Stable Catalyst Research Articles

Optimized porous nanostructure of carbon fibers enabling excellent stability of Pt-based catalysts for oxygen reduction reaction

Facile synthesis of highly-dispersed Pt-based electrocatalysts on porous carbon supports with strong durability is extremely desirable for oxygen reduction reaction but remains challenging. The influence of pores in carbon supports on the stability and activity of catalysts is ambiguous and needs to be elucidated. Targeting this aim, herein, we prepared a series of carbon nanofibers with tunable pore diameter and specific surface area using the resorcinol-formaldehyde (RF) resins as a model system. Homogeneous composite precursors composed of RF resins and silica colloids were synthesized by the surfactant-assisted simultaneous polycondensation of RF resins and tetraethylorthosilicate (TEOS). The diameter of the pores induced by removal of silica could be controllable tailored through thermal treatment of the composite under various target temperatures. Pt3Co alloy nanoparticles loaded on the as-synthesized porous carbon nanofibers were prepared by an optimized wet-impregnation method. The experimental results indicated that the carbon nanofibers with pore size distribution focused on ∼1.27 nm and ∼2.34 nm provided the best stability without limiting current density decay, and negative shift of half-wave potential (E1/2) and mass activity (MA) loss of Pt after 20000 potential cycles are relatively mild. Conversely, negative shift of 21 mV, 15 mV and 22 mV in E1/2 and mass activity loss of 51.8%, 30.2% and 33.0% were observed for the Pt3Co nanoparticles supported on MC-60, MC-100 and MC-140 matrices which have pore size distribution focused on ∼2.73 nm, ∼2.73 nm as well as ∼4.66 nm, and ∼4.66 nm, respectively. This work demonstrates the importance of micropores and small mesopores for activity and long-term stability enhancement of carbon supported Pt-based electrocatalysts.

Reinforced MOF/polymer composite based on a copper metal-organic framework supported on nanoporous hyper cross-linked polycalix[4]resorcinarene for the preparation of phthalazine and 4H-pyran heterocycles

The present study has aimed to prepare a novel MOF/polymer composite called PC4RA@PrSi-CA/Cu-MOF to take benefit from the advantages of both Cu-based metal-organic framework (Cu-MOF) and porous polymer based on Cis-calix[4]resorcinarene (PC4RA). Various processes, including preparation of a 3D network of polycalix, modification of polycalix with (3-aminopropyl)trimethoxysilan (APTMS) and citric anhydride (CA), and functionalization of the modified polymer with Cu-MOF nanostructure, respectively, were used for synthesizing MOF/polymer composite. Next, the characterization and confirmation of the polymer-supported Cu-MOF were analyzed using FT-IR, EDS-Mapping, STA, PXRD, FE-SEM, and TEM techniques. In the continuation, two types of heterocycles, including phthalazines and 4H-pyrans, were synthesized to reveal the efficiency of the PC4RA@PrSi-CA/Cu-MOF nanocomposite. The catalyst showed a reasonable performance by providing a satisfactory yield of the desired products (90–99 %) during a short time (8–20 min) under mild and green conditions (50 °C in H2O). Furthermore, the structure of the heterocycles was validated using FT-IR, 1H/13C NMR. Then, the catalyst was successively reused ten times in the model reaction and studied using FT-IR, EDX, TEM, and elemental mapping analyses to demonstrate the catalyst stability in recoverability. According to the results, this heterogenized catalyst can recover several times without a notable drop in stability and activity.

The Role of the Heterogeneous Catalyst to Produce Solketal from Biodiesel Waste: The Key to Achieve Efficiency

The valorization of the large amount of crude glycerol formed from the biodiesel industry is of primordial necessity. One possible direction with high interest to the biorefinery sector is the production of fuel additives such as solketal, through the acetalization of glycerol with acetone. This is a chemical process that conciliates high sustainability and economic interest, since solketal contributes to the fulfillment of a Circular Economy Model through its use in biodiesel blends. The key to guarantee high efficiency and high sustainability for solketal production is the use of recovery and recyclable heterogeneous catalysts. Reported works indicate that high yields are attributed to catalyst acidity, mainly the ones containing Brönsted acidic sites. On the other hand, the catalyst stability and its recycling capacity are completely dependent of the support material and the acidic sites incorporation methodology. This review intends to conciliate the information spread on this topic and indicate the most assertive strategies to achieve high solketal production in short reaction time during various reaction cycles.

