Formation Of CH Research Articles

Vacancy modulation on NiTi-layered double hydroxides towards highly selective CO2 photoreduction

Photoreduction of carbon dioxide (CO2) is a promising way to achieve sustainable energy production and alleviate environmental problems. Herein, we report a NiTi-layered double hydroxides photocatalyst with bivalent and trivalent metal vacancies (denoted as NiVTiV-LDHs) via alkali-etching amphoteric metal cations (Zn and Al) from NiZnTiAl-LDHs precursor. The NiVTiV-LDHs attains a CH4 selectivity of 94% with a production rate of 2398 µmol g−1 h−1, which is preponderant to the state-of-the-art photocatalysts. Operando X-ray absorption fine structure (XAFS) and Fourier-transform infrared spectroscopy (FT-IR) characterizations combined with density functional theory (DFT) calculations corroborate that Ni2+δ−O(H)−Ti3+ζ sites modulated by adjacent vacancies exhibits a declined 3d-orbital occupancy, accelerating the charge transfer for boosting CH4 formation. Moreover, the unique adsorption configuration (Ni2+δ/Ti3+ζ−CO) not only stabilizes the key intermediate *CO for further protonation, but also induces a decreased energy barrier of the rate-determining step (hydrogenation of *OCH3), accounting for the robust photocatalytic CO2 reduction towards CH4.

Construction of Dual-Active Sites by Interfacing with Polyhydroxy Fullerene on Nickel Hydroxide Surfaces to Promote CO2 Deep Photoreduction to CH4.

Due to the complex series of elementary steps involved, achieving deep photoreduction of CO2 to multielectron products such as CH4 remains a challenging task. Therefore, it is crucial to strategically design catalysts that facilitate the controlled formation of the crucial intermediates and provide precise control over the reaction pathway. Herein, we present a pioneering approach by employing polyhydroxy fullerene (PHF) molecules to modify the surface of Ni(OH)2, creating stable and effective synergistic sites to enhance the formation of CH4 from CO2 under light irradiation. As a result, the optimized PHF-modified Ni(OH)2 cocatalyst achieves a CH4 production rate of 455 μmol g-1 h-1, with an electron-based selectivity of approximately 60%. The combination of in situ characterizations and theoretical calculations reveals that the hydroxyl species on the surface of PHF can participate in stabilizing crucial intermediates and facilitating water activation, thereby altering the reaction pathway to form CH4 instead of CO. This study provides a novel approach to regulating the selectivity of photocatalytic CO2 reduction by exploring molecular surface modification through interfacing with functionalized carbon clusters.

Unveiling the effect of H2S concentration in CH4 hydrate formation and growth: A molecular dynamics study

We used molecular dynamics method to simulate the formation and growth of CH4 hydrates with different concentrations of H2S. At the large scale of simulation time, 10000 ns, it is unlikely to form hydrates at 10 MPa and 260 K if there are only CH4 and water; and if there was a small proportion of H2S in the gas, hydrates would easily form. When the molar concentration of H2S in the gas is 1 %, the formed hydrate is unstable and will eventually disintegrate, leaving the box in a two-phase state of gaseous and liquid. In contrast, at molar concentrations of 5 % or higher of H2S, hydrate formation is accelerated, and the hydrate will grow continuously. However, it is not structure I type as expected. These views are supported by the changes in F3 and F4 order parameters, numbers of different cage types, and the number of water molecules belonging to different states. Moreover, since the formation of hydrates is an energy reduction process, we can easily develop inhibitors targeted at hydrates in actual production and gas transportation. According to IGMH analysis, only van der Waals interactions occur between gas molecules inside the cages and the water cage.

Ultrafine Pt Nanoparticles on Defective Tungsten Oxide for Photocatalytic Ethylene Synthesis.

