Bimetallic Samples Research Articles

Influence of 3D-Printing Parameters on Bimetallic Products Manufacturing Process of Cu-Fe System

The article is devoted to selection of optimal parameters for manufacturing defect-free high quality products. Bimetallic samples with different parameters of modes were printed by the method of electron beam wire-feed additive technology. Materials of stainless steel 304 and copper C11000 selected for printing have different physical properties. Based on macrostructural research, the paper presents various external defects, which were formed in different modes of production. The study showed the effect of external defects on the formation of internal defects in experimental samples. It was noted that in addition to the basic parameters of the manufacturing process, such as beam power and wire feed rate, geometric parameters such as electron beam sweep diameter and substrate thickness play a major role. The article presents macrostructural studies of bimetallic samples of stainless steel 304 and C11000 made using different modes of production.

The Effect of Addition Method of Impregnation Solution on Properties and Performance of Pd-Ag/Al2O3 Catalyst in Tail-End Acetylene Selective Hydrogenation

The impregnation of alumina support with PdCl2 solution was investigated in batch and semi-batch operation modes using a recycle packed-bed reactor. UV-visible analysis was used to evaluate the kinetics of Pd adsorption on alumina support. Transient palladium adsorption data showed that Pd adsorption was very rapid completing within few minutes. Bi-metallic Pd-Ag/Al2O3 catalysts were synthesized by sequential impregnation method. CO-chemisorption, CO-TPD and FE-SEM tests were used to characterize the synthesized bi-metallic samples. Catalytic performance of the samples was evaluated for tail-end acetylene selective hydrogenation process in a fixed-bed reactor. Moreover, the deactivation of the catalysts was evaluated mathematically by integral method of analysis, considering reaction kinetics as power laws in terms of nth orders in H2 and C2H2 partial pressures. It was observed that by batch-wise addition of Pd precursor solution, a sample was obtained with lowest amount of Pd dimmers that had highest ethylene selectivity and lowest hydrogenation reaction rate.

Segregation dynamics of a Pd-Ag surface during CO oxidation investigated by NAP-XPS

The dynamic changes in composition in the near-surface region of a Pd75%Ag25%(100) single crystal were monitored using near-ambient pressure x-ray photoelectron spectroscopy (NAP-XPS) during CO oxidation under oxygen rich conditions at a total pressure of 1.1 mbar. Six CO oxidation temperature cycles were investigated at different heating rates and maximum temperatures of 450 °C or 600 °C. It was found that the history of the bimetallic sample plays an important role, as the CO2 formation profile varies depending on initial conditions, and previous heating rates and maximum temperatures. In terms of CO coverage effects, normal, reversed and no hysteresis behaviour were all observed. In agreement with previous modelling predictions, the NAP-XPS data confirm a dynamic segregation behaviour upon heating/cooling where the amount of Pd in the surface region decreases with increasing temperature. Nevertheless, the Pd 3d5/2 core level relative area assessment is not fully capable of capturing all the surface dynamics inferred from the temperature dependent CO2 formation profiles, due to the probing depth. While residing at ambient temperature in the reaction mixture, however, there is a build-up of adsorbed CO at the surface showing that CO induces segregation of Pd to the topmost surface layer under these conditions. In total, this suggests that the segregation is kinetically relatively facile during temperature cycling, and that adsorbate coverage is the main controlling factor for the surface termination.

Effects of Hydrothermal Aging on CO and NO Oxidation Activity over Monometallic and Bimetallic Pt-Pd Catalysts

By combining scanning transmission electron microscopy, CO chemisorption, and energy dispersive X-ray spectroscopy with CO and NO oxidation light-off measurements we investigated deactivation phenomena of Pt/Al2O3, Pd/Al2O3, and Pt-Pd/Al2O3 model diesel oxidation catalysts during stepwise hydrothermal aging. Aging induces significant particle sintering that results in a decline of the catalytic activity for all catalyst formulations. While the initial aging step caused the most pronounced deactivation and sintering due to Ostwald ripening, the deactivation rates decline during further aging and the catalyst stabilizes at a low level of activity. Most importantly, we observed pronounced morphological changes for the bimetallic catalyst sample: hydrothermal aging at 750 °C causes a stepwise transformation of the Pt-Pd alloy via core-shell structures into inhomogeneous agglomerates of palladium and platinum. Our study shines a light on the aging behavior of noble metal catalysts under industrially relevant conditions and particularly underscores the highly complex transformation of bimetallic Pt-Pd diesel oxidation catalysts during hydrothermal treatment.

