Reactivity of Surface Species in Heterogeneous Catalysts Probed by
In Situ X‑ ray Absorption Techniques
Silvia Bordiga,
†
Elena Groppo,
†
Giovanni Agostini,
†
Jeroen A. van Bokhoven,
‡,§
and Carlo Lamberti*
,†
†
Department of Chemistry and NIS Centre of Excellence, Universita
di Torino and INSTM Reference Center, Via P. Giuria 7, 10125
Torino, Italy
‡
ETH Zurich, Institute for Chemical and Bioengineering, HCI E127 8093 Zurich, Switzerland
§
Laboratory for Catalysis and Sustainable Chemistry (LSK) Swiss Light Source, Paul Scherrer Instituteaul Scherrer Institute, Villigen,
Switzerland
CONTENTS
1. Introduction 1737
2. Experimental Methods 1739
2.1. Materials 1739
2.1.1. Metal-Substituted MFI Frameworks 1740
2.1.2. Cu-Substituted Zeolites 1740
2.1.3. Cr/SiO
2
Phillips catalyst 1740
2.1.4. CuCl
2
/Al
2
O
3
1740
2.1.5. Metal-Supported Catalysts 1740
2.2. Techniques and Experiential Set-ups 1740
2.2.1. X-ray Beam Optimization: Energy Selec-
tion 1740
2.2.2. X-ray Beam Optimization: Ha rmonic
Rejection 1742
2.2.3. X-ray Absorption Spectroscopy: Acquis-
ition Setups for Standard and Time-
Resolved Experiments 1743
2.2.4. X-ray Emission Spectroscopy: Acquisi-
tion Setup 1746
2.2.5. High-Energy Resolution Fluorescence
Detected (HERFD) XANES and EXAFS
and Range-Extended EXAFS Spectros-
copy 1747
2.2.6. In Situ and Operando Cells for Hard and
Soft XAFS 1749
2.2.7. Experimental Set-Ups for Micrometer-
Resolved Experiments 1750
2.3. EXAFS and XANES Theory and Data Analysis 1752
2.3.1. Brief Historical Overview 1752
2.3.2. Single-Scattering Approximation 1753
2.3.3. Multiple-Scattering Expansion 1754
2.3.4. Codes for EXAFS Data Analysis 1755
2.3.5. Codes for XANES Data Analysis 1755
2.3.6. Codes for XES Spectra Simulation 1757
2.3.7. Codes for Handling the Huge Numbers
of Spectra Generated in Time or Space
Resolved Experiments 1757
2.3.8. Debye−Waller Factors and Disorder 1757
2.3.9. Differential XAFS Approach 1758
2.4. Atomic XAFS or AXAFS 1759
2.4.1. Brief Historical Overview 1759
2.4.2. Physical Principles of AXAFS 1760
2.5. Other Related Techniques 1761
2.5.1. X-ray Magnetic Circular Dichroism
(XMCD) 1761
2.5.2. Diff raction Anomalous Fine Structure
(DAFS) 1761
2.5.3. Extended En ergy-Loss Fine Structu re
(EXELFS) 1762
2.5.4. Total scattering: the pair distribution
function (PDF) approach 1762
3. Metal Isomorpho us Substitution in Zeolitic
Frameworks: Ti, Fe, and Ga 1764
3.1. Relevance of Ti-, Fe-, and Ga-Silicalite-1, and
B-CHA in the Field of Catalysis 1764
3.2. TS-1 1766
3.2.1. Brief Historical Overview on the Role
Played by EXAFS and XANES Techni-
ques in Understanding the Nature of Ti
Sites in TS-1 1766
3.2.2 . Template Burning in TS-1: XANES,
EXAFS, and XES Results Compared
with Adsorption of Ligand Molecules 1766
3.2.3. Effect of the Amount of Incorporated
Heteroatom 1768
3.2.4. Modeling of [Ti(OSi)
4
] Perfect Sites in
Interaction with Ligands by an Ab Initio
Periodic Approach: Comparison with
EXAFS Results 1770
3.2.5. Reac tivity of Framework Ti Species
toward H
2
O
2
/H
2
O 1774
3.3. Fe- and Ga-Silicalite 1781
3.3.1. Role of EXAFS in Understanding the
Effect of Template Burning in Ga- and
Fe-Substituted Silicalite 1781
Received: April 3, 2011
Published: February 28, 2013
Review
pubs.acs.org/CR
© 2013 American Chemical Society 1736 dx.doi.org/10.1021/cr2000898 | Chem. Rev. 2013, 113, 1736−1850
3.3.2. Role of EXAFS in the Debate Concerning
the Nuclearity of Extra framework Fe
Species in Zeolites 1782
3.3.3. Fe-Substituted Silicalite: What Has Been
Learnt from XANES 1784
3.3.4. Reactivity of Extraframework Fe Species
Hosted in the MFI Channels toward N
2
O
and NO 1784
3.3.5. New Frontiers of XAS/XES Techniques
Applied to the Characterization of Fe-
Zeolites 1786
3.4. B-CHA 1787
3.4.1. Template Burning in B-SSZ-13 an exam-
ple of low energy XAFS 1787
3.4.2. Reactivity of B-SSZ-13 toward NH
3
1788
3.5. Other Metal Isomorphous Substitutions 1788
4. Cat ion-Exc hanged Zeolites: The Copper Case
Study 1788
4.1. Preparation of Cu
+
-Exchanged Zeolites Ex-
hibiting a Model Compound Character 1789
