Au Pd Bimetallic Catalysts Research Articles

Boosting Solvent-Free Aerobic Oxidation of Benzylic Compounds into Ketones over Au-Pd Nanoparticles Supported by Porous Carbon

The exploitation of highly efficient solvent-free catalytic systems for the selective aerobic oxidation of benzylic compounds to produce corresponding ketones with molecular oxygen under mild conditions remains a great challenge in the chemical industry. In this work, Au-Pd nanoparticles supported on porous carbon catalysts were fabricated by the borax-mediated hydrothermal carbonization method and the chemical reduction method. The physicochemical properties of Au-Pd bimetallic samples were examined by XRD, N2 sorption, SEM, TEM, and XPS techniques. The Au-Pd nanoparticles have successfully immobilized on the spherical carbon support with a porous structure and large surface area. A solvent-free catalytic oxidation system was constructed to selectively convert indane into indanone with Au-Pd nanocatalysts and O2. In contrast with a monometallic Au or Pd catalyst, the resulting bimetallic Au-Pd catalyst could effectively activate O2 and exhibit improved catalytic activity in the controlled oxidation of indane into indanone under 1 bar O2. A total of 78% conversion and >99% selectivity toward indanone can be achieved under optimized conditions. The synergistic effect of Au and Pd and porous carbon support contributed to the high catalytic activity for aerobic benzylic compound oxidation. This work offers a promising application prospect of efficient and recyclable Au-Pd nanocatalysts in functional benzylic ketone production.

Direct epitaxial growth of Au nanoparticles on Pd metallene enables robust oxygen reduction electrocatalysis

Pd-based structures have been demonstrated as promising Pt-free catalysts for the oxygen reduction reaction (ORR), but suffer from undesirable structural degradation and poor durability. Herein, the direct epitaxial growth of Au nanoparticles on Pd metallene (Au@Pd metallene) is reported. The obtained heterostructure exhibits the most positive half-wave potential and the highest mass activity among all reported PdAu bimetallic catalysts for ORR and greatly enhanced stability compared to Pd metallene, with very slight mass activity decay after 10,000 cycles. This work reveals that the epitaxial heterointerfaces between Au nanoparticles and Pd metallene optimize the electronic structure of Pd and suppress Pd dissolution for enhanced activity and stability.

Mechanistic study of the production of ethylene glycol diacetate as a byproduct of the ethylene vapor phase process for vinyl acetate on PdAu(100) surface

With the rapid development of the photovoltaic industry, the demand for new materials such as EVA resin is increasing, and the study of its synthetic monomer vinyl acetate is of great significance. The ethylene vapor phase process is the current mainstream method for producing ethylene acetate. This method mainly uses a PdAu bimetallic catalyst to catalyze the production of ethylene acetate and water from ethylene, acetic acid and oxygen. The reaction process produces ethylene glycol diacetate, a high boiling point byproduct, which not only increases the energy consumption for separating the byproduct and reduces the selectivity of the target product but also may lead to catalyst deactivation. Therefore, reducing its production is of great importance in industrial production. The production mechanism of ethylene glycol diacetate is not clear due to the large variety of surface species and the complexity of the reaction in the ethylene vapor phase method, which makes it challenging to investigate the production mechanism of ethylene glycol diacetate directly by experimental means without interference. Molecular simulation techniques, especially Density Functional Theory (DFT) simulations and kinetic Monte Carlo (kMC) simulations, allow for a targeted study of the catalyst surface reaction mechanism to obtain the mechanism of ethylene glycol diacetate production.In this paper, the elementary reaction in the possible formation path of ethylene glycol diacetate on PdAu(100) surface has been studied by the DFT simulations, and the energy barrier and reaction heat of each elementary reaction have been obtained. Moreover, based on the DFT simulation data, the generation process of ethylene glycol diacetate on PdAu(100) surface is investigated by the kMC simulation, including the processes of reactant adsorption, intermediate species diffusion, surface reaction, and product desorption. The calculation results show that the species are mainly adsorbed on the Pd-Au bridge site or Pd top site; ethylene can firstly generate CH3COOCH2CH2, CH3COOCHCH2 or CH3COOCHCH species and then be combined with CH3COO species to produce ethylene glycol diacetate, where the energy barrier of the reaction of CH3COOCH2CH2 species with CH3COO species is lower than other two species with CH3COO species. The advantage generation path for the ethylene glycol diacetate on PdAu(100) surface is CH2CH2→CH3COOCH2CH2→CH3COOCH2CH2OCOCH3, and the rate-determining step is the reaction of ethylene with CH3COO species to form CH3COOCH2CH2 species.

