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This paper presents a review of recent research on direct upgrading of coal/biomass volatiles into aromatics by catalytic pyrolysis and syngas by gasification with catalytic steam reforming. Coal/b...

The ZSM-5(Z5) was synergistically modified by leaching agent HF (0.5 mol/L) and metallic Pt (0.1, 0.2, 0.5, and 1 wt %) to prepare the bifunctional hierarchical Pt-FZ5 for enhancing light aromatic ...

A series of HZSM-5 treated by NaOH followed by supporting sulfated zirconia (ATxSZ/H5) was prepared and used for catalytic reforming of lignite pyrolysis volatiles. ATxSZ/H5 was found to be a poten...

Promising technology for the conversion of cellulose to aromatics by catalytic fast pyrolysis (CFP) was investigated using five zeolite catalysts, i.e., 5A, SAPO-34, HY, BETA and HZSM-5. The relationship between the porosity and acidity of different zeolites with product selectivity was studied. The results showed that both the acidity and pore size of the zeolite significantly affected the production of aromatics and coke, especially the bio-oil composition. The bio-oils obtained over 5A or SAPO-34 (small pore

In-situ reforming of lignite pyrolysis volatiles over ZSM-5 zeolites with different SiO2/Al2O3 ratios was carried out to obtain light aromatics including BTEXN (benzene, toluene, ethylbenzene, xylene, and naphthalene). In comparison to the commercial zeolites, the zeolites used in this work were synthesized by a one-step method with controlled Al addition. The high Al-containing ZSM-5 (SiO2/Al2O3 = 50) was observed to be more effective in producing BTEXN (20.8 mg/g), likely by removing oxygen atom of volatiles on acidic sites. Moreover, it was still activated even after several regeneration cycles. As indicated by the GC-MS results, the aliphatic hydroxyl and carboxyl groups were decomposed over ZSM-5. High SiO2/Al2O3 ratio was favorable for polyaromatics elimination. However, the as-synthesized ZSM-5 with SiO2/Al2O3 ratio of 25 was less effective in cleaving aliphatic C–C bonds. Besides, the structural properties of ZSM-5 were significantly affected by the SiO2/Al2O3 ratio. High intergrowth and twinning structures were observed with increasing SiO2/Al2O3 ratio. Regardless of the crystal morphology of zeolite, the SiO2/Al2O3 ratio had significant influence on aromatics types, providing insights into ZSM-5 catalyst for the selective control of BTEXN owing to acidity changes.

In order to effectively improve the quality of bio-oil from catalytic pyrolysis (CFP) of sewage sludge (SS) and to produce aromatic-rich bio-oil, the evolution mechanisms of nitrogen and formation of aromatics during CFP of SS over metal-loaded HZSM-5 (HZ) were investigated in depth. The results show that the presence of metals caused the slight decrease in oil-C (carbon in bio-oil) yield and the increase in gas yield and total carbon yield of aromatics. Ni-loaded HZ has a better performance than Co-loaded one in improving the carbon yield of aromatics, while the maximum yield of 11.2% was obtained over 0.5Ni-HZ. Metal-loaded HZ promoted the formation of monocyclic aromatics rather than polycyclic aromatics and Ni significantly enhanced the selectivity of benzene. With the addition of Ni and Co, more nitrogen was released as NH3 or fixed in solids. NH3 yield increased by raising the metal loading, and the highest NH3 yield of 36.8% was obtained over 3.0Ni-HZ. Ni and Co promoted the cracking reactions during CFP to generate more H radicals, which have advantages to the ring-opening of N-containing heterocycles in SS to produce aromatics and NH3. A possible catalytic mechanism of CFP of SS over metal loaded HZ was proposed in this study.

Pore structure and accessible active sites of HZSM-5 (Z5) are the key factors for its catalysis. The bifunctional hierarchical Z5 were prepared with leaching agent HF and loading Ni, and their performance for catalytic fast pyrolysis (CFP) of cellulose was investigated in a drop tube quartz reactor. Z5 modified with 0.5 mol/L HF (0.5F-Z5) showed excellent light aromatics (LAs) yield, which can be attributed to the enhancement in the small mesopores (2–10 nm) and the decrease of Bronsted acid sites during dealumination. Simultaneously, the loading of a 1 wt% Ni produced more LAs than 0.5F-Z5, due to the improvement in deoxidation/hydrogenation reactions. The highest LAs yield (31.3%) was obtained over 1%Ni-0.5 mol/LHF-Z5, which increased by 44.9% compared to the parent Z5. In addition, the reaction routes over different active centers and acid-catalyzed reactions were analyzed, based upon the composition of bio-oils and catalyst characterization.

