Project I.2: Exploring Solid-Liquid Interfacial Chemistry During Catalyst Synthesis
Participants: Williams, Monnier, Regalbuto
Motivation
Solid-liquid interfaces are ubiquitous throughout heterogeneous catalyst synthesis. The
preparation of metal and/or metal oxide nanostructures supported on a variety of materials (i.e.,
oxides, carbon) includes almost universally an impregnation step involving adsorption or
deposition of a relevant precursor (or precursors) from the liquid phase. The resulting
precursor(s)/support interactions are critical for the success of subsequent gas-phase thermal
activation to produce the final catalyst. However, while the importance of solid-liquid interfaces
in catalysis is clear, molecular-level surface investigations are still relatively limited. The major
obstacle to acquiring such data is the presence of the bulk liquid phase, which serves to
considerably complicate the acquisition and analysis of surface-specific information. A few
approaches have been used in recent years to scrutinize the surface chemistry during liquidphase catalyst synthesis. These include quartz crystal microbalance methods [1], nuclear
magnetic resonance imaging [2-5], X-ray photoelectron spectroscopy of liquid jets containing
support particles [6], and the use of model oxide substrates with ultrahigh vacuum-based
approaches [7,8]. Clearly, these limited examples show that there is ample need for
development of new complementary approaches.
Over the past two decades there have been significant advances in applying vibrational
spectroscopy to solid-liquid catalytic systems [9-16]. Of several approaches available,
attenuated total reflection infrared (ATR-IR) spectroscopy offers perhaps the best opportunity to
examine real catalyst supports under true synthetic conditions. The infrared probe light is
directed through an IR-transparent crystal at total internal reflection, creating an evanescent
electromagnetic field (Figure 1). Placing a material (e.g., a support or catalyst) in contact with
the crystal results in IR absorption. The advantage of ATR-IR is that powder supports and
powder-supported catalysts can be examined. Signals from the catalyst surface are greatly
enhanced, relative to those
Liquid
from the bulk liquid phase. Over
Electric
the past two decades, ATR-IR
Field
studies of solid catalyst-liquid
Catalyst
Catalystor
interfaces have gone from the
Metal
Film Film
>
proof-of-principle
stage
to
critical
Ge
ATRelement
Crystal
addressing
more
complex
IR in
IR out
catalytic
chemistries.
The
related
surface-enhanced Figure 1. Overview of ATR-IR applied to metal or catalyst thin films.
infrared absorption (SEIRA)
spectroscopy [14] involves placing a thin metal coating on the ATR crystal, which produces an
enhanced electromagnetic field and thus larger spectroscopic signals. Williams has been at the
forefront of applying ATR-IR to solid catalyst-liquid systems [17-25].
The goal of the proposed research will be to develop and apply these in-situ ATR-IR and SEIRA
approaches for the study of solid-liquid interfaces relevant for catalyst synthesis. Two of the
most traditional and widely used methods of supported bimetallic catalyst synthesis (particularly
for industrial scale preparations) are co-impregnation, where two metal salts are simultaneously
deposited and reduced on the support, and successive impregnation, in which the two metal
salts are successively deposited and reduced on the support. These methods typically result in
the formation of both monometallic and bimetallic catalyst particles as well as bimetallic particles
of varying compositions of each of the two metallic components. Strong electrostatic adsorption
(SEA) [1,26-28] and electroless deposition (ED) [29-32] are scalable, synthetic approaches that
are typically more effective for producing supported monometallic and bimetallic catalysts with
desired properties. In SEA, control of pH relevant to the potential of zero charge (PZC) of a
𝑦+
support (S) allows predictable quantities of metal ions (e.g., M1 , M2𝑧+ ) to be adsorbed. This
allows highly dispersed M1, M2, and M1M2 species to be formed after appropriate thermal
activation treatments. In ED, a supported monometallic catalyst (e.g., M1/S) is placed in an
aqueous bath with a second metal ion (Mz+
2 ), reducing agent (RA), and possibly stabilizing
𝑦+
agent. Through catalytic (on M1) and autocatalytic (on M2) processes, M2 is reduced and
deposited to form a bimetallic catalyst (M2M1/S).