Influence of Compositionally Graded Interface on Microstructure and Compressive Deformation of 316L Stainless Steel to Al12Si Aluminum Alloy Bimetallic Structures.

Bimetallic structures offer properties that can be customized based on applications, manufactured in one operation. Such manufacturing options are fascinating, as joining two metallic materials, especially for two dissimilar metals without significant defects, is challenging. In this study, 316L stainless steel (SS) to Al12Si aluminum alloy structures were processed, tailoring the compositionally graded interface on a SS 316 substrate using a directed energy deposition (DED)-based additive manufacturing (AM) process. Applying such a compositionally graded transition for joining two dissimilar metals could mitigate the mismatch of mechanical and thermal properties. This study's objective was to understand the processing parameters that influence the properties of AM processed SS 316L to Al12Si bimetallic structures. Two different approaches were used to fabricate these bimetallic structures. The results showed no visible defects on the as-fabricated samples using four layers of Al-rich mixed composition as the transition section. The microstructural characterization showed a unique morphology in each section. The microstructural variation was caused due to various processing parameters such as laser power, powder feed rate, and laser scan speed. FeAl, Fe2Al5, and FeAl3 intermetallic phases were formed at the compositionally graded transition section. After stress relief heat treatment of the bimetallic samples, diffused intermetallic phases were seen at the compositionally graded transition. At the interface, as processed bimetallic structures had a microhardness value of 834.2 ± 107.1 HV0.1, which was a result of the FeAl3 phase at the compositionally graded transition area. After heat treatment, the microhardness value reduced to 578.7 ± 154.1 HV0.1 because of a more Fe-dominated FexAly phase formation. Compression test results showed that the non-HT and HT SS 316L/Al12Si bimetallic structures had a similar maximum compressive strength of 299.4 ± 22.1 MPa and 270.1 ± 27.1 MPa, respectively. These results demonstrated that the applied heat treatment conditions only had a minor impact on samples' compression strength.

The role of Pd–Pt Interactions in the Oxidation and Sulfur Resistance of Bimetallic Pd–Pt/γ-Al2O3Diesel Oxidation Catalysts

Diesel oxidation catalysts (DOC) were investigated for oxidation activity, NO conversion stability, and sulfur poisoning/regeneration on Pd/Al2O3, Pt/Al2O3, and Pd-Pt/Al2O3 catalysts. The Pd/Al2O3 catalyst was more active for CO and hydrocarbon (C3H6 and C3H8) oxidation, while the Pt/Al2O3 catalyst efficiently oxidized NO. The formation of a Pd-Pt alloy in the Pd-Pt/Al2O3 catalyst maintained Pd in a more reduced phase, resulting in the superior activity of this catalyst for the oxidation of CO, C3H6, and NO in comparison with its monometallic counterparts. The Pd-Pt alloy not only provided more low-temperature activity but also retained the stability of NO oxidation. The Pd-Pt alloy also favored the spillover of SO2 to the alumina support, resulting in significantly higher adsorption capacity of the Pd-Pt/Al2O3 catalyst, extensively prolonging its lifetime. However, the stable sulfates on Pd-Pt/Al2O3 made it difficult to completely regenerate the catalyst. The bimetallic sample showed higher activity for CO, C3H8, and C3H6 after sulfur poisoning and regeneration.

Bimetallic Hollow Tubular NiCoOx as a Bifunctional Electrocatalyst for Enhanced Oxygen Reduction and Evolution Reaction.

The development of high-efficiency oxygen electrocatalysts with earth-abundant transition metals rather than scarce noble metals has aroused growing interests due to their potential for energy storage and conversion applications. Herein, we developed a facile strategy to synthesize hollow tubular bimetallic Ni-Co oxide rooted with dense nanosheets for enhanced bifunctionality and facilitated redox reaction kinetics. Owing to the rational design of morphology and well-dispersed Ni and Co ions, the bimetallic samples exhibit admirable bifunctional electrocatalytic activities. This bimetallic Ni-Co oxide shows superior oxygen electrocatalytic performance in comparison with the monometallic Ni and Co oxides, according to the electrocatalytic synergistic effect from the bimetallic system. The optimized sample with the specific mass ratio of Ni and Co displays the oxygen reduction reaction (ORR) property comparable to commercial Pt/C and oxygen evolution reaction (OER) performance superior to commercial RuO2. The electrochemical tests and structural characterizations offer in-depth dissection on the electrocatalytic behaviors, especially the superb stability in both ORR and OER tests, as well as the outstanding resistance to methanol poisoning, representing a promising candidate in the renewable energy field.

