Browsing by Author "Ribeiro, M. Filipa"
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- Hydrogenating activity of Pt/zeolite catalysts focusing acid support and metal dispersion influencePublication . Mendes, Pedro S. F.; Lapisardi, Grégory; Bouchy, Christophe; Rivallan, Mickaël; Silva, João; Ribeiro, M. FilipaToluene hydrogenation was studied over catalysts based on Pt supported on large pore zeolites (HUSY and HBEA) with different metal/acid ratios. Acidity of zeolites was assessed by pyridine adsorption followed by FTIR showing only small changes before and after Pt introduction. Metal dispersion was determined by H2–O2 titration and verified by a linear correlation with the intensity of Pt0–CO band obtained by in situ FTIR. It was also observed that the electronic properties of Pt0 clusters were similar for the different catalysts. Catalytic tests showed rapid catalyst deactivation with an activity loss of 80–95% after 60 min of reaction. The turnover frequency of fresh catalysts depended both on metal dispersion and the support. For the same support, it changed by a 1.7-fold (HBEA) and 4.0-fold (HUSY) showing that toluene hydrogenation is structure-sensitive, i.e. hydrogenating activity is not a unique function of accessible metal. This was proposed to be due to the contribution to the overall activity of the hydrogenation of adsorbed toluene on acid sites via hydrogen spillover. Taking into account the role of zeolite acidity, the catalysts series were compared by the activity per total adsorbing sites which was observed to increase steadily with nPt/(nPt + nA). An increase of the accessible Pt atoms leads to an increase on the amount of spilled over hydrogen available in acid sites therefore increasing the overall activity. Pt/HBEA catalysts were found to be more active per total adsorbing site than Pt/HUSY which is proposed to be due to an augmentation in the efficiency of spilled over hydrogen diffusion related to the proximity between Pt clusters and acid sites. The intervention of Lewis acid sites in a greater extent than that measured by pyridine adsorption may also contribute to this higher activity of Pt/HBEA catalysts. These results reinforce the importance of model reactions as a closer perspective to the relevant catalyst properties in reaction conditions.
- Nanoscale insights into Pt-impregnated mixtures of zeolitesPublication . Mendes, Pedro S. F.; Taleb, Anne-Lise; Gay, Anne-sophie; Daudin, Antoine; Bouchy, Christophe; Silva, João; Ribeiro, M. FilipaA series of catalysts prepared by Pt deposition over intimate mixtures of HUSY and HBEA zeolites was investigated for the first time and compared to individual Pt/zeolite solids. The samples were characterized through macroscopic techniques and at the nanoscale by electron microscopy and electron tomography, in order to evaluate both the acid and the hydrogenation functions. Comparable macroscopic properties were observed between Pt-impregnated individuals and zeolite mixtures. In contrast, at the nanoscale, differences were evident. When mixtures of zeolites were impregnated, Pt was not homogeneously distributed over the sample. In fact, Pt was located mainly on the HBEA zeolite rather than on HUSY, as confirmed by TEM-EDS semi-quantification. This selectivity in Pt location was tentatively explained by the higher amount of terminal silanol and EFAL species in the HBEA sample. The preferential Pt location at the nanoscale may open up new possibilities in the design and application of hybrid catalysts.
- Quantification of metal-acid balance in hydroisomerization catalysts: a step further toward catalyst designPublication . Mendes, Pedro S. F.; Silva, João; Ribeiro, M. Filipa; Duchene, Pascal; Daudin, Antoine; Bouchy, ChristopheA methodology was developed to interpret the results of n-.paraffins hydroisomerization over bifunctional catalysts based on two simple kinetic models used consecutively. First, a macrokinetic model was used to obtain the corresponding turnover frequency over the acid sites and the maximum of C-16 isomer yield. Second, a dual-function model was used to correlate these catalytic descriptors to the ratio of metal to acid sites of the catalyst. To illustrate the methodology, Pt/HBEA and Pt/HUSY catalysts with different Pt loadings were evaluated. The impact of metal-acid balance on the catalytic turnover frequency and the maximal C-16 isomer yield were adequately captured for the bifunctional HUSY and HBEA catalysts. Moreover, the parameters of the dual-function model revealed to be intrinsic to the catalytic properties of the zeolite under the scope. This methodology is believed to be of interest for information-driven catalyst design for the hydroisomerization of n-paraffins.