The selective conversion of ethane (C2H6) to ethylene (C2H4) under mild conditions is highly wanted, yet very challenging. Herein, it is demonstrated that a Pt/WO3-x catalyst, constructed by supporting ultrafine Pt nanoparticles on the surface of oxygen-deficient tungsten oxide (WO3-x) nanoplates, is efficient and reusable for photocatalytic C2H6 dehydrogenation to produce C2H4 with high selectivity. Specifically, under pure light irradiation, the optimized Pt/WO3-x photocatalyst exhibits C2H4 and H2 yield rates of 291.8 and 373.4µmolg-1h-1, respectively, coupled with a small formation of CO (85.2µmolg-1h-1) and CH4 (19.0µmolg-1h-1), corresponding to a high C2H4 selectivity of 84.9%. Experimental and theoretical studies reveal that the vacancy-rich WO3-x catalyst enables broad optical harvesting to generate charge carriers by light for working the redox reactions. Meanwhile, the Pt cocatalyst reinforces adsorption of C2H6, desorption of key reaction species, and separation and migration of light-induced charges to promote the dehydrogenation reaction with high productivity and selectivity. In situ diffuse reflectance infrared Fourier transform spectroscopy and density functional theory calculation expose the key intermediates formed on the Pt/WO3-x catalyst during the reaction, which permits the construction of the possible C2H6dehydrogenation mechanism.

A DFT Study of CO Hydrogenation on Graphene Oxide: Effects of Adding Mn on Fischer–Tropsch Synthesis

The hydrogenation of carbon monoxide (CO) offers a promising avenue for reducing air pollution and promoting a cleaner environment. Moreover, by using suitable catalysts, CO can be transformed into valuable hydrocarbons. In this study, we elucidate the mechanistic aspects of the catalytic conversion of CO to hydrocarbons on the surface of manganese-doped graphene oxide (Mn-doped GO), where the GO surface includes one OH group next to one Mn adatom. To gain insight into this process, we have employed calculations based on the density functional theory (DFT) to explore both the thermodynamic properties and reaction energy barriers. The Mn adatoms were found to significantly activate the catalyst surface by providing stronger adsorption geometries. Our study concentrated on two mechanisms for CO hydrogenation, resulting in either CH4 production via the reaction sequence CO → HCO → CH2O → CH2OH → CH2 → CH3 → CH4 or CH3OH formation through the CO → HCO → CH2O → CH2OH → CH3OH pathway. The results reveal that both products are likely to be formed on the Mn-doped GO surface on both thermodynamic grounds and considering the reaction energy barriers. Furthermore, the activation energies associated with each stage of the synthesis show that the conversion reactions of CH2 + OH → CH3 + O and CH2O + OH → CH2OH + O with energy barriers of 0.36 and 3.86 eV are the fastest and slowest reactions, respectively. The results also indicate that the reactions: CH2OH + OH → CH2 + O + H2O and CH2OH + OH → CH3OH + O are the most exothermic and endothermic reactions with reaction energies of −0.18 and 1.21 eV, respectively, in the catalytic pathways.

Numerical analysis of biomass gasification in a fluidized bed reactor using a computational fluid dynamics model integrated with reduced-order reaction kinetics

The use of detailed reaction kinetics in a computational fluid dynamics (CFD) model for simulating the complex reactive gas-solid flow during fluidized bed gasification of biomass (FBGB) is extremely intensive in computations. A reduced-order reaction kinetics model was thus developed and validated that can be integrated with a CFD model to improve the prediction of the formation of tar and syngas components during FBGB at various sizes and chemical compositions of biomass particles. The simulations by the integrated CFD model and reduced-order kinetics showed that pyrolytic products were released from biomass at various temperatures and rates, which created large variations in the concentrations of tar compounds and syngas, and the oxygen to fuel ratio in the bed. The CFD simulations showed that H2 and CO were generated in both heterogeneous phase of the expanded bed and homogenous gas phase in the freeboard region while large portions of CO2 and CH4 were generated in the gas phase near to the top freeboard. Optimization of syngas residence time at a specific gasification temperature can thus reduce the formation of tar, CO2 and CH4.

