We are interested in developing new or improved catalytic materials by
studying how the structure of a catalyst affects its performance in
Recent work from our group has demonstrated the viability of solid bases
and mixed acid-base materials as catalysts for the upgrading of light
alcohols to high energy density fuels. This is achieved via the Guerbet
coupling reaction, which increases the carbon chain length of these
alcohols while producing water as a byproduct. Investigations into the
mechanisms by which metal oxides and metal phosphate catalysts couple
alcohols have provided two proposed routes in the literature:
non-oxidative coupling and tandem dehydrogenation/ hydrogenation with
aldol condensation. Resolving the contributions of one or both
mechanisms to the observed selective synthesis of coupled alcohols over
various metal oxides and metal phosphates is the current focus of our
research. Recent studies on ethanol coupling over magnesium oxide have
shown that surface ethoxides reside on 50% of available Mg–O pairs at
reaction conditions, and acetaldehyde is a primary reaction product.
The influence of catalyst composition and structure on alcohol coupling
is explored using in-house materials synthesis, surface property
characterization (XPS, DRIFTS, adsorption, microcalorimetry), bulk
property characterization (elemental analysis, XRD) and steady-state
kinetic studies. Multi-product steady-state isotopic transient kinetic
analysis is also used to monitor transient kinetic phenomena arising
from steady-state reactant switching from unlabeled to 13C-labeled
reactants as seen in the figure below. This technique allows us to quantify important kinetic
parameters such as surface coverages of reactants and reactive
intermediates, surface residence times, and intrinsic turnover frequencies.
Z.D. Young and R.J. Davis, “Hydrogen Transfer Reactions Relevant to Guerbet Coupling of Alcohols over Hydroxyapatite and Magnesium Oxide Catalysts,” Catal. Sci. Technol. 8 (2018) 1722-1729.
S. Hanspal, Z.D. Young, J.T. Prillaman, R.J. Davis, “Influence of Surface Acid and Base Sites on the Guerbet Coupling of Ethanol to Butanol over Metal Phosphate Catalysts,” J. Catal. 352 (2017) 182-190.
Z.D. Young, S. Hanspal, R.J. Davis. "Aldol Condensation of Acetaldehyde over Titania, Hydroxyapatite, and Magnesia." ACS Catalysis, 2016, 6 (5), pp 3193–3202.
I.M. Hill, S. Hanspal, Z.D. Young, R.J. Davis, “DRIFTS of Probe Molecules Adsorbed on Magnesia, Zirconia and Hydroxyapatite Catalysts” J. Phys. Chem. C, 119 (2015) 9186-9197.
S. Hanspal, Z.D. Young, H. Shou, and R.J. Davis, "Multiproduct Steady-State Isotopic Transient Kinetic Analysis of the Ethanol Coupling Reaction over Hydroxyapatite and Magnesia," ACS Catalysis 5 (2015) 1737−1746.
Joseph T. Kozlowski and Robert J. Davis, “Heterogeneous Catalysts for the Guerbet Coupling of Alcohols.” ACS Catalysis, 3 (2013) 1588–1600.
Joseph T. Kozlowski, Malte Behrens, Robert Schloegl, and Robert J. Davis, “Influence of the Precipitation Method on Acid-Base-Catalyzed Reactions over Mg-Zr Mixed Oxides.” ChemCatChem, 5 (2013) 1989–1997.
Theodore W. Birky, Joseph T. Kozlowski, and Robert J. Davis, “Isotopic Transient Analysis of the ethanol Coupling Reaction Over Magnesia.” Journal of Catalysis, 298 (2013) 130–137.
Joseph T. Kozlowski and Robert J. Davis, “Sodium Modification of Zirconia Catalysts for Ethanol Coupling to 1-butanol.” Journal of Energy Chemistry, 22 (2013) 58–64.
