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Catalyst deactivation and regeneration

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Catalyst: A catalyst is a substance that changes the rate of chemical reaction without itself appearing in the products.Helps to attain equilibrium by reducing PE barrier in the reaction path.Provides an alternate route for reactant molecule to become products with a lower activation energy and different transition state. Enters the reaction cycle and regenerated back without getting consumed.Ideally remains unchanged after the completion of reaction.But does it remain unchanged practically?




INTRODUCTIONWhat is catalyst deactivation?Loss in catalytic activity due to chemical, mechanical or thermal processes.Heterogeneous catalysts are more prone to deactivation.

Mechanism TypeBrief definition/descriptionPoisoningChemicalStrong chemisorption of species on catalytic sites, thereby blocking sites for catalytic reaction.Fouling, CokingMechanical or ChemicalPhysical deposition of species (carbonaceous material) from fluid phase onto the catalytic surface and in catalyst pores.Sintering(Thermal degradation)ThermalThermally induced loss of catalytic surface area, support area, and active phasesupport reactions.Chemical reactions; AndPhase transformationsChemicalChemical Reaction of fluid, support, or promoter with catalytic phase to produce inactive phase.Reaction of gas with catalyst phase to produce volatile compound.Attrition/CrushingMechanicalLoss of catalytic material due to abrasion, Loss of internal surface area due to mechanical-induced crushing of catalyst


DEACTIVATION MECHANISMSNot only blocks the active sites, but also induce changes in the electronic or geometric structure of the surface.Poisons mainly includeGroups VA and VIA elements (N, P, As, Sb, O, S, Se, Te)Group VIIA elements (F, Cl, Br, I )Toxic heavy metals and ions (Pb, Hg, Bi, Sn, Zn, Cd, Cu, Fe)Molecules, which adsorb with multiple bonds(CO, NO, HCN, benzene)Types:SelectiveAnti-selectiveNon-Selective4 POISONING

Reversible Non- reversibleBartholomew C.H., Mechanisms of Catalyst Deactivation, Appl. Catal. A: General, 212, 17-60 (2001).

5ReactionCatalystPoisonsCatalytic CrackingSilica-alumina, ZeolitesOrganic bases, hydrocarbons heavy metalsHydrogenation , dehydrogenationNickel, Platinum, PalladiumCompounds of S, P, As, Zn, Hg, halides, Pb, NH3, C2H2Steam reforming of methane, naphthaNickelH2S, AsAmmonia synthesisIron or RutheniumO2, H2O, CO, S, C2H2, H2OFischerTropsch synthesisCobalt or IronH2S, COS, As, NH3, metal carbonylsHydrocrackingNoble metals on zeolitesNH3, S, Se, Te, P

Industrial examples of catalyst deactivation due to poisoning Example: Sulphur as poison in methane synthesis using Ni/-Al2O3 Catalyst

Legras B., Ordomsky V.V., Dujardin C., Virginie M., Khodakov A.Y., Impact and Detailed Action of Sulfur in Syngas on Methane Synthesis on Ni/-Al2O3 Catalyst, ACS Catal., 4, 27852791 (2014).

Advantages of poisoningPt-containing naphtha reforming catalysts are often pre-sulfided to minimize unwanted cracking reactions. S and P are added to Ni catalysts to improve isomerisation selectivity in the fats and oils hydrogenation industry.V2O5 is added to Pt to suppress SO2 oxidation to SO3 in diesel emissions control catalysts.S and Cu added to Ni catalyst in steam reforming to minimize coking.For selective hydrogenation from alkynes to alkenes, Lindlar catalyst (Pt/CaCO3) is partially poisoned with Pb and quinoline.6 Bartholomew C. H., Farrauto R. J., Fundamentals of Industrial Catalytic Processes Second edition, John Wiley & Sons, Inc., pp 269-323,(2006).

