Study On A Novel Co 3 O 4 @HZSM-5 Catalyst Based On The Oxidation Of Styrene To Benzaldehyde

Benzaldehyde has been widely used as an important intermediate in the field of chemical industry.Benzaldehyde can be synthesized via several methods including oxidation of benzyl alcohol,direct oxidation of toluene,hydrogenation of benzoic acid,indirect electrooxidation of toluene and hydrolysis of benzyl chloride.However,these methods suffer from various disadvantages such as complex synthesis process,expensive raw material,severe environmental pollution,low catalytic convention and poor benzaldehyde selectivity.Recently,the direct oxidation of styrene to benzaldehyde using environmentally friendly oxidant has arosed much attention in the academic community owing to its simple reaction procedure and pollution free feature.In this paper,the catalyst with the cobalt oxide particles encapsulated into HZSM-5 zeolite was prepared and modified.The catalytic performance of these catalysts was performed with the styrene oxidation to benzaldehyde.1.Screening and characterization of Co3O4@HZSM-5 catalytstThe catalysts with cobalt oxide particles encapsulated into HZSM-5 zeolites,noted as Co3O4@HZSM-5,G-Co3O4@HZSM-5 and P-Co3O4@HZSM-5,were synthesized with granule silica(average particle diameter:1 mm),fumed silica and powdered silica(average particle diameter:10 ?m)as the Si source respectively.The XRD and SEM results showed that the catalyst with the granule silica as the Si source had the regular hexagonal cubic-like morphology and high crystallinity.Thus,we chose granule silica as the Si source.The Co3O4@HZSM-5(40),Co3O4@HZSM-5 and Co3O4@HZSM-5(80)catalysts were prepared with the molar ratio of the silica and the aluminum equal to 40,50 and 80 individually.The XRD and SEM results showed that the catalyst with the 50 molar ratio of the silica and aluminum had the regular hexagonal cubic-like morphology and high crystallinity.In addition,the catalysts deprived from different conditions were applied in the styrene oxidation to benzaldehyde.Comparing with the other catalysts,the Co3O4@HZSM-5 catalyst showed apparent priority in catalytic performance in styrene oxidation to benzaldehyde.Therefore,the property of Co3O4@HZSM-5 catalyst was further investigated.2.Characterization and catalytic performance of Co3O4@HZSM-5 catalytstVarious characterization results,such as XRD,SEM,TEM,NH3-TPD,27Al-NMR,show that the Co3O4@HZSM-5 catalyst has well-organized structure with Co3O4 particles compatibly encapsulated in the zeolite crystals.The Co3O4@HZSM-5 catalyst was employed as an efficient catalyst for the selective oxidation of styrene to benzaldehyde with hydrogen peroxide as a green and economic oxidant.The effect of various reaction conditions including reaction time,reaction temperature,different kinds of solvents,styrene/H2O2 molar ratio and catalyst dosage on the catalytic performance were systematically investigated.Under the optimized reaction condition,the yield of benzaldehyde can achieve 78.9%with 96.8%styrene conversion and 81.5%benzaldehyde selectivity.Additionally,the catalyst after being used for six times hardly showed decrease in catalytic performance in styrene oxidation to benzaldehyde.Finally,according to the characterization and catalytic performance of the catalyst,the reaction mechanism with Co3O4@HZSM-5 as the catalyst for the selective oxidation of styrene to benzaldehyde was reasonably proposed.