Fungal Methane Production Controlled by Oxygen Levels and Temperature

Saprotrophic fungi, key players in global carbon cycling, have been identified as methane (CH4) sources not yet accounted for in the global CH4 budget. This study, for the first time, explores the influence of oxygen (O2) and temperature on CH4 production by two fungi, Laetiporus sulphureus and Pleurotus sapidus. To explore the relationship between these parameters and fungal CH4 formation, we examined CH4 formation under varying O2 levels (0 to 98%) and temperatures (17, 27, and 40 °C) during fungal growth on pine wood, beech wood, and grass under sterile conditions. Our findings show that fungal CH4 formation strongly depends on O2 levels. Methane formation was highest when O2 levels exceeded 5%, whilst no CH4 formation was observed after complete O2 consumption. Reintroducing O2 immediately resumed fungal CH4 production. Methane formation normalized to O2 consumption (CH4_norm) showed a different pattern. L. sulphureus showed higher CH4_norm rates with higher O2 levels, whereas P. sapidus showed elevated rates between 0 and 5%. Temperature also significantly influenced CH4 and CH4_norm rates, with the highest production at 27 °C, and comparatively lower rates at 17 and 40 °C. These findings demonstrate the importance of O2 levels and temperature in fungal CH4 emissions, which are essential for refining CH4 source predictions.

A critical review on direct catalytic hydrogasification of coal into CH4: catalysis process configurations, evaluations, and prospects

Coal catalytic hydrogasification (CCHG) is a straightforward approach for producing CH4, which shows advantages over the mature coal-to-CH4 technologies from the perspectives of CH4 yield, thermal efficiency, and CO2 emission. The core of CCHG is to make carbon in coal convert into CH4 efficiently with a catalyst. In the past decades, intensive research has been devoted to catalytic hydrogasification of model carbon (pitch coke, activated carbon, coal char). However, the chemical process of CCHG is still not well understood because the coal structure is more complicated, and CCHG is a combination of coal catalytic hydropyrolysis and coal char catalytic hydrogasification. This review seeks to shed light on the catalytic process of raw coal during CCHG. The configuration of suitable catalysts, operating conditions, and feedstocks for tailoring CH4 formation were identified, and the underlying mechanisms were elucidated. Based on these results, the CCHG process was evaluated, emphasizing pollutant emissions, energy efficiency, and reactor design. Furthermore, the opportunities and strategic approaches for CCHG under the restraint of carbon neutrality were highlighted by considering the penetration of “green” H2, biomass, and CO2 into CCHG. Preliminary investigations from our laboratories demonstrated that the integrated CCHG and biomass/CO2 hydrogenation process could perform as an emerging pathway for boosting CH4 production by consuming fewer fossil fuels, fulfilling the context of green manufacturing. This work not only provides systematic knowledge of CCHG but also helps to guide the efficient hydrogenation of other carbonaceous resources such as biomass, CO2, and coal-derived wastes.

Metal doped TiO2 decorated carbon nanostructured materials as an emerging photocatalysts for solar fuels production

The concept of photocatalytic CO2 and H2O conversion to solar fuels and value-added products provides simultaneous solution for increased energy demands and environmental problems. However, the lack of efficient photocatalysts restrains the large-scale development of photocatalytic technology. In the present study, noble (Pt and Au) and transition metal (Ni) doped nanoflakes assembled on TiO2@carbon microrods with high surface area and rutile crystal structure is prepared via fast, versatile solvothermal method. The photocatalytic performance of the prepared nanocomposites was evaluated in two photocatalytic systems: CO2 reduction and hydrogen production via photoreforming. Pt-doped catalyst showed enhanced hydrogen production efficiency and increased CH4 selectivity, while Ni-doped catalyst exhibited remarkable CO2 reduction activity with higher selectivity towards CO. The mechanism of Pt-promoted CH4 formation and Ni- and Au-promoted CO formation was thoroughly discussed regarding kinetic and thermodynamic parameters.