Physical deposition of species from the fluid phase onto the catalyst surface is foulingFouling of catalyst due to carbon deposition is coking. coke may contains soot, produced in gas phase (non-catalytic carbon), ordered or disordered carbon, produced on an inert surface (surface carbon), ordered or disordered carbon, produced on surface which catalyses formation of carbon (catalytic carbon), condensed high molecular weight aromatic compounds which may be liquid or solid (tar).Coking can be studied under two headings:Coke formation on supported metal catalystsCoke formation on metal oxide and sulphide catalysts


Formation of coke on supported metal catalystsChemically by chemisorption or carbide formation Physically due to blocking of surface sites, metal crystalline encapsulation , plugging of pores and destruction of catalyst pallets


C Adsorbed, atomic (surface carbide); C Polymeric, amorphous films or filamentsCv Vermicular filaments, fibers, and/or whiskers ; C Nickel carbide (bulk) Cc Graphitic (crystalline) platelets or films

Formation, transformation and gasification of carbon on metal surface


Formation of coke on oxides and sulfides Carbonaceous materials (coke precursor) , feed for cracking reaction lead to formation of cokeCatalyzed by acidic sites.Dehydrogenation and cyclization reactions of carbocation intermediates formed on acid sites lead to aromatics which react further to higher molecular weight polynuclear aromatics and condense as coke. Because of the high stability of the polynuclear carbocations, they can continue to grow on the surface for a relatively longer time before a termination reaction occurs through the back donation of a proton.


Zeolite Coking:Shape-selective processesFormation and retention of heavy aromatic clusters in pores and pore intersectionsAcid-site poisoning and pore blockage participate in the zeolite deactivation


Four possible modes of deactivation by carbonaceous deposits in HZSM5(1) reversible adsorption on acid sites (2)irreversible adsorption on sites with partial blocking of pore intersections (3) partial steric blocking of pores, (4)extensive steric blocking of pores by exterior deposits.

Guisnet M., Magnoux P., Martin D., in: Bartholomew C.H.,Fuentes G.A. (Eds.), Catalyst Deactivation, Stud. Surf.Sci. Catal., Vol. 111, Elsevier, Amsterdam, p. 1, (1997).

Support SinteringDriving force is to lower the surface energy and the transport of material Coalescence of particles, particle growth and elimination of the pores.Reaction atmosphere also promotes sintering.eg. Water vapour11DEACTIVATION MECHANISMS SINTERING

-Alumina to -alumina to -phase via -phase

A model representing surface dehydroxylation from contact region of two adjacent particles of alumina. Neyestanaki A.K., Klingstedt F., Salmi T., Murzin D.Y., Deactivation of postcombustion catalysts, a review, Fuel, 83, 395408 (2004).

Metal sinteringTemperature: Sintering rates are exponentially dependent on T.Atmosphere: Decreases for supported Pt in the following order: NO, O2, H2, N2Support: Thermal stability of supports Al2O3 > SiO2 > carbon for given metalPore Size: Sintering rates higher in case of non-porous materialsAdditives: C, O, CaO, BaO, CeO2 decrease atom mobilityPromoters: Pb, Bi, Cl, F, or S; oxides of Ba, Ca, or Sr are trapping agents that decrease sintering rates.


Reactions of gas/vapour with solid to produce volatile compoundsDirect volatilization temperatures for metal vaporization exceed 1000Cmetal loss via formation of volatile metal compounds can occur at moderate temperatures (even room temperature)

13DEACTIVATION MECHANISMS CHEMICAL TRANSFORMATIONS & PHASE TRANSITIONSGaseous environmentCompound typeExample of compoundCO, NOCarbonyls , nitrosyl carbonylsNi(CO)4, Fe(CO)5, (0-300oC)O2OxidesRuO3(25oC), PbO (>850oC), PtO2 (>700oC)H2SSulphidesMoS2 (>550C)HalogensHalidesPdBr2, PtCl4, PtF6

Reactions of gas/vapour with solid to produce inactive phasesChemical modifications are closely related to poisoningBut the loss of activity is due to the formation of a new phase altogether.