Tailored Metal-Organic Frameworks for Water Purification: Perfluorinated Fe-MOFs for Enhanced Heterogeneous Catalytic Ozonation.

An industrially viable catalyst for heterogeneous catalytic ozonation (HCO) in water purification requires the characteristics of good dispersion of active species on its surface, efficient electron transfer for ozone decay, and maximum active species utilization. While metal-organic frameworks (MOFs) represent an attractive platform for HCO, the metal nodes in the unmodified MOFs exhibit low catalytic activity. Herein, we present a perfluorinated Fe-MOF catalyst by substituting H atoms on the metalated ligands with F atoms (termed 4F-MIL-88B) to induce structure evolution. The Lewis acidity of 4F-MIL-88B was enhanced via the formation of Fe nodes, tailoring the electron distribution on the catalyst surface. As a result of catalyst modification, the rate constant for degradation of the target compounds examined increased by ∼700% compared with that observed for the unmodified catalyst. Experimental evidence and theoretical calculations showed that the modulated polarity and the enhanced electron transfer between the catalyst and ozone molecules contributed to the adsorption and transformation of O3 to •OH on the catalyst surface. Overall, the results of this study highlight the significance of tailoring the metalated ligands to develop highly efficient and stable MOF catalysts for HCO and provide an in-depth mechanistic understanding of their structure-function evolution, which is expected to facilitate the applications of nanomaterial-based processes in water purification.

Charge Redistribution of Lattice-Mismatched Co─Cu3P Boosting pH-Universal Water/Seawater Hydrogen Evolution.

Practical applications of the hydrogen evolution reaction (HER) rely on the development of highly efficient, stable, and low-cost catalysts. Tuning the electronic structure, morphology, and architecture of catalysts is an important way to realize efficient and stable HER electrocatalysts. Herein, Co-doped Cu3P-based sugar-gourd structures (Co─Cu3P/CF) are prepared on copper foam as active electrocatalysts for hydrogen evolution. This hierarchical structure facilitates fast mass transport during electrocatalysis. Notably, the introduction of Co not only induces a charge redistribution but also leads to lattice-mismatch on the atomic scale, which creates defects and performs as additional active sites. Therefore, Co─Cu3P/CF requires an overpotential of only 81, 111, 185, and 230mV to reach currents of 50, 100, 500, and 1000mA cm-2 in alkaline media and remains stable after 10 000 CV cycles in a row and up to 110h i-t stability tests. In addition, it also shows excellent HER performance in water/seawater electrolytes of different pH values. Experimental and DFT show that the introduction of Co modulates the electronic and energy level structures of the catalyst, optimizes the adsorption and desorption behavior of the intermediate, reduces the water dissociation energy barrier during the reaction, accelerates the Volmer step reaction, and thus improves the HER performance.

Encapsulating stable perovskite catalysts in hollow nanoreactors for enhanced pollutants degradation

Creating a microenvironment for enhanced peroxymonosulfate (PMS) activation is vital in advanced oxidation processes. The objective of this study was to fabricate nanoshells composed of titanium dioxide embedded with cobalt titanate nanoparticles of perovskite to act as nanoreactors for effectively initiating PMS and degrading contaminants. The unique porous structure and confined space of the nanoreactor facilitated reactant absorption and mass transfer to the active sites, resulting in exceptional catalytic performance for pollutant elimination. Experimental findings revealed close to 100% decomposition efficiency of 4-chlorophenol (4-CP) within an hour utilizing the nanoreactors over a wide pH range. The TiO2/CoTiO3 hollow nanoshells catalysts also displayed adaptability in disintegrating organic dyes and antibiotics. The radicals SO4•-, •OH, and non-radicals 1O2 were determined to be accountable for eliminating pollutants, as supported by trapping experiments and electron paramagnetic resonance spectra. The catalyst was confirmed as an electron donor and PMS as an electron acceptor through electrochemical tests and density functional theory calculations. This study underscores the potential of incorporating stable perovskite catalysts in hollow nanoreactors to enhance wastewater treatment.

