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The demand for middle distillates (kerosene and diesel) in comparison to gasoline fractions is increasing constantly, particularly in the majority of European countries. Thus, maximizing the production of middle distillates in the refining process is of immediate interest to refiners. However, the production of liquid fuels, for instances using a catalytic cracker, always generates a significant amount of lighter fractions, in particular of olefinic nature. Thus, the use of oligomerization reactions to convert the lighter olefin cuts into middle distillates to incorporate in the diesel pool is a promising process for the production of clean diesel fractions. In this work, 1-butene oligomerization over H-ZSM-5 zeolite has been investigated in a differential reactor operating at ambient pressure. The effect of the reaction conditions, such as reaction temperature, contact time and partial pressure was studied on the activity, selectivity and stability of the catalyst. The results show that an increase in the reaction temperature and/or partial pressure and in the contact time produces an improved catalyst activity. The data also show that high partial pressure improves the selectivity to C 8 + . Moreover, when increasing the temperature from 150 °C to 200 °C the C 8 + hydrocarbons selectivity increases, whereas above this temperature it decreases as expected, due to the competition of cracking reactions. Furthermore, a decrease in contact time between the reaction mixture and the acid sites of the catalyst caused the C 8 + hydrocarbons fraction in the product to increase. The highest selectivity towards C 8 + hydrocarbons (∼86 wt.%) was obtained with H-ZSM-5, at 200 °C and 50 kPa of partial pressure and for the lowest value of contact time analyzed (12.5 × 10−3 h). In this way, the operating conditions must be tuned in order to achieve a significant conversion and selectivity in desired fraction ( C 8 + ).

Three different model reactions (methylcyclohexane, m -xylene and 1,3,5-trimethylbenzene transformations) were studied over a series of partially Na-exchanged H-EU-1 zeolites. In the case of methylcyclohexane transformation, the catalytic activity was shown to be directly correlated to the concentrations and strength distribution of the acid sites. Consequently, a maximum in activity and turn-over frequency (TOF) was obtained for an exchange ratio comprised between 26% and 34%, for which the proportion of very strong acid sites was very high. An acidity–activity correlation, based on the Polanyi principle, was successfully applied to this reaction. This was not the case for m -xylene and 1,3,5-trimethylbenzene transformations. During those reactions, the activity and TOF decreased with the protonic site concentration, hence with the increase of the exchange ratio, the activity loss being more pronounced for low exchange ratios. Poisoning experiments using γ - collidine indicated that two kinds of external acid sites could be distinguished, depending on their locations, that is, at the pore mouths and in 12-ring pockets. The fast exchange by sodium cations of the latter sites, which would be particularly active in m -xylene and 1,3,5-trimethylbenzene transformations, could explain the evolution of these activities.

This paper explores the potential of converting a naphtha-cut (C5–C16) obtained from Fischer–Tropsch synthesis into small olefins under conditions close to commercial FCC operation. Comparing the activity of HZSM-5 and H-Y catalysts in the transformation of FT naphtha fraction at 450 °C under FCC conditions, H-ZSM-5 was found to be more active. In the present case, calculation of conversion is not straightforward since boiling point range of reactant molecules overlaps with the boiling point of many observed products. A method to estimate the conversion is proposed based on detailed PIANIO analysis of the liquid products. Hydrothermal deactivation reduces H-ZSM-5 activity and cyclization followed by hydrogen transfer reactions, but can be compensated by an increase in reaction temperature. Results obtained at six distinct H-ZSM-5 percentages (from 0.5 to 20 wt.%) suggest that under commercial FCC conditions, the use of H-Y zeolite to primary crack feed molecules that would further react on ZSM-5 is not necessary. Naphtha from FT synthesis can be potentially used to produce base petrochemical products in a dedicated FCC unit.

A TON zeolite (Si/Al = 31) was treated at 353 K with NaOH solutions of different concentrations C (0.05–0.4 M) and for different times t (30–300 min). The resulting samples were characterized by various techniques: SEM, XRD, nitrogen adsorption–desorption, pyridine chemisorption followed by FTIR and 1-butene isomerisation at 333 K. The filtrate analysis shows a simultaneous dissolution of Si and Al with a large preference for Si (Si/Al from 35 to 150), especially at high t and low C values. The increase with t of the filtrate Si/Al ratio was related to the redeposition of Al on the zeolite under the form of extraframework species with Lewis acidity. The alkali treatment caused the creation of mesopores with ∼20 nm diameter, a limited decrease in the Bronsted acidity and a significant increase in the Lewis acidity. With all samples, 1-butene double bond shift selectively occurred but with a fast deactivation due to carbonaceous deposits which can be eliminated from the zeolite through nitrogen sweeping. Desilication had no effect on the catalyst stability but increased the initial activity. The activity per protonic site (TOF) was shown to be correlated with the volume of created mesopores, which shows that these mesopores facilitate the access of 1-butene molecules to the active sites.

To shed light into the influences of the shape of the main hydrocarbon families constituting FCC feedstocks (naphthenes and alkanes) and of the phenolic molecules size on the MFI additive function during bio-oils and traditional Fluid Catalytic Cracking feedstocks co-processing, the transformations of n-heptane in presence of phenol and guaiacol were performed over an HMFI zeolite, at 350 and 450 °C. For phenol, the results were compared with those previously obtained with methylcyclohexane. A lower impact of phenol was noticed for n-heptane than for methylcyclohexane due to the easier linear alkanes diffusion into the zeolite channels, which reveals that the phenolic molecules influence on the MFI additive function could not be as critical as envisaged for a purely naphthenic feedstock. Whatever the reactant, higher temperatures do not overcome phenol deactivating effect because, once inside the zeolite structure, phenol polar molecules diffusion is very limited. An increase of the coke molecules ramification and aromaticity was observed for the n-heptane transformation in presence of phenol, instead of a reduction of the coke production from the reactant, as noticed for methylcyclohexane. Therefore, for n-heptane the further HMFI deactivation due to phenol mainly proceeds by pore blocking, contrarily to that verified for methylcyclohexane. Furthermore, the greater the size of the phenolic molecules present in the hydrotreated bio-oils, the lower their effect on the MFI additive action. In fact, bulky oxygenated molecules are preferential adsorbed close to the zeolite outer surface, from which they are more easily removed at higher temperatures. This explains the lower guaiacol deactivating effect at 450 °C, when compared with phenol.

