scholarly journals Defining the Qualities of High-Quality Palladium on Carbon Catalysts for Hydrogenolysis

2021 ◽  
Author(s):  
Conor J. Crawford ◽  
Yan Qiao ◽  
Yequn Liu ◽  
Dongmei Huang ◽  
Wenjun Yan ◽  
...  
Keyword(s):  
High Quality ◽  
Carbon Catalysts ◽  
Palladium On Carbon

scholarly journals Clues to a Pd/C catalyst’s efficiency can be found on its surface: Identification of an efficient catalyst for the global hydrogenolysis of ether protecting groups

2020 ◽  
Author(s):  
Conor Crawford ◽  
Yan Qiao ◽  
Yequn Liu ◽  
Dongmei Huang ◽  
Wenjun Yan ◽  
...  
Keyword(s):  
Palladium Catalyst ◽  
Protecting Groups ◽  
Synthetic Material ◽  
High Quality ◽  
Efficient Catalyst ◽  
Tem Analysis ◽  
Wide Variability ◽  
Carbon Catalysts ◽  
Palladium On Carbon

<p>We report insights into our observations of the wide variability in quality of palladium catalyst from different suppliers, finding the fundamental differences can be rationalized through a combination of XRD, XPS, and TEM analysis, offering the possibility to predict a catalysts performance prior to the use of valuable synthetic material and save time consuming efforts to identify high quality palladium on carbon catalysts. The synthetic glycan accessed in this study will allow further steps towards the development of semisynthetic vaccines against cryptococcal infections.</p>

scholarly journals Variation in the Structure and Activity of Commercial Palladium on Carbon Catalysts

2020 ◽  
Author(s):  
Conor Crawford ◽  
Yan Qiao ◽  
Yequn Liu ◽  
Dongmei Huang ◽  
Wenjun Yan ◽  
...  
Keyword(s):  
Reaction Times ◽  
Active Species ◽  
High Quality ◽  
Tem Analysis ◽  
Design And Synthesis ◽  
Wide Variability ◽  
Commercial Sources ◽  
Carbon Catalysts ◽  
Palladium On Carbon ◽  
Key Indicators

<p>Palladium catalysed hydrogenolysis is often the final step in challenging natural product total synthesis and a key step in industrial processes towards fine chemicals. Here we demonstrate that there is wide variability in quality of commercial sources of palladium on carbon (Pd/C), which results in differences in selectivity, reaction times, and yields. This is established through a combination of XRD, XPS, BET and TEM analysis, this will serve as a template for others to quickly identify a high-quality source of Pd/C catalyst — meaning less time spent on time consuming reaction optimisation studies. Key indicators of a high-quality catalyst include: small particle sizes, large surface area, and the presence of both Pd<sup>0</sup> and Pd<sup>2+ </sup>active species (not present in all commercial sources). Further this work will enable the design and synthesis of new high-quality Pd/C catalysts.</p>

scholarly journals Variation in the Structure and Activity of Commercial Palladium on Carbon Catalysts

2020 ◽  
Author(s):  
Conor Crawford ◽  
Yan Qiao ◽  
Yequn Liu ◽  
Dongmei Huang ◽  
Wenjun Yan ◽  
...  
Keyword(s):  
Reaction Times ◽  
Active Species ◽  
High Quality ◽  
Tem Analysis ◽  
Design And Synthesis ◽  
Wide Variability ◽  
Commercial Sources ◽  
Carbon Catalysts ◽  
Palladium On Carbon ◽  
Key Indicators

<p>Palladium catalysed hydrogenolysis is often the final step in challenging natural product total synthesis and a key step in industrial processes towards fine chemicals. Here we demonstrate that there is wide variability in quality of commercial sources of palladium on carbon (Pd/C), which results in differences in selectivity, reaction times, and yields. This is established through a combination of XRD, XPS, BET and TEM analysis, this will serve as a template for others to quickly identify a high-quality source of Pd/C catalyst — meaning less time spent on time consuming reaction optimisation studies. Key indicators of a high-quality catalyst include: small particle sizes, large surface area, and the presence of both Pd<sup>0</sup> and Pd<sup>2+ </sup>active species (not present in all commercial sources). Further this work will enable the design and synthesis of new high-quality Pd/C catalysts.</p>

