High-performance Bimetallic Catalysts Research Articles

Theoretical investigation of CO2 hydrogenation to methanol catalyzed on Pd-Ga bimetallic catalysts: Insights into the effects of Ga in different coordination environments

Methanol is easy to store compared to other gaseous hydrogenation products. Moreover, it can be further converted to other advanced hydrocarbons, so the conversion of CO2 to methanol (CTM) is a promising reaction. PdGa bimetallic catalysts are candidate catalysts for CTM conversion, which can promote H spillover to the active site and react with adsorbed CO2. However, the role of Ga atom in PdGa bimetallic catalysts and the underlying mechanism of CTM are still unclear at the molecular level. In this work, Ga atom with different coordination environments CN3, CN4 and CN5 were obtained on the Pd(111), and three reaction mechanisms of CTM on different catalysts are systematic investigated. Changes in the coordination environments of the Ga atom affected the adsorption configurations of HCOOH*, HCO*, and H2CO*, among others. Three catalysts have similar superior pathways, and the order of CO2 reactivity is CN4 > CN3 > CN5. The PdGa bimetallic catalysts containing 4-coordinated Ga atom are proposed to be the ideal catalysts. We hope that the conclusions obtained can help understand the reasons for the outstanding reactivity and selectivity of CTM on PdGa bimetallic catalysts at the molecular level, and can provide some guidance for the design and development of high-performance bimetallic catalysts.

Designing the bimetallic catalysts by the adsorption strength of metal atoms for efficient oxygen reduction: A density functional theory study

In this paper, a new design principle for bimetallic catalysts is proposed by combining strongly adsorbed atoms (SAA) with weakly adsorbed atoms (WAA) where the SAA and WAA are classified by the free adsorption energy of oxygen-containing intermediates on the metal atom. And the ORR performances of the bimetallic catalysts designed by the method are compared with the common single metal atom catalysts. The method is successfully confirmed as the overpotential of the Mn-based bimetallic catalysts decreases from 0.63 V in G-MnN4 to as low as 0.33 V, and that of the Fe-based bimetallic catalysts decreases from 0.76 V in G-FeN4 to 0.23 V. In addition, the correlation between adsorption free energy and adsorption bond length is revealed for the first time, and the optimal adsorption bond length is determined. Finally, the adsorption energy of O2 is plotted versus the free adsorption energy of three oxygen-containing intermediates for the first time, and a suitable adsorption energy of O2 is found to be -1.4∼-1.0 eV. These findings provide a new perspective for the design of high-performance bimetallic catalysts.

Design and screening of bimetallic catalysts for nitric oxide reduction by CO: a study of kinetic Monte Carlo simulation based on first-principles calculations.

Nitric oxide (NO) emissions pose a significant environmental challenge, and the development of effective catalysts for NO reduction is crucial. This study investigates the potential of striped bimetallic catalysts for NO reduction by CO using kinetic Monte Carlo (KMC) simulations based on first-principles calculations. The simulations reveal that the activity on the striped Ni-Pt-Pt (111) surface is 1-2 orders of magnitude higher than that on the terraced Ni-Pt-Pt (111) surface at the same temperatures, demonstrating the importance of defect engineering. Sensitivity analysis identifies CO oxidation as the rate-determining step, although the 2N* association barrier is higher than CO oxidation, highlighting the need to consider reaction conditions in kinetic simulations. Volcano plots based on the formation energies of NO* and CO* successfully predict the striped Ni-Pd-Pd (111) and Ni-Rh-Rh (111) surfaces as optimal catalysts, which were further validated through DFT calculations and ab initio molecular dynamics simulations. This study offers valuable insights for designing high-performance bimetallic catalysts for NO reduction and underscores the importance of considering specific reaction conditions in kinetic simulations.

Pd–Ag Bimetallic Catalysts with Core–Shell Engineering for Efficient Hydrogen Production from Formic Acid Decomposition

Fine control of the ligand and strain effects of secondary elements on the catalytic function of primary elements is critical for developing high-performance bimetallic catalysts. In this paper, we describe a method for making Pd–Ag bimetallic core–shell nanocatalysts with synergistic ligand and Ag strain effects. (PdAg alloy core)@(ultrathin Pd shell) nanocrystals with regulated core compositions and shell thicknesses, as well as a well-defined octahedral shape, could be achieved through precision core–shell engineering. The produced octahedral PdAg@Pd core–shell nanocrystals showed excellent catalytic activity in the creation of hydrogen from the breakdown of formic acid. The highest catalytic activity was attained using PdAg@Pd nanocrystals made up of PdAg alloy cores with an average Pd/Ag atomic ratio of 3.5:1 and a 1.1 atomic layer of Pd shells, which set a new record for catalytic activity.

