Fisher-Trpsch synthesis (FTS) is a century-old gas-to-liquid (GTL) technology that commonly employs cobalt (Co, on an oxide support) or iron (supported or not) species catalysts. It has been well established that the activity of the Co catalyst depends directly upon the number of surface Co atoms. The addition of promoter (mainly noble) metals has been widely utilized to increase the fraction of Co that is available for surface catalysis. Direct synthesis of Co nanoparticles is a possible alternative approach; our preliminary synthesis and characterization efforts are described. Materials were characterized by various transmission microscopies and energy dispersive spectroscopy. Tri-n-octylphosphine oxide (TOPO) and dicobalt octacarbonyl were heated under argon to a temperature of 180 deg with constant stirring for 1 hr. Quenching the reaction in toluene produced Co-containing nanoparticles with a diameter of 5 to 10 nm. Alternatively, an alumina support (SBA-200 Al2O3) was added; the reaction was further stirred and the temperature was decreased to 140 deg to reduce the rate of further growth/ripening of the nucleated Co nanoparticles. A typical size of Co-containing NPs was also found to be in the range of 5 to 10 nm. This can be contrasted with a range of 50 to 200 nm for conventionally-produced Co-Al2O3 Fischer-Trpsch catalysts. This method shows great potential for production of highly dispersed catalysts that are either supported or unsupported

Cowen, Jonathan

Hepp, Aloysius F.

NASA Technical Reports Server

Jonathan Cowen
Case Western Reserve University, Cleveland, Ohio
Aloysius F. Hepp
Glenn Research Center, Cleveland, Ohio
Synthesis and Characterization of Cobalt-Containing
Nanoparticles on Alumina: A Potential Catalyst for
Gas-to-Liquid Fuels Production
NASA/TM—2016-219138
September 2016
https://ntrs.nasa.gov/search.jsp?R=20160011333 2019-08-29T16:36:05+00:00Z
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Jonathan Cowen
Case Western Reserve University, Cleveland, Ohio
Aloysius F. Hepp
Glenn Research Center, Cleveland, Ohio
Synthesis and Characterization of Cobalt-Containing
Nanoparticles on Alumina: A Potential Catalyst for
Gas-to-Liquid Fuels Production
NASA/TM—2016-219138
September 2016
National Aeronautics and
Space Administration
Glenn Research Center
Cleveland, Ohio 44135
Acknowledgments
Technical discussions with Dr. Michael Kulis (NASA GRC) and Dr. Gary Jacobs (University of Kentucky Center for Applied 
Energy Research) are acknowledged. We thank Mr. David Hull (NASA GRC) and Prof. Michael Hoops (Wheeling Jesuit University, 
NASA GRC Summer Faculty Fellow) for assistance with this work. We are grateful to Sasol North America for donations of the 
high surface-area alumina substrates used in this study.
Available from
Trade names and trademarks are used in this report for identifi cation 
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either expressed or implied, by the National Aeronautics and 
Space Administration.
Level of Review: This material has been technically reviewed by technical management. 
This report contains preliminary fi ndings, 
subject to revision as analysis proceeds.
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NASA/TM—2016-219138 1 
Synthesis and Characterization of Cobalt-Containing 
Nanoparticles on Alumina: A Potential Catalyst for 
Gas-to-Liquid Fuels Production 
 
Jonathan Cowen 
Case Western Reserve University 
Cleveland, Ohio 44106 
 
Aloysius F. Hepp 
National Aeronautics and Space Administration 
Glenn Research Center 
Cleveland, Ohio 44135 
Abstract 
Fisher-Tröpsch synthesis (FTS) is a century-old gas-to-liquid (GTL) technology that commonly 
employs cobalt (Co, on an oxide support) or iron (supported or not) species catalysts. It has been well 
established that the activity of the Co catalyst depends directly upon the number of surface Co atoms. The 
addition of promoter (mainly noble) metals has been widely utilized to increase the fraction of Co that is 
available for surface catalysis. Direct synthesis of Co nanoparticles is a possible alternative approach; our 
preliminary synthesis and characterization efforts are described. Materials were characterized by various 
transmission microscopies and energy dispersive spectroscopy. Tri-n-octylphosphine oxide (TOPO) and 
dicobalt octacarbonyl were heated under argon to a temperature of 180 °C with constant stirring for 1 hr. 
Quenching the reaction in toluene produced Co-containing nanoparticles with a diameter of 5 to 10 nm. 
Alternatively, an alumina support (SBA-200 Al2O3) was added; the reaction was further stirred and the 
temperature was decreased to 140 °C to reduce the rate of further growth/ripening of the nucleated Co 
nanoparticles. A typical size of Co-containing NPs was also found to be in the range of 5 to 10 nm. This 
can be contrasted with a range of 50 to 200 nm for conventionally-produced Co-Al2O3 Fischer-Tröpsch 
catalysts. This method shows great potential for production of highly dispersed catalysts that are either 
supported or unsupported. 
  
