Examinando por Autor "Serrano, D.P."

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Catalytic activity of the beta zeolite with enhanced textural properties in the Friedel-Crafts acylation of aromatic compounds
(ELSEVIER, 2008) Garcia, R.A.; Serrano, D.P.; Vicente, G.; Otero, D.; Linares, M.
Friedel-Crafts acylation is widely used for the production of aromatic ketones applied as intermediates in both fine chemicals and pharmaceutical industries. The reaction is carried out by using conventional homogenous catalysts, which represents significant technical and environmental problems. The present work reports the results obtained in the Friedel-Crafts acylation of aromatic substrates (anisole and 2-methoxynaphthalene) catalyzed by Beta zeolite obtained by crystallization of silanized seeds. This material exhibits hierarchical porosity and enhanced textural properties. For the anisole acylation, the catalytic activity over the conventional Beta zeolite is slightly higher than with the modified Beta material, probably due to the relatively small size of this substrate and the weaker acidity of the last sample. However, the opposite occurred in the acylation of a bulky substrate (2-methoxynaphthalene), with the modified Beta showing a higher conversion. This result is interpreted due to the presence of a hierarchical porosity in this material, which favors the accessibility to the active sites.
Catalytic cracking of HDPE over hybrid zeolitic-mesoporous materials
(ELSEVIER, 2005) Garcia, R.A.; Serrano, D.P.; Otero, D.
The potential application of hybrid ZSM-5/MCM-41 materials for the catalytic degradation of high density polyethylene (HDPE) has been investigated and compared with the behavior of a standard Al-MCM-41 sample. Hybrid zeolitic-mesoporous materials were prepared from zeolite seeds obtained in different stages of ZSM-5 crystallization by variation of the synthesis time. The seeds were assembled around cetyltrimethyl ammonium bromide (CTAB) micelles to obtain hybrid materials having a combination of both zeolitic and mesostructured features. The samples so obtained have exhibited remarkable catalytic activity in the HDPE cracking despite the low temperatures (380 ºC) and catalyst loadings used (plastic/catalyst mass ratio =100), leading to polyolefin conversions higher than Al-MCM-41. The product distribution observed with the hybrid materials is closer to that typically obtained in the HDPE cracking over HZSM-5 zeolite, with a high proportion of light hydrocarbons. Moreover, the products present a high content of C2-C5 olefins, which is an interesting result regarding its possible use as raw chemicals. Increasing the zeolitic crystallinity of the hybrid materials causes an enhancement in the production of heavier products with boiling points within the gasoline range.
Catalytic cracking of polyethylene over zeolite mordenite with enhanced textural properties
(ELSEVIER, 2008) Aguado, José; Serrano, D.P.; Escola, J. M.; Peral, A.
Catalytic cracking of low density polyethylene (LDPE) has been investigated using different samples of mordenite zeolite as catalysts. In order to obtain materials with different textural properties, a new synthesis method based on the functionalization of the zeolite seeds with an organosilane was employed. Mordenite samples with BET and external surface areas in the range 385-485 m2/g and 9-57 m2/g respectively, were prepared. LDPE catalytic cracking reactions were performed at 420 ºC for 2h in a batch reactor provided with a screw stirrer under a continuous nitrogen flow. Thermal cracking of LDPE leads to plastic conversion lower than 30%, while values of 40% are reached when traditional mordenite is used as catalyst. In contrast, when mordenite samples with enhanced textural properties were employed, a plastic conversion of 60% is attained, both gas (C1-C5) and gasoline (C6-C12) fractions being obtained as main products. On the contrary, gasoline fraction is not observed and a heavier hydrocarbon fraction in the range C13-C35 is detected when thermal cracking or even catalytic cracking over traditional mordenite samples are carried out. The formation of lighter hydrocarbon products (C6-C12) over mordenite samples with enhanced textural properties is assigned to the higher activity and accessibility of their acid sites, which promotes both end-chain and random scission cracking reactions of the polymer molecules.
Catalytic hydrodeoxygenation of m-cresol over Ni2P/hierarchical ZSM-5
(Elsevier B.V., 2018) Berenguer, A.; Bennett, J.A.; Hunns, J.; Moreno, I.; Coronado, J.M.; Lee, A.F.; Pizarro, P.; Wilson, K.; Serrano, D.P.
