Synthesis Of Cu-Based LDHS As Catalysts For The Hydroxylation Of Phenol

The conventional Cu-based LDHs catalysts for hydroxylation of phenol generally suffer from low catalytic activity, due to the low dispersion. In this dissertation, the Cu-based LDHs catalysts with controlled size and structure were prepared via several kinds of methods. The relationship between the surface area, dispersion of Cu and the catalytic performances was investigated. The Cu-based LDH catalyst exhibits high catalytic activity for the hydroxylation of phenol. Moreover, considering the exfoliated characteristic of layered double hydroxides, Cu-based LDH catalysts obtained by delaminating the LDHs precursor display high dispersion and high surface area. The correlation between the the catalytic behavior and structural parameters was also studied. The obtained catalyst exhibits excellent phenol hydroxylation performance and high stability, which can be potentially applied in hydroxylation of phenol.The main results of this dissertation are as follows:(1) The CuMgAl-LDH catalysts with different sizes were prepared with methods of the urea hydrolysis, co-precipitation and separate nucleation & aging steps, respectively. The relationship between the surface area, the highly-dispersed Cu species and the catalytic performances was investigated. The best catalytic performance can be found over c-LDH-80 sample with phenol conversion of 35.88%. The SEM and TEM images confirm that the c-LDH-80 has higher dispersion and smaller size of LDH nanosheets than the other samples. XPS and BET measurements also indicate that c-LDH-80 displays high surface area and highly-dispersed Cu species. The c-LDH-80 sample exhibits the highest phenol hydroxylation performances, which can serve as a promising candidate for hydroxylation of phenol.(2) The CuMgAl-LDH@mSiO2 catalyst was fabricated by delaminating the LDHs precursor and followed by coating porous silica, based on the exfoliated character of layered double hydroxides and the highly dispersion of Cu species in LDHs nanosheets. SEM, TEM and AFM images show that the CuMgAl-LDH@mSiO2 nanoplates are highly dispersed and the average size of nanoplate is 3.89nm. The CuMgAl-LDH@mSiO2 sample exhibits the best catalytic reactivity with phenol conversion of 45.56% and dihydroxybenzene selectivity of 97.26% under the conditions of phenol:H2O2=2:1. XPS and BET measurements further show a Cu At.% of 0.61% and SBET of 244.3m2/g for the CuMgAl-LDH@mSiO2 sample. The catalysts prepared by delaminating the LDHs precursor exhibit excellent utilization rate of Cu species, due to its high dispersion of exposed surface Cu active site. The catalyst exhibits high catalytic activity and high stability, which shows potential applications in hydroxylation of phenol.