Preferential Formation of Ethylene via Electrocatalytic CO2 Reduction on Mesoporous Cu2O Nanoparticles: Synergistic Effects of Pore Structure Confinement and Surface Amine

Comprehensive SummaryWe present a facile synthetic strategy to create mesoporous Cu2O nanocrystals with tunable pore structures and surface functional groups of amine derivatives for efficient and preferable electrochemical conversion of CO2 into ethylene. The structural characteristics of these Cu2O nanocrystals can be manipulated using a set of amine derivatives, such as pyridine, 4,4'‐bipyridine, and hexamethylenetetramine, during the oxidative etching process of Cu nanocrystals by bubbling gaseous oxygen in N,N‐dimethylformamide solution. These amine derivatives not only serve as surface functional groups but also significantly affect the resulting pore structures. The synergistic effect of pore structure confinement and surface amine functionalization leads to the superb Faradaic efficiency (FE) of 51.9% for C2H4, respectively, together with the C2H4 partial current density of –209.4 mA·cm−2 at –0.8 V vs. reversible hydrogen electrode (RHE). The relatively high selectivity towards C2H4 was investigated using DFT simulations, where 4,4'‐bipyridine functionalized Cu2O seemed to favor the C2H4 formation with the low free energy of the intermediates. This study provides a feasible strategy to manipulate the pore structure and surface functionalization of mesoporous Cu2O nanocrystals by regulating the oxidative etching process, which sheds light on the rational preparation of high‐performance CO2RR electrocatalysts.

Prediction Challenge: Simulating Rydberg photoexcited cyclobutanone with surface hopping dynamics based on different electronic structure methods.

This research examines the nonadiabatic dynamics of cyclobutanone after excitation into the n → 3s Rydberg S2 state. It stems from our contribution to the Special Topic of the Journal of Chemical Physics to test the predictive capability of computational chemistry against unseen experimental data. Decoherence-corrected fewest-switches surface hopping was used to simulate nonadiabatic dynamics with full and approximated nonadiabatic couplings. Several simulation sets were computed with different electronic structure methods, including a multiconfigurational wavefunction [multiconfigurational self-consistent field (MCSCF)] specially built to describe dissociative channels, multireference semiempirical approach, time-dependent density functional theory, algebraic diagrammatic construction, and coupled cluster. MCSCF dynamics predicts a slow deactivation of the S2 state (10ps), followed by an ultrafast population transfer from S1 to S0 (<100fs). CO elimination (C3 channel) dominates over C2H4 formation (C2 channel). These findings radically differ from the other methods, which predicted S2 lifetimes 10-250 times shorter and C2 channel predominance. These results suggest that routine electronic structure methods may hold low predictive power for the outcome of nonadiabatic dynamics.

Kinetic exploration of CO2 methanation over nickel loaded on fibrous mesoporous silica nanoparticles (CHE-SM)

A novel series of nickel (Ni) loaded on Fibrous Mesoporous Silica Nanoparticles (CHE-SM) support with varying Ni contents (x=1–30 wt%) were synthesized, denoted as xNi/CHE-SM and then investigated for carbon dioxide (CO2) methanation. The catalysts underwent comprehensive characterization using XRD, N2 adsorption-desorption, FESEM, FTIR-KBr, H2-TPR, and CO2-TPD techniques. The XRD and FESEM analyses confirmed the structural integrity of CHE-SM, irrespective of the Ni loading. However, the size of the nanocrystalline NiO particles appeared to be influenced by the Ni loading. Notably, 20Ni/CHE-SM exhibited the highest CO2 conversion of 92% at 350 °C, demonstrating its potential for low-temperature activation. H2-TPR and CO2-TPD results revealed favorable NiO reduction at lower temperatures, indicating medium-strength basicity that facilitated efficient CO2 and H2 adsorption and activation. Consequently, 20Ni/CHE-SM exhibited superior catalytic performance compared to other catalysts, with lower activation energy (61.5 kJ/mol). Kinetic studies focusing on 20Ni/CHE-SM indicated a molecular adsorption mechanism of CO2 and H2 on a single site after evaluation using four Langmuir-Hinshelwood models. This result was attributed to the high amount of medium strength basicity possessed by the 20Ni/CHE-SM catalyst which provided an abundance of adsorption sites, resulting in greater fractional coverage of reactants and enhancing the CH4 formation rate.