In both SEA and ED, the adsorption and/or reduction of metal precursor ions (sometimes
coordinated with ligands) on the support and/or metal surface in the liquid (usually aqueous)
phase is critical. In SEA, the synthesis of bimetallic catalysts requires the co-adsorption of
𝑦+
M1 and M2𝑧+ . The competitive adsorption kinetics, and the molecular interactions between these
co-adsorbed precursors, is critical. In the case of sequential SEA for bimetallics [28], M2𝑧+ is
adsorbed selectively onto M1OX (as opposed to S) through control of the PZC. The state of
supported M1OX during this process is critical to its success. In ED, supported monometallic
nanoparticles can undergo sintering in solution at room temperature in the presence of various
reducing agents [30]. Unpublished work by the PI further suggests that this effect is particularly
pronounced for very small metal nanoparticles (i.e., < 3 nm). A second issue is the difficulty of
producing high M2 coverage on M1 while avoiding deposition of large 3D clusters of the former
through autocatalytic deposition. Even when RA activation is preferred on M1 over M2, this
situation often persists [29,31]. In both synthetic approaches, the adsorbed species on the
metal/support surface (i.e., ionic precursors, activated RA, M2𝑧+ , stabilizers) will play key roles in
governing these phenomena.
Hypothesis: The use of ATR-IR and SEIRA spectroscopy can directly probe support surfaces
in situ under actual liquid-phase synthetic conditions.
Objective: Develop a detailed understanding of surface chemistry during SEA and ED
processes, leading to rational strategies for optimizing bimetallic catalyst synthesis.
Research Plan: The following aspects of catalyst synthesis will be examined with spectroscopy:
A) generally, adsorption of metal salt precursors on the support surface and the affect of
associated nonmetallic species (whether inorganic counter ions or organic ligands) on these
processes; B) in ED, the influence of additives such as reducing agents and stabilizers on
surface speciation and the deposition process; C) in SEA, the stability and state of surface
oxides during selective sequential electrostatic adsorption of a second metal precursor. The
following are specific systems that will be examined in this first year project:
1) The SEA method has been used effectively to produce bimetallic catalysts using the
sequential approach described above. For example, the SEA synthesis of Mn-Rh/SiO2 bimetallic
catalysts for alcohol synthesis from syngas has been recently reported [28]. In the liquid phase,
the SEA of MnO4- species onto supported Rh2O3 (and its stability) will be tracked as a function
of solution conditions. The gas-phase activation to break Mn- and Rh-O bonds to form MnRh
bimetallic particles will also be explored (using Raman spectroscopy), with a view towards
correlating the resulting catalyst structure with the speciation observed during synthesis.
2) The ED method has been used to deposit Ag on highly dispersed supported Pt to produce
catalysts for selective hydrogenation reactions. This system has shown evidence of Pt particle
sintering [30] during ED, as shown by the scanning transmission electron micrographs (STEM)
and particle size histograms in Figure 2. In addition,
this system shows limited catalytic deposition (i.e., Ag
on Pt) effectiveness [29,31], in that high coverages of
Ag are difficult to attain. Pt nanoparticles (1-3 nm)
supported on SiO2 and Al2O3 will be exposed to ED
baths
containing
AgNO3
with
formaldehyde,
dimethylamine borane, and hydrazine. First, reducing
agent adsorption onto catalysts will be examined, along
with the bare supports and a thin polycrystalline Pt
metal film. Next, AgNO3 will be added to the system,
and its effect on reducing agent surface speciation will
be examined. CO will be used to probe sintering and
deposition processes, and as a possible surface
modifier during ED synthesis.
Figure 2. Example of particle sintering
occurring during ED of Ag on Pt/SiO2. Taken
3) The adsorption of metal precursors onto carbon from Ref. 30.
supports is a critical aspect to synthesizing highlydisperse catalysts for pharma applications (see Projects ???), as well as fuel cell and biomass
conversion reactions. SEIRA has been used effectively to probe C-supported metal catalysts
during electrocatalytic reactions. As a prelude to studying Pd precursor-C interactions on
graphene and carbon nanotubes, adsorption of a CO as a probe molecule will be studied.
In addition to in-situ infrared spectroscopy, Raman spectroscopy will be used to probe the
structure of supported oxide species during synthesis steps in the liquid phase. Furthermore,
the surface speciation observed during liquid phase syntheses will be correlated with resulting
activated catalyst structures as determined by techniques such as chemisorption, X-ray
diffraction, scanning transmission electron microscopy, and X-ray photoelectron spectroscopy.
First Year Deliverable: ATR-IR studies of Ag ED on Pt/SiO2 and MnO4- SEA onto supported
Rh2O3/SiO2. Proof of principal of SEIRA of Pd/graphene catalyst.
First Year Milestone(s) 1) Months 1-6: ATR-IR spectroscopy of reducing agent adsorption on
SiO2 and Pt/SiO2; ATR-IR and Raman spectroscopy of MnO4- on Rh2O3/SiO2 in solution; 2)
Months 7-12: ATR-IR studies during Ag ED on Pt/SiO2; FTIR and Raman of MnO4-/Rh2O3
reduction in the gas phase; demonstration of ATR-IR of CO adsorption on Pd/graphene.