Promoting the discoloration of PdO in low concentration H2 by using PdAu bimetallic catalyst for eye-readable hydrogen leakage detection

Developing reliable and low-cost optical hydrogen sensors for hydrogen leakage detection at room temperature is extremely important. It requires that hydrogen sensors have a remarkable and rapid color change in low concentration H2/air mixtures, which it is still quite challenging at present. Herein, we demonstrate an eye-readable hydrogen sensor based on Pd-decorated Au@PdO core-shell nanoparticle arrays (Pd-Au@PdO NAs). Pd-Au@PdO NAs show an obvious color change from brownish-yellow to yellow-gray in 1 v/v% H2/air and gray in 4 v/v% H2/air, with ΔE values of 8.1 and 22.5, respectively. Detailed investigation showed that, at the cracks of PdO shell where Au core is exposed, PdAu bimetallic catalyst is generated during the sample-synthesis process. Compared with Pd catalyst, PdAu bimetallic catalyst significantly prompts the reduction of PdO in low concentration H2, represented as a faster discoloration process and more obvious color change. Additionally, the core-shell structure ensures a long-term stability through protecting the PdAu catalyst. We further show that the irreversible sensing performance of Pd-Au@PdO NAs can be reactivated repeatedly, which favors extending the lifetime of the optical sensor and reducing the cost.

Manipulation of the PdAu‒PdAuOx interface on Pd-Au bimetallic catalysts for the direct synthesis of hydrogen peroxide

Direct synthesis of H2O2 from H2 and O2via heterogeneous catalysis is an environmentally friendly and atomically economic alternative to the traditional anthraquinone oxidation (AO) process. Optimizing the electronic and geometric structures of the active metals to break the current limitations of hydrogenation rate and H2O2 selectivity is a promising and challenging topic. In this study, a series of Pd-Au bimetallic catalysts supported on TiO2 with a metal loading of 3.0 wt% and a constant Pd/Au molar ratio (Pd:Au = 2:1) were prepared. The catalysts were reduced in H2 at different temperatures (473, 573 and 673 K), and their catalytic activity for the direct H2O2 synthesis were evaluated at 283 K and 0.1 MPa. H2 reduced Pd-Au catalysts exhibited superior performance in direct H2O2 synthesis. The maximum H2O2 selectivity of 87.7% and H2O2 yield of 3116.4 mmol h−1 gPd−1 were achieved over the Pd2.0Au1.0-573 catalyst with a H2 conversion of 12.8%. The tailored local chemical environment caused by H2 reduction creates a balanced ratio of Pd0 and PdOx sites, thus improving the selectivity towards H2O2. This work developed an effective strategy for fabrication of highly active and stable Pd-based H2O2 synthesis catalysts with high H2O2 yield.

Promoting effect of trace amount of Pd for p-CNB hydrogenation in Pd-Au/TiO2 bimetallic catalyst

