved in the CO2 electroreduction. In this study, the highly dispersed Pd atoms have two unique functions: active sites for water dissociation and to induce the electron rearrangement of the surrounding Cu atoms to form new active sites for CO conversion, while the Cu far from Pd are the active sites for efficient CO2 conversion to CO, the synergistic functions of these three active sites result in high FE and yields of C2+ products at industrial‐level current density. This research is a remarkable step forward in the methodology for developing efficient and durable catalysts for CO2 electroreduction and beyond.

Influence of the La/Ce ratio on La-Ce oxides promoted by Sr in the methane oxidative coupling reaction

The high methane availability and its significant role as a greenhouse gas have led the scientific community to pursue methods for its use. This paper proposes the usage of the oxidative coupling of methane (OCM) as a promising path to transform methane directly into value-added hydrocarbons, mostly ethylene, which serves as a crucial compound in the petrochemical sector. An efficient OCM catalyst should contain substantial basicity and oxygen vacancies for providing surface electrophilic oxygen species, such as superoxides and peroxides, instrumental for boosting selectivity towards C2 products. Mixed lanthanum-cerium oxide (La-Ce) catalysts have emerged as strong candidates in OCM due to their high thermal stability, oxygen mobility, and high alkalinity. In this study, they were prepared through a surfactant-assisted hydrothermal method with different La/Ce ratios for fine-tuning their basic properties and promoting oxygen mobility on the surface of the catalysts. Samples followed a volcano-shaped relationship between C2 yield and La content, with optimal performance at a La/Ce molar ratio of 2.1, attributed to the interplay between the high amount of basic sites and oxygen vacancies, increasing the presence of superoxide species over lattice oxygen. Moreover, the Sr-promoted catalyst showed high density of strong basic sites while preserving the reactive oxygen species, achieving 20 % CH4 conversion, with 57 % C2 compounds selectivity at 750 °C and GHSV of 18.000 mL.gcat−1.h−1.

Selective CO2 Electroreduction to Multi-Carbon Products on Organic-Functionalized CuO Nanoparticles by Local Micro-Environment Modulation

HighlightsDeveloping surface-functionalized catalysts with exceptional activity and selectivity for the electrocatalytic CO2RR to C2+ products under neutral electrolyte.A remarkable C2+ FE of nearly 90% at an unprecedented current density of 300 mA cm−2 and maintain high FE (> 80%) at the wide current density performance (100–600 mA cm−2) in neutral environments using a flow cell as well as MEA electrolyzer.Mechanical study reveals that reducing the coverage of coordinated K·H2O water increased the probability of intermediate reactants (CO) interacting with the surface, thereby promoting efficient C–C coupling and enhancing the yield of C2+ products.

Compressive strain in Cu catalysts: Enhancing generation of C2+ products in electrochemical CO2 reduction

Elastic strain in Cu catalysts enhances their selectivity for the electrochemical CO2 reduction reaction (eCO2RR), particularly toward the formation of multicarbon (C2+) products. However, the reasons for this selectivity and the effect of catalyst precursors have not yet been clarified. Hence, we employed a redox strategy to induce strain on the surface of Cu nanocrystals. Oxidative transformation was employed to convert Cu nanocrystals to CuxO nanocrystals; these were subsequently electrochemically reduced to form Cu catalysts, while maintaining their compressive strain. Using a flow cell configuration, a current density of 1 A/cm2 and Faradaic efficiency exceeding 80% were realized for the C2+ products. The selectivity ratio of C2+/C1 was also remarkable at 9.9, surpassing that observed for the Cu catalyst under tensile strain by approximately 7.6 times. In-situ Raman and infrared spectroscopy revealed a decrease in the coverage of K+ ion-hydrated water (K·H2O) on the compressively strained Cu catalysts, consistent with molecular dynamics simulations and density functional theory calculations. Finite element method simulations confirmed that reducing the coverage of coordinated K·H2O water increased the probability of intermediate reactants interacting with the surface, thereby promoting efficient C–C coupling and enhancing the yield of C2+ products. These findings provide valuable insights into targeted design strategies for Cu catalysts used in the eCO2RR.

