Tunable Syngas Research Articles

Highly Tunable Syngas Product Ratios Enabled by Novel Nanoscale Hybrid Electrolytes Designed for Combined CO2 Capture and Electrochemical Conversion

AbstractCoupling renewable energy with the electrochemical conversion of CO2 to chemicals and fuels has been proposed as a strategy to achieve a new circular carbon economy and help mitigate the effects of anthropogenic CO2 emissions. Liquid‐like Nanoparticle Organic Hybrid Materials (NOHMs) are composed of polymers tethered to nanoparticles and are previously explored as CO2 capture materials and electrolyte additives. In this study, two types of aqueous NOHM‐based electrolytes are prepared to explore the effect of CO2 binding energy (i.e., chemisorption versus physisorption) on CO2 electroreduction over a silver nanoparticle catalyst for syngas production. Poly(ethylenimine) (PEI) and Jeffamine M2070 (HPE) are ionically tethered to SiO2 nanoparticles to form the amine‐containing NOHM‐I‐PEI and ether‐containing NOHM‐I‐HPE, respectively. At less negative cathode potentials, PEI and NOHM‐I‐PEI‐based electrolytes produce CO at higher rates than 0.1 molal. KHCO3 due to favorable catalyst‐electrolyte interactions. Whereas at more negative potentials, H2 production is favored because of the carbamate electrochemical inactivity. Conversely, HPE and NOHM‐I‐HPE‐based electrolytes display poor CO2 reduction performance at less negative potentials. At more negative potentials, their performance approached that of 0.1 molal. KHCO3, highlighting how the polymer functional groups of NOHMs can be strategically selected to produce value‐added products from CO2 with highly tunable compositions.

Controllable Pd@Cu2O Schottky junction interface with improved anti-poisoning effect for efficiently electroreduction of CO2 into syngas

Syngas is an important precursor to numerous value-added products and can be produced by the electrochemical CO2 reduction reaction (ECO2 RR). However, developing high-performance CO2-to-syngas based-Cu2O electrocatalysts remains challenging. Herein, a series of ultrathin two-dimensional (2D) Pd@Cu2O Schottky junction catalysts was designed to afford finely tunable syngas productivity across a wide potential range (–0.37 V to –0.87 V vs RHE) with a Faraday efficiency >80 % through the ECO2 RR. Detailed experiments and Density functional theory (DFT) calculations revealed that the 2D structure provided a high interfacial contact area to promote charge transfer, leading to an improved charge distribution at the Schottky junction interface to accelerate CO2 activation and stable Cu2O. CO2·− readily participated in the subsequent two proton transfer step with neighboring PdH to form CO, and the competitive hydrogen evolution reaction was significantly inhibited. This work provides a new avenue to efficiently convert electrocatalytic CO2 to syngas by regulating the interface configuration.

In situ reconstructed AgZn3 nanoparticles supported on zinc nanoplates for efficient CO2 electroreduction to tunable syngas.

Developing efficient electrocatalysts for CO2 reduction to syngas with tunable H2/CO ratios and high total faradaic efficiency is challenging. Herein, we report an effective catalyst composed of in situ reconstructed AgZn3 nanoparticles and Zn nanoplates for syngas synthesis, showing nearly 100% Faraday efficiency to syngas with a tunable H2/CO ratio from 2 : 1 to 1 : 2. Moreover, the in situ electrochemical measurements coupled with theoretical calculations disclose that the Zn site in AgZn3 nanoparticles and the hollow site between Ag and Zn in AgZn3 are the possible active sites for CO and H2 generation, respectively. This work has guiding significance for designing dual site catalysts for CO2 electroreduction to tunable syngas.

Bias‐Free Solar‐Driven Syngas Production: A Fe2O3Photoanode Featuring Single‐Atom Cobalt Integrated with a Silver‐Palladium Cathode

AbstractPhotoelectrochemical syngas production from aqueous CO2is a promising technique for carbon capture and utilization. Herein, we demonstrate the efficient and tunable syngas production by integrating a single‐atom cobalt‐catalyst‐decorated α‐Fe2O3photoanode with a bimetallic Ag/Pd alloy cathode. A record syngas production activity of 81.9 μmol cm−2 h−1(CO/H2ratio: ≈1 : 1) was achieved under artificial sunlight (AM 1.5 G) with an excellent durability. Systematic studies reveal that the Co single atoms effectively extract the holes from Fe2O3photoanodes and serve as active sites for promoting oxygen evolution. Simultaneously, the Pd and Ag atoms in bimetallic cathodes selectively adsorb CO2and protons for facilitating CO production. Further incorporation with a photovoltaic, to allow solar light (>600 nm) to be utilized, yields a bias‐free CO2reduction device with solar‐to‐CO and solar‐to‐H2conversion efficiencies up to 1.33 and 1.36 %, respectively.