Polymer-Supported Heterogeneous Fenton Catalysts for the Environmental Remediation of Wastewater

Materials based on polymer hydrogels have demonstrated potential as innovative Fenton catalysts for treating water. However, developing these polymer-supported catalysts with robust stability presents a significant challenge. This paper explores the development and application of polymer-supported heterogeneous Fenton catalysts for the environmental remediation of wastewater, emphasizing the enhancement of metal incorporation into catalysts for improved efficiency. The study begins with an introduction to the heterogeneous Fenton process and its relevance to wastewater treatment. It further delves into the specifics of polymer-supported heterogeneous Fenton catalysts, focusing on iron oxide, copper complexes/nanoparticles, and ruthenium as key components. The synthesis methods employed to prepare these catalysts are discussed, highlighting the innovative approaches to achieve substantial metal incorporation. Operational parameters such as catalyst dosage, pollutant concentration, and the effect of pH on the process efficiency are thoroughly examined. The catalytic performance is evaluated, providing insights into the effectiveness of these catalysts in degrading pollutants. Recent developments in the field are reviewed, showcasing advancements in catalyst design and application. The study also addresses the stability and reusability of polymer-supported heterogeneous Fenton catalysts, critical factors for their practical application in environmental remediation. Environmental applications are explored, demonstrating the potential of these catalysts in addressing various pollutants. The Conclusions offers future perspectives, underlining the ongoing challenges and opportunities in the field, and the importance of further research to enhance the efficacy and sustainability of polymer-supported heterogeneous Fenton catalysts for wastewater treatment.

Strategies for Achieving Ultra-Long ORR Durability-Rh Activates Interatomic Interactions in Alloys.

The stability of platinum-based alloy catalysts is crucial for the future development of proton exchange membrane fuel cells, considering the potential dissolution of transition metals under complex operating conditions. Here, we report on a Rh-doped Pt3Co alloy that exhibits strong interatomic interactions, thereby enhancing the durability of fuel cells. The Rh-Pt3Co/C catalyst demonstrates exceptional catalytic activity for oxygen reduction reactions (ORR) (1.31 A mgPt -1 at 0.9 V vs. the reversible hydrogen electrode (RHE) and maintaining 92 % of its mass activity after 170,000 potential cycles). Long-term testing has shown direct inhibition of Co dissolution in Rh-Pt3Co/C. Furthermore, tests on proton exchange membrane fuel cells (PEMFC) have shown excellent performance and long-term durability with low Pt loading. After 50,000 cycles, there was no voltage loss at 0.8 A cm-2 for Rh-Pt3Co/C, while Pt3Co/C experienced a loss of 200 mV. Theoretical calculations suggest that introducing transition metal atoms through doping creates a stronger compressive strain, which in turn leads to increased catalytic activity. Additionally, Rh doping increases the energy barrier for Co diffusion in the bulk phase, while also raising the vacancy formation energy of the surface Pt. This ensures the long-term stability of the alloy over the course of the cycle.

