Catalyst Selectivity Synthesis gas applications CH4 CH3OH CnH2n+2 CnH2n CnH2n+1OH (n = 1 - 6) H2 / CO Ni Cu Cu + Co Fe, Co Catalysis and Catalysts - Activity, Selectivity and Stability

Examples of Catalyst Deactivation Time (h) 0 3 6 9 12 15 1.0 0.8 0.6 0.4 0.2 0.0 r (rel) 0 500 1000 Time (h) Methanol Yield (gcm-3h-1) p GHSV T = 70 bar = 35000 h-1 = 515 K b CO + 2 H2 CH3OH c FCC Methanol Synthesis HDS a S-344 (660 K) 5 k1.85 (gcm-3h-1%S-0.85) S-324 (655 K) 0 1000 1800 Catalysis and Catalysts - Activity, Selectivity and Stability Time (h)

Catalytic Reforming (Gasoline Production) 0 100 200 30 20 10 Conversion (% olefins/initial paraffins) Time (h) + 0.17% W + 0.17% Re + 0.04% Ru + 0.04% Ir Pt only pH pHC LHSV T = 1.35 bar = 0.10 bar = 1 h-1 = 745 K 2 C12H26 C12H24 + H2 Catalyst Pt (0.2%) / Al2O3 d Deactivation due to coke deposition Alloying quite successful Catalysis and Catalysts - Activity, Selectivity and Stability

Time-Scale of Deactivation 10 -1 1 2 3 4 5 6 7 8 Hydrocracking HDS Catalytic reforming EO Hydrogenations Aldehydes Acetylene Oxychlorination MA Formaldehyde NH oxidation SCR Fat hardening Time / seconds TWC 1 year 1 day 1 hour C dehydrogenation FCC Most bulk processes 0.1-10 year Batch processes hrs-days Catalysis and Catalysts - Activity, Selectivity and Stability

Deactivation of catalysts irreversible loss of activity Types of deactivation: Poisoning: strong chemisorption of impurity in feed (Inhibition: competitive adsorption, reversible) Fouling: secondary reactions of reactants or products, ‘coke’ formation Thermal degradation: sintering (loss of surface area), evaporation Mechanical damage Corrosion/leaching Fouling or ‘self-poisoning’ often cause of deactivation Catalysis and Catalysts - Activity, Selectivity and Stability

Types of Deactivation Catalysis and Catalysts - Activity, Selectivity and Stability

What are poisons? Examples High M.W. product producer Strong chemisorber Surface active metal or ion Sintering accelerator Bases H2S on Ni NH3 on Si-Al ‘Toxic compounds’ (free electron pair) Cu on Ni Ni on Pt Pb or Ca on Co3O4 Pb on Fe3O4 Fe on Cu Fe on Si-Al from pipes acetylenes dienes H2O (Al2O3) Cl2 (Cu) from feed or product Catalysis and Catalysts - Activity, Selectivity and Stability

Typical Stability Profiles in Hydrotreating Initially high rate of deactivation mainly due to coke deposition Subsequently coke in equilibrium metal deposition continues Time-on-Stream Amount of poisoning activity coke metals Catalytic activity I III II Catalysis and Catalysts - Activity, Selectivity and Stability

Influence of Pore Size on Vanadium Deposition Hydrotreating of Heavy Feedstock Catalysis and Catalysts - Activity, Selectivity and Stability

Carbon Formation on Supported Metal Catalyst Catalysis and Catalysts - Activity, Selectivity and Stability

Carbon Filaments due to CH4 Decompostion 873 K, Ni/CaO catalyst Catalysis and Catalysts - Activity, Selectivity and Stability

Sintering of Alumina upon Heating Tcalc (K) SBET (m2/g) Sintering Reduction of surface area Catalysis and Catalysts - Activity, Selectivity and Stability

Sintering of Supported Catalysts monomer dispersion 2-D cluster 3-D particle particles migrate coalesce vapour surface interparticle transport metastable migrating stable Dependent on: carrier properties temperature composition of bulk fluid …. Predictable? Catalysis and Catalysts - Activity, Selectivity and Stability

THüttig and TTamman Sintering is related to melting THüttig : defects become mobile Ttamman: bulk atoms become mobile Tmelting THüttig Ttamman Al2O3 2318 695 1159 Cu 1356 407 678 CuO 1599 480 800 CuCl2 893 268 447 Catalysis and Catalysts - Activity, Selectivity and Stability

Deactivation due to Mechanical Damage during transport, storage, packing, use loading in barrels, unloading, packing of reactor in reactor: weight of column of particles attrition in moving systems (fluid beds, moving beds) during start-up, shut-down temperature variations (thermal shocks) chemical transformations sulphiding, reduction regeneration: high T, steam Catalysis and Catalysts - Activity, Selectivity and Stability

Corrosion / Leaching - Examples Alumina dissolves at pH > 12 and pH < 3, so close to these pH-values corrosion and leaching use carbon instead at very low or very high pH Sulphiding of oxides in the presence of H2S Liquid-phase catalysis in heterogenisation of homogeneous catalysts activity was due to the leached compounds rather than the solid phase in solid-catalysed fat hydrogenation traces of the Ni catalyst appear in the product; with Palladium this is not the case Catalysis and Catalysts - Activity, Selectivity and Stability

Influence of Deactivation on Reaction Rate conversion or kobs process time initial level ‘constant’ ‘variable variable loss of surface area loss of active sites blocking of pores Fouling Sintering Catalysis and Catalysts - Activity, Selectivity and Stability Poisoning

Deactivation - depends on? Catalysis and Catalysts - Activity, Selectivity and Stability

Stability too low; What to do? Understand the cause of deactivation Take logical measures at catalyst level sound reactor and process design good engineering practice Catalysis and Catalysts - Activity, Selectivity and Stability

Catalyst Level improvement of active phase or support e.g. use titania instead of alumina in SCR optimisation of texture use wide-pore catalyst in HDM to prevent pore blocking profiling of active phase e.g. egg-yolk profile will protect active sites against poisoning and fouling if these are diffusion-limited and the reaction is not reduce sintering by structural promoters or stabilisers make catalyst more attrition resistant encapsulation of active material in porous silica shell increases attrition resistance without influencing activity Catalysis and Catalysts - Activity, Selectivity and Stability

Tailored Reactor and Process Design Relation between time-scale of deactivation and reactor type Time scale Typical reactor/process type years fixed-bed reactor; no regeneration months fixed-bed reactor; regeneration while reactor is off-line weeks fixed-bed reactors in swing mode, moving-bed reactor minutes - days fluidised-bed reactor, slurry reactor; continuous regeneration seconds entrained-flow reactor with continuous regeneration Catalysis and Catalysts - Activity, Selectivity and Stability

Different Engineering Solutions allowing for Regeneration Propane dehydrogenation - deactivation by coke formation Catalysis and Catalysts - Activity, Selectivity and Stability

Good Engineering Practice Feed purification for removal of poisons upstream reactor poison trap inside reactor on top of catalyst (if flow is downward) overdesign of reactor if catalyst itself is poison trap Optimisation of reaction conditions use of excess steam in steam reforming decreases coke deposition catalyst deactivation in selective hydrogenation of CCl2F2 strongly increases above 500 K  operate below 510 K Optimisation of conditions as function of time-on-stream compensate for activity loss by increasing T with time Catalysis and Catalysts - Activity, Selectivity and Stability

Examples Catalysis and Catalysts - Activity, Selectivity and Stability