Cost: $60,000 for one year (one graduate student/post doc. and supplies)
References
1.
Hervier, A.; Blanchard, J.; Costentin, G.; Regalbuto, J. R.; Louis, C.; Boujday, S. “The
Genesis of a Heterogeneous Catalyst: In Situ Observation of a Transition Metal Complex
Adsorbing onto an Oxide Surface in Solution,” Chem. Commun. 50(19), 2409-2411
(2014).
2.
Espinosa-Alonso, L.; Beale, A. M.; Wechhuysen, B. M., “Profiling Physicochemical
Changes within Catalyst Bodies during Preparation: New Insights from Invasive and
Noninvasive Microspectroscopic Studies,” Acct. Chem. Res. 43(9), 1279-1288 (2010).
3.
Lysova, A. A.; Bergwerff, J. A.; Espinosa-Alonso, L.; Weckhuysen, B. M.; Koptyug, I. V.,
“Magnetic Resonance Imaging as an Emerging Tool for Studying the Preparation of
Supported Catalysts,” Appl. Catal. A: Gen. 374, 126-136 (2010).
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
Espinosa-Alonso, L.; Lysova, A. A.; de Peinder, P.; de Jong, K. P.; Koptyug, I. V.;
Weckhuysen, B. M., “Magnetic Resonance Imaging Studies on Catalyst Impregnation
Processes: Discriminating Metal Ion Complexes within Millimeter-Sized γ-Al2O3 Catalyst
Bodies,” J. Am. Chem. Soc. 131, 6525-6534 (2009).
Lysova, A. A.; Koptyug, I. V.; Sagdeev, R. Z.; Parmon, V. N.; Bergwerff, J. A.;
Weckhuysen, B. M., “Noninvasive In Situ Visualization of Supported Catalyst Preparations
Using Multinuclear Magnetic Resonance Imaging,” J. Am. Chem. Soc. 127, 11916-11917
(2005).
Brown, M. A.; Beloqui Redondo, A.; Sterrer, M.; Winter, B.; Pacchioni, G.; Abbas, Z;
Bokhoven, J. A., “Measure of Surface Potential at the Aqueous-Oxide Nanoparticle
Interface by XPS from a Liquid Microjet,” Nano Lett. 13, 5403-5407 (2013).
Sterrer, M.; Freund, H.-J. “Towards Realistic Surface Science Models of Heterogeneous
Catalysts: Influence of Support Hydroxylation and Catalyst Preparation Method,” Catal.
Lett. 143, 375-385 (2013).
Wang, H.; Ariga, H.; Dowler, R.; Sterrer, M.; Freund, H.-J., “Surface Science Approach to
Catalyst Preparation - Pd Deposition onto Thin Fe3O4(111) Films from PdCl2 Precursor,” J.
Catal. 286, 1-5 (2012).
Weaver, M. J.; Zou, S. “Vibrational Spectroscopy of Electrochemical Interfaces: Some
Walls and Bridges to Surface Science Understanding,” Adv. Spectrosc., Clark, R. J. H;
Hester, R. E.; Eds.; Wiley: Chichester, UK, 26, 219 (1998).
Foettinger, K.; Weilach, C.; Rupprechter, G. “Sum Frequency Generation and Infrared
Reflection Absorption Spectroscopy,” Edited by Che, M.; Vedrine, J. C., Characterization
of Solid Materials and Heterogeneous Catalysts 1, 211 (2012).
Zaera, F. “Probing Liquid/Solid Interfaces at the Molecular Level,” Chem. Rev. 112(5),
2920 (2012).
Mojet, B. L.; Ebbesen, S. D.; Lefferts, L. “Light at the Interface: The Potential of
Attenuated Total Reflection Infrared Spectroscopy for Understanding Heterogeneous
Catalysis in Water,” Chem. Soc. Rev. 39, 4643 (2010).
Andanson, J.; Baiker, A. “Exploring Catalytic Solid/Liquid Interfaces by In Situ Attenuated
Total Reflection Infrared Spectroscopy,” Chem. Soc. Rev. 39, 4571 (2010).
Aroca, R. F.; Ross, D. J. “Surface-Enhanced Infrared Spectroscopy,” Applied
Spectroscopy 58(11), 324A-338A (2004).
Li, J.-T.; Zhou, Z.-Y.; Broadwell, I.; Sun, S.-G. “In-Situ Infrared Spectroscopic Studies of
Electrochemical Energy Conversion and Storage” Acct. Chem. Res. 45(4), 485-494
(2012).
Sharma, B.; Frontiera, R. R.; Henry, A.-I.; Ringe, E.; Van Duyne, R. P. “SERS: Materials,
Applications, and the Future,” Mater. Today (Oxford, United Kingdom) 15(1-2), 16 (2012).