Bifunctional catalysts comprising Ni2P supported over a hierarchical ZSM-5 zeolite (h-ZSM-5) were synthesized and applied to the hydrodeoxygenation (HDO) of m-cresol, a model pyrolysis bio-oil compound. Surface and bulk characterization of Ni2P/h-ZSM-5 catalysts by XRD, TEM, DRIFTS, TPR, porosimetry and propylamine temperature-programmed desorption reveal that Ni2P incorporation modifies the zeolite textural properties through pore blockage of the mesopores by phosphide nanoparticles, but has negligible impact of the micropore network. Ni2P nanoparticles introduce new, strong Lewis acid sites, whose density is proportional to the Ni2P loading, accompanied by new Brönsted acid sites attributed to the presence of P–OH moieties. Ni2P/h-ZSM-5 is ultraselective (97%) for m-cresol HDO to methylcyclohexane, significantly outperforming a reference Ni2P/SiO2 catalyst and highlighting the synergy between metal phosphide and solid acid support. m-Cresol conversion was proportional to Ni2P loading reaching 80 and 91% for 5 and 10 wt% Ni respectively. Turnover frequencies for m-cresol HDO are a strong function of Ni2P dispersion, evidencing structure sensitivity, with optimum activity observed for 4 nm particles.
Catalytic upgrading of a model polyethylene pyrolysis oil by hydroconversion over Ni-containing hierarchical Beta zeolites with tailored acidity
(Elsevier, 2023) Briones, L.; Cordero, A.; Alonso-Doncel, M.; Serrano, D.P.; Escola, J.M.
Valorization of waste polyolefins by a sequential combination of thermal pyrolysis and catalytic hydroconversion over a bifunctional metal/acid catalyst (e.g. zeolite) is an efficient route to produce transportation fuels. However, the zeolite strong acidity typically causes extensive cracking and loss of liquid fuels. In this work, mild dealumination with oxalic acid of a hierarchical Beta zeolite was used to achieve Ni 7%/h-Beta catalysts with Si/ Al ratios within the 25 – 130 range. These catalysts were tested in the hydroconversion of a model mixture of LDPE thermal pyrolysis product (1-dodecene/n-dodecane, 50/50 w/w). The highest share of liquid fuels (~ 90%) was achieved over 7% Ni/h-Beta (SiAl = 130). Besides, due to its high accessibility and tailored acidity, the product contained a meaningful amount of isoparaffins (12%) and a negligible content of olefins (< 3.5%). Thus, this catalyst holds promise for plastic waste hydroconversion towards transportation fuels.
Catalytic upgrading of lignin-derived bio-oils over ion-exchanges H-ZSM-5 and H-Beta zeolites
(Elsevier, 2023-10-20) Avila, M.I.; Alonso-Doncel, M.M.; Briones, L.; Gómez-Pozuelo, G.; Escola, J. M.; Serrano, D.P.; Peral, A.; Botas, J. A.
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 ex-situ configuration operating at 550 ◦C (thermal zone) and 450 ◦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 biooil* 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 methoxybenzenes), 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.
CO2 adsorption on amine-functionalized clays
(Elsevier B.V., 2019) Gómez-Pozuelo, G.; Sanz-Pérez, E.S.; Arencibia, A.; Pizarro, P.; Sanz, R.; Serrano, D.P.