Unique CuOx–FeOx interfaces in Cu-decorated Fe-based catalysts facilitating CO2 hydrogenation to higher hydrocarbons

Currently, research on iron-based catalysts applied in CO2 hydrogenation to higher hydrocarbon products (C2+), especially light olefins, has gained significant attention. However, a comprehensive understanding of the synergy between active Fe-containing species and promoters on their catalytic performances is still lacking. In this study, ZrO2-supported Cu-decorated iron catalysts were constructed through the coprecipitation with the aid of a microliquid-film reactor and evaluated in CO2 hydrogenation. It was shown that the incorporation of a small amount of Cu promoted the reduction of Fe species and facilitated the formation of surface defective Fe3O4 (FeOx) component containing a large number of oxygen vacancies and thus highly dispersed surface CuOx/FeOx structures. Notably, the 2.0 wt% Cu-incorporated Fe-based catalyst exhibited superior performance, along with high selectivity to C2+ products (77.1 %) and yield of C2+ products (27.3 %) under reaction conditions (i.e., 4800 mL·gcat-1·h−1, 2.0 MPa, and 320 ℃), outperforming the current state-of-the-art Fe-based catalysts. Through a combination of comprehensive structural characterizations and density functional theory calculations with reaction results, it was unveiled that surface FeOx favored CO2 adsorption and H2 dissociation, and meanwhile, CuOx component with high Cu+ fractions adjacent to FeOx on Cu-decorated Fe-based catalysts also could remarkably promote H2 dissociation and the adsorption of CO2 and CO intermediate. Therefore, such-generated unique CuOx–FeOx interfaces in Fe-based catalysts could facilitate the generation of adsorbed adjacent CHx species through both the hydrogen-assisted indirect dissociation pathway of CO intermediate and the formate intermediate pathway, thus promoting CO2 hydrogenation to higher hydrocarbons. This work affords a promising strategy for the construction of Fe-based based catalysts to boost CO2 hydrogenation to higher hydrocarbon products and a deep understanding of the role of CuOx–FeOx interfaces in CO2 hydrogenation.

Oxidative conversion of methane: maximizing the carbon yield in natural gas valorization via the C123 process

The Oxidative Conversion of Methane (OCoM) reactor, within the C123 process, is a novel concept for methane valorization into a product stream with a molar C2H4/CO/H2 composition of 1/1/1, i.e., suitable for further hydroformylation. This overcomes the limitations traditionally encountered during the Oxidative Coupling of Methane in the pursuit of a maximum ethylene yield. An experimental assessment was performed using a MnNaW/SiO2 catalyst under industrially relevant conditions (T=850°C, ptot=100 kPa, Wcat/FCH4,in = 2–2.5 kgcat s mol-1, CH4/O2 inlet molar ratio = 3 – 5 mol mol-1 and inlet CO2 molar fraction <20%) as a basis for kinetic model development. Simultaneously pursuing a C2H4/CO/H2 molar ratio of 1/1/1 and a maximum C2 yield, the impact of the operating conditions on the OCoM performance was simulated. Three different real feedstocks were assessed: natural gas, shale gas and biogas. Shale gas exhibited the highest OCoM potential, with as optimal operating conditions T=850°C, Wcat/FCH4,in = 6.5 kgcat s mol-1, CH4/O2 inlet molar ratio = 10 mol mol-1. The achieved C2H4/CO/H2 molar ratio amounted to 1/1.1/3.7 with a carbon yield (ethylene + CO) of 28% mol mol-1 and ethylene yield of 19% mol mol-1. Last, the considerations to validate the C123 process viability are given.

Coprecipitation preparation of copper -cobalt based catalysts for higher alcohol production

A series of K modified coppercobalt based catalysts were prepared using step by step continuous coprecipitation method, and the catalytic performance of the catalysts was investigated. The experimental results showed that the catalyst exhibited the best activity, CO conversion, the yield of C₂+OH in liquid products and the mass fraction of C₂+OH was 65.74%,0.062 g·(mL·h)-I and 18.95%, respectively, under the condition as follows: mass ratio of cobalt to copper 1:1, K₂CO₃ loading mass fraction 1%, pH=7.2 and reaction temperature 310 ℃.

