Catalyst For Reduction Research Articles

Dissociative Adsorption of O2 on Ag3Au(111) Surface: A Density Functional Theory Study

The catalytic efficiency of oxygen reduction catalysts is notably influenced by the dissociative adsorption of O2. We conducted a systematic investigation into the dissociative adsorption of O2 on the Ag3Au(111) surface using ab initio density functional theory (DFT) calculations. Our computational findings indicate that adsorption the configuration designated t-b-t exhibits favorable energetics on the Ag3Au(111) surface. Regarding the dissociation of O2, we identified a reasonable dissociation pathway, which proceeds from the initial t-b-t state to the creation of two oxygen atoms that occupy a set of neighboring fcc sites. Furthermore, our analysis indicates that the adsorption of O2 on the Ag3Au(111) surface is less favored thermodynamically and more difficult to dissociate than that on the Ag(111) surface. This study furnishes a theoretical framework elucidating the prospective utilization of Ag-Au alloy in the capacity of oxygen reduction catalysts.

Enhanced room temperature CO2 photoreduction on gas-solid interfaces using nanocrystals integrated with ZIF-8 wrapping design

Composites derived from metal-organic frameworks (MOFs) show promise as catalysts for the photocatalytic reduction of CO2. However, their potential is hindered by constraints such as limited light absorption and sluggish electron transfer and separation, impacting the overall efficiency of the photocatalytic process. In this study, TiO2 nanocrystals, modified with Ptx+, underwent laser etching were encapsulated within the traditional MOF-ZIF-8 framework. This enhanced the adsorption capabilities for CO2 reactants and solar light, while also facilitating directed electron transfer and the separation of photogenerated charges. The finely-tuned catalyst demonstrates impressive CH4 selectivity at 9.5 %, with yields of 250. 24 µmol g-1 h-1 for CO and 25.43 µmol g-1 h-1 for CH4, utilizing water as a hole trap and H+ source. This study demonstrates the viability of achieving characteristics related to the separation of photogenerated charges in TiO2 nanocrystals through laser etching and MOF composite catalysts. It offers novel perspectives for designing MOF-based catalysts with enhanced performance in artificial photosynthesis.

TiO<sub>2</sub>-ZnO Catalyst: A New Composite For Selective Catalytic Reduction of NO<sub>x</sub> with NH<sub>3</sub>

Investigations have underscored the pivotal role of NOx gases in the formation of smog and acid rain, posing threats to human health and ecosystems. Selective Catalytic Reduction (SCR) has emerged as a promising strategy for curtailing NOx emissions. SCR involves the catalytic conversion of nitrogen oxides into benign nitrogen and water vapour, thereby offering a viable approach. In this study, a new composite of low-temperature selective catalytic reduction (LT-SCR) catalyst is synthesized by impregnating ZnO onto TiO2 ceramic substrate. The introduction of ZnO not only provides a high surface area but also results in the formation of a catalyst. This research presents the outcomes of an investigation involving a range of catalysts employed in SCR, including a composite catalyst composed of titanium dioxide and zinc oxide. The objective is to evaluate the composite catalyst's capacity to reduce pollutants characterized by observable NOX content. The catalysts, synthesized through the sol-gel processing technique, are characterized by XRD and SEM to ascertain their suitability for catalytic applications. A comprehensive analysis concludes that the laboratory-synthesized samples exhibit acceptable purity, possess a crystalline structure, and hold potential as catalysts.

One-Pot Synthesis of Ce-SSZ-39 Zeolite with Performance in the NH3-SCR Reaction.

Cu-SSZ-39 zeolite with 8-membered rings is regarded as a very promising catalyst in the NH3-SCR reaction, but its hydrothermal stability still remains to be improved. One of the solutions to promote hydrothermal stability is the insertion of rare earth elements in the product. Nevertheless, normal ion exchange of rare earth elements limits their contents in the zeolite product due to their large hydrated ionic radius and alkaline environment under hydrothermal conditions. Herein, we for the first time present a new method for the one-pot synthesis of Ce-SSZ-39 zeolite under solvent-free conditions. The key to success is the use of Ce-FAU zeolite as a precursor. The obtained product shows good crystallinity, sheet-like morphology, large BET surface area, and 4-coordinated Al species. Detailed investigations illustrate that Ce species in the Cu/Ce-SSZ-39 zeolite micropore can prevent the dealumination and thus formation of CuAlOx species during hydrothermal aging at 850 °C for 16 h, giving the excellent hydrothermal stability and thus showing the excellent catalytic performance in the NH3-SCR reaction. One-pot synthesis of Ce-SSZ-39 zeolite with excellent catalytic performance might open a new door for developing very efficient selective catalytic reduction (SCR) catalysts in near future.