Pd-Au bimetallic catalysts supported on TiO2 with traces of Pd for p-chloronitrobenzene (p-CNB) hydrogenation were prepared by the deposition-precipitation method. It is found that the ultra-low loading of Pd can improve significantly the catalytic activities of Pd-Au/TiO2 bimetallic catalyst compared with Au/TiO2. The minimal loading of Pd favors the Au dispersion and leads the Au NPs with small size. The existence of a large number of Au/Pd interfaces and the interaction between Au and Pd make Au NPs surface electron-enriched (Auδ-) and the Pd positively charged (Pdn+). The synergetic effect of Auδ-, Pdn+, and Pd0 improves the catalytic performance of 0.01 %Pd-0.5 %Au/TiO2. For 0.01 %Pd-0.5 %Au/TiO2, the p-CNB conversion is 99.9 %, with p-CAN selectivity of 98.6 %. After eight circles of reuse, the conversion of p-CNB and the selectivity of p-CAN is still as high as 98.18 and 99.97 %, respectively, indicating the good stability of 0.01 %Pd-0.5 %Au/TiO2. Through twenty times scale-up preparation or after sixty days of storage, our catalysts still maintain excellent catalytic performance in p-CNB reduction, demonstrating the promising prospects of 0.01 %Pd-0.5 %Au/TiO2 for industrial applications. This work offers a facile method to design bimetallic noble metal catalysts with excellent catalytic activities and good reusability, and clarifies their potential applications in industry.

Highly efficient aerobic oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid over halloysite nanotubes-templated nitrogen-doped carbon supported bimetallic AuPd catalyst

Aerobic oxidation of biomass-derived 5-hydroxymethylfurfural (HMF) to 2, 5-furandicarboxylic acid (FDCA) is an important way to produce bioplastic monomer. Herein, halloysite nanotubes (HNT)-templated layered porous hollow rod-shaped nitrogen-doped carbon supported bimetallic AuPd catalysts (AumPdn/HRNxC) with different nitrogen contents and bimetallic nanoparticles size were employed for the highly efficient aerobic oxidation of HMF to FDCA in sodium carbonate aqueous solution. Catalytic experimental results uncovered the possible reaction pathway, and the kinetics study further confirmed the oxidation of intermediate FFCA to FDCA was the rate-controlled step. Benefiting from the synergy between nitrogen-doped carbon support and bimetallic nanoparticles, the Au3Pd1/HRN5C catalyst obtained the highest HMF conversion of 100% and FDCA yield of 99.9% under the optimal reaction conditions. In-situ FT-IR study revealed the adsorption configuration of HMF, and the ESR test proved that the active substance was superoxide radical. Furthermore, the catalyst showed good stability and reusability. This work provides an efficient, economical and environmentally friendly raw clay mineral derived heterogeneous catalyst for the large-scale production of FDCA from HMF.

Mechanistic Studies into the Selective Production of 2,5-furandicarboxylic Acid from 2,5-bis(hydroxymethyl)furan Using Au-Pd Bimetallic Catalyst Supported on Nitrated Carbon Material

Aerobic oxidation of bio-sourced 2,5-bis(hydroxymethyl)furan (BHMF) to 2, 5-furandicarboxylic acid (FDCA), a renewable and green alternative to petroleum-derived terephthalic acid (TPA), is of great significance in green chemicals production. Herein, hierarchical porous bowl-like nitrogen-rich (nitrated) carbon-supported bimetallic Au-Pd nanocatalysts (AumPdn/ N-BNxC) with different nitrogen content and bimetal nanoparticle sizes were developed and employed for the highly efficient aerobic oxidation of BHMF to FDCA in sodium carbonate aqueous solution. The reaction pathway for catalytic oxidation of BHMF went through the steps of BHMF→HMF→HMFCA→FFCA→FDCA. Kinetics studies showed that the activation energies of BHMF, HMF, HMFCA, and FFCA were 58.1 kJ·moL−1, 39.1 kJ·moL−1, 129.2 kJ·moL−1, and 56.3 kJ·moL−1, respectively, indicating that the oxidation of intermediate HMFCA to FFCA was the rate-determining step. ESR tests proved that the active species was a superoxide radical. Owing to the synergy between the nitrogen-rich carbon support and bimetallic Au-Pd nanoparticles, the Au1Pd1/N-BN2C nanocatalysts exhibited BHMF conversion of 100% and FDCA yield of 95.8% under optimal reaction conditions. Furthermore, the nanocatalysts showed good stability and reusability. This work provides a versatile strategy for the design of heterogeneous catalysts for the highly efficient production of FDCA from BHMF.

