Preparation Of MCM-41 Supported Iron-Based Catalysts And Their Performance In The Hydroxylation Of Phenol

Catechol and hydroquinone are the major products of phenol hydroxylation. As important fine chemical products, they are widely used in high-value downstream industry. Hydroquinone with good properties in photosensitization, polymerization inhibition and antioxidant is mainly used in the production of photosensitive materials, the storage and transportation of some rubber monomer, the antioxidant in petroleum chemical industry. It’s also important intermediate of anthraquinone dye and medicine raw materials. As to catechol, the main industries include pesticides, pharmaceutical and dye. Besides, it can be used to produce gum hardener, additives and antioxidants in plating bath.The traditional process of dihydroxybenzene production such as oxidation of aniline, hydrolysis of o-chlorophenol, oxidation of p-diisopropylbenzene result in severe environmental pollution, equipment corrosion, high energy consumption, etc. By the contrast, hydroxylation of phenol has shown many advantages with mild reaction conditions, less device corrosion, simpler operation and so on. Besides, as the oxidant of phenol hydroxylation, hydrogen peroxide only converted into water thus the process have fewer outgrowths and less environmental impact.In this study, MCM-41 was synthesized as support through hydrothermal method, with tetraethyl orthosilicate as silicon source and CTAB as template. The regular and well-define channel systems, high specific surface area and good chemical and hydrothermal stability of MCM-41 can help to optimize the process of phenol hydroxylation. However, MCM-41 with pure silicon shows little catalytic activity. In order to greatly improve the catalytic activity, transition metal was introduced to MCM-41 as active component in two different ways namely doping and loading. The characterizations of samples were conducted by means of XRD, TEM and N2 adsorption-desorption to identify and analyze the structure. The synthesis optimization of each way and the comparison of catalytic properties were conducted according to the yield of dihydroxybenzene. The catalyst prepared in loading way (Fe2O3/MCM-41) with a aging time of 90min、loading amount of 2.5mmol/g, precipitation temperature of 65℃, pH of 8-9 and washing to neutral, calcination temperature of 450℃, has a phenol conversion of 34.72% and selectivity of 87.39%. The phenol conversion of Fe-MCM-41 is 28.43% and the selectivity is 90.63% when the source of Si and Fe were added together and the molar ratio of Si to Fe is 40. The induction period of Fe2O3/MCM-41 is seven minutes shorter than Fe-MCM-41.Aiming to further improve the one-way conversion of phenol and selectivity to dihydroxybenzene, MCM-41 supported two different transition metal oxides were synthesized as follows:Fe2O3-CoO/MCM-41, Fe2O3-Cr2O3/MCM-41, Fe2O3-CuO/MCM-41. Among them the iron-copper binary oxide catalyst has the best property compared with other combinations. Impacts of several reaction conditions were also studied with Fe2O3-CuO/MCM-41 as catalyst The results are listed as follows:the yield of products was low with a temperature which was too high or too low; the increasment of phenol can improve the selectivity of products, however, the conversion rate would drop; too much catalyst and reaction time can both reduce the selectivity of products. The optimized conditions were reaction temperature 50℃、molar ratio of phenol to H2O21.25、mass ratio of catalyst to phenol 0.03、reaction time 15 min. The conversion of phenol reached 41.73%, the selectivity of dihydroxybenzene was 91.61%.