Deactivation behaviour

De Klerk, A. 2003. Deactivation behaviour of Zn/ZSM-5 with a Fischer-Tropsch derived feedstock. In Catalysis in application, ed. S. D. Jackson, J. S. J. Hargreaves, and D. Lennon, 24-31. Cambridge Royal Society of Chemistry. 

Akolekar, D.B. (1994) Thermal Stability, addity, catalytic properties, and deactivation behaviour of SAPO-5 catalysts effect of silicon content, add treatment and Na exchange. J. Catal., 149, 1 10. 

Five samples of zeolite HZSM5 have been comparatively investigated for their deactivation behaviour at high temperature (475 °C). Characterization data and results from methanol conversion are given in Table 5. 

In high pressure work, slurry reactors are used when a solid catalyst is suspended in a liquid or supercritical fluid (either reactant or inert) and the second reactant is a high pressure gas or also a supercritical fluid. The slurry catalytic reactor will be used in the laboratory to try different catalyst batches or alternatives. Or to measure the reaction rate under high rotational speeds for assessing intrinsic kinetics. Or even it can be used at different catalyst loadings to assess mass transfer resistances. It can also be used in the laboratory to check the deactivating behaviour. 

There have been a considerable number of papers reporting the properties of sulphur-resistant methanation catalysts, i.e., catalysts which can operate successfully in significant partial pressures of H2S. Most of these report work using catalysts containing vanadium, molybdenum, and such metals. However, attempts have been made to find nickel-based catalysts containing suitable additives to allow them to operate in such atmospheres. For example, Bartholomew and Uken115 have compared the deactivation behaviour of a range of nickel catalysts in 10 p.p.m. H2S. They found that nickel boride catalysts and Raney nickel materials deactivated more slowly than did unsupported nickel and alumina-supported nickel. They attributed this improvement to two factors ... 

Torsten Eckardt, Volker Hagen, Bjorn Schade, Reinhardt Schmidt, Claude Schweitzer, Jurgen Bendig Deactivation Behaviour and Excited-State Properties of (Coumarin-4-yl)methyl Derivatives. 2. Photocleavage of Selected (Coumarin-4-yl)methyl-Caged Adenosine Cyclic d -Monophosphates with Fluorescence Enhancement, J. Org. Chem. 67(3), 703-710 (2002)... 

They find that Vanadium interacts with Nickel in a manner which inhibits the deactivation behaviour of Nickel. They therefore conclude that metals resistant cracking catalysts must be evaluated in the presence of both Nickel and Vanadium. We find that also the mobility of Vanadium is reduced by the presence of Nickel. 

Allowing for some spread in the data it seems as if little deactivation is caused by the first 4-5% wt carbon deposited, after which there is an exponential activity decline. This deactivation behaviour is of course indicative of the way in which coke is deposited on the catalyst surface, The initial deposition of coke mainly takes place on the bare A1203 surface, i,e. does not interfere with the active phase as demonstrated in a previous paper [6], At higher coke levels we observe an exponential activity decline indicative of a fouling type of deactivation rather than selective poisoning. 

Even though Cu/MgO deactivated leasts selectivity was found to be higher for Ion-exchanged Cu/SiO and this catalyst was therefore chosen to study the deactivation behaviour of different alkynes. Catalyst deactivation of acetylene as well as methyl, ethyl and vinylacetylene was studied at 130 C. Figure 2A depicts the deactivation with time on line and Figure 2B shows the Influence of time on Line on selectivity. Methyl and ethylacetylene showed a very similar behaviour with the least deactivation, whereas vinylacetylene and acetylene deactivated the catalyst much zMsre rapidly. 

Fig. 4 Typical deactivation behaviour. (2 g V3-catalyst, T = 590 K, total feed rate 1.5 md/h, calculated - sorption,----------------sorption and deactivation)...

The typical deactivation behaviour of a H Mo V POto catalyst (V3 catalyst) is shoMn in Fig. 4. where the effluent partial pressures of the main product species MAA. acetone and propene from a fixed-bed reactor are presented as functions of time. The filled symbols represent an experiment where water was fed together with IBA into the reactor at a ratio of The open symbols... 

