3D Hierarchical MOF-Derived Defect-Rich NiFe Spinel Ferrite as a Highly Efficient Electrocatalyst for Oxygen Redox Reactions in Zinc-Air Batteries.

The strategy of defect engineering is increasingly recognized for its pivotal role in modulating the electronic structure, thereby significantly improving the electrocatalytic performance of materials. In this study, we present defect-enriched nickel and iron oxides as highly active and cost-effective electrocatalysts, denoted as Ni0.6Fe2.4O4@NC, derived from NiFe-based metal-organic frameworks (MOFs) for oxygen reduction reactions (ORR) and oxygen evolution reactions (OER). XANES and EXAFS confirm that the crystals have a distorted structure and metal vacancies. The cation defect-rich Ni0.6Fe2.4O4@NC electrocatalyst exhibits exceptional ORR and OER activities (ΔE = 0.68 V). Mechanistic pathways of electrochemical reactions are studied by DFT calculations. Furthermore, a rechargeable zinc-air battery (RZAB) using the Ni0.6Fe2.4O4@NC catalyst demonstrates a peak power density of 187 mW cm-2 and remarkable long-term cycling stability. The flexible solid-state ZAB using the Ni0.6Fe2.4O4@NC catalyst exhibits a power density of 66 mW cm-2. The proposed structural design strategy allows for the rational design of electronic delocalization of cation defect-rich NiFe spinel ferrite attached to ultrathin N-doped graphitic carbon sheets in order to enhance active site availability and facilitate mass and electron transport.

Pd-loaded hierarchical titanosilicalite-1 catalysts on CO2 cycloaddition with epoxides: Experimental and DFT investigations.

This work presents the synthesis of Pd-loaded microporous titanosilicalite-1 (Pd/TS-1) and Pd-loaded hierarchical titanosilicalite-1 (Pd/HTS-1) with abundant mesopores (2-30 nm) inside the framework via hydrothermal method using polydiallydimethyl ammonium chloride as the non-surfactant mesopore template. XRD, N2 sorption, FT-IR, FESEM-EDX, TEM, XPS, and DR-UV techniques were used to characterize the morphological and physicochemical properties of the synthesized materials. These materials were tested as heterogeneous catalysts, along with tetrapropylammonium bromide as co-catalyst, for cycloaddition reactions of CO2 with epoxides to produce cyclic carbonates. It was found that the epoxide conversions were influenced by acidity and pore accessibility of the catalysts. Using Pd/HTS-1 facilitated bulky substrates to access active sites, resulting in higher conversions than Pd/TS-1. Over 85 % conversions were achieved for at least five consecutive cycles without significant loss in catalytic activity. The interaction between the Pd active surfaces and epichlorohydrin (ECH) was further studied by DFT calculations. The existence of Pd(200) was more influential on adsorbing epichlorohydrin (ECH) and subsequent formation of dissociated ECH (DECH) intermediate than Pd(111) surface. However, Pd(111) was dominant in enhancing the activity of DECH species for capturing CO2. Therefore, the co-existence of Pd(200) and Pd(111) surfaces was needed for cycloaddition of CO2 with ECH.

Renovated FeCoP-NC nanospheres wrapped by CoP-NC nanopetals: As a tremendously effectual and robust MOF-assisted electrocatalyst for hydrogen energy production.

The future of energy technology is significantly influenced by hydrogen (H2) energy. However, hydrogen energy production through water-splitting entirely depends on the catalyst's performance. Modifying the morphological structure and increasing the number of active sites by changing the metal composition are pivotal factors in enhancing the catalytic activity for the hydrogen evolution reaction (HER). In this context, we introduce the impact of metal-organic framework (MOF) strategies for decorating CoP petals onto α-Fe2O3 and FeCoP-NC (NC-nitrogen-doped carbon) nanoflowers. This method results in an excellent electrocatalyst for HER. The study demonstrated the influence of different MOF precursors, the impact of calcination temperatures, and the importance of composition percentages in Fe1-xCoxP-NC. As a result, FeCoP-NC shows excellent electrochemical performance potential (η) of 57 mV, a rapid kinetic Tafel value of 61 mV/dec, and remarkable electrochemical stability of around 2000 cycles and 20 h in stand potential. Additionally, the composite has numerous active surfaces at 4.7 mF/cm2 during the electrochemical reactions. This work concludes that MOF-assisted FeCoP-NC nanoflowers are an ideal electrocatalyst for HER in an alkaline medium.

