Bifunctional Catalysts Research Articles

Synthesis of palladium-rare earth alloy as a high-performance bifunctional catalyst for direct ethanol fuel cells

Synthesis of palladium-rare earth alloy as a high-performance bifunctional catalyst for direct ethanol fuel cells

Biomass-incorporated KNO3-C/γ-Al2O3 bifunctional catalyst for efficient biodiesel production

Biodiesel has gained attention as a promising renewable and sustainable alternative to fossil fuels, which necessitated the development of an effective and eco-friendly catalyst for transesterification processes. Herein, this research reported the development of a highly efficient bifunctional catalyst by incorporating carbon from oil palm leaves (OPLs) into KNO3/γ-Al2O3 catalyst, synthesized through a facile method, to concurrently catalyze the waste cooking oil (WCO) transesterification and free fatty acids (FFAs) esterification in a one-pot reaction. Proposed Box-Behnken Design (BBD) model's ideal conditions, experimentally yielded an average of 93.74 % biodiesel yield. Meanwhile, analysis revealed that the catalyst with 30 wt% KNO3 loadings and 1.0 g oil palm leaves dosage (OPLD), calcined at 700 °C, has a BET surface area of 46.93 m2/g and exhibited the presence of K2O, K2O2 and K2C2 active species on the catalyst surface. In addition to exhibiting high total basicity and acidity of 2.9 mmol/g and 2.1 mmol/g, respectively, environmental studies suggested this catalyst generated less waste, highlighting its significant potential of being used for efficient biodiesel production. Therefore, present research introduces a new approach for synthesizing a fruitful and ecofriendly bifunctional catalyst to attain one-pot biodiesel production from low-grade oils.

Construction of Molecularly Dispersed Polyoxometalate-Alumina Hybrid Hollow Nanoflowers via Water-Induced Kirkendall Effect.

Hybrid nanomaterials with controllable structures and diverting components have attracted significant interest in the functional materials field. Here, we develop a solvent evaporation-induced self-assembly (EISA) strategy to synthesize nanosheet-assembled phosphomolybdic acid (H3PMo)-alumina hybrid hollow spheres. The resulting nanoflowers display a high surface area (up to 697 m2 g-1), adjustable diameter, high chemical/thermal stability, and especially molecularly dispersed H3PMo species. By employing various microscopic and spectroscopic techniques, the formation mechanism is elucidated, revealing the simultaneous control of the morphology by heteropoly acids and water through the water-induced Kirkendall effect. The versatility of the synthesis method is demonstrated by varying surfactants, heteropoly acids, and metal oxide precursors for the facile synthesis of hybrid metal oxides. Spherical hybrid alumina serves as an attractive support material for constructing metal-acid bifunctional catalysts owing to its advantageous surface area, acidity, and mesoporous microenvironment. Pt-loaded hollow flowers exhibit excellent catalytic performance and exceptional stability in the hydrodeoxygenation of vanillin with recyclability for up to 10 cycles. This research presents an innovative strategy for the controllable synthesis of hybrid metal oxide nanospheres and hollow nanoflowers, providing a multifunctional platform for diverse applications.

Dipeptidic Proline‐Derived Thiourea Organocatalysts for Asymmetric Michael addition Reactions between Aldehydes and Nitroolefins

AbstractThe enantiodivergent synthesis of syn‐Michael adducts can be easily achieved by switching the terminal proline in dipeptidic proline‐thiourea catalysts. In this study, a dipeptidic proline‐derived thiourea organocatalyst was rationally designed and facilely prepared from dipeptidic proline, a chiral diamine as a linker, and isothiocyanate. This asymmetric bifunctional catalyst for Michael addition between aldehydes and nitroolefins provided chiral 4‐nitro aldehyde adducts with yields of up to 99 %, 92 : 8 syn‐diastereoselectivity, and 97 % enantiomeric excess at room temperature.