Catalytic hydrodeoxygenation of biomass-derived pyrolysis oil over alloyed bimetallic Ni3Fe nanocatalyst for high-grade biofuel production

The design of cost-effective and high-performance bimetallic catalysts has become crucial for the effective conversion of biomass-derived pyrolysis-oil (Py-oil) into liquid biofuels. New bimetallic Ni3Fe catalysts were developed for effective hydrodeoxygenation (HDO) of Py-oil derived from date seeds. Ni3Fe catalyst showed a well-defined octagon-like morphology with a diameter of 120 nm and high saturation magnetization (Ms) of 78 emu g−1 at room temperature. Py-oil was subjected to catalytic HDO processes at 250 °C for 120 min in a 10 bar H2 atmosphere in the presence of Ni3Fe catalyst. Characterization results confirmed HDO of several components of Py-oil, including phenols, acids, aldehyde and ketones, sugars and aromatic hydrocarbons over the surfaces of Ni3Fe catalyst. The obtained upgraded Py-oil (HDO Py-oil) showed the highest hydrocarbons content of 23.77%, higher heating value (HHV) of 36.78 MJ kg−1, and lower content of water, total acid number, and viscosity than fresh Py-oil. Bimetallic Ni3Fe catalyst resulted in better HDO performance and re-usability for five consecutive cycles than recently reported monometallic or noble metal nanocatalysts. Plausible reaction pathways for the formation of major components including ethane, ethyl acetate, 2,5-dimethylfuran, D-sorbitol, methylcyclohexane, furfural alcohol, and 1,5-pentane diols are discussed. Results demonstrate that this simple and active bimetallic catalytic system leads to a cutting-edge liquid biofuels production pathway in the future.

Au-Ag synergistic effect in CF3-ketone alkynylation catalyzed by precise nanoclusters

Despite the widespread use of bimetallic nanomaterial catalysts, a molecular-level understanding of the synergistic effects is unclear, limiting our ability to pre-design “tailor-made” bimetallic catalysts. We chose bimetallic Au1Ag24(SR)18 and Au25−xAgx(SR)18 (x = 2–6) nanoclusters (NCs) as models to investigate the relationship between microstructure and performance, comparing them with the corresponding monometallic NCs. Experimental and theoretical analyses demonstrated that the Au@Ag kernel was the essential structural feature for high activity and super stability of Au1Ag24(SR)18 catalyst in the alkynylation of CF3-ketone. This structure-activity relationship was successfully extended to other bimetallic systems bearing an Au@Ag kernel, such as Au12Ag32(SR)30 NC, and is thought to constitute a guiding principle for the intelligent design of high-performance bimetallic catalysts in the future.

Core–Shell Engineering of Pd–Ag Bimetallic Catalysts for Efficient Hydrogen Production from Formic Acid Decomposition

To develop high-performance bimetallic catalysts, fine control over both the ligand and strain effects of secondary elements on the catalytic function of primary elements is crucial. Here we introduce an approach to produce Pd–Ag bimetallic core–shell nanocatalysts with synergistic regulation of the ligand and strain effects of Ag. Through precise core–shell engineering, (PdAg alloy core)@(ultrathin Pd shell) nanocrystals with controlled core compositions and shell thicknesses in addition to a well-defined octahedral morphology could be realized. The prepared octahedral PdAg@Pd core–shell nanocrystals exhibited pronounced catalytic performance toward hydrogen production from formic acid decomposition. The maximum catalytic activity was achieved with PdAg@Pd nanocrystals consisting of PdAg alloy cores with an average Pd/Ag atomic ratio of 3.5:1 and 1.1 atomic layer of Pd shells, which showed a record high turnover frequency of 21 500 h–1 at 50 °C. This catalytic function could be attributed to the optimize...

