Lignocellulosic biomass (LC) is a non-food-competing resource that can be converted into valuable products via pyrolysis. However, its complex polymeric structure makes this process challenging. Acetylation is a promising chemical treatment to enhance the efficiency of biomass pyrolysis. Furthermore, thermogravimetric analysis (TG) is a simple and low-cost technique that can be used to simulate pyrolysis, although dynamic TG curves may not be appropriate for LC. This work investigated the effects of acetylation on the chemical composition, thermal behavior, and catalytic thermo-degradation of three types of LC (wood sawdust, coconut husk, and cow manure). Acetylation was performed using acetic anhydride and sulfuric acid under microwave irradiation, and catalytic thermo-degradation was investigated by dynamic and isothermal TG analysis. Acetylation enhanced carbon content and total mass loss while decreasing residual mass in all biomass types. Interestingly, isothermal TG analysis revealed improved interaction between the catalyst and LC, surpassing dynamic analysis in catalytic thermo-degradation. Remarkably, the isothermal TG analysis showed greater mass loss in the presence of the catalyst. The combined effect of acetylation and the catalyst increased biomass thermo-degradation by 4.5

The synthesis of CaO-based pellets with high energy storage and suitable mechanical resistance after prolonged cycling is pivotal for the successful implementation of the Calcium looping (CaL) technology for energy storage in CSP plants. In this work, CaO-based spherical pellets (CAA) were prepared made up of 60 wt % Ca(OH)2 and varying ratios (0-40 wt %) of commercial gamma-Al2O3 and mesoporous gamma-Al2O3 (m-Al2O3). They were tested in TG in several CO2 carbonation/decarbonation cycles (15 and 50 for selected pellets) and their respective average crushing strengths measured. After 15 cycles, the optimum pellet CAA 20-20 (60 wt % Ca(OH)2/20 wt % gamma-Al2O3/20 wt % m-Al2O3) exhibits a remarkable energy storage density of 1030 kJ/kg with a superb crushing strength of -29 N. This was ascribed to the enhanced formation of the calcium aluminate mayenite (Ca12Al14O33), since the high BET surface area (384 m2 g-1) of mesoporous gamma-Al2O3 promotes the interaction with calcium oxide. Additionally, CAA 20-20 showed meaningful porosity that favored CO2 mass transport. Interestingly, after 50 cycles, the optimum CAA 20-20 pellet maintained a high carbonation yield (0.46), representing an 84 % of the initial value and corresponding to an energy storage density of -873 kJ/kg. Additionally, the optimum CAA 20-20 pellet was coated with an external layer of Al-MCM-41 silica that augmented its crushing strength up to 37 N, with a concurrent slight abatement in the carbonation yield and energy storage density after 50 cycles (0.43 and -824 kJ/kg). Consequently, both uncoated and coated CAA 20-20 pellet are promising for the successful implementation of CaL in CSP plants.

H-ZSM-5 and H-Beta zeolites ion-exchanged with alkali (Na+ and K+) and alkaline-earth (Mg2+) metals have been explored for the catalytic fast pyrolysis of lignin. Incorporating these metals led to a significant change in the acidic properties of the parent zeolites turning into mostly Lewis-type acidity. Catalytic fast pyrolysis experiments of lignin were performed in a fixed bed reactor with exsitu configuration operating at 550 degrees C (thermal zone) and 450 degrees C (catalytic zone), atmospheric pressure and under a nitrogen flow. Moreover, two catalysts to lignin mass ratios (C/L = 0.2 and 0.4) were studied. Compared with non-catalytic tests, the use of parent zeolites caused a decrease in the bio-oil* (water-free basis) yield due to enhanced production of gases, water, and the coke deposition on the catalyst. In addition, the quality of bio-oil* was improved since it presents a lower oxygen content regarding the thermal test. H-Beta zeolite showed a higher deoxygenation degree than H-ZSM-5, but the latter exhibited a higher share of light components in the bio-oil* that can be detected by GC-MS analyses. Both catalysts promoted the production of light oxygenates, aromatics, and oxygenated aromatics. Regarding the effect of the incorporation of metals, oxygenated aromatic compounds were the predominant family in the bio-oil* obtained with all ion-exchanged zeolites. Likewise, significant differences were observed among the catalysts regarding the main components of this family (alkylphenols, guaiacols, syringols, catechols, and methox-ybenzenes), achieving guaiacols concentrations in bio-oil* near to 24 wt.% for NaH-ZSM-5 and KH-ZSM-5 catalysts, and alkylphenols concentrations close to 16 wt.% for MgH-Beta and KH-Beta zeolites.