Tuning the size and spatial distribution of Pt in bifunctional Pt-zeolite catalysts for direct coupling of ethane and benzene

Controlling the dispersion and position of metal active sites in bifunctional metal–acid zeolite catalysts is essential for achieving synergy between the metal and acid sites in tandem catalytic processes, but still challenging nowadays. Herein, we propose an approach to modulate the dispersion and position of Pt particles in ZSM-5 zeolite by employing various types of organic structure-directing agents (OSDAs) in the one-pot synthesis procedure. Systematic characterizations show that the OSDAs mainly influence the encapsulation of the Pt precursor into the ZSM-5 zeolite crystallites during the hydrothermal crystallization process, resulting in discrepancies in the dispersion and spatial distribution of Pt sites in the final Pt-zeolite catalysts. Comparative studies on different Pt-zeolite catalysts show that the formation of subnanometer Pt clusters and the close spatial proximity of Pt and Brønsted acid sites in the zeolite efficiently promote the tandem dehydrogenation-alkylation process and enhance the production rate of ethylbenzene in the direct ethane-benzene coupling reaction. This study offers insights into the design and synthesis of bifunctional metal-zeolite catalysts for tandem catalysis.

Sabatier principle based design of high performance FeCoNiMnMoP high entropy electrocatalysis for alkaline water splitting

FeCoNi-based high entropy intermetallic compounds are promising substitutes for noble metal catalysts for hydrogen evolution reaction (HER) and oxygen evolution (OER), while their activity is restricted by the synergistic effect between the elements. In this paper, the theoretical model of FeCoNiMnMoP bifunctional catalyst has been reasonably designed given the volcanic curve of M−H bond energy as a valuable guide for candidate metal elements. Theoretical calculations show that the synergistic effect between multiple sites not only accelerates the electron transfer but also reduces the rate-determining step (RDS) barrier. At the same time, the introduction of Mo also enhances the total density of states and reduces the d-band center, thus optimizing the adsorption and dissociation of intermediates. The experimental results confirm that the theoretical model has excellent catalytic performance. In the alkaline solution, FeCoNiMnMoP‖FeCoNiMnMoP requires only an ultra-low cell voltage of 1.49 V for overall water splitting when the current density is 10 mA cm−2. In general, novel insights on the effects of intermetallic synergies on water decomposition are provided, which is helpful for the design of bifunctional catalysts based on volcanic diagrams.

Facile synthesis of NiCo2O4 nanosheets efficient for electrocatalysis of water

Effective regulation of transition metal spinel morphology is crucial for stable bifunctional catalysts in the electrocatalysis of water. In this work, we crafted a fine NiCo2O4 (F-NCO) microflower structure assembled by nanosheet arrays, which exhibited highly efficient hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), outperforming most of the previous transition metal catalysts. Electronic microscope analysis revealed that the thickness of the F-NCO catalyst was only 1.6 nm, much smaller than that (58.8 nm) of bulk NiCo2O4 (B-NCO), and the ultrathin lamellar structure facilitated the exposure of active sites and improved the reaction kinetics. Compared with the B-NCO catalyst, the overpotential of the F-NCO catalyst in HER and OER was reduced by 36 and 82 mV, the active surface area increased by 2.68 and 4.16 times, and the charge transfer resistance values were reduced by 0.42 and 0.61 times, respectively. In the assembled cell, F-NCO/CFP(+)||F-NCO/CFP(−) electrolyzer was able to achieve 10 mA cm−2 at a low cell voltage of 1.74 V, which was much lower than B-NCO/CFP(+)||B-NCO/CFP(−) electrolyzer. In the 12-hour stability test, the potentiometric time dropped by only 30 mV, lower than 70 mV of the B-NCO catalyst. This work presents a facile strategy for developing a bifunctional catalyst for the electrocatalysis of water.

Enhancing acidity of Ru/Ce/ZrO2 bifunctional catalysts for promoting N2 selectivity in selective catalytic oxidation of NH3

