Catalysis and Catalysts - Infrared Spectroscopy Infrared Spectroscopy Applications:  Catalyst characterisation –direct measurement of catalyst IR spectrum –measurement of interaction with “probe” molecules: NH 3, pyridine: acidity CO, NO: nature of active sites (e.g. Pt on alumina)  Mechanistic studies –adsorbed reaction intermediates –deactivation by strongly adsorbing species  Analysis of reactants and products (in situ reaction monitoring

Catalysis and Catalysts - Infrared Spectroscopy IRS - General Concepts Frequency ( ) = c/ Wavenumber (  ) = 1/ Energy (E) = h = h c  Electromagnetic Spectrum UVVisibleIR cm -1

Catalysis and Catalysts - Infrared Spectroscopy Solid/Gas-Phase Applications

Catalysis and Catalysts - Infrared Spectroscopy Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS)

Catalysis and Catalysts - Infrared Spectroscopy Liquid-Phase Applications ATR Crystal Liquid Phase IR SourceDetector Attenuated Total Reflection (ATR)

Catalysis and Catalysts - Infrared Spectroscopy Re 2 O 7 /Al 2 O 3 - Preparation NH 4 ReO 4 Dry impregnation on  -Al 2 O 3 Drying Calcination (825 K, 2h) Re 2 O 7 /Al 2 O 3 Structure???

Catalysis and Catalysts - Infrared Spectroscopy Absorbance Wavenumber (cm -1 ) % 3% 6% 12% 18% Re 2 O 7 loading Re 2 O 7 /  -Al 2 O 3 - IR Spectrum in OH stretching region NH 4 ReO 4 Alumina Dry impregnation Drying 383 K, 16 h Calcination 323 K, 2 h Re 2 O 7 / Alumina Basic Neutral Acidic Al OH Al O Al Al H Intensity decreases Re-loading increases

Catalysis and Catalysts - Infrared Spectroscopy Metathesis of Propylene on Re 2 O 7 /Al 2 O 3 2 CH 3 CH=CH 2 CH 2 =CH 2 + CH 3 CH=CHCH 3 Very active catalyst (already at room temperature) N: mol converted/(mol Re-atoms  s)

Catalysis and Catalysts - Infrared Spectroscopy Model for Re-sites based on IRS ReO 4 on Lewis site not active Basic -OH substituted by ReO 4 slightly active Acidic -OH substituted by ReO 4 active

Catalysis and Catalysts - Infrared Spectroscopy Summary IRS Re/Al  Alumina contains Lewis and Brönsted sites  OH-spectrumdifferent acid sites  Impregnation –OH + HOReO 3 -OReO 3 + H 2 O –Al 3+ + HOReO 3 coordination complex  Low-loading Re/Al not effective  IRS gives detailed picture of surface

Catalysis and Catalysts - Infrared Spectroscopy Determination of Nature and Number of Active Sites for F/Al 2 O 3 F/Al 2 O 3 very active in acid-catalysed reactions Al 2 O 3 F/Al 2 O 3 HF F-salt Structure of F/Al 2 O 3 ??? Acid sites? Bronsted, Lewis???, How many??

Catalysis and Catalysts - Infrared Spectroscopy IR Spectra “Probe” Molecule N Pyridine adsorbs on acid sites Spectrum changes N Lewis acid N Brönsted acid Different IR Spectra

Catalysis and Catalysts - Infrared Spectroscopy IR Absorption Spectra of Fluorinated Alumina Background spectrum F/Al 2 O 3 After addition of H 2 O at 330 K and evacuation at 330 K After adsorption of pyridine at 330 K Lewis siteBrönsted site H2OH2O Wavenumber (cm -1 ) Transmission L 1452 L 1619 B 1639 B 1490 L 1497 L 1579 B 1542 b c a

Catalysis and Catalysts - Infrared Spectroscopy Reference Spectra

Catalysis and Catalysts - Infrared Spectroscopy IR results versus Catalytic Activity If Brönsted sites are active sites, DMP is an irreversible poison Conv. Amount DMP added Number of active sites Example: Oligomerisation of Isobutylene

Catalysis and Catalysts - Infrared Spectroscopy Number of Brönsted sites vs. F content

