Ethanol Selectivity Research Articles

Monolayer fullerene network: A promising material for VOCs sensor

Carbon materials hold a great promise for gas sensors due to their diversified dimensionality, tunable structures and easy doping functionalization. Two dimensional polymeric fullerene (2DC60), which was experimentally synthesized recently (Hou et al. Nature 2022, 606, 507), offers a new candidate for gas sensors due to its moderate bandgap and high carrier mobility. Remarkably, the challenging aggregation and restacking issue of conventional 2D materials can be avoided for 2DC60 because of its unique topological structure. In this work, we deliver the first attempt to study the volatile organic compounds (VOCs) sensing capability of 2DC60 by density functional theory (DFT) calculations. Compared with pure C60 nanoclusters, 2DC60 exhibits stronger gas sensing due to formed pore center between C60 nanocages. The quasi-hexagonal 2DC60 (qHP 2DC60) possesses relatively high acetone selectivity while quasi-tetragonal 2DC60 (qTP 2DC60) possesses relatively high ethanol selectivity. B-doping for qHP 2DC60 can significantly facilitate electron transfer and sharply enhance its acetone selectivity. Our theoretical results suggest that 2DC60 is a promising candidate for VOCs sensors, which offers a fresh perspective and opportunity on the application of novel 2DC6.

Cold plasma-activated Cu-Co catalysts with CN vacancies for enhancing CO2 electroreduction to low-carbon alcohol

Electrocatalytic CO2 reduction reaction to low-carbon alcohol is a challenging task, especially high selectivity for ethanol, which is mainly limited by the regulation of reaction intermediates and subsequent C–C coupling. A Cu-Co bimetallic catalyst with CN vacancies is successfully developed by H2 cold plasma toward a high-efficiency CO2RR into low-carbon alcohol. The Cu-Co PBA-VCN (Prussian blue analogues with CN vacancies) electrocatalyst yields methanol and ethanol as major products with a total low-carbon alcohol FE of 83.8% (methanol: 39.2%, ethanol: 44.6%) at −0.9 V vs. RHE, excellent durability (100 h) and a small onset potential of −0.21 V. ATR-SEIRAS (attenuated total internal reflection surface enhanced infrared absorption spectroscopy) and DFT (density functional theory) reveal that the steric hindrance of VCN can enhance the CO generation from *COOH, and the C–C coupling can also be increased by CO spillover on uniformly dispersed Cu atoms. This work provides a strategy for the design and preparation of electrocatalysts for CO2RR into low-carbon alcohol products and highlights the impact of catalyst steric hindrance to catalytic performance.

Interstitial carbon atoms enhance both selectivity and activity of rhodium catalysts toward C-C cleavage in direct ethanol fuel cells

Selective breaking of the C-C bond in ethanol holds the key to many industrial processes, including the operation of direct ethanol fuel cells and steam reforming. Interstitial C atoms in the subsurface region of noble-metal catalysts have major impacts on the selectivity and activity, but an understanding of the mechanistic details is still elusive due to their nature of in situ formation and metastability. Herein, we develop a method to obtain stable RhCx (x ≈ 0.5) by introducing C atoms into the interstitial sites of well-defined Rh nanosheets of 8–10 at. layers in thickness, and further elucidate the electronic and geometric effects of the interstitial C atoms on the cleavage of C-C bond. With the introduction of C atoms into half of the octahedral sites, the Rh lattice changes from a cubic to an orthorhombic structure. The lattice expansion induced by the insertion of C atoms, together with the electron transfer between C and Rh atoms, effectively suppresses the coupling reaction between OH* and CH3CO* to form acetic acid while making the cleavage of C-C bond more exothermic. As such, we obtain a selectivity of ethanol to CO2 as high as 18.1 %, much higher than those of the Rh counterpart (10.0 %), together with 3.1-fold improvement in kinetics. Guided by these findings, a new method is also developed to directly introduce C atoms into the subsurface of a commercial Rh black to enhance its selectivity and activity by 2.5- and 1.6- folds, respectively.

