Conversion Of Carbon Atoms Research Articles

Efficient hybrid solar-to-alcohol system via synergistic catalysis between well-defined Cu–N4 sites and its sulfide (CuS)

Abstract In order to selectively produce liquid hydrocarbon fuels by photoelectroreduction of carbon dioxide (CO2) with titania (TiO2) photoanode, copper sulfide (CuS) nanoparticles (NPs) anchored on Cu-porphyrin (CuPor)-based metal–organic framework nanosheets (NSs) were used as cathode catalysts to efficiently convert CO2 to hybrid alcohol products, in particular, ethanol. Crystal size of CuS increased from 24.6 to 48.1 nm with partial decomposition of CuPor, when sulfuration-time increased from 2 to 6 h. Fractal dimension of CuS/CuPor catalyst surface first surface first increased from 1.12 to 1.31 with the increase in sulfuration-time to 4 h because of generated CuS NPs, and then decreased to 1.26 at 6 h. Formation of the heterojunction between CuS NPs with crystal surface (1 1 0) and CuPor NSs with crystal surface (0 0 4) contributed to synergistic catalytic effect on efficient reduction of CO2. The total carbon atom conversion rate in CO2 photoelectroreduction over stable CuS/CuPor-4 h cathode catalyst reached 5174 nmol h−1 cm−2 with a high selectivity of 74.4% for ethanol product. Density functional theory calculations indicated that CuS exhibited high catalytic activity by strengthening binding energy to adsorb CO* in S atoms (1.5 eV), and then CO* was gradually converted to alcohol on the surface of CuPor NSs. The remarkable performance in CO2 electroreduction over cathode catalysts was attributed to synergistic catalysis between the structure of Cu-N4 in 2D macroporous CuPor NSs and its sulfide CuS NPs with high binding energy toward CO* intermediate.

Development of an efficient catalyst with controlled sulfur vacancies and high pyridine nitrogen content for the photoelectrochemical reduction of CO2 into methanol

To efficiently and selectively produce liquid hydrocarbon fuels, e.g., methanol, by CO2 photoelectrochemical reduction, CdS nanoparticles (NPs) anchored on the nitrogen-doped carbon particles (NCP) with core-shell dodecahedral porous structure were used as cathode catalysts. Electron paramagnetic resonance (EPR) spectra indicated that CdS/NCP treated at 500 °C had the maximum S-vacancies. The heterojunction generated between CdS with abundant S-vacancies and NCP with a high content of pyridinic N acted as synergistic catalyst for CO2 reduction. CdS/NCP-500 catalyst exhibited a selectivity of 77.3% towards methanol with a total carbon atom conversion rate of 3052 nmol·h−1·cm−2. Density functional theory (DFT) calculations revealed that the S-vacancies decreased the energy barrier for CO2 conversion into methanol product. NCP, exhibiting a high adsorption capacity for CO2, allowed the conversion of COOH* into CO* (ΔE = −3.6 eV), which was then transferred to the CdS surface displaying abundant S-vacancies for the reduction into the methanol product.

Enhanced photoelectrochemical hydrogenation of green-house gas CO2 to high-order solar fuel on coordinatively unsaturated metal-N sites containing carbonized Zn/Co ZIFs

