On the origin of high-temperature phenomena in Pt/Al₂O₃

Abstract

Treatments of Pt/γ-AlO with H under harsh conditions have long been known to strongly influence the properties of this important catalytic system, but the true causes of the high-temperature effects still remain unclear. We have performed a more detailed study of this issue, having used H-TPD as a sensitive probe of metal-support interactions. The experimental results are in accordance with previous studies and demonstrate strong changes in adsorption and catalytic properties of Pt/γ-AlO after high-temperature H treatments, as well as the possibility to reverse the changes, completely or in part, through O and HO treatments. Thorough examination has shown that such behaviour is an intrinsic property of Pt/γ-AlO and cannot be attributed to impurities or experimental artifacts. Moreover, there is no abrupt transition to a high-temperature state, but the system undergoes smooth and gradual changes upon increasing the H-treatment temperature (T), with the changes being already apparent at a T of ∼ 300 °C. The results suggest that hydrogen can generate oxygen vacancies on the surface of the support in close vicinity to the Pt particles, and the system appears under equilibrium to be kinetically driven by temperature and thermodynamically driven by the P/P ratio or local concentration of surface hydroxyls near Pt particles. The generated vacancies change the properties of contacting particles, and the changes are most pronounced for sub-nanometric Pt clusters and single atoms. Implications of the phenomena for the synthesis, study, and use of Pt/γ-AlO and its related nanosystems are discussed.

Characterization and Hydroisomerization Performance of Mg‐Promoted, Pt/ZSM‐23‐Based Catalysts

“…The position of TPR peak for Pt/γ‐Al 2 O 3 was dependent on concentration of supported Pt (0.1–2.5 wt. %) but the peak temperature still remained within 200–300 °C and the size of final Pt particles within 1–2 nm [28c] . The latter is in accordance with the high CO/Pt values for ZA‐based samples in Table 3.…”

Construction of Nanoreactors Combining Two-Dimensional Hexagonal Boron Nitride (h-BN) Coating with Pt/Al2O3 Catalyst toward Efficient Catalysis for CO Oxidation

“…In addition, some of the hydroxyl groups formed on the alumina surface can also react with CO to form carbonates, which are converted to CO 2 . This process plays a subsidiary role in the catalytic performance. , …”

“…However, moisture present in the precursor binds to lattice oxygens in alumina at high temperatures, and this results in retention of −Al–OH, which can react with CO under suitable conditions to form carbonate, which decomposes to CO 2 . This accelerates the conversion of CO in the subsidiary to a certain extent. , Figure b shows the XRD patterns of Pt/Al 2 O 3 , Pt/Al 2 O 3 -800, Pt@h-BN/Al 2 O 3 , and Pt@h-BN/Al 2 O 3 -800. The standard PDF files are included to facilitate comparison.…”

“…This process plays a subsidiary role in the catalytic performance. 35,36 Figures 2a and 2c show TEM and HR-TEM images, respectively, of the Pt@(h-BN) 3 /Al 2 O 3 catalyst. Figure 2a shows Pt particles ∼5 nm in diameter, observed as black spheres in the core, uniformly distributed on Al 2c shows the morphology and particle size of the sample.…”

“…This accelerates the conversion of CO in the subsidiary to a certain extent. 35,36 Figure 3b shows the XRD patterns of Pt/Al 2 O 3 , Pt/ Al 2 O 3 -800, Pt@h-BN/Al 2 O 3 , and Pt@h-BN/Al 2 O 3 -800. The standard PDF files are included to facilitate comparison.…”