Effect of microscale C–S–H on the properties of Portland cement and hydration kinetics analysis at different curing temperatures

Microscale calcium–silicate–hydrate (C–S–H) is easily accessible and readily storable, enabling a cleaner production process of cement-waste grinding and simple chemical synthesis technology. However, the temperature effects of microscale C–S–H require further exploration. In this study, we evaluated the impact of microscale C–S–H admixture on the properties of Portland cement at different curing temperatures. Microscale C–S–H can not only increase the early strength of cement pastes, but also achieve high strength in the long term. Adding microscale C–S–H to cement can effectively reduce the apparent activation energy Ea of hydration products and accelerate the reaction of C3S and C2S with water and form more hydration products. At a curing temperature of 10 °C, the microscale C–S–H increased the 1 d compressive strength by 70.0% and shortened the hydration induction period by 1.2 h. Microscale C–S–H also increased the 12 h hydration degree by 38.1%. Microscale C–S–H promoted the formation of CH and xonotlite-like C–S–H and changed the composition of hydrates, although the effects diminished with increasing curing temperature. This paper offers theoretical and fundamental data on the usage of microscale C–S–H as an admixture in cement-based materials.

Photo-methanification of aquatic dissolved organic matters with different origins under aerobic conditions: Non-negligible role of hydroxyl radicals

Lingering inconsistencies in the global methane (CH4) budget and ambiguity in CH4 sources and sinks triggered efforts to identify new CH4 formation pathways in natural ecosystems. Herein, we reported a novel mechanism of light-induced generation of hydroxyl radicals (•OH) that drove the production of CH4 from aquatic dissolved organic matters (DOMs) under ambient conditions. A total of five DOM samples with different origins were applied to examine their potential in photo-methanification production under aerobic conditions, presenting a wide range of CH4 production rates from 3.57 × 10−3 to 5.90 × 10−2 nmol CH4 mg-C−1 h−1. Experiments of •OH generator and scavenger indicated that the contribution of •OH to photo-methanificaiton among different DOM samples reached about 4∼42 %. In addition, Fourier transform infrared spectroscopy and Fourier transform ion cyclotron resonance mass spectrometry showed that the carbohydrate- and lipid-like substances containing nitrogen-bonded methyl groups, methyl ester, acetyl groups, and ketones, were the potential precursors for light-induced CH4 production. Based on the experimental results and simulated calculations, the contribution of photo-methanification of aquatic DOMs to the diffusive CH4 flux across the water-air interface in a typical eutrophic shallow lake (e.g., Lake Chaohu) ranged from 0.1 % to 18.3 %. This study provides a new perspective on the pathways of CH4 formation in aquatic ecosystems and a deeper understanding on the sources and sinks of global CH4.

Reaction Mechanisms and Production of Hydrogen and Acetic Acid from Aqueous Ethanol Using a Rn-Sn/TiO2 Catalyst in a Continuous Flow Reactor

The catalytic reforming of bioethanol can produce green hydrogen (H2) and acetic acid (AcOH). In the present study, the conversion of aqueous ethanol (EtOH) over 4 wt%Ru-4 wt%Sn/TiO2 in a flow reactor was investigated at different temperatures at 0.1 MPa or at various pressures at 260 °C. The ethanol conversion was rather slow in liquid water, while the reactivity increased significantly when water was evaporated. Under gas-phase conditions at 0.1 MPa, the conversion rate increased with increasing reaction temperature, but the AcOH yield and H2 purity decreased due to by-production of CH4, CO, and CO2. The CH4 and CO generated by fragmentation of acetaldehyde (AA), an intermediate, were suppressed by increasing reaction pressure, although the formation of CH4 and CO2 generated from AcOH was pressure independent. Thus, the highest-pressure conditions in steam at a given reaction temperature are preferred for the production of pure H2. The initial step, EtOH → AA, was the rate-determining reaction, and the model experiments using AA as a substrate showed that the Cannizzaro reaction of two AA molecules to form EtOH and AcOH occurred preferentially. This oxidation system was confirmed to be effective at EtOH concentrations of up to 500 g/L in water.

