Catalytic deactivation

Carbon black possesses time-varying catalytic characteristics [16,17, 20, 22]. Catalytic deactivation starts at the beginning of the reaction and it continues gradually without reaching a steady state making the determination of the reaction kinetic parameters indefinite. Thus, it is important to establish an evaluation method of activation energies for carbon blacks which exhibit time-varying catalytic characteristics. 

Sheldon RA, Arends IWCE (2003) In Simandi LI (ed) Advances in catalytic deactivation of dioxygen by metal complexes. Kluwer, Dordrecht, pp 123-155... 

Catalytic deactivation can sometimes be reversed and the original catalytic activity restored by some special operation called regeneration. For example, coked cracking catalyst is regenerated by burning off the coke (see 1.7.3, 1.9). 

Comparison of these data with the curves of the catalytic deactivation leads to the conclusion that a higher initial activity of catalyst is related with the greater content of weakly bonded sulfur (easily replaced by oxygen in DTA experiment). Practically the catalyst deactivation results from accumulation of strongly bonded sulfur in the Mo surrounding. 

It aliows heuseof ryjujejsaUlyjI.garljsks, which can give an effectiveness factor approaching unity. This is especially important if diffusion limitations cause rapid catalytic deactivation or poorer selectivity. 

MEIER JOHNSON Catalytic Deactivation of Benzene Hydrogenation 429... 

During the past decade, percolation theory has been successfully used to analyze condensate desorption from porous solids (14-34), mercury penetration into porous solids (35 -43), and the kinetics of catalytic deactivation... 

V. Catalytic Deactivation by Site Coverage and Pore Blockage... 

Catalytic deactivation adds another level of complexity to sorting out the reaction rate law parameters and pathways. In addition, we need to make adjustments for the decay of the catalysts in the design of catalytic reactors. This adjustment is usually made by a quantitative specification of the catalyst s activity, a(t), In analyzing reactions over decaying catalysts we divide the reactions into two categories separable kinetics and nonseparable kinetics. In separable kinetics, we separate the rate law and activity ... 

The catalytic deactivation is independent of gas-phase concentration and follows a first-order decay rate law, with a decay constant of 0.72 reciprocal minutes. The feedstream is diluted with nitrogen so that as a first approximation, volume changes can be neglected with reaction. The reactor contains 22 kg of catalyst that moves through the reactor at a rate of lOkg/min. The gas oil is fed at a rate of 30mol/min at a concentration of 0.075 mol/dm, Determine the conversion that can be achieved in this reactor. 

Cracking Activity Measurements of Zeolite Catalysts with Catalytic Deactivation J. Medina and L Schifter... 

Methane CPO has been intensively studied to select new advanced catalysts able to maximize hydrocarbon conversion, hydrogen yield and especially to control catalytic deactivation phenomena, strictly connected to coke deposition problem, similar to SR process [18-23]. The role of transition metal-based catalysts in methane CPO reaction mechanism has been detailed [24], evidencing that fuel dissociation step is crucial for a viable overall process rate at reasonable temperatures, as expected taking into account the stability of methane molecule. 

The relative importance of coke and metal depositions towards catalytic deactivation remain unclear. Hie conventional wisdom is that coke deposition becomes stationary after the short initial aging period, so that most of the catalyst aging must be due to metal deposition. Yet recent data with model compounds in... 

Solid base catalysts have gradually gained importance in the catalytic field due to their well-known advantages of non-corrosive and easier product separation[l]. However, in contrast to the extensive application of solid acid catalysts, the utilization of solid bases was limited for their rapid catalytic deactivation [2]. The deactivation problem was also foimd in the continuous synthesis of dimethyl carbonate (DMC). DMC has attracted more and more attention in recent years because of its low toxic and nicely biodegradable property [3,4]. Transesterification between methanol and propylene carbonate (PC) or ethylene carbonate (EC) is an attractive route for the synthesis of DMC. Both acid and base catalysts catalyze the reaction, and base catalyst was reported to be more effective [5]. Among bases, CaO showed unique catalytic activity for the transesterification reaction with high yield and selectivity [6]. Unfortunately, when CaO based catalyst was employed in the continuous synthesis of DMC, its activity gradually decayed with time-on-stream due to... 

Catalytic deactivation may occur for a number of reasons, both chemical and physical in nature. Several authors have reported that chemical poisoning of the noble metal catalysts is the primary mechanism for phosphorus compounds. Nevertheless, inhibition also takes place. The difference between phosphorus inhibitors and poisons is that inhibitors absorb weakly on the surface and the process is often reversible. On the other hand poisoning is the irreversible loss of activity due to the strong chemisorption of the impurities in the feed on the catalytic active sites. 

Polinski et al. and Derbyshire have reviewed catalysis and catalytic deactivation. As noted earlier, there is, however, no discussion of the role of free radicals in these reviews. 

---