Several Manganese Porphyrins Based Porous Materials:Preparation,Characterization And Catalytic Performance

The synthetic metalloporphyrins can mimic the cytochrome P450 and efficiently catalyze a variety of substrate molecules under very mild conditions.However,metalloporphyrins are easily self-oxidized and dimerized in a homogeneous catalytic system.So,in order to improve the catalytic activity and stability of metalloporphyrins,heterogeneous catalysts have been developed.Loading metalloporphyrins on insoluble supports or immobilizing it on framework structures are both effective methods for preparing metalloporphyrin heterogeneous catalysts.Based on the above background,four ester porphyrins were firstly designed and synthesized:5,10,15,20-tetra-（3-carbethoxymethyoxyphenyl）porphyrin（H₂Pp1）,5-（4-imidazol-1-ylphenyl）-10,15,20-tris-（3-carbethoxymethyoxyphenyl）porphyrin（H₂Pp2）,5,10,15,20-tetra-（3-carbethoxymethyoxyphenyl）manganese porphyrin（MnPp1）and 5-（4-imidazol-1-ylphenyl）-10,15,20-tris-（3-carbethoxymethyoxyphenyl）manganese porphyrin（MnPp2）.After hydrolysis,the corresponding carboxy porphyrins H₂Cp1,H₂Cp2,MnCp1 and MnCp2 were obtained.Then characterized by UV-vis,IR,ESI-MS and ¹H NMR.Under solvothermal conditions,MnCp were reacted with SiO₂ sol to obtain MnCp1-SiO₂and MnCp2-SiO₂ gels,and MnCp1-SiO₂ and MnCp2-SiO₂ porous materials were obtained after supercritical CO₂ drying.Then,UV-vis-DRS,FT-IR,XRD,TG,SEM,EDS,TEM characterizations and BET tests were carried out.The optimal conditions of ethylbenzene（EB）catalysis were investigated by changing the amount of solvents and oxidant,temperature and reaction time.Finally,the catalytic performance of EB was characterized under optimized conditions.The results show that the MnCp-SiO₂ can selectively oxidize ethylbenzene to acetophenone,and the biggest theoretical TON number reaches 185.However,MnCp are simply adsorbed on SiO₂,some of them are easily detached from SiO₂ or aggregated during the catalytic process,so the recyclability is weak.Four metalloporphyrin gels were obtained by reacting MnCp with Cr（NO₃）₃·9H₂O and Al（NO₃）₃·9H₂O under solvothermal conditions,dried by supercritical CO₂ to obtain four porous materials:MnCp1-Cr,MnCp2-Cr,MnCp1-Al and MnCp2-Al.then,a series of characterizations were carried out.Finally,the effects of solvents,oxidant quantity,temperature,amount of catalyst and reaction time on the catalytic oxygen of EB were investigated,and then the catalytic performance and recyclability of ethylbenzene were characterized under optimal conditions.The four porous materials MnCp-Cr and MnCp-Al prepared by gel method exhibited catalytic activity in the catalytic oxidation experiments of ethylbenzene.However,due to the influence of peripheral coordination ions,specific surface area and pore size distribution,the catalytic activity of MnCp-Al on ethylbenzene is low,which can only reach 32.9%.The conversion rate of MnCp1-Cr to ethylbenzene is as high as 94.5%,the theoretical TON number can reach 1723,and it shows good catalytic activity after four cycles of catalytic cycling.