To solve the problem of low N2 selectivity of Ru/Ce/ZrO2 (R/C/Z) catalysts in NH3 selective catalytic oxidation (NH3-SCO) reaction, herein ZrO2 supports were treated with sulfuric acid and its effects on NH3-SCO performance were investigated systematically. The results showed that Ru/Ce/ZrO2-10S (R/C/Z-10S) catalyst, in which the mass ratio of sulfuric acid to ZrO2 was 10 %, exhibited N2 selectivity of 95.7 % at 350 °C, that was significantly higher than R/C/Z catalyst (57.8 %). NH3-TPD tests indicated that sulfate treatment of ZrO2 supports in R/C/Z catalysts led to more abundant acidic sites on catalyst surface, which was in favor of enhancing NH3 adsorption capacity remarkably. But when mass ratio of sulfuric acid to ZrO2 increased up to 20 %, an aggregation of metal oxides on the surface of R/C/Z-20S catalyst could be observed clearly, which might impose an adverse impact on NH3-SCO performance. In-situ DRIFTS results revealed that, compared to R/C/Z catalyst, there were much more Brönsted acid sites on the surface of R/C/Z-10S catalyst, and the corresponding NH3 species on acidic sites could be consumed quickly in intermediate reactions. More importantly, amide (-NH2) species rather than imide (-NH) and nitrosyl (-HNO) species, were the majority on the surface of R/C/Z-10S catalyst, implying that there might be a suppressing effect on further dehydrogenation of -NH2 species into -NH species owning to sulfate treatment of ZrO2 supports in R/C/Z catalysts. Therefore, internal selective catalytic reduction (i-SCR) mechanism rather than -NH mechanism played a vital role in NH3-SCO reaction over R/C/Z-10S catalyst.

Trace ruthenium dioxide stabilize active center of CoFe-LDH for efficient water electrolysis

It is immensely meaningful to design efficient electrolysis for water electrolysis and realize green hydrogen production. Herein, a ruthenium dioxide modified CoFe-Layered double hydroxides (LDHs) catalyst (RuO2/CoFe-LDH/NF) was synthesized by combining the advantages of RuO2 and CoFe-LDHs for driving alkaline water and seawater. RuO2/CoFe-LDH/NF display impressive activity and stability at 10 mA cm−2, which only need an overpotential of 59 and 270 mV for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) respectively. Meaningfully, the catalyst only required a small cell voltage of 1.58 V as a bifunctional catalyst, what is superior to commercial RuO2/NF||Pt/C/NF (1.66 V). In addition, RuO2/CoFe-LDH/NF exhibited excellent HER and OER performance with overpotentials of 119 and 260 mv in alkaline seawater at 10 mA cm−2, respectively. Additionally, RuO2/CoFe-LDH/NF displays a larger corrosion potential, smaller corrosion and improved oxygen evolution capacity than CoFe-LDH/NF. Moreover, there is electron transfer between Ru and Co or Fe, which can improve the micro-coordination environment and enhance the stability for RuO2/CoFe-LDH/NF. The method with integration of RuO2 and CoFe-LDH could be broadened to explore other robust bifunctional catalysts for water/seawater electrolysis.

Photocatalytic degradation of low-concentration gaseous benzene in air via bifunctional tin-doped titanium dioxide catalyst

Benzene, a common volatile organic compound (VOC) detected in indoor environments, poses challenges for its removal because of its stable molecular structure and low-concentration. In this study, we successfully synthesized tin-doped titanium dioxide (Sn-TiO2) using a simple hydrothermal method. Various characterization techniques including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunner–Emmet–Teller (BET) and molecular probes were employed to analyze the phase composition, structure and morphology, as well as photocatalytic properties of TiO2 and Sn-TiO2. The characterization results showed that moderate addition of tin doping not only effectively enhanced the capture ability of benzene molecules but also promoted hydroxyl radicals (·OH) generation, which was further validated by in-situ diffuse reflectance infrared Fourier transform (DRIFT) spectra and density function theory (DFT) calculations. Degradation experiments on gaseous benzene revealed that under 15 W ultraviolet (UV) light irradiation in humid and closed conditions for 60 min, 1 % Sn-TiO2 achieved a benzene degradation efficiency of 93.14 %, with almost complete mineralization. Furthermore, flow system experiments demonstrated efficient decomposition of trace amounts of benzene (∼10 mg/m3) in the air to satisfy emission standards when employing 1 % Sn-TiO2 at a flow rate of 100 L/min.