Bias-Free Solar-Driven Syngas Production: A Fe2 O3 Photoanode Featuring Single-Atom Cobalt Integrated with a Silver-Palladium Cathode.

Photoelectrochemical syngas production from aqueous CO2 is a promising technique for carbon capture and utilization. Herein, we demonstrate the efficient and tunable syngas production by integrating a single-atom cobalt-catalyst-decorated α-Fe2 O3 photoanode with a bimetallic Ag/Pd alloy cathode. A record syngas production activity of 81.9 μmol cm-2 h-1 (CO/H2 ratio: ≈1 : 1) was achieved under artificial sunlight (AM 1.5 G) with an excellent durability. Systematic studies reveal that the Co single atoms effectively extract the holes from Fe2 O3 photoanodes and serve as active sites for promoting oxygen evolution. Simultaneously, the Pd and Ag atoms in bimetallic cathodes selectively adsorb CO2 and protons for facilitating CO production. Further incorporation with a photovoltaic, to allow solar light (>600 nm) to be utilized, yields a bias-free CO2 reduction device with solar-to-CO and solar-to-H2 conversion efficiencies up to 1.33 and 1.36 %, respectively.

Pd-modified g-C3N4 with internal donor-acceptor motifs for photocatalytic CO2 reduction to tunable syngas

The conversion of CO2 and H2O to value-added syngas (CO and H2) using light energy is a sustainable strategy for carbon cycle, but efficient CO2 reduction with tunable CO/H2 ratios remains a huge challenge. Here, we designed a Pd modified g-C3N4 with a localized donor–acceptor (D-A) system by depositing Pd on cyano-modified g-C3N4 (Cy-CN). The electron-rich cyano group acts as an electron acceptor and the coordinated N atoms act as electron donors, which collaboratively contributes to an efficient charge transfer and separation. Loading Pd nanoparticles not only further improves the charge transfer efficiency induced by the Schottky junction but also enhances the hydrogen intermediates adsorption activation, allowing the modulation of the CO/H2 ratio. The experimental results show that efficient CO2 reduction to syngas was achieved with yield of 493.95 µmol·g−1 and the molar ratio of CO/H2 can be adjusted from 1:9.29 to 1:2.22 under visible light irradiation. This work provides a promising strategy for the simple and efficient photocatalytic production of tunable syngas from CO2 reduction over g-C3N4 localized D-A systems in synergy with metal sites.

Boosting Electroreduction of CO2 to Tunable Syngas by Using a Pd‐Based Trimetallic Alloy

AbstractElectrochemical reduction of CO2 to produce syngas is an ideal way to alleviate energy crisis and excessive CO2 emissions. The doping of additional elements to the Pd‐based material to form alloy is expected to result in catalyst with high activity, wide CO/H2 ratio and excellent stability for production on different platform chemicals. Here, Cu and Co species in the trimetallic alloy are targeted to solve the problems of Pd, the electronic structure and the synergistic interaction of alloy have a major effect on the reaction pathway. The obtained PdCuCo can achieve high Faradaic efficiency of CO (87.5% at −1.16 V vs RHE) and has a wide range of tunable CO/H2 ratio (from 0.44 to 7). In different downstream application scenarios, PdCuCo can provide high current densities for syngas preparation (44.4 mA cm−2 for Fischer‐Tropsch synthesis, 54.1 mA cm−2 for aldehyde production and 75.8 mA cm−2 for methanol production).

Retraction Note: Colloidal silver diphosphide (AgP2) nanocrystals as low overpotential catalysts for CO2 reduction to tunable syngas

Retraction Note: Colloidal silver diphosphide (AgP2) nanocrystals as low overpotential catalysts for CO2 reduction to tunable syngas

Efficient Photoreduction of Diluted CO2 to Tunable Syngas by Ni-Co Dual Sites through d-band Center Manipulation.

Photocatalytic conversion of CO2 into syngas is a promising way to address the energy and environmental challenges. Here we report the integration of Ni-Co dual sites on Ni doped Co3 O4 ultrathin nanosheets assembled double-hollow nanotube (Ni-Co3 O4 NSDHN) for efficient photoreduction of low-concentration CO2 . Quasi in situ spectra and density functional theory calculations demonstrate that the declining of d-band center of Ni-Co dual sites enables the electrons accumulation in the dxz /dyz -2π* and dz2 -5σ orbitals. As a result, the binding strength of *CO is weakened and the *H adsorption site is modulated from metal sites to an oxygen site. Remarkably, Ni-Co3 O4 NSDHN exhibits superior diluted CO2 photoconversion activity and controllable selectivity under the irradiation of visible light or even natural sunlight. A syngas evolution rate of 170.0 mmol g-1 h-1 with an apparent quantum yield of 3.7 % and continuously adjustable CO/H2 ratios from 1 : 10 to 10 : 1 are achieved.