Rapid “Mix-and-Stir” Preparation of Well-Defined Palladium on Carbon Catalysts for Efficient Practical Use

ChemCatChem ◽  
2017 ◽  
Vol 10 (8) ◽  
pp. 1869-1873 ◽  
Author(s):  
Sergey A. Yakukhnov ◽  
Evgeniy O. Pentsak ◽  
Konstantin I. Galkin ◽  
Roman M. Mironenko ◽  
Vladimir A. Drozdov ◽  
...  
Keyword(s):  
Carbon Catalysts ◽  
Palladium On Carbon

Some problems of objective-prism spectra classification

1966 ◽  
Vol 24 ◽  
pp. 51-52
Author(s):  
E. K. Kharadze ◽  
R. A. Bartaya
Keyword(s):  
Short Wave ◽  
High Quality ◽  
Stellar Spectra ◽  
Objective Prism

The unique 70-cm meniscus-type telescope of the Abastumani Astrophysical Observatory supplied with two objective prisms and the seeing conditions characteristic at Mount Kanobili (Abastumani) permit us to obtain stellar spectra of a high quality. No additional design to improve the “climate” immediately around the telescope itself is being applied. The dispersions and photographic magnitude limits are 160 and 660Å/mm, and 12–13, respectively. The short-wave end of spectra reaches 3500–3400Å.

A non-cyanide method of electropolishing silver

1978 ◽  
Vol 36 (1) ◽  
pp. 146-147
Author(s):  
R. L. Lyles ◽  
S. J. Rothman ◽  
W. Jäger
Keyword(s):  
Electron Microscopy ◽  
Sulphuric Acid ◽  
Methyl Alcohol ◽  
Health Hazards ◽  
Silver Alloy ◽  
High Quality ◽  
Silver Alloys ◽  
Free Sample ◽  
Specimen Quality ◽  
Standard Techniques

Standard techniques of electropolishing silver and silver alloys for electron microscopy in most instances have relied on various CN recipes. These methods have been characteristically unsatisfactory due to difficulties in obtaining large electron transparent areas, reproducible results, adequate solution lifetimes, and contamination free sample surfaces. In addition, there are the inherent health hazards associated with the use of CN solutions. Various attempts to develop noncyanic methods of electropolishing specimens for electron microscopy have not been successful in that the specimen quality problems encountered with the CN solutions have also existed in the previously proposed non-cyanic methods.The technique we describe allows us to jet polish high quality silver and silver alloy microscope specimens with consistant reproducibility and without the use of CN salts.The solution is similar to that suggested by Myschoyaev et al. It consists, in order of mixing, 115ml glacial actic acid (CH3CO2H, specific wt 1.04 g/ml), 43ml sulphuric acid (H2SO4, specific wt. g/ml), 350 ml anhydrous methyl alcohol, and 77 g thiourea (NH2CSNH2).

A High Resolution Scanning Microscope

1968 ◽  
Vol 26 ◽  
pp. 356-357
Author(s):  
A. V. Crewe ◽  
J. Wall ◽  
L. M. Welter
Keyword(s):  
High Resolution ◽  
Field Emission ◽  
Spherical Aberration ◽  
Focal Length ◽  
Spot Size ◽  
Emission Source ◽  
Field Of View ◽  
Scanning Microscope ◽  
Magnetic Lens ◽  
High Quality

A scanning microscope using a field emission source has been described elsewhere. This microscope has now been improved by replacing the single magnetic lens with a high quality lens of the type described by Ruska. This lens has a focal length of 1 mm and a spherical aberration coefficient of 0.5 mm. The final spot size, and therefore the microscope resolution, is limited by the aberration of this lens to about 6 Å.The lens has been constructed very carefully, maintaining a tolerance of + 1 μ on all critical surfaces. The gun is prealigned on the lens to form a compact unit. The only mechanical adjustments are those which control the specimen and the tip positions. The microscope can be used in two modes. With the lens off and the gun focused on the specimen, the resolution is 250 Å over an undistorted field of view of 2 mm. With the lens on,the resolution is 20 Å or better over a field of view of 40 microns. The magnification can be accurately varied by attenuating the raster current.

