Addition of potassium enhanced the activity of preferential CO oxidation on Pt/Al 2 O 3. The additive effect of potassium weakened the interaction between CO and Pt, and it also changed the CO adsorption site. FT-IR observation under the PROX condition suggests the presence of adsorbed species derived from O 2 and H 2 such as OH species, which can be related to the promoting effect of H 2 presence in the PROX reaction.

No abstract

In preferential CO oxidation in H 2 -rich stream (PROX), the additive effect of potassium on Pt catalysts was more remarkable over Al 2 O 3 than over SiO 2 , ZrO 2 , Nb 2 O 5 and TiO 2 . The additive effect of potassium to Pt/Al 2 O 3 was more effective than other alkali metals. Especially, the presence of H 2 drastically promoted CO oxidation over Pt/Al 2 O 3 modified with potassium. On the other hand, the suppressing effect of steam on the PROX was more significant over K-Pt/Al 2 O 3 than over Pt/Al 2 O 3 , although the PROX activity of K-Pt/Al 2 O 3 was much higher than that of Pt/Al 2 O 3 even under the presence of steam. The different effect of steam addition to the PROX over K-Pt/Al 2 O 3 3suggests that the active site can be Pt surface modified with potassium ions.

The promoting and negative effects of addition of alkali metals over Pt/Al 2 O 3 in preferential CO oxidation in H 2 -rich stream (PROX) were investigated in this work. The addition of alkali metals strongly influences the state of Pt metal particles, and coadsorbed species originating from H 2 and O 2 under the PROX condition can be found on highly active catalysts.Preferential CO oxidation in hydrogen-rich stream over Pt catalysts modified with alkali metals : Part II. Catalyst characterization and role of alkali metals Abstract The addition of alkali metals over Pt/Al 2 O 3 has both promoting and negative effects on the 2 catalytic performance in the preferential CO oxidation in H 2 -rich stream (PROX), therefore there is an optimum amount of alkali metal. The Pt/Al 2 O 3 catalysts modified with Na, K, Rb and Cs were characterized by means of transmission electron microscopy (TEM), extended X-ray absorption fine structure (EXAFS), X-ray absorption near-edge structure (XANES), and Fourier transform infrared spectroscopy (FTIR). The results show that the addition of larger amount of alkali metals with stronger basicity causes the aggregation of Pt metal particles. The Pt particles on Pt/Al 2 O 3 modified with alkali metals are more electron-deficient than those on Pt/Al 2 O 3 , and this weakens the strength of CO adsorption on Pt/Al 2 O 3 modified with alkali metals, which is related to the enhancement of turnover frequency of the PROX. In addition, in-situ FTIR observation suggests that the coadsorbed species originating from H 2 and O 2 (e.g., the OH species) under the PROX condition, which promote the CO oxidation, can be found on highly active catalysts.