Capture of single Ag atoms through high-temperature-induced crystal plane reconstruction

The “terminal hydroxyl group anchoring mechanism” has been studied on metal oxides (Al2O3, CeO2) as well as a variety of noble and transition metals (Ag, Pt, Pd, Cu, Ni, Fe, Mn, and Co) in a number of generalized studies, but there is still a gap in how to regulate the content of terminal hydroxyl groups to influence the dispersion of the active species and thus to achieve optimal catalytic performance. Herein, we utilized AlOOH as a precursor for γ-Al2O3 and induced the transformation of the exposed crystal face of γ-Al2O3 from (110) to (100) by controlling the calcination temperature to generate more terminal hydroxyl groups to anchor Ag species. Experimental results combined with AIMD and DFT show that temperature can drive the atomic rearrangement on the (110) crystal face, thereby forming a structure similar to the atomic arrangement of the (100) crystal face. This resulted in the formation of more terminal hydroxyl groups during the high-temperature calcination of the support (Al-900), which can capture Ag species to form single-atom dispersions, and ultimately develop a stable and efficient single-atom Ag-based catalyst.

Non-precious high entropy alloys and highly alkali-resistant composite membranes based high performance anion exchange membrane water electrolyzers

Cost-effective highly efficient and stable catalysts and alkali-resistant anion exchange membranes (AEMs) are critical for practical applications of anion exchange membrane water electrolyzers (AEMWEs). Here, bifunctional non-precious FeCoNiCuMo high entropy alloys (HEAs), electrochemically deposited on nickel mesh as an anode (FeCoNiCuMo/NM) and on carbon paper as a cathode (FeCoNiCuMo/CP), together with a NiFe layered double hydroxide (LDH) loaded AEM (AEM/LDH), were developed for high performance AEMWEs. The AEMWE thus fabricated delivered an ultrahigh current density of 1777 mA cm−2 at 2 V and exhibited remarkable stability with a less than 0.1% cell voltage increase after a 100-hour operation at 100 mA cm−2 at 50 °C, largely outperforming those of the precious metal based AEMWE, composed of IrO2/NM as the anode and Pt/C/CP as the cathode, 1231 mA cm−2@2 V and 4.57% increase in cell voltages. Composition of the alkali-resistant, hydrophilic, and water electrolysis active NiFe LDH into the AEM improved not only the electrolyte uptake and operational stability, but also the efficiency of the AEMWE, with a 10% boost in current density achieved at 2 V and a reduction in cell voltage increases from 2.94% to 0.0951%. The present development demonstrates the practicality of AEMWEs toward green hydrogen production.

Theoretical study of transition metal-doped β12 borophene as a new single-atom catalyst for carbon dioxide electroreduction.

The electrocatalytic carbon dioxide reduction reaction (CO2RR) presents a viable and cost-effective approach for the elimination of CO2 by transforming it into valuable products. Nevertheless, this process is impeded by the absence of exceptionally active and stable catalysts. Herein, a new type of electrocatalyst of transition metal (TM)-doped β12-borophene (TM@β12-BM) is investigated via density functional theory (DFT) calculations. Through comprehensive screening, two promising single-atom catalysts (SACs), Sc@β12-BM and Y@β12-BM, are successfully identified, exhibiting high stability, catalytic activity and selectivity for the CO2RR. The C1 products methane (CH4) and methanol (CH3OH) are synthesized with limiting potentials (UL) of -0.78 V and -0.56 V on Sc@β12-BM and Y@β12-BM, respectively. Meanwhile, CO2 is more favourable for reduction into the C2 product ethanol (CH3CH2OH) compared to ethylene (C2H4) via C-C coupling on these two SACs. More importantly, the dynamic barriers of the key C-C coupling step are 0.53 eV and 0.73 eV for the "slow-growth" sampling approach in the explicit water molecule model. Furthermore, Sc@β12-BM and Y@β12-BM exhibit higher selectivity for producing C1 compounds (CH4 and CH3OH) than C2 (CH3CH2OH) in the CO2RR. Compared with Sc@β12-BM, Y@β12-BM demonstrates superior inhibition of the competitive hydrogen evolution reaction (HER) in the liquid phase. These results not only demonstrate the great potential of SACs for direct reduction of CO2 to C1 and C2, but also help in rationally designing high-performance SACs.

Activating Inert Perovskite Oxides for CO2 Electroreduction via Slight Cu2+ Doping in B-Sites.

