Catalyst For Reduction Research Articles

Bifunctional Catalysts for CO2 Reduction and O2 Evolution: A Pivotal for Aqueous Rechargeable Zn-CO2 Batteries.

The quest for the advancement of green energy storage technologies and reduction of carbon footprint is determinedly rising toward carbon neutrality. Aqueous rechargeable Zn-CO2 batteries (ARZCBs) hold the great potential to encounter both the targets simultaneously, i.e., green energy storage and CO2 conversion to value-added chemicals/fuels. The major descriptor of ARZCBs efficiency is allied with the reactions occurring at cathode during discharging (CO2 reduction) and charging (O2 evolution) which own different fundamental mechanisms and hence mandate the employment of two different catalysts. This presents an overall complex and expensive battery system which requires a concrete solution, while the development and application of a bifunctional cathode catalyst toward both reactions could reduce the complexity and cost and thus can be a pivotal for ARZCBs. However, despite the increasing research interest and ongoing research, a systematic evaluation of bifunctional catalysts is rarely reported. In this review, the need of bifunctional cathode catalysts for ARZCBs and associated challenges with strategies have been critically assessed. A detailed progress examination and understanding toward designing of bifunctional catalyst for ARZCBs have been provided. This review will enlighten the future research approaching boosted performance of ARZCBs through the development of efficient bifunctional cathode catalysts.

Ni-Ag Catalysts for Hydrogen Production through Dry Reforming of Methane: Characterization and Performance Evaluation

To investigate the influence of Ag and the loading of Ni species, Ni-Ag type catalysts were synthesized with varying Ni/Ag ratios (1, 1.5 and 2) using the coprecipitation method. The catalysts were extensively characterized using various techniques such as TG-DSC-SM, XRD, ICP, BET, SEM-EDX and TPR and subsequently tested in the CH4/CO2 reaction without any pretreatment. Regardless of the ratio employed, a phase mixture containing NiO and Ag was observed after calcination under air between 600 °C and 1200 °C. SEM analysis confirmed the presence of a close interface between Ag and NiO. The specific surface area was found to be significantly higher for the catalyst with lower Ni content (R = 1). TPR analysis demonstrated that the inclusion of Ag facilitated the reduction of Ni at lower temperatures. XRD analyses of the spent catalyst confirmed catalyst reduction during the reaction. Among the samples, a catalyst with Ni/Ag = 1 exhibited superior catalytic activity without any pretreatment under a reduction atmosphere, in which case the conversions of methane and CO2 at 650 °C amounted to 38 and 45 mol%, respectively, with H2/CO = 0.7 and 71 mol% of H2. The presence of Ag species enhances the stability of the Ni catalyst and improves catalytic performance in the dry reforming of methane.

Unraveling the activity trends of T-C2N based Single-Atom catalysts for electrocatalytic nitrate reduction via high-throughput screening

Electrochemical nitrate reduction reaction (NO3RR) offers a cost-effective and environmentally friendly method to simultaneously yield valuable NH3and alleviate NO3−pollution under mild operating conditions.However, this complicated eight-electron reaction suffers from low selectivity and Faradaic efficiency, which highlight the importance of developing efficient catalysts, but still a critical challenge. Here, a theoretical screening is performed on transition metal-tetragonal carbon nitride (TM@T-C2N) as active and selective electrocatalysts for NO3RR, where detailed reaction mechanisms and activity origins are explored. In addition, five-step screening criteria and volcano plots enable fast prescreening among numerous candidates.We identify that V@T-C2N and Cr@T-C2N are promising candidates with low overpotentials and high selectivity and stability. In particular, a significant negative correlation between the adsorption strength ofnitrate and the Gibbs free energy for the last proton-electron coupling step (*NH2→*NH3) was existed, which is considerably advantaged to track the activity trend and reveal the origin of activity. This work provides theoretical insights into the rational design of TM–N4/C catalysts for NO3RR andpaves a valuable electrochemical screening framework for other multi-step reactions.