MOFs-derived 3D hierarchical CoFe2O4/RuO2 hollow nanosheet array for efficient overall water splitting

Accelerating hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) kinetics process is crucial to the development of transition metal oxide based materials as bifunctional catalysts for overall water splitting. Herein, a heterostructured CoFe2O4/RuO2 hollow hierarchical nanosheet array (FeRu-CoOx) has been designed by using MOF as template followed by simultaneous etching-doping process combined with calcination for enhanced HER performance without compromise of OER activity. The MOF-derived FeRu-CoOx exhibits an enhancement on HER performance with 58 mV overpotential to achieve 10 mA cm-2 and a small Tafel slop of 73.1 mV dec-1 in the alkaline solution, compared to CoFe2O4 counterpart (Fe-CoOx) using monometallic Fe etching and doping. In addition, the FeRu-CoOx electrode also shows good OER activity (10 mA cm-2 at an overpotential of 229 mV), better than those of Fe-CoOx (239 mV) and commercial RuO2 electrodes (270 mV). The introduction of Ru helps the construction of heterostructure, which is in favor of exposure of active sites, increasing the electron interaction between different composites, and accelerating charge transfer. The alkali electrolyzer using FeRu-CoOx as cathode and anode shows a small cell voltage with only 1.48 V at 10 mA cm-2 and good tolerance toward long-term stability. The MOF template combined with etching-doping strategy to construct hierarchical and heterostructured materials gives a way to develop advanced bifunctional electrocatalysts for water splitting.

Cobalt-promoted palladium confined in HZSM-5 zeolite for toluene storage and oxidation capacity in humid environment

Although oxide-zeolite bifunctional catalysts with storage and oxidation capacity was efficient for VOCs removal, the inevitable moisture in the air usually harms the catalysts performance. Herein, cobalt was in situ confined with palladium in HZSM-5 by a one-pot hydrothermal method and significantly improved the storage and oxidation abilities in humid air. The optimal Pd0.90Co0.10@Z5 catalyst showed a considerable toluene storage capacity of 76.8 mg/g (100 ppm toluene/humid air, GHSV=60,000 h−1), and the best oxidation activity (600 ppm toluene/humid air, GHSV=60,000 h−1, TOFPd = 15.5 × 10−3 s−1 at 200 °C). Pd0.90Co0.10@Z5 formed an intrapenetrated mesoporous structure with the smallest Pd clusters of dAV=2.6 nm. The synergistic effect between palladium and cobalt promoted electron transfer and Pd0.90Co0.10@Z5 had the highest Pd2+/Pd0 ratio of 3.50. Co2+ can activate water to form Co(OH)3 and provide an additional ·OH oxidation pathway, ·OH and reactive oxygen species (O*) together promote the deep oxidation of intermediates. This work provides a novel approach that bimetallic collaboration combined with porous zeolite can improve the catalytic performance and water resistance.

Synergistic Effect of RuCo and Hierarchical ZSM‐5 for Enhanced Hydrogen Generation

AbstractA unique bifunctional catalyst comprised of acid site containing, hierarchical ZSM‐5 (contains acid sites) supported RuCo bimetal, was synthesized using a facile incipient wetness impregnation method. The synergistic interaction between zeolite acid sites and bimetals of this bifunctional material significantly improves its performance as a catalyst of hydrogen producing, dehydrogenation of ammonia borane.

Graphitized carbon-anchored FeSe nanoparticles for stable and efficient bifunctional electrocatalyst in rechargeable zinc-air batteries

Developing zinc-air batteries still heavily relies on the design of stable, high-activity, and inexpensive oxygen-electric bifunctional catalysts. In this work, transition metal iron salts converted amorphous carbon into graphitized carbon at high temperatures, and nitrogen-doped graphitized carbon-anchored iron nanoparticles (Fe–N–C) are prepared. Then, Fe–N–C is pyrolyzed with selenium dioxide (SeO2) to convert iron (Fe) nanoparticles into iron selenide (FeSe) in situ to obtain nitrogen-doped graphitized carbon-anchored FeSe nanoparticle catalysts (FeSe/NC). The catalyst's carbon support has excellent electrical conductivity, which effectively promotes the transport rate of charges and enhances the catalytic activity of FeSe particles. FeSe/NC demonstrates outstanding catalytic activity for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). When utilizing FeSe/NC catalysts in rechargeable zinc-air batteries (ZABs-FeSe/NC), the most excellent power density could exceed 186.6 mW cm−2, and the specific capacity can achieve 905.2 mAh g−1, demonstrating excellent performance. Furthermore, the battery can achieve stable charge-discharge for longer than 200 h at a large current density of 10 mA cm−2, which has excellent practical application feasibility in the future.