The use of renewable fuels is expected to grow in the coming years. A possibility to achieve this consists in blending renewable bio-oils with conventional refining streams to further process in existing refineries. A key aspect of bio-oils is the presence of oxygenate molecules in significant amounts. To shed light into the effect of these compounds on Fluid Catalytic Cracking (FCC), guaiacol was chosen as model compound. Data on the transformation of n-heptane in the presence of small quantities of guaiacol over pure HY and HZSM-5 zeolites at 450 °C is presented and compared to gasoil + guaiacol blend tests using an industrial FCC equilibrium catalyst (E-CAT) pure and blended with a commercial ZSM-5 additive. Guaiacol has a negative influence on both n-heptane and gasoil conversions, since it is responsible for an increase of the coke retained on the catalysts. In the presence of n-heptane and with pure zeolites, guaiacol increases the methane yield, in line with its transformation into phenol. With industrial FCC E-CAT, the presence of guaiacol increases gasoline yield and reduces coke yield, however, increases coke on catalyst. Detailed GC analysis of the liquid product shows presence of phenols in the gasoline cut, suggesting the partial conversion of guaiacol (with methane and water formation). HZSM-5 zeolite was more severely deactivated than HY zeolite in the n-heptane transformation, which agrees with the observed reduction of the ZSM-5 additive effect on the transformation of gasoil.

To evaluate the possibility to partially replace the classical Fluid Catalytic Cracking (FCC) feedstocks by bio-oils derived from lignocellulosic biomass, the transformation of n-heptane was performed in the presence of small quantities of phenol over an HY zeolite, at 350 and 450 °C. The results were compared with those previously obtained with methylcyclohexane. Phenol leads to a further deactivation of the zeolite due to phenol adsorption on the Bronsted and Lewis acid sites along with coke molecules from the reactants transformation. For n-heptane, the additional activity decay due to phenol is observed since the beginning of the reaction, while for methylcyclohexane it was only detected after few minutes. The increase of temperature disfavours phenol adsorption but, contrarily to methylcyclohexane, it does not prevent the phenol deactivating effect for n-heptane. Differences in the reactivity of n-heptane and methylcyclohexane molecules and IR spectroscopy data allow concluding that phenol firstly interacts with the stronger protonic sites, being then retained on the weaker acid sites. Alkylation of phenol is a reaction occurring in a lower extent under the conditions tested, being responsible for the consumption of light olefins. Finally, the adsorption of phenol favours the formation of branched molecules. Hence, the alkanes cracking should be more affected than the naphthenes cracking in the co-processing of conventional FCC feedstocks with hydrotreated bio-oils rich in phenolic compounds, being the deactivating effect certainly dependent on the quantity of bio-oils incorporated.

This paper describes an assessment of the impact of the enforcement of the European carbon dioxide (CO2) emissions trading scheme on the Portuguese chemical industry, based on cost structure, CO2 emissions, electricity consumption and allocated allowances data from a survey to four Portuguese representative units of the chemical industry sector, and considering scenarios that allow the estimation of increases on both direct and indirect production costs. These estimated cost increases were also compared with similar data from other European Industries, found in the references and with conclusions from simulation studies. Thus, it was possible to ascertain the impact of buying extra CO2 emission permits, which could be considered as limited. It was also found that this impact is somewhat lower than the impacts for other industrial sectors.

In this paper a kinetic model for the residue hydrotreating is presented. The model considers kinetics, adsorption and diffusion inside the hydrodemetallization catalyst pellets. The diffusion is described by the Stefan–Maxwell equations extended for starkly different sized molecules, due to molecular size of residue molecules large distribution. Effective diffusion coefficients vary with porosity and tortuosity evolution due to volume constraints in the catalyst pellets. The model's kinetic and thermodynamic parameters were estimated from a set of experiments carried out in a batch reactor with a Middle East vacuum residue. A comparison between experimental and simulated metal profiles inside the catalyst exhibit the slow diffusion, validating the importance of adding mass transfer phenomena and considering volume constraints even in a macroporous demetallization catalyst. The model was validated by other tests performed in the same reactor using the same vacuum residue, but with different catalysts. The differences in the catalyst pore size allowed to predict all the hydrotreatment yields, showing diffusion is a crucial factor.

Acid leaching of a HMCM-22 zeolite (Si/Al = 14.5) was carried out at 100 °C for different times (3, 30, 60 and 480 min) with a 4 M nitric acid solution. The resulting samples were characterised by elemental analysis, X-ray diffraction, pyridine adsorption followed by infrared spectroscopy (FTIR) and nitrogen adsorption and their catalytic properties were established with methylcyclohexane transformation at 350 °C. The role played in this reaction by the three micropore systems was established by coupling selective deactivation of supercages by coking and poisoning of the outer cup acid sites with 2,4-dimethylquinoline. The change in the acid and catalytic properties with the time of acid treatment shows that dealumination is dominated by the accessibility of the framework Al atoms. Thus, the outer cup acid sites are highly sensitive to the acid treatment. The acidity and activity of the supercages are also strongly affected whereas those of the narrow sinusoidal channels are hardly affected.

Key model bio-oil O-compounds representing some of the major oxygenate groups, such as acetic acid, hydroxyacetone and phenol, were mixed with a standard gasoil and tested under fluid catalytic cracking (FCC) conditions in a laboratory-scale unit using an industrial FCC equilibrium catalyst (E-CAT) and a mixture of E-CAT and ZSM-5 additive. As a general trend, acetic acid, phenol or hydroxyacetone when mixed with a conventional gasoil increased the overall conversion, defined as fraction of the feed converted into gases, gasoline and coke, reduced the coke yield and increased fuel gas, LPG and gasoline. The conversion of the gasoil itself over pure E-CAT was not altered significantly by the presence of these compounds. This result could be interpreted by a preferential adsorption of the feed on the catalytic surface instead of the oxygen containing compounds. On the other hand, the ZSM-5 additive effect was attenuated in the presence of the O-compounds, suggesting a preferential interaction of such compounds with the ZSM-5. Up to 10 wt.% of these O-compounds studied can be processed without major problems in a FCC unit except for phenol.

