Bimetallic Formulations Research Articles

In Vivo and in Vitro activity of colistin-conjugated bimetallic silver-copper oxide nanoparticles against Pandrug-resistant Pseudomonas aeruginosa

BackgroundAddressing microbial resistance urgently calls for alternative treatment options. This study investigates the impact of a bimetallic formulation containing colistin, silver, and copper oxide on a pandrug-resistant, highly virulent Pseudomonas aeruginosa (P. aeruginosa) isolate from a cancer patient at the National Cancer Institute, Cairo University, Egypt.MethodsSilver nanoparticles (Ag NPs), copper oxide nanoparticles (CuO NPs), and bimetallic silver-copper oxide nanoparticles (Ag-CuO NPs) were synthesized using gamma rays, combined with colistin (Col), and characterized by various analytical methods. The antimicrobial activity of Col-Ag NPs, Col-CuO NPs, and bimetallic Col-Ag-CuO NPs against P. aeruginosa was evaluated using the agar well diffusion method, and their minimum inhibitory concentration (MIC) was determined using broth microdilution. Virulence factors such as pyocyanin production, swarming motility, and biofilm formation were assessed before and after treatment with bimetallic Col-Ag-CuO NPs. The in vivo efficacy was evaluated using the Galleria mellonella model, and antibacterial mechanism were examined through membrane leakage assay.ResultsThe optimal synthesis of Ag NPs occurred at a gamma ray dose of 15.0 kGy, with the highest optical density (OD) of 2.4 at 375 nm. Similarly, CuO NPs had an optimal dose of 15.0 kGy, with an OD of 1.5 at 330 nm. Bimetallic Ag-CuO NPs were most potent at 15.0 kGy, yielding an OD of 1.9 at 425 nm. The MIC of colistin was significantly reduced when combined with nanoparticles: 8 µg/mL for colistin alone, 0.046 µg/mL for Col-Ag NPs, and 0.0117 µg/mL for Col-Ag-CuO NPs. Bimetallic Col-Ag-CuO NPs reduced the MIC four-fold compared to Col-Ag NPs. Increasing the sub-inhibitory concentration of bimetallic nanoparticles from 0.29 × 10-2 to 0.58 × 10-2 µg/mL reduced P. aeruginosa swarming by 32–64% and twitching motility by 34–97%. At these concentrations, pyocyanin production decreased by 39–58%, and biofilm formation was inhibited by 33–48%. The nanoparticles were non-toxic to Galleria mellonella, showing 100% survival by day 3, similar to the saline-treated group.ConclusionsThe synthesis of bimetallic Ag-CuO NPs conjugated with colistin presents a promising alternative treatment for combating the challenging P. aeruginosa pathogen in hospital settings. Further research is needed to explore and elucidate the mechanisms underlying the inhibitory effects of colistin-bimetallic Ag-CuO NPs on microbial persistence and dissemination.

Enhanced Heterogeneous Fenton Degradation of Organic Dyes by Bimetallic Zirconia-Based Catalysts.

The qualitative impact of pollutants on water quality is mainly related to their nature and their concentration, but in any case, they determine a strong impact on the involved ecosystems. In particular, refractory organic compounds represent a critical challenge, and several degradation processes have been studied and developed for their removal. Among them, heterogeneous Fenton treatment is a promising technology for wastewater and liquid waste remediation. Here, we have developed mono- and bimetallic formulations based on Co, Cu, Fe, and Mn, which were investigated for the degradation of three model organic dyes (methylene blue, rhodamine B, and malachite green). The treated samples were then analyzed by means of UV-vis spectrophotometry techniques. Bimetallic iron-based materials achieved almost complete degradation of all three model molecules in very short time. The Mn-Fe catalyst resulted in the best formulation with an almost complete degradation of methylene blue and malachite green at pH 5 in 5 min and of rhodamine B at pH 3 in 30 min. The results suggest that these formulations can be applied for the treatment of a broad range of liquid wastes comprising complex and variable organic pollutants. The investigated catalysts are extremely promising when compared to other systems reported in the literature.

CuNi Alloy NPs Anchored on Electrospun PVDF-HFP NFs Catalyst for H2 Production from Sodium Borohydride.