Despite being discovered more than 25 years ago, mesoporous aluminosilicates are still very relevant materials, considering the huge number of publications appearing every year harnessing them. Their notable features such as high BET surface area, accessible mesopore size, mild acidity and tunable pore wall thickness have resulted in different successful catalytic applications. Additionally, different kinds of mesoporous aluminosilicates may be found in literature (MCM-41, MCM-48, HMS, SBA-15, SBA-16, etc.) that allow to tailor to certain extent some physicochemical properties such as the spatial group, mesopore size and dimension, the pore wall thickness and consequently the hydrothermal stability, for the wanted catalytic application. This review is focused on discussing the main characteristics of the most common mesoporous aluminosilicates and exploring their reported performance in literature as supports of bifunctional catalysts for the hydrodearomatization (HDA) and desulfurization (HDS) of fuels. Although their hydrothermal stability has always been questioned by their lack of crystallinity, several successful applications of both MCM-41 and SBA-15 as supports of bifunctional catalysts for HDA/HDS of model compounds such as dibenzothiophene (DBT) can be found in literature, which in some cases interestingly also point out the prolonged stability of the catalyst, leading towards high yields of fuels by its mild acidity. Additionally, supported metal catalysts over mesoporous aluminosilicates might be the basis for the preparation of advanced bulk metal hydroprocessing catalysts, by application of different etching strategies. Therefore, this review will show these promising catalytic outcomes that opens up the application of mesoporous aluminosilicates as supports of bifunctional catalysts devoted to HDA/HDS of not only model sulfur/aromatic compounds but true fuels as well such as those proceeding from Kazakhstan oil.

The development of zeolites possessing dendritic features represents a great opportunity for the design of novel materials with applications in a large variety of fields and, in particular, in the energy sector to afford its transition towards a low carbon system. In the current work, ZSM-5 zeolite showing a dendritic 3D nanoarchitecture has been synthesized by the functionalization of protozeolitic nanounits with an amphiphilic organosilane, which provokes the branched aggregative growth of zeolite embryos. Dendritic ZSM-5 exhibits outstanding accessibility arising from a highly interconnected network of radially-oriented mesopores (3 – 10 nm) and large cavities (20 – 80 nm), which add to the zeolitic micropores, thus showing a well-defined trimodal pore size distribution. These singular features provide dendritic ZSM-5 with sharply enhanced performance in comparison with nano- and hierarchical reference materials when tested in a number of energy related applications, such as VOCs (toluene) adsorption (improved capacity), plastics (low-density polyethylene) catalytic cracking (boosted activity) and hydrogen production by methane catalytic decomposition (higher activity and deactivation resistance).