Efficient Photoreduction of Diluted CO2to Tunable Syngas by Ni−Co Dual Sites through d‐band Center Manipulation

AbstractPhotocatalytic conversion of CO2into syngas is a promising way to address the energy and environmental challenges. Here we report the integration of Ni−Co dual sites on Ni doped Co3O4ultrathin nanosheets assembled double‐hollow nanotube (Ni−Co3O4NSDHN) for efficient photoreduction of low‐concentration CO2.Quasiin situ spectra and density functional theory calculations demonstrate that the declining ofd‐band center of Ni−Co dual sites enables the electrons accumulation in thedxz/dyz‐2π* anddz2‐5σorbitals. As a result, the binding strength of *CO is weakened and the *H adsorption site is modulated from metal sites to an oxygen site. Remarkably, Ni−Co3O4NSDHN exhibits superior diluted CO2photoconversion activity and controllable selectivity under the irradiation of visible light or even natural sunlight. A syngas evolution rate of 170.0 mmol g−1 h−1with an apparent quantum yield of 3.7 % and continuously adjustable CO/H2ratios from 1 : 10 to 10 : 1 are achieved.

Strain-Regulated Pd/Cu Core/Shell Icosahedra for Tunable Syngas Electrosynthesis from CO2

Strain-Regulated Pd/Cu Core/Shell Icosahedra for Tunable Syngas Electrosynthesis from CO₂

LaNixFe1−xO3 as flexible oxygen or carbon carriers for tunable syngas production and CO2 utilization

The current study reports LaFe1−xNixO3−δ redox catalysts as flexible oxygen or carbon carriers for CO2 utilization and tunable production of syngas at relatively low temperatures (∼700 °C), in the context of a hybrid redox process. Specifically, perovskite-structured LaFe1−xNixO3−δ with seven different compositions (x = 0.4–1) were prepared and investigated. Cyclic experiments under alternating methane and CO2 flows indicated that all the samples exhibited favorable reactive performance: CH4 and CO2 conversions varied between 85% and 98% and 70–88%, respectively. While H2/CO ratio from Fe-rich redox catalysts was ~2.3:1 in the methane conversion step, Ni-rich catalysts produced a concentrated (~ 93.7 vol%) hydrogen stream via methane cracking. The flexibility of LaFe1−xNixO3−δ to produce syngas (or hydrogen) with tunable compositions was found to be governed by the iron/nickel (Fe/Ni) ratio. Redox catalysts with higher Fe contents act as a lattice oxygen carrier via chemical looping partial oxidation (CLPOx) of methane whereas those with higher Ni contents function as a carbon carrier via chemical looping methane cracking (CLMC) scheme. XRD analysis and temperature-programmed reactions revealed that both types of catalysts involve the formation of La2O3 and Ni0 /Ni-Fe phases under the methane environment. The ability to re-incorporate La2O3 and Ni/Fe into a perovskite structure gives rise to oxygen-carrying capacity whereas stable Ni0 or Ni/Fe phases would catalyze methane cracking without lattice oxygen exchange in the reaction cycles. Temperature programmed oxidation and Raman spectroscopy indicated the presence of graphitic and amorphous carbon species, which were effectively gasified by CO2 to produce concentrated CO. Stability tests over LaFe0.5Ni0.5O3 and LaNiO3 revealed that the redox performance was stable over a span of 50 cycles.

Effect of torrefaction on the evolution of carbon and nitrogen during chemical looping gasification of rapeseed cake