Non-noble CuxNi1-x (x = 0, 0.1, 0,2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1) alloy nanoparticles supported on poly(vinylidene fluoride-co-hexafluoropropene) (PVDF-HFP) nanofibers (NFs) are successfully fabricated. The fabrication process is executed through an electrospinning technique and in situ reduction in Cu2+ and Ni2+ salts. The as-synthesized catalysts are characterized using standard physiochemical techniques. They demonstrate the formation of bimetallic NiCu alloy supported on PVDF-HFP. The introduced bimetals show better catalytic activity for sodium borohydride (SBH) hydrolysis to produce H2, as compared to monometallic counterparts. The Cu0.7 Ni0.3/PVDF-HFP catalyst possesses the best catalytic performance in SBH hydrolysis as compared to the others bimetallic formulations. The kinetics studies indicate that the reaction is zero order and first order with respect to SBH concentration and catalyst amount, respectively. Furthermore, low activation energy (Ea = 27.81 kJ/mol) for the hydrolysis process of SBH solution is obtained. The excellent catalytic activity is regarded as the synergistic effects between Ni and Cu resulting from geometric effects over electronic effects and uniform distribution of bimetallic NPs. Furthermore, the catalyst displays a satisfying stability for five cycles for SBH hydrolysis. The activity has retained 93% from the initial activity. The introduced catalyst has broad prospects for commercial applications because of easy fabrication and lability.

3D printed catalytic reactors for aerobic selective oxidation of benzyl alcohol into benzaldehyde in continuous multiphase flow

In this work, novel, patterned monolithic reactors were devised to explore more efficient routes for reactant conversion in order to investigate their potential to replace the packed bed and batch reactors conventionally employed in chemical industries. Well-defined bimetallic formulations were developed to substitute platinum group metals and critical raw materials such as palladium and cobalt, at least in part, by less active, but more sustainable and cost-effective metals such as earth-abundant iron. FePd and FeCo based monoliths were 3D printed and stacked in a continuous flow tubular reactor for testing the selective oxidation of benzyl alcohol (BA) into benzaldehyde (BZ) under mild conditions (80–100 °C and atmospheric pressure). The novel monolithic reactors were evaluated against current state-of-the-art reactor technologies, conventional packed bed and batch reactors. The FeCo- and FePd-Al2O3-supported monolithic catalyst beds showed higher conversion and TOF than their packed bed counterparts under the same operating conditions, revealing the impact of the novel design on both regular geometry and composition. What is of particular interest in the catalytic measurements shown is that the combined stacking of two monoliths in a flow reactor, Al2O3-supported Fe and GO-supported FePd catalysts, can significantly improve the performance with an increase in TOF of up to 90% in comparison to their FePd analogues. Mathematical modelling was used to obtain additional insights into the physical and chemical processes governing the rate of BA conversion. It was found that due to the flow regime inside the microchannels, an axial dispersion model was appropriate, which allowed for mapping the concentration profiles of the reactants and products within the respective monolith geometries.

Dictating Selectivity in the Catalytic Vapor-Phase Conversion of Glycerol

A viable route for the vapor-phase conversion of glycerol into value-added chemicals is herein presented. This procedure allows to dictate selectivity towards hydroxyacetone (acetol) or methylglyoxal (pyruvaldehyde) by simply tuning the experimental conditions while retaining the same catalytic system. A series of gold- and copper-based catalysts supported on gamma-alumina, including bimetallic formulations, were prepared by incipient wetness impregnation method and tested in a continuous-flow fixed-bed vertical glass reactor at ambient pressure and T = 250-300°C. The best performance was achieved with 1%wt Au/Al2O3. Accordingly, the selectivity could be directed to acetol (sel. 72%) at 87% conversion when performing the reaction at 300°C and adding H2 to the carrier N2, or towards pyruvaldehyde (sel. 79%) at 92% conversion when adding O2 to N2 at 250°C. These relatively mild conditions not only allow for energy savings with respect to the common procedures so far reported, but also for catalyst stability that can be easily regenerated after use. Furthermore, the low metal loading in the catalyst (1% wt) and its small amount requested for each test (0.1 g catalyst) make this procedure economically sustainable.