H5 was developed to mesoporous system via alkali treatment, and sulfated zirconia (SZr) modified hierarchical HZSM-5 (AT0.2/H5) catalysts (named AT0.2/SZxH5) were successfully prepared by a series of post-treated method followed by Zr(NO3)4·5H2O and H2SO4 as active component. The innovative approach really enhanced acidity of AT0.2/H5 support, which results from the interaction of the sulfate groups attached to zirconia that doped on MFI framework with silanol groups. Adding active component can not only compensate for the loss of acid sites caused by NaOH treatment, but also re-develop more active sites owing to the formation of SZr. Meanwhile, NH3-TPD showed higher strong acid sites and weak acid sites in AT0.2/SZ6:1H5 than other prepared catalysts. The catalytic activity in converting lignite pyrolysis volatiles to light aromatics, including benzene, toluene, ethylbenzene, xylene and naphthalene (BTEXN), correlates well with the enhanced acidity. Compared with H5, the yield of light aromatics increased significantly from 15.2 to 19.3 mg/g over AT0.2/SZ6:1H5 at 600 °C. According to the characterization of N2 adsorption–desorption, SEM, and XRD, both the S species as SO42− and Z species as ZrO2 improved the textural properties of the support itself. Besides, the molar ratio of S/Zr was in direct proportion to the yield of BTEXN in a certain range, and 6:1 exhibited the optimal catalytic performance. The prepared solid acid catalyst provides a promising strategy to directional prepare light aromatics during lignite catalytic pyrolysis.

HZSM-5 was modified via alkaline treatment and wet impregnation method which loading transition metals (Co, Mo–Co and Ni–Co). The performance of catalysts for the catalytic fast pyrolysis of lignite was tested in a drop tube reactor at 600 °C. In comparison to non-catalytic experiment, the chemical composition of upgrading tar was obviously simplified, which mainly contains light aromatics such as benzene, toluene, ethylbenzene, xylene and naphthalene (BTEXN). The yield of BTEXN was significantly increased from 12.9 to 26.4 mg/g when Ni/Co-H-5 was used. Meanwhile, the Ni/Co-H-5 treated by NaOH solution achieved considerable deoxygenation performance (86.6%) than other ones. The addition of bimetallic Mo–Co or Ni–Co significantly enhanced the BTEXN selectivity of HZSM-5. Ni promoted H2 formation in gaseous product and caused the decrease of naphthalenes yield. Whereas the yields of toluene and o-xylene increased after the pyrolysis vapors pass through Mo/Co-H-5. The zeolite treated by NaOH solution (AT-HZSM-5) favors the generation of aromatics and phenolics, conversely naphthalene derivatives. Moreover, AT-Mo/Co-H-5 and AT-Ni/Co-H-5 inhibited the coke formation. A catalytic pathway was also proposed to describe the diffusion process of pyrolysis vapors on the active site of catalyst.

To upgrade pyrolysis vapors derived from the catalytic fast pyrolysis (CFP) of Baiyinhua lignite (BYHL) in a drop tube reactor, various Co-loading (1, 3, 6 and 10 wt%) zeolites were prepared via wet impregnation. The effect of Co-loading and pyrolysis temperature ranged from 400 to 700 °C on product yields and tar properties were investigated in this work. The results showed that the product yield and the composition of pyrolysis tar were significantly affected by Co-modified HZSM-5 and parent HZSM-5 compared with no catalyst. Incorporation of metal-Co in HZSM-5 had an additional effect on the performance of the parent HZSM-5. The total content of benzene (B), toluene (T), ethylbenzene (E), xylene (X) and naphthalene (N) significantly increased and it reached 24.2 mg/g at Co-loading of 3 wt% (3Co-H-5) at 600 °C. 3Co-H-5 exhibited also a promising performance in lowering the oxygen content from 49.8% without a catalyst to 14.6% by GC–MS analysis. The deoxygenation mechanisms over metal-Co active centers and acid-catalyzed reactions, such as isomerization and cracking, over acid sites of HZSM-5 were speculated in this work. In addition, the temperature of 600 °C is not only appropriate for fast pyrolysis of lignite to obtain a higher pyrolysis tar, but also for catalytic pyrolysis to obtain BTEXN.