Effect of support nature on catalytic activity of the bimetallic RuCo nanoparticles for the oxidative removal of 1,2-dichloroethane

The nature of porous support (mesoporous Al2O3 and MgO (denoted as meso-Al2O3 and meso-MgO, respectively) and microporous HZSM-5) on catalytic performance of the bimetallic RuCo nanoparticles (NPs) was investigated for the oxidation of 1,2-dichloroethane (1,2-DCE). Redox and acid properties and reaction intermediates of the samples were measured by means of various techniques. The RuO2 species were dominantly present in the supported bimetallic samples, and Co doping could increase the length of the Ru−O bond. Compared with RuCo/meso-MgO and RuCo/meso-Al2O3, RuCo/HZSM-5 exhibited the highest catalytic activity (T90% =281 °C, TOFNoble metal = 3.6 × 10−3 s−1, reaction rate at 270 °C = 18.7 μmol/(gNoble metal s), and apparent activation energy =36 kJ/mol at SV = 20,000 mL/(g h)) and the best Cl-resistant performance, which was associated with its strong redox ability, suitable acidity, good 1,2-DCE adsorption capacity, highly dispersed RuCo NPs, and strong interaction between RuCo NPs and HZSM-5. Loading of RuCo NPs on the support could suppress the formation of C2H3Cl and improve the Cl-resistant performance. Over the RuCo/HZSM-5 sample, the partial deactivation induced by water vapor or HCl addition was reversible, while that induced by SO2 introduction was irreversible. Based on the characterization results, we believe that the oxidation of 1,2-DCE over RuCo/meso-Al2O3, RuCo/meso-MgO or RuCo/HZSM-5 might take place concurrently via the Langmuir−Hinshelwood and Mars−van Krevelen mechanisms. This work can provide a strategy to develop the efficient catalysts with low Cl-containing by-products formation, high CO2 selectivity, and good Cl-resistance in the oxidative removal of Cl-VOCs under the practical conditions.

Synthesis and characterization of highly dispersed bimetallic Au-Rh nanoparticles supported on titanate nanotubes for CO oxidation reaction at low temperature.

Low-temperature CO oxidation was carried out by using rhodium incorporated into titanate nanotubes (Rh/NTs) prepared by the sol-gel and hydrothermal methods; otherwise, gold nanoparticles were deposited homogeneously onto the Rh/NT surface through the deposition-precipitation with urea (DPU) method. The Au-Rh/NT sample exhibited high metal dispersion (55%), outstanding CO oxidation at low temperature, and better resistance to deactivation than the monometallic Rh/NT and Au/NT samples. The characterization of bimetallic samples, with particle sizes from 1 to 3 nm, revealed the remarkable presence of interacting Au and Rh species in metallic state. In this way, Au0 and Rh0 were answerable for the higher catalytic activity observed in the bimetallic samples. The interaction between Au and Rh in the nanoparticles of Au-Rh/NT promoted a synergistic effect on the CO oxidation reaction, explained by the creation of new CO adsorption sites.

Microstructure and mechanical properties of wire arc additive manufactured bi-metallic structure

Wire arc additive manufacturing (WAAM) with better material utilisation efficiency and higher deposition rate was employed to fabricate bi-metallic structure (BMS) of non-stabilised austenitic stainless steel (SS904L), and solid solution strengthened Hastelloy C-276. The micrographs confirmed the existence of directionally elongated, columnar, and equi-axed dendrites in the BMS. Significant grain coarsening was observed in the re-melted layers. The tensile properties of Hastelloy C-276 and SS904L were comparable with wrought counterparts, while the bi-metallic interface sample fractured in the SS904L side. The presence of secondary phases and varying microstructure along the building direction is responsible for the anisotropy in mechanical properties. Microhardness results revealed the steep increase at the bi-metallic interface due to the dilution of elements between two materials.

