scholarly journals Enhanced Performance of Bimetallic Co-Pd Catalysts Prepared by Mechanical Alloying

Metals ◽  
2019 ◽  
Vol 9 (3) ◽  
pp. 335
Author(s):  
Steven Knauss ◽  
Laura Guevara ◽  
Mark Atwater
Keyword(s):  
Catalytic Activity ◽  
Mechanical Alloying ◽  
Ball Milling ◽  
Bimetallic Catalysts ◽  
Reactant Ratio ◽  
Pd Catalysts ◽  
Close Proximity ◽  
Intermediate Time ◽  
Underlying Mechanisms ◽  
Co Precipitation

Bimetallic catalysts can provide enhanced performance, and Co-based catalysts in particular have been studied in various respects for their activity in the deposition of carbon nanofibers (CNFs). The majority of studies on CNF catalysis use co-precipitation to create alloys, but recent work has demonstrated the suitability of mechanical alloying (MA) by ball milling to reduce cost and increase catalytic activity. This work establishes the unique ability of MA to control the microstructure to produce bimetallic composites, which retain distinct metallic phases that improve catalytic activity. It is demonstrated that Co-Pd alloys reach a maximum in catalytic activity at an intermediate time of mechanical activation, where 30 min of milling outperformed samples milled for 5, 15, 60, and 240 min at a reaction temperature of 550 °C and a 1:4 C2H4:H2 reactant ratio. This indicates there is benefit to retaining the metals in distinct phases in close proximity. Ball milling provides a relatively simple and scalable method to achieve these unique microstructures, and in the optimal condition tested here, the activity toward carbon deposition is increased fourfold over prior work. Furthermore, the minimum temperature for deposition is also reduced. The characteristics of these materials, the effects of milling and annealing, and the underlying mechanisms of deposition are discussed.

scholarly journals Preparation of Pd/SiO2 Catalysts by a Simple Dry Ball-Milling Method for Lean Methane Oxidation and Probe of the State of Active Pd Species

Catalysts ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 725
Author(s):  
Li Yang ◽  
Chao Fan ◽  
Li Luo ◽  
Yanyan Chen ◽  
Zhiwei Wu ◽  
...  
Keyword(s):  
Catalytic Activity ◽  
Low Temperature ◽  
Ball Milling ◽  
Methane Oxidation ◽  
Oxidation State ◽  
Catalytic Performance ◽  
The State ◽  
Pd Catalysts ◽  
Tight Contact ◽  
Milling Method

A series of Pd/SiO2 catalysts were prepared with different Pd precursors by a dry ball-milling method and used in the catalytic oxidation of lean methane at low temperature. The effect of Pd precursors on the catalytic performance was investigated and the state of the most active Pd species was probed. The results indicate that dry ball-milling is a simple but rather effective method to prepare the Pd/SiO2 catalysts for lean methane oxidation, and palladium acetylacetonate is an ideal precursor to obtain a highly active Pd/SiO2-Acac catalyst with well- and stably dispersed Pd species, owing to the tight contact between acetylacetonate and Si–OH on the SiO2 support. Besides the size and dispersion of Pd particles, the oxidation state of Pd species also plays a crucial role in determining the catalytic activity of Pd/SiO2 in lean methane oxidation at low temperature. A non-monotonic dependence of the catalytic activity on the Pd oxidation state is observed. The activity of various Pd species follows the order of PdOx >> Pd > PdO; the PdOx/SiO2-Acac catalysts (in particular for PdO0.82/SiO2-Acac when x = 0.82) exhibit much higher activity in lean methane oxidation at low temperature than Pd/SiO2-Acac and PdO/SiO2-Acac. The catalytic activity of PdOx/SiO2 may degrade during the methane oxidation due to the gradual transformation of PdOx to PdO in the oxygen-rich ambiance; however, such degradation is reversible and the activity of a degraded Pd/SiO2 catalyst can be recovered through a redox treatment to regain the PdOx species. This work helps to foster a better understanding of the relationship between the structure and performance of supported Pd catalysts by clarifying the state of active Pd species, which should be beneficial to the design of an active catalyst in lean methane oxidation at low temperature.

