Platinum Metals Rev., 1965, 9, (1), 6
The Release of Hydrogen Atoms from the Surface of a Platinum Catalyst
Gaseous or Superficial Migration?
The reduction of yellow tungsten oxide, WO3, to the blue W4O11 is effected at room temperature by hydrogen atoms but not by hydrogen molecules and so this reaction can be used as a means, both qualitative and quantitative (1), for the detection of hydrogen atoms. Khoobiar, of Esso Research and Engineering Company, has recently shown (2) that when molecular hydrogen is passed at 50°C over a mechanical mixture of platinum on γ-alumina reforming catalyst and WO3, a blue coloration appears immediately. This indicates that hydrogen atoms have been formed on the platinum surface and that they have migrated over the alumina support (possibly as protons) before reaching the WO3 which is then reduced. A mixture of WO3 and γ-alumina had to be heated to 200° before any sign of reduction appeared.
Kohn and Boudart, working at the University of California, have reported some further related experiments (3). They observed that on mixing reduced platinum-alumina catalyst with WO3 in hydrogen no visible reaction occurred at room temperature, but on admission of oxygen the gradual appearance of the blue coloration was noted. They concluded that the migration of hydrogen atoms occurs through the gas phase, hydrogen atoms being released from the platinum surface by the reaction
This interesting system deserves further attention, especially since it could provide a ready means of assessing the state of dispersion of platinum on its support.
- 1 H. W. Melville and J. C. Robb, Proc. Roy. Soc, 1956, A196, 445
- 2 S. Khoobiar, J. Phys. Chem., 1964, 68, 411
- 3 H. W. Kohn and M. Boudart, Science, 1964, 145, 149