Many authors reported chemisorption of hydrogen on nickel, but they said nothing about the conditions they used. But this kind of experiment is less obvious as it seems. What are the best conditions for observing the phenomenon by pulse chemisorption analysis coupled with TCD ? We used several samples containing from 1 to 40 wt.% of Ni nanoparticles supported on carbon. Prior to the pulse chemisorption experiment (at 303K), the samples were reduced by an Ar/H2 (10%) mixture at 973K, and then were cooled down under pure Ar to 303K. A 1 cc injection loop was used and the sample mass varied from 0.05 to 0.4g. We could never observe chemisorption with the TCD detector (even with 0.4g of the 40 wt.% Ni sample). What could be the reason of this? Poisoning, too big loop? Have we done something wrong, or forgotten an important detail ? Any suggestions ?
Thank you in advance.
We have had the same problems with Ni. Because our loop was one of high volumen (we have three 0.5, 1 and 5 cc), we sent our samples to other lab (Instituto de Catálisis y Petroleoquímica,ICP- CSIC) with lower volumen loop (0.1 cc), and the result was the same: no H2 chemisorption. Because we cannot change easily the reducing atmosphere (10% H2/Ar), at ICP-CSIC also change the H2 content of the mixture, without again positive results. We also tried with CO instead of H2, but with the same problems. Our idea is that there is a kinetic problem with Ni chemisorption and the pulse chemisorption method is not the adequate one for this metal. The most adequate should be the static method to obtain the complete chemisorption isotherm, But it is difficult to find a lab with this equipment. Micromeritics ASAP2020 has a chemisorption module to incorporate to the equipment, but I do not know the price of it.
Dear Prof. Alain
it can be related to contamination nano Ni with oxygen. Although, the nano particles were reduced, it looks that the reduction was not enough. The same behavior was also observed for TiC-based cermets. As suggested, reduction can be improved by vacuum furnace at 1200 C for 1h, subsequent the nano particles coated by Zn solution. For more information, kindly find attachment file and look to highlighted section.
Hi Alain:
The reduction of the Ni sample was carried out at 970 K that is similar to the values reported in the literature. After the sample is reduced, you should increase the temperature to approximately 450 K until you can detect the first hydrogen desorption signals by your TCD. My understanding of your question is that you only keep the sample temperature at 303 K, which is not high enough.
See also the following paper, specifically its Fig.3, which might be useful
J. Hazardous Materials 211-212, 208 (2012).
Muhammad
The situation addressed some months ago by Dr. Alain Celzard and debated by other fellow researchers is really captivating, and has been also observed in our own studies devoted to the characterization of unsupported Ni nanoparticles (NiNPs). We have been preparing NiNPs by thermal decomposition of Ni(CH3COOH)2.H2O, an easy one-pot route to obtain carbon-encapsulated NiNPs that can be safely stored unprotected as a dry powder for months without any noticeable oxidation. We were taught that the carbonaceous layer not only conveniently avoids adverse air oxidation but also entirely discards the fixing of hydrogen by conventional pulsed chemisorption. Before this interesting discussion in researchgate, we thought that this performance was somehow distinctive of our NiNPs and not a trend also observed by others in open literature. Does anyone know if Alain have had any progress in his quest for true hydrogen chemisorption in his carbon-supported NiNPs?
I am also facing the same problem with various loading of Ni on Alumina. I have tried various weights also with the AMI 200 in my lab. What I could gather is, Ni as a metal has always been a trouble to decipher using H2-Chemisorption. Other indirect approaches like TPD helps to get percentage of metal dispersion.
- Badges
- Science topic
- Similar topics
- Chemistry
- Nanotechnology
- Nanoparticle Research