4.2. Cu
+
-ZSM-5 1790
4.2.1. XANES Characterization of Intrazeolitic
Cuprous Carbonyl Complexes in Cu
+
-
ZSM-5 1790
4.2.2. EXAFS Determination of the Structure of
Cu
+
(CO)
n
Complexes 1791
4.3. Cu
+
-MOR 1792
4.3.1. XANES and EXAFS Study of Cu
+
(CO)
n
Complexes Hosted in Cu
+
−MOR: Com-
parison with Cu
+
-ZSM-5 1792
4.4. Reactivity toward NO: In Situ Cu
+
→ Cu
2+
Oxidation in Cu
+
-ZSM-5 and Cu
+
-MOR 1793
4.4.1. Temperature Dependent NO Reaction
in Cu
+
-ZSM-5 1793
4.4.2. Temperature-Dependent NO Reaction
in Cu
+
-MOR 1794
4.5. Bent mono-( μ-oxo)dicupric and bis(μ-oxo)-
dicopper Biomimetic Inorganic Models for
NO Decomposition and Methane Oxidation
in Cu-ZSM-5: Comparison with Fe-ZSM-5 1795
5. Structure and Reactivity of Metallorganic Frame-
works Probed by In Situ XAFS and XES 1795
5.1. Adsorption of CO on Cu
2+
Sites in Cu
3
(BTC)
2
or HKUST-1 1796
5.2. Adsorption of O
2
on Cr
2+
Sites in Cr
3
(BTC)
2
1797
5.2.1. XANES Study 1797
5.2.2. XES Study 1797
5.3. Adsorption of NO, CO, and N
2
on Ni
2+
sites
in Ni-CPO-27 1798
6. Cr/SiO
2
Phillips Catalyst: In Situ Ethylene Poly-
merization 1801
6.1. Relevance of the Catalyst and Still Open
Questions 1801
6.2. XAFS Applied on the Phillips Catalyst 1802
6.2.1. A 4 wt % Cr/SiO
2
Sample: XAFS in
Transmission Mode 1803
6.2.2. A 0.5 wt % Cr/SiO
2
Sample: XAFS in
Fluorescence Mode 1806
6.3. SEXAFS Applied on the Phillips Catalyst:
Bridging the Gap between Heterogeneous
Catalysis and Surface Science 1807
6.3.1. Brief Overview on SEXAFS Applied to
Catalysis 1807
6.3.2. SEXAFS Applied to a Planar Model of
the Phillips Catalyst 1808
7. Space-Resolved X-rays Experiments 1809
7.1. Brief Introduction to X-ray Space-Resolved
Studies in Catalysis 1810
7.2. Cu/ZnO Case Study 1810
8. Time-Resolved XAFS on Catalyst at Work:
OPERANDO Experiments 1810
8.1. Brief Introduction to Time-Resolved Studies
in Catalysis 1810
8.2. CuCl
2
/Al
2
O
3
Case Study 1811
8.2.1. Industrial Relevance of the CuCl
2
/Al
2
O
3
System 1811
8.2.2. Preliminary in Situ XAFS Experiments 1811
8.2.3. Operando Experiments 1812
9. XAS and XES Studies on Supported Metal
Nanoparticles 1814
9.1. XAFS Applied to Supported Metal Nano-
particles: A Brief Overview 1814
9.2. Preparation of Pd-Supported Catalysts Fol-
lowed by EXAFS, from the Impregnation to
the Reduction Steps 1815
9.3. Catalytic Reactions over Supported Metal
Nanoparticles Involving Hydrogen: Applica-
tion of ΔXANES 1816
9.3.1. Relationship between Reaction Rates
and Types of Surface Metal-Hydrides 1816
9.3.2. ΔXANES, How It Works 1817
9.3.3. Temperature-Dependent Hydrogen
Coverage on Pt Surfaces 1819
9.3.4. Influence of Hydrogen on Hydrogenol-
ysis: A Key Study for ΔXANES 1819
9.4. Determination of the CO adsorption sites on
Pt nanoparticles Combining Experimental in
Situ High-Energy-Resolution Fluorescence-
Detected (HERFD), XAS and RIXS Maps 1820
9.5. Correlation between AXAFS and IR Spec-
troscopy of Adsorbed CO on a Set of Pt
Supported Catalysts 1821
10. Conclusions and Perspectives 1822
Author Information 1823
Corresponding Author 1823
Notes 1823
Biographies 1823
Acknowledgments 1825
Acronym List 1825
References 1825
1. INTRODUCTION
Starting from the late seventies, the progressively increased
availability of synchrotron light sources allowed the execution
of experiments requiring a high X-ray flux in a continuous
interval.
1−6
Among them, X-ray absorption spectroscopy (XAS,
also known as X-ray absorption fine-structure, XAFS),
7−12
in
both near (XANES) and post (EXAFS) edge regions, has
become a powerful characterization technique in all the fields of
materials science,
12− 35
and in particular in cataly-
sis.
13,16,22,23,25,30,31,36−40
After a slow start in the 1980s, mainly
because of the difficulties in performing in situ experiments at
the synchrotrons, the progres sive developm ent of more
sophisticated and better performing experimental set-ups that
allow the catalyst’s state to be monitored under reactive
Chemical Reviews Review
dx.doi.org/10.1021/cr2000898 | Chem. Rev. 2013, 113, 1736−18501737