Construction of ZnO@ZIF-CoZn bimetallic core-shell nanospheres for enhanced ethanol sensing performance

In order to achieve highly sensitive, stable and preferential monitoring of ethanol, a new core-shell structure of ZnO@ZIF-CoZn (zeolite imidazole framework-CoZn) was hydrothermally synthesized to meet actual detection requirements. The micro-morphology, crystal phase and element composition of the synthesized materials were studied by SEM, TEM, XRD, XPS and other characterization methods. It was found that the porous ZIF-CoZn film (∼100 nm) was uniformly and densely coated on the surface of the ZnO nanospheres (∼400 nm), and a core-shell structure of ZnO@ZIF-CoZn was successfully synthesized. In the gas sensitivity test, the response of ZnO@ZIF-CoZn to 100 ppm ethanol reached 18.4 at 200 °C, which is almost 3.6 times than that of pure ZnO, and the optimal working temperature of ZnO@ZIF-CoZn was lower than that of pure ZnO (240 °C). In addition, ZnO@ZIF-CoZn exhibited excellent selectivity and stability to ethanol. A heterojunction model and surface sensing response are proposed to explain the enhanced sensing response. Therefore, based on the unique nanostructure, low cost, high sensitivity and excellent selectivity of ethanol sensing performance, ZnO@ZIF-CoZn is expected to become a promising candidate in the ethanol sensor market.

Ceo2 /Cus Nanoplates Electroreduce Co2 to Ethanol withStabilized Cu+ Species.

Copper-based electrocatalysts effectively produce multicarbon (C2+ ) compounds during the electrochemical CO2 reduction (CO2 RR). However, big challenges still remain because of the chemically unstable active sites. Here, cerium is used as a self-sacrificing agent to stabilize the Cu+ of CuS, due to the facile Ce3+ /Ce4+ redox. CeO2 -modified CuS nanoplates achieve high ethanol selectivity, with FE up to 54% and FEC2+ ≈ 75% in a flow cell. Moreover, in situ Raman spectroscopy and in situ Fourier-transform infrared spectroscopy indicate that the stable Cu+ species promote CC coupling step under CO2 RR. Density functional theory calculations further reveal that the stronger * CO adsorption and lower CC coupling energy, which is conducive to the selective generation of ethanol products. This work provides a facile strategy to convert CO2 into ethanol by retaining Cu+ species.

Electrocatalytic conversion of methane to ethanol by ultrathin WO3 nanosheets: Oxygen vacancy engineering

Electrocatalytic conversion of CH4 into valuable liquid products is an attractive strategy for utilization of natural gas, however, it was still constrained by low product yields. Herein, ultrathin WO3 nanosheets with adequate oxygen vacancies (Ov) as robust electrocatalysts for highly efficient CH4 conversion to ethanol were synthesized. Using the optimized sample, the ultrahigh ethanol yield and selectivity of 125,090 μmol gcat−1 h−1 and 99.4% are achieved within 8 h at low potential of 1.2 V vs. RHE, both of which outperform the previous reports as we know. The corresponding ethanol Faradic efficiencies is 50.7%. In-situ Raman spectra and density functional theory calculation reveal that Ov effectively enable CH activation and CC coupling, and eventually promotes the electrocatalytic activity and ethanol selectivity for CH4 conversion. This work provides a constructive avenue for designing electrocatalysts with both high activity and selectivity to realize CH4 conversion.

