Implications of Co-Feeding Water on the Growth Mechanisms of Retained Species on a SAPO-18 Catalyst during the Methanol-to-Olefins Reaction

The dynamics of retained and deactivating species in a SAPO-18 catalyst during the methanol-to-olefins reaction have been followed using a combination of ex-situ and in-situ techniques in differential and integral reactors.The retained species were analyzed using extraction, in-situ FTIR and in-situ UV-vis spectroscopies combined with online product analysis (gas chromatography and mass spectrometry). The composition of the extracted soluble species was determined using gas chromatography-mass spectrometry and that of the insoluble species using high-resolution mass spectrometry. We observe a decrease in the formation and degradation rates of retained species when co-feeding water, whereas the extent of the decreases is the same across the entire spectrum of retained molecules. This indicates that co-feeding water unselectively quenches the formation of active and deactivating species. At the same time, the catalyst has an extended lifetime when co-feeding water due to the diffusion of species (particularly olefins) out of the SAPO-18 crystals, and subsequent growth of heavy polycyclic aromatic structures that imply less deactivation. These conclusions can be extrapolated to other MTO catalysts with relatively similar pore topology such as SAPO-34 or SSZ-13 structures.This work was possible thanks to the financial support of the Ministry of Economy, Industry and Competitiveness of the Spanish Government (Project CTQ2016-79646-P, co-founded with ERDF funds), the Basque Government (Project IT748-13, IT912-16) and the King Abdullah University of Science and Technology (KAUST). J.V. is thankful for his fellowship granted by the Ministry of Economy, Industry and Competitiveness of the Spanish Government (BES-2014-069980). The authors are thankful for technical and human support provided by IZO-SGI SGIker of UPV/EHU and European funding (ERDF and ESF)

Evaluating catalytic (gas-solid) spectroscopic cells as intrinsic kinetic reactors: Methanol-to-hydrocarbon reaction as a case study

Commercial spectroscopic gas-solid cell reactors are routinely used to analyze the dynamics of the catalyst (catalyst pelletized as a disc) structure and retained/adsorbed species using multiple operando techniques. These instruments have revolutionized the understanding of many catalytic reactions, including the methanol-to-hydrocarbon reactions. We propose a reaction engineering framework to evaluate spectroscopic cells based on (a) analyzing the fluid dynamic performance, (b) comparing their performance with a reference packed-bed reactor, and (c) the assessment of the external and internal mass transfer limitations. We have used a Specac HTHP and a Linkam THMS600 cell reactors coupled with the corresponding gas conditioning, spectroscopic, and mass spectrometry apparatuses. Our results reveal that these cells approach a perfect mixing only with several equivalent tanks in series and they are reliable at low catalyst loadings (thin disc) and high flowrates (low spacetimes). Under these conditions, we can avoid external-internal mass transfer limitations and fluid dynamic artifacts (e.g., bypassing or dead/stagnant volume zones), obtaining intrinsic kinetics with the corresponding operando spectroscopic signatures. The proposed methodology allows to understand the influence of process parameters and potential design modifications on the observed kinetic performance.This work was possible due to the financial support of the Ministry of Economy, Industry, and Competitiveness of the Spanish Government (project CTQ2016-79646-P, cofounded with ERDF funds), the Basque Government (projects IT1218-19 and IT1645-22), and the King Abdullah University of Science and Technology (KAUST, project BAS/1/1403). J.V. is grateful for the fellowship granted by the Ministry of Economy, Industry, and Competitiveness of the Spanish Government (BES-2014-069980). The authors are grateful for the technical and human support provided by IZO-SGI SGIker of the University of the Basque Country (UPV/EHU) and European funding (ERDF and ESF)

Stability of a NiAl2O4 Derived Catalyst in the Ethanol Steam Reforming in Reaction-Regeneration Cycles: Effect of Reduction Temperature

