Synthesis and Structural Characterization of Branched Bimetallic AuPd Nanoparticles with a Highly Tunable Optical Response

Funding Information: This work received financial support from Portugal national funds [Fundação para a Ciência e Tecnologia and Ministério da Ciência, Tecnologia e Ensino Superior (FCT/MCTES)] through the Projects UIDB/50006/2020 and UIDP/50006/2020. Silvia Nuti, Carlos Lodeiro, José-Luis Capelo-Martinez, Adrián Fernández-Lodeiro, and Javier Fernández-Lodeiro thank the financial support from national funds (FCT/MCTES) through Project Met4Cat (EXPL/QUI-COL/0263/2021). The authors thank the financial support by the PROTEOMASS Scientific Society (Portugal) (General Funding Grant 2023). The authors acknowledge funding from the European Union’s Horizon 2020 Research and Innovation Program under Grant 823717-ESTEEM3, and Ana B. Hungría thanks the financial support from Junta de Andalucía Project P20_00968. Silvia Nuti thanks FCT/MCTEC (Portugal) for her doctoral grant associated with the chemistry Ph.D. program (SFRH/BD/144618/2019). Javier Fernández-Lodeiro thanks FCT for the research contract through the Program DL 57/2016-Norma Transitória. The work was carried out partially through the INL User Facilities (Braga, Portugal) and the Electron Microscope Division (DME) of the Servicios Centrales de Investigación Científica y Tecnológica (SC-ICYT) at Cadiz University (Cadiz, Spain). The authors thank Dr. Jamila Djafari for the assistance with the design of the graphical abstract. Funding Information: This work received financial support from Portugal national funds [Fundação para a Ciência e Tecnologia and Ministério da Ciência, Tecnologia e Ensino Superior (FCT/MCTES)] through the Projects UIDB/50006/2020 and UIDP/50006/2020. Silvia Nuti, Carlos Lodeiro, José-Luis Capelo-Martinez, Adrián Fernández-Lodeiro, and Javier Fernández-Lodeiro thank the financial support from national funds (FCT/MCTES) through Project Met4Cat (EXPL/QUI-COL/0263/2021). The authors thank the financial support by the PROTEOMASS Scientific Society (Portugal) (General Funding Grant 2023). The authors acknowledge funding from the European Union’s Horizon 2020 Research and Innovation Program under Grant 823717-ESTEEM3, and Ana B. Hungría thanks the financial support from Junta de Andalucía Project P20_00968. Silvia Nuti thanks FCT/MCTEC (Portugal) for her doctoral grant associated with the chemistry Ph.D. program (SFRH/BD/144618/2019). Javier Fernández-Lodeiro thanks FCT for the research contract through the Program DL 57/2016–Norma Transitória. The work was carried out partially through the INL User Facilities (Braga, Portugal) and the Electron Microscope Division (DME) of the Servicios Centrales de Investigación Científica y Tecnológica (SC-ICYT) at Cadiz University (Cadiz, Spain). The authors thank Dr. Jamila Djafari for the assistance with the design of the graphical abstract. Publisher Copyright: © 2023 The Authors. Published by American Chemical Society.Bimetallic nanostructures composed of gold (Au) and palladium (Pd) have garnered increased interest for their applications in heterogeneous catalysis. This study reports a simple strategy for manufacturing Au@Pd bimetallic branched nanoparticles (NPs), which offer a tunable optical response, using polyallylamine-stabilized branched AuNPs as template cores for Pd overgrowth. The palladium content can be altered by manipulating the concentration of PdCl42- and ascorbic acid (AA) that are injected, which permit an overgrowth of the Pd shell up to ca. 2 nm thick. The homogeneous distribution of Pd at the surfaces of Au NPs can be carried out regardless of their size or branching degree, which allows for an adjustment of the plasmon response in the near-infrared (NIR) spectral range. As a proof of concept, the nanoenzymatic activity of pure gold and gold-palladium NPs was compared, exploring their peroxidase-like activity in the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB). The bimetallic AuPd NPs demonstrate an increase in the catalytic properties attributed to the presence of palladium at the surface of gold.publishersversionpublishe