Covalent Organic Framework with Donor1‐Acceptor‐Donor2 Motifs Regulating Local Charge of Intercalated Single Cobalt Sites for Photocatalytic CO2 Reduction to Syngas

AbstractCovalent organic framework (COF) has attracted increasing interest in photocatalytic CO2 reduction, but it remains a challenge to achieve high conversion efficiency owing to the insufficient active site and fast charge recombination. Rationally optimizing the electronic structures of COF to regulate the local charge of active sites precisely is the key point to improving catalytic performance. Herein, intercalated single Co sites coordinated by imine‐N motifs have been designed by using trinuclear copper‐based imine‐COFs with distinct electronic moieties via a molecular engineering strategy. It is confirmed that the charge delivery property and local charge distribution of these heterometallic frameworks can be profoundly influenced by electronic structures. Among these featured structures with mixed‐state copper clusters, Co/Cu3‐TPA‐COF stands out for an exceptional photocatalytic CO2 reduction activity and tunable syngas (CO/H2) ratio by changing various bipyridines. Experimental and theoretical results indicate that interlayer Co‐imine N motifs on the donor1‐acceptor‐donor2 structures facilitate the formation of a highly separated electron‐hole state, which effectively induces the oriented electron transfer from dual electron donors to Co centers, achieving an enhanced CO2 activation and reduction. This work opens up an avenue for the design of high‐performance COF‐based catalysts for photocatalytic CO2 reduction.

Covalent Organic Framework with Donor1-Acceptor-Donor2 Motifs Regulating Local Charge of Intercalated Single Cobalt Sites for Photocatalytic CO2 Reduction to Syngas.

Covalent organic framework (COF) has attracted increasing interest in photocatalytic CO2 reduction, but it remains a challenge to achieve high conversion efficiency owing to the insufficient active site and fast charge recombination. Rationally optimizing the electronic structures of COF to regulate the local charge of active sites precisely is the key point to improving catalytic performance. Herein, intercalated single Co sites coordinated by imine-N motifs have been designed by using trinuclear copper-based imine-COFs with distinct electronic moieties via a molecular engineering strategy. It is confirmed that the charge delivery property and local charge distribution of these heterometallic frameworks can be profoundly influenced by electronic structures. Among these featured structures with mixed-state copper clusters, Co/Cu3-TPA-COF stands out for an exceptional photocatalytic CO2 reduction activity and tunable syngas (CO/H2) ratio by changing various bipyridines. Experimental and theoretical results indicate that interlayer Co-imine N motifs on the donor1-acceptor-donor2 structures facilitate the formation of a highly separated electron-hole state, which effectively induces the oriented electron transfer from dual electron donors to Co centers, achieving an enhanced CO2 activation and reduction. This work opens up an avenue for the design of high-performance COF-based catalysts for photocatalytic CO2 reduction.

Oxygen functionalized diamond nanocone arrays coupling cobalt phthalocyanine for enhanced electrochemical CO2 reduction

The development of high-efficiency catalysts plays a crucial role in advancing CO2 electroreduction techniques. Among potential candidates, diamond-based electrocatalysts show promise due to their broad electrochemical windows, which effectively suppress competitive hydrogen evolution and ensure high CO2 reduction efficiency. In this study, we report an integrated electrode composed of oxygen-terminated diamond nanocone (ODcone) with CoPc-molecules anchoring (CoPc/ODcone). The CoPc/ODcone electrodes exhibited remarkable performance, achieving a maximum Faradaic efficiency (FE) of 94.1% for CO at −0.97 V vs reversible hydrogen electrode (RHE), and maintaining an FECO higher than 80% over a wide potential range of −0.67 V to −1.07 V vs RHE. The outstanding performance of the CoPc/ODcone electrode can be attributed to the synergistic effects between the nanostructured diamond surface and the CoPc catalyst. The hydroxyl-rich nature of the diamond surface facilitates the anchoring of CoPc molecules and bonding with Co atoms in CoPc. Simultaneously, the nanostructured diamond with sharp tips enhances CO2 adsorption, thereby improving the catalyst's performance. This study provides valuable insights into the utilization of non-metallic carbon materials, particularly diamond, as metal-free catalysts in CO2 electrochemical reduction and tackles challenges such as low current density and poor Faradaic efficiency, thus contributing to the advancement of more effective catalysts for CO2 electroreduction.