Mesoporous CuCe dual-metal catalysts for efficient electrochemical reduction of CO2 to methane

In this manuscript, we report the successful synthesis of CuxCe1-xO2 bimetallic mesoporous oxides using a straightforward two-step hydrothermal method aided by CTAB, demonstrating exceptional selectivity for methane (CH4). We hypothesize that the superior CH4 selectivity of CuxCe1-xO2 can be attributed to the strong adsorption of ∗CO facilitated by the mesoporous structure, which effectively promotes the conversion of ∗CO to ∗CHO.

Effect of β-fluorinated porphyrin in changing selectivity for electrochemical O2 reduction

The development of catalytic systems that selectively convert O2 to water is required to progress fuel cell technology. As an alternative to platinum catalysts, derivatives of iron and cobalt porphyrin molecular catalysts provide one benchmark for catalyst design. However, the inclusion of these catalysts into homogeneous platforms remains a difficulty. Co-porphyrins have been studied as heterogeneous O2 reduction catalysts; however, they have not been explored much in homogeneous systems. Moreover, they suffer from poor selectivity for the desired four-electron reduction of O2 to H2O. Herein, we present two cobalt-based β-fluorinated porphyrin complexes (CoTPF8(OH)2 and CoTPF8(OH)4) and demonstrate applicability as effective catalysts for the oxygen reduction reaction. Using rotating ring-disk electrochemistry, the catalysts, CoTPF8(OH)2 and CoTPF8(OH)4, showed maximum Faradaic efficiency for H2O of 92 % and 97 %, respectively. DFT calculations suggest that the formation of a phlorin intermediate could occur before O2 reduction and that a stronger H2O2 binding in the cobalt-based β-fluorinated porphyrin species compared to the unsubstituted parent compound, CoTP(OH)2, was responsible for the observed experimental selectivity for H2O. These results reveal that the β-fluorinated porphyrin catalyst serves as a novel platform for investigating molecular electrocatalytic reactions.

Supported tetra-atom clusters on g-CN as catalysts for electrochemical reduction of carbon dioxide to formate: A computational study

Single-cluster catalysts (SCCs) have emerged as highly efficient catalysts for the CO2 reduction reaction (CO2RR), providing a promising avenue to solve the carbon dilemma. Based on density functional theory calculations, we systematically investigated the capability of 12 tetra-atom transitional-metal clusters anchored on g-CN (TM4@g-CN) for CO2RR and found that all clusters have good stability on the substrate. Notably, the charge variation of the top metal atom (TM4) of six SCCs is close to zero which makes them readily donate electrons to the adsorbate CO2 and subsequent reaction intermediates. Our results demonstrate that CO2 can be efficiently reduced to HCOOH on Ni4, Cu4, and Au4@g-CN with low limiting potentials of −0.21, −0.22, and −0.19 V, respectively, outperforming the corresponding single-atom counterparts. Both ΔG(∗CO2) and ΔG(∗OCHO/∗COOH) exhibit a volcano relationship with the reaction activity, and the TM4 serves as electron reservoirs throughout the entire reaction process. This work offers valuable insights for the advancement of cost-effective supported single cluster catalysts.