Structurally optimized rosette-like microspheres carbon with Fe-Ni single atom sites for bifunctional oxygen electrocatalysis in Zinc-Air batteries

Developing a secure and effective bifunctional oxygen catalyst for the ORR and OER is still a significant obstacle in the design of rechargeable zinc-air batteries. Here, a hollow rose-shaped bifunctional electrocatalyst is synthesized with an sacrificial template strategy (FeNi-NC). X-ray absorption fine structure analysis reveals the FeNi-NC catalyst contains FeN4 and NiN4 active sites as well as FeNi3 alloy. This hollow, flower-like structure performs low density, large specific surface area, and high permeability. Its inner cavities not only provide additional triple-phase interfaces to accelerate the reduction and oxidation of O2, but also enhance the diffusion of reactants on the catalyst. By controlling the input of Fe and nickel metal salts, the dispersion of active sites can be effectively tuned. Owing to the large number of exposed active sites on the carbon nanosheets, the synthesized FeNi-NC catalysts exhibit high electrocatalytic activity in both ORR (E1/2 = 0.852 V) and OER (ηj=10 = 359 mV). The construction of rechargeable zinc-air batteries resulted in a high power density of 135.78 mW cm−2, a better specific capacitance of 726.9 Wh kgZn−1 and 210 h enduring durability. More importantly, density functional theory (DFT) calculations indicate that the electronic interactions between Fe/Ni and nitrogen-doped carbon matrices play a pivotal role in enhancing the electrocatalytic performance of functional groups. These interactions effectively disrupt the electronic neutrality of carbon atoms, thereby accelerating the kinetics of the reaction. This research provides a new method for the preparation of single atom catalysts with bifunctional activities.

Microwave-catalyzed co-pyrolysis of Chlorella vulgaris and marine waste plastics using Ni-Fe@C bifunctional catalyst: Characterization, pyrolysis oil analysis and reaction mechanism

The co-pyrolysis of Chlorella vulgaris (CV) and marine waste plastics (MW) is beneficial in solving the shortcomings of microalgae conversion and alleviating marine ecological problems. In this paper, the monometallic (Ni, Fe) and bimetallic (Ni-Fe) based metal-organic frameworks (MOFs) derived catalysts were prepared, and the effects of catalysts with different additions amounts (10 %, 20 % and 30 %) on co-pyrolysis of CV and MW were studied by microwave oven. The results showed that the catalysts improved co-pyrolysis characteristics and pyrolysis oil yield. The maximum average weight loss rate (0.02395 wt%/s) and pyrolysis oil yield (14.17 %), as well as the minimum reaction time (2971 s) under 30 % Fe-Ni@C. GC-MS showed that adding catalysts to C8M2 (CV/MW = 8:2) increased the hydrocarbon content (>30 %) and the denitrogenation efficiency (>31 %) in pyrolysis oil, while enhancing the selectivity of low carbon numbers (<20). Furthermore, Fe-Ni@C promoted the Diels-Alder reaction, deoxygenation, dehydration, decarboxylation, cyclization, and deamidation, intensifying the generation of aromatic compounds and reducing nitrogen compounds. Specifically, the highest aromatic hydrocarbon content (23.48 %) and denitrogenation efficiency (43.87 %) were obtained under 30 % Fe-Ni@C.

Rational Construction of Honeycomb-like Carbon Network-Encapsulated MoSe2 Nanocrystals as Bifunctional Catalysts for Highly Efficient Water Splitting.