Unveiling structural evolution of Fe single atom catalyst in nitrate reduction for enhanced electrocatalytic ammonia synthesis

Unveiling structural evolution of Fe single atom catalyst in nitrate reduction for enhanced electrocatalytic ammonia synthesis

Investigation of m- and p-xylene linked bimetallic Ni-cyclam-complexes as potential electrocatalysts for the CO2 reduction

Among the various molecular CO2 reduction catalysts, the [Ni(cyclam)]2+ (Ni-{N4}) complex with its earth-abundant metal center and macrocyclic ligand proved to be efficient for the selective electrochemical conversion of CO2 to CO. In the present study we now connected the two Ni-cyclam units by using para- and meta-xylene as organic linkers attached to the amines of the macrocycle to form the p-{Ni2} andm-{Ni2} complexes, respectively, and test them as catalysts for the electrochemical CO2 reduction reactions. Notably, the p-{Ni2} complex demonstrates a higher faraday efficiency in the electrochemical reduction of CO2 to CO compared to the m-{Ni2} complex. This finding highlights the significant role played by the M-M distance in influencing this catalytic process.

Transition metal single-atom supported on W2N3 as efficient electrocatalysts for the nitrogen reduction reaction: A DFT study

The problems of poor Faraday efficiency and high overpotential usually limit electrochemical nitrogen reduction (NRR) catalysts. In this paper, 28 different transition metal single-atoms (TM-SAs) supported on W2N3 (TM@W2N3) were designed by density functional theory (DFT) for catalytic N2 reduction. The stability, N2 activation capacity, selectivity and NRR mechanism of TM@W2N3 were analyzed. Following the screening process, only 9 TM@W2N3 (TM=Sc, Ti, V, Co, Cu, Y, Mo, Ag, W) structures were identified as exhibiting high stability, strong activation capacity and high NRR selectivity. And then N2 activation mechanism of V@W2N3, Mo@W2N3 and W@W2N3, as well as the Gibbs free energies of its four NRR reaction pathways were further discussed. The overpotentials (η) of Mo@W2N3 and V@W2N3 to NRR are 0.129 V and 0.470 V, respectively. The overpotential (η) of W@W2N3 is the lowest at 0.059 V, while its catalytic activity is the highest. V@W2N3 and W@W2N3 are more likely to follow the distal pathway for NRR, while Mo@W2N3 is more likely to follow the enzymatic pathway. This study offers some theoretical foundation and reference for the design of new and efficient electrocatalytic NRR catalysts.

One-Step synthesis of nanosized Cu-Ag films using atmospheric pressure plasma jet

Thin films of copper-silver (Cu-Ag) composed of nanosized particles were successfully synthesised and deposited on glass and carbon substrates under various metal ratios in a single step using an atmospheric pressure plasma jet (APPJ) system. This rapid synthesis and deposition technique only requires very low power input (20 W) and rudimentary solutions of metal salt precursors and DI water without additives, pretreatment, or post-treatment process. Successful Cu-Ag alloying was observed, with excellent compositional and deposition area control. Strongly adherent films can be formed on conductive and non-conductive substrate, making APPJ an ideal and sustainable approach for large-scale deposition of multi-component thin metallic films. A comprehensive characterisation of Cu-Ag alloys deposited using APPJ and their potential use as electrocatalytic CO2 reduction catalysts is discussed.

