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Journal ArticleDOI: 10.1016/J.APCATA.2021.118018

Insights into coke location of catalyst deactivation during in-situ catalytic reforming of lignite pyrolysis volatiles over cobalt-modified zeolites

05 Mar 2021-Applied Catalysis A-general (Elsevier)-Vol. 613, pp 118018
Abstract: HZSM-5, Co-incorporated HZSM-5 (3Co/Z5) and Co-incorporated hierarchical HZSM-5 (3Co/DZ5) were employed in catalytic reforming of volatiles from lignite pyrolysis in a drop bed reactor aiming at high yields of light aromatics. The co-effect of hierarchical pores and metallic sites on 3Co/DZ5 promoted the formation of benzene, toluene, xylene and naphthalene, and improved the service lifespan by decreasing coke formation. The influence of hierarchical pores and metallic sites on the deposition and nature of coke and on its location in the channels or/and the outer surface of zeolites was investigated. For 3Co/DZ5, the hierarchical pores retarded its deactivation by preventing internal coke formation while facilitating the external coke formation, owing to the reduced diffusion resistance of coke precursors (aromatic species) out of channels. The introduction of metallic sites brought the suppression of O-containing species depositing on zeolite. After continuous operation, the skeleton structures of both spent and regenerated catalysts were seriously damaged by coke deposition and sintering. The main causes of catalyst deactivation were assigned to two deactivating carbonaceous species with aromaticity and aliphaticity located on the inner pores and outer surface. The soluble long-chain aliphatics from coke extracts located on the outer surface were attributed to the decomposition of inherent aliphatic chain structure in lignite. The residual coke trended to graphite-like structure. The coking behavior was revealed by means of some technologies that the internal coke mainly had impact on the catalyst performance, especially for the insoluble aromatics with high polycondensation, whereas the external coke consumes the surface active sites, resulting in uninterrupted accumulation of coke precursors, eventually blocking the accessibility to channels.

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Topics: Coke (66%), Catalytic reforming (53%), Pyrolysis (52%) ... show more
Citations
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7 results found


Journal ArticleDOI: 10.1016/J.FUPROC.2021.106854
Xue-Yu Ren1, Jing-Pei Cao2, Jing-Pei Cao1, Shi-Xuan Zhao1  +6 moreInstitutions (2)
Abstract: Ni-encapsulated (Ni@HZ5) and Ni-incorporated (xNi/HZ5) zeolites were prepared via one-pot hydrothermal synthesis and impregnation method, respectively, and further employed for hydroconversion of pyrolytic volatiles of spent coffee grounds into benzene, toluene, ethylbenzene, xylene, naphthalene (BTEXN) in a drop tube reactor under H2 atmosphere. The properties of metallic Ni species on Ni@HZ5, xNi/HZ5 and Ni/Al2O3 were comparably characterized. Ni@HZ5 displayed superior selectivity for BTEXN production among those catalysts, especially for B and T. Metallic Ni species encapsulated MFI-type framework plays crucial roles in enhancing aromatics selectivity, promoting oligomerization, cyclization and aromatization of small molecular hydrocarbons in channels. On the contrary, Ni species presented on the external zeolite surface is in favor of hydrocracking and hydrogenolysis of macromolecular pyrolytic fragments. It also exhibited high coke content containing “soft” and “hard” coke, which was mainly caused by metallic particles sintering. An important difference was proposed in the effect of Ni species on reaction pathway for catalytic upgrading of volatiles to BTEXN. The configured Ni@HZ5 inhibits sintering and has potential of enhancing BTEXN by catalytic hydropyrolysis of biomass.

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Topics: Xylene (53%), Ethylbenzene (52%), Catalysis (51%) ... show more

3 Citations



Open access
31 Dec 2017-
Abstract: Rapid coking and catalyst deactivation are significant problems during catalytic fast pyrolysis of biomass. Cellulose and lignin were found to coke via different mechanisms, resulting in two distinct types of catalyst deactivation. Lignin pyrolysis vapors cause coke formation mainly by external surface coking without limiting access to the active acid sites in the microchannels. Lignin deactivates the surface cracking capability of ZSM-5, resulting in unreacted primary vapors passing through while maintaining aromatization reactions. Cellulose pyrolysis vapors generate coke mainly as an extension of the aromatization reactions on the acid sites, which leads to occlusion of the internal acid sites. This deactivates the upgrading reactions, resulting in decreased aromatics formation, generation of oxygenated intermediates and increased alkylation of 1-ring aromatics and reduced multi-ring aromatics selectivity. The results indicate that the decrease in aromatics formation observed during catalytic pyrolysis...