Porous carbon-based catalysts facilitate CO2 photoelectrochemical reduction reaction (CO2PRR) through the high charge transfer ability and CO2 adsorption ability. However, the design of catalysts with high selectivity towards high-order solar fuels (such as ethanol and propanol) remains challenging. Herein, catalysts of carbonized Zn/Co Zeolitic Imidazolat Frameworks with various pyrolysis hours (xh-C-Zn/Co ZIFs) were synthesized and accessed for high selective CO2PRR for the first time. XRD and TEM analyses show that the C containing functional groups in pristine Zn/Co ZIF are carbonized and turned into amorphous porous carbon, while many Co and ZnO nanoparticles are formed during the pyrolysis process. Electrochemical characterizations of the catalysts prove that increasing pyrolysis time of Zn/Co ZIF from 1 h to 3 h, resulting in a decreased light current density from 3.3 mA/cm2 to 2.3 mA/cm2, which is much higher than that of Zn/Co ZIF (1.9 mA/cm2). Meanwhile, increasing pyrolysis time of Zn/Co ZIF from 1 h to 3 h results in decreased BET surface area and CO2 adsorption ability. XPS spectra suggest a decreased content of metal-nitrogen bonds in C–Zn/Co ZIF, which leads to the formation of coordinatively unsaturated metal-nitrogen sites. Density functional theory (DFT) calculations reveal that the coordinatively unsaturated CoN3V sites in C–Zn/Co ZIF had the highest catalytic activity towards high-order organics. The total carbon atom conversion rate reaches 5459 nmol/h·cm2 when 1h-C-Zn/Co ZIF is employed as catalyst in the CO2PRR system and the selectivity towards high-order solar fuel reaches 84%.

Solar driven reduction of CO2 using Pt-Cu/C as a catalyst in a photoelectrochemical cell: experiment and mechanism study.

Carbon supported nano-metal catalysts are expected to improve CO2 reduction selectivity and efficiency due to the addition of more active sites and enhancement of electron transport ability. In this study, HKUST-1 was pyrolyzed and decorated with Pt to prepare Pt–Cu/C catalysts. The catalytic effect of the catalysts with different Pt contents in the CO2 photoeletrochemical reduction reaction (CO2PRR) were compared. The total carbon atom conversion rate in CO2PRR experiments using Pt–Cu/C catalysts first increased to a peak when using 1.6 wt% Pt–Cu/C catalyst and then decreased with the increase of Pt content. The 1.6 wt% Pt–Cu/C catalyst showed good hydrogen evolution reaction (HER) inhibiting ability compared with other Pt–Cu/C catalysts. Density functional theory (DFT) calculations were conducted to give an insight into the CO2PRR mechanism on some possible active sites in Pt–Cu/C catalysts. The result demonstrated that HER was more likely to be inhibited on the Cu/Pt active surface and at the same time CO2PRR was promoted.

Selective reduction of CO2 to alcohol products on octahedral catalyst of carbonized Cu(BTC) doped with Pd nanoparticles in a photoelectrochemical cell

In order to directionally convert CO2 into liquid fuels, Cu(BTC) doped with Pd nanoparticles was carbonized to obtain a novel octahedral catalyst C-Pd/Cu for selective reduction of CO2 to alcohol products. XRD patterns showed that Cu characteristic peak in C-8 wt% Pd/Cu catalyst shifted to the lowest angle at 2θ=43.22°among all the prepared catalysts (2θC-1.6 wt% Pd/Cu = 43.3°, 2θC-4.8 wt% Pd/Cu = 43.29°, 2θC-11.2 wt% Pd/Cu = 43.26°, 2θC-14.4 wt% Pd/Cu = 43.28°). The inter planar distance of Cu nanoparticles in C-8 wt% Pd/Cu catalyst was 2.0915 nm, which was larger than those in other catalysts. XPS spectra showed main peak shift to lower binding energy, representing the influence of Pd doping to Cu. SEM and TEM indicated that many ∼70 nm Cu particles and ∼10 nm Pd nanoparticles uniformly distributed in ∼250 nm porous carbon-based octahedral particles. Raman spectrum implied that C-Pd/Cu catalyst with many defects (band ratio ID/IG = 0.84) provided more active sites for intermediates adsorption and facilitated electron transfer. BET result showed C-Pd/Cu catalyst had many mesporous. It was found by density functional theory (DFT) calculations that C-Pd/Cu catalyst had good selectivity towards alcohol products such as methanol, the reaction energy towards producing CH3OH was 19.5 eV lower than that of producing HCOOH. The pathway CO2 → COOH∗ → CO∗ + H2O → COH∗ → HCOH∗ → CH2OH∗ → CH3OH was the most favored to produce CH3OH. CO2 photoelectrochemical reduction reaction was then conducted in a photoelectrochemical reduction cell (PEC) to verify the calculation result. The total carbon atom conversion rate over C-8 wt% Pd/Cu catalyst reached 2380 nmol·h−1 cm−2 with a high liquid products selectivity towards alcohol products, which was in good agreement with DFT calculation results. And the PEC system was proved to have more energy input under the same applied voltage compared with the electrochemical system.

