Examinando por Autor "Fermoso, J."

Mostrando 1 - 3 de 3

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∗
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.
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.