Base-Free Aerobic Oxidation of Furfuralcohols and Furfurals to Furancarboxylic Acids over Nitrogen-Doped Carbon-Supported AuPd Bowl-Like Catalyst.

Upgrading furfuralcohols and furfurals to furancarboxylic acids is of great significance for high value-added downstream chemicals synthesis and biomass conversion. Developing an efficient catalyst is the key to acquiring a completely sustainable process. Herein, nitrogen-doped carbon-supported bimetallic AuPd bowl-like catalysts were synthesized. The surface wettability of nitrogen-doped carbon was well adjusted by the nitrification process. Benefiting from the alloying effect of bimetallic AuPd catalyst and the formation of hydroxyl radical initiated by H2 O dissociation on the hydrophilic surface of nitrated nitrogen-doped carbon, base-free aerobic oxidation of 5-hydroxymethylfurfural (HMF) could produce the highest 2,5-furandicarboxylic acid (FDCA) yield of 93.9 %. In-situ infrared spectroscopy uncovered adsorption configuration of HMF, and the nitrated carbon surface was favorable for HMF and intermediates to enter the active sites, greatly promoting the catalytic oxidation process. Employing other furfuralcohols (furfuryl alcohol, furan-2,5-diyldimethanol, 2,5-bishydroxymethylfuran) as well as furfural and 5-methylfurfural as starting materials, 35.6-95.4 % yield of furancarboxylic acids (FDCA, 2-furoic acid, 5-methyl-2-furoic acid) were also obtained. Moreover, the developed catalysts could maintain excellent stability and activity after four successive runs. This deep insight into the role of bimetallic synergy and surface wettability provides a basis for the rational design of the highly efficient catalysts for the oxidation of furfuralcohols and furfurals and related reactions.

Mechanisms and Energetics of Complete Ethylene Oxidation on a PdAu Bimetallic Catalyst from a Theoretical Perspective

Mechanisms and Energetics of Complete Ethylene Oxidation on a PdAu Bimetallic Catalyst from a Theoretical Perspective

Recent Advances in Supported Bimetallic Pd–Au Catalysts: Development and Applications in Organic Synthesis with Focused Catalytic Action Study

Recent Advances in Supported Bimetallic Pd–Au Catalysts: Development and Applications in Organic Synthesis with Focused Catalytic Action Study

Electroreduction of CO2 with Tunable Selectivity on Au-Pd Bimetallic Catalyst: A First Principle Study.

The electroreduction of CO2 exhibits great promise in mitigating CO2 from the atmosphere. However, it is quite challenging to produce C1 products selectively on metal surfaces due to inefficient binding of CO with a metal surface. Here, using density functional theory, we studied an experimentally viable system of gold alloyed with a high CO-binding metal palladium. It is observed that the selectivity toward formic acid and methane can be tuned on Au-Pd bimetallic catalysts. Pd-rich alloy surfaces such as Pd deposited on the (211) surface of Au (Pd@Au) are found to be highly selective toward formic acid with an ultralow limiting potential of -0.23 V vs SHE. Interestingly, as the surface of the alloy become Au-rich, the selectivity toward methane increases. Among all the Au-Pd bimetallic systems, the Au-rich (211) surface of Au3Pd alloy has a very low limiting potential of -0.9 V vs SHE for CO2 electroreduction to methane. The selectivity toward methane on this surface is enhanced due to its optimum CO* binding and the ease of CO* protonation to CHO*. The higher feasibility of CO* protonation is a result of the stabilization of adsorbed CHO*. This stabilization is attributed to the interaction of both C and O of the CHO* molecule with the surface Au and Pd. It is found that the selectivity of a catalyst depends upon the stability of various intermediates, which can be regulated by modifying the composition of Au and Pd in the alloy. The results presented here demonstrate broad opportunities to tune the selectivity of the catalyst with varying alloy compositions, which will help to develop novel catalysts for CO2 electroreduction.