The Underlying Catalytic Role of Oxygen Vacancies in Fatty Acid Methyl Esters Ketonization over TiOx Catalysts.

Recently, interest in converting bio-derived fatty acid methyl esters (FAMEs) into added-value products has significantly increased. The selectivity of ketonization reaction in the conversion of the FAMEs has significantly hampered the efficiency of this process. Herein, this work reports the preparation of catalysts with different levels of oxygen vacancies while the crystal phase remained unchanged. The catalyst with the highest level of oxygen vacancy exhibited the maximum selectivity. The density functional theory (DFT) simulation showed an increase in interatomic distances leading to the formation of frustrated Lewis pairs (FLPs) upon the creation of oxygen vacancies. The surface measurements, type and density of acid sites of the catalysts, showed that the Lewis acid sites enhanced the selectivity for ketone production; while Bronsted acid sites increased the formation of by-products. Moreover, the ketone formation rate was directly proportional to acid density. The findings of this research provide a different approach for catalyst design, based on defects engineering and their effect on the surface activity, which could be used for enhancing the catalytic performance of novel metal oxides.

Photoactivity of amorphous and crystalline TiO2 nanotube arrays (TNA) films in gas phase CO2 reduction to methane with simultaneous H2 production.

This study assessed the photoactivity of amorphous and crystalline TiO2 nanotube arrays (TNA) films in gas phase CO2 reduction. The TNA photocatalysts were fabricated by titanium anodization and submitted to an annealing treatment for crystallization and/or cathodic reduction to introduce Ti3+ and oxygen vacancies into the TiO2 structure. The cathodic reduction demonstrated a significant effect on the generated photocurrent. The photoactivity of the four TNA catalysts in CO2 reduction with water vapor was evaluated under UV irradiation for 3 h, where CH4 and H2 were detected as products. The annealed sample exhibited the best performance towards methane with a production rate of 78 µmol gcat-1 h-1, followed by the amorphous film, which also exhibited an impressive formation rate of 64 µmol gcat-1 h-1. The amorphous and reduced-amorphous films exhibited outstanding photoactivity regarding H2 production (142 and 144 µmol gcat-1 h-1, respectively). The annealed catalyst also revealed a good performance for H2 production (132 µmol gcat-1 h-1) and high stability up to five reaction cycles. Molecular dynamic simulations demonstrated the changes in the band structure by introducing oxygen vacancies. The topics covered in this study contribute to the Sustainable Development Goals (SDG), involving affordable and clean energy (SDG#7) and industry, innovation, and infrastructure (SDG#9).

Evaluation of the hydrogenation reaction on the electrocatalytic nitrobenzene degradation over (FeCoNiCuZn)xOy high entropy oxides (HEOs).

Environmental pollution is one of the main challenges currently faced by mankind; especially industrial waste-waters treatment and remediation using energy-efficient methodologies. This research focused on the electrochemical degradation of the hazardous nitrobenzene (NB) in aqueous solutions, using novel high-entropy oxide (HEO) electrodes to elucidate the influence of the electrochemical reduction step on the degradation process. The effect of solution pH, dissolved oxygen concentration, anodic applied potential, and cell configurations on NB hydrogenation reaction were evaluated. A synergistic effect between the hydrogenation of nitrobenzene and the degradation was found to drastically enhance the conversion rates. The presence of dissolved oxygen promoted the oxidation reactions, reaching more than 90% nitrobenzene removal at 1.7 V and pH 14. The degradation of the organic by-products was attributed to the formation of the superoxide radical (O2*-) as the main oxidant species. A degradation mechanism was proposed based on the detected intermediates and the decoupling of electrochemical surface reactions observed by EIS at different solution pH.

Effect of Strontium Modification in Mg-Al Mixed Oxide Catalysts on Product Distribution toward Catalytic Reaction of Ethanol.