The acid-catalysed transformation of hydrocarbons constitutes a very important set of reactions for industrial applications of zeolites. These transformations have a high degree of complexity due both to the variability of the loads that are used, usually an intricate mixture of different hydrocarbons with various reactivities, and to the fact that zeolites possess acid sites with a wide range of acid strength distribution. In this paper we intend to give a contribution to the analysis of the transformation of hydrocarbons over zeolites taking into account this latter effect. An example on the conversion of propene over ZSM-5 catalysts, with Si/Al = 15 and 24, 30 and 32% H + exchanged by Na cations is described; in this example we show that it is possible to correlate the catalytic activity of a series of catalysts with their acid strength distribution, as measured using ammonia TPD, using Polanyi-type relationships. The use of these acidity–activity relationships allows the description of the behaviour of a set of catalysts using a single set of kinetic parameters that includes the sensitivity of the reaction to the acidity of the site and opens the way to the prediction of the activity of a catalyst based solely on the characterization of its acid site distribution.

The microporosity of H-MCM-22 samples, fresh and deactivated by coke during methylcyclohexane transformation at 350 °C for 10 h, was characterised by adsorption of nitrogen and organic molecules of different size, namely, p - and o -xylenes, mesitylene and methylcyclohexane. Nitrogen adsorption was also carried out on the fresh sample after pre-adsorption of the hydrocarbons. All of these can fit the outer 12 MR cups, but show differences in their ability to enter the internal microporosity. p -Xylene can enter all the inner micropores, methylcyclohexane adsorbs in the supercages and at some sinusoidal channel entrances, o -xylene is adsorbed at the pore windows of the supercages only, and mesitylene is completely excluded from the inner micropores. It was deduced that the microporosity of the MCM-22 sample investigated consists of 0.01 cm 3 g −1 of outer pockets (∼5% of the total volume), 0.06 cm 3 g −1 of sinusoidal channels (∼32%) and 0.12 cm 3 g −1 of supercages (∼63%). Coke deposited during methylcyclohexane transformation caused the complete blockage of the supercages but had no effect on the outer cups and sinusoidal channels.

The transformation of a mixture of methylcyclohexane and a small amount of phenol, as representative of the transformation of a mixture of biomass-derived oxygenates and Fluid Catalytic Cracking (FCC) feedstock was studied at 350 and 450 °C over a USHY zeolite. At 350 °C, the addition of phenol increases the deactivation of the zeolite catalyst, which is due to phenol adsorption on both Bronsted and Lewis acid sites, in addition to the formation of coke from methylcyclohexane. Whatever the contact time and the phenol amount, this deactivation is always partial, which suggests that a substantial portion of the active sites of the HY zeolite is not affected by deactivation. Finally, the increase of the reaction temperature (to 450 °C) allows limiting the effect of phenol addition on the zeolite activity and stability.

n-Heptane transformation was carried out at 350 °C over a HMCM-22 zeolite (Si/Al = 14.5) previously characterized by various techniques: X-ray diffraction, nitrogen adsorption, scanning electron microscopy, pyridine and 2,4-dimethylquinoline (2,4-DMQ) adsorption followed by FTIR. A pronounced deactivation was shown to occur in the first 10 min reaction, due to a very fast initial coke formation, followed by a quasi-plateau in activity. Cracking was the main reaction. The role played by each of the three pore systems was established by selectively deactivating the supercage sites by coking then by selectively poisoning the protonic sites of the external cups with a bulky base molecule (2,4-DMQ). The supercage sites (∼70% of the inner ones) were found to be responsible for 97% of n-heptane transformation, those of the sinusoidal channels (∼20%) for only 3%, which means that these latter sites were ∼16 times less active probably because of pronounced steric constraints. Unexpectedly, the protonic sites of the external cups, which were demonstrated as able to catalyse efficiently various reactions including methylcyclohexane cracking, were found to be completely inactive.

At 350°C, over a HMWW zeolite (Si/Al = 14.5), methylcyclohexane (mch) transforms into four types of products: isomers (I), C 1 -C 8 aliphatic hydrocarbons (C), benzenic hydrocarbons (A), and trapped carbonaceous compounds (coke). The role played by the various micropores was established through a two-step method: deactivation of supercages by coking and poisoning of the outer hemicage sites by 2,4-dimethylquinoline. More than 85% of mch transformation occurs in the supercages, ∼11% occurs in the outer hemicages, and only

The objective of this work is the study of fundamental common aspects of NO x catalytic reduction over a Co/Pd-HFER zeolite catalyst, using methanol or methane as reducing agent. Temperature Programmed Surface Reaction (TPSR) studies were performed with reactant mixtures comprising NO 2 and one of the reducing agents. The formation of formaldehyde was detected in both studied reactions (NO 2 –CH 4 and NO 2 –CH 3 OH) in the temperature range between 100 and 220 °C. At higher temperature, when the NO x reduction process effectively begins, formaldehyde starts to be consumed. Using methanol as reducing agent, nitromethane and nitrosomethane, are detected. At 300 °C these species are consumed and cyanides and iso-cyanides formation occurs. On the contrary, with methane, these last species were not detected; however, there are strong evidences for CH 3 NO and CH 3 NO 2 formation. Thus, using methanol or methane, similar phenomena were detected. In both cases, common intermediary species seem to play an important role in the NO x reduction process to N 2 . These results suggest that methanol can be considered as a reaction intermediate species in the mechanism of the reduction of NO 2 with methane, over cobalt/palladium-based ferrierite catalysts.