Perovskite oxides are proven as a striking platform for developing high-performance electrocatalysts. Nonetheless, a significant portion of them show CO2 electroreduction (CO2RR) inertness. Here a simple but effective strategy is reported to activate inert perovskite oxides (e.g., SrTiO3) for CO2RR through slight Cu2+ doping in B-sites. For the proof-of-concept catalysts of SrTi1-xCuxO3 (x=0.025, 0.05, and 0.1), Cu2+ doping (even in trace amount, e.g., x=0.025) can not only create active, stable CuO6 octahedra, increase electrochemical active surface area, and accelerate charge transfer, but also significantly regulate the electronic structure (e.g., up-shifted band center) to promote activation/adsorption of reaction intermediates. Benefiting from these merits, the stable SrTi1-xCuxO3 catalysts feature great improvements (at least an order of magnitude) in CO2RR activity and selectivity for high-order products (i.e., CH4 and C2+), compared to the SrTiO3 parent. This work provides a new avenue for the conversion of inert perovskite oxides into high-performance electrocatalysts toward CO2RR.

Role of Hexagonal Mesoporous Silica (HMS) in Enhancing the Stability of Ge Catalyst

Role of Hexagonal Mesoporous Silica (HMS) in Enhancing the Stability of Ge Catalyst

Two 2D Metal-Organic Frameworks Based on Purine Carboxylic Acid Ligands for Photocatalytic Oxidation of Sulfides and CO2 Chemical Fixation.

Two two-dimensional (2D) layered metal-organic frameworks (MOFs), namely, {[Yb(L)(H2O)2NO3]·2H2O}n (Yb-MOF) and [Er(L)(H2O)3Cl]n (Er-MOF) (H2L = 5-((6H-purin-6-yl)amino)isophthalic acid), were constructed by a solvothermal method and characterized. The catalytic performance study showed that the Yb-MOF could efficiently catalyze the oxidation of sulfides to sulfoxides under 15 W light-emitting diode (LED) blue light irradiation. Electron paramagnetic resonance spectroscopy and free-radical trapping experiments demonstrated that the photocatalytic reaction process involved •O2-, and the corresponding mechanism was proposed. Moreover, Er-MOF exhibited good catalytic efficiency and excellent substrate tolerance in the cycloaddition reaction of CO2, and the reaction conditions were mild. After 5 cycles, the catalytic activities of two MOFs did not significantly decrease, and the framework structures remained unchanged. Therefore, the Yb-MOF and Er-MOF were considered efficient and stable heterogeneous catalysts.

Mechanistic Insights into Electrocatalytic Hydrogen Evolution by an Exceptionally Stable Cobalt Complex.

Co(aPPy) is one of the most stable and active molecular first-row transition-metal catalysts for proton reduction reported to date. Understanding the origin of its high performance via mechanistic studies could aid in developing even better catalysts. In this work, the catalytic mechanism of Co(aPPy) was electrochemically probed, in both organic solvents and water. We found that different mechanisms can occur depending on the solvent and the acidity of the medium. In organic solvent with a strong acid as the proton source, catalysis initiates directly after a single-electron reduction of CoII to CoI, whereas in the presence of a weaker acid, the cobalt center needs to be reduced twice before catalysis occurs. In the aqueous phase, we found drastically different electrochemical behavior, where the Co(aPPy) complex was found to be a precatalyst to a different electrocatalytic species. We propose that in this active catalyst, the pyridine ring has dissociated and acts as a proton relay at pH ≤ 5, which opens up a fast protonation pathway of the CoI intermediate and results in a high catalytic activity. Furthermore, we determined with constant potential bulk electrolysis that the catalyst is most stable at pH 3. The catalyst thus functions optimally at low pH in an aqueous environment, where the pyridine acts as a proton shuttle and where the high acidity also prevents catalyst deactivation.

