2016 Volume 37 Issue 11 Pages 560-566
The role of promoting materials for the preferential oxidation (PROX) reaction of CO in H2 on Pt-catalysts was elucidated by using the Pt-catalyst supported on a CNT with Ni-MgO at its terminal end and the CNT-p with no Ni-MgO. The role of Ni-MgO is not the synergy effect on the Pt but set up a new catalytic oxidation reaction cycle of CO in the presence of H2O. The dynamic In-situ IR spectroscopy suggested the rate determining slow step of HCOO + OH → CO2 + H2O, where H2O molecule plays like a molecular catalyst in cooperation of Pt and promoting materials. The contribution of H2O is expressed by n(CO + 1/2O2) + H2O → n CO2 + H2O, where n is CO2 molecules by one H2O molecule staying on the surface. According to this new concept, the selectivity is given by n/(n+1), which takes 50%∼100% depending on the staying time of H2O on the catalyst. The mysterious high selectivity reported on the Pt-nano rods in SiO2-nano-tube and the curious selectivity on Au/CeO2 depending on the crystal shape of CeO2 are well rationalized by this new mechanism.