Preparation of a Cu(BTC)-rGO catalyst loaded on a Pt deposited Cu foam cathode to reduce CO2 in a photoelectrochemical cell.

To increase the reaction productivity and selectivity of the CO2 photoelectrochemical reduction reaction, a Cu (benzene 1,3,5-tricarboxylic acid [BTC])-reduced graphite oxide (rGO) catalyst was prepared by using a facile hydrothermal method and used in a CO2 photoelectrochemical cell (PEC) as a cathode catalyst. Characterization of the catalyst proved that successfully bonding of rGO to Cu(BTC) not only facilitated faster transfer of electrons on the surface of the catalyst but also created more active sites. CO2 photoelectrochemical reduction experimental results showed that the total carbon atom conversion rate was up to 3256 nmol h−1 cm−2 which was much higher than when pure Cu(BTC) was used as a cathode catalyst. The liquid product's selectivity to alcohols was up to 95% when −2 V voltage was applied to the system with Cu(BTC)-rGO used as the cathode catalyst.

Pt/graphene aerogel deposited in Cu foam as a 3D binder-free cathode for CO2 reduction into liquid chemicals in a TiO2 photoanode-driven photoelectrochemical cell

A nanostructured Pt/graphene aerogel directly deposited in Cu foam (Pt/GA/CF) was used as a 3D binder-free cathode to convert CO2 into liquid chemicals in a TiO2 photoanode-driven photoelectrochemical cell. The surface morphology, microstructure, mineralogical and elemental compositions, and electrochemical performance of the Pt/GA/CF electrode were characterized via SEM/EDX, TEM, X-ray diffraction, X-ray photoelectron spectroscopy, electrochemical impedance spectroscopy (EIS), and chronocoulometry (CC). EIS analysis revealed that Pt/GA/CF with reduced impedance possessed a better electron transfer capacity than the electrode that combines Pt-modified reduced graphene oxide with CF through polymer binders (Pt/RGO/CF). SEM and CC analyses confirmed that the uniform dispersion of 3D nanoporous Pt/GA in CF scaffold effectively prevented its self-agglomeration and increased the electrochemical adsorption surface area of Pt/GA/CF to 15 times higher than that of Pt/RGO/CF. The efficient charge transportation and high reactant adsorptivity of the Pt/GA/CF electrode significantly improved CO2 reduction and facilitated the conversion of C1 products to high-order products. Formic acid, acetic acid, propionic acid, methanol, and ethanol were detected as the liquid products of CO2 reduction. The carbon atom conversion rate of CO2 reduction on Pt/GA/CF markedly increased to 5040nmol/(hcm2).

CO2 Synergistic Reduction in a Photoanode-Driven Photoelectrochemical Cell with a Pt-Modified TiO2 Nanotube Photoanode and a Pt Reduced Graphene Oxide Electrocathode

CO2 synergistic reduction in a photoanode-driven photoelectrocatalytic (PEC) cell was conducted with a Pt-modified TiO2 nanotube (Pt-TNT) photoanode and a Pt-modified reduced graphene oxide (Pt-RGO) electrocathode to reduce energy consumption and increase CO2 PEC reduction efficiency. The carbon atom conversion rate of CO2 reduction under PEC conditions was 2.3 times higher than that of the total rate under photocatalytic and electrocatalytic conditions. Synergistic CO2 reduction in the PEC cell was mainly due to the use of the photoanode, which played a dual role during CO2 reduction: (1) anode photovoltage compensated and conferred more negative cathode potential for CO2 reduction and (2) anode water decomposition provided protons and electrons for cathode CO2 reduction. System current density, product generation rate of CO2 reduction, and carbon atom conversion rate increased first and then decreased with increasing deposition amount of Pt on TNT. The optimal photocatalytic activity of the Pt-TNT anode...