The aim of this research was to examine the effect of strontium content in the MgAlO catalyst for the catalytic ethanol reaction on the product distribution. The structure of the catalysts and the actual amount of strontium on the catalysts were verified using XRD and ICP techniques, respectively. The acid and basic strength characteristics of catalysts were examined using NH3-TPD and CO2-TPD techniques, respectively. The strontium content was found to influence the textural properties and the acidic and basic characteristics of the catalysts, leading to differences in product selectivity and ethanol conversion. The MgAlO catalyst with 1.9 wt % strontium provided the maximum ethylene and butanol selectivity, probably due to the presence of appropriate medium acidic and strong basic sites. All catalysts can efficiently produce ethylene by a dehydration reaction and acetaldehyde by a dehydrogenation reaction. Acetaldehyde selectivity was dominant with increased strontium loading.

A density functional theory study on how γ-Al2O3 - Boehmite transformation affects carbon evolution during aqueous-phase reaction.

Gamma-alumina (γ-Al2O3), one of the most common materials, is commercially used in many catalytic applications, including the active catalyst and support. However, the problem of fast deactivation makes the utilization of the γ-Al2O3 challenging. This work elucidates the mechanism of coke formation consisting of coke deposition and evolution on γ-Al2O3(110) surfaces in differential conditions, including; clean and hydroxylation γ-Al2O3(110) in terms of partial and fully hydroxylation of OH/γ-Al2O3(110) and AlOOH(010), respectively. We demonstrated that the γ-Al2O3(110) surface is proper for atomic coke deposition and dimerization in the initial state, where the presence of OH species promotes the coke evolution to higher coke, Cn (where n ≥ 3). Also, the higher coke formation thermodynamically preferred the cyclic form to the aliphatic one. The electron transfer from substrates to adsorbed coke illustrates the role of the electron donor of catalyst surfaces corresponding to the electron acceptor of adsorbed cokes.

Noble metals (Pd, Ag, Pt, and Au) doped bismuth oxybromide photocatalysts for improved visible light-driven catalytic activity for the degradation of phenol.

The doping of noble metals onto the semiconductor metal oxides has a great impact on the intrinsic properties of the materials. This present work reports the synthesis of noble metals doped BiOBr microsphere by a solvothermal method. The various characteristic findings reveal the effective incorporation of Pd, Ag, Pt, and Au onto the BiOBr and the performance of synthesized samples was test for the degradation of phenol over visible light. The Pd-doped BiOBr material showed enhanced phenol degradation efficacy, which is ∼4-fold greater than pure BiOBr. This improved activity was on reason of good photon absorption, lower recombination rate, and higher surface area facilitated by surface plasmon resonance. Moreover, Pd-doped BiOBr sample displayed good reusability and stability after 3 cycles of run. A plausible charge transfer mechanism for phenol degradation is disclosed in detail over Pd-doped BiOBr sample. Our findings disclose that the incorporation of noble metal as the electron trap is a feasible approach to enhance visible light activity of BiOBr photocatalyst used in phenol degradation. This work represents new vision interested in the outline and development of noble metal doped semiconductor metal oxides as a visible light material for the elimination of colorless toxins from untreated wastewater.

Influence of Highly Stable Ni2+ Species in Ni Phyllosilicate Catalysts on Selective Hydrogenation of Furfural to Furfuryl Alcohol.

Enhancing the catalytic performance of non-noble Ni catalysts in the selective hydrogenation of furfural to furfuryl alcohol (FA) in terms of furfural conversion, selectivity, and good recyclability is challenging. Here, spherical nickel phyllosilicate catalysts (Ni_PS) with fibrous-like structures are prepared via a modified sol-gel method with Ni loadings of 2-30 wt %. Upon exposure to air, all the reduced Ni_PS catalysts exhibit more than 80% Ni0/Niphyllosilicate species on the surface, whereas a large portion of Ni oxide species (>55%) is presented on the impregnated catalyst. The Ni2+ species in nickel phyllosilicate catalysts are active and highly stable during reduction, reaction, and regeneration, yielding stable catalytic performance for multiple recycle tests in furfural hydrogenation to FA. Furfural conversion over the Ni_PS catalysts increased monotonically with increasing Ni loading without an FA selectivity drop. The presence of both metallic Ni0 and Niphyllosilicate also produces a synergistic promotional effect for FA formation.