Promotional effects of Fe2O3 additive on the NH3-SCR activity and alkali resistance of MoTiOx catalysts

Catalyst is the core of selective catalytic reduction (SCR) technology, and an ideal SCR technology requires that the catalyst should have high activity and resistance to alkali metal poisoning. Therefore, in this paper, the influence of Na poisoning on the catalytic performance of Fe2O3-MoTiOx catalysts in the selective catalytic reduction (SCR) reaction was investigated, and the anti-alkali mechanism was revealed. The Fe2O3-MoTiOx catalyst demonstrated the NO conversion was 90 % at a broad temperature range of 225-400 °C when the Fe2O3 loading ratio was 20 wt%. Besides, 80 % NO conversion rate of the Fe2O3-MoTiOx catalyst at 320 °C was still achieved even at a Na+ concentration of 300 μmol g-1. The phenomenon was attributed to the interaction between Fe and Ti species, which could generate more Lewis acid centers and facilitate the adsorption activation of NH3. During the Na poisoning process, Na ions predominantly adsorbed on the Fe2O3, effectively safeguarding the MoTiOx catalyst. Additionally, although the Brønsted acid sites were deteriorated because of Na poisoning, the abundant Lewis acid sites were preserved for NHx adsorption. Therefore, the Na-poisoned Fe2O3-MoTiOx catalyst maintained efficient NH3 adsorption and NO activation. The work provided theoretical guidance and data support for the development of novel alkali-resistant SCR catalysts.

High entropy borides as efficient catalysts for electrochemical reduction of nitrate to ammonia

Electrochemical reduction of nitrate (NO3-RR) to ammonia has attracted great attention as a strategy for simultaneously achieving pollutant removal and economic product acquisition. To achieve high Faradaic efficiency of ammonia (FE) and ammonia selectivity, it is necessary to develop highly active catalysts with strong hydrogenation ability. In this work, we report high-entropy-borides (HEB) with tunable cation composition as high-performance catalysts for NO3-RR. Taking (TiVCrMo)B2 as the model material systems, we systematically investigate the effect of doping (Co, Fe, and Ni) on the activity of NO3-RR. Electrochemical test results show that the HEB doped with Co element exhibits the optimal performance, with a FE reaching 97.9 %. Combining several advanced spectroscopic techniques, we find that Co dopant can effectively facilitate the hydrogenation process of NO3-RR. This work demonstrates high-entropy ceramics as an excellent platform for rational design of highly active catalysts for energy and environmental applications.

“Capture-activation-recapture” mechanism-guided design of double-atom catalysts for electrocatalytic nitrogen reduction

Compared with the traditional industrial nitrogen fixation, electrocatalytic methods, especially those utilizing double-atom catalysts containing nonmetals, can give good consideration to the economy and environmental protection. However, the existing “acceptance-donation” mechanism is only applicable to bimetallic catalysts and nonmetallic double-atom catalysts containing boron atoms. Herein, a novel “capture-activation-recapture” mechanism for metal-nonmetal double-atom catalyst is proposed to solve the problem by adjusting the coordination environments of nonmetallic atoms and utilizing the activation effect of metal atoms on nitrogen. Based on this mechanism, the nitrogen reduction reaction (NRR) activity of 48 structures is calculated by density functional theory calculation, and four candidates are selected as outstanding electrocatalytic nitrogen reduction catalysts: Si-Fe@NG (UL = –0.14 V), Si-Co@NG (UL = –0.15 V), Si-Mo@BP1 (UL = 0 V), and Si-Re@BP1 (UL = –0.02 V). The analyses of electronic properties further confirm “capture-activation-recapture” mechanism and suggest that the difference in valence electron distribution between metal and Si atoms triggers the activation of N≡N bonds. In addition, a machine learning approach is utilized to generate an expression and an intrinsic descriptor that considers the coordination environment to predict the limiting potential. This study offers profound insight into the synergistic mechanism of TM and Si for NRR and guidance in the design of novel double-atom nitrogen fixation catalysts.

N‐Doped Carbon Nanofibers and Carbon Nanotubes‐Encapsulated CoNi Alloy as Highly Active Oxygen Reduction Catalysts for Direct Methanol Fuel Cells

