Thermokinetic and Spectroscopic Mapping of Carbon Monoxide Adsorption on Highly Dispersed Pt/γ-Al₂O₃

Abstract

The understanding and quantification of the CO adsorption modes and strength on ultradispersed platinum catalysts supported on γ-Al2O3 is of prominent importance for analytic and catalytic purposes. We report a multiscale experimental (AEIR, CO-TPD) and theoretical approach to provide vibrational properties, adsorption enthalpies, and desorption behaviors. First principles calculations on Pt13(CO) m /γ-Al2O3 and Pt(111) surface models (using various exchange-correlation functionals) provide a complementary view to experimental approches. Adsorption enthalpies computed with the RPBE functional appear to be the most compatible with the AEIR results. The occupation of top sites by CO dominates the behavior of supported Pt clusters. CO coverage reaches higher values in comparison to Pt(111) for similar operating conditions, and considerable cluster reconstruction is observed at high coverage. First principles calculations also confirm the IR assignment related to the various adsorption modes on top and bridge sites and demonstrate a particle size effect, lowering the frequency of linear adsorption at top sites with respect to extended Pt(111) surfaces. Finally, first principles-based microkinetic modeling of CO-TPD experiments shows that the adsorption strengths predicted on the small-size cluster by DFT are compatible with the experimental values. We discuss possible reasons for the experimental desorption pattern to be much broader than the computed pattern.

Mechanistic Understanding of Ring-Opening of Tetrahydrofurfuryl Alcohol over WOx-Modified Pt Model Surfaces and Powder Catalysts

“…To examine whether WO x loading resulted in deposition on the surface of Pt nanoparticles, the adsorption of CO as a probe molecule was investigated using DRIFTS (Figure b). Such measurements reveal the electronic and structural characteristics of Pt sites by observing the vibrational frequency of the CO bond, ,− and adsorption of CO on WO x is not expected at room temperature . While STEM images demonstrated that WO x existed indiscriminately across the catalyst surface, previous work has demonstrated that the WO x structure evolves dynamically under reaction conditions, leading to the decoration of reduced metal nanoparticle surfaces. , To explore this, particularly following the reduction of the catalyst before catalytic activity measurements, catalysts were pretreated at 598 K in 10% H 2 /Ar to dehydrate the catalyst, fully reduce Pt, and facilitate WO x mobility prior to CO adsorption.…”

Structure, Location, and Spatial Proximities of Hydroxyls on γ-Alumina Crystallites by High-Resolution Solid-State NMR and DFT Modeling: Why Edges Hold the Key

“…Aluminas are highly valued materials for their versatility in various catalytic processes such as biomass conversion, 1,2 olefin metathesis, 3,4 natural gas conversion, 5 petrochemistry, 5,6 and exhaust gas cleaning, 7,8 as a result of their tunable surface physicochemical properties. 6 γ-Alumina (γ-Al 2 O 3 ) is one of the most widely used alumina polymorphs.…”

“…Aluminas are highly valued materials for their versatility in various catalytic processes such as biomass conversion, , olefin metathesis, , natural gas conversion, petrochemistry, , and exhaust gas cleaning, , as a result of their tunable surface physicochemical properties . γ-Alumina (γ-Al 2 O 3 ) is one of the most widely used alumina polymorphs. , Since the early work of Knözinger and Ratnasamy, the nature and atomic-scale structure of surface hydroxyl (−OH) groups on γ-Al 2 O 3 surface have been thoroughly examined using various spectroscopic − and computational approaches. ,,− This extensive search for an ever more refined determination of the γ-Al 2 O 3 surface chemistry is motivated by the need to better control, on the one hand, the intrinsic reactivity driven by the Brønsted and Lewis surface sites for various reactions, , and on the other hand, the grafting, impregnation, and activation of metal precursors on γ-Al 2 O 3 acting as a catalytic support. ,, However, the surface structural features of γ-Al 2 O 3 are still questioned due to its complexity at multiple scales, from crystallite morphology to crystallinity or hydration level.…”

The Role of Sulfur in the S‐PtRe/Al2O3 Catalysts: The Endogenous Deposition Effect on the Metal/acid Micro‐environment

“…Alumina‐supported catalyst is widely used for industry catalytic processes due to their high structural stability and low cost [1–7] . However, there are also disadvantages of insufficient surface active sites and inappropriate electronic structure, which do not facilitate the catalytic process.…”