The hydrolysis reaction of p-nitrophenyl butyrate catalyzed by lipases was followed with in situ UV/vis diode array spectrophotometry. Five enzymes - Candida antarctica lipase B and Fusarium solani pisi cutinase wild-type and three single-mutation variants - were tested as catalysts in homogeneous conditions and immobilized on zeolite NaY, on a polyacrylate support and as cross-linked aggregates. Using deconvolution techniques and kinetic modeling, the thermal stability of the different biocatalysts was compared in operational conditions and the results were supported by steady-state enzyme fluorescence measurements. We concluded that both the mutagenesis and the immobilization on zeolite NaY had a positive effect on the thermal stability of F. solani pisi cutinase.

To select a suitable system for the racemization of 1-phenylethanol, a commercially relevant chiral alcohol, four acid zeolites and five solvents were screened. Results show that the zeolite/solvent combination influences not only the reaction rate but also the product yield because of their influence on side reactions. As a general rule we can say that the higher the racemization rate, the lower the product yield. The choice of solvent is also important for avoiding catalyst deactivation over time, especially when recycling of the catalyst is envisaged. Kinetic modeling of the results was performed in order to allow a better comparison of the different reaction systems and a more complete analysis of the phenomena underlying their behavior. Of the 20 combinations tested, zeolite H-Beta Si:Al = 75 in ethyl acetate and zeolite H-Beta Si:Al = 12.5 in isooctane, water and vinyl acetate showed the most promising results.

A novel biocomposite electrode containing horseradish peroxidase (HRP) and zeolite co-immobilized on gelatin particles mixed with graphite was described. Comparing the composite (zeolite/graphite) and the biocomposite (gelatin/HRP/zeolite/graphite) electrodes showed that the latter presented an enhancement on the electrodes diffusion properties and, apparently, the enzyme co-immobilized with zeolite on gelatin was electro-active and functioned as mediator in the electro-oxidation of phenol. Various HRP/zeolite ratios were tested and the best result was obtained with the 1:100 m HRP / m zeo biocomposite electrode. These results confirm the existence of HRP–zeolite interactions, as previously observed in pseudo-homogeneous oxidation of phenol.

The activity of various lipases was compared, in both free and immobilized forms, using the kinetics of the hydrolysis reaction of p-nitrophenyl butyrate, which was followed with in situ UV/Vis diode array spectrophotometry. Several enzymes were used to catalyze the reaction, namely Candida antarctica lipase B and Fusarium solani pisi cutinase wildtype and three single-mutation variants. The enzymes were tested in three different forms: free, immobilized as cross-linked aggregates and supported on zeolite NaY. A simple kinetic model was used to allow a quantitative comparison of the behavior of the different catalysts. It was concluded that although immobilization reduces the activity of the enzyme, the zeolite offers a much higher specific activity when compared to the cross-linked aggregates, thus supplying a heterogeneous catalyst with promising catalytic properties.

The present work discloses some of the less clear aspects regarding the deactivation of acidic USY zeolites due to coke formation and poisoning with basic nitrogen molecules (3-methylpyridine, 2,6-dimethylpyridine, and quinoline). Coke formation occurs essentially in the supercages; consequently, the Bronsted acid sites located in these structures lose their activity quite rapidly. Nitrogen-containing molecules also interact preferentially with the Bronsted acid sites located in the supercages. 2,6-Dimethylpyridine has a higher poisoning ability than the other two bases, probably due to steric hindrance, which limits the interaction with the nonactive Lewis sites. (Only Bronsted acid sites are poisoned, and hence deactivation is more pronounced.) This work also demonstrates that quantification of the PyH+ band on pyridine adsorption is an inaccurate method for determining the decrease in the number of Bronsted acid sites during the deactivation of catalytic cracking catalysts. Indeed, only the surface of the hydroxyl vibration bands can be used to determine the decrease in the number of accessible active sites. Acidity–activity correlations show that only the Bronsted acid sites located in the supercages are active in methylcyclohexane transformation; as a result, an average turnover frequency for these sites can be determined with the slope of the activity versus acidity curve (0.33 s−1).

The acid-catalysed transformation of light olefins was studied at various temperatures and partial pressures over ZSM-5 of varying acidic contents. It was observed that, as the temperature increased, the rate of consumption of ethene and propene decreased, whereas the rate of consumption of butene increased. Despite the fact that this reaction proceeds by a rather complex network mechanism, a single kinetic model describing the rate of consumption of the three reactants was developed, with the explicit inclusion of the step corresponding to the adsorption of the reactant molecules.

This research work consisted in the assessment of the damaging effect of basic nitrogen in the performance of industrial catalytic cracking catalysts. Laboratory evaluation of an industrial equilibrium catalyst was done with four feedstocks with very distinct nitrogen contents: a gasoil with 1307 ppm of basic N (feedstock A); feedstock A after an acid treatment with the objective of partially removing the basic nitrogen (feedstock B: 135 ppm of basic N); feedstock B after adding 1172 ppm of quinoline (feedstock C: 1307 ppm of basic N); and feedstock A after adding 1172 ppm of quinoline (feedstock D: 2479 ppm of basic N). Characterization of the gasoils showed that only the basic nitrogen content was affected by the acid treatment. The evaluation results showed that basic nitrogen reduces the gasoil cracking conversion in 5–10 wt% points, depending on the catalyst to oil ratio. In addition, at constant conversion, the increase in basic nitrogen content also resulted both in a decrease in gasoline yield and an increase in coke and hydrogen yields. Nitrogen contained in the quinoline molecule had similar effects to that present in the original gasoil.