Properties of Iron-Modified-by-Silver Supported on Mordenite as Catalysts for NOx Reduction

A series of mono and bimetallic catalysts based on a Fe-Ag mixture deposited on mordenite was prepared by ion-exchange and evaluated in the catalytic activity test of the de-NOx reaction in the presence of CO/C3H6. The activity results showed that the most active samples were the Fe-containing ones, and at high temperatures, a co-promoter effect of Ag on the activity of Fe catalysts was also observed. The influence of the order of cation deposition on catalysts formation and their physicochemical properties was studied by FTIR (Fourier Transform Infrared Spectroscopy) of adsorbed NO, XANES (X-ray Absorption Near-Edge Structure), and EXAFS (Extended X-ray Absorption Fine Structure) and discussed in terms of the state of iron. Results of Fe K-edge XANES oscillations showed that, in FeMOR catalysts, iron was present in a disordered state as Fe3+ and Fe2+. In FeAgMOR, the prevailing species was Fe3+, while in the AgFeMOR catalyst, the state of iron was intermediate or mixed between FeMOR and FeAgMOR. The Fe K-edge EXAFS results were characteristic of a disordered phase, the first coordination sphere being asymmetric with two different Fe-O distances. In FeAgMOR and AgFeMOR, coordination of Fe-O was similar to Fe2O3 with a few amount of Fe2+ species. We may conclude that, in the bimetallic FeAgMOR and AgFeMOR samples, a certain amount of tetrahedral Al3+ ions in the mordenite framework is replaced by Fe3+ ions, confirming the previous reports that these species are active sites for the de-NOx reaction. Based on the thermodynamic analysis and experimental data, also, it was confirmed that the order of deposition of the components influenced the mechanism of active sites’ formation during the two steps ion-exchange synthesis.

Charge transfer and hydrogen adsorption in the Pd/Ag bimetallic nano system: an experimental and theoretical DFT cluster approach

We aimed to understand the characteristics of bimetallic systems samples with porous and large surface areas. In doing this we studied in particular the surface structure of the Pd/Ag system. Our cluster models were based on high resolution transmission electron microphotographs of samples with defects. For the modelling of our Pd/Ag nano systems, we combined a variety of experimental and theoretical methods, such as: sputtering, acrylamide sol–gel, high resolution transmission electron microscopy, energy dispersive X-ray spectrometry, and density functional theory. This study explores the connection between nanocrystal structure, electron density distribution, and charge transfer. Charge transfer was determined via density difference analysis. Charge density as a function of the orbital radius was calculated. Vertical electron affinity, vertical first ionization potential, and vertical electronegativity of the Pd 18 and Ag 24 clusters were calculated. In addition, Voronoi, Bader, Becke, Loewdin, Mulliken, NPA, and NBO population analyses were conducted.

Insights into the role of Pt on Pd catalyst stabilized by magnesia-alumina spinel on gama-alumina for lean methane combustion: Enhancement of hydrothermal stability

It is an urgent desire to decrease release of methane, a potential greenhouse gas, over methane-oxidation catalysts. However, the commonly used Pd-based catalysts normally suffer from poor hydrothermal stability. Here, we report a Pd-Pt bimetallic nano-catalyst stabilized by magnesia-alumina spinel via a facile doping strategy for lean methane combustion. The promoted effects of platinum on the hydrothermal stability of the catalyst are confirmed by XRD, HRTEM, STEM, XPS, CO-DRIFTS characterizations. Pd-Pt bimetallic catalyst can almost maintain its intrinsic catalytic activity (2.7 × 10−5 molCH4 gnoble metal-1s-1 at 260 °C) after harshly hydrothermal aging, while the aged analogous sample without Pt promotion presents remarkably reduced catalytic performance with an increment in CH4 light-off temperature of ca. 50 °C. Kinetic analysis further reveals a much higher turnover frequency (0.011 s-1 at 260 °C) and lower apparent activation energy (119 kJ/mol) of CH4 oxidation on the aged Pd-Pt bimetallic samples. Pt stabilized by magnesia-alumina spinel has a strong interaction with PdO. This interaction could stabilize Pd species in active PdO and also suppress the decomposition of active PdO to less reactive Pd°. Consequently, the sintering resistance of Pt and PdO crystallite and the electron interaction between them could be responsible for the enhanced hydrothermal stability.

Microstructure and mechanical properties of TA15-Ti2AlNb bimetallic structures by laser additive manufacturing

The TA15-Ti2AlNb bimetallic samples with no defects were prepared by laser additive manufacturing. The evolution of the composition and microstructure in transition zone, and the mechanical properties were investigated. Composition in the transition region shows a step-and-platform distribution due to the rapid solidification and diffusion during the depositing process. The phase transformation from TA15 alloy side to Ti2AlNb-based alloy side is α (lath) +β→α (coarse acicular) +β→β+α2→α2+O + B2. The TA15-Ti2AlNb bimetallic structures present tensile properties with average tensile strength of 1025 MPa and elongation of 7.3%. The fracture position of samples is located in diffusion zone, and the fracture mode is quasi-cleavage fracture. The TA15-Ti2AlNb bimetallic circular structure with bell mouth was fabricated and this work shows great potential for fabricating bimetallic structures by laser additive manufacturing technology.

