Research Of Modified Zeolite Catalyst For Selective Solvent-free Oxidation Of Toluene To Benzaldehyde

In this paper, we use different concentrations of Na OH（0.1mol/L-0.4mol/L） aqueous solution processing HZSM-5 molecular sieve. Then, we use the immersion method and the process is simple prepared. A variety of Fe₂O₃ load alkali-treatment HZSM-5 molecular sieve, which were non-toxic and security. Many characterizations of modified zeolite were tested by SEM, XRD, NH₃-TPD and N₂ adsorption stripping technology in order to determine the surface morphology, composition and structure of them. Using NH₃-stripping temperature programmed to determine the surface acid strength of material preparation.Using hydrogen peroxide as oxidant, We discussed the different alkali-treatment zeolite catalyst for selective solvent-free oxidation of toluene to benzaldehyde. At the same time, we discussed modified zeolite catalyst preparation conditions and the strength of the modified zeolite acidity, the changes of specific surface area and Si/Al ratio on the influence of toluene conversion and benzaldehyde selectively. After many experiments we concluded that a moderate acid catalyst can improve the toluene conversion rate. As well, we discussed the Fe₂O₃ load alkali-treatment HZSM-5 molecular sieve catalyst catalytic activity. The change of the catalyst on the surface of the acid and alkali after the Fe₂O₃ load have impact on toluene conversion and the selectivity of benzaldehyde. We found that compared with different alkali-treatment zeolite catalyst, after the iron catalyst load, although the toluene conversion rate decreased, but the selectivity of benzaldehyde is also improved. Through the analysis of the product selectivity, The improvement of selectivity of benzaldehyde related to the significantly decrease of by-products of benzyl alcohol and phenol selectivity. The causes of this phenomenon may be iron promoted the conversion of benzyl alcohol to benzaldehyde, and inhibit the oxidation of toluene to phenol.At the same time, We determined the optimal preparation conditions of catalyst: the zeolite（HZSM-5, Si/Al=38） was calcined at 550 °C for 6h in an oven. After cooling down, 2.0g of HZSM-5 was added to 40 m L of 0.2 mol/L of Na OH aqueous solution and then stirred at 80℃ in the water bath for 2h, the suction filter washing made white solid powder. At last, the alkali-treated zeolite was dried at 120 °C for 12 h after filtrating. Then, optimal concentration of Fe（NO）₃·9H₂O solution in anhydrous ethanol for preparing catalyst with higher activity was 0.5 mol/L. We made catalyst Fe₂O₃/HZSM-5-0.2.We inspected the Fe₂O₃/HZSM-5-0.2 for producing Bz H from toluene in the catalytic performance of this catalyst showed good catalytic activity. And the optimal preparation conditions: the reaction temperature 90 ℃, the toluene/H₂O₂ molar ratio 1:3, the reaction time 4 h, amount of the catalyst 0.4 g. Under the optimal conditions we can get the about 9.95 % toluene conversion and 66.8 % selectivity of Bz H. Then, the alkali-treatment HZSM-5-x load other metals catalyst and different Si/Al ratio of catalyst HZSM- 5 catalyst were tested to explore.