In this work a new enzyme–zeolite interaction was examined. Horseradish peroxidase (HRP-C), a heme-containing enzyme, shows an activity increase for HRP-C catalysed phenol and 4-aminoantipyrine co-oxidation in aqueous medium, in the presence of NaY zeolite, although the attempts to use this enzyme immobilized on the zeolite resulted in an almost complete loss of activity. Pseudo-homogeneous mechanical mixtures of enzyme and zeolite in solution were compared at five different temperatures (10, 20, 25, 30 and 35 °C), and have shown possible interactions which influence the enzyme activity. In order to better analyse the interactions effects, co-immobilization of the enzyme and zeolite was performed in gelatin particles; in this case the enhancement in enzymatic activity was much larger than when pseudo-homogeneous mixtures were used. HRP-C immobilized in gelatin showed activity increases as large as 100% when zeolite NaY is co-immobilized in the same particles, depending on the experimental conditions. Although the mechanism by which the zeolite induces this effect still requires clarification, one possible explanation is that some ionization of OH groups of the enzyme occurs, due to ion exchange of Na-ions of the zeolite and protons of the enzyme, an effect which might also occur in the gelatin matrix; the zeolite may also influence the conformation of the enzyme by means of the electrical fields that are generated at the surface of these materials, which are known to influence the catalytic action of zeolites.

Three HBEA samples were prepared through ion exchange followed by calcination under dry air flow at 550 °C from parent samples synthesized with different total Si/Al ratios or crystal sizes and characterized by various techniques. The denomination, Si/Al ratio and crystal size were the following—Cal: 12.5, ∼20 nm; LC: 14.5, 3000–10,000 nm; RAl: 7.0, ∼50 nm. Pyridine adsorption followed by FTIR shows very different values of the Lewis/Bronsted site concentration ratio: 1.2 with Cal, 0.2 with LC and 0.6 with RAl, which indicates a predominant positive effect of the crystal size on the framework stability. Methylcyclohexane transformation at 450 °C was found to occur through both protolysis and the carbenium ion chain mechanism. Protolysis plays a significant role on Cal only. This very difficult reaction which requires very strong protonic sites, most likely sites resulting from interaction of bridging OH groups with neighbouring Lewis sites was 3 and 12 times faster on Cal than on RAl and LC samples, respectively. Furthermore, from the low turnover frequency value of the protonic sites of LC, severe diffusion limitations were demonstrated to occur on this large crystal size sample.

The effect of the introduction of phosphorus on H-MFI zeolite before and after hydrothermal treatment was studied. The samples were characterized by XRF, nitrogen adsorption, 27Al and 31P MAS NMR, n-propylamine temperature-programmed decomposition, n-hexane cracking and vacuum gasoil cracking. Results showed that P stabilizes the MFI zeolite structure by preventing the segregation of the framework Al atoms during the steaming treatment. Although there is an optimum phosphorus content, its effect on the selectivity towards light olefins will depend on the severity of the steaming treatment, i.e., with more severe treatment the stabilization is more evident. NMR results evidenced the presence of several types of aluminium and phosphorus species. Besides the classical framework tetracoordinated Al, which is the main responsible for the acidity of the samples, another tetrahedral aluminium probably in a distorted environment also seems to be active in n-hexane cracking, besides favouring the light olefins production during gasoil cracking.

This review paper presents the significant advances which were made in the last decade in the understanding of the transformation over acid and bifunctional zeolite catalysts of the cheap and readily available C2–C4 alkanes into more valuable products: mechanism of activation, reaction scheme, nature of the active sites. Both the transformations of pure alkanes: n-butane isomerization, C2–C4 alkane aromatization and of alkanes in mixture with alkenes: isobutane–butene alkylation or with aromatic hydrocarbons: benzene alkylation with ethane or propane are considered.

In this research work the deactivation of an H-MFI (Si/Al fr = 12) zeolite was studied during the methylcyclohexane transformation at 350 °C. Besides the normal activity decay with time on stream due to the formation of coke molecules, the poisoning with three nitrogen basic compounds (3-methylpyridine, quinoline and 2,6-dimethylpyridine) was studied. All three bases cause a strong decrease in conversion. The decrease in activity is proportional to the amount of nitrogen retained in the zeolite. On the other hand, the intrinsic poisoning effect of the bases seems to correlate well with its proton affinity, following the order: 2,6-dimethylpyridine > quinoline > 3-methylpyridine. Although the relatively small pores of the MFI structure, until a saturation amount, the total injected amount of nitrogen bases stays in the zeolite in the protonated form. Even so, results show that the bulkier base cannot penetrate as deep into zeolites crystallites and accumulates on the external surface which can partially explain its higher poisoning ability. Besides the actual bases, no nitrogen coke molecules were found by GC–MS coupling; soluble coke molecules were polyaromatics with 2–4 rings.

On previous papers it was shown that composite electrodes, incorporating Y zeolite, in its sodium form, were able to induce the electro-oxidation of phenol; it was also established that exchanging sodium by protons seriously deteriorated the electrode's ability to oxidise phenol, indicating that cation composition of the zeolite was very important in the electrode's performance. In this work the influence of the nature and content of cations in the zeolite and in the supporting electrolyte were studied for this electro-oxidation. Cations such as lithium, sodium, potassium, calcium and praseodymium were used. The presence of these cations, as compensating cations in the zeolite, bears a direct influence the electrode's performance, but the cation content of the electrolyte also has a bearing on this performance. Although ion exchange processes probably occur during measurements, it was not significant in comparison with the phenol diffusion into the electrode. The influence of having different cations in the electrolyte, such as sodium, potassium, cesium or ammonium (NH4+) was also inspected and it was observed that they also have a bearing on the electro-oxidation of phenol, probably due to their influence in the mass transfer of phenol into the composite zeolite/graphite electrode and probably to molecular traffic effects originated in the ion-exchange processes that occur simultaneously with the electro-oxidation, in which the last one has less influence. Among all conditions and zeolites that were tested, the electrode using a sodium Y zeolite with a Si/Al ratio of 2.5, composited with graphite, in the combination with a sodium phosphate buffer, gave the best results for the electro-oxidation of phenol.

