The Preparation Of Bimetallic Co-Cr Doped Mesoporous Molecular Sieve And Its Application In Deperoxidation Of Cyclohexyl Hydroperoxide

Cyclohexanone is an important organic chemical material. It’s produced mainly by cyclohexane oxidation process. Cyclohexyl hydroperoxide(CHHP) is an important intermediate product during the cyclohexane oxidation reaction, which can decompose into cyclohexanol and cyclohexanone and cyclohexanol can be further dehydrogenated to produce cyclohexanone. Traditional CHHP decomposition process exists a low selectivity about 87% towards cyclohexanol and cyclohexanone. In addition, it produced large amount of waste alkali solution, leading to severe environmental pollution. Therefore, it’s the key step to develop an environmentally friendly decomposition process with higher selectivity to cyclohexanol and cyclohexanone for increasing the efficiency of cyclohexane oxidation. In this thesis, we introduced the metal cobalt, chromium, copper into mesoporous molecular sieve TUD-1 and SBA-15. The prepared catalysts were applied in CHHP decomposition process without alkali, aimed at studying the relationship between structure and performance and also reusability of the catalysts.Firstly, we applied direct hydrothermal synthesis(DHT) method to prepare monometallic Co-TUD-1, Cr-TUD-1 and bimetallic Co-Cr-TUD-1 by using TUD-1 as catalyst carrier. The catalysts were characterized with multiple methods to obtain the structure information and their catalytic performance were studied in decomposition of CHHP. The results showed that the catalytic performance and stability of bimetallic catalysts were higher than that of monometallic catalysts, showing the synergistic effect of the metals. Co-Cr-TUD-1(25)(Si/(Co+Cr)=25) showed the best performance, the CHHP conversion was 96.9%, the selectivity to cyclohexanol and cyclohexanone was 22.5% and 73.9%, respectively. The catalytic performance decreased to some degree after the third run, which could be regenerated by calcination. However, it was still unstable.Secondly, three methods were used to study the inactivation reason of Co-TUD-1.(1) The catalysts were calcinated after reuse;(2) The cyclohexane oxidation liquid mixture was pretreated with 10% Na2CO3 aqueous to reduce the acidity of the raw material;(3) Hexamethyldisilazane(HMDS) as silylation was used to improve the hydrophobicity by building the hydrophobic environment inside the catalyst. Various kinds of characterization results and catalytic performance evaluation showed that the calcination can remove the residual organics on the surface of catalysts so that activity can be recovered, but inactivation was still existed in the new cycle. Moreover, decreasing the acidity of cyclohexane oxidation liquid and increasing the hydrophobicity of the catalyst can’t solve the problem of the metal loss, which was resulted from an inreversible inactivation. To study the influence of metal species, the catalysts Cu-TUD-1 and Co-Cu-TUD-1 were prepared using direct hydrothermal synthesis(DHT) method with copper(II) nitrate as copper source. The materials were characterized and applied in the decomposition reaction, which showed that the best performance was over Co-Cu-TUD-1(50). The conversion was 81.4% and the selectivity to cyclohexanol and cyclohexanone was 63.8% and 37.2%, respectively. The conversion after the first run was decreaced to 73.3% with no change of the selectivity. The activity and stability of bimetallic catalysts containing copper and chromium decreased to some extend.Finally, monometallic Co/SBA-15, Cr/SBA-15 and bimetallic Co-Cr/SBA-15 were prepared by impregnation method with SBA-15 as carrier, which were characterized and tested to the decomposition of CHHP. The effects of metal content and calcination temperature on structure and catalytic performance were also studied. It was suggested that the catalytic performance of Co/SBA-15 was higher than that of Cr/SBA-15. 8%Co/SBA-15 showed the best activity with the conversion of CHHP 98.1% and the selectivity to cyclohexanol and cyclohexanone 70.9% and 27.9%, respectively. While the problem of metal loss was inevitable. The performance of Co-Cr/SBA-15 was excellent and the selectivity of cyclohexanol and cyclohexanone could be improved. 8%Co-4%Cr/SBA-15 showed the best performance with CHHP conversion 98.0% and the selectivity to cyclohexanol and cyclohexanone 55.2% and 42.0%, respectively. What’s more, strong relationships between metal and support, also two metals in bimetallic catalysts can enhance the activity and stability by inhibition of metal loss.