The use of organosilanes as mesopore generating agents produces hierarchical zeolites with enhanced accessibility, outstanding catalytic properties and great potential for the development of nanocomposite materials. The current work investigates the changes undergone by the samples recovered from the synthesis gel of hierarchical ZSM-5 at different stages of the crystallization, covering for the first time in this strategy the whole range from X-ray amorphous embryonic zeolites to fully crystalline materials. Increase of the silica connectivity, reduction of the BET surface and appearance of zeolitic-like entities are observed in the early stages of the synthesis, which is accompanied by an enhancement of the interactions between the organic structure directing agent (OSDA) and the inorganic components. Likewise, the hydrothermal treatment induces important variations in the Al coordination and the acid properties. All these changes have a noticeable effect on the catalytic behaviour of the embryonic zeolites for LDPE cracking, showing increasing plastic conversion from 25 to 85%. The occurrence of different types of evolving zeolite embryos is envisaged, exhibiting hybrid configurations (combination of cage encapsulation and core/shell structures) that reconciliate earlier opposite models. Likewise, it is concluded that crystal growth proceeds through aggregative events (first random, then oriented) of nanounits, which are partially hindered by the grafted organosilane molecules, thus affording the generation of globular particles with hierarchical porosity.

Crystallization of hierarchical ZSM-5 zeolite has been performed under hydrothermal conditions from silanized protozeolitic units. The role of amine and phenyl groups present in the organosilanes, as well as the use of dipodal silanization agents, on the creation of mesoporosity in the zeolite samples has been investigated. The presence of amine groups and dipodal moieties in the organosilane increases their interactions with the protozeolitic nanounits in the gel, which results in hierarchical zeolites showing enhanced secondary porosity and a higher degree of modification of the textural properties. Nevertheless, dipodal organosilanes hinder strongly the aggregation of the nanounits, leading to non-completely crystalline materials. In contrast, the combination of phenyl and amine groups into a single organosilane has shown to be effective for the generation of more uniform mesopores. Thus, N-(2-N-Benzylaminoethyl)-3-aminopropyltrimethoxysilane (Ph-2A) has been found as the best silanization agent, affording a hierarchical zeolite with a narrow mesopore size distribution and a high concentration of strong Bronsted acid sites. Moreover, during LDPE catalytic cracking in TGA tests, the latter material allowed the conversion of the polymer to occur in a narrow temperature range as a consequence of its more uniform acid and textural properties. Likewise, this sample exhibited a high activity in LDPE cracking at 340 degrees C using a laboratory scale reaction system to produce mainly gasoline-range hydrocarbons and light olefins.

Hierarchical ZSM-5 zeolite has been synthesized by hydrothermal crystallization of protozeolitic nanounits previously functionalized with two types of commercially available organosilanes. The first one (N,N-diethyl-3-aminopropyl-trimethoxysilane, DEAMP) is a monopodal organosilane that contains a tertiary amine group, whereas the second one (1,2-bis(trimethoxysilyl)decane, BTMDC) includes a long aliphatic chain and two tri-alkoxysilyl groups (dipodal organosilane). The properties of the samples obtained have been compared with two nanocrystalline ZSM-5 materials as references. While both organosilanes are effective in generation of a secondary porosity, enhancing strongly the textural properties of ZSM-5 zeolite, DEAMP affords for more uniform nanounits in the aggregates with narrower mesopore size distribution compared to BTMDC. On the other hand, varying the concentration of DEAMP during the silanization step (in the range of 2.5-10 mol%, referred to the silica content of the synthesis gel) it has been possible to synthesize hierarchical ZSM-5 samples showing progressively smaller size of the nanounits in the aggregates. This fact has led to important changes in both the textural and acid properties of the zeolite samples. In particular, a decrease in the Brunsted/Lewis acid sites ratio has been observed with increasing the concentration of DEAMP introduced in the synthesis gel. These materials have been tested as catalysts for low-density polyethylene (LDPE) cracking, showing enhanced catalytic activity in comparison with the two reference nanocrystalline ZSM-5 samples. A maximum of the LDPE conversion has been obtained with the h-ZSM-5 zeolite prepared with 5 mol% of silanization agent as this material exhibits an optimum combination of acidic features and accessibility.