Insights into the active sites of chlorine-resistant Pt-based bimetallic catalysts for benzene oxidation

Since the Pt-based catalysts often suffer severe deactivation by chlorine, development of a catalyst with good activity and chlorine-resistant ability is of importance in effectively controlling emissions of (chlorinated) volatile organic compounds ((C)VOCs). In this work, we prepared the Al2O3-supported bimetallic catalysts with narrow metal particle size distributions and their application in benzene oxidation. It is found that PtW/Al2O3 showed the highest catalytic activity and the lowest activation energy. The characterization results were well correlated with the catalytic activities, and a Pt–MOx (M = W, Mo) bimetallic synergistic effect was proposed. In situ FTIR studies reveal that the transformation from phenol to benzoquinone was the key step in benzene oxidation process. The influence of 1,2-dichloroethane (DCE) on catalytic activity for benzene oxidation of the as-obtained samples was also examined. It is demonstrated that there was a competitive adsorption between benzene and DCE molecules, and the DCE exerted an inhibitive effect on benzene oxidation. We conclude that excellent catalytic performance of the bimetallic sample was associated with its good abilities to adsorb and activate benzene on small ensembles of the MOx in proximity contact with Pt as well as the strong interaction between the highly dispersed metallic Pt species and the MOx clusters (which led to enhancement in anti-deactivation of the Pt species under the oxygen-rich and Cl-containing reaction conditions). We are sure that the present work can provide an idea for understanding the nature of bimetallic active sites and rationally designing the efficient bimetallic catalysts for the oxidative removal of VOCs.

PdCu nanoalloy supported on alumina: A stable and selective catalyst for the conversion of bioethanol to linear α-alcohols

PdCu/Al2O3 (Pd = 0.1 wt.%, Cu = 0.1 wt.%) catalyst and its monometallic analogues (Pd/Al2O3 and Cu/Al2O3) were prepared by combination of deposition-precipitation and impregnation methods. The structure of the catalysts was studied by means of XRD, TEM, EDS, TPD-NH3, and DRIFTS. In a standard run (275 ○C, 5 h), Cu/Al2O3 converts 11 % of ethanol to α-alcohols with 0.6 % selectivity, whereas Pd/Al2O3 converts 24 % of ethanol to α-alcohols with 70 % selectivity. The high performance of Pd/Al2O3 was attributed to the catalysis on the Pd°-Al2O3 interfaces. After 3 sequential runs, the activity of Pd/Al2O3 decreases by 98 %. It was explained by blocking of Pd° sites in Pd/Al2O3 by CO molecules produced in side reactions. Modification of Pd/Al2O3 with Cu species results in the formation of PdCu/Al2O3 catalyst containing PdCu alloy particles with the size of 4 nm. This leads to an increased durability of bimetallic sample, because of suppressing CO sorption on Pd° sites in alloy particles. As a result, for the PdCu/Al2O3 catalyst, sustained and high conversion (41 %) accompanied by high selectivity to α-alcohols (91 %) was observed in 20 sequential runs.

Hierarchical Co–Mo–S nanoflowers as efficient electrocatalyst for hydrogen evolution reaction in neutral media

The development of hydrogen evolution reaction (HER) catalysts composed of inexpensive and abundant elements is an effective strategy to realize the hydrogen economy, particularly in neutral media. Herein, we report the design and synthesis of a series of hierarchical Co–Mo–S nanoarchitectures by a facile and efficient hydrothermal method in a water-ethylene glycol mixed solvent system. Such as-synthesized bimetallic sulfide samples as HER electrocatalysts exhibit good performance in phosphate buffer solution (1 M PBS), especially Co–Mo0.4-S nanocomposite (0.4 is the molar number of Na2MoO4·2H2O adding in the experimental section) shows the highest activity for HER. Co–Mo0.4-S only requires an overpotential of 213 mV to reach 10 mA cm−2 with 94 mV dec−1 of Tafel slope, which outperforms those of Co–S (455 mV) and Mo–S (>500 mV). The excellent HER performance of Co–Mo0.4-S electrocatalyst can be attributed to the strong electronic interactions of Co–S and Mo–S, the improvement electrical conductivity and the high specific surface. In addition, such a Co–Mo0.4-S nanoflower may be employed as a promising non-precious electrocatalyst for HER to substitute the Pt/C material in neutral media.

