Phenol Efficient Catalysts Of Selective Hydrogenation Of Cyclohexanone

Cyclohexanone is an important chemical material which is widely used in the production of fiber, synthetic rubber, industrial coating, medicine, pesticide and also used as an organic solvent. Currently, Cyclohexanone is produced mainly by either oxidation of cyclohexane in the liquid-phase or by hydrogenation of phenol to cyclohexanol followed by dehydrogenation to cyclohexanone; such processes usually cause pollution of environment and waste of energy. The one-step hydrogenation of phenol to cyclohexanone has the advantage of simple operation and reduced undesirable products. The current researches centered on the gas-phase hydrogenation of phenol, although the liquid-phase method was energy saving and operation conveniently, little attention had been focused on this field. The key was the shortage of suitable catalysts. The amorphous alloys are a kind of materials with short-range ordering while long-range disordering structure. Their unique structure can result in excellent catalytic properties. Meanwhile, little or even no environmental pollution may be produced during the preparation process of amorphous alloys and their application in catalysis. Thus the amorphous alloys represent new powerful catalysts for modern chemical engineering production, i.e. the green chemistry and the economic reaction. Due to the industrial requirements and environmental considerations, amorphous alloy catalysts caused much attention by both chemists and chemical engineers. However, the preparation of metal amorphous alloy catalysts had the drawbacks of easy crystallization and poor thermal stability.In this thesis, the catalytic performances of the amorphous catalysts were evaluated using phenol hydrogenation to cyclohexanone in the liquid-phase. This thesis covered the following aspects: (1) The preparation and filtration of various catalysts; (2) The evaluation of catalytic performances and characterization of various catalysts; (3) The kinetic studies and the correlation of the catalytic performance to both the structural properties and electronic characteristics were discussed. The followings were in details: 1. Catalyst preparation(1) Prepare double metal Pd-Ce-B amorphous catalysts: the Pd-Ce-B amorphous catalysts were prepared by chemical reduction of the PdCl₂ and Ce(NO₃)₃ mixed solutions by KBH₄ in aqueous solution which was added drop-wise into the solution. Change the quantity of the Ce(NO₃)₃ in the solution resulted in the Pd-Ce-B amorphous alloys with different Ce-dopants.(2) Prepare the Pd-Ce-B catalysts assisted by using ultra method: the Pd-Ce-B amorphous catalysts were prepared by chemical reduction of the PdCl₂ and Ce(NO₃)₃ mixed solutions by KBH₄ in aqueous solution while ultrasonic with a certain ultra power.(3) prepare the supported catalysts: Different supports were impregnated with some precursor solution, dried by the oven and then were calcined and reduced by KBH₄ aqueous solution to obtain the supported amorphous catalysts.2. Activity testPhenol hydrogenation was performed in a 250 ml stainless steel autoclave containing certain amount of the as-prepared catalysts, 0.5 g/ml phenol solution and EtOH, at 1.0 MPa hydrogen pressure and a desired temperature. The results showed:(1) the catalytic performance of ultra-fine Pd-Ce-B catalysts increased with the increscent of Ce dopants. The maximum yield of cyclohexanone reached 83.0% after reacted for 3 hours on the Pd-Ce-B catalyst with X_Ce = 0.44%. After used repeatedly for 5 times without obvious deactivation, showing the promising industrial application;(2) the hydrogenation activity enhanced greatly by using ultra during the preparation of catalysts, the selectivity to cyclohexanone remained very high even after the phenol was totally converted. In the same reaction conditions, with the ultra-power 90W, the maximum yield of cyclohexanone reached 91% after reacted for 45 min; (3) Comparing different supports on the performance of the Pd-Ce-B catalysts. When the hydrotalcite support with different acid-base sites was chose, the undesired-product was restrained effectively. The maximum yield of cyclohexanone reached 65.6% after reacted for 3 hours on the 5.8%Pd-Ce-B/HT catalysts. 3. The correlation of the catalytic performance and the structural propertiesAccording to a series of characterizations of the catalysts, the following questions were discussed briefly:(1) By doping rare earth Ce to obtain Pd-Ce-B catalysts, the Ce element was existed in the form of Ce₂O₃. The promoting effects of Ce to catalytic performance and the selectivity of cyclohexanone could be attributed to the stabilizing effects of Pd-B amorphous structure; donating partial electrons to active sites Pd; enhancing the basic sites on the surface of the catalysts because of the formation of Ce₂O₃.(2) The Pd-Ce-B catalysts prepared by using the ultra method could reduce the size, increase the dispersion of active sites, create more surface defects, add more active hydrogen in the catalyst interior, fortify the adsorption intensity of hydrogen, it could also force the active hydrogen enter the crystal lattice of the catalysts by shock wave and participate the formation of catalysts.(3) By using different supports to prepare supported catalysts could reduce the quantity of noble metal and inhibit the formation of undesirable products. The supports with suitable acid-base sites favored the formation of cyclohexanone, on the one hand, basic sites favored the non-planar form of phenol, thus hydrogenated to cyclohexanone; on the other hand, certain acid sites favored the isomerisation of 1-hydroxycyclohexene to cyclohexanone.