Studies On MPV Reduction Of Aromatic Ketone Over Supported Alkaline-earthoxides

Aromatic alcohol are important intermediates in the production of food additive and blender of cosmetics,and fragrances.Compared with other reaction approaches,the heterogeneous MPV reduction of aromatic ketone provides a convenient way for preparation aromatic alcohol.The method shows some advantages of high chemical selectivity for the reduction of C=O,mild conditions for reaction process and simple treatment after reaction.MgO has a few catalytic activity in the MPV reduction of aromatic ketone.As we all know,it is a good way for enhancing the catalytic activity to supporting the active component on support.Magnesium oxide supported on active carbon,siliceous mesoporous molecular sieve MCM-41,silica and ?-Al2O3,respectively,was prepared by the impregnation method.Their catalytic activities in the MPV reduction of acetophenone with 2-propanol as a reducer were investgated,and campared to that of pure alkaline-earth metal oxides catalyst.At the same time,the catalysts were characterized with XRD,TEM,N2 adsorption-desorption,XPS and CO2-TPD methods.The results show that the catalytic activity of pure MgO is low,due to the smaller specific surface area resulting the lesser basic sites on its surface.In the MgO-AC catalyst,the high surface area of AC and no strong interaction of MgO with AC support favor the high dispersion of MgO on the surface of AC.On the other hand,the concentration of acetophenone near the active sites in the catalyst increases because of the ?-electron interaction between the benzene ring in the acetophenone and graphite layer of AC support.The effects of above two aspects lead to a significant increase of the catalytic activity of MgO-AC campared to pure MgO.The MgO-MCM-41,MgO-SiO2,MgO-?-Al2O3 are hardly active due to the strong interaction of MgO with the support materials resulting the dramatic decrease of number of basic sites on the surface of these catalysts.By the same method,alkaline-earth metal oxides supported on active carbon was prepared.The best calcination temperatures for alkaline-earth metal oxides supported on active carbon catalysts shift to the higher temperature when the atomic number of alkaline-earth metal increases.The catalytic activity increases with increasing number of basic sites and base strength.Besides of above two factors,the steric effect also affect catalytic activities of these catalysts.Enough space was necessaried to form the six-member ring transition state in the MPV reduction,therefore,the active components loaded on the small pore in these catalysts were possibly unused.The MgO-AC catalyst having 10wt%of MgO with Mg(NO3)2 as the precursor salt calcinated at 600 ? had the best activity in the MPV reduction of acetophenone.The different aromatic ketone,hydrogen supply alcohol,ratio of ketone and alcohol,primary kinetics and reusability were investigated using this catalyst.The results manifest that the electron-withdrawing and electron-releasing groups have a lower degree of effect to the reduction rate of acetophenone as reported by some literatures because of the substituting effect and the ?-electron interaction between the benzene ring in the acetophenone and graphite layer of AC support.Secondary alcohol is better as the reducer.The best ratio of ketone and alcohol is 8.The observed order of reaction of MPV reduction of acetophenone is first-order and the apparent activation energy is 47.4 kJ/mol over MgO-AC catalyst.The activity of MgO-AC decreases about 15%in the first three uses,and has no change in the following uses.