Precursor salts influence in Ruthenium catalysts for CO2 hydrogenation to methane

The intermittency in power generation that characterizes renewable energy sources requires a way to convert the energy surplus. Among all the possibilities, the conversion of power in hydrogen via water electrolysis and then into methane via CO2 methanation represents a competitive storage system. CO2 methanation is an exothermic reaction which requires the use of low temperatures in order to achieve sufficiently high conversions: for this reason, there is a strong need in low-temperature active catalyst. In this work, several Ru/CeO2-ZrO2 and Ru-Ni/CeO2-ZrO2 were prepared and compared with Ni/CeO2-ZrO2, in order to evaluate the effect of Ru loading and Ru precursor salt. The results showed that in monometallic formulations the higher was the Ru amount the better were the reaction performances achieved, particularly at low temperatures. In bimetallic formulations, the presence of Ru enhances the catalyst activity; in particular, the use of the Ru acetylacetonate, for the deposition of the noble metal on support, remarkably reduces the catalyst onset temperature. The effect is due to the templating effect of the precursor molecule, which allows a better dispersion of the active compounds.

Synergistic effects in bimetallic Pd\u2013CoO electrocatalytic thin films for oxygen evolution reaction

Bimetallic catalysts due to the synergistic effects often outperform their single-component counterparts while exhibiting structure and composition-dependent enhancement in active sites, thereby having the potential to improve the current density and over-potential parameters in the water oxidation reaction. Herein, we demonstrate a simple and rapid, yet highly efficient method to fabricate Pd–CoO films of immaculate homogeneity as characterized using different imaging and spectroscopic techniques. The SEM images revealed that the films were composed of bimetallic spherical granules wherein both metals were uniformly distributed in an atomic ratio of ~ 1:1. The time-dependent investigations of the film fabrication behavior demonstrated that the films formed in shorter deposition times (1–2 h) display more porous character, allowing better access to the reaction centers. This character was transcribed into their enhanced electrocatalytic performance toward the oxygen evolution reaction (OER). Using this specific bimetallic formulation, we could attain a low over-potential of 274 mV for a current density of 10 mA cm−2, whereas the high current density value of > 200 mA cm−2 was achieved while still under 600 mV of over-potential. The cycling and current generation stability was also found to be sufficiently high, which can only be attributed to the facile electron transfer processes and a higher number of active sites available in homogeneous bimetallic films.

Promotional Effect of Cu, Fe and Pt on the Performance of Ni/Al2O3 in the Deoxygenation of Used Cooking Oil to Fuel-Like Hydrocarbons

Inexpensive Ni-based catalysts can afford comparable performance to costly precious metal formulations in the conversion of fat, oil, or greases (FOG) to fuel-like hydrocarbons via decarboxylation/decarbonylation (deCOx). While the addition of certain metals has been observed to promote Ni-based deCOx catalysts, the steady-state performance of bimetallic formulations must be ascertained using industrially relevant feeds and reaction conditions in order to make meaningful comparisons. In the present work, used cooking oil (UCO) was upgraded to renewable diesel via deCOx over Ni/Al2O3 promoted with Cu, Fe, or Pt in a fixed-bed reactor at 375 °C using a weight hourly space velocity (WHSV) of 1 h−1. Although all catalysts fully deoxygenated the feed to hydrocarbons throughout the entire 76 h duration of these experiments, the cracking activity (and the evolution thereof) was distinct for each formulation. Indeed, that of the Ni-Cu catalyst was low and relatively stable, that of the Ni-Fe formulation was initially high but progressively dropped to become negligible, and that of the Ni-Pt catalyst started as moderate, varied considerably, and finished high. Analysis of the spent catalysts suggests that the evolution of the cracking activity can be mainly ascribed to changes in the composition of the metal particles.

