Bimetallic Heterogeneous Catalysts Research Articles

Development of an Effective Au : Pd Bimetallic Heterogeneous Catalyst for Oxidative Lignin Depolymerization to Low Molecular Weight Aromatics

AbstractLignin, a phenolic‐rich biomass component, holds promise for producing value‐added products. However, its complex structure and recalcitrance present challenges for its effective utilization. To overcome this, a AuPd/Li−Al layered double hydroxide (LDH) catalyst was developed to facilitate lignin depolymerization. Various AuPd bimetallic nanoparticle compositions were supported on a basic Li−Al LDH support via a sol‐immobilization method and characterized using N2‐physisorption, X‐ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). The catalysts were then evaluated in the oxidation of several benzylic alcohols using O2 as the oxidant, from which Au7Pd3/Li−Al LDH and Au1Pd1/Li−Al LDH were identified as possessing promising catalytic activity. Further investigations focused on the aerobic oxidation of β‐O‐4 linked lignin model dimers under atmospheric pressure. The tested catalysts demonstrated sequential oxidation of the model compounds, leading to cleavage of the β‐O‐4 linkage. Finally, the catalysts were applied to the oxidative deconstruction of γ‐valerolactone (GVL) extracted maple lignin at 120 °C. Au1Pd1/Li−Al LDH emerged as the most effective catalyst, yielding a range of aromatic monomers with a total monomer yield of 27 %. These results highlight the potential of the Au1Pd1/Li−Al LDH catalyst system as an eco‐friendly approach for lignin depolymerization under mild conditions.

Selective oxidation of alkenes catalyzed by palladium-based bimetallic heterogeneous catalysts under atmospheric pressure

Wacker oxidation using palladium–copper bimetallic catalysts under atmospheric air.

Bimetallic Fenton-like Catalysts in the Remediation of Dyes

Remediation of organic dyes in natural waters is a significant environmental need under active study. This review analyzes bimetallic catalytic degradation systems that are based on the Fenton chemistry concept and that generate reactive oxygen species (ROS) as the agent of dye breakdown. Recently developed advanced oxidation processes (AOPs) take advantage of bimetallic heterogeneous catalysts to facilitate rapid rates and full degradation. Catalysts based on two metals including iron, copper, molybdenum, cobalt and magnesium are discussed mechanistically as examples of effective radical ROS producers. The reactive oxygen species hydroxyl radical, superoxide radical, sulfate radical and singlet oxygen are discussed. System conditions for the best degradation are compared, with implementation techniques mentioned. The outlook for further studies of dye degradation is presented.

Visualizing the Birth and Monitoring the Life of a Bimetallic Methanation Catalyst.

Well-defined bimetallic heterogeneous catalysts are not only difficult to synthesize in a controlled manner, but their elemental distributions are also notoriously challenging to define. Knowledge of these distributions is required for both the as-synthesized catalyst and its activated form under reaction conditions, where various types of reconstruction can occur. Success in this endeavor requires observation of the active catalyst via in situ analytical methods. As a step toward this goal, we present a composite material composed of bimetallic nickel-ruthenium nanoparticles supported on a protonated zeolite (Ni-Ru/HZSM-5) and probe its evolution and function as a photoactive carbon dioxide methanation catalyst using in situ X-ray absorption spectroscopy (XAS). The working Ni-Ru/HZSM-5, as a selective and durable photothermal CO2 methanation catalyst, comprises a corona of Ru nanoparticles decorating a Ni nanoparticle core. The specific Ni-Ru interactions in the bimetallic particles were confirmed by in situ XAS, which reveals significant electron transfer from Ni to Ru. The light-harvesting Ni nanoparticle core and electron-accepting Ru nanoparticle corona serve as the CO2 and H2 dissociation centers, respectively. These Ni and Ru nanoparticles also promote synergistic photothermal and hydrogen atom transfer effects. Collectively, these effects enable an associative CO2 methanation reaction pathway while hindering coking and fostering high selectivity toward methane.