14Catalytic ProcessGas-vapour composition CatalystsInactive phases formedAutomobile emission control N2,O2,HCS,CO NOPt-Rh / Al2O3RhAl2O4Ammonia synthesis and regenerationH2,N2,O2,H2OFe/K/Al2O3FeOCatalytic crackingHCs,H2,H2OLa-Y zeoliteH2O induced Al migration from zeolite causing zeolite destructionFischer TropschCO, H2O, H2, HCsCo/SiO2CoO.SiO2 and collapse of SiO2 , by product waterSteam reforming and regeneration in H2OCH4,CO,CO2,H2, H2ONi/Al2O3Ni2Al2O4

Catalytic processCatalytic SolidDeactivating Chemical reactionAmmonia SynthesisFe/K/Al2O3Formation of KAlO2 on catalytic surfaceCatalytic cumbustionPdO/Al2O3,PdO/ZrO3PdOPd at temp.>800oCFischer TropschFe/K,Fe/K/CuOTransformation of active carbides to inactive carbidesBenzene to maleic anhydrideV2O5-MoO3Decreased selectivity due to loss in MoO3 and formation of inactive vanadium compounds.

15 Solid-state reactions

Crushing of granular, pellet or monolithic catalyst forms due to a load.Attrition, the size reduction and/or breakup of catalyst granules or pellets to produce fines, especially in fluid or slurry beds.Erosion of catalyst particles or monolith coatings at high fluid velocities.collisions of particles with each other or with reactor walls, shear forces created by turbulent eddies or collapsing bubbles (cavitations) at high fluid velocities gravitational stress at the bottom of a large catalyst bed. Thermal stresses occur as catalyst particles are heated and/or cooled rapidly16DEACTIVATION MECHANISMS MECHANICAL DEGRADATION

Surface area ; Pore volume ; Pore size distributionThe deactivation of Cu/ZnO/Al2O3 catalyst used in a methanol synthesis because of sintering. After reaction overall surface area of a catalyst and a metal area of Cu decreases

Gas mixture (Oxygen diluted in Helium) is used to perform analysisDynamic TPO with on-line mass spectrometry is used to monitor oxygen consumption and which confirms percent coking occurred in a catalystImportant technique to measure coking17CHARACTERIZATION BET Surface areaCatalystFresh Cu/ZnO/Al2O3Spent Cu/ZnO/Al2O3BET surface area (m2/g)96.041.5Cu surface area (m2/g)25.411.1

TPO( Temperature programmed oxidation) Sun J.T., Metcalfe I.S., and Sahibzada M., Deactivation of Cu/ZnO/Al2O3 Methanol Synthesis Catalyst by Sintering", Ind. Eng. Chem. Res., 38, 3868-3872 (1999).

Give information of external morphology (texture), surface topography.

Provide information on the structure, texture, shape and size of the sample.

18 SEM (Scanning Electron Microscopy)

SEM images of de-NOx catalyst V2O5-WO3/TiO2 before and after deactivation TEM (Transmission Electron Microscopy)

TEM images of fresh and deactivated Co-alumia catalyst in Fischer-Tropsch synthesis Sahib A.M., Moodleya D.J., Ciobica I.M., Haumana M.M., Sigwebela B.H., Weststrate C.J., Niemantsverdriet J.W., Loosdrecht J., Fundamental understanding of deactivation and regeneration of cobalt FischerTropsch synthesis catalysts, Catal. Today, 154, 271 (2010).

Identify the elemental composition of materialsEDX spectra of V2O5-WO3/TiO2 catalysta: fresh catalyst b: deactivated catalyst

EDX is used as attachment with SEM and TEM so that to give elemental composition along with surface analysis.19 EDX (Energy Dispersive X-ray analysis)

Yu Y., He C., Chen J., Meng X., Deactivation mechanism of de-NOx catalyst (V2O5-WO3/TiO2) used in coal fired power plant, J. Fuel Chem. Technol., 40, 11, 13591365 (2012).