A comparison of the pore structural properties and catalytic activity of MCM-41 containing aluminium, prepared at room temperature with different aluminium sources, is presented. In addition, they are compared with those of MCM-41 obtained by two conventional hydrothermal procedures and room temperature synthesised Al-MCM-48 grades. Al-MCM-41 samples were prepared by direct synthesis at room temperature with tetraethoxysilane (TEOS) and aluminium isopropoxide, aluminium sulfate or sodium aluminate, and by two hydrothermal routes using silica Ludox suspension and sodium aluminate (at 377 K) or Cab-O-Sil silica and alumina (at 377 K and 423 K). The synthesis of MCM-48 grades was also carried out at room temperature with TEOS and aluminium sulfate or nitrate. The materials were characterised by X-ray diffraction, nitrogen adsorption at 77 K and solid-state 27Al MAS NMR. The catalytic activity was evaluated in the reaction of double bond position isomerisation of 1-butene to 2-butenes at 373 K. It is concluded that the room temperature synthesis method used resulted in the preparation in a short period of time of well structured MCM-41 materials that contained predominantly tetracoordinated aluminium and presented acidic catalytic activity similar to or better than those prepared by the two hydrothermal procedures. Aluminium sulfate is a good alternative to isopropoxide in the room temperature synthesis as it resulted in samples with very uniform pore size, good hexagonal ordering and increasing catalytic performance at least up to Si/Al of 13. The most active sample was a MCM-48 grade also prepared at room temperature with the same precursor.

Methylcyclohexane transformation was carried out at 450 °C over HBEA samples resulting from dealumination of the same parent HBEA zeolite by three different methods: steaming, treatment with aqueous solutions of hydrochloric acid or ammonium hexafluorosilicate. With all the samples, methane, C2–C4 and C7 alkenes, isomers and toluene appear as primary products, the other products C2–C4 alkanes, C5 and C6 alkenes and alkanes, benzene, xylenes and trimethylbenzenes being secondarily formed. These products were shown to result from two mechanisms: carbenium ion chain, protolytic cracking and dehydrogenation. The activities of all the HBEA samples for each of the processes were estimated. A linear correlation was found between the activity of the samples for the carbenium ion chain process and the square of the concentration of protonic sites, which suggests a demanding process. Furthermore a close similarity could be observed between the change of the protolytic activity and Lewis acidity of the HCl treated samples with their Al content. Strong protonic sites resulting from interaction of bridging OH groups with neighbouring Lewis species: structure defects and monomeric extraframework Al species were proposed to be the active sites.

The influence of 0.5 wt.% of quinoline (540 ppm of nitrogen) in the feed was tested for the methylcyclohexane transformation at 350 °C over an H-USY zeolite (framework Si/Al ratio of 5.4). The selectivities for the fresh catalyst do not seem to be altered by the presence of quinoline. Oppositely, for the deactivated zeolite, the aromatics yield increases for the tests performed with quinoline. Deactivation with time on stream is very pronounced, even for tests carried out without the base molecule; this can be attributed to the formation of highly polyaromatic coke molecules that block the acid sites and the microporous structure. In presence of quinoline, deactivation is enhanced due to its cumulative poisoning effect, especially for smaller contact times. This deactivation is caused by the strong interaction of the nitrogen base with the Bronsted acid sites responsible for the cracking mechanism. Quinoline molecule also participates in coke formation reactions, leading to an increase in the produced amount of coke, particularly of the more polyaromatic compounds insoluble in dichloromethane.

The acidities (number and strength of the Bronsted acidic sites) of two zeolite samples, H-MFI and H-BEA, were measured by ammonia temperature-programmed desorption (ATPD) and proton nuclear magnetic resonance (1H MAS NMR). Deconvolutions of the ATPD and 1H MAS NMR spectra lead to acid sites distributions (number and strength) that are nearly similar. Acid sites of increasing acid strength are characterized by higher desorption temperatures and higher 1H NMR chemical shifts. A linear relationship was found between the activation energy for ammonia desorption and the 1H NMR chemical shift. The acid strength distributions determined by ATPD and 1H MAS NMR have been quantitatively correlated.

The acidity and the catalytic activity for n-hexane cracking of three related HZSM-5 catalysts have been determined. A method is described for obtaining the distribution of acid strength by deconvoluting ammonia TPD spectra and it is shown that a linear relationship exists between the enthalpy of the reaction and the activation energy for the desorption of ammonia. Both the Polanyi and the Marcus models were used to derive relationships between the reaction activation energy and the ammonia desorption activation energy. As expected, the former decreases when the latter increases; the reaction activation energy is lower on acidic sites of greater strength. Similarly, equations were derived relating the catalytic activity to the acid strength of the catalytic sites expressed by the activation energy for the desorption of ammonia. Observed activities for the cracking of n-hexane were correlated satisfactorily to theoretical ones evaluated using the Polanyi and the Marcus models, considering the distribution of acid site strength. For the cracking of n-hexane and the range of experimental conditions used, the Marcus model does not present a significant improvement relative to the Polanyi model. The strategy described in this work indicates that it is possible to predict the activity of a zeolite for a given reaction, provided the acid sites strength distribution is known; one simple method for obtaining the latter being ammonia TPD.

In this paper, a new parameterised microkinetic model for the catalytic cracking of paraffins is described. This model allows us to simulate the complex network of reactions involved in the catalytic cracking of paraffins over an acidic solid; the model includes six different elementary steps (adsorption, desorption, protolytic scission, β-scission, chain growth and hydride transfer). The reaction scheme is detailed to the carbon atom number of the species and explicitly distinguishes between carbenium ions, paraffins and olefins. The number reaction rate constants required to describe all the individual reactions that are possible within the network is well over one hundred and, by using a system of equations which describes the dependency of the rate constants with the nature of the reaction and the species involved, the number of parameters that are fitted in the model is reduced to fourteen. This microkinetic model was fitted, using a genetic algorithm, to the experimental data for the catalytic cracking of n -hexane over a protonic ZSM-5 catalyst at 450 °C with very satisfactory results. The model parameters obtained from n -hexane data, were then used to simulate the catalytic cracking of n -heptane under similar conditions; this simulation compared very well with actual experimental results on n -heptane cracking. This ability to predict the catalytic behaviour for one reaction based on data obtained for other reactions is a significant step in the goal of obtaining models that are able to describe the transformation of a wide range of compounds using a limited number of parameters.