(Ag)Pd-Fe3O4 Nanocomposites as Novel Catalysts for Methane Partial Oxidation at Low Temperature.

Nanostructured composite materials based on noble mono-(Pd) or bi-metallic (Ag/Pd) particles supported on mixed iron oxides (II/III) with bulk magnetite structure (Fe3O4) have been developed in order to assess their potential for heterogeneous catalysis applications in methane partial oxidation. Advancing the direct transformation of methane into value-added chemicals is consensually accepted as the key to ensuring sustainable development in the forthcoming future. On the one hand, nanosized Fe3O4 particles with spherical morphology were synthesized by an aqueous-based reflux method employing different Fe (II)/Fe (III) molar ratios (2 or 4) and reflux temperatures (80, 95 or 110 °C). The solids obtained from a Fe (II)/Fe (III) nominal molar ratio of 4 showed higher specific surface areas which were also found to increase on lowering the reflux temperature. The starting 80 m2 g−1 was enhanced up to 140 m2 g−1 for the resulting optimized Fe3O4-based solid consisting of nanoparticles with a 15 nm average diameter. On the other hand, Pd or Pd-Ag were incorporated post-synthesis, by impregnation on the highest surface Fe3O4 nanostructured substrate, using 1–3 wt.% metal load range and maintaining a constant Pd:Ag ratio of 8:2 in the bimetallic sample. The prepared nanocomposite materials were investigated by different physicochemical techniques, such as X-ray diffraction, thermogravimetry (TG) in air or H2, as well as several compositions and structural aspects using field emission scanning and scanning transmission electron microscopy techniques coupled to energy-dispersive X-ray spectroscopy (EDS). Finally, the catalytic results from a preliminary reactivity study confirmed the potential of magnetite-supported (Ag)Pd catalysts for CH4 partial oxidation into formaldehyde, with low reaction rates, methane conversion starting at 200 °C, far below temperatures reported in the literature up to now; and very high selectivity to formaldehyde, above 95%, for Fe3O4 samples with 3 wt.% metal, either Pd or Pd-Ag.

Synthesis of bimetallic CuxNiy nanoparticles for selective hydrogenation of 1-nitroanthraquinone with gaseous H2 to 1-aminoanthraquinone

Bimetallic CuxNiy nanoparticles were prepared by the liquid chemical reduction method starting from nickel acetate and copper nitrate with the use of hydrazine hydrate as the reductant under mild reaction temperature. The sizes of metallic Cu0 and Ni0 nanoparticles in the bimetallic CuxNiy samples were smaller than those of the monometallic Cu0 and Ni0 nanoparticles, which could be attributed to the interactions between metallic Cu0 and metallic Ni0 nanoparticles. When the hydrogenation of 1-nitroanthraquinone with gaseous H2 was catalyzed by the bimetallic Cu0.25Ni0.75 nanoparticles at 120 °C for 4 h, the 1-aminoanthraquinone selectivity of 98.7% was obtained at the 1-nitroanthraquinone conversion of 99.7%. The dispersion of metallic Ni0 nanoparticles and the interaction between metallic Ni0 and Cu0 probably play important roles in the catalytic hydrogenation reaction.

Selective aerobic oxidation of benzyl alcohol on alumina supported Au-Ru and Au-Ir catalysts

Selective oxidation of benzyl alcohol to benzaldehyde with molecular oxygen was studied over sol-derived alumina supported bimetallic Au-Ru and Au-Ir (nominal atomic ratio 1:1) with respect to Au, Ru and Ir monometallic catalysts in both calcined and subsequently reduced states with and without equimolar K2CO3 in toluene at 80 °C. The Au and after an induction period also Au-Ru and Au-Ir samples had good activity and selectivity in the presence of K2CO3, the monometallic Ir and Ru ones showed negligible activity. The different pretreatments did not cause large difference in the catalytic performance, except the Ir containing samples, which were more active in reduced state.The samples were characterized by TEM, STEM-EDS, UV-Vis spectroscopy, XRD and TPR. The surface of the catalysts was investigated by XPS and CO adsorption followed by infrared spectroscopy. We confirmed the interaction between Au and both second metals, and a strongly decreased CO adsorption on gold in the bimetallic samples compared to the monometallic one. Based on the reaction rates related to the estimated Au and second metal surfaces in the bimetallic and corresponding monometallic catalysts synergetic effect is suggested for the calcined and reduced Au-Ru and reduced Au-Ir catalysts in reaction with base addition.