Catalytic Decomposition of n-C-7 Asphaltenes Using Tungsten Oxides-Functionalized SiO2 Nanoparticles in Steam/Air Atmospheres

A wide range of technologies are being developed to increase oil recovery, reserves, and perform in situ upgrading of heavy crude oils. In this study, supported tungsten oxide nanoparticles were synthesized, characterized, and evaluated for adsorption and catalytic performance during wet in situ combustion (6% of steam in the air, in volumetric fraction) of n-C-7 asphaltenes. Silica nanoparticles of 30 nm in diameter were synthesized using a sol-gel methodology and functionalized with tungsten oxides, using three different concentrations and calcination temperatures: 1%, 3%, 5% (mass fraction), and 350 degrees C, 450 degrees C, and 650 degrees C, respectively. Equilibrium batch adsorption experiments were carried out at 25 celcius with model solutions of n-C-7 asphaltenes diluted in toluene at concentrations from 100 mg center dot L-1 to 2000 mg center dot L-1, and catalytic wet in situ combustion of adsorbed heavy fractions was carried out by thermogravimetric analysis coupled to FT-IR. The results showed improvements of asphaltenes decomposition by the action of the tungsten oxide nanoparticles due to the reduction in the decomposition temperature of the asphaltenes up to 120 degrees C in comparison with the system in the absence of WOX nanoparticles. Those synthesis parameters, such as temperature and impregnation dosage, play an important role in the adsorptive and catalytic activity of the materials, due to the different WOX-support interactions as were found through XPS. The mixture released during the catalyzed asphaltene decomposition in the wet air atmosphere reveals an increase in light hydrocarbons, methane, and hydrogen content. Hydrogen production was prioritized between 300 and 400 degrees C where, similarly, the reduction of CO, CH4, and the increase in CO2 content, associated with water-gas shift, and methane reforming reactions occur, respectively. The results show that these catalysts can be used either for in situ upgrading of crude oil, or any application where heavy fractions must be transformed

Effects of alloying palladium with gold in furfural hydrogenation:An in situ ATR-IR spectroscopy and density functional theory study

Furfural is a versatile platform molecule and a model compound to explore the key factors influencing activity and selectivity in heterogeneous catalysis. In this study, Pd and AuPd nanoparticles (average size 3.5–4 nm) were deposited on TiO2 by sol immobilization method and were evaluated for liquid-phase furfural hydrogenation. Alloying Au and Pd caused a decrease in activity, an enhancement in stability, and a change in selectivity, favouring the complete hydrogenation of furfural over the decarbonylation reaction. These variations in catalytic performance were elucidated by combining in situ attenuated total reflectance infrared spectroscopy and density functional theory studies

Dual-Site Mediated Hydrogenation Catalysis on Pd/NiO: Selective Biomass Transformation and Maintaining Catalytic Activity at Low Pd Loading

Creating a new chemical ecosystem based on platform chemicals derived from waste biomass has significant challenges; catalysts need to be able to convert these highly functionalised molecules to specific target chemicals, economical – not relying on large quantities of precious metals - and maintain activity over many cycles. Herein, we demonstrate how Pd/NiO is able to direct the selectivity of furfural hydrogenation and maintain performance at low Pd loading by a unique dual-site mechanism. Sol-immobilization was used to prepare 1 wt% Pd nanoparticles supported on NiO and TiO2, with the Pd/NiO catalyst showing enhanced activity with a significantly different selectivity profile; Pd/NiO favours tetrahydrofurfuryl alcohol (72%), whereas Pd/TiO2 produces furfuryl alcohol as the major product (68%). Density functional theory studies evidenced significant differences on the adsorption of furfural on both NiO and Pd surfaces. Based on this observation we hypothesised that the role of Pd was to dissociate hydrogen, with the NiO surface adsorbing furfural. This dual-site hydrogenation mechanism was supported by comparing the performance of 0.1 wt% Pd/NiO and 0.1 wt% Pd/TiO2. In this study, the 0.1 and 1 wt% Pd/NiO catalysts had a comparable activity, whereas there was a 10-fold reduction in performance for 0.1 wt% Pd/TiO2. When using TiO2 as the support the Pd nanoparticles are responsible for both hydrogen dissociation and furfural adsorption, and the activity is strongly correlated with the effective metal surface area. This work has significant implications for the upgrading of bio-derived feedstocks, suggesting alternative ways for promoting selective transformations and reducing the reliance on precious metals