OXIDATION OF GLYCEROL USING TITANIA SUPPORTED Au–Pd BIMETALLIC CATALYSTS: EFFECT OF Au–Pd RATIOS ON CATALYTIC PERFORMANCE

2011 ◽  
Vol 04 (03) ◽  
pp. 309-313 ◽  
Author(s):  
AINOL HAYAH AHMAD NADZRI ◽  
NORAINI HAMZAH ◽  
NIK IDRIS NIK YUSOFF ◽  
MOHD AMBAR YARMO
Keyword(s):  
Catalytic Activity ◽  
Bimetallic Catalysts ◽  
Catalytic Performance ◽  
Active Species ◽  
Precipitation Method ◽  
Oxidation Reactions ◽  
Pd Catalysts ◽  
Tartronic Acid ◽  
Pd Alloy ◽  
Urea Decomposition

Oxidation of glycerol to form various types of short chain oxygenated derivative compounds became an important reaction to support biodiesel industries. In this study, bimetallic Au–Pd catalysts supported on TiO2 with different Au/Pd atomic ratios have been successfully prepared by deposition-precipitation method with urea decomposition. The catalysts were tested in the glycerol oxidation reactions in order to examine the effect of Au–Pd ratio on the conversion and selectivity. Catalytic activity of all the catalysts were as follow: Au7Pd3/TiO2 > Au5Pd5/TiO2 > Au8Pd2/TiO2 > Au9Pd1/TiO2 > Au6Pd4/TiO2 . Analysis by XRD revealed the presence of metallic Au and gold-enriched Au–Pd alloy phase which were located between the [111] and [200] peaks of Au and Pd in the Au–Pd bimetallic catalysts. XPS analysis ascertained the formation of Au0 , Au3+ , Pd0 and PdO species together with Au–Pd alloy phase in the bimetallic Au–Pd catalysts. This shows that the catalytic activity of the catalysts was depended to the formation of mixture of active species namely Au0 , Au3+ , Pd0 dan PdO together with the presence of "synergisti" effect in the Au–Pd alloy. The reactions were performed at low and high temperatures (50°C and 100°C) and it was found that the selectivity to tartronic acid was enhanced at lower reaction temperature. The highest selectivity to tartronic acid (55% at 99% conversion) was obtained by using Au9Pd1/TiO2 at 50°C and after 8 h of reaction time.

scholarly journals Development of palladium catalysts modified by ruthenium and molybdenum as anode in direct ethanol fuel cell

2021 ◽  
Vol 10 (1) ◽  
Author(s):  
Yonis Fornazier Filho ◽  
Ana Caroliny Carvalho da Cruz ◽  
Rolando Pedicini ◽  
José Ricardo Cezar Salgado ◽  
Priscilla Paiva Luz ◽  
...  
Keyword(s):  
Catalytic Activity ◽  
Palladium Catalysts ◽  
Carbon Support ◽  
X Ray Diffraction ◽  
Direct Ethanol Fuel Cell ◽  
Pd Catalysts ◽  
Bifunctional Mechanism ◽  
Catalytic Activities ◽  
Intrinsic Mechanism ◽  
Ternary Catalysts

AbstractPhysical and electrochemical properties of Pd catalysts combined with Ru and Mo on carbon support were investigated. To this end, Pd, Pd1.3Ru1.0, Pd3.2Ru1.3Mo1.0 and Pd1.5Ru0.8Mo1.0 were synthesized on Carbon Vulcan XC72 support by the method of thermal decomposition of polymeric precursors and then physically and electrochemically characterized. The highest reaction yields are obtained for Pd3.2Ru1.3Mo1.0/C and Pd1.5Ru0.8Mo1.0/C and, as demonstrated by thermal analysis, they also show the smallest metal/carbon ratio compared the other catalysts. XRD (X-ray Diffraction) and Raman analyses show the presence of PdO and RuO2 for the Pd/C and the Pd1.3Ru1.0/C catalysts, respectively, a fact not observed for the Pd3.2Ru1.3 Mo1.0 /C and the Pd1.5Ru0.8Mo1.0/C catalysts. The catalytic activities were tested for the ethanol oxidation in alkaline medium. Cyclic voltammetry (CV) shows Pd1.3Ru1.0/C exhibiting the highest peak of current density, followed by Pd3.2Ru1.3Mo1.0/C, Pd1.5Ru0.8Mo1.0/C and Pd/C. From, chronoamperometry (CA), it is possible to observe the lowest rate of poisoning for the Pd1.3Ru1.0/C, followed by Pd3.2Ru1.3Mo1.0/C, Pd1.5Ru0.8Mo1.0/C and Pd/C. These results suggested that catalytic activity of the binary and the ternary catalysts are improved in comparison with Pd/C. The presence of RuO2 activated the bifunctional mechanism and improved the catalytic activity in the Pd1.3Ru1.0/C catalyst. The addition of Mo in the catalysts enhanced the catalytic activity by the intrinsic mechanism, suggesting a synergistic effect between metals. In summary, we suggest that it is possible to synthesize ternary PdRuMo catalysts supported on Carbon Vulcan XC72, resulting in materials with lower poisoning rates and lower costs than Pd/C. Graphic abstract