Y. Xi and R.J. Davis, “Nanocrystalline MgO Catalysts for the Henry Reaction of Benzaldehyde and Nitromethane.” J. Mol. Cat. A: Chem. 341 (2011) 22-27.
Catalytic Fuel Cracking
Endothermic fuel cracking represents a possible solution to the thermal
management challenges that arise with vehicles during high supersonic
and hypersonic flight speeds. Endothermic fuel cracking operates as a
heat sink by using both the heat capacity of the fuel as well as the
heats of reaction of various hydrocarbon cracking reactions. Zeolites
are excellent solid acid catalysts for the catalytic cracking of
hydrocarbons, but they also deactivate from coking at relatively short
reaction times. Thus, it is necessary to develop alternative non-zeolitic
solid acids that are thermally stable under supercritical fuel cracking
conditions. Zirconia-supported semiconductor oxide nanostructures (WO3
) have been shown in the literature to exhibit Brønsted
acidity, which is necessary for catalytic cracking to occur. The major
goal of this study is to determine fundamental structure/property
relationships that will allow for the rational design of novel solid
acid catalysts for hydrocarbon cracking reactions. Currently, our work
is focused on screening WO3
catalysts to identify an
active and stable catalyst for hydrocarbon cracking reactions under
supercritical conditions. A combination of X-ray diffraction (XRD),
electron microscopy, spectroscopic materials characterization (XAS,
Raman, UV-vis), and analysis of adsorbed species (IR, microcalorimetry)
is being utilized in this work to understand the nature of the catalyst
Catalysis of Biorenewable Feedstocks
Hydrogenolysis of Alcohols
Biorenewable resources such as carbohydrates are alternative feedstocks
for the production of oxygenated chemicals. In some processing schemes,
conversion of carbohydrates involves the initial hydrogenation of a
simple sugar, such as glucose, to the sugar alcohol sorbitol. The
subsequent hydrogenolysis of sorbitol yields lower molecular weight
polyols like glycerol, propylene glycol and ethylene glycol, along with
organic acids such as lactic acid. Glycerol, which is also a byproduct
from biodiesel production, reacts further to glycols and lactic acid.
All of these reactions are typically conducted in the aqueous phase in
the presence of a supported transition metal catalyst.
Our group is investigating a variety of monometallic (Ru, Pt) and
bimetallic catalysts (Pt-Ru, Au-Ru, Pt-Re) for the hydrogenolysis of
glycerol. Interestingly, Re promotes the activity and shifts the
selectivity of Pt to produce some 1,3 propanediol, which is not observed
over monometallic catalysts. Extensive characterization of the metal
catalysts by microscopy, X-ray absorption spectroscopy and chemisorption
is a major component of this work.
Decarbonylation and Hydrogenolysis of Fatty Acids
Fatty acids found in natural fats and oils are potential feedstocks for
biorenewable fuels and chemicals. However, the presence of oxygen in
fatty acids decreases its quality and stability, especially for fuel.
Therefore, removal of oxygen from biorenewable fatty acids is needed to
enhance fuel enthalpies, decrease viscosity, and enhance thermal
stability. In this work, we are studying deoxygenation reactions in
which the oxygen from the carboxylic acid is removed via production of
and/or CO, thus producing a linear hydrocarbon.
Fatty acids can also be converted into fatty alcohols for use in
detergents, lubricants, and biofuels. In this work, we are
interested in studying the mechanism for removing a single oxygen from
a fatty acid functional group, leaving behind a 1-ol compound. As
part of our participation in the Center for Biorenewable Chemicals
(CBiRC), we are exploring the roles of metal-support composition and
reaction conditions on the activity and selectivity of transition metal
catalyst for the fatty acid deoxygenation and hydrogenolysis reactions.
Oxidation of Alcohols
Adipic acid is a valuable monomer for the production of nylon-6,6, which
is widely used in the textiles, plastics and automotive industries. The
current production of adipic acid from fossil resources is not renewable
and produces substantial amounts of greenhouse gases. Thus, the production
of adipic acid from renewable feedstocks with an environmentally benign
reaction chemistry is an attractive target.
