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

Abstract

The kinetics of propane oxidation over Pt/Al 2 O 3 are investigated in this work as a function of O 2 /C 3 H 8 ratio in the 150-300 ˚C temperature range. At high O 2 /C 3 H 8 ratios, the platinum nanoparticles are saturated with oxygen and the reaction rate is zero-order with respect to the oxygen partial pressures in this regime. As the oxygen coverage decreases with decreasing O 2 /C 3 H 8 ratio, the reaction rate increases and the reaction order changes from zero-order to negative-order in the oxygen partial pressure. The reaction rate is controlled to a large extent by the oxygen coverage on the platinum nanoparticles. However, at lower temperatures and higher oxygen pressures there is a slow deactivation of the catalyst that cannot be explained by a slow change in the oxygen coverage. Diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTS) of adsorbed CO was performed to track the evolution of the nanoparticle structure over the course of the propane oxidation reaction and to determine whether the slow deactivation © 2016. This manuscript version is made available under the Elsevier user license http://www.elsevier.com/open-access/userlicense/1.0/ 2 was caused by reconstruction of the platinum nanoparticles. We found that the platinum nanoparticles are significantly reconstructed during the course of the reaction, including the formation of a platinum oxide (PtO) which has a characteristic CO-DRIFTS band at 2123 cm -1 .The extent of PtO formation decreases with increasing temperature and, as a result, deactivation of the catalyst is less severe at higher temperatures. Unexpectedly, increasing the oxygen partial pressure resulted in less PtO formation. We believe that a different platinum oxide phase (e.g. PtO 2 or Pt 3 O 4 ) is formed at higher oxygen pressures, which is reduced to metallic platinum during CO exposure at 25 ˚C, and therefore is not detectable by CO-DRIFTS. These results are unique because they show how the nanoparticle structure evolves over many hours of propane oxidation, and how the temperature and oxygen pressure influence the reconstruction of the nanoparticles, which has implications for a wide range of reactions not limited to propane oxidation.

Surface oxygenation of multicomponent nanoparticles toward active and stable oxidation catalysts

“…After propane oxidation for 5 min at 150 °C, peaks in regions A, B, and C were blue-shifted by ~10, ~20, and ~30 cm −1 , respectively. The increased CO adsorption capacity is evidenced by doubling of peak intensity, in contrast to the reduced adsorption capacity on Pt catalyst 11 , 24 . The CO adsorption characteristics showed little change after further propane oxidation at 200 °C for 1 h.…”

“…In contrast, Type II–V species were not detected for Pt catalyst, but Type I at 1727 (aliphatic ester, υ as (RC(=O)O)) and 1701 cm −1 (acetone, υ as ((CH 2 ) 2 C(=O))) were detected (Supplementary Fig. 7b ), which were less reactive and typically more strongly bonded on the surface 24 .

Fig.

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“…4a, b ). The apparent distribution ratio of the different species in terms of the sum of the peak area integral ( A ), as determined by , where LT represents the lower-temperature active Type II, IV, and V species, whereas HT represents the higher-temperature Type I and III species (based on a previous study of reactivities of these species on Pt catalysts 24 ), reveals DR ~ 6.3 for PtNiCo–PtNiOCoO and ~2.2 for Pt after 1500 s reaction (Supplementary Fig. 16a ).…”

“…During catalytic sweeping loops by varying O 2 /C 3 H 8 ratios a hysteresis was revealed and maximized at 5:1 ratio (Supplementary Fig. 18 ), revealing a higher activity in the backward sweep than the forward one, which is opposite for Pt catalyst 24 . It confirms the higher stability of Pt-sites on the catalyst.…”

Improving the Performance of BaMnO3 Perovskite as Soot Oxidation Catalyst Using Carbon Black during Sol-Gel Synthesis

“…All catalysts deactivate during successive NO x -TPR cycles, but BM-C700 shows the most stable performance. Therefore, although the BM-C700 catalyst shows a lower catalytic activity than the platinum-based catalyst used as a reference, the catalytic activity of the former remains after three consecutive cycles, while the platinum-based catalyst shows a deactivation, probably related to the sintering of platinum particles and/or to irreversible oxidation [61,62]. The same trend is observed for the CO 2 selectivity, being higher than 95% during the successive NO x -TPR cycles for all tested BM-CX catalysts.…”