Quantitative defect studies in semiconductor TEM samples prepared by low angle ion milling

1995 ◽  
Vol 53 ◽  
pp. 512-513
Author(s):  
L. Mulestagno ◽  
J.C. Holzer ◽  
P. Fraundorf
Keyword(s):  
Sample Preparation ◽  
Milling Time ◽  
High Density ◽  
Low Density ◽  
Ion Milling ◽  
High Quality ◽  
Variable Angle ◽  
Major Disadvantage ◽  
Induced Defects

Due to the wealth of information, both analytical and structural that can be obtained from it TEM always has been a favorite tool for the analysis of process-induced defects in semiconductor wafers. The only major disadvantage has always been, that the volume under study in the TEM is relatively small, making it difficult to locate low density defects, and sample preparation is a somewhat lengthy procedure. This problem has been somewhat alleviated by the availability of efficient low angle milling.Using a PIPS® variable angle ion -mill, manufactured by Gatan, we have been consistently obtaining planar specimens with a high quality thin area in excess of 5 × 104 μm2 in about half an hour (milling time), which has made it possible to locate defects at lower densities, or, for defects of relatively high density, obtain information which is statistically more significant (table 1).

Structural changes in silicon-on-insulator material during post-implantation annealing

1986 ◽  
Vol 44 ◽  
pp. 736-737
Author(s):  
C. O. Jung ◽  
S. J. Krause ◽  
S.R. Wilson
Keyword(s):  
Integrated Circuits ◽  
Oxide Layer ◽  
High Speed ◽  
Structural Changes ◽  
Device Fabrication ◽  
Silicon On Insulator ◽  
High Quality ◽  
Radiation Hardened ◽  
Post Implantation ◽  
Very High

Silicon-on-insulator (SOI) structures have excellent potential for future use in radiation hardened and high speed integrated circuits. For device fabrication in SOI material a high quality superficial Si layer above a buried oxide layer is required. Recently, Celler et al. reported that post-implantation annealing of oxygen implanted SOI at very high temperatures would eliminate virtually all defects and precipiates in the superficial Si layer. In this work we are reporting on the effect of three different post implantation annealing cycles on the structure of oxygen implanted SOI samples which were implanted under the same conditions.

Performance and applications of a field-emission gun TEM/STEM

1992 ◽  
Vol 50 (2) ◽  
pp. 942-943
Author(s):  
Judith M. Brock ◽  
Max T. Otten ◽  
Marc. J.C. de Jong
Keyword(s):  
Field Emission ◽  
High Resolution Imaging ◽  
High Quality ◽  
Small Energy ◽  
High Brightness ◽  
Small Probe ◽  
Resolution Imaging ◽  
Convergent Beam ◽  
Beam Patterns ◽  
Beam Diffraction

A Field Emission Gun (FEG) on a TEM/STEM instrument provides a major improvement in performance relative to one equipped with a LaB6 emitter. The improvement is particularly notable for small-probe techniques: EDX and EELS microanalysis, convergent beam diffraction and scanning. The high brightness of the FEG (108 to 109 A/cm2srad), compared with that of LaB6 (∼106), makes it possible to achieve high probe currents (∼1 nA) in probes of about 1 nm, whilst the currents for similar probes with LaB6 are about 100 to 500x lower. Accordingly the small, high-intensity FEG probes make it possible, e.g., to analyse precipitates and monolayer amounts of segregation on grain boundaries in metals or ceramics (Fig. 1); obtain high-quality convergent beam patterns from heavily dislocated materials; reliably detect 1 nm immuno-gold labels in biological specimens; and perform EDX mapping at nm-scale resolution even in difficult specimens like biological tissue.The high brightness and small energy spread of the FEG also bring an advantage in high-resolution imaging by significantly improving both spatial and temporal coherence.

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