Morphology-controllable synthesis and characterization of carbon nanotube/polypyrrole composites and their hydrogen storage capacities

Sphere-like and layer-by-layer growth mechanisms of polypyrrole are controlled by changing pyrrole monomer concentration and using carbon nanotubes (CNT) as template. Pristine polypyrrole has sphere-like structures but remarkable change in types of polypyrrole growth is observed from spherical-like to layer-by-layer structures in the presence of CNT. Acid treatment enhances polypyrrole coverage on CNT surface by preventing agglomeration of polypyrrole due to an increase in surface oxygen groups and sp2 bonds in CNT structure. The crystallinity of powders comparably decreases after polypyrrole coating due to the amorphous structure of polypyrrole and a sharp decrease in the intensity of 002 peak. The influence of surface functionalization and polymer coating on the structural parameters of multi-walled CNT and their composites is investigated by tailoring the feeding ratio of polypyrrole. The hydrogen sorption measurements at ambient conditions by Intelligent Gravimetric Analyzer demonstrate that hydrogen uptake of CNT/polypyrrole composite is 1.66 wt.% which is almost 3 times higher than that of pristine CNT. Higher hydrogen uptake values are obtained by keeping the mass ratio of pyrrole monomer and CNT equal by using non-functionalized CNT in composite production. Hydrogen adsorption/desorption kinetics of polypyrrole/CNT composites is improved by increasing adsorption sites after polymer coating and acid treatment. The desorption curves of these modified surfaces are higher than their adsorption curves at lower pressures and hysteresis loop is observed in their isotherms since hydrogen is chemically bonded to the modified surfaces by the conversion of carbon atoms from sp2 to sp3 hybridization.

Optimizing CO2 reduction conditions to increase carbon atom conversion using a Pt-RGO||Pt-TNT photoelectrochemical cell

This study aimed to determine the optimum conditions required to increase the carbon atom conversion rate in a Pt-RGO||Pt-TNT photoelectrochemical cell. The effects of Pt-RGO reduction time on CO2 conversion, voltage applied through the cell, catholyte pH, and pore size of nickel foam as a catalyst support were investigated. The conversion rate of C atoms initially increased and then decreased with increasing Pt-RGO reduction time, increasing electrolyte pH, and decreasing nickel foam pore size. Although carbon atom conversion showed sustainable growth as the applied voltage increased, the current efficiency of CO2 reduction products decreased because of enhanced proton interference when the voltage applied through the cell exceeds 2V. A maximum carbon atom conversion rate of 1500nmol/(cm2h) was obtained by Pt-RGO reduction for 24h when a 2V voltage was applied through the cell, the catholyte pH was 8.8, and nickel foam with an average pore size of 160μm was used as a support. Under optimum conditions, the liquid product selectivity of CO2 reduction reached 99%. The results of the study indicate that RGO-based catalysts have potential use as blueprints for CO2 reduction.

Photoelectrocatalytic reduction of CO2 into chemicals using Pt-modified reduced graphene oxide combined with Pt-modified TiO2 nanotubes.

The photoelectrocatalytic (PEC) reduction of CO2 into high-value chemicals is beneficial in alleviating global warming and advancing a low-carbon economy. In this work, Pt-modified reduced graphene oxide (Pt-RGO) and Pt-modified TiO2 nanotubes (Pt-TNT) were combined as cathode and photoanode catalysts, respectively, to form a PEC reactor for converting CO2 into valuable chemicals. XRD, XPS, TEM, AFM, and SEM were employed to characterize the microstructures of the Pt-RGO and Pt-TNT catalysts. Reduction products, such as C2H5OH and CH3COOH, were obtained from CO2 under band gap illumination and biased voltage. A combined liquid product generation rate (CH3OH, C2H5OH, HCOOH, and CH3COOH) of approximately 600 nmol/(h·cm(2)) was observed. Carbon atom conversion rate reached 1,130 nmol/(h·cm(2)), which were much higher than those achieved using Pt-modified carbon nanotubes and platinum carbon as cathode catalysts.

