Preparation Of A Novel Photothermal Catalyst And Its Selective Oxidation Of Aromatic Alcohols

Aromatic aldehydes play an indispensable role in the synthesis of drugs,the preparation of perfumes and the synthesis of other fine chemicals,and have great application value in industry.At present,the process of preparing aromatic aldehydes in the industry is high in energy consumption,and it is necessary to use toxic heavy metal oxidizing agents(KMnO₄,Cr^IV,etc.),which can seriously pollute the environment and do not conform to the development philosophy of green chemistry in today’s society.Photocatalysis has many advantages of low environmental and energy consumption,and attracts a large number of scholars’attention in the direction of selective oxidation of aromatic alcohols to form corresponding aromatic aldehydes.In this paper,we successfully combined photocatalyst with thermal catalyst to prepare a new photothermal catalyst Cr₂O₃-Al₂O₃/CdS.The prepared photothermal catalysts were subjected to X-ray diffraction（XRD）,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,X-ray photoelectron spectroscopy（XPS）,ultraviolet visible diffuse reflectance spectroscopy（DRS）and BET adsorption desorption,respectively.Analytical and other characterizations are used to analyze the physicochemical properties.The experimental results show that when the content of thermal catalyst Cr₂O₃-Al₂O₃ is 50%,the photocatalytic activity of selective photocatalytic oxidation of benzyl alcohol is the best.The yield and selectivity of the target product benzaldehyde reach 51.6%and 99.0%,respectively.Compared with the monomer thermocatalyzed Cr₂O₃-Al₂O₃ and the monomer photocatalyst CdS,the yield of benzaldehyde was increased by 3.1 times and 2.8 times,respectively.After analysis,the increased catalytic activity is mainly attributed to the coupling of photocatalysis and low temperature thermal catalysis.In this regard,we propose a possible experimental mechanism.On the photothermal catalyst Cr₂O₃-Al₂O₃/CdS,On the photothermal catalyst Cr₂O₃-Al₂O₃/CdS,when the temperature rises,the thermal catalyst Cr₂O₃-Al₂O₃can interact with the alcoholic hydroxyl group of the aromatic alcohol,so that the C-Hαand O-H bonds on the aromatic alcohol are weakened.When light is irradiated onto the surface of the catalyst,the photocatalyst CdS can generate photogenerated electrons and holes,and the holes interact with oxygen on the surface of the catalyst to generate superoxide radicals（.O₂^-）,which makes it easier to remove the H atoms and make the aromatic alcohol conversion to aromatic aldehydes.The results of this study demonstrate that the combination of thermal catalyst and photocatalyst can greatly improve the feasibility of selective oxidation of aromatic alcohol to aromatic aldehyde.It has far-reaching significance in the fields of thermal catalysis and photocatalysis.In addition,we also studied the low-cost composite of graphite powder and noble metal Pt to selectively reduce cinnamaldehyde to phenylpropanol at low temperature,while catalyst C and Pt/C were respectively X-ray diffraction（XRD）.X-ray photoelectron spectroscopy（XPS）,scanning electron microscopy（SEM）and transmission electron microscopy（TEM）were used to characterize the physicochemical properties,and the corresponding possible mechanisms were proposed.