Uniform mesoporosity has been effectively developed in hierarchical Beta zeolite by means of a hydrothermal treatment at 110 degrees C with an ammonia/surfactant solution. As a result, the broad pore size distribution, existing within the supermicropore-mesopore range in the parent hierarchical Beta sample, was rearranged into a uniform one centred at 40 A. In contrast, this treatment was less effective when applied to a conventional Beta zeolite sample with little secondary porosity. Neither amorphous phases nor MCM-41-like materials were detected after the mesopore narrowing treatment. Likewise, FTIR/pyridine measurements of the zeolite samples indicated that their acid properties were preserved after the ammonia/surfactant treatment, while just small variations were observed in the Si/Al ratio. Veratrole acylation tests were employed for assessing the catalytic properties of the samples. In spite of the reduction in the BET surface area produced by the mesopore narrowing treatment, the samples with uniform mesopores exhibited enhanced catalytic activity. In particular, the highest veratrole conversion was attained with the h-Beta (mnt) sample, obtained from the hierarchical Beta material. This result denotes the benefits derived from the presence of a high quality uniform mesoporosity on the catalytic performance of hierarchical Beta zeolite, as it increases the accessibility to the active sites and decreases the zeolite deactivation by product inhibition.

The catalytic performance of two types of heterogeneous acid catalysts—sulfonic acid-functionalized materials and aluminum containing zeolites,—in the dehydration of sorbitol to isosorbide, in solventless and autogenous pressure conditions, has been studied. Catalysts screening evidenced strong differences between sulfonic acid-based materials and acid zeolites in terms of catalytic performance. Whereas sulfonic materials, such as Amberlyst-70 and SBA-15-Pr-SO3H, showed a very high catalytic activity, zeolites with beta structure evidenced good catalytic performance together with minimized promotion of side reactions (production of non-desired sorbitans, humins, etc.). Kinetic studies performed at different temperatures, adjusting to a Langmuir–Hinshelwood type model, allowed correlating the physicochemical properties of the acid materials with their catalytic performance in sorbitol dehydration. Thus, the analysis of initial selectivity through kinetic constants comparison indicated that commercial beta zeolite with a Si/Al ratio of 19 is the most selective catalyst for the production of isosorbide, though following a slower kinetics than the sulfonic materials. Furthermore, an equivalent hierarchical beta zeolite has been synthesised and evaluated, resulting in a slight improvement of the catalytic performance, in terms of both yield and selectivity to isosorbide. This improvement is attributed to the superior textural properties.

Hierarchical Beta zeolites have been prepared employing two strategies of synthesis for the generation of mesopores with different size distribution. In both cases, the starting gel was subjected to pre-crystallization to induce the formation of protozeolitic nanounits. The first strategy involves the reorganization of the protozeolitic nanounits by incorporation of a surfactant (cetyltrimethylammonium bromide, CTAB), whereas the second one is based on the use of a silanization agent (phenylaminopropyl-trimethoxysilane, PHAPTMS) that it is grafted to the outer part of the nanounits to avoid their total merge during the crystallization process. In addition, conventional Beta zeolite and ordered mesoporous aluminosilicates have been prepared and employed as reference samples. All materials have been characterized by a number of techniques, whereas their catalytic behavior has been evaluated in the cracking of high density polyethylene (HDPE). The h-Beta (CTAB) sample shows a narrower mesopore size distribution, more uniform and stable tetrahedral Al species and a higher acid strength than the material obtained from silanized nanounits, although the latter exhibits a larger accessibility as denoted by its higher mesopore/external surface area (351 m(2)/g in h-Beta (PHAPTMS) versus 228 m(2)/g in h-Beta (CTAB)). While the ordered mesoporous aluminosilicates were almost inactive in HDPE cracking (<5 wt% of conversion) due to its weak acidity, high plastic conversions were obtained over the zeolite Beta samples (>50 wt% of conversion). The results obtained indicate that the overall catalytic activity depends mainly on the accessibility to the active sites, whereas the product selectivity is rather determined by the acid strength of the zeolite catalysts. Thus, h -Beta (crAB) sample promoted in a great extension both end-chain cracking and aromatization reactions due to its high acid strength. (C) 2016 Elsevier B.V. All rights reserved.