Sn/SnO2 Nanocomposite Encapsulated on Nitrogen-Doped Carbon as a Highly Efficient Catalyst for the Electrochemical Reduction of CO2 to Formate

Sn/SnO₂ Nanocomposite Encapsulated on Nitrogen-Doped Carbon as a Highly Efficient Catalyst for the Electrochemical Reduction of CO₂ to Formate

Screening transition metal and nonmetal atoms co-doped graphyne as efficient single-atom catalysts for nitrogen reduction

Despite the great potential of electrocatalytic nitrogen reduction reaction (NRR) for more sustainable and energy-efficient ammonia (NH3) production, significant challenges remain, including low activity and poor selectivity of currently available catalysts. In this study, we systematically investigate the electrocatalytic NRR performance of 43 types of single-atom catalysts (SACs) constructed by introducing single transition metal (TM) or/and nonmetal (NM) atoms in graphyne (TM-NM-GY) through first-principles calculations. It is found that Mn-, Os-, B-, Ti-B-, V-B-, Cr-B-, Ru-B-, and Os-B-GY exhibit remarkable efficiency for NRR, showcasing overpotentials lower than 0.34 V. Particularly, Os-B-GY stands out by demonstrating ultra-high catalytic activity, selectivity, and stability for NRR as well as good experimental feasibility, with an impressively low overpotential of merely 0.13 V. The co-doping of Os and B allows for adjusting moderately positive charge densities around Os, which enables strong d-2π* coupling between Os and N2. As a result, the N≡N triple bond is remarkably weakened, facilitating the subsequent NRR process. Moreover, benefiting from the cooperative doping of NM and TM, the potential limiting step is changed, which breaks the inherent linear volcanic relationship between the free energy of the critical intermediate N2H* and limiting potential (UL) on the sole TM-doped system, further enhancing the activity and selectivity. We anticipate that the insights gained from this comprehensive and systematic study can offer valuable guidance for the design and synthesis of novel and highly efficient SACs toward NRR.

The temperature dependence of electrochemical CO2 reduction on Ag and CuAg alloys

Ag is often studied as catalyst for electrochemical CO2 reduction as it shows high selectivity towards CO and is easily alloyed with Cu to enhance performance using CuAg catalysts. In this study, we investigated the effect of temperature on Ag and CuAg catalysts and compare these with previous results on Au and Cu catalysts. We show that the temperature effect is complicated as it shows an interplay with CO2 concentration, potential and mass transport. It is therefore crucial to deconvolute these parameters and study the effect of temperature under different conditions. Moreover, we show that alloying Ag with Cu can inhibit some of the deactivation effects observed at high temperatures on pure Cu. CuAg alloys can prevent the dominance of hydrogen evolution at elevated temperatures, although an optimum of C2+ products with temperature is still observed.

Improved understanding of carbon nanotube growth via autonomous jump regression targeting of catalyst activity

Catalyst control is critical to carbon nanotube (CNT) growth and scaling their production. In supported catalyst CNT growth, the reduction of an oxidized metal catalyst enables growth, but its reduction also initiates catalyst deactivation via Ostwald ripening. Here, we conducted autonomous experiments guided by a hypothesis-driven machine learning planner based on a novel jump regression algorithm. This planning algorithm iteratively models the experimental response surface to identify discontinuities, such as those created by a material phase change, and targets further experiments to improve the fit and reduce uncertainty in its model. This approach led us to identify conditions that resulted in the greatest CNT yields as a function of the driving forces of catalyst reduction in a fraction of the time and cost of conventional experimental approaches. By varying temperature and the reducing potential of the growth atmosphere, we identified discontinuous jumps in CNT growth for two thicknesses of an iron catalyst, resulting in largest observed yields in narrow and distinct regions of thermodynamic space where we believe the reduced catalyst is in equilibrium with its oxide. At these jumps, we also observed the longest growth lifetimes and a greater degree of diameter control. We believe that conducting CNT growth at these conditions optimizes catalyst activity by inhibiting Ostwald ripening-induced deactivation, thereby keeping catalyst nanoparticles smaller and more numerous. This work establishes a thermodynamic framework for a generalized understanding of metal catalysts in CNT growth, and demonstrates the capability of iterative, hypothesis-driven autonomous experimentation to greatly accelerate materials science.