Ortiz-Hernandez, I.; Williams, C. T. “In situ Studies of Butyronitrile Adsorption and
Hydrogenation on Pt/Al2O3 Using Attenuated Total Reflection Infrared Spectroscopy,”
Langmuir 23(6), 3172 (2007).
Ortiz-Hernandez, I.; Owens, D. J.; Strunk, M. R.; Williams, C. T. “Multivariate Analysis of
ATR-IR Spectroscopic Data:
Applications to the Solid-Liquid Catalytic Interface,”
Langmuir, 22, 2629 (2006).
Ortiz-Hernandez, I.; Williams, C. T. “In-Situ Investigation of Solid-Liquid Catalytic
Interfaces by Attenuated Total Reflection Infrared Spectroscopy,” Langmuir, 19, 2956
(2003).
Liu, D.; Gao, J.; Murphy, C. J.; Williams, C. T. “In-Situ Attenuated Total Reflection Infrared
Spectroscopy of Dendrimer-Stabilized Platinum Nanoparticles Adsorbed on Alumina,” J.
Phys. Chem. B 108(34), 12911 (2004).
Sun, X.; Williams, C. T. “In-situ ATR-IR Investigation of Methylcinnamic Acid Adsorption
and Hydrogenation on Pd/Al2O3,” Catal. Commun. 17(1), 13-17 (2012).
22.
23.
24.
25.
26.
27.
28.
29.
30.
31.
32.
Tan, S.; Sun, X.; Williams, C. T., “In Situ ATR-IR Study of Prochiral 2-Methyl-2-Pentenoic
Acid Adsorption on Al2O3 and Pd/Al2O3,” Phys. Chem. Chem. Phys. 13, 19573-19579
(2011).
Tan, S.; Williams, C. T. “An In Situ Spectroscopic Study of Prochiral Reactant-Chiral
Modifier Interactions on Palladium Catalyst: Case of Alkenoic Acid and Cinchonidine in
Various Solvents,” J. Phys. Chem. C 117(35), 18043-18052 (2013).
Zapata, R. B.; Luz Villa, A.; Montes de Correa, C.; Williams, C. T. “In situ FTIR
Spectroscopic Studies of Limonene Epoxidation over PW-Amberlite,” Appl. Catal. A: Gen.
365(1), 42-47 (2009).
Cortes-Concepcion, J. A.; Williams, C. T.; Amiridis, M. D. “ATR-IR Study of the Adsorption
of 2′-Hydroxyacetophenone and Benzaldehyde on MgO,” Catal. Commun. 16(1), 198-204
(2011).
Regalbuto, J. R., “Chapter 3: Electrostatic Adsorption” in Synthesis of Solid Catalysts, de
Jong, K., ed., Wiley-VCH Verlag, (2009).
Schreier, M.; Timmons, M.; Feltes, T.; Regalbuto, J. “The Determination of Surface
Charging Parameters for a Predictive Metal Adsorption Model.” J. Colloid Interf. Sci. 348,
571 (2010).
Liu, Jingjing; Tao, Runzhe; Guo, Zhao; Regalbuto, J. R.; Marshall, C. L.; Klie, R. F.; Miller,
J. T.; Meyer, R. J. “Selective Adsorption of Manganese onto Rhodium for Optimized
Mn/Rh/SiO2 Alcohol Synthesis Catalysts,” ChemCatChem 5(12), 665-3672 (2013).
Schaal, M. T.; Pickerell, A. C.; Williams, C. T.; Monnier, J. R. “Characterization and
Evaluation of Ag-Pt/SiO2 Catalysts Prepared by Electroless Deposition,” J. Catal. 254(1),
131-143 (2008).
Schaal, M. T.; Rebelli, J.; McKerrow, H. M.; Williams, C. T.; Monnier, J. R. “Effect of Liquid
Phase Reducing Agents on the Dispersion of Supported Pt Catalysts,” Appl. Catal. A: Gen.
382(1), 49-57 (2010).
Rebelli, J.; Rodriguez, A. A.; Ma, S.; Williams, C. T.; Monnier, J. R. “Preparation and
Characterization of Silica-Supported, Group IB-Pd Bimetallic Catalysts Prepared by
Electroless Deposition Methods,” Catal. Today, 160(1), 170-178 (2011).
Rodriguez, A. A.; Williams, C. T.; Monnier, J. R. “Selective Liquid-Phase Oxidation of
Glycerol over Au-Pd/C Bimetallic Catalysts Prepared by Electroless Deposition,” Appl.
Catal. A: Gen., 475, 161-168 (2014).