The catalyst regeneration is still a challenge to make the ethanol steam reforming (ESR) process feasible for sustainable H2 production. NiAl2O4 spinel derived catalysts are highly active and selective for ESR, but they require avoiding irreversible deactivation to ensure their regeneration. Their stability depends on the catalyst structure, and herein we report different Ni/Al2O3-NiAl2O4 catalysts obtained upon reduction of a NiAl2O4 spinel at 700, 750, or 850 °C. The catalysts were tested in ESR reaction-regeneration cycles, with reaction at 600 °C and regeneration by coke combustion at 850 °C followed by reduction at the corresponding temperature. The fresh, spent, and regenerated catalysts were characterized using X-ray diffraction, N2 physisorption, temperature programmed reduction and oxidation, and scanning electron microscopy. The irreversible deactivation is due to Ni volatilization and catalyst particle fragmentation. These phenomena are prompted by a high filamentous carbon deposition favored by the Al2O3 content in the catalyst. The reduction in the 700–750 °C range is optimum for controlling the Al2O3 content, increasing the NiAl2O4/Al2O3 ratio in the resulting catalyst. These catalysts show a period of partial reversible deactivation by coke with a change in the H2 formation mechanism reaching a pseudo-stable state with a H2 yield of 40% and a reproducible performance in successive reaction-regeneration cycles.This research was funded by the Ministry of Science and Innovation of the Spanish Government (grant RTI2018-100771-B-I00 and PhD grant BES-2019-090943 for S.I.-V. funded by MCIN/AEI/10.13039/501100011033 and by “ERDF A way of making Europe”); the European Commission (HORIZON H2020-MSCA RISE 2018. Contract No. 823745); the Department of Education, Universities and Investigation of the Basque Government, grant number IT1645-22

Insights into the Reaction Routes for H2 Formation in the Ethanol Steam Reforming on a Catalyst Derived from NiAl2O4 Spinel

[EN]This work describes the satisfactory performance of a Ni/Al2O3 catalyst derived from NiAl2O4 spinel in ethanol steam reforming and focuses on studying the prevailing reaction routes for H-2 formation in this system. NiAl2O4 spinel was synthesized using a coprecipitation method and reduced at 850 degrees C to obtain a Ni/Al2O3 catalyst. The spinel structure and catalyst were characterized using XRD, TPR, N-2 physisorption, NH3 adsorption and TPD, TPO, SEM, and TEM. The experiments were carried out in a fluidized-bed reactor at 500 or 600 degrees C and different spacetime values, using pure ethanol, ethanol-water, pure ethylene, or ethylene-water feeds. The reaction takes place through two paired routes activated by each catalyst function (metal and acid sites) whose extent is limited by the selective catalyst deactivation. The results evidence that at the beginning of the reaction the main route for the formation of H-2 and carbon (nanotubes) is the dehydration of ethanol on acid sites followed by decomposition of ethylene on the Ni-Al2O3 interface. This route is favored at 500 degrees C. After the rapid deactivation of the catalyst for ethylene decomposition, the route of H-2 formation by steam reforming of ethanol and water gas shift reactions over Ni sites is favored. The morphology of the carbon deposits (nanotubes) allows the catalyst to maintain a notable activity for the latter pathways, with stable formation of H-2 (during 48 h in the experiments carried out). At 600 degrees C, the extent of the gasification reaction of carbon species lowers the carbon material formation. The high formation of carbon material is interesting for the coproduction of H-2 and carbon nanotubes with low CO2 emissions.This work was possible thanks to the financial support of the Department of Education, Universities and Investigation of the Basque Government (IT1218-19), the European Comisssion (HORIZON H2020-MSCA RISE 2018, contract 823745), and the Ministry of Science, Innovation and Universities of the Spanish Government cofinanced with European Regional Development Funds (AEI/FEDER, UE) (Project RTI2018-100771-B-I00). S.I.-V. is thankful for his PhD grant (PRE-2019-090943) awarded by the Ministry of Science, Innovation and Universities. The authors thank for technical and human support provided by SGIker (UPV/EHU/ERDF, EU)

Comparison of the NiAl2O4 derived catalyst deactivation in the steam reforming and sorption enhanced steam reforming of raw bio-oil in packed and fluidized-bed reactors