Lamellar and pillared ZSM-5 zeolites (L-ZSM-5 and PI-ZSM-5, respectively) were synthesized and tested in the catalytic cracking of low-density polyethylene (LDPE).

Hierarchical ZSM-5 with uniform mesoporosity was synthesized by the sequential coupling of two strategies: generation of secondary porosity by the crystallization of silanized protozeolitic units and a subsequent treatment with a basic surfactant-containing solution. The ZSM-5 zeolite obtained exhibited high crystallinity and contained two levels of uniform porosities within the micro-and mesopore ranges, respectively. The uniform mesoporosity is the result of the reorganization of irregular mesopores, created initially from the silanized protozeolitic units, via the local rearrangement of zeolitic fragments, and promoted by contact with a cationic surfactant under mild basic conditions. Interestingly, this second treatment was less effective when it is applied to a non-hierarchical ZSM-5 sample, showing that the presence of initial secondary porosity is essential for allowing the surfactant/ammonia solution to modify the zeolite and form uniform mesopores. Characterization of the zeolite samples using different techniques showed that the crystallinity, Al coordination and acidic features of the zeolite do not change significantly after the mesopore narrowing treatment, even though significant variations in the textural properties are observed as expected. The effects of the occurrence of regular mesoporosity on the catalytic properties of the hierarchical ZSM-5 zeolite were proven using the acylation of 2-methoxynaphthalene as a test reaction. The material with uniform mesopores showed both the highest activity and selectivity towards 6-acetyl-2-methoxynaphthalene, which was interpreted as the result of the presence of a more regular and less rough mesopore surface, which in turn facilitated the interaction between the reactant molecules and the active sites located and distributed over the mesopores.

The catalytic cracking of low density polyethylene (LDPE) was accomplished using nanocrystalline HZSM-5 zeolites. Nanocrystalline ZSM-5 zeolites were synthesized by a seed-assisted method from an organic template-free system employing three different seeding strategies: two of these strategies based on aqueous clear solutions containing the ZSM-5 precursors (silanized and non-silanized) and the third strategy based on a commercial ZSM-5 zeolite in powder form. The plastic cracking reactions were carried out at 380-420 degrees C, employing really mild conditions (plastic to catalyst mass ratio of 100). Nanocrystalline HZSM-5 zeolites prepared by seed-induced synthesis based on liquid solutions exhibit a superior catalytic activity than the reference microcrystalline zeolite. Conversion values very close to 100% are achieved at 420 degrees C, by using these catalysts, while significant conversion values (>50%) are still attained at 380 degrees C. Moreover, these nanocrystalline HZSM-5 zeolites promote the production of a high proportion of light olefins (>60% at 380 degrees C), propylene, 1-butene, isobutene, being the main products (similar to 50%). Nanocrystalline HZSM-5 synthesized from a clear solution containing an organic structure-directing agent (TPA(+)) exhibits a 100% conversion value at 380 degrees C. However, the economic and environmental advantages of the seed assisted synthesis from a TPA(+) free system and the remarkable activity showed by the nanocrystalline zeolites obtained, makes of these materials interesting catalysts in the LDPE catalytic cracking. (C) 2015 Elsevier B.V. All rights reserved.