C–H Bond Activation Mechanism by a Pd(II)–(μ-O)–Au(0) Structure Unique to Heterogeneous Catalysts

We focused on identifying a catalytic active site structure at the atomic level and elucidating the mechanism at the elementary reaction level of liquid-phase organic reactions with a heterogeneous catalyst. In this study, we experimentally and computationally investigated efficient C–H bond activation for the selective aerobic α,β-dehydrogenation of saturated ketones by using a Pd–Au bimetallic nanoparticle catalyst supported on CeO2 (Pd/Au/CeO2) as a case study. Detailed characterization of the catalyst with various observation methods revealed that bimetallic nanoparticles formed on the CeO2 support with an average size of about 2.5 nm and comprised a Au nanoparticle core and PdO nanospecies dispersed on the core. The formation mechanism of the nanoparticles was clarified through using several CeO2-supported controlled catalysts. Activity tests and detailed characterizations demonstrated that the dehydrogenation activity increased with the coordination numbers of Pd–O species in the presence of Au(0) species. Such experimental evidence suggests that a Pd(II)–(μ-O)–Au(0) structure is the true active site for this reaction. Based on density functional theory calculations using a suitable Pd1O2Au12 cluster model with the Pd(II)–(μ-O)–Au(0) structure, we propose a C–H bond activation mechanism via concerted catalysis in which the Pd atom acts as a Lewis acid and the adjacent μ-oxo species acts as a Brønsted base simultaneously. The calculated results reproduced the experimental results for the selective formation of 2-cyclohexen-1-one from cyclohexanone without forming phenol, the regioselectivity of the reaction, the turnover-limiting step, and the activation energy.

A tandem process for in situ H2O2 formation coupled with benzyl alcohol oxidation using Pd-Au bimetallic catalysts.

Alcohol oxidation is one of the most important industrial organic reactions. Traditionally, the best-suited catalysts are Pd, Pt and Au supported nanoparticles. The research community has recently started developing strategies for synthesizing carbon-supported Pd/Au bimetallic nanoparticles (NPs), leading to higher activities and selectivities. However, the metallic active species in these catalysts are usually generated using sodium borohydride (NaBH4), which is not synthetically easy to reproduce. In fact, minor modifications in pH, concentration and/or other parameters have a prominent effect on the nature of the promoted material. In this work, a robust process involving dihydrogen flow (H2) at 200 °C as a reducing agent for synthesizing Pd/Au supported bimetallic materials was considered an alternative to the common pathway. The physicochemical properties of the materials derived from different reducing reagents and of varying composition ranges were studied using HR-TEM, XRD, CO chemisorption, and XPS. Their stability and activity were also tested for benzyl alcohol oxidation to benzaldehyde under mild reaction conditions (60 °C, water as the solvent, and PO2 = 1.5 bar). Notably, a catalyst from the hydrogen reduction process with a metal composition of 0.8%Pd-0.2%Au/C consisting of bimetallic clusters (≈1.5 nm) proved to be the best material (C = 94%, S = 99%). Catalytic performances were strongly correlated with structural properties, such as nanoparticle size and distribution, which, in turn, were affected by the reduction step and the metal composition range. Finally, the influence of oxidants on benzyl alcohol oxidation has also been studied, along with the first approach for the tandem in situ formation of H2O2 coupled with alcohol oxidation.

Near-Ambient Pressure XPS and MS Study of CO Oxidation over Model Pd-Au/HOPG Catalysts: The Effect of the Metal Ratio.