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Topics: Biomass (59%), Biofuel (54%), Pyrolysis (53%)

1 Citations


Open accessJournal ArticleDOI: 10.1016/J.MCAT.2021.111969
Abstract: Mo, V and W oxides supported on montmorillonite (Mt) have shown good activity in catalytic glycerol oxidehydration. However, these catalysts deactivate rapidly due to coking. Understanding the role of Mo, V and W oxides in coke formation is essential to overcome the coking problem. Herein, individual and combination of Mo, V and W oxides supported on Mt were investigated to reveal the contribution of Mo, V and W oxides to coke formation. Among single metal oxide catalysts, Mo-Mt and W-Mt suffered more from coke formation than V-Mt. A mixture of Mo5+ and Mo6+ in the Mo-Mt catalyst hindered full oxidation during the oxidehydration, thus promoting coking. The oxidation of V4+ to V5+ helped diminish coke in mixed Mo-V-Mt and W-V-Mt. This work is expected to provide new information for designing high-performance Mo, V and W oxide catalysts with superior coke resistance.

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Topics: Coke (57%), Catalysis (53%), Oxide (52%)

Journal ArticleDOI: 10.1016/J.JAAP.2021.105064
Zhen Yang1, Jing-Pei Cao2, Jing-Pei Cao1, Tian-Long Liu1  +5 moreInstitutions (2)
Abstract: A multifunctional catalyst of Ga-Sn anchored on hierarchical HZSM‑5 (Sn-Ga/AT0.2H5) was investigated in catalytic reforming of lignite pyrolysis volatile. A strong synergy was observed between Ga and Sn for the production of aromatics. The addition of Ga into AT0.2H5 remarkably promoted the selectivity of aromatics including benzene, toluene, ethylbenzene, xylene and naphthalene (BTEXN) compared to pure HZSM-5 (H5). The BTEXN yields increased to 24.1 mg/g over monometallic 5%Ga/AT0.2H5, in which the benzene yield was attained to 14.8 mg/g. With the introduction of Sn, the yield of aromatics was further improved to 25.1 mg/g. An explanation of this scenario was that introduced active metals could enhance the transformation of cyclic intermediates into aromatics and H5 support with an appropriate concentration of the acid sites provided acidic protons for aromatization. Additionally, the bimetallic Sn-Ga/AT0.2H5 exhibited higher stability with the yield of BTEXN maintained over 22 mg/g after three recycle experiments, which offered an efficient strategy to prolong the catalyst lifetime.

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Topics: Xylene (53%), Ethylbenzene (52%), Catalytic reforming (52%) ... show more

References
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66 results found


Journal ArticleDOI: 10.1016/J.APCATB.2012.08.030
Abstract: The main objective of the present work was the study of different ZSM-5 catalytic formulations for the in situ upgrading of biomass pyrolysis vapors. An equilibrium, commercial diluted ZSM-5 catalyst was used as the base case, in comparison with a series of nickel (Ni) and cobalt (Co) modified variants at varying metal loading (1–10 wt.%). The product yields and the composition of the produced bio-oil were significantly affected by the use of all ZSM-5 catalytic materials, compared to the non-catalytic flash pyrolysis, producing less bio-oil but of better quality. Incorporation of transition metals (Ni or Co) in the commercial equilibrium/diluted ZSM-5 catalyst had an additional effect on the performance of the parent ZSM-5 catalyst, with respect to product yields and bio-oil composition, with the NiO modified catalysts being more reactive towards decreasing the organic phase and increasing the gaseous products, compared to the Co 3 O 4 supported catalysts. However, all the metal-modified catalysts exhibited limited reactivity towards water production, while simultaneously enhancing the production of aromatics and phenols. An interesting observation was the in situ reduction of the supported metal oxides during the pyrolysis reaction that eventually led to the formation of metallic Ni and Co species on the catalysts after reaction, which was verified by detailed XRD and HRTEM analysis of the used catalysts. The Co 3 O 4 supported ZSM-5 catalysts exhibited also a promising performance in lowering the oxygen content of the organic phase of bio-oil.

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Topics: Catalysis (56%), Pyrolysis (54%), Transition metal (52%) ... show more

348 Citations


Journal ArticleDOI: 10.1016/J.APCATB.2011.02.024
Pedro Castaño1, Gorka Elordi1, Martin Olazar1, Andrés T. Aguayo1  +2 moreInstitutions (2)
Abstract: The effect of the zeolite structure (HZSM-5, Hβ and HY) on coke deposition during the cracking of high-density polyethylene has been studied by combining the results of multiple spectroscopic and analytical techniques: FTIR, Raman, UV–vis, 13 C NMR and coke extraction, followed by GC-MS and 1 H NMR analysis. In addition, by combining FTIR and temperature programmed oxidation (TPO) analysis we obtained information on the coke: properties, burn-off, and changes in composition during catalyst regeneration. Samples of the spent catalysts were obtained in a state-of-the-art pilot plant (conical spouted bed reactor) after the continuous treatment of 900 g (1 g min −1 , 15 h) of high-density polyethylene at 500 °C, using 30 g of catalyst. The results show that as the pore diameter of the zeolite is increased, bimolecular reactions (hydrogen transfer and oligomerizations), condensations and cyclizations are enhanced, yielding more aromatic coke. Furthermore, the pore topology of the HZSM-5 zeolite improves the flow of coke precursors (also favored by the high flow rate of N 2 ) to the outside of the catalyst; viz. HZSM-5 catalyst preserves its activity for longer.

