Preparation Of ?-Al₂O₃ Supported Metal Oxide Catalysts And Its Catalytic Performance In Phenol Hydroxylation

Dihydroxybenzenes?DHB?are important intermediates and products of organic chemistry,which can be further processed to produce dyes,polymers,and pharmaceuticals.Up to now,hydroxylation of phenol with hydrogen peroxide as the oxidant becomes the most general way to obtain diphenols,owing to its environmental acceptability.Scattering active component onto appropriate carrier to prepare supported catalyst can reduce the dosage of active component and further save the cost of catalyst.In this paper,supported catalysts with mono-metal and composite metal as active component are prepared by vacuum volumetric immersion method,with the low-price ?-alumina as carrier and metal nitrate as precursor.In the experiment schedule,mono-metal supported catalyst is firstly prepared and Fe/?-Al₂O₃ has the best performance.The conversion of phenol is 37.65% and selectivity to hydroquinone is 67.65%.It is found that hydroxylation of phenol with Fe/?-Al₂O₃ as catalyst has an unneglectable induction period.Increasing the load of iron,higher reaction temperature can shorten the induction period,but the effect is not ideal.In consideration of the above problems,composite metal is loaded to ?-alumina carrier in the second step of the experiment schedule and catalyst performance of Fe/?-Al₂O₃ is the best,with the induction period shortened dramatically.When the load of Cu in catalyst is more than 0.04,the reaction induction period is disappear,but the reaction rate is too fast,with the serious exotherm.Adding Pb component can improve the performance and will not influence the hydroxylation of phenol at the same time.As a result,Fe-Cu-Pb is supposed to be the optimal catalyst.The optimal process conditions are concluded though the optimization experiments of catalyst calcination temperature,reaction time and temperature of the hydroxylation of phenol and the result are: catalyst calcination temperature 600 ?,the mass ratio of catalyst and phenol is 5%,reaction temperature 50 ?,reaction time 1 h,molar ratio of H2O2/ phenol was 0.90.The conversion of phenol is 56.48% and selectivity to DHB is 89.01% under the optimal conditions.Finally the Fe-Cu-Pb/?-Al₂O₃ catalyst is characterized by BET,XRD,SEM and TEM.The results can be summarized as follows: the specific surface area is 129 m2/g,and the mesoporous structure of the carrier is maintained.Active components are loaded uniformly on the carrier in the form of oxide: Fe2O3,CuO,which Fe has interaction with ?-Al₂O₃ carrier.During hydroxylation of phenol,the erosion rate of Cu is faster than that of Fe.The uniform dispersity of the active component in the catalyst is maintained after the reaction.