In this study, the dependence of the catalytic activity of highly oriented pyrolytic graphite (HOPG)-supported bimetallic Pd-Au catalysts towards the CO oxidation based on the Pd/Au atomic ratio was investigated. The activities of two model catalysts differing from each other in the initial Pd/Au atomic ratios appeared as distinctly different in terms of their ignition temperatures. More specifically, the PdAu-2 sample with a lower Pd/Au surface ratio (~0.75) was already active at temperatures less than 150 °C, while the PdAu-1 sample with a higher Pd/Au surface ratio (~1.0) became active only at temperatures above 200 °C. NAP XPS revealed that the exposure of the catalysts to a reaction mixture at RT induces the palladium surface segregation accompanied by an enrichment of the near-surface regions of the two-component Pd-Au alloy nanoparticles with Pd due to adsorption of CO on palladium atoms. The segregation extent depends on the initial Pd/Au surface ratio. The difference in activity between these two catalysts is determined by the presence or higher concentration of specific active Pd sites on the surface of bimetallic particles, i.e., by the ensemble effect. Upon cooling the sample down to room temperature, the reverse redistribution of the atomic composition within near-surface regions occurs, which switches the catalyst back into inactive state. This observation strongly suggests that the optimum active sites emerge under reaction conditions exclusively, involving both high temperature and a reactive atmosphere.

Pd–Au Bimetallic Catalysts for the Hydrogenation of Muconic Acid to Bio-Adipic Acid

The hydrogenation reaction of muconic acid, produced from biomass using fermentative processes, to bio-adipic acid is one of the most appealing green emerging chemical process. This reaction can be promoted by catalysts based on a metal belonging to the platinum group, and the use of a second metal can preserve and increase their activity. Pd–Au bimetallic nanoparticle samples supported on high-temperature, heat-treated carbon nanofibers were prepared using the sol immobilization method, changing the Pd–Au molar ratio. These catalysts were characterized by TEM, STEM, and XPS analysis and tested in a batch reactor pressurized with hydrogen, where muconic acid dissolved in water was converted to adipic acid. The synthesized Pd–Au bimetallic catalysts showed higher activity than monometallic Au and Pd material and better stability during the recycling tests. Moreover, the selectivity toward the mono-unsaturated changed by decreasing the Pd/Au molar ratio: the higher the amount of gold, the higher the selectivity toward the intermediates.

Effect of the coverage of modulated Au(Pd) atoms over bimetallic Pd-Au catalysts on catalytic performance for direct oxidative esterification of methacrolein into methyl methacrylate

• Bimetallic Pd-Au catalysts with different coverageof modulated Au(Pd)atomsare used to model surface composition. • The presence of pre-adsorbed O on Pd modulated Au catalysts exhibit best stability for resistance toward deactivation induced by H2O. • CH3O species are formed via CH3OH+O+*→CH3O+OH rather than CH3OH+*→CH3O+H. • Pd modulated Au catalysts with higher coverage of modulated Pd atoms show better catalytic performance for direct oxidation esterification. • The better catalytic performance for direct oxidation esterification is relatedto surface charge andFermi level. Aiming at examining the effect of the coverage of modulated Au(Pd) atoms over bimetallic Pd-Au catalysts on the catalytic performance for direct oxidative esterification of methacrolein with methanol to methyl methacrylate. Here, two kinds of surface composition with different coverage of modulated Au(Pd) atoms on Au modulated Pd (AuPd) and Pd modulated Au (PdAu) catalysts have been designed and employed to investigate direct oxidative esterification using density functional theory calculation. The results showed that Pd modulated Au catalysts with higher coverage of modulated Pd atoms in the presence of pre-adsorbed O exhibited higher stability for resistance toward deactivation induced by H 2 O deposition than Au modulated Pd and pure Au(Pd) catalysts. The formation of CH 3 O species mainly came from pre-adsorbed O assisted CH 3 OH activation rather than the direct breakage of CH 3 OH via O-H bond, and it was more advantageous than the activation of CH 3 OH via C-H bond with and without pre-adsorbed O. Additionally, Pd modulated Au catalysts with higher coverage of modulated Pd atoms improved the activity for MMA formation via MAL+*→CH 2 C(CH 3 )CO+(H)+CH 3 O+*→MMA than Au modulated Pd and pure Au(Pd) catalysts. Moreover, the better catalytic performance (stability and activity) for direct oxidation esterification of Pd modulated Au catalysts with higher coverage of modulated Pd atoms were attributed to less average charge of surfaces atoms and the d -band center close to the Fermi level compared with pure Au(Pd) and Au modulated Pd catalysts. Therefore, it is proposed that Pd modulated Au catalysts are promising for direct oxidative esterification reaction of methacrolein with methanol to methyl methacrylate. This study not only helps understanding theory on direct oxidative esterification mechanism on bimetallic Pd-Au catalysts, but also provides clues for the design of high-effectively bimetallic Pd-Au catalysts for direct oxidative esterification.