Our strategy is to develop effective and stable oxidation catalysts for
the selective oxidation of 1,6-hexanediol, which can be derived from
fructose. We have studied the kinetics of diol oxidation over supported
Pt as a function of Pt particle size, carbon support, alcohol structure,
and start-up conditions. Ongoing work focuses on the modification of the
catalysts to increase their stability and activity.
J.D. Kammert, J. Xie, I.J. Godfrey, R.R. Unocic, E. Stavitski, K. Attenkofer, G. Sankar, and R.J. Davis, “Reduction of Propionic Acid over a Pd-Promoted ReOx/SiO2 Catalyst Probed by X-Ray Absorption Spectroscopy and Transient Kinetic Analysis” ACS Sustainable Chem. Eng. 6 (2018) 12353-12366.
J. Xie, P. Duan, N. Kaylor, K. Yin, B. Huang, K. Schmidt-Rohr, and R.J. Davis, “Deactivation of Supported Pt Catalysts during Alcohol Oxidation Elucidated by Spectroscopic and Kinetic Analyses,” ACS Catal. 7 (2017) 6745-6756.
J. Xie, K. Yin, A. Serov, K. Artyushkova, H.N. Pham, X. Sang, R.R. Unocic, P. Atanassov, A.K. Datye, R.J. Davis, “Selective Aerobic Oxidation of Alcohols over Atomically-dispersed Non-Precious Metal Catalysts,” ChemSusChem 10 (2017) 359-362.
N. Kaylor, J. Xie, Y.-S. Kim, H.N. Pham, A.K. Datye, Y.-K. Lee, R.J. Davis, “Vapor Phase Deoxygenation of Heptanoic Acid over Silica-Supported Palladium and Palladium-Tin Catalysts,” J. Catal. 344 (2016) 2002-2012.
J. Xie, B. Huang, K. Yin, H. Pham, R. Unocic, A. Datye, R.J. Davis, “Influence of Dioxygen on the Promotional Effect of Bi during Pt-catalyzed Oxidation of 1,6-Hexanediol,” ACS Catal. 6 (2016) 4206-4217.
D.D. Falcone, J.H. Hack, and R.J. Davis, “Aqueous-Phase Hydrogenation of Saturated and Unsaturated Ketones and Aldehydes over Supported Pt-Re Catalysts,” ChemCatChem 8 (2016) 1074-1083.
J. Xie, D.D. Falcone and R.J. Davis, “Restructuring of Supported PtSn Bimetallic Catalysts during Aqueous Phase Oxidation of 1,6-Hexanediol,” J. Catal. 332 (2015) 38-50.
J.A. Lopez-Ruiz, H. Pham, A. Datye, R.J. Davis, “Reactivity and Stability of Supported Pd Nanoparticles during the Liquid-Phase and Gas-Phase Decarbonylation of Heptanoic Acid” Appl. Catal. A: Gen., 504 (2015) 295-307.
D.D. Falcone, J.H. Hack, A.Yu. Klyushin, A. Knop-Gericke, R. Schlögl, and R.J. Davis, “Evidence for the Bifunctional Nature of Pt-Re Catalysts for Selective Polyol Hydrogenolysis,” ACS Catalysis 5 (2015) 5679-5695.
M.S. Ide, D.D. Falcone and R.J. Davis, “On the deactivation of supported platinum catalysts for selective oxidation of alcohols,” J. Catal. 311 (2014) 295-305.
M.S. Ide and R.J. Davis, Perspectives on the Kinetics of Diol Oxidation over Supported Platinum Catalysts in Aqueous Solution,” J. Catal. 308 (2013) 50-59.
S.E. Davis, M.S. Ide and R.J. Davis, “Selective Oxidation of Alcohols and Aldehydes over Supported Metal Nanoparticles,” Green Chem. 15 (2013) 17-45.