The scalable fabrication of cost-efficient bifunctional catalysts with enhanced hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) performance plays a significant role in overall water splitting in hydrogen production fields. MoSe2 is considered to be one of the most promising candidates because of its low cost and high catalytic activity. Herein, hierarchical nitrogen-doped carbon networks were constructed to enhance the catalytic activity of the MoSe2-based materials by scalable free-drying combined with an in situ selenization strategy. The rationally designed carbonaceous network-encapsulated MoSe2 composite (MoSe2/NC) endows a continuous honeycomb-like structure. When utilized as a bifunctional electrocatalyst for both HER and OER, the MoSe2/NC electrode exhibits excellent electrochemical performance. Significantly, the MoSe2/NC‖MoSe2/NC cells require a mere 1.5 V to reach a current density of 10 mA cm-2 for overall water splitting in 1 M KOH. Ex situ characterizations and electrochemical kinetic analysis reveal that the superior catalytic performance of the MoSe2/NC composite is mainly attributed to fast electron and ion transportation and good structural stability, which is derived from the abundant active sites and excellent structural flexibility of the honeycomb-like carbon network. This work offers a promising pathway to the scalable fabrication of advanced non-noble bifunctional electrodes for highly efficient hydrogen evolution.

A3B Zn(II)-Porphyrin-Coated Carbon Electrodes Obtained Using Different Procedures and Tested for Water Electrolysis

In the context of water electrolysis being highlighted as a promising technology for the large-scale sustainable production of hydrogen, the water-splitting electrocatalytic properties of an asymmetrically functionalized A3B zinc metalated porphyrin, namely, Zn(II) 5-(4-pyridyl)-10,15,20-tris(4-phenoxyphenyl)-porphyrin, were evaluated in a wide pH range. Two different electrode manufacturing procedures were employed to outline the porphyrin’s applicative potential for the O2 and H2 evolution reactions (OER and HER). The electrode, manufactured by coating the catalyst on a graphite support from a dimethylsulfoxide solution, displayed electrocatalytic activity for the OER in an acidic electrolyte. An overpotential value of 0.44 V (at i = 10 mA/cm2) and a Tafel slope of 0.135 V/dec were obtained. The modified electrode that resulted from applying a Zn(II)-porphyrin-containing catalyst ink onto the same substrate type was identified as a bifunctional water-splitting catalyst in a neutral medium. OER and HER overpotentials of 0.78 and 1.02 V and Tafel slopes of 0.39 and 0.249 V/dec were determined. This is the first Zn(II)-porphyrin to be reported as a heterogenous bifunctional water-splitting electrocatalyst in neutral aqueous electrolyte solution and is one of very few porphyrins behaving as such. The TEM analysis of the porphyrin’s self-assembly behavior revealed a wide variety of architectures.

One‐Pot Cascade Reaction from Epoxide to Carboxylic Acids Using Bifunctional Fe‐ZSM‐5

AbstractThe quest for sustainable synthesis of carboxylic acids has led to the exploration of innovative routes and catalysts for the oxidative cleavage of carbon−carbon double bonds, prevalent in bio‐derived molecules. This process involves multiple steps including epoxidation, hydrolysis and vicinal diol cleavage, often catalysed by unsustainable homogeneous or noble‐metal catalysts. In this study, we present the utilization of Fe‐ZSM‐5 as a versatile bifunctional catalyst capable of catalysing both hydrolysis and vicinal diol cleavage steps, utilizing propylene oxide as model compound and H2O2 as oxidizing agent. The prepared Fe‐ZSM‐5 features the zeolite intrinsic Lewis and Brønsted acidity functions, essential for the hydrolysis step, as well as high fractions of monomeric FeOx species, crucial for the subsequent vicinal diol cleavage, leading to streamlined carboxylic acids formation in a one‐pot, two‐step process. Moreover, by combining Fe‐ZSM‐5 with TS‐1, renowned for its epoxidation activity, we demonstrate the complete cascade reaction in one pot, under mild conditions, starting from ethylene. Our study expands the utility of cost‐effective zeolite‐based catalysts enriched with abundant Fe metal for the one‐pot oxidative cleavage of C=C double bonds, offering a promising pathway towards sustainable carboxylic acid synthesis.

Tandem hydroformylation/hydrogenation of olefins to alcohols using atomically dispersed bifunctional catalysts

Tandem hydroformylation/hydrogenation of olefins to alcohols using atomically dispersed bifunctional catalysts