High sensitivity and selectivity of ZnO nanoparticle-decorated 1D a-MoO3 nanobelts toward ethanol by microwave heating

One-dimensional layer structure a-MoO3 nanobelts with abundant oxygen defects were effectively synthesized through a hydrothermal route and decorated by ZnO nanoparticles via a liquid-phase chemical process. ZnO nanoparticles (NPs) with a size of approximately 50 nm were uniformly dispersed on the a-MoO3 nanobelt surface, forming an n-n heterostructure at the two-phase interface. The crystalline structure, microtopography, element composition, valence state, surface-to-volume ratios, optical properties, and work function of the ZnONP-decorated a-MoO3 samples were analyzed. ZnONP-decorated a-MoO3 nanobelts with different proportions of ZnO were synthesized and subjected to ethanol sensing. The 25% loaded ZnONP-decorated a-MoO3 nanobelts were found to offer the best response (Ra/Rg = 19.2 at 100 ppm), which was 3.6 times higher than that of pristine α-MoO3 (5.37) with a low detection limit (108 ppb). The response time was significantly lower (14–27 s) than that of pristine a-MoO3 (5–8 s). Furthermore, the sensor has ultrahigh selectivity and reliable stability for ethanol. Layered MoO3 nanobelts have a unique sensing mechanism, which is the catalytic oxidation of lattice oxygen on the MoO3 surface to form oxygen vacancies and free electrons. The excellent sensing performance was ascribed to the unique 1-D nanobelt morphology of the a-MoO3 carrier, the abundance of oxygen defects, and the formation of heterojunction barriers at the two-phase interface.

Tunable C2 Products via Photothermal Steam Reforming of CO2 over Surface-Modulated Mesoporous Cobalt Oxides.

The conversion of CO2 to high-value products by renewable energy is a promising approach for realizing carbon neutralization, but the selectivity and efficiency of C2+ products are not satisfying. Herein, we report the controllable preparation of highly ordered mesoporous cobalt oxides with modulated surface states to achieve efficient photothermal water-steam reforming of CO2 to C2 products with high activity and tunable selectivity. Pristine mesoporous Co3O4 exhibited an acetic acid selectivity of 96% with a yield rate of 73.44 μmol g-1 h-1. By rationally modifying mesoporous Co3O4 surface states, mesoporous Co3O4@CoO delivered a radically altered ∼100% ethanol selectivity with a yield rate of 14.85 μmol g-1 h-1. Comprehensive experiments revealed that the pH value could strongly influence the selectivity of C2 products over mesoporous cobalt oxides. Density functional theory verified that reduced surface states and rich oxygen vacancies on surface-modified mesoporous cobalt oxides could facilitate further variation of C2 products from acetic acid to ethanol.

Rationally Designed Water Enriched Nano Reactor for Stable CO2 Hydrogenation with Near 100% Ethanol Selectivity over Diatomic Palladium Active Sites

CO2 (CO) hydrogenation presents the widest route to synthesis of various valuable organic molecules, but precise carbon–carbon coupling control to targeted products along with the elimination of byproducts remains a challenge. We overcome these limitations by synthesizing a CeO2-supported dual Pd site catalyst that could actively catalyze CO2 conversion into single-product ethanol almost without C1 byproducts in a continuous-flow fixed-bed reactor. This surprising finding is derived from the observation that the synergistic catalysis between dual Pd atoms leads to extraordinary ability for the cleavage of C–O bond in *CHxOH species and the carbon–carbon coupling between *CHx and *CO species. Furthermore, the dual Pd sites could be stabilized through enriching in situ formed water in the nano reactor with a hydrophobic shell layer, thus leading to remarkably improved catalytic stability for ethanol production. As a result, the as-constructed dual Pd site catalyst exhibited superior selectivity to ethanol at 98.7%, corresponding to a productivity up to 11.6 g per gram of Pd per hour and excellent stability during the continuous test for 60 h. Our results demonstrate that multifunctional synergistic catalysis of dual active sites can break through the restriction of a reaction involving a single active site catalyst.