S.E. Davis, B.N. Zope and R.J. Davis “On the Mechanism of Selective Oxidation of 5-Hydroxymethylfurfural to 2,5-Furandicarboxylic Acid over Supported Pt and Au Catalysts,” Green Chem. 14 (2012) 143-147.
B.N. Zope, S.E. Davis and R.J. Davis, “Influence of Reaction Conditions on Diacid Formation during Au-catalyzed Oxidation of Glycerol and Hydroxymethylfurfural,” Topics in Catalysis, 55 (2012) 24-32.
B.N. Zope and R.J. Davis, “Inhibition of Gold and Platinum Catalysts by Reactive Intermediates Produced in the Selective Oxidation of Alcohols in Liquid Water,” Green Chem. 13 (2011) 3484-3491.
S.E. Davis, L.R. Houk, E.C. Tamargo, A.K. Datye, and R.J. Davis, “Oxidation of 5-Hydroxymethylfurfural over Supported Pt, Pd and Au Catalysts,” Catalysis Today 160 (2011) 55-60.
B.N. Zope, D.D. Hibbitts, M. Neurock and R.J. Davis, “Reactivity of the Gold-Water Interface during Selective Oxidation Catalysis” Science 330 (2010) 74-78.
Carbon Oxidation Catalysis
Oxidation of Coke
In the petrochemical industry, ethylene is produced by the steam cracking
of feedstock such as ethane and naphtha. Cracking occurs by free-radical
reactions at high temperature (Typically above 800°C). Although the
hydrocarbons are diluted by steam and the residence time is very short
(<1s), the steam cracking reactions are always accompanied with coke
formation, which eventually deposits on the walls of the reaction coils.
Coke deposition is undesired because it reduces heat transfer, increases
pressure drop and decreases the selectivity of the reaction toward
ethylene. Coke can be removed by oxidation of the solid with dioxygen,
which is the same reaction used to remove soot particles from diesel
engine particulate filters. A major goal of this project is the
exploration of ceria-based materials as potential catalysts for solid
carbon oxidation reactions.
Selective Oxidation of Light Alkanes from Natural Gas
In recent years there has been growth in the supply of natural gas, and
methane, the primary component of natural gas, represents a significant
potential feedstock for the production of chemicals and liquid fuels. A
catalyst capable of the conversion of methane to a valuable commodity
chemical such as methanol is therefore highly desirable. Despite intensive
research efforts, no industrially-viable catalyst for this reaction has
been found. In 2005 it was discovered that Cu-exchanged zeolites could
convert methane to methanol with high selectivity at low temperature.1
The overall reaction is a cyclic process involving high-temperature oxygen
activation and water-assisted methanol desorption at lower temperature.
Recently, the first example of catalytic conversion of methane to methanol
with dioxygen using Cu-exchanged zeolites was reported.2
Our work in this area
is focused on elucidating the structure of the catalytic sites, understanding
the relationship between catalytic and stoichiometric sites, and developing
methods for increasing the density of the catalytic sites. The potential
use of molecular copper complexes anchored to solid supports for the
methane-to-methanol reaction is an important part of collaborative research
with the Gunnoe group in the Chemistry department.
1. Groothaert, M. H., Smeets, P. J., Sels, B. F., Jacobs, P. A. &
Schoonheydt, R. A. Selective Oxidation of Methane by the Bis (μ-oxo)
dicopper Core Stabilized on ZSM-5 and Mordenite Zeolites. J. Am. Chem.
Soc. 127, 1394–1395 (2005).
2. Narsimhan, K., Iyoki, K., Dinh, K. & Román-Leshkov, Y. Catalytic
Oxidation of Methane into Methanol over Copper-Exchanged Zeolites with
Oxygen at Low Temperature. ACS Cent. Sci. 2, 424–429 (2016).