Rhodium-Containing Multi-Layered Mixed-Metal Oxides As Active Supports for Dispersed PtRu Nanoparticles during Electrooxidation of Ethanol

Recently, there has been growing interest in development of fuel cells (e.g. utilizing small organic molecules) as alternative technologies to hydrogen based electrochemical energy systems. For example, ethanol (biofuel) can be ideally oxidized to carbon dioxide thus delivering twelve electrons. But realistically the reaction is rather slow at ambient conditions. Obviously, there is a need to develop novel electrocatalytic materials. Platinum has been recognized as the most active catalytic metal towards oxidation of ethanol at low and moderate temperatures. But Pt anodes are readily poisoned by the strongly adsorbed intermediates, namely by CO-type species, requiring fairly high overpotentials for their removal. To enhance activity of Pt catalysts towards methanol and ethanol oxidation, additional metals including ruthenium, tin, molybdenum, tungsten or rhodium are usually introduced as the alloying component. More recently it has been demonstrated that catalytic activity of platinum-based nanoparticles towards electrooxidation of ethanol has been significantly enhanced through interfacial modification with ultra-thin monolayer-type films of metal oxo species of tungsten, titanium or zirconium. Also gold in combination with platinum has been demonstrated to produce novel high performance bimetallic catalysts. We pursue a concept of utilization of mixed metal (e.g. zirconium/tungsten or titanium/tungsten) oxide matrices for supporting and activating noble metal nanoparticles (e.g. PtRu) during electrooxidation of methanol and ethanol. Among important issues is incorporation of Rh nanostructures capable of weakening, or even breaking, the C-C bond in the ethanol molecules. On the other hand, rhodium itself is not directly electrocatalytic toward oxidation of ethanol. The oxides and noble metal nanoparticles have been deposited in a controlled manner using the layer-by-layer method. Remarkable increases of electrocatalytic currents measured under voltammetric and chronoamperometric conditions have been observed. The most likely explanation takes into account possibility of specific interactions of noble metals with transition metal oxide species as well as existence of active hydroxyl groups in the vicinity of catalytic noble metal sites. In addition, formation of “nanoreactors” where ethanol is partitioned (at Rh) to methanolic residues further oxidized at PtRu cannot be excluded.

A one-pot route to the synthesis of alloyed Cu/Ag bimetallic nanoparticles with different mass ratios for catalytic reduction of 4-nitrophenol

Copper-based alloy nanoparticles (NPs) have recently triggered much research interest for the development of low-cost and high-performance bimetallic catalysts that have industrial applications.

Importance of Support and Interactions with Noble Metal Nanocenters in Electrocatalysis

Recently there has been growing interest in low-temperature fuel cells as alternative sources of energy. The most commonly considered electrocatalytic systems (e.g. for oxygen reduction) utilize precious platinum and, therefore, there is a need to minimize contents of Pt (e.g. by activating it with certain metal oxo-species including polyoxometallates of tungsten) as well as to look for alternate molecular catalysts comprising metalloporphyrins or N-chelates combined with Ru-based chalcogenides, and bifunctional materials inducing reduction of both oxygen and hydrogen peroxide intermediate. Broad utilization of hydrogen-oxygen fuel cells would require development of effective means of hydrogen production and storage. In this context, the visible-light induced photelectrocatalytic water splitting is an important concept that will be addressed in this presentation as well. We have found that modification of a regular mesoporous WO3 film with colloidal gold nanoparticles resulted in a significant improvement of the delivered photocurrent. Enhanced optical properties of WO3 implemented with colloidal gold nanoparticles are induced by plasmonic excitation of gold nanoparticles.The problem of oxygen reduction is even more severe case of alcohol-utilizing fuel cells. In this respect, heat-treated carbon-supported macrocyclic complexes and their derivatives as well as chalcogen modified transition metals are promising and selective (e.g. methanol tolerant) platinum-free catalysts for oxygen reduction.Our research interests also concern development of electrocatalytic systems for the reduction of carbon dioxide. For example, as catalytic materials commercial palladium nanoparticles and the macromolecular complex of palladium, namely [Pd(C14H12N2O3)Cl2]2∙MeOH, were considered. The electrochemical data clearly imply that the process of electroreduction of carbon dioxide begins at the less negative potentials when pursued at the palladium complex in addition to the significant enhancement of the net (background-subtracted) CO2-reduction current densities relative to those observed at conventional nanostructured palladium. Among important issues are specific interactions between nitrogen coordinating centers and electrogenerated metallic palladium sites at the electrocatalytic interface.We have interest in the better understanding and controlling of electrocatalytic phenomena appearing in the direct alcohol fuel cells as alternative technology to hydrogen based electrochemical energy systems. The most common Pt anodes are readily poisoned by the strongly adsorbed intermediates, namely by CO-type species, requiring fairly high overpotentials for their removal. We have recently demonstrated that catalytic activity of platinum-based nanoparticles towards electrooxidation of ethanol has been significantly enhanced through interfacial modification with ultra-thin monolayer-type films of polyoxometallates particularly heteropolymolybdates. Also gold in combination with platinum has been demonstrated to produce novel high performance bimetallic catalysts. We are going to describe here a concept of utilization of functionalized or mixed titanium dioxide, tungsten oxide or zirconium oxide matrices for supporting and activating noble metal nanoparticles (Pt, Pt-Ru or Pt-Rh) during electrooxidation of ethanol. We are going to consider protonically/electronically conducting zeolite-type cesium salts of Keggin-type heteropolyacids of molybdenum and tungsten as matrices for Vulcan-supported Pt, PtRu and PtSn nanoparticles during electrooxidation of methanol and ethanol.