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Topics: Coke (60%), Zeolite (52%), Catalysis (52%) ... show more

152 Citations


Journal ArticleDOI: 10.1016/J.JCAT.2013.07.004
Abstract: Desilication has become a standard method to prepare mesoporous zeolite catalysts that display improved lifetime or resistance toward deactivation in hydrocarbon transformation processes involving coking. In this contribution, the deactivation behaviors of a regular, commercial ZSM-5 catalyst and its mesoporous, desilicated counterpart have been investigated and compared. After partial deactivation in the conversion of methanol to hydrocarbons at elevated reaction pressure, the catalyst beds were fractionated from top to bottom of the reactor. These fractions were analyzed by several spectroscopic techniques, gas adsorption measurements, thermogravimetry, coke analysis by a catalyst dissolution/extraction protocol, and measurements of residual activity for the individual catalyst fractions. Remarkable differences between the desilicated and the parent H-ZSM-5 catalysts are seen, in particular with respect to the mode of deactivation along the catalyst beds. It appears that the more uniform deactivation of the desilicated catalyst is due to a complex interplay among alterations of porosity, activity, and rate of deactivation upon desilication.

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Topics: ZSM-5 (55%), Catalysis (53%), Zeolite (51%) ... show more

144 Citations


Journal ArticleDOI: 10.1016/J.APCATA.2012.10.003
Hiroshi Mochizuki1, Toshiyuki Yokoi1, Hiroyuki Imai1, Seitaro Namba1  +2 moreInstitutions (1)
Abstract: The effects of external surface and acid properties of desilicated H-type ZSM-5 zeolites (H-ZSM-5) on their catalytic performance in hexane cracking were investigated. H-ZSM-5 with two different crystallite sizes of 100 nm and 1 μm were treated with NaOH solution of different concentrations. The external surface area (SEXT) was increased with an increase in the NaOH concentration, because of the formation of mesopores inside the H-ZSM-5 crystallites as a result of desilication. The increase in the SEXT of the H-ZSM-5 catalysts contributed to mitigating the catalyst deactivation during the hexane cracking. Although the amount of coke deposited on the alkali-treated H-ZSM-5 was larger than that on the parent H-ZSM-5, the micropore volume of the alkali-treated H-ZSM-5 decreased less due to coke deposition than that of the parent. The deactivation rate and the decrease in the micropore volume of the small-sized H-ZSM-5 catalysts were smaller than those of the large-sized catalysts, because they had shorter average diffusion path lengths. Thus the activity of the alkali-treated H-ZSM-5, especially small-sized one is less sensitive to coke deposition. Lewis acid sites (LASs) were generated by treating with NaOH of high concentrations. The selectivities to benzene, toluene and xylene (BTX) in the hexane cracking were increased with an increase in the LASs amount at high reaction temperatures (≥873 K). The LASs on the alkali-treated H-ZSM-5 were selectively removed by acid treatment. The resultant H-ZSM-5 exhibited a slightly lower hexane conversion and a lower selectivity to BTX but a small amount of coke compared to the parent and alkali-treated H-ZSM-5 catalysts, suggesting that LASs on alkali-treated H-ZSM-5 accelerated the dehydrogenation including hydride transfer and aromatization, forming BTX, which would be precursors of coke.

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Topics: Coke (54%), Xylene (53%), Benzene (52%) ... show more

142 Citations


Journal ArticleDOI: 10.1021/EF401458Y
Huiyan Zhang1, Shanshan Shao1, Rui Xiao1, Dekui Shen1  +1 moreInstitutions (1)
16 Jan 2014-Energy & Fuels
Abstract: Coke deposition on the zeolite catalysts in the conversion of furan (a main intermediate of biomass fast pyrolysis) is of serious concern for catalyst deactivation and product distribution. It is important to find out the nature and composition of coke on the spent ZSM-5 catalyst to study the coke-depositing behaviors. In this work, spent ZSM-5 catalysts obtained from furan catalytic conversion for chemicals at different reaction times and pyrolysis temperatures were characterized. The spent catalysts were first treated with hydrofluoric acid, and then the organics were extracted with CH2Cl2. The characterization of the origin coke and the treated insoluble coke were analyzed by the combination of some analytical techniques, including Fourier transform infrared spectroscopy (FTIR), high-performance liquid chromatography (HPLC), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and thermogravimetric analysis (TGA). The extracted organics were analyzed by HPLC to determine the chem...

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Topics: Coke (59%), Pyrolysis (55%), Catalysis (51%) ... show more

141 Citations