Investigation of the bulk phase composition, degree of crystallinity, unit cell parameters, new crystalline phases of solid catalysts samples

Determine mass loss or gain due to decomposition, oxidation, or loss of volatiles20XRD (X-ray Diffraction)

X-ray diffraction patterns of catalyst V2O5-WO3/TiO2 (De-NOx catalyst)a: fresh catalyst, b: deactivated catalyst

TGA (Thermogravimetric analysis)

Thermogravimetry analysis of De-NOx catalystsa: fresh catalyst, b: deactivated catalyst

Yu Y., He C., Chen J., Meng X., Deactivation mechanism of de-NOx catalyst (V2O5-WO3/TiO2) used in coal fired power plant, J. Fuel Chem. Technol., 40, 11, 13591365 (2012).

FCC catalyst consists of a mixture of an inert matrix (kaolin), an active matrix (alumina), a binder (silica or silicaalumina) and a HY zeolite.Reversible deactivation in FCCCokingCharge propertiesOperating conditionsZeolite acidityZeolite porous structureOxygen poisoningOxygenated molecules present in feedstock21DEACTIVATION CASE STUDY Fluidized catalytic cracking (FCC) Cerqueira H.S., Caeiro G., Costa L., Rama Ribeiro F., Deactivation of FCC catalysts, J. Mol. Catal. A: Chemical, 292 ,1 (2008).


Nitrogen PoisoningImpurities in feed like alkyl derivatives of pyridine, quinoline, isoquinoline, acridine and phenanthridine. Prevented by hydrotreatment, adsorption, liquid/liquid extraction, neutralization, use of nitrogen-resistant FCC catalysts.

Sulphur PoisoningNon hydrotreated feeds like alkylated thiophenes, benzothiophenes and dibenzothiophenesSulphur contained coke on oxidation in regenerator produces toxic SOx22 Cerqueira H.S., Caeiro G., Costa L., Rama Ribeiro F., Deactivation of FCC catalysts, J. Mol. Catal. A: Chemical, 292 ,1 (2008).

Irreversible deactivation in FCCHydrothermal dealuminationDuring reaction and regeneration temperatures 700-800oC in presence of steam

Metal PoisoningMost common are V, Ni, Na and FeTrace elements such as Fe, Zn, Pb, Cu, Cd, Cr, Co, As, Sb, Te, Hg, Au or Ag Deposition of these metal porphyrins and increase cokingV and Na damage alumina in presence of steam at high temperature.23

a. Dehydroxylation. Al-segregation

Cerqueira H.S., Caeiro G., Costa L., Rama Ribeiro F., Deactivation of FCC catalysts, J. Mol. Catal. A: Chemical, 292 ,1 (2008).

PoisoningPurification of feed (desulfurization followed by ZnO guard bed)Additives, which selectively adsorb poisonReaction conditions, which lower adsorption strengthCoking Avoid coke precursors Add gasifying agents (e.g. H2, H2O)Incorporate catalyst additives to increase rate of gasification (eg. In steam reforming. MgO, K2O, U3O8, promote the gasification of carbon by facilitating H2O adsorption. Decrease acidity of oxide or sulfideUse shape selective molecular sievesControl on temperature


SinteringLower reaction temperatureUse of thermal stabilizers (e.g. addition of Ba , Zn ,La ,Mn as promoters that improves thermal stability of alumina); (Ru, Rh to Ni as thermal stabilizer) Avoid water and other substances that facilitate metal migration.Mechanical degradationIncreasing strength by advanced preparation methodsAdding binders to improve strength and toughness Coating aggregates with a porous but very strong material such as ZrO2Chemical or thermal tempering of agglomerates to introduce compressive stresses, which increase strength and attrition resistance25

Some frequently used regeneration techniques include (regeneration of sulfur-poisoned Ni, Cu, Pt, and Mo) treatment withO2 at low oxygen partial pressureSteam at 700-800oC

80% removal of surface sulfur from Mg- and Ca-promoted Ni steam reforming catalysts occurs at 700C in steam.

26REGENERATION Regeneration of poisoned catalysts

Hashemnjad S.M, Parvari M., Deactivation and Regeneration of Nickel-Based Catalysts for Steam-Methane Reforming, Chin. J. Catal., 32, 273 (2011).