A novel S-scheme Ws2/BiYWO6 electrostatic heterostructure for enhanced photocatalytic degradation performance towards the degradation of Rhodamine B.

Constructing S-scheme heterojunction between two semiconductor materials is an effective route to increase the photocatalytic degradation efficiency. Here, a novel S-scheme WS2/BiYWO6 heterojunction photocatalyst was prepared by wet chemical route. At the same time, the photocatalytic degradation performance of the fabricated materials was analyzed by the degradation of Rhodamine B under visible light. Of all prepared WS2/BiYWO6 composites, the 20 wt.% WS2 loaded WS2/BiYWO6 composite exhibited an enhanced photocatalytic degradation ability than other prepared photocatalysts. Here, O2·- and ·OH radicals are performing a pivotal role in the Rhodamine B degradation and the optimized composite shows greater photocurrent intensity than pure BiYWO6 and WS2, respectively. Also, the synthesized photocatalyst maintains its stability with negligible changes even after three cycles. Thereby, the constructed S-scheme WS2/BiYWO6 heterojunction is a potential material for the wastewater remediation.

Catalytic deoxygenation of fatty acids via ketonization and α-carbon scissions over layered alkali titanate catalysts under N2.

The ketonization of fatty acid with subsequent McLafferty rearrangement of the fatty ketone allows the deoxygenation to hydrocarbons. Here, we report the cascade reaction of palmitic acid (C16) to hydrocarbons (≤C14) over lepidocrocite-type alkali titanate K0.8Zn0.4Ti1.6O4, K0.8Mg0.4Ti1.6O4, and K0.8Li0.27Ti1.73O4 and the reassembled TiO2 catalysts at ≤400 °C under atmospheric N2 in a continuous fixed-bed flow reactor. The C16 acid is coupled to C31 ketone prior to the scissions mostly to a C17 methyl ketone and C14 hydrocarbons (i.e., the McLafferty rearrangement). The hydrocarbons yield increases with temperature and is proportional to partial charge at the O atom, suggesting that basic sites are responsible for C31 ketone scissions. The layered alkali titanate catalysts with two-dimensional (2D) space inhibit diffusion of the ketone primarily formed and promote its scissions to hydrocarbons within the confined space. Otherwise, low hydrocarbons yield (but high ketone yield) is obtained over TiO2 and the Mg/Al mixed oxide catalysts possessing no interlayer space. Meanwhile, the semi-batch experiment with pre-intercalated palmitic acid favors a direct deoxygenation, demonstrating the essential role of reaction mode toward ketone scission reaction pathway. Over K0.8Li0.27Ti1.73O4, the complete palmitic acid conversion leads to ∼47% hydrocarbons yield, equivalent to ∼80% reduction of the oxygen content in the feed under N2.

High-throughput materials screening algorithm based on first-principles density functional theory and artificial neural network for high-entropy alloys.

This work introduced the high-throughput phase prediction of PtPd-based high-entropy alloys via the algorithm based on a combined Korringa-Kohn-Rostoker coherent potential approximation (KKR-CPA) and artificial neural network (ANN) technique. As the first step, the KKR-CPA was employed to generate 2,720 data of formation energy and lattice parameters in the framework of the first-principles density functional theory. Following the data generation, 15 features were selected and verified for all HEA systems in each phase (FCC and BCC) via ANN. The algorithm exhibited high accuracy for all four prediction models on 36,556 data from 9139 HEA systems with 137,085 features, verified by R2 closed to unity and the mean relative error (MRE) within 5%. From this dataset comprising 5002 and 4137 systems of FCC and BCC phases, it can be realized based on the highest tendency of HEA phase formation that (1) Sc, Co, Cu, Zn, Y, Ru, Cd, Os, Ir, Hg, Al, Si, P, As, and Tl favor FCC phase, (2) Hf, Ga, In, Sn, Pb, and Bi favor BCC phase, and (3) Ti, V, Cr, Mn, Fe, Ni, Zr, Nb, Mo, Tc, Rh, Ag, Ta, W, Re, Au, Ge, and Sb can be found in both FCC and BCC phases with comparable tendency, where all predictions are in good agreement with the data from the literature. Thus, the combination of KKR-CPA and ANN can reduce the computational cost for the screening of PtPd-based HEA and accurately predict the structure, i.e., FCC, BCC, etc.

