Catalyst deactivation and regeneration

What are the main interactions that can occur between metals and support materials  

What is meant by the term texmre of a catalyst support  

The chemisorption properties of platinum group metals for CO and H2 are less pro-noimced on Ti02 supports. 

The chemisorption of H2 is reduced on Ni/SiC and Si02 formation of Ni-Si alloys is assumed. 

What influence do potassium promoters have on acidic cracking catalysts  

During the course of operation, the activity of the catalyst gets reduced and it will not be able to provide the desired performance. The achvihes of a catalyst normally decrease with time. In the development of a new catalyhc process, the life of the catalyst is usually a major economic consideration. Shuthng down a process for regenerating or replacing the catalyst at frequent intervals is economically prohibitive. The rate at which the catalyst is deactivated may be very fast, such as for hydrocarbon-cracking catalysts, or may be very slow, such as for the promoted iron catalysts used for ammonia synthesis, which may remain on-stream for several years without appreciable loss of activity. 

An understanding of how catalysts lose activity is important. In some systems, catalyst activity decreases so slowly that exchange for new material or regeneration is required 

Some of the Well-Known Adsorption Isotherm Models 

Temkm (1940) ( e = Bj- Ln.JC7 + Bj InC (i) The heat of adsorption of aU the molecules in the layer decreases linearly with coverage due to adsorbate-adsorbate interactions, and (ii) that the adsorption is characterised by a uniform distribution of binding energies up to some maximum binding energy 

Redlich-Peterson (1959) KrC, l + fl C It approaches the FrermcUich model at high concentrations and is in accord with the low concentration limit of the Langmuir equation. Furthermore, the R-P equation incorporates three parameters into an empirical isotherm and, therefore, can be applied in either homogeneous or heterogeneous systems due to its high versatility. 

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Aiello, R. et al., Hydrogen production via direct cracking of methane over Ni/Si02 Catalyst deactivation and regeneration, Appl. Catal. A General, 192, 227, 2000. 

D.Y. (2006) Isomerization of n-butane to isobutane over Pt-modified beta and ZSM-5 zeolite catalyst catalyst deactivation and regeneration. Chem. Eng. ]., 120, 83-89. 

Ahmed S, Aitani A, Rahman F, Ali Al-Dawood, Al-Muhaish F (2009) Decomposition of hydrocarbons to hydrogen and carbon. Appl Catal A-Gen 359 1-24 Aiello R, Fiscus JE, Eoye HC, Amiridis MD (2000) Hydrogen production via the direct cracking of methane over Ni/SiO catalyst deactivation and regeneration. Appl Catal A-Gen 192 227-234... 

C. Bartholomew, Catalyst deactivation and regeneration, in Kirk-Othmer Encyclopedia of Chemical Technology Wiley, Hoboken, NJ, 2003. 

The removal of impurities that deposit from the reactant mixture p>oses particular challenge. Sulfur, arsenic, phosphorous, and vanadium are often deposited during oil refining. The reader is referred to publications that deal with these special problems of catalyst deactivation and regeneration (e.g., see references [9, 10]). 

Table S-43 Naphtha reforming with 0.6 % Pt /AI2O3 catalyst deactivation and regeneration [T35]...

G. (2010) Photocatalytic oxidation of cyclohexane by titanium dioxide catalyst deactivation and regeneration. J. Catal., 272, 198-201. 

Contents /. B. Butt Catalyst Deactivation and Regeneration. - /. Pasquon, U. Giannini Catal3d ic Olefm Pol)merization. - G. Maire, F. Garin Metal Catalysed Skeletal Reactions of Hydrocarbons on Metal Catalysts. - K. Foger Dispersed Metal Catalysts. 

A major advantage of vapor phase processes is the easy separation of reaction products from the catalytic system. Selectivity and catalyst deactivation and regeneration procedures, however, appear to be more critical compared to the liquid phase process. 

Catalyst deactivation and regeneration. The activity of a rhenium-based catalyst in the metathesis of unsaturated esters is unavoidably limited by the complexation of the ester group to the active site [8]. Moreover, there are many routes that lead to deactivation of the catalyst. Polar compounds such as H2O or free acids, alcohols and peroxides, which might be present as an impurity in the substrate(s), can act as catalyst poisons. Other possible routes for the deactivation of rhenium-based catalysts include (i) reduction of the rhenium below its optimum oxidation state (ii) adsorption of (polymeric) product molecules on the surface of the catalyst, blocking the active sites (iii) reductive elimination of the metallacyclobutane intermediate [59]. Even when the greatest care is taken, deactivation of the rhenium catalyst cannot be avoided. 

Solid catalyst Problems of catalysts deactivation and regeneration ... 

Fig. 9.46 Consequent experiments adding the fresh catalyst. (From 0. SImakova, E.V. Murzina, A.-R. Leino, P. Maki-Arvela, S. Willfor, D.Yu. Murzin, Gold catalysts for selective aerobic oxidation of the lignan hydroxymatairesinol to oxomatairesinol catalyst deactivation and regeneration, Catal. Lett. 142 (2012) 1011. Copyright 2012 Springer).

Bartholomew C (2003) Catalyst Deactivation and Regeneration. Kirk-Othmer Encyclopedia of Chemical Technology. John Wiley Sons, Inc. New York. 

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