The slow oxygen reduction kinetics of direct methanol fuel cell (DMFCs) are one of the limiting factors affecting its application. Therefore, exploring nonprecious catalysts with high activity and methanol resistance is urgently needed. Herein, zeolitic imidazolate framework‐8 particles are first blended with different proportions of metal salts (Ni as well as Co) and further electrospun to obtain a nanofiber precursor. After pyrolysis treatment, a composite catalyst (CoNi@N‐CNFs) with a highly dispersed CoNi alloy phase supported by porous N‐doped carbon nanofiber and carbon nanotube is prepared. The surface electronic structure can be reasonably adjusted by optimizing the doping ratio of Ni and Co. The CoNi@N‐CNFs shows high oxygen reduction activity and methanol resistance. Half‐wave potential and the onset potential of Co1Ni1@N‐CNFs (Co: Ni mole ratio = 1:1) are 0.79 and 0.87 V. Additionally, Co1Ni1@N‐CNF‐modified DMFC endows a high power density (24.07 mW cm−2), which is close to Pt/C‐based DMFC (27.59 mW cm−2). Rich active sites, large specific surface area, and synergy between CoNi alloy and N configuration of CoNi@N‐CNFs effectively accelerate electron transfer, resulting in the superior catalytic activity. This work provides a new strategy to design effective 1D oxygen reduction reaction catalysts in fuel cells.

Boosting Electrochemical Ammonia Synthesis via NOx Reduction over Sulfur‐Doped Copper Oxide Nanoneedle Arrays

AbstractThe electrochemical NOx reduction reactions, involving nitrate and nitrite reduction reactions (NO3−RR and NO2−RR), have emerged as promising approaches for both NO3− and NO2− removal, and ammonium (NH3) synthesis under ambient conditions. However, the incorporation and stabilization of sulfur dopants in the catalysts for efficient NOx reduction are rarely explored, leading to an unclear effect of sulfur on the NOx reduction mechanism. Herein, sulfur‐doped Cu2O (S‐Cu2O) nanoneedle arrays via in situ electrochemical treatment are synthesized. The S‐Cu2O catalyst possesses excellent durability and selectivity for NH3 over a wide range of potentials in NO3−RR, attaining a maximum NH3 Faradaic efficiency of 94% at −0.6 VRHE and a maximum NH3 yield as high as 1.06 mmol h−1 cm−2. In NO3−RR, the sulfur dopant can accelerate the step from NO2− to NH3, contributing superior performance in NO2−RR and assembled Zn−NO2− battery device. Density functional theory (DFT) calculations reveal that the presence of sulfur can enhance the initial step of *NO3 adsorption, lower the reaction barriers for the formation of *NHO intermediate, and activate the H2O dissociation process. The work sheds light on the role of sulfur in enhancing electrocatalytic performance and provides a unique perspective for understanding the NOx reduction mechanism.

Electrochemical Reductive Cross-Coupling of Alkyl or Alkenyl Halides with gem-Difluoroalkenes.

Herein, we describe an electroreductive cross-electrophile coupling protocol for the construction of valuable monofluoroalkenes from easily accessible alkyl or alkenyl halides with gem-difluoroalkenes. The reaction can be conducted under sustainable and mild conditions delivering valuable and functionalized monofluoroalkenes with excellent Z-selectivity. The protocol's most notable advantage is the in situ release of nickel catalyst from the inexpensive electrodes without the addition of extra hazardous metal catalyst and superstoichiometric reductant.

Systematic analysis of dual-functional catalysts for simultaneous CO-NOx reduction: Toward an effective catalyst design strategy

The development of a multifunctional catalyst suitable for application in existing facilities with limited space, with specific emphasis on its capability to concurrently remove CO and NOx is vital for meeting stringent environmental regulations. This is particularly pertinent to industries such as liquefied natural gas-based power plants and multipollutant-emitting industrial facilities. Another important consideration is that the catalyst should operate over a wide temperature range to facilitate its application across various industrial sites. In this study, we synthesized vanadium-based catalysts with a series of noble metals (Pt, Pd, and Au). The V–W–Pd/TiO2 catalyst achieved a simultaneous CO–NOx reduction efficiency greater than 90% in the widest temperature range, 228–321 °C. The excellent catalytic activities resulted from the Pd active sites, which oxidated CO and adsorbed NOx. This enables the catalyst to easily participate in the NH3-SCR reaction and facilitates NOx reduction. Moreover, we systematically analyzed the reaction properties of each catalyst using diffuse reflectance infrared Fourier transform and temperature programmed desorption methods. This enabled the elucidation of the reaction characteristics and competitive adsorption properties of the catalysts.

