scholarly journals Solid electrochemical mass spectrometry (SEMS) for investigation of supported metal catalysts under high vacuum

2010 ◽  
Vol 40 (10) ◽  
pp. 1893-1900 ◽  
Author(s):  
Cyril Falgairette ◽  
Chun Xia ◽  
YongDan Li ◽  
Wolfgang Harbich ◽  
Christos Comninellis

Deuterium NMR spectroscopy, gas chromatography and mass spectrometry have been used to examine the products from the reaction of 2-methylpropene with deuterium over supported metal catalysts. The detailed information, so obtained, about the number, location and grouping of deuterium atoms in both the exchanged alkenes and the 2-methylpropanes formed by addition provided evidence about possible mechanisms. With palladium, exchange was faster than addition and the deuterium atoms were randomly distributed in the alkene, probably through a π-allyl dissociative mechanism. With platinum and rhodium, exchange occurred preferentially in the methylene groups of the alkene and the results indicated a dissociative mechanism involving adsorbed vinyl intermediates together with some intramolecular double-bond movement through a π-allyl type of species. Relatively little exchange occurred with iridium. The activities of the metals for production of alkane at 235 K were Rh > Ir > Pd > Pt but the spread was only a factor of about 20. With all metals except palladium further exchange occurred during the addition process, but this was mainly concentrated in one methyl group. This behaviour was explained in terms of mechanisms that permitted additional exchange of the methylene group of the alkene to take place during the addition process.


Author(s):  
Nan Yao ◽  
Gerard E. Spinnler ◽  
Richard A. Kemp ◽  
Don C. Guthrie ◽  
R. Dwight Cates ◽  
...  

In order to fully understand the general loss of activity for supported metal catalysts during the catalytic process, attempts of investigations of the microstructure and of observed structural changes of supported metal catalysts have been made by using environmental-cell TEM (EC-TEM). The EC-TEM used throughout the experiments reported here consists of a Philips-EM430 (300kV) TEM fitted with a Gatan environmental cell (E-cell). The key design feature is the ability to operate at high gas pressure in the specimen region while still maintaining high vacuum in the rest of the microscope. Fig.1 shows a sideview of the schematic arrangement of the E-cell (A). The standard Phi 1ips-EM430 twin pole pieces (B) have been modified by Gatan Inc. (with a resolution better than 0.34nm) in order to accept the E-cell. Specifically, a groove or “terrace” was machined around a diameter of the upper and lower pole pieces in order to seal with the top and bottom 0-rings (C) of the E-cell.


1999 ◽  
Vol 589 ◽  
Author(s):  
Jingyue Liu

AbstractThe use of a high-brightness field emission gun and novel secondary electron detection systems makes it possible to acquire nanometer-resolution surface images of bulk materials, even at low electron beam voltages. The advantages of low-voltage SEM include enhanced surface sensitivity, reduced sample charging on non-conducting materials, and significantly reduced electron range and interaction volume. High-resolution images formed by collecting the backscattered electron signal can give information about the size and spatial distribution of metal nanoparticles in supported catalysts. Low-voltage XEDS can provide compositional information of bulk samples with enhanced surface sensitivity and significantly improved spatial resolution. High-resolution SEM techniques enhance our ability to detect and, subsequently, analyze the composition of nanoparticles in supported metal catalysts. Applications of high-resolution SEM imaging and microanalysis techniques to the study of industrial supported catalysts are discussed.


Synthesis ◽  
2021 ◽  
Author(s):  
Tamao Ishida ◽  
Zhenzhong Zhang ◽  
Haruno Murayama ◽  
Eiji Yamamoto ◽  
Makoto Tokunaga

The C–H functionalization has been extensively studied as a direct C–C bond forming reaction with high atomic efficiency. The efforts have also been made on the reaction using supported catalysts, which are superior in terms of catalyst separation from the reaction mixture and reusability. In this review, an overview of the C–H functionalization reactions, especially for Pd and Au supported catalysts will be described. In particular, we discuss reaction mechanisms, active species, leaching, reusability, etc. 1 Introduction 2 Types of supported metal catalysts and their active species 3 Modes of C–H bond activation 4 Oxidative C–H C–H coupling of aryl compounds 5 C–H C–H coupling where one side is aromatic 6 C–H acylation of aromatic compounds and related reactions 7 Conclusion


2015 ◽  
Vol 54 (30) ◽  
pp. 8728-8731 ◽  
Author(s):  
René Kopelent ◽  
Jeroen A. van Bokhoven ◽  
Jakub Szlachetko ◽  
Jacinta Edebeli ◽  
Cristina Paun ◽  
...  

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