Carbon capture using amine-modified porous sorbents is one of the main proposed technologies to reduce the CO2 atmospheric concentration. In this work, a wide series of inexpensive clays have been selected to assess their role as supports of amine-containing sorbents for CO2 capture. Montmorillonite, bentonite, saponite, sepiolite and palygorskite have been hydrated and functionalized by three routes: (a) grafting with aminopropyl (AP) and diethylenetriamine (DT) organosilanes; (b) impregnation with polyethyleneimine (PEI); and (c) double functionalization by impregnating previously grafted samples. XRD, FTIR and N2 adsorption-desorption analyses along with nitrogen content and CO2 adsorption properties (thermogravimetry and fixed bed) have been evaluated for bare and functionalized clays. Under dry conditions (45 °C, 1 bar), grafted and impregnated samples yielded CO2 uptakes as high as 61.3 and 67.1 mg CO2/g ads (for Sepi-DT and Paly-PEI, respectively), with the latter being the best-performing sample in terms of CO2 uptake. On the contrary, double-functionalized samples displayed poor CO2 adsorption properties, probably due to pore-blocking problems related to their high organic loading. The presence of 5% H2O in the feed gas resulted in CO2 uptake increments from 17 to 27%. The adsorption performance of AP, DT and PEI-containing samples was maintained after three adsorption-desorption cycles
Engineering the acidity and accessibility of the zeolite ZSM-5 for efficient bio-oil upgrading in catalytic pyrolysis of lignocellulose
(Royal Society of Chemistry, 2018) Hernando, H.; Hernández-Gimenez, A.M.; Ochoa-Hernández, C.; Bruijnincx, P.C.A.; Houben, K.; Baldus, M.; Pizarro, P.; Coronado, J.M.; Fermoso, J.; Cejka, J.; Weckhuysen, B.M.; Serrano, D.P.
The properties of the zeolite ZSM-5 have been optimised for the production and deoxygenation of the bio-oil∗ (bio-oil on water-free basis) fraction by lignocellulose catalytic pyrolysis. Two ZSM-5 supports possessing high mesopore/external surface area, and therefore enhanced accessibility, have been employed to promote the conversion of the bulky compounds formed in the primary cracking of lignocellulose. These supports are a nanocrystalline material (n-ZSM-5) and a hierarchical sample (h-ZSM-5) of different Si/Al ratios and acid site concentrations. Acidic features of both zeolites have been modified and adjusted by incorporation of ZrO2, which has a significant effect on the concentration and distribution of both Brønsted and Lewis acid sites. These materials have been tested in the catalytic pyrolysis of acid-washed wheat straw (WS-ac) using a two-step (thermal/catalytic) reaction system at different catalyst/biomass ratios. The results obtained have been assessed in terms of oxygen content, energy yield and composition of the produced bio-oil∗, taking also into account the selectivity towards the different deoxygenation pathways. The ZrO2/n-ZSM-5 sample showed remarkable performance in the biomass catalytic pyrolysis, as a result of the appropriate combination of accessibility and acidic properties. In particular, modification of the zeolitic support acidity by incorporation of highly dispersed ZrO2 effectively decreased the extent of secondary reactions, such as severe cracking and coke formation, as well as promoted the conversion of the oligomers formed initially by lignocellulose pyrolysis, thus sharply decreasing the proportion of the components not detected by GC-MS in the upgraded bio-oil∗
Feedstock recycling of agriculture plastic film wastes by catalytic cracking
(ELSEVIER, 2004) Serrano, D.P.; Aguado, José; Escola, J. M.; Garagorri, E.; Rodríguez, J. M.; Morselli, L.; Palazzi, G.; Orsi, R.
Feedstock recycling by catalytic cracking of a real plastic film waste from Almeria greenhouses (Spain) towards valuable hydrocarbon mixtures has been studied over several acid catalysts. The plastic film waste was mostly made up of ambient degraded low-density polyethylene (LDPE) and ethylene-vinyl acetate copolymer (EVA), the vinyl acetate content being around 4 wt %. Nanocrystalline HZSM-5 zeolite (crystal size ¿ 60 nm) was the only catalyst capable of degrading completely the refuse at 420ºC despite using a very small amount of catalyst (plastic / catalyst mass ratio of 50). However, mesoporous catalysts (Al-SBA-15 and Al-MCM-41), unlike it occurred with virgin LDPE, showed fairly close conversions to that of thermal cracking. Nanocrystalline HZSM-5 zeolite led to 60 wt % selectivity towards C1 - C5 hydrocarbons, mostly valuable C3 - C5 olefins, what would improve the profitability of a future industrial recycling process. The remarkable performance of nanocrystalline HZSM-5 zeolite was ascribed to its high content of strong external acid sites due to its nanometer dimension, which are very active for the cracking of bulky macromolecules. Hence, nanocrystalline HZSM-5 can be regarded as a promising catalyst for a feasible feedstock recycling process by catalytic cracking.