Time‐Resolved Oxidation State Changes Are Key to Elucidating the Bifunctionality of Perovskite Catalysts for Oxygen Evolution and Reduction

In a unified regenerative fuel cell (URFC) or reversible fuel cell, the oxygen bifunctional catalyst must switch reversibly between the oxygen reduction reaction (ORR), fuel cell mode, and the oxygen evolution reaction (OER), electrolyzer mode. However, it is often unclear what effect alternating between ORR and OER has on the electrochemical behavior and physiochemical properties of the catalyst. Herein, operando X‐ray absorption spectroscopy (XAS) is utilized to monitor the continuous and dynamic evolution of the Co, Mn, and Fe oxidation states of perovskite catalysts Ba0.5Sr0.5Co0.8Fe0.2O3‐δ (BSCF) and La0.4Sr0.6MnO3‐δ (LSM), while the potential is oscillated between reducing and oxidizing potentials with cyclic voltammetry. The results reveal the importance of investigating bifunctional catalysts by alternating between fuel cell and electrolyzer operation and highlight the limitations and challenges of bifunctional catalysts. It is shown that the requirements for ORR and OER performance are divergent and that the oxidative potentials of OER are detrimental to ORR activity. These findings are used to give guidelines for future bifunctional catalyst design. Additionally, it is demonstrated how sunlight can be used to reactivate the ORR activity of LSM after rigorous cycling.

Testing functional anchor groups for the efficient immobilization of molecular catalysts on silver surfaces

Modifications of complexes by attachment of anchor groups are widely used to control molecule-surface interactions. This is of importance for the fabrication of (catalytically active) hybrid systems, viz. of surface immobilized molecular catalysts. In this study, the complex fac-Re(S-Sbpy)(CO)3Cl (S-Sbpy = 3,3′-disulfide-2,2′-bipyridine), a sulfurated derivative of the prominent Re(bpy)(CO)3Cl class of CO2 reduction catalysts, was deposited onto the clean Ag(001) surface at room temperature. The complex is thermostable upon sublimation as supported by infrared absorption and nuclear magnetic resonance spectroscopy. Its anchoring process has been analyzed using scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. The growth behavior was directly contrasted to the one of the parent complex fac-Re(bpy)(CO)3Cl (bpy = 2,2′-bipyridine). The sulfurated complex nucleates as single molecule at different surface sites and at molecule clusters. In contrast, for the parent complex nucleation only occurs in clusters of several molecules at specifically oriented surface steps. While this shows that surface immobilization of the sulfurated complex is more efficient as compared to the parent, symmetry analysis of the STM topographic data supported by DFT calculations indicates that more than 90% of the complexes adsorb in a geometric configuration very similar to the one of the parent complex.

Recent Advances in Carbon-Based Single-Atom Catalysts for Electrochemical Oxygen Reduction to Hydrogen Peroxide in Acidic Media.

Electrochemical oxygen reduction reaction (ORR) via the 2e- pathway in an acidic media shows great techno-economic potential for the production of hydrogen peroxide. Currently, carbon-based single-atom catalysts (C-SACs) have attracted extensive attention due to their tunable electronic structures, low cost, and sufficient stability in acidic media. This review summarizes recent advances in metal centers and their coordination environment in C-SACs for 2e--ORR. Firstly, the reaction mechanism of 2e--ORR on the active sites of C-SACs is systematically presented. Secondly, the structural regulation strategies for the active sites of 2e--ORR are further summarized, including the metal active center, its species and configurations of nitrogen coordination or heteroatom coordination, and their near functional groups or substitute groups, which would provide available and proper ideas for developing superior acidic 2e--ORR electrocatalysts of C-SACs. Finally, we propose the current challenges and future opportunities regarding the acidic 2e--ORR pathway on C-SACs, which will eventually accelerate the development of the distributed H2O2 electrosynthesis process.

