Pressure‐Dependent Effect of Hydrogen Adsorption on Structural and Electronic Properties of Pt/γ‐Al₂O₃ Nanoparticles

Abstract

Understanding the interaction of hydrogen with subnanometer platinum nanoparticles (NPs) under industrially relevant conditions is of great importance to heterogeneous catalysis. In this work, we investigate the pressure‐dependent changes in hydrogen coverage on size‐ and shape‐selected Pt/γ‐Al2O3 NPs by in situ X‐ray absorption near‐edge structure (XANES) analysis. Difference XANES calculations revealed an increase in the H/Pt ratio from 1.9 to 2.5 upon increasing the hydrogen pressure from 1 to 21 bar at room temperature (1 bar=100 kPa). In addition, extended X‐ray absorption fine structure measurements of the local geometrical structure showed changes in PtPt bond length and coordination number, revealing a morphological transformation in the NPs from a 2 D to a 3 D shape under increasing H2 pressure at room temperature. Such shape evolution leads to a decrease in the NP–support contact area and is thus expected to affect the NP stability against coarsening.

Perspective of Surfactant‐Free Colloidal Nanoparticles in Heterogeneous Catalysis

“…[10,[95][96][97][98][99][100][101] Yet, cluster-sized NPs or even atom-doped catalysts do not generally achieve the highest catalytic activity apart from stability issues [88,89] and are also often prone to degradation under reactive atmospheres. [5,9,16,86,102] The catalyst degradation mechanisms are caused e. g. by changes of the carrier surface structure (for example carbon corrosion and particle detachment) or of the nanoparticles (for example agglomeration, Ostwald ripening or NP dissolution). [13] To that end, Meier et al correlated the catalyst stability to the average inter-particle distance (AID) and proposed a design rule for electrocatalysts used under ambient temperature conditions where highest stability can be achieved if AID values are kept greater than 25 nm.…”

“…However, under reaction conditions, active sites often tend to degrade and lose the initial selectivity or overall activity e. g. because of morphology changes due to structural rearrangements, [5][6][7][8][9][10][11] partial loss of catalyst components [12,13] or by-product poisoning. [12,14] Typical mechanisms describing the degradation of active sites are among others Ostwald ripening, [7][8][9]11] dealloying, [15] sintering, [12,16,17] and coking. [12,14] These processes naturally lead to a diminished active surface area and a total number of active sites per mass unit (of catalyst).…”

Density functional theory simulations of complex catalytic materials in reactive environments: beyond the ideal surface at low coverage

“…140,165 Experimental characterization is currently being performed to validate some key-features of our theoretical study, in our team and by other research groups. 140 The impact of tin on the interaction with hydrogen is also being investigated. Other perspectives are oriented towards the reactivity of such particles with alkanes having a longer chain length.…”

Aberration‐Corrected Transmission Electron Microscopy and In Situ XAFS Structural Characterization of Pt/γ‐Al2O3 Nanoparticles

“…Supported Pt nanoparticles have been extensively studied previously by a plethora of techniques including electron microscopy, X‐ray absorption spectroscopy, and a range of other techniques . An important parameter for controlling the structural and chemical properties of supported metal nanoparticles is the reduction treatment during which cluster formation occurs.…”

“…Supported Pt nanoparticles have been extensivelys tudied previously by ap lethora of techniques including electron microscopy, [2][3][4] X-ray absorption spectroscopy, [5][6][7][8][9][10][11][12] and ar ange of other techniques. [13] An important parameter for controlling Aberration-corrected( AC) STEM,A CT EM and in situ X-ray absorptionf ine structure spectroscopy (XAFS) wereu sed to characterizet he Pt clusters present on a0 .35 wt %P to ng-alumina support after reduction in hydrogen at 700 8C.…”