Hierarchical ZSM-5 zeolites were prepared by crystallization of silanized protozeolitic units employing silylated polypropylene oxide diamine polymers as organosilanes. The influence of the (Si-pol/Si-gel) molar ratio was investigated within 0-0.15 range. High synthesis yields (similar to 90%) of well-crystallized hierarchical zeolites exhibiting a high proportion of secondary porosity (additional to the zeolitic micropores) was reached for (Si-pol/Si-gel) molar ratios lower than 0.08. The usage of the silylated polymer resulted in hierarchical ZSM-5 with larger mesopores (4-20 nm) in higher share than the hierarchical ZSM-5 prepared with a smaller organosilane (phenyl-aminopropyl-trimethoxysilane, PHAPTMS). However, it also contained meaningfully lower amount of acid sites and with less acid strength. The best catalytic performance in the cracking of low density polyethylene (LDPE) was showed by the material prepared from a (Si-pol/Si-gel) ratio of 0.03. Noteworthy, in addition to the gasoline range fraction (C-6-C-12), light C-1-C-5 olefins are the main reaction products, which are interesting feedstock for the petrochemical industry. Its catalytic performance is similar to the hierarchical ZSM-5 prepared using the smaller organosilane (PHAPTMS), which is indicative that the enhanced accessibility to the acid sites due to the presence of larger mesopores (4-20 nm) makes up for the lower amount and strength of its acid sites. Thereby, it is possible to enhance the mesoporosity by using bulkier organosilane (silylated polymers) but at the expense of losing acid properties. (C) 2013 Elsevier B.V. All rights reserved.

A variety of H-ZSM-5 zeolites with hierarchical porosity, that is, containing both the characteristic zeolite micropore system and additional mesoporosity were prepared according to the method of crystallization from silanized seeds. These materials differing in crystallinity and textural properties were compared with nanocrystalline H-ZSM-5 samples, and tested in the catalytic cracking of low density polyethylene (LDPE). The selected catalysts range from fully crystalline according to XRD and FTIR to amorphous ones. As crystallinity diminishes, microporosity decreases, BET surface area increases (up to 1085 m2g-1) and secondary mesoporosity appears, with pore diameters centered at 20 and 400 Å. Cracking reactions were carried out employing really mild conditions: 340 oC and plastic/catalyst mass ratio of 100. Turnover frequencies values (TOF) from 0.03 to 0.90 were attained, the most active materials being those combining high crystallinity and acid sites fully accessible through the additional mesopores generated (20-70 Å). The selectivity depends on the catalyst employed but the major products were C1-C5 hydrocarbons, percentages always higher than 50% being attained. The amount of middle distillates (>C13) was always below 2%.

The synthesis of hierarchical TS-1 zeolites has been accomplished following a strategy based on the silanization of protozeolitic units. This kind of zeolites is characterized by having a secondary porosity in the supermicro/mesopore range and, therefore, enhanced textural properties. The generation of this secondary porosity is caused by the presence of the silanization agent, which acts as crystal growth inhibitor. However, when a high proportion of organosilane is introduced into the synthesis medium, a highly viscous gel is formed, which reduces the anchoring of the organosilane molecules onto the protozeolitic units. In order to improve the silanization process in these conditions, a variety of alcohols (methanol, ethanol and 2-propanol) has been tested as solvents during the silanization step. The alcohol addition increases the incorporation of the silanization agent onto the zeolite, which is attributed to a reduction in the synthesis media viscosity. Likewise, the alcohols may also undergo grafting onto the external surface of the protozeolitic units through alkoxylation reactions, improving the crystal growth inhibitor effect of the silanization agent. As a consequence, these materials exhibit enhanced textural properties, with a higher secondary porosity contribution, especially when ethanol is used as solvent. Hierarchical TS-1 zeolites prepared adding alcohols in the silanization step show improved catalytic activity in 1-octene epoxidation using tert-butylhydroperoxide as oxidant, due to a higher proportion of more accessible titanium sites. Moreover, it is noteworthy that a reasonable correlation exists between the catalytic activity and the surface attributed to the secondary porosity.