H2 Production from methane pyrolisis over commercial carbon catalysts: Kinetic and deactivation study
(ELSEVIER, 2009) Serrano, D.P.; Botas, Juan Ángel; Guil Lopez, R.
Hydrogen production from catalytic methane decomposition (DeCH4) is a simple process to produce high purity hydrogen with no formation of carbon oxides (CO or CO2). However, to completely avoid those emissions, the catalyst must not be regenerated. Therefore, it is necessary to use inexpensive catalysts, which show low deactivation during the process. Use of carbon materials as catalysts fulfils these requirements. Methane decomposition catalysed by a number of commercial carbons has been studied in this work using both constant and variable temperature experiments. The results obtained showed that the most active catalyst at short reaction times was activated carbon, but it underwent a fast deactivation due to the deposition of the carbon formed from methane cracking. On the contrary, carbon blacks, and especially the CB-bp sample, present high reaction rates for methane decomposition at both short and long reaction times. Carbon nanotubes exhibit a relatively low activity in spite of containing significant amounts of metals. The initial loss of activity observed with the different catalysts is attributed mainly to the blockage of their micropores due to the deposition of the carbon formed during the reaction.
Influence of the calcination treatment on the catalytic properties of hierarchical zsm-5
(Elsevier, 2012-01) Serrano, D.P.; García, R.A.; Linares, M.; Gil, B.
The effect on the calcination conditions on the properties and catalytic performance of hierarchical and standard ZSM-5 zeolite samples have been investigated using different reactions as catalytic tests: acylation of aromatic substrates (anisole and 2- metoxynaphtalene) and rearrangement of linear and cyclic epoxides (1,2-epoxyoctane and isophorone oxide). The h-ZSM-5 material was prepared by crystallization of silanized protozeolitic units. The removal of the organics present in the as-synthesized forms of both ZSM-5 samples has been carried out using two different calcination procedures. The first one takes place under air atmosphere from room temperature to 550ºC for 5 hours, whereas the second one is performed under nitrogen at 400ºC for 4 hours, followed by treatment at 550ºC for 5 hours under air atmosphere. Clear differences are noticed related to the textural properties of the ZSM-5 samples. Thus, h- ZSM-5 presents not only higher BET surface than standard ZSM-5 zeolite, but 75% of its total area is shared by surface located outside the zeolite micropores. FTIR studies showed almost no differences between the acidic properties of the conventional zeolite calcined by both methods. However, noticeable changes were observed over the hierarchical zeolite. Thus, the concentration of Brønsted acid sites decreases by half in the case of one-step air calcination, but only a quarter when using two-step nitrogen/air calcination. These changes in the acidic properties denote that the aluminium present in hierarchical ZSM-5 is very sensitive to the calcination conditions. Furthermore, this has also significant effects on the catalytic properties of this material in both aromatic acylation and epoxide rearrangement reactions. For both types of reactions, the hierarchical sample calcined under a two-step nitrogen/air treatment presents higher activity and product yields than the same material when calcined under one-step air atmosphere. Therefore, controlling the calcination conditions is an effective method in preserving the acidic features of hierarchical ZSM-5, which in turn has a positive influence on its catalytic behaviour.
Insights on the acetic acid pretreatment of wheat straw: Changes induced in the biomass properties and benefits for the bio-oil production by pyrolysis
(Elsevier B.V., 2023) Pagano, M.; Hernando, H.; Cueto, J.; Cruz, P.L.; Dufour, J.; Moreno, I.; Serrano, D.P.
This work discloses how the pretreatment of wheat straw with acetic acid (AA) solutions modifies the biomass composition, strongly affecting the pyrolysis product distribution. AA in diluted solutions is a renewable and eco-friendly reagent, being also one of the main components of the pyrolysis bio-oil* (water-free basis). In comparison with water and diluted ammonia treatments, AA washing leads to a higher removal degree of alkali and alkaline-earth elements (AAEMs) from the biomass ash. In addition, the AA pretreatment reduces the content of char and gas precursors, as is the case of soluble lignin and extractives. Consequently, the bio-oil* yield is drastically increased up to ∼53 wt% during the pyrolysis of the AA washed wheat straw, being much higher than the value obtained for the raw biomass (∼35 wt%). Likewise, the bio-oil* composition is highly improved by the pretreatment with AA, dramatically increasing the concentration and yield of levoglucosan, which is a valuable precursor to produce both advanced biofuels and bio-based chemicals. In contrast, the opposite occurs during the pyrolysis of the extracted matter samples, recovered from the washing solutions, since its high content of AAEMs, lignin and extractives promotes the formation of char and gases in the detriment of the bio-oil fraction. Based on a preliminary technoeconomic analysis, it is concluded that pretreatment with AA solutions may improve significantly the economic performance of the wheat straw pyrolysis process. This is due to the increased incomes coming from the higher yield of both bio-oil* and levoglucosan that largely compensate the additional capital and fresh AA costs.