Bimetallic Heterogeneous Catalysts for the Oxidation of Sulfur-Containing Compounds with Hydrogen Peroxide

Bimetallic Heterogeneous Catalysts for the Oxidation of Sulfur-Containing Compounds with Hydrogen Peroxide

Bimetallic Heterogeneous Catalysts for the Oxidation of Sulfur-Containing Compounds with Hydrogen Peroxide

Bimetallic heterogeneous catalysts based on SBA-15 containing molybdenum and iron oxides were studied in the oxidation reactions of model mixtures of organosulfur compounds. Iron additive (in the form of iron(III) oxide) in the amount of 0.05 wt % to the catalyst 5%Mo/SBA-15 turns out to be the most effective. The catalysts were confirmed by a complex of physicochemical methods: low-temperature adsorption-desorption of nitrogen, X-ray phase analysis, transmission electron microscopy, X-ray photoelectron spectroscopy. The influence of the main oxidation parameters (reaction time, temperature, composition and amount of catalyst, amount of oxidizer) on the conversion of dibenzothiophene as a component of the model mixture weas investigated. Optimal oxidation conditions that allow to achieve total transformation of the substrate were selected: H2O2 : S = 2 : 1, 0.5 wt % of the catalyst FeMo/SBA-15, 60 min, 60°C; catalysts can be used for at least 5 cycles without loss of activity during their intermediate washing from oxidation products.

The resin-supported iron-copper bimetallic composite as highly active heterogeneous Fenton-like catalysts for degradation of gaseous toluene.

In this study, a resin-supported iron-copper bimetallic heterogeneous Fenton catalyst with excellent removal performance, superior economy and outstanding recoverability was synthesized by an impregnation method and used to remove gaseous toluene. Experiments disclosed that 3-FeCu@LXQ-10 possessed extremely high catalytic capacity. At a temperature of 30 °C, an initial toluene concentration of 200 mg/m3 and H2O2 atomization amount of 3 mmol/h, the toluene removal efficiency of 3-FeCu@LXQ-10 was 97.50%. Experimental tests had revealed that the bimetallic supported catalysts exhibited higher catalytic activity than single metal-supported catalysts, owing to an interaction effect between iron and copper metal ions. Furthermore, electron paramagnetic resonance (EPR) and radical quenching tests were carried out, and the results indicated •OH radicals performed a key role in the Fenton-like process. In addition, the iron-copper bimetallic catalysts exhibited good reusability and stability characteristics during six degradation cycles. This study shows promising potential in using FeCu@LXQ-10 as a heterogeneous catalyst for removing toluene.

Oxygen effect on the synthesis of vinyl acetate on Pd (100) and Pd/Au (100) surfaces: A periodic DFT study

Vinyl acetate is mainly produced by oxidative acetoxylation of ethylene over the Pd/Au bimetallic heterogeneous catalyst. This process requires the involvement of oxygen, but the role of oxygen has not been well studied. The oxygen effect on the synthesis of vinyl acetate is of considerable economic benefit, as the process conditions can be better optimized. In this study, the O2 adsorption and dissociation on the Pd (100) and Pd/Au (100) surfaces, the effect of the co-adsorbed O atom on the C2H4, CH3COOH and CH3COO adsorptions, and the reaction mechanism have been investigated using ab initio density functional theory (DFT) method. The calculated results suggest that the O adatoms are detrimental to the adsorption of C2H4 and CH3COO, but favorable for CH3COOH. For the reaction, the O adatoms reduce the energy barrier of CH3COOH dehydrogenation and VA formation, and increase the reaction enthalpy (more exothermic). This study provides further mechanistic insight into VA synthesis on the Pd-based catalysts.

Atomic-Scale Site Characterization of Cu–Zn Exchange on Cu(111)

An accurate understanding of the physicochemical properties of bimetallic heterogeneous catalysts relies on atomic-scale knowledge of the surface morphology and the atomic distribution. Alloys of Cu and Zn created during catalyst operation are frequently studied and debated in relation to a description of the active phase of Cu/ZnO/Al2O3 methanol synthesis catalysts. This makes it relevant to build a better understanding of Zn dissolution pathways in Cu surfaces and the resulting surface morphology. Herein, we use scanning tunneling microscopy to investigate surface morphology and the distinct atom site configurations of Zn and Cu on Cu(111) resulting from room-temperature Zn exchange from a Zn monolayer into the topmost layer of Cu(111). A gradual dissolution of Zn islands induces an extensive element intermixing at room temperature, resulting in Zn alloying at Cu terrace lattice sites. In addition, we observe and address an interlayer element exchange between the Zn submonolayers in direct contact with Cu. The exchange process is driven by lattice strain and is strongly facilitated at the perimeter of Zn edges. The STM contrast associated with the resulting intermixed sites is reported together with the simulation of these sites based on density functional theory, showing that imaging of isolated Zn sites in Cu(111) is sensitive to the STM tip state. The findings provide new insight into the atomic-scale exchange for Zn/Cu bimetallic surfaces, which may be used onward for understanding the debated surface morphology that develops during reductive activation and alloy formation in the Cu/ZnO/Al2O3 methanol synthesis catalyst.

