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Abstract: A parent acidic H-BEA with crystallites very small in size and high external surface area was used to prepare a series of materials loaded with increasing Cs+ contents by firstly ion-exchange and then impregnation with CsOH solutions. The monitoring of the ion-exchange process by chemical analysis and by IR spectroscopy in presence of CO or NH3 reveals that a relevant amount of Brønsted acid sites in dehydrated H-BEA is related to framework Al sites that, in aqueous solution, turn into partially extraframework Al species unable to act any longer as sites of cationic exchange. This limits the exchange capacity in solution and higher levels of ion-exchange are attained by subsequent impregnation and calcination. A possible explanation for such a behaviour is proposed. The formation of carbonates by adsorption of CO2, monitored by IR, confirms that the basic character induced on framework oxygen atoms by exchange of H+ with Cs+ is significantly weaker than that reached upon Cs-overloading. For the latter, the strong basicity is related to the presence of Cs2O-like nanoparticles (also detected by EXAFS), dispersed within the zeolite pores (as shown by pore volume and TEM/EDX measurements). IR spectroscopy of adsorbed CO shows that Cs+ as countercations or as surface sites of occluded Cs2O-like species exhibit a similar Lewis acid strength. Noticeably, in Cs-overloaded BEA, pairs of Cs+ sites (formed by two countercations and/or one countercation and a Cs+ at the surface of Cs2O-like particles) are present, where CO can be adsorbed in a head–tail form, producing a distinct ν CO band at 2145cm−1. [Copyright &y& Elsevier]

Abstract: Various acido-basic BEA zeolites having different Cs contents and containing supported Pt particles were prepared using two acidic parent BEA supports with same framework Al content but with strongly different morphology of the zeolite crystallites. In spite of highly different exchange capacities in aqueous solution, the two parent BEA supports behaved similarly towards formation of Cs-oxide like nanospecies. Thus, the addition of a similar amount of Cs was necessary in the two samples to extinguish all Brønsted acidic sites and a further introduction of Cs led to the presence of highly dispersed Cs2O like species with strong basic character as shown by the adsorption of CO2 followed at 293K by FT-IR spectroscopy. FT-IR experiments were also conducted at 100K and 293K using CO as probe molecule to give further insights on the Cs and reduced Pt species, respectively. In the presence of co-hosted Cs-oxide like, highly dispersed Pt0 nanoparticles are formed with sizes close to 1nm as observed by TEM. Both the high dispersion of the Pt0 nanoparticles in the more basic samples and the phenomenon of electro-donation by the basic support contribute to the changes in electronic behaviour of the Pt0 particles shown by FT-IR of adsorbed CO. [Copyright &y& Elsevier]

A parent acidic H–BEA sample characterised by crystallites with very small sizes and high external surface area has been used to prepare a series of Pt/Cs–BEA catalysts. The exchange three times of the highly defective H–BEA in a 0.5 M CsCl solution allowed to exchange only about half of the protons, as evaluated from both chemical analysis and FTIR spectroscopy in the presence of adsorbed NH3. The further exchange by Pt(NH3)4 2+ followed by impregnation with CsOH, calcination and finally reduction, led to a series of Pt/Cs–BEA samples with progressive increase of the caesium loading and concomitant change of the reducibility of the calcined Pt species and decrease of the size of the reduced Pt particles. The analysis of the FTIR data in the νOH and δNH ranges indicates a progressive removal of the protons. Finally, the selectivities to cracking, isomerisation, and aromatisation during conversion of n-hexane are in line with the variations of acido–basicity and Pt particle sizes in the samples. [Copyright &y& Elsevier]