Subsurface Oxygen on Pt(111) and Its Reactivity for CO Oxidation

Abstract

Temperature has an important effect on the dissociative adsorption of molecular oxygen on platinum surfaces. Here, we show that if the substrate temperature is increased to 400-600 K, the total amount of oxygen loaded onto Pt(111) can be more than twice the well-established maximum coverage of 0.25 ML. While low energy electron diffraction and STM reveal a conventional p(2 9 2) structure of the topmost layer, temperature programmed desorption measurements indicate that additional oxygen is stored under the surface of platinum. Reactivity measurements show that this sub-surface oxygen layer does not lower the activity of such platinum surface towards CO oxidation. Therefore, while sub-surface oxygen layer does form under catalytically relevant temperatures on Pt(111), it has no great influence on the oxidizing ability of such surface. This sheds new light on the initial stages of platinum oxide formation, and may help bridge the understanding of catalytic oxidation of CO on Pt in ultra high vacuum and in high-pressure catalysis studies.

Deactivation of Pt/Al2O3 during propane oxidation at low temperatures: Kinetic regimes and platinum oxide formation

“…The increasing extent of platinum oxidation with decreasing temperature in the 200-300 °C range is not surprising. Bashlakov et al [46] showed that the maximum uptake of oxygen on Pt(111) occurred around 500 K (227 °C), and 20 decreased with increasing temperature up to 800 K. This trend of increasing extent of oxidation with decreasing temperature is consistent with our hypothesis that platinum oxide formation is responsible for deactivating the catalyst: slow deactivation of platinum ( Figure 4) is only observed at lower temperatures and higher O 2 /C 3 H 8 ratios. With increasing temperature, the main absorption band near 2094 cm -1 decreases in intensity and shifts to lower wavenumber.…”

“…A more plausible explanation is that increasing the O 2 /C 3 H 8 ratio from 5 to 20 results in the formation of a different oxide phase which interacts differently with CO. This hypothesis is supported by a wide body of literature which indicates that there are many types of platinum oxides that are formed on the surface of platinum nanoparticles during oxidation reactions-including PtO [51,52], Pt 3 O 4 [53,54], PtO 2 [51,[53][54][55][56][57], and subsurface oxide [14,16,46]-and the formation of these oxides depends on a number of factors including the oxygen coverage. For example, it has recently been shown that oxide growth on Pt(111) proceeds through several phase transitions with increasing oxygen coverage [19].…”

“…The structure of this highly reactive oxide has been identified as PtO 2 [55,57] and Pt 3 O 4 [54]. On the contrary, several experimental studies [18,46,50,53,54,60] show that platinum oxides are inactive for CO oxidation near room temperature. The structure of the low activity oxides has been identified as PtO 2 [53,54,60] and Pt 3 O 4 [53], which were also the oxide phases identified as highly reactive.…”

It's not just the defects – a curved crystal study of H2O desorption from Ag

“…The Omicron STM system has been described in detail before. 13 Spatially resolved temperature-programmed desorption (TPD) experiments were carried out in a third UHV chamber with a base pressure of 9 Â 10 À11 mbar as measured with a uncalibrated cold cathode pressure gauge (Pfeiffer IKR 261). This system has been described previously as well.…”

Catalytic Oxidation of CO on a Curved Pt(111) Surface: Simultaneous Ignition at All Facets Through a Transient CO-O Complex

“…[1][2][3][4] Pt itself is of the upmost importance as a catalyst for car exhaust cleaning or for the water gas shift reaction, 5,6 whereas Pt crystal surfaces are model systems for investigating the catalytic CO oxidation at the atomic scale. [7][8][9][10][11][12] In the last four decades many researchers have studied the separate, sequential and simultaneous interaction of CO [13][14][15][16][17][18][19][20][21][22][23] and oxygen [24][25][26][27][28][29][30][31][32][33][34][35] with Pt crystal surfaces under High or Ultra-High Vacuum (HV or UHV) conditions. All such works have provided a good description of fundamental steps in the reaction, such as O 2 dissociation, 8 CO and O chemisorption, [13][14][15]21,27,28 and CO-O interaction.…”