Controlling the Fe2O3-SiO2 interaction: The effect on the H2S selective catalytic oxidation and catalyst deactivation.

Biogas utilization is one of the most promising options for reducing the consumption of fossil fuels for energy production, but the presence of H2S represents a serious industrial and environmental problem. In this work, two different synthesis methods (sol-gel and incipient wetness impregnation) were used to synthesize iron oxide supported on silica catalysts (Fe2O3/SiO2) with metal loadings ranging from 0.5 to 10 %wt. The catalysts were tested for the selective oxidation of H2S, changing the operating conditions like O2/H2S (0.5-2.5), temperature (170-250°C), and water content (0-50%). The optimum condition was O2/H2S = 0.5 and no water at 230 °C with the conversion of approximately 100%, the selectivity of 97%, and the deactivation of 0.6%. A detailed characterization of the fresh and spent catalysts' surface revealed the presence of four deactivation mechanisms: metal surface reduction, oxygen vacancy loss, pore plugging, and sintering. Among the observed deactivation mechanisms, the sintering showed the highest impact on catalytic activity and deactivation. The sol-gel catalysts (SG) showed the highest metal-oxide/support interaction, which reduced the metal-oxide nanoparticles sintering compared with the incipient wetness impregnation method (IWI), reporting a lower sintering, higher activity, and selectivity, lower deactivation rates and lower sensitivity to the operating conditions. A catalytic cycle representing the possible surface intermediate states of the catalyst is proposed based on the performance and characterization results obtained.

Formation and growth characteristics of nanostructured carbon films on nascent Ag clusters during room-temperature electrochemical CO2 reduction.

Synthesis of carbon nanostructures at room temperature and under atmospheric pressure is challenging but it can provide significant impact on the development of many future advanced technologies. Here, the formation and growth characteristics of nanostructured carbon films on nascent Ag clusters during room-temperature electrochemical CO2 reduction reactions (CO2RR) are demonstrated. Under a ternary electrolyte system containing [BMIm]+[BF4]-, propylene carbonate, and water, a mixture of sp2/sp3 carbon allotropes were grown on the facets of Ag nanocrystals as building blocks. We show that (i) upon sufficient energy supplied by an electric field, (ii) the presence of negatively charged nascent Ag clusters, and (iii) as a function of how far the C-C coupling reaction of CO2RR (10-390 min) has advanced, the growth of nanostructured carbon can be divided into three stages: Stage 1: sp3-rich carbon and diamond seed formation; stage 2: diamond growth and diamond-graphite transformation; and stage 3: amorphous carbon formation. The conversion of CO2 and high selectivity for the solid carbon products (>95%) were maintained during the full CO2RR reaction length of 390 min. The results enable further design of the room-temperature production of nanostructured carbon allotropes and/or the corresponding metal-composites by a viable negative CO2 emission technology.

Differences in Deterioration Behaviors of Cu/ZnO/Al2O3 Catalysts with Different Cu Contents toward Hydrogenation of CO and CO2.

The deterioration behaviors of Cu/ZnO/Al2O3 (CZA) catalysts upon different Cu contents were elucidated. The fresh and spent catalysts after being used in CO and CO2 hydrogenation at 250 °C under atmospheric pressure were properly characterized using various techniques including X-ray powder diffraction, X-ray photoelectron spectroscopy, and temperature-programmed reduction for the changes of metal sites, while the textural and chemical properties and carbon deposition on spent CZA catalysts were analyzed by N2 physisorption, energy-dispersive X-ray spectroscopy, and temperature-programmed oxidation. During the hydrogenation reaction for both CO and CO2, the unstable Cu0 site on the spent CZA catalyst having a low Cu loading (sCZA-L) was oxidized to CuO and the aggregation of metal crystallite sites (Cu-ZnO and ZnO) was observed. Moreover, the amount of carbon deposition on sCZA-L (ca. >2%) is higher than the spent CZA catalyst having a high Cu loading (sCZA-H, ca. <0.5%). These phenomena led to a decrease in the surface area and the blockage of active sites. These findings can be determined on the catalytic deactivation and the obvious decrease in the catalytic activity of the CZA catalyst having a low Cu content (CZA-L, Cu:Zn = 0.8).

