(242d) Hydrogen Production Over Carbon Nanotube Supported Platinum Catalyst: Effect of Oxygen Functionalization On Catalysis
Hydrogen production from aqueous phase reforming (APR) has been carried out on a large variety of different supports by many research groups. We have shown that carbon nanotubes (CNT), including both single-walled carbon nanotube (SWNT) and multi-walled carbon nanotube (MWNT), work as good catalyst supports for platinum (Pt) in APR. In order to increase the dispersion of the Pt catalyst, the CNT supports were subjected to nitric acid functionalization. The HNO3 treatment created some defects on the CNT tube walls, thus increased the specific surface area of the CNT supports. However, the treatment also introduced some oxygen-containing groups on the CNT surface.
With the increased surface area, the HNO3 treated CNT supports do improve the Pt dispersion, but the APR activity does not increase with the increase of dispersion. On the contrary, the APR activity decreases on the HNO3 treated CNT supports in terms of turnover frequency (TOF): the TOF on HNO3 treated MWNT is less than half of the TOF on raw MWNT, and for SWNT, the conversion dropped to almost zero after HNO3 treatment. The activity can be recovered by removing the oxygen containing groups via high temperature annealing, presumably leaving the carbon defects as anchors for the Pt particles.
To further investigate the effect of the oxygen containing groups, different hydrogen reforming reactions, including both steam reforming and liquid phase reforming, both hydrocarbons and oxygenates, have been carried on the CNT supported catalyst with different oxygen containing groups. A comparison of these reaction results suggests the nature of oxygen containing groups' effect on catalysis.