Toward the Green Production of H2: Binary Pt–Ru Promoted Nb-TiO2 Based Photocatalysts

Hydrogen photoproduction using methanol:water mixtures was essayed with PtRu titania-based materials. All materials contain a high-surface-area Nb-doped anatase support. Six bimetallic formulations with Pt:Ru ratios from 4:1 to 1:4 and two (Pt and Ru) monometallic reference samples were utilized. The catalytic response of the materials to three main experimental variables (methanol:water molar ratio, catalyst concentration, and light intensity) was studied through a Box-Benhken factorial design and the calculation of the true quantum efficiency. The optimum activity is achieved using a bimetallic PtRu (2:1) composition, which provides outstanding efficiency under ultraviolet (UV), visible, and sunlight illumination, as well as long-term stability. The interpretation of the activity was performed using characterization results, the outcome of an analysis of charge recombination with photoluminescence spectroscopy and of an in situ infrared study under reaction conditions. This proves that the photophysical and chemical properties of metallic Pt particles in contact with Ru oxidized particles are key to render highly active systems.

Sulfur Poisoning Effects on Modern Lean NOx Trap Catalysts Components

In the present work, a series of different materials was investigated in order to enhance the understanding of the role of modern lean NOx trap (LNT) components on the sulfur poisoning and regeneration characteristics. Nine different types of model catalysts were prepared, which mainly consisted of three compounds: (i) Al2O3, (ii) Mg/Al2O3, and (iii) Mg/Ce/Al2O3 mixed with Pt, Pd, and Pt-Pd. A micro flow reactor and a diffuse reflectance infrared Fourier transform spectrometer (DRIFTS) were employed in order to investigate the evolution and stability of the species formed during SO2 poisoning. The results showed that the addition of palladium and magnesium into the LNT formulation can be beneficial for the catalyst desulfation due mainly to the ability to release the sulfur trapped at relatively low temperatures. This was especially evident for Pd/Mg/Al2O3 model catalyst, which demonstrated an efficient LNT desulfation with low H2 consumption. In contrast, the addition of ceria was found to increase the formation of bulk sulfate species during SO2 poisoning, which requires higher temperatures for the sulfur removal. The noble metal nature was also observed to play an important role on the SOx storage and release properties. Monometallic Pd-based catalysts exhibited the formation of surface palladium sulfate species during SO2 exposure, whereas Pt-Pd bimetallic formulations presented higher stability of the sulfur species formed compared to the corresponding Pt- and Pd-monometallic samples.

Alkali-Metal-Mediated Synergistic Effects in Polar Main Group Organometallic Chemistry.

The development of synthetic chemistry since the early 1900s owes much to the service of organolithium reagents. Brilliant bases (e.g., deprotonating C-H bonds), nucleophiles (e.g., adding to unsaturated molecules), and transfer agents (e.g., delivering ligands to other metals), these versatile virtuosi and to a lesser extent the organic derivatives of the other common alkali metals sodium and potassium have proved indispensable in both academia and technology. Today these monometallic compounds are still utilized widely in synthetic campaigns, but in recent years they have been joined by an assortment of bimetallic formulations that also contain an alkali metal but in company with another metal. These bimetallic formulations often exhibit unique chemistry that can be interpreted in terms of synergistic effects, for which the alkali metal is essential, though it is often the second metal that performs the synthetic transformation. Here, this "alkali-metal-mediated" chemistry is surveyed focusing mainly on bimetallic formulations containing two alkali metals or an alkali metal paired with magnesium, calcium, zinc, aluminum, or gallium. In this International Year of the Periodic Table (IYPT), we ponder whether a Pairiodic Table of Element Pairs will emerge in the future.

Biogas Upgrading Via Dry Reforming Over a Ni-Sn/CeO2-Al2O3 Catalyst: Influence of the Biogas Source

Biogas is a renewable, as well as abundant, fuel source which can be utilised in the production of heat and electricity as an alternative to fossil fuels. Biogas can additionally be upgraded via the dry reforming reactions into high value syngas. Nickel-based catalysts are well studied for this purpose but have shown little resilience to deactivation caused by carbon deposition. The use of bi-metallic formulations, as well as the introduction of promoters, are hence required to improve catalytic performance. In this study, the effect of varying compositions of model biogas (CH4/CO2 mixtures) on a promising multicomponent Ni-Sn/CeO2-Al2O3 catalyst was investigated. For intermediate temperatures (650 °C), the catalyst displayed good levels of conversions in a surrogate sewage biogas (CH4/CO2 molar ratio of 1.5). Little deactivation was observed over a 20 h stability run, and greater coke resistance was achieved, related to a reference catalyst. Hence, this research confirms that biogas can suitably be used to generate H2-rich syngas at intermediate temperatures provided a suitable catalyst is employed in the reaction.

