Acid Strength of Pt-Zeolite Catalysts: Evidence of Metal-Support Interaction from Linear Free-Energy Relationship

Abstract

The acid strength of Pt-HBeta and Pt-HMordenite zeolite catalysts were estimated by H/D exchange of substituted benzenes with the use of linear free-energy relationship, through the use of the Hammet-Brown equation. The results indicated that compared with the parent acidic zeolite, the incorporation of Pt metal leads to a significant decrease in the acid strength, estimated by the slope (q) of the logarithm of the relative rate (k X /k H ) with the r ? constant of the substituent, indicating a lower degree of proton transfer to the ring in the transition state.The results support the model of metal-support interaction in Pt-zeolite catalyst, with formation of a metal-proton adduct.

Effect of Noble Metals on the Strength of Brønsted Acid Sites in Bifunctional Zeolites

“…Furthermore, this decrease of the strength of the Brønsted acid sites was found to be more pronounced for Ir‐modified zeolites Y and Beta than for the Pt‐modified materials. The observed decrease of acid strength upon Pt modification agrees well with the results of Tourinho et al 12. who investigated H/D exchange rates of substituted benzenes and the thermodesorption of n ‐butylamine on zeolites Pt/Beta and Pt/mordenite.…”

“…and Kubička et al 10. The formation of specific metal‐proton adducts with a lower acid strength, as suggested by Tourinho et al.,12 however, would lead to new 1 H MAS NMR signals in the spectra of noble‐metal‐modified zeolites, which were not observed in this study.…”

“…In an earlier study,11 evidence was obtained by the same group for the effect of the zeolite structure type and the Pt loading on the strength of the acid sites by using pyridine adsorption on Pt‐modified zeolites Y, mordenite, and Beta in comparison with the same materials in their H,Na forms. Very recently, Tourinho et al 12. investigated the acid strength of Si(OH)Al groups in Pt‐modified mordenite ( n Si / n Al =6) and zeolite Beta ( n Si / n Al =14) by evaluating the H/D exchange rates of substituted benzenes and the thermodesorption of n ‐butylamine.…”

Catalytic upgrading of vegetable oils into jet fuels range hydrocarbons using heterogeneous catalysts: A review

“…On the other hand, heteropoly acids can provide the desired acidity but are subject to quick deactivation by solvation and are of poor thermal stability. The various inconsistencies with these materials therefore attributed a shift by the refineries to zeolite-based catalysts [103], [107] and [108]. Reactions over zeolites are strongly dependent on structure-acidity properties and these are in turn critical for the hydroisomerization process.…”

Green Acetylation of Solketal and Glycerol Formal by Heterogeneous Acid Catalysts to Form a Biodiesel Fuel Additive

“…A recent study on the free energy relationship with acidic strength of solid acid catalysts showed that the acid strength varied in the order Amberlyst‐15>zeolite Beta>niobic acid>K‐10 Montmorillonite, whereas n ‐butylamine thermodesorption showed strong/weak acidity ratios in the order of zeolite Beta>K‐10 Montmorillonite>niobic acid 18. 19 Amberlyst‐15 could not be measured by this method due to its low thermal stability. Niobium phosphate is expected to have a higher acid strength than that of niobic acid from NH 3 adsorption studies;20 however, this technique measures both Lewis and Brønsted acid sites, which may not both be catalytically active 16.…”