Browsing by Author "Shen, Dekui"

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    Deoxygenation in anisole decomposition over bimetallic catalysts supported on HZSM-5
    (Elsevier, 2018-10-29) Zhang, Jiajun; Fidalgo, Beatriz; Wagland, Stuart; Shen, Dekui; Zhang, Xiaolei; Gu, Sai
    This work investigated the deoxygenation reaction in anisole decomposition over HZSM-5 (HZ(25)) zeolite supported bimetallic catalysts to produce benzene, toluene and xylene (BTX). Experiments were performed in order to evaluate the synergistic effect between the two active metals with the focus on the effect of temperature, metal type, and metal loading ratio. Experimental results showed that 1%Ni-1%Mo/HZ(25) led to both the highest BTX yield (i.e. 30.0 wt%) and selectivity (i.e. 83.7%). On the contrary, bimetallic catalysts containing Fe were less effective in promoting the BTX production. It was identified that the optimum temperature for BTX production over 1%Ni-1%Mo/HZ(25) catalysts was 500 °C. Characterization of fresh and spent catalysts showed microcrystal particles of bi-metal loadings highly dispersed on the zeolite surface, and some agglomeration of metallic particles were also observed. Large amount of carbonaceous deposit was observed on the spent catalysts mainly in the form of amorphous. Density Functional Theory (DFT) modelling was carried out in order to study the adsorption energy of anisole and phenol molecules onto Ni-Mo, Ni-Fe and Mo-Fe surfaces; and the interactions between phenol molecule and bimetal surfaces were further analysed. All the analysed bimetal surfaces exhibited strong interactions with the adsorbed molecule. Ni-Mo surface declined electrons energy levels mainly around 1.5 eV in the adsorbate molecule and released the highest adsorption energy; while Ni-Fe and Mo-Fe surface led to more electrons exchange with the adsorbate during the adsorption. The modelling results agreed well with experiments by revealing that the strong binding between phenolic compounds (Phs) and the Ni-Mo based catalysts bimetal surface would lead to a higher BTX production in the deoxygenation reaction in the decomposition of anisole.
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    Mechanism of deoxygenation in anisole decomposition over single-metal loaded HZSM-5: Experimental study
    (Elsevier, 2017-11-20) Zhang, Jiajun; Fidalgo, Beatriz; Kolios, Athanasios; Shen, Dekui; Gu, Sai
    This work investigates the deoxygenation reaction during the decomposition of anisole (methoxy-rich model compound of lignin) over bi-functional catalyst. The bi-functional catalyst consisted of a single metal loaded on an acid support; the active metals, i.e. Ni, Co, Mo and Cu, were loaded at various rates, and the acid support was HZSM-5 zeolite with a Si/Al ratio of 25 (HZ(25)). Experiments were conducted in a bench-scale fluidised bed reactor within the temperature range from 400°C to 600°C. Experimental results revealed that the increase in temperature and metal loading promoted the selectivity of BTX fraction. Nevertheless, a simultaneous increase in the yield of carbonaceous deposits was also observed at the expense of liquid fraction, both phenolics compounds (Phs) and aromatic hydrocarbons (AHs). 500°C was the preferred temperature for BTX production. Ni-loaded HZ(25) catalyst could dramatically facilitate the conversion of Phs to monoaromatics and increase the selectivity of BTX fraction by 43.4%; Mo-loaded HZ(25) catalyst exhibited the best catalytic activity towards the total production of AHs and promoted the BTX yield by 27.1%. It was also found that 1 wt.% was the optimum loading ratio for both Ni and Mo on HZ(25) to obtain the highest BTX yield and selectivity. Characterization of fresh bi-functional catalysts showed that micro polycrystalline metal sites, in the range of 4 -10 nm, existed on the fresh catalyst and exhibited strong interaction with the HZ(25) support. For the spent catalysts, large amount of amorphous carbonaceous deposit was observed, ascribed to the polycondensation of aromatic compounds during the reaction. Three reaction pathways were proposed for the catalytic deoxygenation of anisole, with the hydrogen being available in-situ as product of the polycondensation reactions
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    Mechanism of transmethylation in anisole decomposition over HZSM-5: Experimental study
    (Elsevier, 2016-09-15) Zhang, Jiajun; Fidalgo Fernandez, Beatriz; Shen, Dekui; Xiao, Rui; Gu, Sai
    This work investigated the decomposition of anisole (methoxyl-based lignin model compound) in a fluidized bed reactor over no catalysts and a series of HZSM-5 zeolite catalysts with different Si/Al atomic ratios. Transmethylation reaction was identified as the initial step of the thermal decomposition of anisole, leading to the prominent production of phenolic compounds. Methyl phenols were identified as the main products, with the yield of o-cresol being higher than that of p-cresol at the temperatures below 600° C. The transmethylation reaction over HZSM-5 zeolite catalyst was found to occur at temperatures 150° C lower than those for non-catalytic reaction, with the yield of the phenolic compounds being promoted by 2.5 times. Production of the main phenolic compounds during the catalytic decomposition of anisole was enhanced to different extents depending on the Si/Al ratio. The highest selectivity of 79 wt.% was achieved over the zeolite catalyst with a Si/Al ratio of 80. The Brønsted acid sites of the catalyst played a significant role in both the preferential formation of phenolic compounds and preservation of the methyl group.