Catalysis and Catalysts - Infrared Spectroscopy Correlation IR - DMP Poisoning

Catalysis and Catalysts - Infrared Spectroscopy Summary IR F/Al 2 O 3  Al 2 O 3 –Lewis sites: weak adsorption of Py and DMP  F/Al 2 O 3 –Lewis sites: weakly adsorbed DMP –Brönsted sites: strongly adsorbed DMP –DMP specific poison number of Brönsted sites –Oligomerisation of isobutylene occurs at Brönsted sites

Catalysis and Catalysts - Infrared Spectroscopy NO Adsorption on Fe-ZSM5 Catalyst Fe-based zeolites have high activity for:  deNO x -SCR  N 2 O-mediated selective oxidation of benzene to phenol  Catalytic N 2 O decomposition NO acts as reactant and has been used as probe molecule Preparation of Fe-ZSM5:  liquid ion exchange  solid ion exchange  special route: –incorporation of Fe into zeolite structure during synthesis –extraction of Fe (and Al and Si) to non-framework positions by steaming

Catalysis and Catalysts - Infrared Spectroscopy  Ex-[Fe,Al]MFI: –Si/Al: 31.3 –Si/Fe: –Fe (wt%): 0.67  Fe species: –(FeO) n ; n < 5: “oligonuclear clusters” –FeAlO x : “nano-particles” Fe extracted from the framework MFI: class of zeolites, e.g. ZSM-5, silicalite

Catalysis and Catalysts - Infrared Spectroscopy

Assignments of Absorption Bands of NO on Fe-zeolite

Catalysis and Catalysts - Infrared Spectroscopy Fe-containing sites in MFI

Catalysis and Catalysts - Infrared Spectroscopy IR Absorption Spectra of ex-[Fe,Al]MFI Wavenumber (cm -1 ) Absorbance Fe II AlO x -NO FeAlO x -NO 2 NO + Iso Fe II -NO (  ) (Fe II O) n -NO (  )

Catalysis and Catalysts - Infrared Spectroscopy Au/TiO 2 Catalysed Oxidation of Propylene to Propylene Oxide

Catalysis and Catalysts - Infrared Spectroscopy Desorption of PO as a Function of Time

Catalysis and Catalysts - Infrared Spectroscopy IR Spectra of Au/TiO 2 and Au/TiO 2 /SiO 2

Catalysis and Catalysts - Infrared Spectroscopy Chemical Interaction of PO with Au Catalysts

Catalysis and Catalysts - Infrared Spectroscopy ATR Spectroscopy Nafion Catalysed Esterification

Catalysis and Catalysts - Infrared Spectroscopy Equipment - Glass Reactor with Dicomp Probe

Catalysis and Catalysts - Infrared Spectroscopy “Waterfall Graph” of Esterification cm -1 n-Decane Ester Hexanoic acid 1-Octanol (shoulder) Abs Wavenumber (cm -1 ) Time (h)

Catalysis and Catalysts - Infrared Spectroscopy Transient Spectra of Hexanoic acid and Ester cm -1 Ester Hexanoic acid Abs Time (h) Wavenumber (cm -1 )

Catalysis and Catalysts - Infrared Spectroscopy Concentration Profiles Ester Hexanoic acid

Catalysis and Catalysts - Infrared Spectroscopy Esterification in n -decane

Catalysis and Catalysts - Infrared Spectroscopy Transient Spectra cm -1 Ester Hexanoic acid 1-Octanol (shoulder) Abs Time (h) Wavenumber (cm -1 )

Catalysis and Catalysts - Infrared Spectroscopy Subtracted Transient Spectra cm -1 1-Octanol Ester Wavenumber (cm -1 ) Time (h) Abs

Catalysis and Catalysts - Infrared Spectroscopy 1-Octanol Concentration Profile

Catalysis and Catalysts - Infrared Spectroscopy Esterification in n-decane 1-Octanol (GC)1-Octanol (IR)

Catalysis and Catalysts - Infrared Spectroscopy Concluding Remarks  IR spectroscopy very useful in heterogeneous catalysis –ex-situ –in-situ  Simple technique  Study of catalytic sites on catalyst surface, both qualitatively and quantitatively  Information on reaction mechanism and reaction intermediates  Analysis of liquid-phase catalytic reactions