Synthesis of novel graphene aerogel encapsulated bismuth oxyiodide composite towards effective removal of methyl orange azo-dye under visible light.

Development of novel and eco-friendly composite photocatalysts for the efficient removal of contaminants from wastewater is the need of the hour. In this study, visible light responsive novel graphene aerogel/bismuth oxyiodide (GA/BiOI) composite was synthesized via low-temperature solvothermal method. The synthesized GA/BiOI composite was tested for methyl orange (MO) azo-dye degradation under visible light. The graphene aerogel nanosheets were wrapped onto the surface of the each individual BiOI microsphere, which encourages the interconnection charge transfer process. The light absorption properties of GA/BiOI composite were increased with the addition of graphene aerogel. The optimal 5%-GA/BiOI composite displayed higher MO removal efficiency, which is ∼2 fold more than the bare BiOI photocatalyst. This enhanced photocatalytic activity was on account of lower recombination rate of charge carriers, improved light absorption, and the high surface area. In addition, the 5%-GA/BiOI composite showed good stability until 3 cycles without deactivation. The plausible MO degradation mechanism was also proposed over GA/BiOI under visible light. This work provides a new perspective on the design and synthesis of graphene aerogel-based composite for environmental applications.

A review on sensitivity of operating parameters on biogas catalysts for selective oxidation of Hydrogen Sulfide to elemental sulfur.

Hydrogen sulfide (H2S) is a critical problem for biogas applications, such as electricity and heat generation, or the production of different chemical compounds, due to corrosion and toxic effluent gases. The selective catalytic oxidation of H2S to S is the most promising way to eliminate H2S from biogas due to the lack of effluents, therefore can be considered a green technology. The most extensively used catalysts for H2S selective oxidation can be classified in two groups: metal oxide-based catalysts, including vanadium and iron oxides, and carbon-based catalysts. Numerous studies have been devoted to studying their different catalytic performances. For industrial applications, the most suitable catalysts should be less sensitive to the operating parameters like the temperature, O2/H2S ratio, and H2O content. More specifically, for metal oxides and carbon-based catalysts, the temperature and O2/H2S ratio have a similar effect on the conversion and selectivity, but carbon-based catalysts are less sensitive to water in all operating conditions.

On a high photocatalytic activity of high-noble alloys Au-Ag/TiO2 catalysts during oxygen evolution reaction of water oxidation.

The analysis via density functional theory was employed to understand high photocatalytic activity found on the Au-Ag high-noble alloys catalysts supported on rutile TiO2 during the oxygen evolution of water oxidation reaction (OER). It was indicated that the most thermodynamically stable location of the Au-Ag bimetal-support interface is the bridging row oxygen vacancy site. On the active region of the Au-Ag catalyst, the Au site is the most active for OER catalyzing the reaction with an overpotential of 0.60 V. Whereas the photocatalytic activity of other active sites follows the trend of Au > Ag > Ti. This finding evident from the projected density of states revealed the formation of the trap state that reduces the band gap of the catalyst promoting activity. In addition, the Bader charge analysis revealed the electron relocation from Ag to Au to be the reason behind the activity of the bimetallic that exceeds its monometallic counterparts.

Optimal Conditions for Butanol Production from Ethanol over MgAlO Catalyst Derived from Mg-Al Layer Double Hydroxides.

The MgAlO catalyst was obtained from thermal decomposition of the MgAl-LDH catalyst having Mg/Al molar ratio of 5. The catalytic Guerbet reaction of ethanol was investigated to determine the effect of WHSV and nitrogen flow rate on butanol production and product distribution. It was performed in a fixed-bed microreactor under continuous flow of vaporized ethanol mixed with N2. The MgAlO catalyst had high total basic sites and high total acid sites that were crucial for ethanol Guerbet reaction. The MgAlO catalyst showed the highest butanol selectivity at 300℃ under WHSV = 3.10 h-1 and nitrogen flow rate = 3,600 mL/h, and the highest butanol yield at 400℃ under WHSV = 3.10 h-1 and nitrogen flow rate = 900 mL/h. It can be summarized that in order to enhance the butanol yield, the low WHSV is preferred to increase the contact time of ethanol and catalyst under moderate temperature.