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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.
- 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.
- Bifunctional intimacy and its interplay with metal-acid balance in shaped hydroisomerization catalystsPublication . Mendes, Pedro; Silva, João M; Ribeiro, M Filipa; Daudin, Antoine; Bouchy, ChristopheThe combined impact of platinum location and metal-acid balance on the catalytic performances of HUSY zeolite alumina-shaped bifunctional catalysts was evaluated inn-hexadecane hydroconversion reaction. For well-balanced catalysts, the deposition of Pt in the alumina resulted in lower isomerization selectivity as compared to when platinum was located in the zeolite. In the latter case, the maximal distance between Pt and acid sites was found to be in the nanometric scale (high intimacy) whereas in the former it was in the micrometric scale (low intimacy), particularly due to the presence of large clusters of HUSY zeolite. Nevertheless, whenever proper balance between functions was not ensured in high-intimacy catalysts, the low-intimacy and well-balanced catalysts were shown to perform better. The requirement for nanometric metal-acid sites intimacy must be hence combined with an adequate metal-acid balance to achieve optimal catalytic performance.
- Bridging the gap between academic and industrial hydrocracking: on catalyst and operating conditions' effectsPublication . Mendes, Pedro S. F.; Silva, João M; Ribeiro, M Filipa; Daudin, Antoine; Bouchy, ChristopheThis work aims at bridging the knowledge gap between the well-studied Pt/zeolite catalysts and the industrially-employed NiMoS/(Al2O3+ zeolite) ones. To do so, catalyst series based on HUSY zeolite were evaluated in the hydroconversion of n-hexadecane under similar operating conditions, but the industrially-relevant H2S and NH(3)contaminants were added when evaluating the latter. The intrinsic performance of Pt/HUSY and NiMoS/(Al2O3+ HUSY) catalysts was noticeably similar, when well-balanced, with the catalytic activity being however much lower in the latter (temperature gap of 125 K). Ammonia inhibition of more than 99% of the protonic sites was revealed to be the origin of such low activity. On the other hand, the metal-acid balance was only reached at sufficiently low reaction temperatures (ca.593 K),i.e.when the NH(3)inhibiting effect increased the metal to acid site ratio in NiMoS/(Al2O3+ HUSY) to values five orders of magnitude larger than those in the Pt/HUSY one. In addition to the understanding achieved on the role of metal-acid balance in industrial-like catalysts and its key controlling parameters, these findings also point to the need to develop better hydrogenating functions to improve the efficiency, and consequently the sustainability of liquid fuel production.
- 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.
- Synergies, cooperation and other effects: a review for hydroconversion catalystsPublication . Mendes, Pedro S. F.; Silva, João M; Ribeiro, M Filipa; Daudin, Antoine; Bouchy, ChristopheMixing different components is the basis of chemistry. In heterogeneous catalysis, combinations of different active phases are frequently used, but involved in a mysterious way similar to alchemy. The language employed to describe such systems is typically imprecise due to the lack of clear definitions and efforts to quantify the observed performances. In this review, focused in the particular case of bifunctional catalysis, a set of definitions is provided aiming at an analytical and coherent examination of the literature. The works on hybrid zeolite based catalysts for hydroconversion processes are reviewed, and an attempt to classify the various origin of potential cooperation effects is provided. By such means, we hope to provide not only a clear view on the current state-of-the-art on hydroconversion catalysts but also a common framework for a more rigorous investigation of possible synergies of hybrid catalysts over all catalysed reactions.
- 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.
- 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.