Preparation And Performance Of Catalysts For The Hydrodeoxygenation Of Phenolic Model Compounds In The Bio-oil

With the rapid development of economy,the demand for energy increases year by year.The excessive exploitation of fossil energy leads to environmental pollution and ecosystem destruction.Therefore,the development of renewable energy is becoming more and more important.Bio-oil is a kind of liquid fuel through biomass pyrolysis,which has the advantages of large production,no pollution,renewable,zero carbon dioxide net emission and so on,and is considered as an excellent alternative to fossil fuels.But the oxygen content of bio-oil is much higher than that of conventional crude oil.Although the presence of oxygen in bio-oil will not cause environmental pollution in the combustion process,it will still bring some adverse effects,such as low calorific value of combustion,low solubility with hydrocarbon fuels and poor chemical stability,which hinder its wide application.Therefore,to develop bio-oil as a renewable alternative energy source,it must be improved by hydrooxygenation(HDO).Because the fracture of C-O bond in aromatic ring oxygen-containing compounds,such as phenols,is more difficult than that of other C-O bonds,and the proportion of phenolic compounds in bio-oil is up to more than 60%,therefore,the study of HDO reaction of phenolic compounds is representative and of important scientific significance for the study of deoxidation and improvement of bio-oil.A variety of different catalysts were designed and prepared in this paper.The catalytic performance in the HDO reaction of typical phenolic oxygen-containing compounds in bio-oil was studied by regulating the composition,structure and morphology of catalysts.Firstly,three MoS2 catalysts were synthesized by hydrothermal method with thiourea,L-cystine and sulfur as sulfur source.The effects of sulfur source on structure,morphology and catalytic activity of MoS2 in the HDO reaction of p-cresol were investigated.The results showed that sulfur source had significantly affected the morphology and surface area of hydrothermal synthetic MoS2 catalyst.The HDO activity of all synthetic MoS2 was significantly higher than that of commercial MoS2.Among the three MoS2 catalysts,the catalyst prepared with thiourea presented a flower-like structure with a specific surface area of 78.0 m2/g,showing the highest activity in the HDO reaction of p-cresol:at 300?,the raw material conversion reached 99.4%,the deoxidation degree(D.D.)reached 99.3%,and the selectivity of toluene was 79.65%.Secondly,the CoS2/MoS2 catalyst was prepared by two-step hydrothermal method.MoS2 was firstly synthesized by hydrothermal method,then CoS2 was prepared by hydrothermal method and deposited on the MoS2 surface.The characterization results showed that CoS2 and MoS2 existed in independent phases,and the surface area of CoS2/MoS2 was much larger than that of Co-Mo-S prepared by one-step method.In the HDO reaction of p-cresol,the presence of CoS2 increased the activity of catalyst,but excessive CoS2 coating on MoS2 surface decreased its activity.By optimizing the catalyst composition,CoS2/MoS2 showed excellent HDO activity and direct deoxidation selectivity:the D.D.reached 98%and toluene selectivity 99%at 250? for 1 h.At the same time,the consumption of hydrogen is reduced,which is beneficial to improve economic benefits.The CoS2/MoS2 catalyst also showed high catalytic activity for HDO reaction of other phenolic compounds and hydrodesulfurization of benzothiophene,a typical sulfur compound.Thirdly,in order to suppress the negative influence of water generated in HDO process on sulfide catalyst,hydrophobic sulfide catalyst was proposed and prepared by two-step hydrothermal method:hydrothermal synthesis of hydrophobic MoS2 was conducted by adding silicomolybdic acid.The optimum preparation parameters were obtained by optimizing the preparation conditions,and then used as the substrate for NiS2 or CoS2.The HDO activity of 4-ethylphenol was tested.The results showed that there were two independent phases(NiS2 and MoS2)in the hydrophobic NiS2/MoS2,and the air-water contact Angle was 140°,showing excellent hydrophobicity.In the HDO reaction of 4-ethylphenol,the conversion and D.D.were 81.5%and 79.7%respectively after 6h reaction at 275?.After the catalyst was recycled for 5 times at 275? the conversion of 4-ethylphenol decreased only 2.1%,showing good stability.There were also two independent phases(CoS2 and MoS2)in CoS2/MoS2.The air-water contact angle reached 143°and the reaction was conducted at 225? for 3h.The conversion and D.D.of 4-ethylphenol reached 99.9%.The high hydrophobicity promoted the rapid detachment of water and inhibited the contact between water and catalyst surface.Therefore,such catalysts showed excellent stability in the HDO reaction.In addition to the sulfide catalyst,the carrier of noble metal catalyst was also researched.Hydrotalcite-like compounds were prepared by coprecipitation method,and were used as the carrier of Pt catalyst to test HDO activity of p-cresol.The results showed that the activity of Pt-based catalyst was related to the composition and structure of the carrier,and that the catalytic activity of Pt supported on hydrotalcite in HDO of p-cresol was higher than that of Pt supported on mixed metal oxides.In the HDO reaction of p-cresol,the conversion of Pt-Ni-Al-H was 99.8%,the toluene selectivity was 1.4%,and the toluene selectivity reached 84.1%on the Pt-Zn-Al-H catalyst at 275? and 2 MPa for 1 h.Moreover,Pt-based catalyst had a certain dehydrogenation activity for methylcyclohexane,which can catalyze further dehydrogenation of methylcyclohexane to toluene and effectively reduced hydrogen consumption in HDO.