Chemical looping gasification (CLG) is a novel approach to efficiently convert rapeseed cake (RC) to tunable syngas and NH3. However, the low energy density of RC seriously hinders its utilization. Meanwhile, torrefaction is an effective pretreatment for biomass upgrading. Hence, the combination of torrefaction with CLG is proposed as an alternative technology to efficiently utilize RC. In this work, the effect of torrefaction temperature on the evolution behaviors of carbon and nitrogen in CLG of RC with Ca2Fe2O5 OC was systematically investigated using TG-FTIR. Results show that torrefaction can effectively improve the physiochemical properties of RC. The torrefied RC possesses higher energy density and HHV, and lower atomic H/C and O/C ratios. Additionally, higher torrefaction temperature can facilitate the thermal degradations of N-IN and labile NP, with the productions of NH3 and HCN. During CLG, the rise of OC/Fuel mass ratio can increase the yields of the major gases (CO2, CO, CH4, NH3 and HCN), owing to both the oxidative effect of the lattice oxygen (O*) and the catalytic effects of Fe3+ and Ca2+ in OC. Moreover, torrefaction pretreatment can improve the CLG behavior of RC and the optimal torrefaction temperature is 250 °C, attributing to the improvement of fuel stability after torrefaction. Besides, torrefaction can marginally reduce the yields of the major nitrogen species (NH3 and HCN). This is ascribed to both the more stable structure of heterocyclic-N and the insufficiency of H radical in the torrefied RC compared to the raw. These findings provide a feasible guidance for the effective insight in nitrogen evolution during CLG coupled with torrefaction, and thereafter for the efficient utilization of biomass.

LDHs-based bifunctional electrocatalyst for effective tunable syngas generation via CO2 reduction

Electrocatalytic reduction of CO2 into syngas (CO and H2) has been recognized to be a promising approach to achieve carbon neutrality. However, producing syngas with tunable H2/CO ratios in a wide range is still challenging. Herein, nitrogen doped graphene aerogel (GA) supported both single-atomic Ni and Ni nanoparticles (NPs) with a surface atomic ratio of 1.11 were constructed by using layered double hydroxide (LDHs) and g-C3N4 as Ni and N precursors, respectively. H2 and CO are the only products of CO2 electroreduction and the ratio of H2/CO can be tuned from 0.4 to 2.5 by changing applied potentials. In addition, the catalyst exhibits a large CO Faradaic efficiency (74%) and good long-term stability (12 h) at a relatively small potential (−0.67 V vs. RHE). This study will shed a new light on the construction of bifunctional catalysts for efficient tunable syngas generation via electroreduction of CO2.

Electrocatalysis CO2 to Tunable Syngas upon Fe Clusters Catalyst Dispersed on Bamboo-like NCTs.

Herein, we report a catalyst of Fe@NBCT with a high performance in electrocatalytic CO2 to syngas with tunable H2/CO ratio. Both in situ synchrotron radiation Fourier transform infrared spectra (SR-FTIR) and density functional theory (DFT) calculation proved that the differing N-doping carbon matrix and Fe nanoclusters (NCs) play dramatic roles in tuning the ratio of syngas during the electrocatalytic carbon dioxide reduction reaction (EC-CO2RR) process.

Tunable syngas production from biomass: Synergistic effect of steam, Ni–CaO catalyst, and biochar

The production of tunable syngas from biomass will further establish the role of biomass-derived syngas as a versatile platform for liquid fuels and value-added chemical synthesis. This study introduced steam, Ni–CaO catalyst, and biochar into a proposed two-stage sorption-enhanced catalytical thermochemical conversion process, aiming to obtain the tunable syngas through the in-situ stepwise generation of high purity H2 and CO. The presence of steam and Ni–CaO catalyst shows unprecedented performance in enhancing the H2 generation due to the promotional tar steam reforming/cracking and water-gas shift reactions at the first stage, and the control experiments indicate that the steam performs a higher selectivity to H2 than the Ni–CaO catalyst. The introduction of biochar with a supplementary carbon source, remarkably promotes the CO generation at the second stage, which could be further pronounced by the addition of Ni–CaO catalyst. A synergistic effect of steam, Ni–CaO catalyst, and biochar contributes to a significant enhancement in H2 and CO generation with an inherently separated generation of H2 (88.2 ± 2.3 vol% of purity) and CO (55.6 ± 1.3 vol% of purity). And the combined use of steam, Ni–CaO catalyst, and biochar could lead to a superior syngas quality with high LHVsyngas and energy recovery efficiency.

Evolution of carbon and nitrogen during chemical looping gasification of rapeseed cake with Ca-Fe oxygen carrier