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    Mechanism of transmethylation in anisole decompostion over Brønsted acid sites: Density Functional Theory (DFT) study
    (Royal Society of Chemistry, 2017-08-15) Zhang, Jiajun; Fidalgo, Beatriz; Kolios, Athanasios; Shen, Dekui; Gu, Sai
    In this work, the mechanism and intrinsic reaction energy barriers of transmethylation, as the initial stage of the catalytic and non-catalytic anisole decomposition, were investigated by Density Functional Theory (DFT). Molecule analyses indicated that methyl free radical transfer happened in the absence of catalyst, and the catalytic transmethylation over Brønsted acid sites was considered based on the dual electrophilic attack mechanism with protonation and carbocation substitution respectively. Reactions modelling for the formation of methyl-contained compounds in both non-catalytic and catalytic anisole decomposition indicated that the energy barriers were significantly decreased in the presence of catalyst by 60 kcal/mol at the most in the case of o-cresol. The results also revealed that the intrinsic transmethylation orientation preferred the ortho- and para-positions on the acceptor compounds contained oxygen-rich substituents due to its large electronegativity, and the lowest energy barrier was observed in the case of transmethylation towards the para-position of the cresol molecule (54.1 kcal/mol).
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    Study of the mechanism of thermocatalytic decomposition of anisole for producing aromatic-rich fuel additives.
    (2017-05) Zhang, Jiajun; Fidalgo, Beatriz; Shen, Dekui; Wagland, Stuart
    In the context of the bio-based economy, lignin is a major source of aromatic compounds. Fast pyrolysis of lignin with catalytic reforming of the liquid fraction provides an efficient approach for producing aromatic hydrocarbons (AHs) as fuel additives. Methoxy compounds abundantly exist in the primary liquid products from fast pyrolysis of lignin, which further convert into phenolic and aromatic compounds via secondary pyrolysis and the upgrading reactions. This thesis focuses on the decomposition mechanism of the methoxyl group, using anisole as a model compound. Methyl transfer (transmethylation) as the primary reaction of the thermal decomposition of anisole, led to the prominent production of phenolic compounds (Phs). Plausible mechanisms for both non-catalytic and catalytic transmethylation were proposed, based on the analyses of the active sites on anisole and phenol by the means of DFT modelling. The intrinsic transfer orientation preferences onto relevant compounds were then predicted by corresponding reaction energy barriers. Experiments investigated the decomposition of anisole in a fluidized bed reactor over no catalysts and a series of HZSM-5 zeolite catalysts with different Si/Al atomic ratios. Study on transmethylation illustrated how the acid catalysts promoted the preferential formation of Phs. Deoxygenation reaction of the Phs as second stage reaction at higher temperatures produced AHs. Metal loaded acid (Bi-functional) catalysts designed by multiscale modelling were used in the investigation. Novel mechanism of anisole decomposition over bi-functional catalyst was proposed with the illustration of each role for metal and acid site in the catalysis. DFT modelling also predicted the reaction energy barriers of deoxygenation for various Phs to exhibit the metals effect in promoting the reactions. Experiments of anisole decomposition over the designed single and bi-metal based bi-functional catalysts revealed the distinct characteristics of each metal loading and their synergistic effect in promoting the BTX production.