Gasification with O2, H2O, CO2, and H2C + O2 CO2 C + H2O CO + H2 C + CO2 2CO C + 2H2 CH4 Promoters can be added to increase rate of gasification (eg.K or Mg in Ni for steam reforming)Washing with chlorobenzenes or liquefied propanes Other foulants can also be removed by such as shaking or abrasion.Metal-catalyzed coke removal with H2 or H2O can occur at a temperature as low as 400C But more graphitic or less reactive carbons or coke species in H2 or H2O may require temperatures as high as 700-900C27 Regeneration of coked catalysts Trimm D.L., The regeneration or disposal of deactivated heterogeneous catalysts, Appl. Catal. A: General, 212, 153160 (2001).

28 Redispersion of sintered catalysts High-temperature treatment oxychlorination Sintering is very hard to reverse

Redispersion of alumina-supported platinum is also possible in a chlorine-free oxygen atmosphere if chlorine is present on the catalyst

A mechanism for platinum redispersion by oxygen and chlorine Bartholomew C. H., Farrauto R. J., Fundamentals of Industrial Catalytic Processes Second edition, John Wiley & Sons, Inc., pp 269-323,(2006).

20 wt % Co on alumina promoted with 0.5 wt % Pt prepared by slurry phase impregnationDeactivationPoisoning by means of sulphur and nitrogen containing compoundImpact of nitrogen containing compounds can be reversed with a mild hydrogen treatment.Inactive phase formation with reaction with Oxygen i.e. cobalt oxide formationCobalt aluminate or silicate formation accelerated by water (does not significantly influence)Sintering contribute 30% loss in activityCoking due to dissociation of COCoking is important deactivation mechanism in F-T Synthesis due to both bulk cobalt carbide and polymeric carbon29CASE STUDY OF CATALYST DEACTIVATION AND REGENERATION Fischer-Tropsch synthesis catalyst: Supported Co catalyst

Regeneration procedure:The spent catalyst was solvent washed with heptane at 100 o C to remove excess wax.The catalyst sample was subsequently subjected to a calcinations (i.e. oxidation) step in a fluidized bed calcination unit, using an air/N2 mixture and the following heating program: 2 C/min to 300oC, 68 h hold at 300 o C. The oxygen concentration was gradually increased from 3 to 21% O2/N2 to control the exotherm.The oxidized catalyst sample was subsequently subjected to a reduction in pure hydrogen in a fluidised bed unit using the following heating program: 1 oC/min to 425 o C, 15 h hold at 425 C. The reduced catalyst was off loaded into wax.

30 Sahib A.M., Moodleya D.J., Ciobica I.M., Haumana M.M., Sigwebela B.H., Weststrate C.J., Niemantsverdriet J.W., Loosdrecht J., Fundamental understanding of deactivation and regeneration of cobalt FischerTropsch synthesis catalysts, Catal. Today, 154, 271 (2010).

Regeneration results


TPO analyses of a 56-day-old spent catalyst following hydrogenation at 350 C as compared to the same sample following regeneration

Comparison between TEM images of fresh, deactivated and regenerated cobalt catalyst.

The oxidative regeneration procedure is able to reverse the major deactivation mechanism, i.e. sintering, carbon deposition and surface reconstruction. Moodley D.J., Loosdrecht J., Saib A.M., Overett M.J., Datye A.K., Niemantsverdriet J.W., Carbon deposition as a deactivation mechanism of cobalt-based FischerTropsch synthesis catalysts under realistic conditions, Appl. Catal. A:Gen, 354, 102(2009).

In addition of having high catalyst activity, selectivity; catalyst deactivation and ease of regeneration is very important topic for industrial catalyst development.The regeneration of deactivated heterogeneous catalysts depends on chemical, economic and environmental factors.Regeneration of precious metals is always necessary.Disposal of catalysts containing non-noble heavy metals (e.g. Cr, Pb, or Sn) is environmentally problematic and should be regenerated.Generally poisoned, coked, fouled catalysts are regenerated by washing, abrasion and careful oxidation.In case of sintering; best way is to add promoters and additives to prevent sintering


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