Model-based catalyst screening and optimal experimental design for the oxidative coupling of methane

The oxidative coupling of methane (OCM) to produce ethane and ethylene (C2 compounds) as platform chemicals involves complex chemistry with reactions both in the gas phase and on the catalyst surface, resulting in a distribution of products at the expense of C2 selectivity. This work uses experimental data from a variety of mixed metal oxides on supports at different reaction conditions (temperature, contact time, and reactant flow rates) to train a random forest regressor that predicts methane conversion and C2 selectivity (key performance indicators (KPIs)). The kinetically validated random forest models are deployed to locate optimal conditions that maximize C2 yield for each of the catalysts. Investigating the regressor interpretability via feature importance reveals that the choice of metals and support are crucial to C2 selectivity predictions in addition to the reaction conditions, while the predictions of methane conversion are largely governed by the reaction conditions. The machine learning (ML) regressor is used as a kinetic surrogate to find a locus of optimal reaction conditions that maximize both selectivity-conversion for each of the catalysts via a multi-objective optimization routine. The maximum C2 yields for catalysts are projected to be improved by 15% on average. Analyzing the catalysts with respect to a popular OCM catalyst, Mn-Na2WO4/SiO2, using the optimal locus eliminates variability in the process conditions to reveal distinct patterns based on intrinsic properties of metals and supports. Further, the decision space with catalyst descriptors and reaction conditions is optimized for high C2 yields using the ML surrogate, in a static multi-objective optimization routine, and an adaptive Bayesian routine, where the latter was found to have a wider field focus in proposing catalyst formulations and reaction conditions. Transition metal oxides on a variety of supports were proposed but not their lanthanide oxide counterparts. The framework has the potential to lend itself to materials acceleration platforms where it is crucial to consider multi-scale phenomena that impact downstream KPIs.

Breakthrough in CO2 Electroreduction to Multi-Carbon Products at Ampere-Level Enabled by Active Sites Engineering.

Efficient production of value-added chemicals with high selectivity from CO2 electroreduction at industrial-level current density is highly demanded, yet remains a big challenge. In a recent issue of Angewandte Chemie, Han and colleagues have elegantly increased the Faradaic efficiency (FE) of multi-carbon (C2+) products to over 70 % at amperes level (1.4 A cm-2) by engineering the active sites for the key reactions involved in the CO2 electroreduction. In this study, the highly dispersed Pd atoms have two unique functions: active sites for water dissociation and to induce the electron rearrangement of the surrounding Cu atoms to form new active sites for CO conversion, while the Cu far from Pd are the active sites for efficient CO2 conversion to CO, the synergistic functions of these three active sites result in high FE and yields of C2+ products at industrial-level current density. This research is a remarkable step forward in the methodology for developing efficient and durable catalysts for CO2 electroreduction and beyond.

Deciphering the structural evolution and real active ingredients of iron oxides in photocatalytic CO2 hydrogenation

Photocatalytic CO2 hydrogenation reactions can produce high-value-added chemicals for industry, solving the environmental problems caused by excessive CO2 emissions. Iron oxides are commonly used in photocatalytic reactions due to their various structures and suitable band gaps. Nevertheless, the structural evolution and real active components during photocatalytic CO2 hydrogenation reaction are rarely studied. Herein, a variety of iron oxides including α-Fe2O3, γ-Fe2O3, Fe3O4 and FeO were derived from Prussian blue precursors to investigate the CO2 hydrogenation performance, structural evolution and active components. Especially, the typical α- and γ-Fe2O3 are converted to Fe3O4 during the reaction, while Fe/FexOy remains structurally stable. Meanwhile, it is confirmed that Fe3O4 is the main active component for CO production and the formation of hydrocarbons (CH4 and C2–C4) are highly dependent on the Fe/FexOy heterojunctions. The optimal yields of CO, CH4 and C2–C4 hydrocarbons over the best catalyst (FeFe-550) can achieve 4 mmol g−1 h−1, 350 μmol g−1 h−1 and 150 μmol g−1 h−1, respectively due to their suitable metal/oxide component distribution. This work examines the structural evolution of different iron oxide catalysts in the photocatalytic CO2 hydrogenation reaction, identifies the active components as well as reveals the relationship between components and the products, and offers valuable insights into the efficient utilization of CO2.

Enhanced Proximity of Rh1,2‐Rhn Ensembles Encaged in UiO‐67 Boosting Catalytic Conversion of Syngas to Oxygenates