The curve obtained from these equations is shown in fig. 6 together with that obtained for semiregenerative Pt-Re/Al203 CR catalysts. It is clear the difference in deactivation behaviour for both catalysts. Pt-Sn catalysts show a monotonic decrease in activity, whereas Pt-Re catalysts have a fast initial deactivation but then it stabilizes out from around 11 to 45 Blls/lbcat (aproximately 50 to 200 days) followed by a slow deactivation process. 

Deactivation can have a profound influence on selectivity. Let us consider a molecule with two reactive functional groups Ar and Bv, which react to products ArBp and ApBr in a parallel fashion (Figure 8.37), and are different in their deactivation behaviour. 

In a previous study, we reported the superior performance of a Co-Ni bimetallic catalyst for methane reforming. Higher hydrocarbon substrates, however, tend to coke more easily, and hence the present study explores the deactivation behaviour of the Co-Ni catalyst in a fluidised bed reactor for propane reforming. 

The deactivation behaviour was studied by monitoring the change in product spectra with time on stream and over multiple reaction-regeneration cycles. The findings were based on macroscopic observations only. 

Fig. 1 Deactivation behaviour of Cr0x/La203/Zr02 catalyst at 530 C...

The deactivation of bulk iron oxide during methane combustion has been studied. The observed deactivation behaviour has been explained as the result of two simultaneous deactivation mechanisms. In the initial phase of reaction both are in operation and the activity drops rapidly as a consequence of both catalyst sintering and of the depletion of lattice oxygen in the outer layers, due to a partial reduction of the catalytic surface. In later stages, catalyst deactivation is almost exclusively due to sintering imder reaction conditions. A kinetic model of deactivation is presented, together with the physicochemical characterization of fresh and partially deactivated catalysts. 

Time on Stream Data. Figure 9 reports the results of a set of exp)eriments (not shov>7n in Table II) designed to assess the deactivation behaviour of the catalyst. In these experiments the feed was a mixture of the six oils. It was injected for a fixed time in the reactor assembly maintained at 400 C. Then the gases leaving the reactor were analyzed and the injection of oil was stopped until the chromatographic analysis was completed, at vdiich time the injection was restarted for another fixed time and this operation was repeated three times. 

PEP experiments are performed using either NHs or [ 0]-02 to obtain further insight in the reaction mechanism and deactivation behaviour. Transient ammonia pulse experiments are performed to study the adsorption and dissociation of ammonia on pure platinum catalysts, followed by the focus on the deactivation of platinum. Finally, we will briefly discuss the influence of the alumina support. 

Behm et al. [135] studied the effect of H2, CO2 and H2O on the deactivation behaviour of oxidatively and reductively pretreated Au/Ce02 catalyst. They found that pretreatment has huge influence on the WGS activity of gold catalysts. Reductive pretreatment leads to higher stability compared to oxidative pretreatment. Addition of CO2 and H2 decreases both the activity and stability of the catalysts. For oxidative pretreatment catalysts the addition of H2 leads to more deactivation compared to addition of CO2. However, for reductive pretreatment catalysts the trend is the opposite. Increase in the water concentration leads to better stabihty. 

Basically, catalyst activity is defined as a ratio of reaction rates. To quantify the deactivation behaviour of a catalyst, the rate of the desired reaction at a certain time on stream r(t) is related to the rate of reaction as determined for the fresh catalyst. This leads to the definition of activity... 

The classical treatments of activity loss by poisoning by Thiele 2 and Wheeler support the above distinctions, since the poi on was not considered to have any influence upon the pore geometry or effective diffusivity. Uniform, non-uniform and anti-selective poisoning do give rise to a wide spectrum of deactivation behaviour, but the non-comprehensive capability of a theory of poisoning to explain deactivation when significant accumulation takes place, requires that new approaches be made. This is confirmed by several more recent observations. 

The present paper deals with the development of a simple two-parameter model describing the deactivation behaviour of residue-desulfurization catalysts. The validity of the model is being checked against the results of a large number of experiments with a variety of catalysts, two feedstocks and under different operating conditions. 

Schade. B., Hagen,V., Schmidt, R., Herbrich, R., Krause, E., Eckardt, T., and Bendig, J., Deactivation behaviour and excited-state properties of (coumarin-4-yl)methyl derivatives. 1. Photocleavage of (7-methoxycoumarin-4-yl)methyl-caged acids with fluorescence enhancement, J. Org. Chem., 64, 9109-9117, 1999. 

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