Comparative computational study of CO2 dissociation and hydrogenation over Fe-M (M = Pd, Ni, Co) bimetallic catalysts: The effect of surface metal content

Density functional theory (DFT) calculations were performed to study CO2 adsorption, dissociation and hydrogenation over Fe-M (M = Pd, Ni, Co) bimetallic catalysts, with a focus on probing the effect of surface content of the added transition metals to Fe. Various Fe-M bimetallic surfaces were constructed with varied surface atomic ratios of Fe/(Fe + M), based on which CO2 and atomic H* adsorptions were systematically examined. The H* was found to be energetically favorable adsorbed at the 4-fold hollow site of Fe-M catalysts and the adsorption stability was slightly impacted by the surface content of the introduced transition metal. For CO2 adsorption, stable bent structures adsorbed on the 4-fold hollow sites were identified on Fe-Ni and Fe-Co surfaces, no matter at which Fe-M formulations. However, on Fe-Pd surfaces, CO2 adsorption configurations were found to be sensitive to surface Pd content, resulting in large distinctions in adsorption stabilities of CO2 as compared to Fe-Co and Fe-Ni surfaces. CO2 dissociation and initial hydrogenation were comparatively investigated on Fe-M bimetallic surfaces, and the calculation results demonstrated that CO2 conversion properties are similar over Fe-Ni and Fe-Co catalysts, with CO* and HCOO* as the preferred intermediates but the barriers are still above 0.8 eV. While on Fe-Pd bimetallic surfaces, CO2 reactions exhibit significant distinctions with varying the surface Pd content, showing a dramatic preference (Eact around 0.3∼0.4 eV) towards HCOO* and CO* formation at surface Pd/(Pd + Fe) atomic ratios of 4/9 and 5/9. The superior catalytic activities of Fe-Pd catalysts are attributed to the particular surface structures and electronic features at specific bimetallic formulations which result in unique adsorption configurations of CO2 and facilitate the stabilization of transition states in CO* and HCOO* formation pathways in CO2 conversion.

Trapping of Metal Atoms and Metal Clusters by Chabazite under Severe Redox Stress

The remarkable ability of Al-containing CHA zeolite to trap and stabilize noble single-metal atoms and metal clusters has facilitated the design of sinter-resistant materials for catalytic applications that require severe reaction conditions. At high temperatures in O2, volatile MOx species appear to be fixated by the zeolite Al centers to prevent Ostwald-ripening sintering mechanisms, whereas small metal clusters (<100 atoms) are stabilized in H2 without further aggregation as coalescence by Brownian motion is inhibited because of an encapsulation effect. Evidences of the possibility to trap the metal released from a second adjacent surface (e.g., SiO2 and Al2O3), upon metal migration over micrometer distances, are provided. These properties have opened the possibility to prepare several noble-metal atoms and clusters inside small-pore zeolites, including bimetallic formulation, by simple wetness impregnations or solid-to-solid transformations followed by standard calcination procedures, resulting in imp...

Multicomponent Ni-CeO2 nanocatalysts for syngas production from CO2/CH4 mixtures

The dry reforming of methane with CO2 is a common route to transform CO2/CH4 mixtures into added value syngas. Ni based catalysts are highly active for this goal but suffer from deactivation, as such promoters need to be introduced to counteract this, and improve performance. In this study, mono- and bi-metallic formulations based on 10 wt.% Ni/CeO2-Al2O3 are explored and compared to a reference 10 wt.% Ni/γ-Al2O3. The effect of Sn and Pt as promoters of Ni/CeO2-Al2O3 was also investigated. The formulation promoted with Sn looked especially promising, showing CO2 conversions stabilising at 65% after highs of 95%. Its increased performance is attributed to the additional dispersion Sn promotion causes. Changes in the reaction conditions (space velocity and temperature) cement this idea, with the Ni-Sn/CeAl material performing superiorly to the mono-metallic material, showing less deactivation. However, in the long run it is noted that the mono-metallic Ni/CeAl performs better. As such the application is key when deciding which catalyst to employ in the dry reforming process.

