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- Investigation of cooperative effects between Pt/zeolite hydroisomerization catalysts through kinetic simulationsPublication . Mendes, Pedro; Silva, João; Ribeiro, M Filipa; Daudin, Antoine; Bouchy, ChristopheA kinetic dual-function model was employed to simulate the performance of binary mixtures of Pt/zeolite catalysts (so-called hybrid catalysts) in the hydroconversion of n-paraffins. The catalytic activity and the maximal yield in feed isomers were simulated for mixtures of catalysts with distinct characteristics to investigate the conditions in which cooperative effects based on metal-acid balance may arise. Superior performances of the hybrids compared to both individual catalysts could be achieved in most of the simulated systems, particularly when mixing Pt-catalysts containing zeolites with dissimilar characteristics. A careful choice of the proportion and metal-acid balance of individual catalysts is, nevertheless, necessary. Moreover, the cooperation in the hybrid catalysts was rationalized based on the performance of the individual catalysts being mixed. The more alike the individual catalysts, to a certain extent, the broader the range of metal to acid sites ratio over which hybrids perform better than both individuals. On the other hand, the relative gain in performance arising from the cooperative effect would decrease. This study unveils hence the influence of each one of the preparation parameters of hybrid catalysts on its behaviour shedding light into the complexity of such catalytic systems.
- Study of Pt/MCM-22 based catalysts in the transformation of n-hexane: effect of rare earth elements and mode of platinum introductionPublication . Martins, Angela; Silva, João; Ribeiro, Fernando Ramôa; Filipa Ribeiro, M.The bifunctional transformation of n-hexane was carried out over Pt/MCM-22 based catalysts. MCM-22 was synthesized and submitted to ion exchange with rare earth nitrate solutions of La, Nd and Yb, followed by Pt introduction. Three different methods were used to introduce about 1 wt% of Pt in the zeolite: ion exchange, incipient wetness impregnation and mechanical mixture with Pt/Al(2)O(3). The bifunctional catalysts were characterized by transmission electron microscopy and by the model reaction of toluene hydrogenation. These experiments showed that, in the ion exchanged sample, Pt is located both within the inner micropores and on the outer surface, whereas in the impregnated one, the metal is essentially located on the outer surface under the form of large particles. The presence of RE elements increases the hydrogenating activity of Pt/MCM-22 since the location of these species at the vicinity of metal particles causes modification on its electronic properties. Whatever the mode of Pt introduction, a fast initial decrease in conversion is observed for n-hexane transformation, followed by a plateau related to the occurrence of the catalytic transformations at the hemicages located at the outer surface of the crystals. The effect of rare earth elements on the hydrogenating function leads to a lower selectivity in dibranched isomers and increased amounts of light products.
- 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.
- Effects of oxidante acid treatments on carbon-templated hierarchical SAPO-11 materials: synthesis, characterization and catalytic evaluation in n-decane hydroiosomerizationPublication . Bertolo, Raquel; Silva, João; Ribeiro, Filipea; Maldonado-Hodar, Francisco J.; Fernandes, Auguste; Martins, Ângela Maria PereiraHierarchical SAPO-11 was synthesized using a commercial Merck carbon as template. Oxidant acid treatments were performed on the carbon matrix in order to investigate its influence on the properties of SAPO-11. Structural, textural and acidic properties of the different materials were evaluated by XRD, SEM, N-2 adsorption, pyridine adsorption followed by IR spectroscopy and thermal analyses. The catalytic behavior of the materials (with 0.5 wt.% Pt, introduced by mechanic mixture with Pt/Al2O3), were studied in the hydroisomerization of n-decane. The hierarchical samples showed higher yields in monobranched isomers than typical microporous SAPO-11, as a direct consequence of the modification on both porosity and acidity, the later one being the most predominant. (C) 2014 Elsevier B.V. All rights reserved.
- From powder to extrudate zeolite-based bifunctional hydroisomerization catalysts: on preserving zeolite integrity and optimizing Pt locationPublication . Mendes, Pedro; Silva, João; Ribeiro, M Filipa; Daudin, Antoine; Bouchy, ChristopheThe development of zeolite-based hydroisomerization catalysts in the powder form is widely spread in scientific literature but shaped bodies are the ones being employed in industry. This work aims at bridging that gap. The shaping procedure for HUSY zeolite in presence of an alumina binder disclosed herein achieved a full conservation of zeolite properties, e.g. porosity and Brønsted acidity. When Pt was located inside the zeolite and an homogeneous Pt distribution along the extrudate was ensured, shaped Pt-containing catalysts had similar hydroisomerization performances to those of powder Pt/zeolite in terms of turnover frequency per Brønsted acid site and maximal feed isomers yield. Conversely, non-uniform distribution of Pt along the extrudates diameter (millimetric scale) was observed to reduce the feed isomers yield. This was tentatively explained by the lower local metal to acid sites ratio in the core of the extrudates. Optimal performance of shaped bifunctional catalysts requires, hence, an adequate metal to acid sites ratio throughout the whole catalyst (i.e. at millimetric and nanometric scale), even if full intimacy between catalytic functions is ensured at the nanoscale by the selective deposition of Pt inside the zeolite.