FTIR in situ transmission studies on the kinetics of paper degradation via hydrolytic and oxidative reaction paths

This study deals with the quantitative and qualitative interpretation of transmission FTIR spectra of aged model paper samples to prepare the basis for a kinetic model of cellulose degradation involving mixed hydrolytic and oxidative mechanism. The ageing experiments were performed in situ under various conditions (pure water vapour, dried air, 100, 150 °C) to discriminate between hydrolytic and oxidative paths. Our focus was on the spectra between 1500–1900 cm-1, where the products of paper ageing appear in the form of various carbonyl groups. A procedure of spectra standardization was used to interpret the bands area in terms of the conversion of carbon atoms in cellulose. From the time evolution of the bands the overall kinetic curves were generated. The positions of the carbonyl bands were verified by independent experiments and theoretical calculations (DFT method). A simple model involving a hydrolytic reaction route and first order kinetics was positively tested on the available experimental basis.

Conversion of 5-S-methyl-5-thio-D-ribose to methionine in Klebsiella pneumoniae. Stable isotope incorporation studies of the terminal enzymatic reactions in the pathway.

Extracts of Klebsiella pneumoniae convert 5-S-methyl-5-thio-D-ribose (methylthioribose) to methionine and formate. To probe the terminal steps of this biotransformation, [1-13C]methylthioribose has been synthesized and its metabolism examined. When supplemented with Mg2+, ATP, L-glutamine, and dioxygen, cell-free extracts of K. pneumoniae converted 50% of the [1-13C]methylthioribose to [13C]formate. The formation of [13C]formate was established by 13C and 1H NMR spectroscopy studies of the purified formate, and by 13C and 1H NMR spectroscopy and mass spectrometry studies of its p-phenylphenacyl derivative. By contrast, no incorporation of label from [1-13C]methylthioribose into the biosynthesized methionine was detected by either mass spectrometry or 13C and 1H NMR spectroscopy. The most reasonable interpretation of these results is that C-1 of methylthioribose is converted directly to formate concomitant with the conversion of carbon atoms 2-5 to methionine. The penultimate step in the conversion of methylthioribose to methionine and formate is an oxidative carbon-carbon bond cleavage reaction in which an equivalent of dioxygen is consumed. To investigate the fate of the dioxygen utilized in this reaction, the metabolism of [1-13C]methylthioribose in the presence of 18O2 was also examined. Mass spectrometry revealed the biosynthesis of substantial amounts of both [18O1]methionine and [13C, 18O1]formate under these conditions. These results suggest that the oxidative transformation in the conversion of methylthioribose to methionine and formate may be catalyzed by a novel intramolecular dioxygenase. A mechanism for this dioxygenase is proposed.

Synthesis of conjugated polymers with alternating aromatic and quinonoid sequences via elimination on precursors

Abstract : An elimination reaction for the formation of conjugated polymers from polymer precursors containing alternating sp superscript 3 carbon atom and conjugatged segments in the main chain is described. The resulting conjugated polymers with alternating aromatic and quinonoid sequences are inaccessible by conventional polymerization processes. The Pi-electron conjugation extension process is exemplified by reactions performed on poly(5,5',alpha-bithiophenediyl p acetoxybenzylidene) at 23 C and followed by electronic and infrared spectra. The semiconductor band gap narrowed from an initial value of 1.53 ev for the precursor polymer to about 0.83 ev for the conjugated derivative. Further evidence for the sp superscript 3 to sp superscript 2 carbon atom conversion by the elimination process is provided by infrared data.