Hydrogen Production with a Microchannel Reactor by Tri-Reforming; Reaction System Comparison and Catalyst Development

In this work, Pt based mono and bimetallic catalysts were tested under conditions of tri-reforming (TR). All the catalysts contained 25% of CeO2 and a metal loading of 2.5 or 5.0% (wt%). The bimetallic catalysts contained 2.5% Pt and 2.5% of Me, where Me = Ni, Co, Mo, Pd, Fe, Re, Y, Cu or Zn. For all the experiments, a synthetic biogas which consisted of 60% CH4 and 40% CO2 (vol.) was mixed with water, S/C = 1.0, and oxygen, O2/CH4 = 0.25, and fed to a fixed bed reactor (FBR) system or a microreactor. The 2.5Pt catalyst was used in order to compare the performance of each reaction system. The tests were performed at reaction temperatures between 700 and 800 °C, and at volume hourly space velocities (VHSV) between 100 LN/(h gcat) and 200 LN/(h gcat) for the FBR system and between 1000 LN/(h gcat) and 2000 LN/(h gcat) for the microreactor, at atmospheric pressure. Then, all catalysts were deposited into microchannel reactors and tested at a constant VHSV of 2000 LN/(h gcat) and reaction temperatures between 700 and 800 °C. Catalysts under investigation were characterized applying the following techniques: inductively coupled plasma optical emission spectroscopy (ICP-OES), N2 Physisorption, Temperature Programmed Reduction (TPR), CO chemisorption, Transmission Electron Microscopy (TEM) and X-ray Photoelectron Spectroscopy (XPS). The microreactor was identified as the most efficient and promising reaction system, and the 2.5(Pt–Pd) catalyst as the bimetallic formulation with the highest activity. Therefore its activity and stability was compared with the reference 5.0Pt catalyst at 700 °C and VHSV of 2000 LN/(h gcat) for more than 100 h. Although slightly lower activity was measured operating with the 2.5(Pt–Pd) catalyst, a significant reduction of the Pt content compared to the reference 5.0Pt catalyst was achieved through the incorporation of Pd.

Promotional effect of Mo and Ni in plasma-synthesized Co–Fe/C bimetallic nano-catalysts for Fischer–Tropsch synthesis

Abstract Two carbon-supported Fischer–Tropsch Synthesis (FTS) catalysts with ternary metallic formulations (10% Mo–70% Co–20% Fe and 10% Ni–70% Co–20% Fe) were synthesized through suspension plasma-spray (SPS) technology. Their average particle size determined by Transmission Electron Microscopy was 8.4 and 13.3 nm respectively and their BET specific surface areas were between 69–85 m2 g−1. As their analogous monometallic and bimetallic formulations presented in previous publications, these catalysts were both non-porous and nanometric with Scanning Electron Microscopy showing uniform metal-nanoparticle distribution in the carbon-support matrix. FTS test conditions in a 3-phase continuously stirred-tank slurry reactor operated for 24 h were: 260 °C, 2 MPa pressure, H2:CO = 2, gas hourly specific velocity = 3600 cm3 h−1 g−1 of catalyst. Basing catalyst performance on the bimetallic 80% Co–20% Fe/C catalyst, Ni-addition enhanced catalyst activity from ∼42 to 50% CO conversion, and boosted selectivity towards gasoline fraction (C5–C12) from ∼19 to 50%. Enriching the catalyst-surface acidity by Mo-promotion improved selectivity for both gasoline-fraction (19 → 33%) and the C5–C20 fraction (74 → 87%) and lowered H2O production by 30%, although at lower CO conversion (∼38%). The catalysts’ α-values were ∼0.8 in the C10+ region, and from mass balance their estimated H2 efficiency decreased in the order of Mo–Co–Fe/C >> Co-Fe/C > Ni–Co–Fe/C.

