The Post-treatment Of Beta Molecular Sieves And Its Application In Hydrodeoxygenation Of Phenol

Considering the lack of petrochemical resources,increasing energy demand and frequent environmental problems,the development of biomass energy is important.As an important biomass energy source,biomass pyrolysis oil contains oxygen compounds（e.g.,phenol）,which have a high viscosity,corrosivity,poor chemical stability and low calorific value of combustion.Therefore,hydrodeoxygenation treatment of biomass pyrolysis oil is needed to meet the application demands.In order to solve issues above,a novel alkaline treatment method is proposed to introduce the mesoporous structure in Beta molecular sieves while protecting the microporous structure.A novel Pt/Beta hydrodeoxygenation catalysts were developed for phenol hydrodeoxygenation using Beta molecular sieves as supports.Firstly,the effects of heating method,alkaline strength and alkaline solvent on the framework and pore structure of Beta molecular sieve were investigated in detail.Compared with untreated Beta molecular sieve,alkaline treatment etches the framework atoms of Beta molecular sieve,introduces mesopores,and destroys the microporous structure.The relative crystallinity and BET specific surface area decreased obviously.Compared with conventional water bath heating,microwave heating assisted alkaline treated Beta molecular sieves have a more uniform mesopore distribution and higher Br?nsted acid retention.Compared with sodium carbonate alkaline source and ethylene glycol solvent,when Beta molecular sieves are treated in sodium hydroxide aqueous solution,the mesopore volume of Beta molecular sieve is 0.52 cm3/g and the average pore size is about 5.13 nm.Based on above conclusions,surfactant molecules are added in the process of alkaline treatment of Beta molecular sieve to achieve the goal of introducing mesoporous structure while reducing the loss of microporous structure.Compared with alkaline treated Beta molecular sieve without surfactants,surfactants adsorb on the external surface of Beta molecular sieve crystals,protect the molecular sieve from alkaline etching,and selectively etch internal surface of Beta molecular sieve crystals.Beta molecular sieve treated by alkaline with surfactants（i.e.,Beta-S and Beta-D）have a hollow morphology.The relative crystallinity is 55.1 and 51.7%,and the BET specific surface area is 481 m2/g and 508 m2/g.The surface Si/Al ratio decreases from 12.3 to 5.9 and 5.8.Compared to Beta molecular sieves without alkaline treatment（i.e.,Beta-P）,the total acid sites decrease as follows:Beta-S>Beta-P>Beta-D.In the hydrodeoxygenation reaction of phenol,Pt and acid sites show a competitive adsorption of phenol and intermediate products（cyclohexanol and cyclohexene）.When the loading amount of Pt is excessive（i.e.,metal loading>0.5 wt%）,a suitable acidity and acid content of efficient Pt/Beta catalyst is needed which can meet the demand of dehydration of cyclohexanol to produce cyclohexane and the inhibit carbon deposition.Finally,the protective mechanism of surfactant molecules on the microporous structure and acidity of Beta molecular sieves in the alkaline treatment process is investigated by changing the amount and adding time of surfactants.It suggests that when CTAB is added in 30 min and 60 min after the start of alkaline treatment,CTAB is preferential to adsorb on the outer surface and defects of Beta crystals,which inhibits the further destroy of small mesopores.When CTAB is added in 90 min after the start of alkaline treatment,Beta molecular sieve is seriously destroyed.CTAB could only partially protect the edge of mesopores and a further etch of mesopores occurs to form large mesopores.The ratio of Br?nsted/Lewis（B/L）to Beta zeolite decreased as the delay addition of CTAB.When the Si（OSi）₃（OAl）species are removed,the framework tricoordinated Al atoms act as Lewis acids.Therefore,when CTAB is added in 30 min and 60 min after the start of alkaline treatment,CTAB interacts with the tricoordinated Al atoms to protect the tricoordinated Al atoms from being removed.After the removal of CTAB,alkaline treated Beta molecular sieve was obtained with a high concentration of Lewis acid sites.The yield of cyclohexane increases which is consistent with that amount of Lewis acid sites due to the high dehydration activity of Lewis acid sites.The novel alkaline treatment method of Beta molecular sieve proposed in this thesis solves the contradiction of introducing mesoporous structure and destroys microporous structure,and provides a method support for alkaline treatment of other alumina-silicon molecular sieves.The results of hydrodeoxygenation of phenol provide references for the design of acidity of bi-functional catalysts and the route upgrading of bio-oil treatments.