Supported of gold nanoparticles on carboxymethyl lignin modified magnetic nanoparticles as an efficient catalyst for reduction of nitroarenes and treatment of human melanoma

This article represents the synthesis and characterizations of Au NPs immobilized and carboxymethyl lignin (CML) modified Fe3O4 nanoparticles (Fe3O4@CML/Au NPs) following a bio-inspired protocol without the participation of any toxic and harmful reductant or stabilizers. Following various physicochemical methodologies, such as FT-IR, FE-SEM, TEM, EDX, XRD, VSM, and ICP-OES, the textural characteristics and different structural aspects were evaluated. The Fe3O4@CML/Au NPs nanocomposite was subsequently explored towards the catalytic reduction of diverse aromatic nitro functions using green conditions. An excellent yield were achieved within very short reaction time. Nine recycling runs of the nanocatalyst were completed without a discernible loss of catalytic activity, thanks to its easy magnetic recovery. The DPPH assay was carried out to examine the antioxidant effectiveness. The Fe3O4@CML/Au NPs nanocomposite inhibited half of the DPPH in a 250 μg/mL solution. To measure the anti-human melanoma efficacy of Fe3O4@CML/Au NPs nanocomposite, MTT assay was applied on HT144, MUM2C, IPC-298 and SKMEL24 cell lines. Fe3O4@CML/Au NPs nanocomposite had high anti-human melanoma efficacy on above tumor cells. The best finding of anti-human melanoma properties of Fe3O4@CML/Au NPs nanocomposite was seen in the case of the SKMEL24 cell line. The IC50 of Fe3O4@CML/Au NPs nanocomposite was 137, 145, 185, and 125 μg/mL against HT144, MUM2C, IPC-298 and SKMEL24 cells, respectively. This research exhibited remarkable anti-human melanoma and antioxidant efficacies of Fe3O4@CML/Au NPs nanocomposite in the in vitro condition.

Efficient recovery and recycling/upcycling of precious metals using hydrazide-functionalized star-shaped polymers

There is a growing demand for adsorption technologies for recovering and recycling precious metals (PMs) in various industries. Unfortunately, amine-functionalized polymers widely used as metal adsorbents are ineffective at recovering PMs owing to their unsatisfactory PM adsorption performance. Herein, a star-shaped, hydrazide-functionalized polymer (S-PAcH) is proposed as a readily recoverable standalone adsorbent with high PM adsorption performance. The compact chain structure of S-PAcH containing numerous hydrazide groups with strong reducibility promotes PM adsorption by enhancing PM reduction while forming large, collectable precipitates. Compared with previously reported PM adsorbents, commercial amine polymers, and reducing agents, S-PAcH exhibited significantly higher adsorption capacity, selectivity, and kinetics toward three PMs (gold, palladium, and platinum) with model, simulated, and real-world feed solutions. The superior PM recovery performance of S-PAcH was attributed to its strong reduction capability combined with its chemisorption mechanism. Moreover, PM-adsorbed S-PAcH could be refined into high-purity PMs via calcination, directly utilized (upcycled) as catalysts for dye reduction, or regenerated for reuse, demonstrating its high practical feasibility. Our proposed PM adsorbents would have a tremendous impact on various industrial sectors from the perspectives of environmental protection and sustainable development.

Reinforcing the efficiency of photocatalytic CO2 conversion with H2O vapor through the integration of photothermal Cu/C@Bi/C supported on 3D g-C3N4 under full-spectrum solar irradiation

Developing an efficient photocatalyst for CO2 conversion to chemical fuels that maximizes the utilization of solar energy, particularly near-infrared light, remains a persistent challenge. Meanwhile, it is difficult to suppress the H2 evolution during the photocatalytic process. Herein, Cu/C@Bi/C grafted on the surface of 3D g-C3N4 (NCN) can serve as a highly durable and active catalyst for photothermal synergistic catalytic CO2 reduction under full-spectrum solar irradiation in solid-liquid-gas three-phase interfaces, wherein the Cu/C@Bi/C serves as a harvesting-near-infrared light nanoreactor and an electron transport bridge for the enhancement of the interface local temperature and the efficient transfer of photoinduced electrons. As a result, the hybrid catalyst shows excellent photothermal catalytic activity of CO2 to CO (169.26 μmol·g−1·h−1) and CO2 to CH4 (1.94 μmol·g−1·h−1), outperforming the majority of the conventional photocatalysts, whereas the competitive reaction of H2 evolution can be inhibited. This study presents a feasible approach for the efficient utilization of solar energy by harnessing near-infrared light through nano-reactors, thereby providing a viable strategy for photothermal catalytic CO2 reduction.