Fine-tuned combination of cell and electrode designs unlocks month-long stable low temperature Cu-based CO2 electrolysis

The urgency of achieving green chemical production through Cu-based CO2 electroreduction necessitates a rapid transition towards technical maturity and commercialization in the pursuit of addressing the global imperative of decarbonization. Surprisingly, limited emphasis has been placed on exploration of readily scalable cell and electrode designs, which are pivotal in ushering in the era of stable and selective CO2 electrolyzers, showcasing the innovative potential within this area. Herein, we report a breakthrough in achieving month-long stability in the production of C2H4, representing an unprecedented milestone in low-temperature CO2 to C2+ electrolysis. Initial investigations involved the evaluation of five distinct cell architectures for Cu-based CO2 electrolyzers, guided by considerations of cell potentials, scalability with current technology, and CO2 crossover. An innovative multilayer Gas Diffusion Electrode (GDE), featuring an anion exchange ionomer and metal oxide layer, is introduced for CEM-based zero-gap cells, enabling C2H4 formation despite acidic surroundings. However, selectivity towards C2H4 proved suboptimal for extended stability testing. Conversely, the tailored multilayer GDE for one-gap cell architecture achieves a commendable 54 % faradaic efficiency (FE) towards C2+ products at 300 mA/cm2. Remarkably, chronopotentiometric tests demonstrate 720 h of stability (FEC2H4 > 20 %) at 100 mA/cm2. At higher current densities (300 mA/cm2), stability is reduced to 75 h, with detailed analyses revealing distinct degradation mechanisms. At 100 mA/cm2, salt formation predominates, while at 300 mA/cm2, catalyst layer restructuring degrades catalytic activity towards C2H4. Our research underscores the potential for stable, high C2+ selectivity through innovative electrode design and scalable cell architectures, advancing sustainable CO2 utilization.

Nitrogen admixture effects on growth characteristics and properties of carbon nanowalls

The plasma functionalization of carbon nanowalls (CNWs) is of great interest due to their potential applications in electron field emission and energy storage devices. In this study, the effects of nitrogen on the growth and properties of CNWs are thoroughly investigated by varying a wide range of the N2 concentrations in the CH4/H2/N2 discharge plasma. Nitrogen-doped carbon nanowalls (NCNWs) were synthesized in a single-step growth using the hydrogen radical injection plasma-enhanced chemical vapor deposition technique. The formation of dense NCNWs was found to be enhanced by nitrogen and was three times higher in the sample with a 150 sccm N2 flow rate than in the sample without N2 addition (N-0). As the N2 concentration increased from 0 to 200 sccm, the morphology of CNWs changed from relatively straight to curly-like nanowall structures. A high-resolution optical emission spectroscopic observation shows that as N2 flow increased, CN radicals became the dominant species, suppressing the formation of C2 and CH. Photoelectron spectroscopy analysis revealed the nitrogen doping effect on graphene layers at high N2 concentrations. According to Raman and Transmission Electron Microscopy analyses, the NCNWs had more branched and thicker nanowalls with higher defect concentrations than the N-0 sample. The wettability of NCNWs was improved, particularly for the sample with a N2 flow rate of 150 sccm.

In-target production of [11C]CH4 from a nitrogen/hydrogen gas target as a function of beam current, irradiation time, and target temperature

BackgroundProduction of [11C]CH4 from gas targets is notorious for weak performance with respect to yield, especially when using high beam currents. Post-target conversion of [11C]CO2 to [11C]CH4 is a widely used roundabout method in 11C-radiochemistry, but the added complexity increase the challenge to control carrier carbon. Thus in-target-produced [11C]CH4 is superior with respect to molar activity. We studied the in-target production of [11C]CO2 and [11C]CH4 from nitrogen gas targets as a function of beam current, irradiation time, and target temperature.Results[11C]CO2 production was practically unchanged across the range of varied parameters, but the [11C]CH4 yield, presented in terms of saturation yield YSAT(11CH4), had a negative correlation with beam current and a positive correlation with target chamber temperature. A formulated model equation indicates behavior where the [11C]CH4 formation follows a parabolic graph as a function of beam current. The negative square term, i.e., the yield loss, is postulated to arise from Haber–Bosch-like NH3 formation: N2 + 3H2 → 2NH3. The studied conditions suggest that the NH3 (liq.) would be condensed on the target chamber walls, thus depleting the hydrogen reserve needed for the conversion of nascent 11C to [11C]CH4.Conclusions[11C]CH4 production can be improved by increasing the target chamber temperature, which is presented in a mathematical formula. Our observations have implications for targetry design (geometry, gas volume and composition, pressure) and irradiation conditions, providing specific knowledge to enhance [11C]CH4 production at high beam currents. Increased [11C]CH4 radioactivity is an obvious benefit in radiosynthesis in terms of product yield and molar radioactivity.