Catalytic Steam Reforming of Ethanol to Produce Hydrogen: Modern and Efficient Catalyst Modification Strategies

AbstractHydrogen is regarded as one of the most promising renewable energy that carriers with a high heating value for replacing fossil fuels and meeting clean energy requirements. Steam reforming has shown considerable promises in the creation of hydrogen. Many studies on catalytic steam reforming of ethanol have been published. Hence, developing efficient and stable catalysts capable of producing large H2 yields and ethanol conversion is a crucial step. Nickel is an essential industrial catalyst because it enhances hydrogenation and dehydrogenation reactions by promoting the scission of C−C bonds. Many studies have been conducted by employing noble metal‐based catalysts to reduce coke deposition and enhance metal stability against sintering since they are known to successfully break the C−C bond, resulting in less carbonaceous deposits and hence more stable catalysts. To avoid carbon production, alkaline promoters, and bimetallic heterogeneous catalysts are commonly utilized in catalysis. However, because huge amounts of by‐product CO2 produced by SRE courses are usually regarded as the primary cause of hydrogen purity degradation, it is recommended to remove CO2 in‐situ to achieve high hydrogen production.

Degradation of carbamazepine over MOFs derived FeMn@C bimetallic heterogeneous electro-Fenton catalyst

A highly efficient heterogeneous electro-Fenton (Hetero-EF) catalyst with core-shell structure was successfully prepared by calcination of Mn-doped Mil-53 (Fe) precursor at high temperature. FeMn@C-800/2 prepared at pyrolysis temperature of 800 °C and Fe:Mn molar doping ratio of 2:1 showed the best catalytic performance for the degradation of carbamazepine (CBZ). The characterization, properties and stability of FeMn@C-800/2 were systematically investigated, obtaining the apparent first-order reaction rate of Hetero-EF was 8.9 and 17.8 times higher than that on Fe@C-800 and Mn@C-800 at the optimized conditions of current density 10 mA cm−2, catalyst dosage of 50 mg L−1 and initial pH 4.0, respectively. The incorporation of Mn promoted the generation of more Fe0 and Fe3C during the pyrolysis process, and enhanced the internal micro-electrolysis between Fe0 and carbon shell. At the same time, the presence of Mn0 also promoted the regeneration of Fe2+, and improved the activity of iron-carbon heterogeneous catalysis in the EF process, so as to degrade organic pollutants more effectively. This work would help to gain insight into the design of MOFs derived Fe–Mn bimetal catalyst and its mechanism for enhanced heterogeneous electro-Fenton.

Bimetallic Pd‐Au Nanoparticles Supported Monodisperse Porous Silica Microspheres as an Efficient Heterogenous Catalyst for Fast Oxidation of Benzyl Alcohol

AbstractA bimetallic heterogeneous catalyst in the form of PdAu nanoparticle supported monodisperse‐porous SiO2 microspheres (PdAu@APTES@SiO2) was prepared for fast oxidation of benzyl alcohol (BzOH). The mesoporous support obtained by an originally developed staged‐shape templated hydrolysis‐condensation protocol provided large surface area and high pore volume for parking of noble metal nanoparticles. PdAu@APTES@SiO2 provided higher BzOH conversion, benzaldehyde (BzH) selectivity and BzH formation yield with respect to monometallic catalysts containing Pd or Au nanoparticles supported with SiO2 microspheres. BzOH conversions and BzH formation yields higher than 95 % were obtained in 30 min at 80 °C. The maximum TON and TOF values were determined as 300 and 600 h−1, respectively. BzOH conversions and TOF were also higher with respect to similar catalysts prepared using different supports also carrying PdAu nanoparticles. PdAu@APTES@SiO2 exhibited good stability with a decrease of BzOH conversion less than 2.5 % over five consecutive runs.

