Heterogeneous catalysis
Lecture 9
Zeolites in oil refinement

Zeolites - synthesis
•Reaction mixture: …, …, …, …
•
–pH adjustment, (gelation)
–Hydrothermal treatment in an autoclave
–…
–…
•
•Result: H-zeolite (Brønsted acidic with H+ ions)
•
•
•
•

Zeolites - synthesis
•Reaction mixture: Na2SiO3, Al2O3, quarternary ammonium salt (=structure directing agent), water
•
–pH adjustment, (gelation)
–Hydrothermal treatment in an autoclave
–Ion exchange (Na+ for NH4+)
–Calcination (= NH3 removal)
•
•Result: Crystalline H-zeolite (Brønsted acidic with H+ ions)
•
•
•
•

Zeolites - synthesis
•Pore size
•
•
•
•
•
•
•
•
•Si/Al ratio ≥ 1
•
DOI: 10.1039/c3cs60394f

Zeolites - acidity
•Brønsted:  …
•
–Structure:
•
•
•
•Lewis: …
–Structure:
•
•
•
•

Zeolites - acidity
•Brønsted:  negative charge of the aluminosilicate net balanced by strongly acidic protons
–Structure:
•
•
•
•Lewis: Al atoms that are not embedded in the aluminosilicate net (e.g. surface species, amorphous
stuff, alumina particles) = extraframework aluminum species (EFAL)
–Structure:
•
•
•
•
Fluorination of the ε-Keggin Al13 polycation - Chemical Communications (RSC Publishing)
H+

Zeolites - acidity
•Brønsted:  depends on the second coordination sphere (i.e. Si/Al ratio)
•
•
•
•
•
•Lewis: Extraframework aluminum species (EFAL) depends on
–Si/Al ratio
–Aging (time on stream, steaming)
–Can be washed out (depending on pH – acid washing)
•
•
•
•

Zeolites - acidity
•High Si/Al ratio
–Strong Brønsted acid sites
–Weak Brønsted acid sites
–Strong Lewis acid sites
–Weak Lewis acid sites
•
•Low Si/Al ratio
–Strong Brønsted acid sites
–Weak Brønsted acid sites
–Strong Lewis acid sites
–Weak Lewis acid sites
•
•
•
•

Zeolites - acidity



Zeolites - acidity
•Confinement effect
•
•
•
•
•
•Superacidity
–Various probes at RT – acid site strength similar to 70 % H2SO4 (=NO!)
–Ability to protonate hydrocarbons at working conditions (=YES!)
–?
•
•
•
•

Zeolites – diffusion/shape selectivity
•Diffusion
–Big difference between zeolites with 8 membered vs. 12 membered ring pore openings
–Big difference between zeolites with 1D, 2D, and 3D-connected pore structure
•Shape selectivity
•
•
•
•
DOI: 10.1039/c3cs60394f

Zeolites in oil refinement
•Fluid catalytic cracking
•
•Isobutane-butene alkylation
•
•Reforming (+ steam reforming)
•
•Hydrocracking
•
•Linear paraffin isomerization
•
•
•
•
DOI: 10.1039/c3cs60394f

Zeolites in oil refinement
•Fluid catalytic cracking
•
•
•

Zeolites in oil refinement
•Fluid catalytic cracking
–Zeolite Y 10-50 wt%
–Binders 50-90 wt%
–At the beginning – AlCl3
–Addition of HZSM-5
•
•
•

Zeolites in oil refinement
•Fluid catalytic cracking
–Shortening of long linear hydrocarbons
–Isomerization to branched hydrocarbons
–„Aromatization“
–HZSM-5 for higher propylene production
•
•
•

Zeolites in oil refinement
•Fluid catalytic cracking
–Protonation + protolytic cracking
–H- abstraction + β scission
•
•
•

Zeolites in oil refinement
•Fluid catalytic cracking
–Protonation + protolytic cracking
–H- abstraction + β scission
•
•
•

Zeolites in oil refinement
•Fluid catalytic cracking
–Protonation + protolytic cracking
•We need strong Brøsted acid sites (zeolite Y)
•
–H- abstraction + β scission
•We need strong Lewis acid sites (steamed/(acid washed) zeolite Y)
•
–Long linear hydrocarbons diffusion
•Precracking on alumina and silica-alumina (non-innocent binders)
•Hierarchical porosity in zeolites (steamed/(acid washed) zeolite Y)
•
•
•
•

Zeolites in oil refinement
•Isobutane-butene alkylation
–We want highly branched C8 hydrocarbons (high octane number)
–HF and H2SO4 catalyzed alkylation still running in industry
–Large pore zeolites as a substitution
•
•
•
•

Zeolites in oil refinement
•Isobutane-butene alkylation
–Large pore zeolites as a substitution
–BUT! 2-butene dimerization…oligomerization…coking…deactivation
•
•
•
•

Zeolites in oil refinement
•Linear paraffin isomerization
–Linear C8 (C7) → branched C8 (C7)
–Requires strong Brønsted acidity and hydrogenation/dehydrogenation activity (Pt(Ni) on mordenite)
–Mordenite – large pore, monodirectional pores
–Mordenite – dealuminated (strong H+), acid washed (low EFAL)
–Protonation = carbocations
–Stability of carbocations? Branched hydrocarbons?
•
•
•
•

Zeolites in oil refinement
•Linear paraffin isomerization
–Pt(Ni) on mordenite
–How do we deposit Pt on a zeolite? (Lecture 3)
•
•
•
•

Zeolites in oil refinement
•Linear paraffin isomerization
–Pt, Pd, Ni on mordenite
–Electrostatic interaction = Ion exchange
•Competitive ion exchange
[NH4+]

Zeolites in oil refinement
•Linear paraffin isomerization
–Pt, Pd, Ni on mordenite
–Electrostatic interaction = Ion exchange
•Competitive ion exchange

Zeolites in oil refinement
•Hydrocracking (i.e. cracking in the presence of H2)
–Shortening of long hydrocarbons
–From linear to branched (alkylation, carbocations,…)
–Hydrogenation/dehydrogenation
–Pt, Pd on mordenite (also zeolite Y and β)
•
•
•
•

Zeolites in oil refinement
•Reforming and steam reforming
–Cyclization, isomerization of cyclic compounds to cyclohexene, cyclohexene and its derivatives
dehydrogenation to benzene, toluene, xylene (BTX), and other aromatics
–H2 as a useful „by-product“
–Pt on high surface area support, non-acidic
–Reforming in the presence of H2O = H2 production
•
•
•
•