Directing reaction pathways via in situ control of active site geometries in PdAu single-atom alloy catalysts

The atomic scale structure of the active sites in heterogeneous catalysts is central to their reactivity and selectivity. Therefore, understanding active site stability and evolution under different reaction conditions is key to the design of efficient and robust catalysts. Herein we describe theoretical calculations which predict that carbon monoxide can be used to stabilize different active site geometries in bimetallic alloys and then demonstrate experimentally that the same PdAu bimetallic catalyst can be transitioned between a single-atom alloy and a Pd cluster phase. Each state of the catalyst exhibits distinct selectivity for the dehydrogenation of ethanol reaction with the single-atom alloy phase exhibiting high selectivity to acetaldehyde and hydrogen versus a range of products from Pd clusters. First-principles based Monte Carlo calculations explain the origin of this active site ensemble size tuning effect, and this work serves as a demonstration of what should be a general phenomenon that enables in situ control over catalyst selectivity.

Bimetallic PdAu Catalysts within Hierarchically Porous Architectures for Aerobic Oxidation of Benzyl Alcohol.

Hierarchically porous (HP) zeotype materials (possessing both micropores and mesopores) offer improved diffusional access to intra-framework active sites, analogous to mesoporous materials, yet retain the high selectivity of the microporous (MP) bulk. We have recently designed crystalline hierarchically porous silicoaluminophosphates (SAPOs) with enhanced mass-transport characteristics, which can lead to significant improvement in catalytic activity and catalyst lifetime. In this study, we have prepared PdAu bimetallic nanostructures supported on HP-SAPO frameworks by an incipient impregnation of metal precursors followed by H2 reduction at 300 °C, for the aerobic oxidation of benzyl alcohol to benzaldehyde. PdAu NPs supported on HP framework displayed significantly enhanced catalytic activities, when compared with their MP analogues, clearly highlighting the benefits of introducing hierarchical porosity in the SAPO support matrix.

Oxidation of 5-Hydroxymethylfurfural on Supported Ag, Au, Pd and Bimetallic Pd-Au Catalysts: Effect of the Support

Oxidation of 5-hydroxymethylfurfural (HMF), a major feedstock derived from waste/fresh biomass, into 2,5-furandicarboxylic acid (FDCA) is an important transformation for the production of biodegradable plastics. Herein, we investigated the effect of the support (unmodified and modified titania, commercial alumina, and untreated and treated Sibunit carbon) of mono- and bimetallic catalysts based on noble metals (Ag, Au, Pd) on selective HMF oxidation with molecular oxygen to FDCA under mild and basic reaction conditions. The higher selectivity to FDCA was obtained when metals were supported on Sibunit carbon (Cp). The order of noble metal in terms of catalyst selectivity was: Ag < Au < Pd < PdAu. Finally, FDCA production on the most efficient PdAu NPs catalysts supported on Sibunit depended on the treatment applied to this carbon support in the order: PdAu/Cp < PdAu/Cp-HNO3 < PdAu/Cp-NH4OH. These bimetallic catalysts were characterized by nitrogen adsorption-desorption, inductively coupled plasma atomic emission spectroscopy, high resolution transmission electron microscopy, energy dispersive spectroscopy, X-ray diffraction, Hammet indicator method and X-ray photoelectron spectroscopy. The functionalization of Sibunit surface by HNO3 and NH4OH led to a change in the contribution of the active states of Pd and Au due to promotion effect of N-doping and, as a consequence, to higher FDCA production. HMF oxidation catalyzed by bimetallic catalysts is a structure sensitive reaction.