Effect of the diatomite pretreatment on the catalytic performance of TS-1/diatomite for toluene hydroxylation by H2O2 in fixed-bed reactor

•TS-1/diatomite is effective for toluene hydroxylation with H2O2 in fixed-bed reactor.•Surface acidity, pore size are key factors on catalytic activity of TS-1/diatomite.•Properties of diatomite are altered by treated with H2SO4/HF mixed acid solution.•Pore diameter of diatomite turns larger after calcination at 1000 °C.

Supporting the TS-1 catalyst on diatomite and adopting fixed-bed reactor technique for the toluene hydroxylation by H2O2 are in favor of the separation of TS-1 catalyst from liquid reactants and continuous production, to reduce the product cost. Diatomite was treated with the H2SO4/HF mixed acids solution and calcined at 1000 °C, and the effect of pretreatment on its physicochemical properties was investigated by ICP-AES, XRD, low-temperature N2 absorption and NH3-TPD techniques. After diatomite was treated with H2SO4/HF mixed acid solution and calcined at 1000 °C, some mineral impurities (as Al, Fe and Mg) in diatomite were removed and its pores were cleared, resulting in an increase in its surface area and pore sizes; while the acidic strength of relatively strong-acid sites on the diatomite surface was weakened, and its amount of acid sites was increased. Interestingly, the HF concentration in the mixed acid solution would remarkably affect the surface properties of diatomite. As the diatomite support of TS-1 catalyst for toluene hydroxylation by H2O2 in fixed-bed reactor, the suitable ratio of H2SO4/HF in the mixed acid solution is 8/2. After diatomite was treated with the H2SO4/HF (8/2) mixed acid solution and calcined at 1000 °C, the catalytic performance of TS-1/diatomite for the toluene hydroxylation was improved remarkably, for instance, the conversion of toluene and utilization of H2O2 at 60 °C reached 14.3% and 94.3%, respectively.

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