Dissertation > Industrial Technology > Chemical Industry > Reagents and the production of pure chemicals > Catalyst ( catalyst )

Based on ultrasonic technology, new skeleton -type nickel catalyst and its catalytic properties of

Author MengZuo
Tutor LiHeXing
School Shanghai Normal University
Course Physical and chemical
Keywords Ultrasonic wave Raney Ni Raney Ni-p Mo- modified Raney Ni Catalytic Hydrogenation
Type Master's thesis
Year 2004
Downloads 138
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The skeleton-type nickel (Raney Ni) catalyst due to its inexpensive and highly active, etc., has become one of the most commonly used catalyst in the chemical production, research relating to methods for their preparation as well as catalytic properties has been an active topic in the field of catalysis, by changing the Ni- Al alloy synthesis method and the method and conditions of the aluminum extraction, have been prepared W1 ~ W8, including a large number of Raney Ni catalyst, and to add other components to be modified in the Raney Ni catalyst and its catalytic properties can be further improved. In recent years, the unique ultrasonic cavitation phenomenon has aroused interest in catalytic scientists, in the preparation of oxide catalysts, heteropoly acid catalyst and supported catalyst has been widely applied in the papers ultrasonic role in the Ni-Al alloy aluminum extraction process, the preparation of a new type of Raney Ni catalyst; using quenched Ni-Al-P alloy prepared by the combination of ultrasonic assisted pumping aluminum skeleton-type Ni-P amorphous alloy catalyst (Raney Ni-P) . Applying the above catalyst in the hydrogenation of benzene, and its catalytic activity was significantly higher than that prepared by conventional methods of Raney Ni catalyst; under ultrasonic irradiation, the Raney Ni modified, can further improve the catalytic activity; combined with the catalyst system characterization, a preliminary discussion of ultrasonic, amorphous alloy structure as well as the role of the modifier on the catalytic activity. First, a certain amount of Ni-Al alloy catalyst preparation and pretreatment, in an ice water bath under conditions, while stirring slowly added to the NaOH solution, the constant temperature for a certain time first ultrasonic treatment, and then continue pumping aluminum to give Raney Ni catalyst saved After repeatedly washed with water and anhydrous ethanol (EtOH) in EtOH spare. Will the appropriate of Na 2 of MoO 4 solution was slowly added dropwise to the above non-ultrasound prepared aqueous solution of the Raney Ni catalyst in a different time of the ultrasonic treatment, obtained after repeated washing Mo-modified Raney Ni catalyst. Preparation of Ni-Al-P alloy quenched aluminum similar to the preparation of Raney Ni pumping and washing method, skeleton-type Ni-P amorphous alloy catalyst (Raney Ni-P). Second, the catalyst performance was evaluated in the liquid phase benzene saturated hydrogenation and the glucose hydrogenation probe investigated the catalytic performance of the various catalysts, wherein the benzene hydrogenation reaction conditions were as follows: 0.5g catalyst, 10 ml of benzene and 30mLEtOH, reaction temperature = 383K, H 2 pressure = 1.0MPa, gas chromatography analysis shows that in the present experimental conditions, the selectivity to cyclohexane, 100%; glucose hydrogenation reaction conditions were as follows: 0.5g catalyst, 40mL aqueous dextrose (40wt%), the reaction temperature = 383K, H: pressure = 1 .2 MPa, gas chromatography analysis shows that, in the present experimental conditions, the selectivity was 100% sorbitol. By measuring the conversion rate in the initial hydrogen absorbing rate or the reaction after a certain period of time (2h or 3h) to determine the hydrogenation activity of the catalyst, the results are as follows: 1 in the hydrogenation of benzene, the ultrasonic waves act on the preparation of Raney Ni catalyst, it is possible to significantly improve their catalytic activity, sonicated Qiao min is the best, the hydrogenation activity is more than 1.5 times without ultrasonic treatment RaneyNi catalyst. 2 in the same reaction, the catalytic activity of amorphous alloy structure significantly RaneyNi to higher than on crystalline Where now eyNi and crystallization process after a P, the ultrasonic wave applied to the preparation of the Raney Ni-P catalyst can be further improved its hydrogenation activity, ultrasonic Qiao and n is the best, its catalytic activity is approximately not after ultrasonic treatment of the Raney Ni-P catalyst is 1.5 times. 3. In glucose hydrogenation reaction, investigated M. Modified RaneyNi hydrogenation activity of the catalyst was found to ultrasonic action in the catalyst modification can significantly enhance the catalytic activity, sonicated for 10 min as the best, and its hydrogenation activity without ultrasonic treatment of the catalyst, of more than 1.5 times. Third, the relationship between the catalytic performance and structure using XRD, XPS, ICP, DSC, EXAFS, SEM, EDX, hydrogen adsorption and TPD, and BET modern characterization methods were measured body composition and crystalline structure of the various catalysts, surface morphology and composition, the amount of hydrogen adsorption and adsorption strength is better than the surface area and the activity of specific surface area and surface electronic states, combined with the catalytic reaction kinetics studies the system study catalytic performance and catalyst geometry and electronic structure of the relationship, and focuses on the following issues : 1. role of ultrasound: an appropriate time of the ultrasonic treatment can significantly improve of RaneyNi the catalytic activity, taking into account the ultrasonic treatment did not affect the body of crystalline structure of the sample, therefore, ultrasonic promoting effect on the catalytic activity mainly attributed to the (L) cleaning action: the ability to effectively remove the impurities, so that more of the active sites in the catalyst surface and pores exposed on the catalyst surface, there are conducive to improving the activity ratio of the surface area, while increasing the pore volume and pore size of the catalyst; (2) dispersing action: can effectively inhibit the agglomeration of the catalyst, to reduce the particle size of the catalyst and to improve the degree of dispersion of the active sites of the catalyst, conducive to improve the catalytic activity; energy effects of (3): the ultrasonic energy provided to remaining in the catalyst, is conducive to activate the adsorbed hydrogen or reactants molecules, to improve the catalytic activity. However, the energy effects will also lead to the catalyst particles due to local high temperature fusion, the particle size increases, and even lead to destruction of the pores of the catalyst, so that the active specific surface area decreased, the catalytic activity also decreases. Therefore, it is necessary to control the ultrasound time. The role of the amorphous alloy structure: under the same conditions, the amorphous alloy structure Raney Ni RaneyNi a P catalytic activity was significantly higher than its corresponding catalyst, RaneyNi P is subjected to a high temperature heat treatment, the Raney Ni a P catalysts by the amorphous alloy structure into the crystalline structure, the catalytic activity dropped significantly, these results show that the amorphous alloy structure has a significant role in promoting the catalytic hydrogenation, mainly due to the following factors: (l) an amorphous alloy having a unique long range disorder and short-range order structure, the performance of the active position highly coordinatively unsaturated and uniform distribution, presence of a strong synergism between the active site, etc., can contribute to the reactants in the catalyst surface adsorption, increasing the catalytic activity: (2) Although the XPS spectra display a significant role in the electron does not exist between the Ni-P, but due to the presence of metal P, it is possible to effectively prevent the oxidation of the surface of the metal Ni, i.e. from the active site protective effect, thereby to maintain the catalyst has high activity; (3) ultrasonic treatment does not change of RaneyNi a P amorphous alloy structure, but its?

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