Physico-Chemical nanomaterials science

Multi-walled carbon nanotubes catalytic properties in hydrogenation of organic compounds
Bychko I.B.1, Strizhak P.E.1
1 Institute of Physical Chemistry, National Academy of Sciences of Ukraine, Nauki Prospect 31, 03039 Kyiv, Ukraine.
E-mail: igorbychko@ukr.net

Multi-walled carbon nanotubes (MWCNTs) is considered as alternative to the conventional catalyst supports for a number of reasons. Also, according to the high stability of carbon materials to the carbonization, a development of novel carbon materials for hydrogenation and dehydrogenation is of great interest. In this work, we give our report on the MWCNT catalytic properties as a catalyst for the ethylene, and acetylene hydrogenation.
The hydrogenation reactions were investigated on the MWCNT, which structure was characterized by TEM, SEM, XPS, Raman spectroscopy, and Boehm titration. Results indicate that catalytic reaction occurs on the MWCNT-400 surface with sufficiently high defectiveness, low oxygen content, and a basic surface in a presence of hydroxyl and carbonyl groups.
Our experiments show that raw MWCNTs are not active, while treatment in hydrogen or argon at elevated temperatures is a prerequisite for catalytic activity appearance. The ethylene conversion increases from 0,2% at 100 oC to 18,5% at 300 oC, and the ethylene hydrogenation rate increases from 2,5•10-9 mol•s-1•m-2 to 2,1•10-7 mol•s-1•m-2 respectively. The acetylene conversion increases from 3% at 80oC to 90% at 350oC and the hydrogenation rate increases from 4,7*10-8 mol*s-1*m-2 to 1,4*10-6 mol*s-1*m-2 respectively. The selectivity to ethylene increases dramatically at low temperatures from 30% at 80oC to 60% at 100oC, and then gradually increases to 85% at 350oC and 90% at 400oC 
Also, our experiments indicate a fairly high stability of MWCNTs in a comparison with the typical hydrogenation catalysts in both, hydrogen-rich and ethylene-rich, atmospheres. This offers new opportunities for the carbon nanotubes-based catalysts application in the hydrogenation reaction at high temperatures, in particular, under conditions when the metal-containing catalysts deactivate due to the carbonaceous deposits formation.