Efficient Electrocatalytic Reduction of CO2 to Ethanol Enhanced by Spacing Effect of CuCu in Cu2‐xSe Nanosheets

AbstractIt is highly desired yet challenging to strategically steer carbon dioxide (CO2) electroreduction reaction (CO2ER) toward ethanol (EtOH) with high activity, which provides a promising way for intermittent renewable energy reservation. Controlling spatial distance between the adjoining active centers and promoting the CC coupling progress are crucial to realize this purpose. Herein, ultrathin 2D Cu2‐xSe is prepared with abundant Se vacancies, where the spatial distance between the CuCu around the Se vacancies is effectively shortened because of the lattice stress. Besides, the moderate spatial distance induced by Se vacancies can significantly decrease the Gibbs free energy of asymmetric *CO*CHO coupling progress, effectively change the local charge distribution, decrease the valence state of Cu atoms and increase the electron‐donating capacity of the dual active sites. Combining experimental observations and density functional theory simulations, the CuCu dual sites with spatial distance of 2.51 Å in VSe‐Cu2‐xSe sample can catalyze CO2ER to EtOH with high selectivity in a potential range from −0.4 to −1.6 V, and reach the highest faradaic efficiency of 68.1% at −0.8 V. This work reveals the influence of spacing effect on ethanol selectivity, and provides a new idea for future design of catalysts with chain elongation reaction, which can bring extensive attention.

Steering CO2 electroreduction pathway toward ethanol via surface-bounded hydroxyl species-induced noncovalent interaction

Selective electroreduction of carbon dioxide (CO2RR) into ethanol at an industrially relevant current density is highly desired. However, it is challenging because the competing ethylene production pathway is generally more thermodynamically favored. Herein, we achieve a selective and productive ethanol production over a porous CuO catalyst that presents a high ethanol Faradaic efficiency (FE) of 44.1 ± 1.0% and an ethanol-to-ethylene ratio of 1.2 at a large ethanol partial current density of 501.0 ± 15.0 mA cm-2, in addition to an extraordinary FE of 90.6 ± 3.4% for multicarbon products. Intriguingly, we found a volcano-shaped relationship between ethanol selectivity and nanocavity size of porous CuO catalyst in the range of 0 to 20 nm. Mechanistic studies indicate that the increased coverage of surface-bounded hydroxyl species (*OH) associated with the nanocavity size-dependent confinement effect contributes to the remarkable ethanol selectivity, which preferentially favors the *CHCOH hydrogenation to *CHCHOH (ethanol pathway) via yielding the noncovalent interaction. Our findings provide insights in favoring the ethanol formation pathway, which paves the path toward rational design of ethanol-oriented catalysts.

Highly Selective Photoelectroreduction of Carbon Dioxide to Ethanol over Graphene/Silicon Carbide Composites

AbstractUsing sunlight to produce valuable chemicals and fuels from carbon dioxide (CO2), i.e., artificial photosynthesis (AP) is a promising strategy to achieve solar energy storage and a negative carbon cycle. However, selective synthesis of C2compounds with a high CO2conversion rate remains challenging for current AP technologies. We performed CO2photoelectroreduction over a graphene/silicon carbide (SiC) catalyst under simulated solar irradiation with ethanol (C2H5OH) selectivity of>99 % and a CO2conversion rate of up to 17.1 mmol gcat−1 h−1with sustained performance. Experimental and theoretical investigations indicated an optimal interfacial layer to facilitate the transfer of photogenerated electrons from the SiC substrate to the few‐layer graphene overlayer, which also favored an efficient CO2to C2H5OH conversion pathway.

Highly Selective Photoelectroreduction of Carbon Dioxide to Ethanol over Graphene/Silicon Carbide Composites.

Using sunlight to produce valuable chemicals and fuels from carbon dioxide (CO2 ), i.e., artificial photosynthesis (AP) is a promising strategy to achieve solar energy storage and a negative carbon cycle. However, selective synthesis of C2 compounds with a high CO2 conversion rate remains challenging for current AP technologies. We performed CO2 photoelectroreduction over a graphene/silicon carbide (SiC) catalyst under simulated solar irradiation with ethanol (C2 H5 OH) selectivity of>99 % and a CO2 conversion rate of up to 17.1 mmol gcat -1 h-1 with sustained performance. Experimental and theoretical investigations indicated an optimal interfacial layer to facilitate the transfer of photogenerated electrons from the SiC substrate to the few-layer graphene overlayer, which also favored an efficient CO2 to C2 H5 OH conversion pathway.