Combined Effect of Pressure and Temperature on Nitrogen Reduction Reaction in Water

The synthesis of ammonia starting from nitrogen and using electrochemical processes is considered an interesting strategy to produce ammonia in a sustainable way. However, it requires not only the development of efficient catalysts for nitrogen reduction but also the optimization of the operating conditions of the employed electrochemical devices. In this work, we optimize the kinetics and the thermodynamics of the electrocatalytic nitrogen reduction reaction in water by developing a pressurized H-cell that may operate at temperatures up to 80 °C. Ni foam with low Au loading (0.08 mg cm−2) has been adopted as a catalyst at the cathode. Ammonia has been produced during chronoamperometry experiments in a saturated N2 atmosphere and measured by the indophenol blue method. The effect of voltage, temperature, and pressure has been studied. The nitrogen reduction experiments have been repeated under saturated Ar. To remove contributions due to environmental contamination, we determined the net value as the difference between the produced ammonia in N2 and in Ar. The ammonia yield increases by increasing the temperature and the pressure. The best results have been obtained by using the combined effects of temperature and pressure. Operating at 5 bar of saturated N2 and 75 °C, a production rate of 6.73 μg h−1·cm−2 has been obtained, a value corresponding to a 5-fold enhancement, compared to that obtained under ambient conditions and room temperature.

Density functional theory study of transition metal dual-atom anchored phthalocyanine as high-performance electrocatalysts for carbon dioxide reduction reaction

The electrocatalytic reduction of carbon dioxide (CO2RR) to valuable chemicals provides as a promising approach to reduce the excessive CO2 gas, but the scaling relationship between adsorbed intermediates on catalysts with single active site limits the catalytic activity. The introduction of secondary sites is expected to be an effective way to break this linear relationship to achieve high-performance. Therefore, we designed 28 homonuclear and 18 heteronuclear dual-atom catalyst in rectangular-shaped expanded phthalocyanine (Pc) to explore their CO2RR catalytic activities. After density functional theory screening of catalyst stability, activity and selectivity, FeTi@Pc was identified as an ideal catalyst for the deep reduction of CO2 to CH4 with low limiting potential of −0.18 V. Analysis shows the introduction of Fe heteroatom to homonuclear Ti2@Pc leads to the polarization of the electronic structure, which helps to adjust the binding strength with C and O atom of intermediates. The adsorption configuration and projected density of state of *CHO further confirm that heteronuclear bimetal centers can effectively provide the adsorption sites and synergistically adjust the adsorption intensity for C and O, thereby enhancing the catalytic activity. Finally, this study provides valuable theoretical guidance for the development of efficient CO2RR catalysts with multiple active centers.

Insights into Na+/Ca2+ poisoning mechanisms of Zr-modified and unmodified La-Mn perovskite oxide catalysts for NH3-SCR reaction

The presence of alkali metal/alkaline earth metal in fuel gas is one of the important reasons for the deactivation of catalyst for selective catalytic reduction of NOx with NH3 (NH3-SCR). In this work, the Na+/Ca2+ poisoning mechanisms of Zr-modified and unmodified La-Mn perovskite oxides for NH3-SCR reaction were studied. It is found that the deposition of Na+ into LaMnO3 (LM) catalyst has a much larger effect than that of Ca2+, while such a result is opposite for the Na+/Ca2+-deposited La0.8Zr0.2MnO3 (ZLM) catalysts. The deposition of Na+/Ca2+ compounds can block the pores and affect the adsorption and activation of NH3 on the catalysts. After Zr modification, the catalyst with a higher Mn4+ content shows a better redox property and increased acid sites. These acidic sites can trap Na+, thereby delaying the catalyst poisoning and causing a better activity of ZLM catalyst than LM catalyst. The deposition of Ca2+ in the form of CaCO3 on the catalyst surface leads to a serious pore blockage, showing a poor resistance to Ca2+. After regeneration, the pores of the catalyst are dredged, and the active sites originally occupied by Na+/Ca2+ are released, resulting in an recovery of catalyst activity. The recovery of adsorbed oxygen and Mn4+ content is the key factor for returning the SCR activity.