• Higher OC/RC ratio is beneficial to the transformation of carbon. • NH 3 and HCN are the major N species in CLG of rapeseed cake. • Fe and Ca in CaFe 2 O 5 can increase the yields of NH 3 and HCN. • The reaction pathways of nitrogen in CLG are summarized. • CLG is promising process for the sustainable production of NH 3 . Rapeseed cake (RC) is an attractive fuel for its high caloricity, but the high-nitrogen content seriously hinders its utilization. Meanwhile, chemical looping gasification (CLG) is a promising technology for the production of N 2 free high-quality syngas. Inspired by using RC as a source of C for syngas production, it also can be a possible source of N and H for the sustainable production of NH 3 . Hence, recycling N and H from RC via CLG was proposed for NH 3 production. This paper evaluates the effects of oxygen carrier (CaFe 2 O 5 (CaFe) and 60% Fe 2 O 3 /Al 2 O 3 (FeAl)) on kinetic parameters, as well as the evolutions of carbon and nitrogen during CLG of rapeseed cake using TG-FTIR. Results show that the gasification behavior is remarkably influenced by oxygen carrier at both devolatilization and char reaction stages. CaFe shows a remarkably higher reduction activity compared to FeAl, especially at char reaction stage. The superior activity of CaFe can be also reflected in the lower activation energy compared to FeAl. As regards to nitrogen emission, NH 3 and HCN are the dominant nitrogen species, whereas HNCO is minor. Meanwhile, the migration of nitrogen includes catalytic pyrolysis and oxidation by lattice oxygen (O*). It is feasible to control the migration path of nitrogen by adjusting the operating conditions. Thus, CLG is an attractive pathway for efficiently utilizing rapeseed cake, which can not only produce tunable syngas, but also possibly make the most use of nitrogen as valuable chemicals.

Boosting CO desorption on dual active site electrocatalysts for CO2 reduction to produce tunable syngas

The electrochemical conversion of CO 2 to generate syngas (H 2 and CO) is regarded as a promising alternative technique to facilitate CO 2 reduction in the ambient atmosphere. However, it is still a great challenge to acquire high catalytic activity with an adjustable H 2 /CO ratio over a wide range. Here, we construct an electrocatalyst with Fe-containing dual active sites on N-doped porous carbon (Fe/FeN 4 C) to promote a CO 2 reduction reaction for tunable syngas production. The Fe/FeN 4 C catalysts have a positive onset potential (−0.18 V RHE ), approximately 100% of the sum of the Faradaic efficiency (FE) of CO and H 2 , a high total current density (>39.33 mA cm −2 ), and a wide H 2 /CO ratio (1.09∼7.08). Density functional-theory calculations suggest that the Fe single atoms dispersed into the N-doped carbon structure, along with the incorporation of Fe nanoparticles, may decrease the adsorption energy of ∗CO, thus synergistically enhancing the catalytic activity. Fe/FeN 4 C serves as a dual active site catalyst for CO 2 RR to syngas The Fe/FeN 4 C catalyst displays superior CO 2 RR performance toward syngas DFT study confirms the decrease in ∗CO adsorption energy benefits syngas production There is interest in developing active catalysts for the electrochemical conversion of carbon dioxide to syngas with a tunable H 2 /CO ratio. Here, Hua et al. report Fe-containing, N-doped, porous carbon to promote CO 2 reduction for tunable syngas production.

Ag-decorated GaN for high-efficiency photoreduction of carbon dioxide into tunable syngas under visible light

Visible light-driven photoreduction of CO2 and H2O to tunable syngas is an appealing strategy for both artificial carbon neutral and Fischer–Tropsch processes. However, the development of photocatalysts with high activity and selectivity remains challenging. For this case, we here design a hybrid catalyst, synthesized by in situ deposition of Ag crystals on GaN nanobelts, that delivers a tunable H2/CO ratio between 0.5 and 3 under visible light irradiation (λ > 400 nm). The obtained photocatalyst delivers a maximal turnover frequency value of 3.85 h–1 and a corresponding yield rate of 2.12 mmol h–1 g–1 for CO production, while the photocatalytic activity keeps stable during five cycling tests. Additionally, syngas can be detected even at λ > 600 nm. Experiments and mechanistic studies reveal that the existence of Ag crystals not only extends the light absorption region but also promotes the charge transfer efficiency, and thereby leading to a photocatalytic improvement. Accordingly, the present work affords an opportunity for developing an efficient photo-driven system by using solar energy to alleviate CO2 emissions.

Electrochemical conversion of CO2 into tunable syngas on a B, P, N tri-doped carbon

The fabrication of syngas by CO2 reduction reaction (CO2RR) can avoid the disadvantages of its traditional industrial productions that exacerbate energy crisis and environmental problems. Herein, a series of B, P, N tri-doped carbon (BPNC) catalysts are developed for CO2RR. The results show that, the products of CO2 electroreduction on as-prepared BPNC are CO and H2 with no other products. And on the optimal BPNC (1000 °C, nC48H40BP: nmelamine = 1:200), the faradaic efficiency of CO can reach 81.8 %, with the ratio of H2/CO from 0.2 to 6.8 easily regulated by controlling the applied potential during CO2RR process. This study would provide a good option for production of tunable syngas feedstock by CO2RR process using carbon-based catalysts for numerous downstream processes.