Developing and understanding Leaching-Resistant cobalt nanoparticles via N/P incorporation for liquid phase hydroformylation

The ultimate target in heterogeneous catalysis is the achievement of robust, resilient and highly efficient materials capable of resisting industrial reaction conditions. Pursuing that goal in liquid-phase hydroformylation poses a unique challenge due to carbon monoxide-induced metal carbonyl species formation, which is directly related to the formation of active homogeneous catalysts by metal leaching. Herein, supported heteroatom-incorporated (P and N) Co nanoparticles were developed to enhance the resistance compared with bare Co nanoparticles. The samples underwent characterization using operando XPS, XAS and HR electron microscopy. Overall, P- and N-doped catalysts increased reusability and suppressed leaching. Among the studied catalysts, the one with N as a dopant, CoNx@NC, presents excellent catalytic results for a Co-based catalyst, with a 94% conversion and a selectivity to aldehydes of 80% in only 7.5 h. Even under milder conditions, this catalyst outperformed existing benchmarks in Turnover Numbers (TON) and productivity. In addition, computational simulations provided atomistic insights, shedding light on the remarkable resistance of small Co clusters interacting with N-doped carbon patches

Chemistry, nanostructure and magnetic properties of Co-Ru-B-O nanoalloys

© the Partner Organisations 2014. In our previous works, Co-B-O and Co-Ru-B-O ultrafine powders with variable Ru content (xRu) were studied as catalysts for hydrogen generation through sodium borohydride hydrolysis. These materials have shown a complex nanostructure in which small Co-Ru metallic nanoparticles are embedded in an amorphous matrix formed by Co-Ru-B-O based phases and B2O3. Catalytic activity was correlated to nanostructure, surface and bulk composition. However, some questions related to these materials remain unanswered and are studied in this work. Aspects such as: 3D morphology, metal nanoparticle size, chemical and electronic information on the nanoscale (composition and oxidation states), and the study of the formation or not of a CoxRu1-x alloy or solid solution are investigated and discussed using XAS (X-ray Absorption Spectroscopy) and Scanning Transmission Electron Microscopy (STEM) techniques. Also magnetic behavior of the series is studied for the first time and the structure-performance relationships discussed. All Co-containing samples exhibited ferromagnetic behavior up to room temperature while the Ru-B-O sample is diamagnetic. For the xRu = 0.13 sample, an enhancement in the Hc (coercitive field) and Ms (saturation magnetization) is produced with respect to the monometallic Co-B-O material. However this effect is not observed for samples with higher Ru content. The presence of the CoxB-rich (cobalt boride) amorphous ferromagnetic matrix, very small metal nanoparticles (Co and CoxRu(1-x)) embedded in the matrix, and the antiferromagnetic CoO phase (for the higher Ru content sample, xRu = 0.7), explain the magnetic behavior of the series.Peer Reviewe

Microwave-Assisted synthesis and luminescence of mesoporous RE-Doped YPO 4 (RE = Eu, Ce, Tb, and Ce + Tb) nanophosphors with lenticular shape

Mesoporous tetragonal RE:YPO 4 nanophosphors (RE = Eu, Ce, Tb, and Ce + Tb) with a lenticular morphology, narrow size distribution, and high surface area have been prepared by an homogeneous precipitation procedure consisting of aging, at low temperature (80-120 °C) in a microwave oven, ethylene glycol solutions containing only yttrium acetylacetonate and phosphoric acid. This synthesis method involves important advantages such as its simplicity, rapidness (reaction time = 7 min), and high reaction yields. The mechanism of nanoparticle growth has been also addressed finding that the lenticular nanoparticles are formed through an ordered aggregation of smaller entities, which explains their porosity. In all cases, the doping levels were systematically varied in order to optimize the nanophosphors luminescence. All optimum nanophosphors presented a high luminescence quantum yield (QY). In particular, for the Eu and Tb doped systems, the obtained QY values (60% for Eu and 80% for Tb) were the highest so far reported for this kind of nanomaterial. The morphological, microstructural, and luminescent properties of these nanophosphors and their dispersibility in water make them suitable for biomedical applications. © 2011 American Chemical Society.Peer Reviewe