scholarly journals Influence of Co-Precipitation Agent on the Structure, Texture and Catalytic Activity of Au-CeO2 Catalysts in Low-Temperature Oxidation of Benzyl Alcohol

Catalysts ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 641
Author(s):  
Lukasz Wolski ◽  
Grzegorz Nowaczyk ◽  
Stefan Jurga ◽  
Maria Ziolek
Keyword(s):  
Gold Nanoparticles ◽  
Catalytic Activity ◽  
Low Temperature ◽  
Benzyl Alcohol ◽  
Low Temperature Oxidation ◽  
Temperature Oxidation ◽  
Oxidation Of Benzyl Alcohol ◽  
Key Factor ◽  
Au Particle Size ◽  
Co Precipitation

The aim of the study was to establish the influence of a co-precipitation agent (i.e., NaOH–immediate precipitation; hexamethylenetetramine/urea–gradual precipitation and growth of nanostructures) on the properties and catalytic activity of as-synthesized Au-CeO2 nanocomposites. All catalysts were fully characterized with the use of XRD, nitrogen physisorption, ICP-OES, SEM, HR-TEM, UV-vis, XPS, and tested in low-temperature oxidation of benzyl alcohol as a model oxidation reaction. The results obtained in this study indicated that the type of co-precipitation agent has a significant impact on the growth of gold species. Immediate co-precipitation of Au-CeO2 nanostructures with the use of NaOH allowed obtainment of considerably smaller and more homogeneous in size gold nanoparticles than those formed by gradual co-precipitation and growth of Au-CeO2 nanostructures in the presence of hexamethylenetetramine or urea. In the catalytic tests, it was established that the key factor promoting high activity in low-temperature oxidation of benzyl alcohol was size of gold nanoparticles. The highest conversion of the alcohol was observed for the catalyst containing the smallest Au particle size (i.e., Au-CeO2 nanocomposite prepared with the use of NaOH as a co-precipitation agent).

scholarly journals Structure-Phase Transformations in the Course of Solid-State Mechanical Alloying of High-Nitrogen Chromium-Manganese Steels

Metals ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 301
Author(s):  
Kirill Lyashkov ◽  
Valery Shabashov ◽  
Andrey Zamatovskii ◽  
Kirill Kozlov ◽  
Natalya Kataeva ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Solid State ◽  
Mechanical Alloying ◽  
Ball Milling ◽  
Ball Mill ◽  
Subsequent Annealing ◽  
High Nitrogen ◽  
Transmission Electron ◽  
Structure Phase ◽  
Manganese Steels

The solid-state mechanical alloying (MA) of high-nitrogen chromium-manganese austenite steel—MA in a planetary ball mill, —was studied by methods of Mössbauer spectroscopy and transmission electron microscopy (TEM). In the capacity of a material for the alloying we used mixtures of the binary Fe–Mn and Fe–Cr alloys with the nitrides CrN (Cr2N) and Mn2N. It is shown that ball milling of the mixtures has led to the occurrence of the α → γ transitions being accompanied by the (i) formation of the solid solutions supersaturated with nitrogen and by (ii) their decomposition with the formation of secondary nitrides. The austenite formed by the ball milling and subsequent annealing at 700–800 °C, was a submicrocrystalline one that contained secondary nano-sized crystalline CrN (Cr2N) nitrides. It has been established that using the nitride Mn2N as nitrogen-containing addition is more preferable for the formation and stabilization of austenite—in the course of the MA and subsequent annealing—because of the formation of the concentration-inhomogeneous regions of γ phase enriched with austenite-forming low-mobile manganese.