The choice of appropriate reactors and reforming strategies is key to make progresses on scaling up H2 production processes from raw bio-oil. This work compares the performance (conversion, product yields and deactivation) of packed-bed and fluidized-bed reactors (PBR and FBR, respectively) using a NiAl2O4 spinel derived catalyst for the H2 production from raw bio-oil via steam reforming (SR) and sorption enhanced SR (SESR, with dolomite to capture CO2). The experiments were carried out at 600 °C; steam/carbon ratio, 3.4; space time, 0.15 h; time on stream, 5 h; dolomite/catalyst ratio, 10 (SESR runs); and with prior thermal separation of the pyrolytic lignin from the raw bio-oil. The initial H2 yields are 80 % and 69 % in the SR runs with PBR and FBR, respectively, and 99 % and 92 % in the CO2 capture period (of 30 min duration) of the SESR runs in the PBR and FBR, respectively. The lower H2 yield in the FBR is due to the less efficient gas–solid contact (bubbling or slugging phenomena). Based on the analysis of the spent catalysts with varied techniques the catalyst deactivation is related to the coke deposition, whose quantity and nature (amorphous or structured) depends on the reactor type and reforming strategy. The catalyst deactivation is slower in the FBR due to the rejuvenation of the catalyst surface by the moving particles that favor external coke gasification. The presence of dolomite prolongs the period of stable catalyst activity in both reactors with different effects on the coke quantity and nature. The results are of interest to advance on scaling up the SESR process that would require a FBR integrated with a regeneration unit for the catalyst and sorbent.This work has been carried out with the financial support of the grant RTI2018-100771-B-I00 and PID2021-127005OB-I00 funded by MCIN/AEI/10.13039/501100011033 and by “ERDF A way of making Europe”, the European Commission (HORIZON H2020-MSCA RISE 2018. Contract No. 823745) and the Department of Education, Universities and Investigation of Basque Government (Project IT1645-22 and PhD grant PRE_2021_2_0147 for L. Landa). The authors thank for technical and human support provided by SGIker (UPV/EHU/ERDF, EU), and to Calcinor S.A. for supplying the dolomite

Unveiling the deactivation by coke of NiAl2O4 spinel derived catalysts in the bio-oil steam reforming: Role of individual oxygenates

The catalyst stability, mainly affected by coke deposition, remains being a challenge for the development of a sustainable process for hydrogen production by steam reforming (SR) of bio-oil. In this work, the influence of oxygenates composition in bio-oil on the deactivation by coke of a NiAl2O4 spinel derived catalyst has been approached by studying the SR of a wide range of model oxygenates with different functionalities, including acetic acid, acetone, ethanol, acetaldehyde, acetol, catechol, guaiacol and levoglucosan. A fluidized bed reactor was used in the following conditions: 600 and 700 degrees C; steam/carbon ratio, 3 (6 for levoglucosan); space-time, 0.034 gcatalyst h/gbio-oil (low enough to favor the rapid catalyst deactivation), and; time on stream, 5 h. The spent catalysts were analyzed with several techniques, including Temperature Programed Oxidation (TPO), X-ray Diffraction (XRD), N2 adsorption-desorption, Scanning and Transmission Electron Microscopy (SEM, TEM) and Raman Spectroscopy. The main factors affecting the catalyst stability are the morphology, structure and location of coke, rather than its content, that depend on the nature of the oxygenate feed. The deposition of pyrolytic and amorphous coke that blocks the Ni sites inhibiting the formation of filamentous carbon causes a rapid deactivation in the guaiacol SR. Conversely, the large amount of carbon nanotubes (CNTs) giving rise to a filamentous coke deposited in the SR of aliphatic oxygenates only causes a slight deactivation. The increase in the temperature significantly reduces coke deposition, but has low impact on deactivation.This work has been carried out with the financial support of the Ministry of Science and Innovation of the Spanish Government (grant RTI2018-100771-B-I00 funded by MCIN/AEI/10.13039/501100011033 and by "ERDF A way of making Europe") , the European Commission (HORIZON H2020-MSCA RISE 2018. Contract No. 823745) and the Department of Education, Universities and Investigation of the Basque Government (Project IT1645-22, IT1218-19 and PhD grant PRE_2021_2_0147 for L. Landa) . The authors thank for technical and human support provided by SGIker (UPV/EHU/ERDF, EU)

Effect of reaction conditions on the deactivation by coke of a NiAl2O4 spinel derived catalyst in the steam reforming of bio-oil

[EN]The steam reforming of bio-oil is a promising and economically feasible technology for the sustainable H-2 production, yet with the main challenge of designing highly active and stable catalysts. This work aimed to study the deactivation mechanism of a NiAl2O4 spinel derived catalyst, the role of Ni and alumina sites in this mechanism and the appropriate reaction conditions to attenuate deactivation. The reaction tests were carried out in a fluidized bed reactor with prior separation of the pyrolytic lignin. The fresh or used catalysts were characterized using X-ray diffraction, temperature-programmed oxidation, X-ray photoelectron spectroscopy, scanning electron microscopy combined with energy dispersive X-ray spectroscopy, and Raman spectroscopy. For steam/carbon ratios > 3.0, space time above 0.075 h and temperature between 600-700 degrees C, high initial hydrogen yield is obtained (in the 85-90 % range) with CO yield near 20 %, CH4 yield below 5 % and negligible initial yield of hydrocarbons. The catalyst is more stable at 600 degrees C, with coke formation preferentially located on Ni sites inside the catalyst particle. Increasing the temperature favors the coke development and consequent deposition on the alumina support, leading to a rapid catalyst deactivation because the limited availability of Ni and alumina sites. These results contribute to understand the phenomenon of catalyst deactivation in the steam reforming of bio-oil and set appropriate reaction conditions to mitigate this problem with a NiAl2O4 spinel derived catalyst.This work was carried out with the financial support of the Department of Education, Universities and Investigation of the Basque Government (IT1218-19), theEuropean Commission(HORIZON H2020MSCA RISE 2018. Contract No. 823745), the Ministry of Economy and Competitiveness of the Spanish Government jointly with European Regional Development Funds(AEI/FEDER, UE) (Projects CTQ201568883-R and RTI2018-100771-B-I00), and PhD grant (BES-2016078132) for N. Garcia-Gomez. The authors thank for technical and human support provided by SGIker (UPV/EHU/ERDF, EU)