SYNTHESIS OF HIERARCHICAL TS-1 ZEOLITE FROM SILANIZED SEEDS
(ELSEVIER, 2010) Serrano, D.P.; Sanz, Raúl; Pizarro, Patricia; Moreno, Inés
Hierarchical TS-1 zeolites with a bimodal pore architecture, consisting of the typical MFI micropores and an additional mesoporosity, have been synthesized by grafting an organosilane compound to the zeolitic seeds previously prepared from two different raw materials: a liquid gel and an amorphous SiO2-TiO2 xerogel. These hierarchical TS-1 zeolites show an excellent catalytic behavior in olefin epoxidation reactions employing organic hydroperoxides as oxidants due to the presence of the secondary mesoporosity, which makes possible the access and interaction of bulky molecules with the Ti active sites
SYNTHESIS OF HIERARCHICAL ZSM-5 BY SILANIZATION AND ALKOXYLATION OF PROTOZEOLITIC UNITS
(ELSEVIER, 2011) Serrano, D.P.; Aguado, J.; Escola, J.M.; Peral, Ángel; Morales, Gabriel; Abella, E.
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. 1H and 13C-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.
The role of the surface acidic/basic centers and redox sites on TiO2 in the photocatalytic CO2 reduction
(Elsevier B.V., 2022) Collado, L.; Reñones, P.; Fermoso, J.; Fresno, F.; Garrido, L.; Pérez-Dieste, V.; Escudero, C.; Hernández-Alonso, M.; Coronado, J.M.; Serrano, D.P.; de la Peña O´Shea, V.A.
The development of sustainable processes for CO2 reduction to fuels and chemicals is one of the most important challenges to provide clean energy solutions. The use of sunlight as renewable energy source is an interesting alternative to power the electron transfer required for artificial photosynthesis. Even if redox sites are mainly responsible for this process, other reactive acidic/basic centers also contribute to the overall reaction pathway. However, a full understanding of the CO2 photoreduction mechanism is still a scientific challenge. In fact, the lack of agreement on standardized comparison criteria leads to a wide distribution of reported productions, even using the same catalyst, which hinders a reliable interpretation. An additional difficulty is ascertaining the origin of carbon-containing products and effect of surface carbon residues, as well as the reaction intermediates and products under real dynamic conditions. To determine the elusive reaction mechanism, we report an interconnected strategy combining in-situ spectroscopies, theoretical studies and catalytic experiments. These studies show that CO2 photoreduction productions are influenced by the presence of carbon deposits (i.e. organic molecules, carbonates and bicarbonates) over the TiO2 surface. Most importantly, the acid/base character of the surface and the reaction medium play a key role in the selectivity and deactivation pathways. This TiO2 deactivation is mainly initiated by the formation of carbonates and peroxo- species, while activity can be partially recovered by a mild acid washing treatment. We anticipate that these findings and methodology enlighten the main shadows still covering the CO2 reduction mechanism, and, most importantly, provide essential clues for the design of emergent materials and reactions for photo(electro)catalytic energy conversion.
Towards the improvement of methane production in CO2 photoreduction using Bi2WO6/TiO2 heterostructures
(Elsevier, 2023) Collado, L.; Gómez-Mendoza, M.; García-Tecedor, M.; Oropeza, F.E.; Reynal, A,; Durrant, J.R.; Serrano, D.P.; de la Peña O´Shea, V.A.