Synthesis of Nano-catalysts by Induction Suspension Plasma Technology (SPS) for Fischer–Tropsch Reaction

Nanometric catalysts were synthesized through induction suspension plasma technology (SPS) for application in the Fischer–Tropsch synthesis (FTS). Carbon-supported single metal catalysts (Co/C, Fe/C), bimetallic formulations (Co–Fe/C), and ternary (Co–Fe–Mo and Co–Fe–Ni) systems have been considered in this work. SPS has been selected because it simultaneously allows for: (1) atomizing and generating metallic nanoparticles; (2) creating particularly Fe carbides, which are important in Fe-based FTS reaction mechanism; (3) in situ production of the nanometric graphitic-carbon matrix; and (4) saving time in catalyst synthesis, limiting sample preparation steps and eliminating post synthesis treatment before use. Porosity measurements by the Brunauer–Emmett–Teller method indicate that the samples are essentially non-porous. The synthesized catalysts characterized by X-ray Diffraction analysis show the presence of both metallic and carbidic species. The graphitic-carbon matrix has substantial structural defects that make it partly amorphous. Scanning Electron Microscopy analysis coupled with Energy Dispersive X-ray Spectroscopy mapping shows uniform dispersion of the metal moieties in the carbon support. Analysis by Transmission Electron Microscopy imaging displays metal nanoparticles with mean particle size within the 9–15 nm range enveloped in the carbon matrix.

Steam reforming of hydrocarbons from biomass-derived syngas over MgAl2O4-supported transition metals and bimetallic IrNi catalysts

This study presents an investigation into the steam reforming of hydrocarbons from biomass gasifier-derived syngas over MgAl2O4-supported transition metals (Ni, Rh, Ir, Ru, Pt, and Pd) and novel bimetallic IrNi catalysts. Using a model syngas consisting of H2, CO, CO2, CH4, C2H4, and H2O, Ir and Rh catalysts were found to be the most stable catalysts (at 850°C, 1bar, 114,000h−1). When benzene and naphthalene are added to the feed (as a tar simulant) stability is affected by both tar concentration and type of tar. Catalytic deactivation, caused primarily by coking can be minimized by operating at a high reaction temperature (e.g., 850°C). In addition, promoting Ni catalyst with Ir significantly enhances stability. By using bimetallic formulations of Ir and Ni (0.5–5.0% Ir, 15%Ni), nickel sintering during the reaction is reduced. Surprisingly, IrNi catalysts also offer more stability than catalysts with Ir particles alone. In agreement with theoretical calculations, small Ir° clusters (∼2–3 atoms) supported on large Ni° particles (≥5nm) present more resistance to coking than either small Ir° clusters or Ni° particles alone. Hence, superior stability of the bimetallic catalysts results from both resistance to coking and a decrease in nickel sintering. Minimal loss of activity of 12% for TOS=80h is demonstrated for a bimetallic catalyst with optimal concentrations of 2.5% Ir and 15% Ni. Both monometallic Ir and Ni catalysts suffer substantial loss of activity (i.e., ≥40% loss, TOS=80h) under comparable conditions.

Density functional theory study of propane steam reforming on Rh–Ni bimetallic surface: Sulfur tolerance and scaling/Brønsted–Evans–Polanyi relations

Enhanced sulfur tolerance on binary Rh–Ni metals is examined for the propane steam reforming process on close packed metal surfaces of Rh, Ni, Rh1Ni2, and Rh2Ni1 with and without co-adsorbed S atoms. Scaling and Brønsted–Evans–Polanyi (BEP) correlations are constructed from density functional theory (DFT) methods. The combined use of these methods produces significant errors among these similar metal surfaces; however, BEP relations applied within reaction types are reliable across Rh, Ni, and binary Rh–Ni surfaces with and without co-adsorbed S atoms. The potential energy surface of propane steam reforming, estimated using the BEP correlations, shows that the C–C cleavages of CHC*, CH3CC* and CH2C* along with the O addition to CH* are kinetically significant elementary steps. Three of these steps show only slight barrier increases with co-adsorbed S on the Rh2Ni1 surface, suggesting an energetic explanation for enhanced S tolerance. The average poisoning effect by the presence of co-adsorbed sulfur for bond breaking is minimized on binary Rh–Ni metals, suggesting a high sulfur resistance can be induced using a bimetallic formulation of Rh and Ni.