Combined effect of bio-oil composition and temperature on the stability of Ni spinel derived catalyst for hydrogen production by steam reforming

A challenge for scaling up hydrogen production by raw bio-oil steam reforming (SR) is the rapid catalyst deactivation that is strongly sensitive to the temperature and bio-oil composition. This work studies the combined effect of both variables on the stability of a Ni/Al2O3 catalyst with high Ni dispersion in the internal and external surfaces of the particles, obtained by reduction of a NiAl2O4. The raw bio-oil composition is modified by (i) removal of phenolic compounds by liquid-liquid extraction or (ii) use of an online pre-reforming step with dolomite. Then, SR tests of the bio-oils at 600 and 700 ?C are carried out in a system with two online units, the first one for controlled deposition of pyrolytic lignin (and also pre-reforming with dolomite) and the second one (fluidized bed reactor) for the SR of the volatile oxygenates. The time on stream evolution of the conversion and products yields is related to the amount, nature and location of coke in the catalyst particles, determined with several techniques. For bio-oils with high or moderate phenolic content (raw or pre-reformed bio-oil, respectively), the SR at 600 ?C leads to a moderate deactivation. However, at 700 ?C, a refractory coke is formed, mainly composed of carbon filaments and turbostratic carbon among them that causes a rapid catalyst deactivation by blocking the external surface of the catalyst particle. Conversely, the removal of phenolic compounds from raw bio-oil leads to a more stable SR operation at 700 ?C, because the formation of turbostratic carbon is slowed down.This work has been carried out with the financial support of the grant RTI2018-100771-B-I00 and PhD grant BES-2016-078132 (N. GarciaG ' omez) funded by MCIN/AEI/10.13039/501100011033 and by "ERDF A way of making Europe", the European Commission (HORIZON H2020MSCA RISE 2018. Contract No. 823745) and the Department of Education, Universities and Investigation of Basque Government (Projects IT1218-19 and IT1645-22). The authors thank for technical and human support provided by SGIker (UPV/EHU/ERDF, EU), and to Calcinor S.A. for supplying the dolomite

Slowing down the deactivation of H-ZSM-5 zeolite catalyst in the methanol-to-olefin (MTO) reaction by P or Zn modifications

The benefits of H-ZSM-5 zeolite modification with H3PO4 or ZnCl2 have been analyzed during the methanol to olefins (MTO) reaction. The catalysts were prepared, characterized and tested using three different reactors: fixed-bed, operando FTIR and UV-vis. The spent catalysts were further characterized for analyzing the nature and location of the species trapped. The results show that the zeolite modified with H3PO4 has suffered a simultaneous dealumination, leading to a decrease of number of acid sites and activity. However, the zeolite modified with ZnCl2 shows the inclusion of Zn transforming Brønsted into Lewis acid sites, leading to reaction intermediates (hydrocarbon pool species) that decreases the rate of reaction but improves propylene selectivity (+10%), slows downs coke formation (-42%) and expands catalytic lifetime (+80%). The distinct effect of Zn modification, typically associated with the promotion of aromatics, is explained on the grounds of the severe transformation of the strong and Brønsted acid sites.This work was possible thanks to the financial support of the Ministry of Economy, Industry and Competitiveness of the Spanish Government (Project CTQ2016-79646-P, co-founded with ERDF funds) and the Basque Government (Project IT748-13, IT912-16). J.V. is thankful for his fellowship granted by the Ministry of Economy, Industry and Competitiveness of the Spanish Government (BES-2014-069980). The authors are thankful for technical and human support provided by IZO-SGI SGIker of UPV/EHU and European funding (ERDF and ESF)