A graphdiyne-based carbon material for electroless deposition and stabilization of sub-nanometric Pd catalysts with extremely high catalytic activity

2019 ◽  
Vol 7 (21) ◽  
pp. 13142-13148 ◽  
Author(s):  
Liang-Liang Yang ◽  
Hong-Juan Wang ◽  
Juan Wang ◽  
Yu Li ◽  
Wen Zhang ◽  
...  
Keyword(s):  
Catalytic Activity ◽  
Carbon Material ◽  
Electroless Deposition ◽  
Suzuki Coupling ◽  
High Catalytic Activity ◽  
Coupling Reactions ◽  
Pd Catalysts ◽  
Catalytic Activities

A new graphdiyne-based carbon material was synthesized as an ideal substrate for electroless deposition and stabilization of sub-nanometric Pd catalysts, which showed extremely high catalytic activities for the reduction of nitroarenes and Suzuki coupling reactions.

scholarly journals Chemical environment of Ag atoms contained in Au Ag bimetallic catalysts and the generation of the catalytic activity for CO oxidation

2014 ◽  
Vol 483 ◽  
pp. 63-75 ◽  
Author(s):  
Yasuo Iizuka ◽  
Ryou Inoue ◽  
Takumi Miura ◽  
Nobuyasu Morita ◽  
Naoki Toshima ◽  
...  
Keyword(s):  
Catalytic Activity ◽  
Co Oxidation ◽  
Bimetallic Catalysts ◽  
Chemical Environment

scholarly journals Molecular edge effects in the Endangered golden-brown mouse lemur Microcebus ravelobensis

Oryx ◽  
2018 ◽  
Vol 53 (4) ◽  
pp. 716-726 ◽  
Author(s):  
U. Radespiel ◽  
J. Schulte ◽  
R. J. Burke ◽  
S. M. Lehman
Keyword(s):  
Edge Effects ◽  
Deciduous Forest ◽  
Mitochondrial Control Region ◽  
Mouse Lemur ◽  
Continuous Forest ◽  
Ecological Changes ◽  
Close Proximity ◽  
Geographical Distances ◽  
Dry Deciduous Forest ◽  
Underlying Mechanisms

AbstractHabitat fragmentation creates habitat edges, and ecological edge effects can cause major changes in the ecology and distribution of many taxa. However, these ecological changes may in turn influence animal movements and lead to molecular edge effects and edge-related genetic structure, matters that are largely unexplored. This study aims to infer molecular edge effects and to test three possible underlying mechanisms in the Endangered golden-brown mouse lemur Microcebus ravelobensis, a nocturnal species in the dry deciduous forest of the Ankarafantsika National Park in north-western Madagascar. Mouse lemurs were sampled in one edge and two interior habitats in close proximity to each other (500–1,400 m) in a continuous forest. A total of 41 mouse lemur samples were genotyped with seven nuclear microsatellites, and a fragment of the mitochondrial control region was sequenced for all samples. The overall genetic diversity (allelic richness, heterozygosity, haplotype richness, nucleotide diversity) was lower in the edge habitat compared to the two interior sites and all subpopulations showed signals of relatively low genetic exchange and significant genetic differentiation between them despite the short geographical distances, supporting the local preference model. These findings can be interpreted as preliminary signals of a molecular edge effect and suggest the potential for local adaptation. They are highly relevant for the conservation of fragmented populations, because a further subdivision of already small populations may increase their vulnerability to stochastic demographic changes and collapse.

Solid-state mechanical alloying of plastic crystals

1997 ◽  
Vol 12 (12) ◽  
pp. 3254-3259 ◽  
Author(s):  
J. Font ◽  
J. Muntasell ◽  
E. Cesari ◽  
J. Pons
Keyword(s):  
Solid State ◽  
Binary System ◽  
Mechanical Alloying ◽  
Ball Milling ◽  
Room Temperature ◽  
Binary Systems ◽  
Solid Phase ◽  
Stable State ◽  
Plastic Crystals ◽  
Dsc Measurements

Ball milling has been used as a solid-state mechanical alloying technique in two binary systems of plastic crystals: neopentylglycol/pentaglycerin (NPG/PG), showing a partial solubility in the ordered phase, and 2-amino-2-methyl-1,3-propanediol/tris(hydroxymethyl) (AMP/TRIS) whose immiscibility in this ordered solid phase is almost total. For the AMP/TRIS system the stable state at room temperature was reached by milling. Contrarily, for NPG/PG, DSC measurements reveal that an annealing period is required after milling. These results have been compared with those of the pentaglycerin/pentaerythritol (PG/PE) binary system, previously studied, whose miscibility is total at room temperature.

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