Catalysts reactivation

A typical catalyst can operate for a number of years, and any slow loss of activity can be compensated for by a gradual increase in process operating temperature until the reactor temperature limit is reached. Regeneration is then possible, either in the reactor or externally, by burning accumulated coke in dilute air. This restores the activity of most nickel/molybdate or nickel/tungstate catalysts, which must then be resulfided before further use. 

Deactivated palladium supported on zeolite can also be regenerated, and the catalyst must also be reactivated before being reused. This is because palladium in the zeolite framework sinters. By treating the catalyst with an excess of ammonium hydroxide solution, however, the agglomerated palladium dissolves to form a tetramine complex. Calcination in air then decomposes the complex and the original palladium distribution and activity are restored.  

The first Y-zeolite hydrocracking catalysts contained residual sodium ions in the sodalite cages that were mobile during operation and they entered the supercage. This led to a loss of cracking activity. Treatment of the zeolite with an anunonium salt solution removed the mobile sodium ions and restored acidity. The redistribution of palladium with ammonia solution could be combined with an exchange of sodium ions to rejuvenate the catalyst in one step. This was done before reactivation by burning off the carbon deposits. 

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At the downstream of the extrusion process a suitable reaction catalyst, reactive diluent, e.g., crosslinking monomer, is fed into the molten polymer mix. 

It was previously reported that magnesium oxide with a moderate basicity formed reactive surface carbonate species, which reacted with carbon deposited on foe support by foe methane decjomposition [6]. Upon addition of Mg to foe Ni/HY catalyst, reactive carbonate was formed on magnesium oxide and carbon dioxide could be activated more easily on the Mg-promoted Ni/HY catal t. Reactive carbonate species played an important role in inhibiting foe carbon deposition on the catalyst surface. 

The results of the kinetic study and model discrimination show that insertion of SM is rate-controlling. Two reasons may explain why this step is ratecontrolling. First, the protection group in om SM is very bulky, making the reaction slow, which is consistent with literature data (8) showing the size effect on reactivity. Second, a free aniline group in the SM could bond with Rh and reduce the catalyst reactivity. 

Catalyst Reactivation Using Propargyl Acetate. The Wiped-Film Evaporator/02 reactivation procedure and the Capture of Active Catalyst Using Solid Acidic Support with FI2 Elution procedure (see above) both involve the separation of uncomplexed phosphine from rhodium complex. Since the value of the uncomplexed phosphine is significant, technology that does not require separation of phosphine during catalyst reactivation is desirable. 

Catalyst reactivation without the need for concentration of the catalyst solution and/or separation of the organophosphine ligand has been disclosed [40] using a variety of compounds including alkynes having the formulae shown in Figure 2.13. 

CO conversion and product distribution were investigated. The experimental data used for the fitting were collected in two different long-term runs of the unit previously described, adopting a new batch of catalyst each time. The reproducibility of the results obtained in the two runs was checked by comparing the catalyst reactivity at standard conditions. A good agreement was found in terms of both CO conversion and product distribution (data not reported). 

By applying a potential to the electrode equal to the reduction potential of the catalyst (the redox mediator) the catalyst is reduced, but, upon contact with the oxidized form Ox, a redox reaction takes place in which Ox is reduced to Red and the mediator reoxidized. At this point the continuous cathodic reduction of the catalyst reactivates the whole process and the catalytic cycle is repeated. 

B. Nkosi, N. J. Coville, G. J. Hutchings, M. D. Adams, J. Friedl, and F. Wagner, Hydrochlorination of acetylene using carbon-supported gold catalysts A study of catalyst reactivation, J. Catal. 128(2), 378-386(1991). 

Dynamic ETEM experiments on CS defects have shown mat mey consume anion vacancies and grow (figure 3.7). These correlation studies indicate mat CS planes are secondary or detrimental to catalytic reactivity. They eliminate anion vacancies by accommodating the supersaturation of the vacancies in the reacting oxide catalyst and me catalyst reactivity (selectivity) begins to decrease with the onset of CS formation, i.e. CS planes are the consequence of catalyst reduction reactions rather than the origins of catalytic reactivity (Gai 1981,1992, 1993, Gai etfl/ 1982). 

Section 11.06.4 of this chapter highlights the substrate scope of olefin CM reactions. Based on this survey of the literature, olefins will then be placed into their appropriate category based upon catalyst activity and substrate tolerance, citing specific examples (Section 11.06.4.6). It is important to note that olefin-type characterization can change in response to catalyst reactivity. For example, an olefin may be characterized as a type III olefin in CM... 

The reader should also be aware that some information provided in this section and in the sections below does not directly address the subject of biodiesel synthesis. Some discussions, for instance, are about the transesterification of simple esters or the production of monoglycerides by transesterification of vegetable oils nevertheless, the information provided is relevant to the topic of biodiesel synthesis since knowledge of catalyst reactivity in these systems is directly applicable to reactions involving TGs and FFAs. 

Most industrial reactors and high pressure laboratory equipment are built using metal alloys. Some of these same metals have been shown to be effective catalysts for a variety of organic reactions. In an effort to establish the influence of metal surfaces on the transesterification reactions of TGs, Suppes et collected data on the catalytic activity of two metals (nickel, palladium) and two alloys (cast iron and stainless steel) for the transesterification of soybean oil with methanol. These authors found that the nature of the reactor s surface does play a role in reaction performance. Even though all metallic materials were tested without pretreatment, they showed substantial activity at conditions normally used to study transesterification reactions with solid catalysts. Nickel and palladium were particularly reactive, with nickel showing the highest activity. The authors concluded that academic studies on transesterification reactions must be conducted with reactor vessels where there is no metallic surface exposed. Otherwise, results about catalyst reactivity could be misleading. 

Based on this, it is apparent that the exothermic catalyst reactivation reactions need to be appropriately controlled to avoid Ni sintering/catalyst deactivation. 

At 500°C the reaction rate over the platinum electrode-catalyst appeared to be independent of the e.m.f. of the cell. At 550°C two reaction rate branches were observed, depending on whether the catalyst had been pretreated in oxidising or reducing conditions (see Figure 9). The e.m.f. of the cell also exhibited two branches dependent upon pretreatment (see Figure 9), in a similar manner to other SEP work on oxide catalysts.86,87 It was suggested that the catalyst state (i.e., catalyst oxygen content or 5) was a function of the catalyst history. Different catalyst states corresponded with different catalyst reactivities and the e.m.f. of the cell reflected the catalyst state. 

If the avoidance of deactivation by poisoning is difficult, could a partially deactivated catalyst be regenerated by chemical or physical means In the oil and chemical industry, catalyst reactivation is a standard procedure, done sometimes in situ or after removal from the reactor. Logistically, it does not seem to be feasible to remove an automotive... 

In situ purification of raw materials and catalyst reactivation can lead to... 

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