Preparation And Catalytic Performance Of Hydrotalcite Precursor Cu - Mg - Al Catalyst For Synthesis Of O - Phenol

O-phenylphenol (OPP) is a kind of fine chemical products, widely used in biocide, pharmaceutical additives, textile auxiliaries, heat stabilizer and so on. The demand for OPP is also increasing due to the application in some industrial fields. The major process for the preparation of OPP used the dehydrogenation of cyclohexanone dimmer which used as the raw material. For this process, it usually uses precious metal catalyst, platinum as a dehydrogenation active ingredient. Thus, it made the production cost high for OPP. Therefore, there is a great sifnificance for the research and development of efficient and economical dehydrogenation catalyst. In this paper, we used the copper, a non-precious metal, as the active ingredient into the hydrotalcite with an excellent structural characteristic. It was used as the dehydrogenation catalyst after calcined and reduction, aiming to improve the catalytic activity and stability. The samples were characterized and analyzed by XRD, SEM, FT-IR, TG/DTG, BET and other technical means.A series of Cu-Mg-Al-CO3hydrotalcite compounds with different molar ratio of copper to magnesium to aluminum were synthesized by coprecipitation method, then to obtain the composite metal oxide catalyst after calcining the precursor. We studied the effects of different copper content, different calcination temperatures, different reaction temperatures and different H2flow rate on the performance of catalytic dehydrogenation. Studies have shown that we have prepared a sieries of ordered structure hydrotalcites with changing the Cu:Mg ratio=0.43-1.73in fixed composition M2+/M3+=3. The catalyst show a better dehadrogenation performance at the compostion of nCu:nMg:nAl2.5:3.5:2and calcination temperature450℃. The initial conversion of the cyclohexanone dimer is99.91%, and the selectivity of OPP is up to89.5%at reaction temperature330℃and H2flow rate20mL/mim.The effects of different aluminum content on hydrotalcite structure, acidity and catalytic dehydrogenation performance were also investigated. The results shows that the regularity of the hydrotalcite structure is poor, which is ncu:nMg:nAi is2.5:3.5:1.5, but has the good performance of dehydrogenation. The conversion of the cyclohexanone dimer is99.16%, and the selectivity of OPP is73.12%when the reaction time is up to6hours. That is due to the excessive aluminum amount added will decrease the base of catalyst, and side reactions caused by acid sites increased, which resulted in the low selectivity of OPP. The catalyst with a small amount of aluminum has a suitable acid/basic properties.In addition, a series of Cu-Mg-Al-C03hydrotalcite compounds with different molar ratio of copper to magnesium to aluminum were synthesized by hydrothermal crystallization method. All samples appear well developed layered and plate-like structure, that is "sand rose" morphology formed by lamellae bonded edge-face staggered. The average thickness of platelets is at the range of20-36nm. Two types of pore size distributions were observed for the catalyst samples in this work. The effects of various copper content on hydrotalcite structure and activity of the catalyst were examined. Studies have shown that we have prepared a sieries of ordered structure hydrotalcites with changing the Cu:Mg ratio=0.07-0.71in fixed composition M2+/M3+=3.The catalyst show a better dehadrogenation performance at the compostion of ncu:nMg:nAl1.8:4.2:2and calcination temperature450℃. The conversion of the cyclohexanone dimer is99.91%, and the selectivity of OPP is up to89.5%at reaction temperature330℃and H2flow rate20mL/mim when the reaction time is up to6hours.