This is the first of a series of papers concerning the transformation of propane over a H-ZSM5 catalyst comprising experimental data, a kinetic model, and molecular dynamics calculations. The aim of this work is to provide a more fundamental insight on the catalytic processes involving light alkanes activation over solid acid catalysts. Experimental data for propane cracking was collected in the temperature range 623–773 K and low propane feed partial pressures varying from 3.0 to 9.1 kPa. The results show the existence of two parallel reaction pathways: (1) two monomolecular initiation steps (protolytic cracking or dehydrogenation), characterized by a relatively high activation energy, which becomes predominant at low conversions and high temperatures. Bond rupture may occur on either a CC or CH position leading to stoichiometric amounts of methane and ethene, or hydrogen and propene, respectively, when extrapolated at zero conversion; (2) a bimolecular route (classical cracking mechanism) with lower activation energy which involves carbenium ions chain carriers, and whose relative importance grows with increasing conversion and decreasing temperature, as secondary products, mainly olefins, become important. It is also clear that dehydrogenation reactions are favored at low temperatures, while at higher temperatures cracking is the dominant reaction pathway.

A microkinetic model for the catalytic cracking of n-heptane is proposed comprising a set of significant elementary steps which generate a complex reaction network. This approach constitutes a compromise between fundamental and lumped models since the reaction scheme is detailed to the carbon atom level by considering separately olefins, paraffins and adsorbed carbenium ions with the same carbon atom number. Elementary rate constants are estimated through expressions relating species reactivity with their carbon atom number. Fitting the model against experimental data over a large parameter space was performed using a micro-genetic algorithm with binary encoding and logarithmic distribution. The advantage of this approach is that it allows modelling the reaction network without supposition of rate determining steps. The model predicts very well the observed transient activity for n-heptane cracking over H-USY zeolite at 623 K and in general, it reasonably predicts the experimental trends for the products distribution.

PtAl/MCM-41 and PtAl/SBA-15 materials were prepared by post-synthesis alumination followed by introduction of platinum by ion exchange. The samples were characterized by pyridine adsorption followed by FTIR and TPR of hydrogen. The catalytic behavior was explored in the transformation of n-hexane.

Fusarium solani pisi recombinant cutinase was immobilized on sodium form of zeolite Y (NaY) and polyamide Accurel PA6 and used to catalyze the alcoholysis reaction of butyl acetate with hexanol, in isooctane. The influence of some of the relevant parameters to the enzyme alcoholysis activity, such as temperature, buffer molarity and pH of the enzyme solution, hexanol and butyl acetate concentrations, were studied by means of a factorial design plan. By knowing the system response to the experimental design, the effects of each factor and its interactions were determined. In the case of the preparations with NaY zeolite, the main effects are due to temperature and buffer molarity, while pH and hexanol concentration have little effect on activity. In case of the cutinase adsorbed on Accurel PA6 the main effects are due to temperature, buffer molarity and pH of the enzyme solution.

A series of HBEA samples were prepared by dealumination through three different methods (steaming, treatments with hydrochloric acid and ammonium hexafluorosilicate (HFS) solutions) of a parent sample with total and framework Si:Al ratios of 12.5 and 33, respectively, constituted of 20 nm crystallites. The samples were characterized by XRD, nitrogen adsorption and pyridine adsorption–desorption followed by IR spectroscopy. Whereas the three dealumination treatments have practically no effect on crystallinity and nitrogen adsorption properties, they cause large changes in the ranges of the O–H bond stretching modes (3300–3800 cm−1) and of the most intense IR absorption of pyridine (1400–1700 cm−1). Treatments with HCl or HFS cause the most significant changes: disappearance of the 3662 and 3782 cm−1 bands corresponding to extraframework Al species and to tricoordinated Al species partially connected to the framework, respectively, appearance of additional bands at 1603 and 1446 cm−1 ascribed to a new type of pyridine species coordinated to Lewis sites (PyL2) and for desorption temperatures above 350 °C, of a band at 1462 cm−1 generally ascribed to iminium ions, apparently at the expense of the PyL2 band. In agreement with this formation of iminium ions, desorption at high temperatures causes the complete disappearance of pyridinium ions without complete restoration of the acidic bridging hydroxyl band. PyL2 species are proposed to be pyridine molecules coordinated to Lewis sites and interacting through hydrogen bond with protonic sites.

Two trimetallic ZnCuAl and MnCuAl hydrotalcites have been successfully synthesized by a co-precipitation method. The manganese based material was identified as a new hydrotalcite phase. Both lamellar precursors were calcined at 450 and 600 degrees C and the resulting catalysts were tested on reaction of total oxidation of toluene. The solids were characterized by X-ray diffraction, thermal analysis, atomic absorption spectroscopy, Fourier transformed infrared spectroscopy, N(2) adsorption and H(2) temperature-programmed reduction. It was found that ZnCuAl materials are composed of copper and zinc oxides supported on alumina; while MnCuAl ones comprise basically spinel phases, which were not completely identified. The catalytic behavior of the calcined samples showed that Mn hydrotalcite calcined at 450 degrees C exhibited the best catalytic performance that corresponds to 100% toluene conversion into CO(2) at about 300 degrees C.

Thermal stabilities of a recombinant cutinase from Fusarium solani pisi, immobilized by adsorption/deposition on NaA and NaY zeolites, and on the reference supports polyamide Accurel-PA6 and alumina, were evaluated for long periods of time at different temperatures. The prepared samples were equilibrated in closed vessels with saturated salt solutions, in order to achieve a water level in the preparations correspondent to a water activity of ≈0.97, which was the optimal value for the alcoholysis reaction of butyl acetate with hexanol in isooctane, and stored in the saturation vessels at 30, 40 and 50 °C. The activity of the immobilized cutinase, for the alcoholysis transformation, was measured as a function of the storage period of time. A 24 h thermal treatment at 90, 120 and 150 °C was also applied, over some immobilized preparations, in order to check the level and reversibility of the immobilized cutinase deactivation.