Composition-Dependent Morphostructural Properties of Ni–Cu Oxide Nanoparticles Confined within the Channels of Ordered Mesoporous SBA-15 Silica

NiO and NiO-CuO polycrystalline rodlike nanoparticles were confined and stabilized within the channels of ordered mesoporous SBA-15 silica by a simple and viable approach consisting in incipient wetness impregnation of the calcined support with aqueous solutions of metal nitrates followed by a mild drying step at 25 °C and calcination. As revealed by low- and high-angle XRD, N2 adsorption/desorption, HRTEM/EDXS and H2 TPR analyses, the morphostructural properties of NiO-CuO nanoparticles can be controlled by adjusting their chemical composition, creating the prerequisites to obtain high performance bimetallic catalysts. Experimental evidence by in situ XRD monitoring during the thermoprogrammed reduction indicates that the confined NiO-CuO nanoparticles evolve into thermostable and well-dispersed Ni-Cu heterostructures. The strong Cu-Ni and Ni-support interactions demonstrated by TPR and XPS were put forward to explain the formation of these new bimetallic structures. The optimal Ni-Cu/SBA-15 catalyst (i.e., Cu/(Cu+Ni) atomic ratio of 0.2) proved a greatly enhanced reducibility and H2 chemisorption capacity, and an improved activity in the hydrogenation of cinnamaldehyde, as compared with the monometallic Ni/SBA-15 or Cu/SBA-15 counterparts, which can be associated with the synergism between nickel and copper and high dispersion of active components on the SBA-15 host. The unique structure and controllable properties of both oxidic and metallic forms of Ni-Cu/SBA-15 materials make them very attractive for both fundamental research and practical catalytic applications.

High-performance Pd–Au bimetallic catalyst with mesoporous silica nanoparticles as support and its catalysis of cinnamaldehyde hydrogenation

A high-performance bimetallic catalyst with mesoporous silica nanoparticles as support, PdAu/MSN, was prepared by an organic impregnation–hydrogen reduction approach. A series of investigations were conducted to assess the effects of (i) the porous nanoparticle support on the dispersion of active components and on the catalyst’s performance, (ii) the addition of gold on the dispersion of active components and the catalyst’s activity, and (iii) the preparation parameters, such as solvent, pressure, and temperature, on the catalyst’s activity. The active metallic components were highly dispersed, with particle size 2.5nm. The addition of gold to the catalyst favorably promoted the hydrogenation of cinnamaldehyde. The activity of PdAu0.2/MSN (with Au/Pd molar ratio 0.2:1) was up to four times higher than that of Pd/MSN (without Au as a promoter) and eight times higher than that of commercial Pd/C catalyst. The enhanced activity of PdAu0.2/MSN can be attributed to the synergistic effect of Pd with the added Au and the highly dispersed active components. The ultrahigh activity, as well as its novel structure with controllable compositions, makes this catalyst very attractive for both fundamental research and practical applications.

A high performance bimetallic catalyst for photo-Fenton oxidation of Orange II over a wide pH range

Abstract A bimetallic catalyst supported on MCM-41 was synthesized by chemical vapour deposition and evaluated in the photo-Fenton degradation of Orange II. An in situ oxidation method recently developed in our group was applied to stabilize the metal catalyst supported on MCM-41, achieving an extremely low metal leaching level. This FeCu/MCM-41 shows TOC removals of 93%, 83%, and 78% at pHs of 3, 5.5, and 7, respectively, and maintains its high catalytic activity after 10 consecutive runs. This catalyst successfully overcomes the two problems faced by the heterogeneous photo-Fenton process – metal leaching and narrow working pH range.