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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.
- Enhancement of sintering resistance of CaO-based sorbents using industrial waste resources for Calooping in the cement industryPublication . Teixeira, P.; Mohamed, Ismail; Fernandes, Auguste; Silva, João; Ribeiro, M Filipa; Pinheiro, CarlaKeeping a high stability and CO2 capture capacity of CaO-based sorbents during the Ca-looping process is still a challenge. The main goal and the innovative idea addressed in this study consists of investigating if solid industrial waste resources such as a coal fly ash (CFA) and a spent Fluid Catalytic Cracking (SFCC) catalyst, can be used as particle spacers to improve the sintering resistance of two CaO-based sorbents. These two inert industrial waste materials are used in the present work for increasing the CaO particles separation and consequently, reducing their coalescence and hindering severe sintering at the high Ca-looping temperatures. There are currently no studies in the literature on the use of industrial SFCC wastes in blends with CaO based sorbents acting as CaO particles spacer with the objective of reducing the Ca-looping sorbents deactivation along the cycles of carbonation-calcination. Despite the mineralogical and textural differences between the CFA and SFCC catalyst industrial wastes, the tests carried out in a fixed bed laboratory reactor showed that the addition of a small fraction of waste to the CaO sorbent (ca. 10%) seems to be an interesting option to improve the CO2 capture technology efficiency. During the Ca-looping, the volume and stability of sorbent mesopores is essential to achieve higher and stable carbonation conversion values, and since the CFA and SFCC increase the SBET, they contribute to enhance the sintering resistance. The innovative results presented in this study show that the industrial CFA and SFCC wastes have potential to be an economically attractive option thus contributing to reduce the cost of the Ca-looping cycle CO2 capture process, as well as to minimize the adverse environmental impacts of the high volume of industrial wastes generated.
- Elucidation of the zeolite role on the hydrogenating activity of Pt-catalystsPublication . Mendes, Pedro; Gregório, André F. C.; Daudin, Antoine; Bouchy, Christophe; Silva, João; Ribeiro, M FilipaToluene hydrogenation was studied over model catalysts with a fixed hydrogenating function (Pt/Al2O3) mechanically mixed with either HUSY or HBEA zeolites. Such mechanical mixtures showed improved platinum turnover frequencies compared to single Pt/Al2O3. Comparing to Pt-impregnated zeolite catalysts, the mechanical mixtures have lower activities per site showing that the contribution of acid sites decreases (and so the hydrogenating activity) with increased distance between Pt clusters and acid sites. Therefore, toluene hydrogenation can be used as a powerful tool to evaluate Pt-acid site intimacy in bifunctional catalysts.
- Interplay of the adsorption of light and heavy paraffins in hydroisomerization over H-beta zeolitePublication . Mendes, Pedro S. F.; Chizallet, Céline; Pérez-Pellitero, Javier; Raybaud, Pascal; Silva, João; Ribeiro, M Filipa; Daudin, Antoine; Bouchy, ChristopheThe effect of pressure on the activity and selectivity of well-balanced Pt/H-beta zeolite bifunctional catalysts in n-hexadecane (n-C16) hydroisomerization was studied. The turnover frequency per Brønsted acid site of the catalyst decreased when the total pressure was increased due to the lower concentration of olefins at equilibrium, in line with the classical bifunctional mechanism. Conversely, when the total pressure was increased, the C16 isomer yield unexpectedly decreased in contradiction with the pure kinetic/ thermodynamic effect of olefin pressure on the reaction rates. Thanks to grand canonical Monte Carlo (GCMC) calculations, non-idealities in adsorption behavior in the zeolite micropores were revealed when a representative reaction medium was considered. Via mechanistic kinetic simulations combined with GCMC simulations for the relevant intermediate concentrations, the pressure effect on catalyst selectivity is proposed to be due to the interplay between the (light) cracked products and the (heavy) hexadecanes in the pores of beta zeolite which leads to a pressure dependency on the adsorption behavior.
- A systematic study on mixtures of Pt/zeolite as hydroisomerization catalystsPublication . Mendes, Pedro; Marques Mota, Filipe; Silva, João; Ribeiro, M Filipa; Daudin, Antoine; Bouchy, ChristopheMixtures of bifunctional catalysts were studied in the hydroisomerization of n-hexadecane. The study focused on the impact of the properties of individual catalysts on the hybrid catalysts' performance. On the one hand, a Pt/HUSY catalyst was mixed with a series of Pt/zeolites with different topologies and acidities, all of the catalysts being individually well-balanced. Despite the diversity of Pt/zeolite catalysts in terms of both activity and isomerization selectivity, the performances of the hybrid catalysts corresponded to the average of individual components. Cooperative effects are proposed to be caused by a great difference in the relative activity of the Pt/zeolite catalysts rather than in selectivity. On the other hand, mixtures of large-pore Pt/HUSY and Pt/HBEA catalysts with different Pt loadings were tested. The performance of the resulting hybrid catalysts was observed to be a function of global metal-acid balance. Mixtures of poorly-balanced and well-balanced catalysts can be at the origin of cooperative effects, as demonstrated experimentally by an improved C-16 isomer yield. The use of a dual-function kinetic model to simulate the performance of the hybrid catalysts corroborated these interpretations. This comprehensive work is expected to serve as a guideline for uncovering hybrid catalytic systems with industrial applications such as in the hydroisomerization of long chain n-paraffins.
- Quantification of the available acid sites in the hydrocracking of nitrogen-containing feedstocks over USY shaped NiMo-catalystsPublication . Mendes, Pedro; Silva, João; Ribeiro, M Filipa; Bouchy, Christophe; Daudin, AntoineThe inhibition of Brensted acid sites by nitrogen -containing molecules was quantified under industrially relevant hydrocracking conditions. This was achieved by testing bifunctional catalysts based on HUSY zeolite in cyclohexane hydroconversion. For ammonia partial pressures within 0.2-2.8 kPa, the percentage of inhibited Brensted sites was superior to 98% at 623 K. Significant reduction in the ammonia content caused rather moderate variations on the number of available sites. Conversely, a temperature raise from 600 to 640K triplicated the vacant Brensted sites due to the significant endothermicity of ammonia desorption. The inhibiting effect of ammonia can be therefore easily modulated by temperature. (C) 2018 The Korean Society of Industrial and Engineering Chemistry.
- 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.