Metallo-Porous Organic Polymer as a CO2 Reduction Catalyst toward Selective Solar Fuel Production

Metallo-Porous Organic Polymer as a CO₂ Reduction Catalyst toward Selective Solar Fuel Production

Vacancy-Rich SnO2 Quantum Dot Stabilized by Polyoxomolybdate as Electrocatalyst for Selective NH3 Production.

The pronounced conductivity of tin dioxide (SnO2) nanoparticles makes it an ideal multifunctional electrode material, while the challenge is to stabilize the quantum dot (QD) SnO2 nanocore in water. An Anderson-type polyoxomolybdate, (NH4)6[Mo7O24], is employed as an inorganic ligand to stabilize a ca. 6 nm SnO2 QD (Mox@SnO2). X-ray scattering and diffraction studies confirm the tetragonal SnO2 nanocore in Mox@SnO2. Elemental analyses are in good agreement with the mass spectrometric detection of the [Mo7O24]6- cluster present in Mox@SnO2. The ionic POMs attached to the SnO2 surface through [Mo-O-Sn] covalent linkages have been established by surface zeta potential, shift of the [Mo = O]t Raman vibration, and extended X-ray absorption fine structure (EXAFS) analyses. The presence of the [Mo7O24]6- cluster in the Mox@SnO2 is responsible for the remarkable aqueous stability of Mox@SnO2 in the pH range of 3-9. Dominant oxygen vacancy in the SnO2 core, identified by EXAFS data and the anisotropic electron paramagnetic resonance (EPR) signals (g ∼ 2.4 and 1.9), results in facile electronic conduction in Mox@SnO2 while being deposited on the electrode surface. Mox@SnO2 acts as an active catalyst for the electrocatalytic nitrate reduction (eNOR) to ammonia with 94% faradaic efficiency (FE) at -0.2 V vs RHE and a yield rate of 28.9 mg h-1 cm-2. The stability of Mox@SnO2 in acidic pH provides scope to reuse the Mox@SnO2 electrode at least four times with notable NH3 selectivity and a superior production rate (239.06 mmol g-1(cat) h-1). This study demonstrates the essential role of POM in stabilizing SnO2 QD, harnessing its electrochemical activity toward electrocatalytic ammonia production.

First Principles Study of O2 Dissociative Adsorption on Pt-Skin Pt3Cu(111) Surface

The O2 dissociative adsorption serves as a pivotal criterion for assessing the efficacy of oxygen reduction catalysts. We conducted a systematic investigation into O2 dissociative adsorption on the Pt-skin Pt3Cu(111) surface by means of the density functional theory (DFT). The computational findings reveal that the O2 adsorption on Pt-skin Pt3Cu(111) surface exhibits comparatively lower stability when contrasted with that on the Pt(111) surface. For O2 dissociation, two paths have been identified. One progresses from the t-f-b state towards the generation of two oxygen atoms situated within nearest-neighbour hcp sites. The other commences from the t-b-t state, leading to the generation of two oxygen atoms occupying nearest-neighbour fcc sites. Moreover, the analysis of the energy barrier associated with O2 dissociation indicates that O2 on the Pt-skin Pt3Cu(111) surface is more difficult to dissociate than on the Pt(111) surface. This study can offer a valuable guide for the practical application of high-performance oxygen reduction catalysts.