Alkali and Alkaline Earth Metals (K, Ca, Sr) Promoted Cu/SiO2 Catalyst for Hydrogenation of Methyl Acetate to Ethanol

The advancing effects of various alkali and alkaline earth metals (inclusive of K, Ca, and Sr) modified Cu/SiO2 catalysts, prepared with a modified precipitation-gel method, were investigated for the production of ethanol via hydrogenation of methyl acetate. Our results showed that Sr-doped catalysts exhibited the best and most consistent results during catalytic tests. A series of techniques, including X-ray diffraction technique, Raman spectroscopy, N2 adsorption/desorption, N2O titration method, FTIR spectroscopy, and H2 temperature, programmed desorption and reduction (TPD and TPR), and X-ray Photoelectron Spectroscopy, which was used to check the detailed characterization of Sr modification in the catalyst and its structural impacts on the properties of the catalyst. These results demonstrated that the addition of 5%Sr could strengthen the intrinsic stability of the catalyst by formulating the appropriate ratio of Cu+/(Cu0 + Cu+) to facilitate catalytic outcome improvement. The addition of 5%Sr-30%Cu/SiO2 under the most favorable conditions, resulting in the peak conversion of MA (95%) and ethanol selectivity (96%), indicates its magnificent catalytic stabilizing effects. Furthermore, the best performing catalyst was compared and tested under various conditions (LHSV and temperatures) and a 300 h long life run.

Electrochemical CO2 reduction to ethanol: Synergism of (n-Bu4N)3SVMo11O40 and an In catalyst

The synthesis of ethanol by electrochemical CO2 reduction is attractive because CO2 is one of the key synthons in organic synthesis for the chemical and fuel industries. However, the reactions of electrochemical CO2 reduction to ethanol have the limitations of lower Faraday efficiency (FE) and insufficient understanding of the mechanisms. Herein, we reported the synergism of commercial indium (In) catalysts and a polyoxometalate electrolyte, i.e., (n-Bu4N)3SVMo11O40 for ethanol generation (FE 69.5%) by the electrochemical reduction of CO2. In-depth characterizations and computational studies of the In-based materials indicated that CC coupling caused the generation and consumption of oxygen vacancies in situ formed In2O3, where In acted as the active sites. The polyoxometalate electrolyte induced multiple proton-coupled electron transfers via MoVI/IV in the H2nSVVMoIVnMoVI11-nO403− species for enhanced ethanol selectivity.

Boosting the C–C Coupling of Bioethanol to Higher Alcohols by Inhibiting Aqueous Phase Reforming Reaction

A suitable catalyst with an exact match of the acidity/basicity, ingenious geometric structure, and proper electronic environment is vital to the Guerbet reaction for the synthesis of C6+ higher alcohols. Herein, we synthesized a series of Ni/MgAlO and NiSn/MgAlO catalysts based on hydrotalcite laminate for one-pot upgrading of aqueous bioethanol to C6+ higher alcohols. Through the introduction of Sn to form NiSn alloys, the Ni–Ni interactions were attenuated and the cleavage of C–C bonds was suppressed with a yield of 21.9% of C6+ higher alcohols at 250 °C. Meanwhile, by precisely adjusting the ratio of the metal cation Mg2+ to Al3+, the acidity and basicity of the catalysts were optimized and Ni/(4-Mg)AlO with an optimal ratio of 4 presented a considerable C6+ alcohol yield (25.2%) at even 220 °C, as well as an impressive ethanol conversion of 67.7%. Such an excellent activity achieved at lower temperature was attributed to highly dispersed Ni metal with a Ni(Mg)O solid solution structure, leading to the enormously inhibited aqueous ethanol reforming process and significant increased yield of higher alcohols. The results reveal that the electronic structure and coordination environment of metal sites as well as higher moderately basic and strong acid sites were demonstrated to be beneficial for carbon-chain extension of higher alcohols and ethanol selectivity for dehydrogenation/hydrogenation. Moreover, the number of metal, acid, and base sites should be balanced to inhibit side reactions.