Supported Ce/Zr pyrochlore monolayers as a route to single cerium atom catalysts with low temperature reducibility

Summary: The combination of structural characterization at atomic resolution, chemical data, and theoretical insights has revealed the unique nanostructures which develop in ceria supported on yttria-stabilized zirconia (YSZ) after being submitted to high-temperature reducing treatments. The results show that just a small ceria loading is needed for creating a supported Zr-rich pyrochlore (111) nanostructure, resembling the structure of single cerium atom catalysts. The specific atomic arrangement of this nanostructure allows to explain the improvement of the reducibility at low temperature. The reduction mechanism can be extrapolated to ceria-zirconia mixed oxides with pyrochlore-like cationic ordering, exposing Zr-rich (111) surfaces. The results gathered here provide key information to understand the redox behavior of these types of systems, which may contribute to improving the design of new ceria-zirconia based materials, with lower content of the lanthanide element, nearly 100% cerium atom utilization, and applications in environmental catalysis

Catalytic Decomposition of n-C7 Asphaltenes Using Tungsten Oxides–Functionalized SiO2 Nanoparticles in Steam/Air Atmospheres

A wide range of technologies are being developed to increase oil recovery, reserves, and perform in situ upgrading of heavy crude oils. In this study, supported tungsten oxide nanoparticles were synthesized, characterized, and evaluated for adsorption and catalytic performance during wet in situ combustion (6% of steam in the air, in volumetric fraction) of n-C7 asphaltenes. Silica nanoparticles of 30 nm in diameter were synthesized using a sol–gel methodology and functionalized with tungsten oxides, using three different concentrations and calcination temperatures: 1%, 3%, 5% (mass fraction), and 350 °C, 450 °C, and 650 °C, respectively. Equilibrium batch adsorption experiments were carried out at 25 ℃ with model solutions of n-C7 asphaltenes diluted in toluene at concentrations from 100 mg·L−1 to 2000 mg·L−1, and catalytic wet in situ combustion of adsorbed heavy fractions was carried out by thermogravimetric analysis coupled to FT-IR. The results showed improvements of asphaltenes decomposition by the action of the tungsten oxide nanoparticles due to the reduction in the decomposition temperature of the asphaltenes up to 120 °C in comparison with the system in the absence of WOX nanoparticles. Those synthesis parameters, such as temperature and impregnation dosage, play an important role in the adsorptive and catalytic activity of the materials, due to the different WOX–support interactions as were found through XPS. The mixture released during the catalyzed asphaltene decomposition in the wet air atmosphere reveals an increase in light hydrocarbons, methane, and hydrogen content. Hydrogen production was prioritized between 300 and 400 °C where, similarly, the reduction of CO, CH4, and the increase in CO2 content, associated with water–gas shift, and methane reforming reactions occur, respectively. The results show that these catalysts can be used either for in situ upgrading of crude oil, or any application where heavy fractions must be transformed

Enhanced activity of Au/NiO nanohybrids for the reductive amination of benzyl alcohol

Gold nanoparticles were prepared by sol immobilization (AuSI) or deposition precipitation (AuDP), then deposited on NiO and commercial TiO2 (P25). The Au/NiO catalysts showed higher activity and yield to the secondary amine, compared to Au/TiO2 catalysts, when tested for the reductive amination of benzyl alcohol with isopropylamine. We attribute this result to a synergistic effect between Au and NiO. Moreover, as a result of the protective effect of the polyvinyl alcohol used in the sol immobilization synthesis, the gold nanoparticles on NiO demonstrate an increased resistance to structural changes during the reaction. This effect results in enhanced catalytic efficiency in terms of activity, and better stability against deactivation