Russelite bismuth tungstate (Bi2WO6) has been widely reported for the photocatalytic degradation and mineralization of a myriad of pollutants as well as organic compounds. These materials present perovskite-like structure with hierarchical morphologies, which confers excellent optoelectronic properties as potentials candidates for photocatalytic solar fuels production. Here, we propose the development of Bi2WO6/TiO2 heterojunctions for CO2 photoreduction, as a promising solution to produce fuels, alleviate global warming and tackle fossil fuel shortage. Our results show an improvement of the photocatalytic activity of the heterojunctions compared to the pristine semiconductors. Near Ambient Pressure X-ray Photoelectron Spectroscopy (NAP-XPS) experiments reveals a preferential CO2 adsorption over TiO2. On the other hand, transient absorption spectroscopy measurements show that the charge transfer pathway in Bi2WO6/TiO2 hybrids leads to longer-lived photogenerated carriers in spatially separated redox active sites, which favor the reduction of CO2 into highly electron demanding fuels and chemicals, such as CH4 and C2H6.
Unravelling the effect of charge dynamics at the plasmonic metal/semiconductor interface for CO2 photoreduction
(Nature Publishing Group, 2018) Collado, L.; Reynal, A.; Fresno, F.; Barawi, M.; Escudero, C.; Pérez-Dieste, V.; Coronado, J.M.; Serrano, D.P.; Durrant, J.R.; de la Peña O´Shea, V.A.
Sunlight plays a critical role in the development of emerging sustainable energy conversion and storage technologies. Lightinduced CO2 reduction by artificial photosynthesis is one of the cornerstones to produce renewable fuels and environmentally friendly chemicals. Interface interactions between plasmonic metal nanoparticles and semiconductors exhibit improved photoactivities under a wide range of the solar spectrum. However, the photo-induced charge transfer processes and their influence on photocatalysis with these materials are still under debate, mainly due to the complexity of the involved routes occurring at different timescales. Here, we use a combination of advanced in situ and time-resolved spectroscopies covering different timescales, combined with theoretical calculations, to unravel the overall mechanism of photocatalytic CO2 reduction by Ag/TiO2 catalysts. Our findings provide evidence of the key factors determining the enhancement of photoactivity under ultraviolet and visible irradiation, which have important implications for the design of solar energy conversion materials.
ZSM-5 zeolites performance assessment in catalytic pyrolysis of PVC-containing real WEEE plastic wastes
(Elsevier, 2022-05-01) Marino, A.; Aloise, A.; Hernando, H.; Fermoso, J.; Cozza, D.; Giglio, E.; Migliori, M.; Pizarro, P.; Giordano, G.; Serrano, D.P.
Catalytic pyrolysis of plastic wastes is a promising way for their conversion into valuable products. By modulating the catalyst properties and operating conditions, it is possible to direct the product distribution to obtain oils that may be suitable both as fuels and as chemicals. However, the efficient and safe removal of the halogens, often contained in plastic wastes, remains as a great challenge. In this work, the catalytic behaviour of ZSM-5 zeolites in the pyrolysis of a real chlorinated plastic waste of the electric and electronic equipment sector (WEEE), consisting of PE with about 3.4% of PVC, was investigated. To that end, three zeolite samples with different acidity and accessibility were synthesized and assayed. A thermal pre-treatment was applied to the plastic waste at 350 ºC, which allowed a chlorine removal of 87% from the WEEE feedstock. The pyrolysis tests were carried out in a downdraft fixed-bed stainless steel reactor, with a catalyst/feedstock ratio of 0.2, at temperatures of 600 ºC and 450 ºC in the thermal and catalytic zones, respectively, of the reaction system. In comparison with thermal pyrolysis, that mainly produced waxes, the product distribution changed considerably by contacting the pyrolysis vapours with ZSM-5 zeolites, leading to a strong enhancement in the yield of oil and gases. The largest yield of oil (about 60 wt%), having a concentration of monoaromatics (mainly BTX) above 50 wt%, was attained over the desilicated ZSM-5 sample. Regarding chlorine distribution, about 90% was accumulated in the char fraction, probably captured by the inorganic components present in the raw WEEE waste. Coke was the second fraction in terms of Cl concentration, followed by wax and oil, whereas this halogen was almost not detected in the gases. The lowest concentration of Cl in the oil was attained with the desilicated zeolite, with a value below 90 ppm, which could facilitate the subsequent processing of this stream in refinery units.