AbstractMaintaining high conversion under the premise of high oxygenates selectivity in syngas conversion is important but a formidable challenge in Rh catalysis. Monometallic Rh catalysts provide poor oxygenate conversion efficiency, and efforts have been focused on constructing adjacent polymetallic sites; however, the one‐pass yields of C2+ oxygenates over the reported Rh‐based catalysts were mostly &lt;20 %. In this study, we constructed a monometallic Rh catalyst encapsulated in UiO‐67 (Rh/UiO‐67) with enhanced proximity to dual‐site Rh1,2‐Rhn ensembles. Unexpectedly, this catalyst exhibited high efficacy for oxygenate synthesis from syngas, giving a high oxygenate selectivity of 72.0 % with a remarkable CO conversion of 50.4 %, and the one‐pass yield of C2+ oxygenates exceeded 25 %. The state‐of‐the‐art characterizations further revealed the spontaneous formation of an ensemble of Rh single atoms/dimers (Rh1,2) in the proximity of ultrasmall Rh clusters (Rhn) confined within the nanocavity of UiO‐67, providing adjacent Rh+‐Rh0 dual sites dynamically during the reaction that promote the relay of the undissociated CHO species to the CHx species. Thus, our results open a new route for designing highly efficient Rh catalysts for the conversion of syngas to oxygenates by precisely tuning the ensemble and proximity of the dual active sites in a confined space.

Enhanced Proximity of Rh1,2-Rhn Ensembles Encaged in UiO-67 Boosting Catalytic Conversion of Syngas to Oxygenates.

Maintaining high conversion under the premise of high oxygenates selectivity in syngas conversion is important but a formidable challenge in Rh catalysis. Monometallic Rh catalysts provide poor oxygenate conversion efficiency, and efforts have been focused on constructing adjacent polymetallic sites; however, the one-pass yields of C2+ oxygenates over the reported Rh-based catalysts were mostly <20 %. In this study, we constructed a monometallic Rh catalyst encapsulated in UiO-67 (Rh/UiO-67) with enhanced proximity to dual-site Rh1,2-Rhn ensembles. Unexpectedly, this catalyst exhibited high efficacy for oxygenate synthesis from syngas, giving a high oxygenate selectivity of 72.0 % with a remarkable CO conversion of 50.4 %, and the one-pass yield of C2+ oxygenates exceeded 25 %. The state-of-the-art characterizations further revealed the spontaneous formation of an ensemble of Rh single atoms/dimers (Rh1,2) in the proximity of ultrasmall Rh clusters (Rhn) confined within the nanocavity of UiO-67, providing adjacent Rh+-Rh0 dual sites dynamically during the reaction that promote the relay of the undissociated CHO species to the CHx species. Thus, our results open a new route for designing highly efficient Rh catalysts for the conversion of syngas to oxygenates by precisely tuning the ensemble and proximity of the dual active sites in a confined space.

The investigation of oxygen species in silicalite-1 supported MnOx-Na2WO4 catalyst towards efficient oxidative coupling of methane

The oxidative coupling of methane (OCM) as a promising single-step method towards olefins has attracted significant attention in efficient methane conversion and utilization. Here, we report a promising porous MnOx-Na2WO4/S-1 catalyst. The microporous silicalite-1 support ensures a uniform distribution of the elements Na, W and Mn on the catalyst surface, resulting in more active sites. In addition, the catalyst with weakly bonded and easily reduced lattice oxygen favors the generation of oxygen defect sites on the MnOx, further promoting the formation of electrophilic species (peroxide and superoxide). Hence, a high ratio of (O2- + O-)/O2- was achieved to boost the OCM performance. Furthermore, the MnOx-Na2WO4 catalyst supported by S-1 exhibited the ability to inhibit the loss of active components. As a result, an excellent C2 yield of 24.2% was achieved at 760 ℃ for OCM, accompanied by 43.1% CH4 conversion and 56.2% C2 selectivity. Moreover, the catalyst exhibited excellent stability without any deactivation in 50 hours.

Effect of operating conditions on the performance of riser reactor for oxidative coupling of methane

Oxidative coupling of methane (OCM) is characterized by high temperature and strong heat released. A riser reactor is designed for the OCM process to improve gas-solid contacting and heat transfer. This work illustrates the effect of hydrodynamic conditions and feed gas composition on the performance of an OCM riser reactor. The findings suggest that oxidative reactions predominantly occur within the acceleration zone and developed flow zone. Furthermore, at the low superficial gas velocity accompanied by a high solid circulating rate, the C2 yield initially increases in the acceleration zone, followed by a decrease in the developed flow zone and deceleration zone. The optimal operating conditions are a specific region corresponding to the solids holdup ranges from 0.015 to 0.02. Moreover, the C2 yield can be elevated using an appropriate feed mixture.