HZSM-5 was post-treated by piperidine-assisted desilication (PAD) and metallic Co and/or Zr modification to introduce the meso-/microporous system and metal active sites to enhance the activity for catalytic fast pyrolysis (CFP) of lignite for aromatic products. CFP was conducted over parent and hierarchical HZSM-5 in a drop tube reactor at 600 °C and a gas residence time of 1.5 s. The results showed that assisted desilication with piperidine (PI) concentration of 0.3 mol/L (AT0.2–PI0.3), retained the morphology of HZSM-5, and avoided severe alkaline corrosion. This was due to the shield of the zeolite crystals from extensive dissolving of NaOH by organic amines. It not only decreased the deactivation rate of the catalyst, but also enhanced the mass transfer in the catalyst. The selectivity of light aromatics (LAs) such as benzene, toluene, ethylbenzene, xylene, and naphthalene remarkably increased to 24.9% over AT0.2–PI0.3 in comparison to the HZSM-5. In addition, introducing bimetallic Zr–Co facilitated...

A novel porous carbon catalyst was prepared by carbonization of D151 resin exchanged with nickel ion (Ni/RC). TEM images and XRD patterns manifest that nickel crystallite size (NCS) relies greatly on solution pH value and carbonization temperature. The as-prepared Ni/RC in pH 11 at 650 °C achieved the maximal specific surface area of 213 m 2 /g and metallic nickel particles are highly dispersed with a NCS of 5.7 nm. Ni/RC exhibited higher activity for corncob tar reforming than commercial Ni/Al 2 O 3 and produced a gas yield of 46.8 mmol/g at 650 °C. The nickel particles growth above 650 °C causes the decline in catalytic activity of Ni/RC. In the presence of steam, a high tar-free gas of 84.5 mmol/g was obtained at 650 °C. This study sheds light on the possibility of Ni/RC as a promising candidate for H 2 -rich gas production from biomass under mild conditions.

This work is aimed to study in situ upgrading of Shengli lignite pyrolysis vapors over different metal-loaded HZSM-5 in a drop tube reactor. Co/HZSM-5, Mo/HZSM-5 and Ni/HZSM-5 (5.0 wt%) were prepared by wet impregnation and characterized by N 2 adsorption-desorption analyzer, X-ray diffraction, transmission electron microscope, Fourier transform infrared spectrometer and temperature programmed desorption of ammonia. The effects of temperature and catalyst on product yields and tar properties were investigated. The results show that the optimal temperature for liquid product was 600 °C and aromatics can be directly produced from solid lignite by catalytic fast pyrolysis over metal-loaded HZSM-5 under such mild condition. Due to the participation of metal and acid sites, the bifunctional metal-loaded HZSM-5 showed comparable catalytic activity for deoxygenation reaction in the valorization of oxygen content below 7.1%. The introduction of metal causes the increase of aromatics and the decrease of organic oxygen species in upgraded tar remarkably. Among the catalysts, Ni/HZSM-5 exhibited the best performance for production of high quality tars with highest aromatics content of 94.2% (area%), which can be used as a potential candidate for catalytic upgrading of pyrolysis oil.

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.

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.

ZSM-5 zeolites with different physicochemical property were synthesized using different silicon (Si) and aluminum (Al) sources by hydrothermal method with controlling Al and Si addition. Different crystal shapes were observed from three Si sources. Al sources can influence crystal formation during crystallinity. Al nature causes different amorphous species which affect zeolite activity by blocking the accessible pores. A feasible mechanism of Si and Al sources for crystallization of zeolite was proposed. The activity for lignite volatiles-to-aromatics (LVTA) reaction was investigated to obtain light aromatics. Zeolite using tetraethylortho silicate and aluminum sulfate octahydrate as Si and Al sources shows large surface area and more accessible pores which cause excellent BTEXN yield (23.7 mg/g). The tar yield in the process of LVTA reaction is associated with both porous and acid properties while excessive acidity may cause the formation of coke on the zeolite which causes the blockage. ZSM-5 with optimum and accessible acid sites and abundant pores give a high tar yield and low coke yield. This work provides a ZSM-5 catalyst with suitable acidity and pore property for LVTA reaction.