Copper doped Fe-N-C as an excellent Fenton-like catalyst for membrane fouling mitigation against natural organic matters at neutral pH

The presence of humic substances as a component of natural organic matter (NOM) may cause inefficiency towards drinking water treatment processes, especially the membrane fouling during filtration process. Therefore, to enhance the efficiency of the conventional membrane filtration process, several copper doped Fe-N-C bimetallic heterogeneous Fenton-like catalysts (Cux@FeNC) were prepared and evaluated by executing their catalytic degradation performance against NOM. Results indicated that humic acid (HA, 10 mg/L) could be significantly degraded (95%) within 30 min application of Cu5p@FeNC-Fenton under neutral pH, which was relatively higher than of FeNC-Fenton (70%) under identical conditions. The macromolecular organic matters in NOM could be destroyed more effectively while the overall mineralization degree also became relatively higher. Meanwhile, a lower membrane fouling of UF (PES 20 kDa)/NF (DOW 270) and highest flux recovery after backwash were observed with Cu5p@FeNC-Fenton treatments. Characterization and chemical analysis further explored the introduction of Cux in FeNC was responsible for the rapid reactive oxygen species (ROS) generation and efficient degradation of NOM. Additionally, a possible copper-iron synergetic mechanism in Fenton-like system was proposed. This work gives a deep insight into the potential NOM degradation using Fenton-like Cux@FeNC catalysts and ensures the membrane fouling mitigation for effective water treatment processes.

Degradation of Carbamazepine Over Mofs Derived Femn@C Bimetallic Heterogeneous Electro-Fenton Catalyst

Degradation of Carbamazepine Over Mofs Derived Femn@C Bimetallic Heterogeneous Electro-Fenton Catalyst

Peroxymonosulfate activation by brownmillerite-type oxide Ca2Co2O5 for efficient degradation of pollutants via direct electron transfer and radical pathways

• Ca 2 Co 2 O 5 catalyst with multiple Co oxidation states was prepared. • The catalyst showed high activity and stability via PMS activation. • Both radicals and direct electron transfer process contribute to the reaction. • The role of Co species with different oxidation states was discussed. The development of mixed metal oxides with excellent activity and stability for pollutants degradation via peroxymonosulfate (PMS) activation is highly desired in recent years. In this work, the brownmillerite-type oxide, Ca 2 Co 2 O 5 (CCO) with unique Ca 2 CoO 3 and CoO 2 layer structure and multiple oxidation states such as Co(II), Co(III) and Co(IV), was prepared and used to degrade organic pollutants with PMS as oxidant for the first time. It was found that CCO exhibited higher activity than other Co-based catalysts such as Co 2+ and Co 3 O 4 , and more than 93% of acid orange 7 (50 μM) was degraded after 7.5 min under mild reaction conditions. The catalysts were also stable during five successive runs. The easy oxidation of Co(II) species, the strong interactions among CCO, PMS and the pollutants, and the synergistic effect between Co and Ca were identified by several technologies and contributed to the high performance of the catalyst. Moreover, different from the conventional mechanism, radicals produced from low valent Co species oxidation by PMS, as well as the direct electron transfer process through the high valent Co species contributed the degradation reaction simultaneously. These findings provide an ideal bimetallic heterogeneous catalyst and a new mechanism for PMS-mediated reaction.

Crednerite CuMnO2 as highly efficient Fenton-like catalysts for p-nitrophenol removal:Synergism between Cu(I) and Mn (III)

p-Nitrophenol (PNP) is one of the highly toxic and mutagenic pollutants existed in aquatic environment. In this work, the crednerite CuMnO2 nanoflake was prepared and used to degrade PNP with peroxymonosulfate (PMS) as the oxidant. It was found that CuMnO2 exhibited much higher activity than other Cu-based catalysts such as CuO, Cu2O, CuFe2O4 and CuFeO2, with 90% of PNP degraded after 10 min under mild reaction conditions. The catalyst was also stable during five successive runs. Sulfate and hydroxyl radicals produced from PMS reduction by Cu(I) species, as well as superoxide ions and single oxygen, contribute to the degradation of PNP. More importantly, the interactions between Mn and Cu species in CuMnO2 were identified by X-ray photoelectron spectroscopy (XPS), fourier transform infrared spectroscopy (FT-IR) and linear sweep voltammetry (LSV), and were further confirmed by the control experiment with the mixture of Cu2O + Mn2O3. The results implied that the high valent Mn(III) species acted as Lewis acids to withdraw electron from PMS, resulting that the Cu(I) species can be easier oxidized to Cu(II) by PMS with the formation of radicals. These findings provide an ideal bimetallic heterogeneous catalyst and a new mechanism for PMS-mediated reaction.

