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Phenol Hydrogenation Reaction Efficient Catalyst For The Development Of Its Anti-sulfur Performance

Posted on:2005-06-14Degree:MasterType:Thesis
Country:ChinaCandidate:L ZhuangFull Text:PDF
GTID:2191360122480535Subject:Physical chemistry
Abstract/Summary:PDF Full Text Request
The amorphous alloy is a kind of material with short-range ordering while long-range disordering structure. Its unique structure can result in excellent catalytic properties, such as high catalytic activity and selectivity as well as strong resistance to the sulfur poison during many reactions, especially in various hydrogenation reactions. Meanwhile, little or even no environmental pollution may be caused during the preparation process of amorphous alloys and their application in catalysis, which represents the trend of 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. Even today, the preparation of amorphous alloy catalysts and the study on their catalytic performance are still in the forefront of recent catalysis research.In this thesis, both the Ni-B and Pd-La-B amorphous alloys in the form of ultrafine particles were prepared by chemical reduction. Their catalytic performance was evaluated using liquid phase phenol hydrogenation to cyclohexenol or cyclohexenone, both of them are of great industrial importance. According to a series of characterizations and kinetic studies, the correlation of the catalytic performance to both the structural properties and electronic characteristics was discussed. Furthermore, the promoting effect of the La-dopant on the catalytic behavior of the Pd-B amorphous catalyst was also investigated and the optimum content of the La-dopant was determined. The followings are in details: 1 .Catalyst preparationAll the Ni-B, Pd-B and Pd-La-B amorphous catalysts were prepared by chemical reduction of their corresponding metallic ions by KBH4 in aqueous solution, followed by thoroughly washing with distilled water and ethanol (EtOH) and finally kept in EtOH until the time of use. In most cases, the KBH4 solution was added dropwise into the solution containing the corresponding metallic ions. Only one Ni-B amorphousalloy was obtained by addition NiCl2 solution into KBH4 solution. Change the concentration of either the KBH4 or the LaCl3 in the solution resulted in the amorphous alloys with different content B or La-dopants. 2.Activity testPhenol hydrogenation was performed in a stainless steel autoclave containing certain amount of the as-prepared catalysts, phenol and EtOH, at 1.0 MPa hydrogen pressure and a desired temperature and under vigorous stirring (ca. 1200 rpm) to eliminate the diffusion effect. The reaction mixture was sampled every one hour for product analysis on a gas chromatograph (GC 9800) equipped with a FID. During poisoning test, trace CS2 was added initially into the reaction mixture as a poison. 3. Catalytic performance(1) The amorphous alloys exhibited much higher activity than their corresponding crystalline counterparts during the phenol hydrogenation. On one hand, this could be attributed to the unique amorphous structure (i.e., the short-range ordering and long-range disordering) and other structural parameters including homogeneous distribution of active sites and high un-saturation of coordination of these active sites. On the other hand, for all metal-B amorphous alloys, the metal always accepts partial electrons from B owing to the electronic interaction between metals and the boron. The electron-deficient B was favorable for phenol adsorption while the electron-enriched Ni favored desorption of the products, which could also account for their excellent sulfur resistance.(2) The La-dopant exhibited promoting effects on both the activity and selectivity to cyclohexanone as well as sulfur resistance, which could be mainly attributed to the high surface area of the catalyst resulted from La2O3 as a support, the stabilization of the amorphous alloy structure by the La-dopant, and the electron-donation of the La2O3 to the Pd active center.
Keywords/Search Tags:Phenol hydrogenation, cyclohexenol, cyclohexenone, Ni-B and Pd-B amorphous alloys, sulfur resistance, La-dopant
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