The acid–base properties of a series of zeolite NaX samples, impregnated with several rare-earth nitrates (Ce, Nd, Eu, Dy, Er, Tm, Yb and Lu) and thermally treated under air, have been tested on the model reaction of 1-butene double bond position isomerization at different temperatures (200–300 °C). The activity rises with the reaction temperature increase and the participation of the basic mechanism decreases, while that of the acidic process increases. At 250 °C, the initial catalytic activities do not present significant differences among the rare-earth series (0.5–1.5 mmol/(h g)) with the exception of Yb; in this case, the total activity is quite higher (11.5 mmol/(h g)). The basic character of the transformation, evaluated from the cis / trans -2-butene ratio, is superior for part of the impregnated samples than for the rare-earth-free NaX sample, which presents a value of 0.94 for this parameter. The nature of the rare earth does not induce important changes in the basicity among the series, the cis / trans ratio decreasing from 1.9 (Ce) to 1.3 (Lu), with the same exception of the Yb impregnated sample ( cis / trans =2.4); the basic character of this sample is higher than the other one.

The temperature dependence of the USHY+HZSM-5 zeolites mixing effect on the catalytic properties for the n-heptane transformation is analysed; several mixture compositions were tested at 350, 400 and 450°C. The observed activities and product selectivities for the mixtures were compared to the predicted ones based on the pure zeolite tests assuming its relative contributions to the product yields and conversion with no mechanistic interactions. The most important detected synergism in the product selectivities, which is the increased C4 products ramification, is reduced with the temperature rising.

Fusarium solani pisi recombinant cutinase was immobilized by adsorption on NaY zeolite. The kinetics of the alcoholysis reaction of butyl acetate with hexanol in isooctane catalyzed by cutinase immobilized on NaY zeolite, was studied. The reaction kinetics is suggested to follow a Ping-Pong bi–bi mechanism in which competitive inhibition by excess of alcohols has been identified. No evidence of any significant external diffusional limitation has been detected. The time validation of the model was successfully achieved simultaneously for 15 experimental product evolutions in a batch stirred tank reactor (BSTR) for different initial reactant concentrations.

The ground-state and transient absorption, prompt and delayed fluorescence of tetraphenylporphyrin (TPP) adsorbed onto the external surface of different zeolites was monitored using diffuse-reflectance steady-state and laser flash photolysis. The delayed fluorescence (DF) of TPP detected in the presence of O 2 is attributed to the energy transfer from 3 TPP to 3 O 2 to form 1 O 2 and subsequent energy transfer from 1 O 2 to some other 3 TPP within the organised molecular ensembles on the zeolite surface. The spectroscopic and kinetic parameters, namely the yield of DF (2–20% relative to prompt fluorescence), depend on the zeolite properties: the observed differences were correlated with the acid-base properties of the two zeolite series studied in this work (KA, NaA, CaA) and (NaA, NaX, NaY).

The transformation of cyclohexanone was carried out on a series of bifunctional PdHFAU catalysts with Pd contents between 0.1 and 0.5 wt.% and framework Si/Al ratios equal to 5, 20, 40 and 100, under the following conditions: flow reactor, 473 K, pressures of cyclohexanone and hydrogen equal to 0.17 and 0.83 bar, respectively. With all the catalysts, cyclohexylcyclohexanone, the formation of which requires successive steps of aldolization, dehydration and hydrogenation, is directly formed. The effect of the balance between the hydrogenating and acid functions of the catalysts (taken as the ratio between their activity for toluene hydrogenation and their number of protonic acid sites, A H / B ) on their activity, stability and selectivity is the one expected from a bifunctional catalytic process. The activity per protonic site first increases with A H / B , then remains constant above a certain value of A H / B (0.4 h −1 ), the limiting step of cyclohexylcyclohexanone formation being then cyclohexanone aldolization. The selectivity to cyclohexylcyclohexanone as well as the stability increase with A H / B remaining constant for A H / B >1 h −1 . While a high selectivity to cyclohexylcyclohexanone is obtained, the catalyst stability is relatively poor due to the retention inside the zeolite micropores of polar tricyclic C 18 compounds.

In this paper we will have a detailed look at a numerical procedure that allows the estimation of the acid site strength distribution using a single temperature programmed desorption (TPD) experiment. The possibility of estimating these parameters is of paramount importance in the determination of quantitative relationships between activity and acidity. The application of the procedure to a set of simulated thermograms gives a clear view of the applicability of this method. The procedure was tested both in single and multi energy distributions, as well as quasi-continuum distributions. Then the method has been applied on TPD thermograms obtained from catalysts based on two different forms of zeolite Y. In part 3 of this series, the acid site distributions obtained here will be used in an activity–acidity relationship, using a Bronsted type equation, similar to the one used in homogeneous acid catalysis.

A new predictive semi-lumped model developed for the cracking of paraffins has been applied to n-heptane. The model is based on a complex network reaction scheme including the ensemble of reactions taking place during the catalytic cracking of paraffins. The reaction scheme is detailed to the carbon atom number level and a large number of reactions are taken into account, ranging from cracking, hydride transfer and chain growth, which eventually leads to coking. It is considered that all the species present can participate in all of the above reactions, creating a complex network where all the species interact with all the others by means of the three sets of reactions included. Since the reaction network involves 1125 reactions, written in terms of elementary steps, an important problem to be solved hereby is to assign values to the corresponding reaction rate constants. For most of the elementary reactions considered experimental data is not directly available in the literature so, for their kinetic rate constants quite simple arbitrary equations were used to estimate them for each set of reactant/products considered. Each kinetic expression was parameterised with three parameters in order to describe the dependence of the corresponding kinetic rate constant on the number of carbon atoms of the adsorbed and gas phase species involved. The estimation of the nine rate constant parameters is discussed, as well as their influence on the evolution with time on stream of the profiles of global gas phase and predicted surface species distributions, coke content, catalytic activities and deactivation curves. The model is applied to the cracking of n-heptane and validated using experimental data. It can be shown that, despite the assumptions that were considered in this approach, very meaningful results are obtained. The model computes the product distributions at the exit of the reactor as well as the global distribution of surface adsorbed species, the coke content at the surface and the global activities, can be predicted as a function of time on stream.