| With the continuing depletion of the reserves of fossil resources and the worsening environment pollution,the development of new energy is attracting wide attention from the international community.Meanwhile,China has put forward"Peaking CO2"and"Neutralizing CO2"goals,emphasizing the importance and urgency of renewable energy.As a green and renewable liquid fuel,lignin-derived bio-oil will play a critical role in reducing petroleum dependence.However,because this oil contains many oxygen-containing compounds,it suffers from serious flaws such as low heat value,high viscosity and low mutual solubility and so on,limiting its direct utilization as a substitute or supplementary energy for petroleum.Hydrodeoxygenation(HDO)refining for lignin-oil by means of current petrochemical systems is able to reduce oxygen content and improve oil quality,and the key is to construct superior HDO catalysts.In the researches,Mo-based sulfides catalysts were synthesized via liquid phase method primarily.The crystal phase,morphology and S vacancy of product were controlled by changing preparation conditions.Taking the HDO of the typical O-containing phenols in lignin-derived bio-oil as a probe,the intrinsic relationship between structure defect,morphology and catalytic activity of Mo-based sulfides.Furthermore,utilizing the physico-chemical properties of the uncoordinated atom in defect,the metal-edge interface was constructed in-situ on active Rim-Edge site and inert Basal plane,respectively,forming high-efficiency metal-defect synergistic sites.Advanced characterizations such as XPS,EXAFS,AC-STEM are carried out to study the existence and formation of the site,and DFT calculations to reveal the properties and catalytic mechanism.The catalytic performance was investigated in the HDO of real lignin-oils.The specific research is as follows:(1)Molybdenum disulfide was synthesized by microwave assisted hydrothermal method,and the high-frequency vibration of the dipole under microwave field strengthened the reaction rate of the raw materials,a 91.8%yield of product was obtained within 0.5 h,which is 1/48 of the time required by traditional thermal.Studies showed that the synthesized molybdenum disulfide is in the form of slight crystallization with a S/Mo stoichiometric ratio less than 2 on the surface,containing a large number of S vacancy defects.A proper p H value is conducive to the spread of molybdenum disulfide flakes into a flower-like structure,exposing more S defect-enriched Mo edges,which is beneficial to p-cresol adsorption,exhibiting higher activity in HDO reaction.After reaction at 300°C for 6 h,the conversion rate and DDO of p-cresol over the synthesized molybdenum disulfide reached 95.4%and 92.4%,respectively,which is 1.4 times activity of per unit edge area of commercial Mo S2.(2)By adjusting the p H value of the system and taking advantage of microwave heating,The additives that NixSy with different phase composition and Co S2 with different morphologies were synthesized,and the preparation time was also effectively shortened.Studies showed that the p H value,preparation temperature and heating rate of the system have a great influence on the composition and morphology of additives.High temperature and lower p H value are beneficial to the formation of phase with a high S/Ni stoichiometric.The formation of Ni S2 is followed anti-Ostwald ripening process of large particles splitting to small ones,forming cubic structure with regular morphology;The formed Co S2 is agminated octahedral particles at a heating rate of 7.5°C/min,while heating rate is 30°C/min,crystals nucleated and grow on the surface of the microbubbles to form hollow nanospheres.The HDO activity of NixSy is very low,but after Mo S2 is mixed with it,the HYD path of p-cresol is enhanced,showing a good synergistic catalysis which supports hydrogen spilled-over reaction mechanism.Among them,the promotion effect of Ni S2 phase is the highest,while Co S2 has a little promotion.(3)Sulfur vacancy-enriched Mo S2-x was prepared by hydrothermal method,and then Co precursor was reduced and anchored on the surface of Mo S2-x by using the adsorption and reduction properties of the vacancies.Co region in the catalyst is primarily made up of zero-valent cobalt,which tend to be anchored on the active edge of molybdenum disulfide,forming a metal-edge interface,and there is obvious electron transfer between Co and Mo S2-x.In the HDO reaction of lignin-derived bio-oil,the synthesized catalyst showed excellent catalytic activity.The reaction temperature for direct deoxygenation of p-cresol was reduced to 120°C,and the selectivity of product aromatics was as high as99.5%.Combining the characterization analysis and DFT theoretical calculation results,the high activity of the catalyst is mainly due to the strong interaction between Co and Mo S2-x and the formation of the metal-edge interface,in which metal-defect synergetic can promote the adsorption of reactant and reduce the energy barrier of C-O bond breakage.The catalyst also showed good stability and universality.After recycling for 8times,the conversion rate and aromatics selectivity of p-cresol did not decrease significantly.In the HDO of real lignin-oil,Co0-Mo S2-x completely converted it into benzene,toluene and ethylbenzene,providing a green resource of bulk chemical aromatics.(4)As a 2D material,the active sites of molybdenum disulfide locates on its edge,while the main exposed Basal surface is inert.Therefore,how to activate the Basal surface is the key to strengthen activity of the material.Further,using the reducibility of the low-valence state Mo at the S vacancy and the metastability of 1T phase of molybdenum disulfide,a series of Pt0-Mo S2-x catalysts were prepared.The characterization results showed that Pt ions are inserted into the inert Basal surface of Mo S2-x through spontaneous redox reaction insteading of Mo atoms.After liquid phase hydrogen-thermal process,the Pt atoms are deintercalated and reassembled into nanoclusters,then adsorbed on the newly formed edge of the Basal plane,in-situ forming metal-edge interface.The catalytic activity of the molybdenum disulfide with activated Basal plane improved significatively in p-cresol HDO,which product is mainly naphthenic hydrocarbon.When the reaction temperature is reduced to 120°C,both conversion rate and DDO of the lignin-oil reached99.9%,meanwhile,the activity of the catalyst did not decrease after 7 cycles.The HYD of Pt0-Mo S2-x catalyzed real lignin bio-oil exceeds 99%with a 88.1%yield of total carbon.The catalyst synthesis method provides a new strategy for increasing the edge of molybdenum disulfide and efficiently activating the inert Basal surface. |
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