Characteristics of bio-tar catalytic cracking by char’s inherent Fe2O3 and K2O for biomass gasification process

In this research, a newly-designed micro fluidized bed reaction analyzer (MFBRA) was used to evaluate the catalytic activity of char’s inherent Fe2O3 and K2O on bio-tar in Ar at temperatures of 1023 K, 1073 K, 1123 K, and 1173 K. The adopted samples of char and tar were obtained by biomass pyrolysis in Ar at 1273 K. Fe2O3- and K2O-loaded char were prepared by doping metal oxides on the demineralized char samples to simulate the inherent metal oxides in char. The real-time cracking properties of tar were examined and compared on the basis of the analyzer’s high heating rate, quick sample loading at the predetermined temperature, and online analysis of gas products. The results show that both Fe2O3 and K2O displayed obviously catalytic activity by improving tar conversion and reaction rate, and lowering activation energy (Ea). Compared to K2O at 1173 K, Fe2O3-loaded char promoted the generation of H2, CO, CO2, CH4, C3H6, and the total gas products with the conversion ratio (XFe2O3/K2O) of 2.04, 1.02, 1.24, 1.32, 1.56, and 1.12, respectively. However, it suppressed the formation of C2H6 with the XFe2O3/K2O of 0.43. Meanwhile, the maximum generation rates for CO, CO2, CH4, and the total gas products improved to different extent. During tar catalytic cracking, Fe2O3 suppressed carbon deposition on the char surface because of the larger specific area after experiments. Finally, the generation Ea of CH4, H2, CO, CO2, C3H6 and the total gas products by Fe2O3-loaded char further decreased drastically and that of C2H6 increased obviously. All of these indicated the catalytic activity of the inherent Fe2O3 in char was better than K2O.

Ru/MgO catalyst with dual Ru structure sites for efficient CO production from CO2 hydrogenation

The development and comprehension of supported metal catalysts for CO2 hydrogenation is of paramount importance in mitigating the net CO2 emissions. Supported Ru catalysts have been widely recognized in facilitating CO2 methanation, on which recent findings suggest that the CO2 hydrogenation process can be manipulated to favor the reverse water–gas shift (RWGS) pathway by precisely adjusting the size of Ru particles. However, the size-dependent impact of Ru remains a topic of lively debate. In this work, Ru/MgO catalysts with Ru in the form of single atoms (Ru1) and few-atom cluster (RuFAC) structures were prepared for CO2 hydrogenation. The 1.0Ru/MgO catalyst (with 1 wt.% of Ru), featuring a mixture of Ru1 and RuFAC with a size of 0.6–1.0 nm, showed the highest CO yield (38% at 500 °C) with balanced CO2 conversion and CO selectivity. Transient CO2 hydrogenation and temperature-programmed surface reaction (TPSR) studies suggested that the adsorbed CO2 species participated in CO2 hydrogenation. On Ru1 sites, CO2 hydrogenation followed the RWGS pathway, resulting in the production of CO. In contrast, on RuFAC sites, the enhanced H2 dissociation ability, along with the presence of adsorbed bidentate and monodentate carbonate species at the Ru−MgO interfaces, facilitated the formation of CH4 through the CO2 methanation pathway. This study highlights the critical roles of Ru structure and local environment in defining the CO2 hydrogenation pathways and provides new design principles for highly active Ru-based catalysts.