Rational design of tandem catalysts using a core-shell structure approach.

A facile and rational approach to synthesize bimetallic heterogeneous tandem catalysts is presented. Using core–shell structures, it is possible to create spatially controlled ensembles of different nanoparticles and investigate coupled chemocatalytic reactions. The CO2 hydrogenation to methane and light olefins was tested, achieving a tandem process successfully.

A Smart Heterogeneous Catalyst for Efficient, Chemo- and Stereoselective Hydrogenation of 3-Hexyn-1-ol

We examine the easy preparation of mono- and bi-metallic heterogeneous catalysts with low Pd and Cu contents on alumina and provide a detailed study of many reaction parameters in the catalyzed selective semihydrogenation of 3-hexyn-1-ol to (Z)-3-hexen-1-ol, a very important fragrance with an herbaceous note. In particular, two different protocols of Pd catalyst preparation, substrate/catalyst molar ratio, the effect of time and temperature, introduction of some additives to the reaction mixture, and the nature of the solvent were investigated. These factors are not independent variables. The results show that it is possible to control the reaction outcome to obtain the target (Z)-alkenol using different experimental conditions. The best result, as an appropriate compromise between conversion and selectivity, may be obtained by working with a very high substrate/catalyst molar ratio (>6000/1), with one type of Pd catalyst, in a short time (about 150 min) at 60 °C.

Designing a bifunctional metal-organic framework by tandem post-synthetic modifications; an efficient and recyclable catalyst for Suzuki-Miyaura cross-coupling reaction

A new Cu/Pd bimetallic Cu-MOF-[Pd] was synthesized through covalent, dative and inorganic post-synthetic modifications. In order to achieve the Cu-MOF-[Pd], Zn-MOF (TMU-17-NH2) was initially selected and fabricated by grafting of salicylaldehyde via Schiff-base formation followed by complex formation with Pd(II). Then, the as-synthesis MOF, Zn-MOF-[Pd], was subjected as 3D-template to obtain Cu-MOF-[Pd] by transmetalation process. The Cu-MOF-[Pd] was characterized by FT-IR spectroscopy, atomic absorption spectroscopy (AAS), field emission scanning electron microscopy (FE-SEM), powder X-ray diffraction (PXRD), energy dispersive X-ray spectroscopy (EDS), and EDS mapping techniques. The feasibility of using Cu-MOF-[Pd] as a highly active recoverable catalyst was confirmed in the Suzuki–Miyaura cross-coupling reaction in a mixed water/ethanol solvent. The results show that this novel nano-composite could serve as an efficient bimetallic heterogeneous catalyst and reuse at least for 5 times without loss in activity.

Designing a Bifunctional Metal-Organic Framework by Tandem Post-Synthetic Modifications; an Efficient and Recyclable Catalyst for Suzuki-Miyaura Cross-Coupling Reaction

A new Cu/Pd bimetallic Cu-MOF-[Pd] was synthesized through covalent, dative and inorganic post-synthetic modifications. In order to achieve the Cu-MOF-[Pd], Zn-MOF (TMU-17-NH2) was initially selected and fabricated by grafting of salicylaldehyde via Schiff-base formation followed by complex formation with Pd(II). Then, the as-synthesis MOF, Zn-MOF-[Pd], was subjected as 3D-template to obtain Cu-MOF-[Pd] by transmetalation process. The Cu-MOF-[Pd] was characterized by FT-IR spectroscopy, atomic absorption spectroscopy (AAS), field emission scanning electron microscopy (FE-SEM), powder X-ray diffraction (PXRD), energy dispersive X-ray spectroscopy (EDS), and EDS mapping techniques. The feasibility of using Cu-MOF-[Pd] as a highly active recoverable catalyst was confirmed in the Suzuki–Miyaura cross-coupling reaction in a mixed water/ethanol solvent. The results show that this novel nano-composite could serve as an efficient bimetallic heterogeneous catalyst and reuse at least for 5 times without loss in activity.