O‐2p Hybridization Enhanced Transformation of Active γ‐NiOOH by Chromium Doping for Efficient Urea Oxidation Reaction

O‐2p Hybridization Enhanced Transformation of Active γ‐NiOOH by Chromium Doping for Efficient Urea Oxidation Reaction

Crystallographic dependence of carbon deposition in the Fischer-Tropsch synthesis over cobalt catalysts: HCP versus FCC

A very challenging issue with Co-catalyzed FTS, surface carbon deposition and thus FTS catalyst deactivation, remains unresolved for many years. This research is designed to overcome the challenge by using theoretical calculations together with the FTS experiments. Our theoretical calculations for the first time reveal that HCP Co not only have much higher anti-carbon deposition stability but also exhibits a better anti-carbonization capability than FCC Co; the higher stability of HCP Co is attributed to its much denser active sites with the step B5-type active unit to eliminate surface carbon species. Our FTS experiments confirm the theoretical calculation results. The great dependence of anti-carbon deposition stability on the crystallographic structure and morphology of the catalysts revealed here may open a new avenue for better, stable catalysts with maximum mass-specific reactivity.

An active, stable cubic molybdenum carbide catalyst for the high-temperature reverse water-gas shift reaction.

Although technologically promising, the reduction of carbon dioxide (CO2) to produce carbon monoxide (CO) remains economically challenging owing to the lack of an inexpensive, active, highly selective, and stable catalyst. We show that nanocrystalline cubic molybdenum carbide (α-Mo2C), prepared through a facile and scalable route, offers 100% selectivity for CO2 reduction to CO while maintaining its initial equilibrium conversion at high space velocity after more than 500 hours of exposure to harsh reaction conditions at 600°C. The combination of operando and postreaction characterization of the catalyst revealed that its high activity, selectivity, and stability are attributable to crystallographic phase purity, weak CO-Mo2C interactions, and interstitial oxygen atoms, respectively. Mechanistic studies and density functional theory (DFT) calculations provided evidence that the reaction proceeds through an H2-aided redox mechanism.

3D printed CuFe2O4 electrode with dominant facet (111) for boosting hydrogen evolution performance

The utilization of hydrogen energy is an important way to low carbon economy, and the development of active electrodes is the most critical step for efficient hydrogen evolution reaction. With the addition of KNO3 as a capping agent, the exposed crystal facet of CuFe2O4 is regulated, and the crystal facet (111) becomes dominant. Compared to CuFe2O4 (3 1 1), CuFe2O4 (111) exhibits low barrier of water dissociation and suitable *H binding strength, resulting in high intrinsic activity. Furthermore, the 3D printed electrodes show more excellent performance. At 3D printed CuFe2O4 (111) electrode, the overpotential is only 152 mV (vs. reversible hydrogen electrode) at 100 mA cm−2, and Tafel slope is as low as 33 mV dec-1. In addition, 3D printed CuFe2O4 (111) electrodes shows high stability. The superior performance of 3D printed CuFe2O4 (111) electrodes originates from high intrinsic activity and more exposed active sites. This study provides a new path for the development of efficient, stable and inexpensive monolithic catalyst electrodes for alkaline hydrogen evolution.

Niacin based MOF as efficient nano-catalyst in the synthesis of some new benzothiazoles and benzimidazoles as anti-Alzheimer (AChE inhibitors)

Metal-organic frameworks (MOFs) presented as an efficient, economic, sustainable and green stable catalyst. Co/Niacin-MOF in nano shape was prepared by hydrothermal method and illustrated by IR, SEM and XRD. The prepared Co/Niacin-MOF used in the synthesis of some new benzothiazoles and benzimidazoles (3a-3f, 4a-4f). The prepared benzo heterocyclic compounds were checked as acetylcholine esterase inhibitors (AChE inhibitors) and the data obtained from in vitro and molecular docking explained that there two promised values for compounds 4-(benzo[d]thiazol-2-yl)phenyl benzoate (3e) and 4-(1H-benzo[d]imidazol-2-yl)phenyl 4-methylbenzenesulfonate (4f) compared with Donepezil as a reference Alzheimer drug.