Hierarchical ZSM-5 zeolite has been synthesized by means of a method involving a precrystallization stage to form the protozeolitic units, the addition and subsequent grafting of both silanization and alkoxylation agents, and a final hydrothermal crystallization. The influence of the alkoxylation with different alcohols (methanol, ethanol, 2-propanol and n-butanol) on the properties of the final hierarchical ZSM-5 samples has been investigated. In every case, the alcohol addition increased the incorporation of the seed silanization agent as it decreases the gel viscosity. In addition, the presence of alcohols deeply affects the physicochemical properties of the final materials. The samples prepared with 2-propanol and methanol were highly crystalline and presented improved textural properties with regard to the reference h-ZSM-5 and n-ZSM-5. In contrast, the samples obtained with ethanol and n-butanol were partially and totally X-ray amorphous, respectively. H-1 and C-13-CP solid state MAS NMR spectra proved the alkoxylation of the external surface of the protozeolitic units. Catalytic cracking of LDPE pointed out the higher TOF values obtained over the hierarchical samples prepared with methanol and 2-propanol due to a right combination of accessibility and crystallinity in these materials. The differences observed among the samples prepared with alcohols were ascribed to the strong interaction produced between the silanization agent and the linear alcohols on the surface of the protozeolitic nanounits, which form a very stable protective layer, hindering their aggregation and subsequent crystallization. (C) 2010 Elsevier B.V. All rights reserved.

The hydroreforming of the liquid product resulting from LDPE thermal cracking at 400°C (C5–C40) has been studied using Ni supported hierarchical zeolites (Ni/h-ZSM-5, Ni/h-Beta) and mesostructured materials (Ni/Al-MCM-41 and Ni/Al-SBA-15) as catalysts. Hydroreforming experiments were carried out at 310°C under 20bar of hydrogen. All the catalysts were synthesized with a Si/Al atomic ratio of 30 and a Ni content of 7wt%. According to XRD, TPR and TEM data, the activated catalysts displayed Ni particles both over the external surface and inside the catalyst pores in different percentages depending on their porous structure and nature. Complete hydrogenation of the olefins was observed over both mesostructured catalysts (Ni/Al-SBA-15 and Ni/Al-MCM-41) and hierarchical Ni/h-Beta. In contrast, over Ni/h-ZSM-5, there is always left about 30% of olefins, due to an imbalance in the acid and metal function. Ni/h-ZSM-5 led towards significant amounts of gases (∼18%) while gasoline range hydrocarbons were the main products (55%) over Ni/h-Beta, at the expense of diesel fractions. In contrast, the hydrocracking extent was far lower over Ni/Al-MCM-41 and Ni/Al-SBA-15, the latter showing additionally the appearance of a slight degree of oligomerization, which led towards an increase in the heavy diesel fraction (C19–C40). Hydroisomerization reactions also occur, mostly in the case of Ni supported hierarchical zeolites. Likewise, aromatics were formed over these catalysts in a large extent. The RON number of the gasolines obtained at 310°C was within 81–89 depending on the chosen catalysts while the cetane index (CCI) of the diesel fraction was around 70–80. On the other hand, Ni leaching was not detected.

Two series of hierarchical nanocrystalline ZSM-5 zeolites prepared by different synthesis strategies (at low temperature and from silanized seeds) and with external surface areas ranging from 150 to 250 m(2) g(-1) were tested in the cracking of pure LDPE and HDPE at 340 degrees C and of waste polyethylene at 360 degrees C Hierarchical zeolites showed quite higher activity with values even six times higher than a standard nanocrystalline sample used as reference (n-HZSM-5) The activity values decreased from LDPE to HDPE due to the occurrence of some degree of branching in the former polymer which act as preferential cracking sites The major products were C-1-C-4 hydrocarbons (in the range 30-70% mostly C-3-C-4 olefins) and C-5-C-12 hydrocarbons (20-60%) whose share depends on both the polyolefin and the catalyst The amount of C-13-C-40 hydrocarbons was practically negligible (< 1%) due to the high acid strength of the zeolites which promotes end chain cracking reactions Likewise hierarchical nanocrystalline HZSM-5 zeolites prepared from silanized protozeolitic units showed higher activities than the hierarchical nanocrystalline HZSM-5 samples synthesized at low temperature and atmospheric pressure The differences were especially remarkable in the case of waste polyethylene cracking These results were ascribed to the stronger acidity of the hierarchical zeolite samples prepared from silanized seeds (C) 2010 Elsevier Inc All rights reserved