High-Pressure oxidative coupling of methane on alkali metal catalyst – Microkinetic analysis and operando thermal visualization

To introduce promotional H2O effects for both CH4 rate and C2 selectivity, the OH radical formation, catalyzed through H2O activation with O2 surface species, was critical for modeling selective Mn-K2WO4/SiO2 catalysts. Based on our reported experimental evidence, which demonstrates the formation of H2O2 through surface alkali peroxide intermediate, the elementary reactions that account for the OH-mediated pathway were added into the microkinetic model. The advanced model adeptly replicated the promotional H2O effects on both OCM rate and selectivity. The data from a low-pressure microkinetic study were treated isothermally, and extended for near-industrially relevant pressures up to 901 kPa. Thermal visualization using an infrared camera found substantial temperature increases at undiluted high-pressure conditions which caused C2 selectivity to drop significantly. When the furnace temperatures were decreased after ignition, side reactions after O2 depletion (e.g., hydrocarbon reforming) were suppressed, obtaining 13.7 (11.8) % yields at 19.9 % CH4 conversion with 68.6 (59.1) % selectivities for C2-4 (C2) at 901 kPa. The temperature was found to be the determining factor of C2 yield which was perturbed by varying space velocity or CH4/O2 ratios. The optimum temperature for high-pressure conditions was predicted as 885 °C at 901 kPa. The study provides mechanistic and industrially relevant understandings for further OCM catalyst design and system application.

Cooperation of Different Active Sites to Promote CO2 Electroreduction to Multi‐carbon Products at Ampere‐Level

AbstractElectroreduction of CO2 to C2+ products provides a promising strategy for reaching the goal of carbon neutrality. However, achieving high selectivity of C2+ products at high current density remains a challenge. In this work, we designed and prepared a multi‐sites catalyst, in which Pd was atomically dispersed in Cu (Pd−Cu). It was found that the Pd−Cu catalyst had excellent performance for producing C2+ products from CO2 electroreduction. The Faradaic efficiency (FE) of C2+ products could be maintained at approximately 80.8 %, even at a high current density of 0.8 A cm−2 for at least 20 hours. In addition, the FE of C2+ products was above 70 % at 1.4 A cm−2. Experiments and density functional theory (DFT) calculations revealed that the catalyst had three distinct catalytic sites. These three active sites allowed for efficient conversion of CO2, water dissociation, and CO conversion, ultimately leading to high yields of C2+ products.

Cooperation of Different Active Sites to Promote CO2 Electroreduction to Multi-carbon Products at Ampere-Level.

Electroreduction of CO2 to C2+ products provides a promising strategy for reaching the goal of carbon neutrality. However, achieving high selectivity of C2+ products at high current density remains a challenge. In this work, we designed and prepared a multi-sites catalyst, in which Pd was atomically dispersed in Cu (Pd-Cu). It was found that the Pd-Cu catalyst had excellent performance for producing C2+ products from CO2 electroreduction. The Faradaic efficiency (FE) of C2+ products could be maintained at approximately 80.8 %, even at a high current density of 0.8 A cm-2 for at least 20 hours. In addition, the FE of C2+ products was above 70 % at 1.4 A cm-2. Experiments and density functional theory (DFT) calculations revealed that the catalyst had three distinct catalytic sites. These three active sites allowed for efficient conversion of CO2, water dissociation, and CO conversion, ultimately leading to high yields of C2+ products.

Controllably Modulating Oxygen Vacancies on Nonstoichiometric Nd−Ce−O Binary Oxides for Low‐temperature Oxidative Coupling of Methane

AbstractHerein, we synthesised a series of nonstoichiometric Nd−Ce−O composite oxides with a fluorite or rare‐earth C‐type phase structure using the glycine combustion method for the oxidative coupling of methane (OCM) reaction. As the amount of Nd3+ increases, the oxygen vacancies in this series of composite oxides gradually increase, leading to an amount increasing in the C2‐selective oxygen species O2− generated by the oxygen vacancies. In addition, with the increase in Nd3+, the number of moderate basic sites on the catalyst surface also improves, another significant factor affecting the OCM reaction performance of the composite oxides. Nd0.9Ce0.1O1.55 possesses optimal low‐temperature OCM reaction performance, achieving 8.0 % C2 yield at 450 °C and 14.1 % C2 yield at 700 °C. This can be attributed to the nonstoichiometric rare‐earth C‐type crystalline phase structure of Nd0.9Ce0.1O1.55, which exhibits the highest abundance of oxygen vacancies, selective oxygen species O2−, and moderate basic sites.