Guiding catalytic CO2 reduction to ethanol with copper grain boundaries.

The grain boundaries (GBs) in copper (Cu) electrocatalysts have been suggested as active sites for CO2 electroreduction to ethanol. Nevertheless, the mechanisms are still elusive. Herein, we describe how GBs tune the activity and selectivity for ethanol on two representative Cu-GB models, namely Cu∑3/(111) GB and Cu∑5/(100) GB, using joint first-principles calculations and experiments. The unique geometric structures on the GBs facilitate the adsorption of bidentate intermediates, *COOH and *CHO, which are crucial for CO2 activation and CO protonation. The decreased CO-CHO coupling barriers on the GBs can be rationalized via kinetics analysis. Furthermore, when introducing GBs into Cu (100), the product is selectively switched from ethylene to ethanol, due to the stabilization effect for *CH3CHO and inapposite geometric structure for *O adsorption, which are validated by experimental trends. An overall 12.5 A current and a single-pass conversion of 5.18% for ethanol can be achieved over the synthesized Cu-GB catalyst by scaling up the electrode into a 25 cm2 membrane electrode assembly system.

Membrane-controlled CO2 electrocatalysts with switchable C2 product selectivity and high faradaic efficiency for ethanol

Membrane-modified Ag and Cu catalysts convert CO2 to ethanol with up to 72% faradaic efficiency.

Ethanol formation via CO2 electroreduction at low overvoltage over exposed (111) plane of CuO thin film

In this study, we fabricated CuO thin films using the sol-gel spin coating method. The fabricated thin films were utilized for electrocatalytic reduction of CO2 (CO2ER). Fabrication of thin film is vital to provide a large surface area and a more exposed (111) crystal plane for ethanol selectivity. This is verified by comparing it with bulk powder material which does not give such activity. CO2ER over thin film electrode specifically forms CO(g) and Ethanol(l), 2 and 12 electron reduction products, and eliminates the possibility of unwanted HER as a side reaction in the CO2 saturated NaHCO3 electrolyte. We achieved significant product selectivity and faradaic efficiency, utilizing the very low potential for both CO and ethanol. Specific formation of only CO and ethanol makes the process efficient as the separation of gas and liquid is easy. Results based on density functional theory calculations suggest that CuO (111) and CuO (-111) surfaces promote CO2 adsorption and subsequent formation of CO. However, a direct CO-dimerization is observed only on the CuO (111) surface that facilitates the formation of ethanol as the C2 product. This comparative study of bulk and thin-film opens new insight and highlights the importance of catalyst fabrication for the specific product formation utilizing significantly less energy.

Hierarchical Ag-Cu interfaces promote C-C coupling in tandem CO2 electroreduction

Electrocatalytic CO2 reduction into ethanol driven by renewable energy represents a promising strategy for energy storage and mitigation of global warming, but it has remained challenging to gain high activity and selectivity of ethanol. Here we take advantage of atomic arrangement in immiscible Ag-Cu composite during annealing and establish hierarchical interfaces in the obtained core-shell catalyst. The atomic Ag-Cu interactions increase electrochemical surface area and expedite charge dynamics, resulting in an unprecedented electrocatalytic performance with the faradaic efficiency of C2+ products, ethanol as 80.2 %, 52.6 % and the current density of ∼320 mA cm−2 at −1.0 V (versus reversible hydrogen electrode). Moreover, the Ag-Cu catalyst exhibits a notable stability for ∼60 h. Mechanism studies reveal that local CO intermediates preferentially accumulate on the core, then migrate to the continuous Cu surface for C-C coupling energy-favorably toward ethanol. Our work highlights a novel design principle as interface engineering for advanced tandem electrocatalysts.