NASA/TM—2016-219138 2 
Introduction 
Fisher-Tröpsch synthesis (FTS) is a century-old gas-to-liquid (GTL) technology that commonly 
employs Co (on an oxide support) or Fe (supported or not) species catalysts. The raw material is a 
gaseous mixture of CO and H2 (synthesis gas or syngas) typically produced by the slightly exothermic 
partial oxidation of methane (1). Through FTS, a syngas feedstock is converted into various liquid 
hydrocarbons (2) (Ref. 1). 
 
 CH4 + ½ O2  CO + 2 H2 ΔH = –9 kcal/mol (1) 
 
 n CO + (2n+1) H2  CnH(2n+2) + n H2O  ΔH = –49 kcal/mol (2) 
 
It has been well established that the catalytic activity of the cobalt catalyst depends directly upon the 
number of surface cobalt (Co) atoms as determined by hydrogen chemisorption. The turnover number 
(TON) remains constant as the cobalt dispersion increases up to about 12 percent (Ref. 2). Since the TON 
is constant with Co dispersion, approaches to increase catalyst productivity include increasing dispersion 
and/or increasing the fraction of cobalt that is reduced to the metal. The addition of promoter (mainly 
noble) metals has been widely utilized to increase the fraction of cobalt that is available for surface 
catalysis (Ref. 3). Direct synthesis of Co nanoparticles is a possible alternative approach; our preliminary 
synthesis and characterization efforts are described. 
Experimental Details and Results 
All chemicals were used as received. Tri-n-octylphosphine oxide (TOPO, Alfa Aesar) (73.46 g, 
0.19 moles) was added to a three neck (24/40) 300 mL round-bottom flask (RBF) containing 150 mL of 
toluene (C6H5CH3, Sigma-Aldrich) and heated under argon to a temperature of 180 °C with constant 
stirring for 1 hr. Separately, 6.5 g (1.910–3 moles) of dicobalt octacarbonyl (Co2(CO)8, Strem Chemicals) 
was added to a 50 mL RBF in an inert atmosphere glovebox (Vacuum Atmospheres). Moderate 
application of a heating gun was employed to aid dissolution of Co2(CO)8 in 30 mL of toluene.  
An addition funnel was added to the 300 mL RBF and heated prior to adding Co2(CO)8 solution to 
ensure the compound did not precipitate out upon loading via the addition funnel. The Co2(CO)8 solution 
was then added to the TOPO solution under constant stirring and constant temperature of 180 °C at rate of 
approximately 2 drops/sec. Note: vent the reaction vessel at this step due to the immediate out-gassing of 
CO, this is especially critical if the Co2(CO)8 solution is added rapidly. Upon completion of the addition 
of the Co solution, the reaction was stirred for 1 hr; a 2 mL aliquot was then withdrawn and quenched in 
10 mL of toluene for TEM analysis. A schematic diagram and photograph of CO nanoparticle samples is 
shown in Figure 1(a) and (b), respectively. Transmission electron micrographs (Phillips CM-20) are 
shown in Figure 2. 
Immediately after the removal of the aliquot, 7.72 g of SBA-200 alumina (Al2O3, Sasol) was added 
with the aid of a paper funnel. The reaction was further stirred and the temperature was decreased to 
140 °C to reduce the rate of further growth/ripening of the nucleated Co nanoparticles. The solution was 
held at 140 °C for 3 hr with continuous stirring. The temperature was lowered to 100 °C and the stirring 
ended.  
After 1 hr sitting at 100 °C without stirring, the contents were transferred to an alumina boat and 
placed inside a tube furnace under a constant flow of argon (1.5 slpm). The furnace was heated to 230 °C 
(the controller was actually set to 255 °C because the thermocouples were placed inside the furnace 
heating elements, but outside the inner calcination tube) and held at this temperature for 2 hr. This 
processing step is added to decompose the organic constituents and facilitate binding of Co-NPs to the 
substrate. Figure 3 compares a standard FT catalyst (Ref. 3) with a typical Co-containing NP-loaded 
alumina substrate. 
NASA/TM—2016-219138 3 
 
Figure 1.—(a) Diagram of typical synthesis of Co nanoparticles; (b) Aliquots from reaction quenched in toluene. 
 
 
Figure 2.—(a) Bright field (left) and (b) high-resolution transmission electron micrographs (right) of typical Co 
nanoparticles.  
 
 
Figure 3.—Bright field TEM images comparing (a) typical standard Co/Al2O3 FT catalyst (left) with 
(b) Co NP/Al2O3 samples (right).  
NASA/TM—2016-219138 4 
A HR-TEM bright field image (Fig. 4) yields a typical crystallite size of 5 to 10 nm for Co-containing 
nanoparticles. These are similar in size to the toluene-quenched Co-containing nanoparticles shown above 
(Fig. 2), and quite a bit smaller than the conventionally-processed Co-Al2O3 catalyst above (Fig. 3). While 
we did not analyze the oxidation state of the Co-containing nanoparticles, these are most likely CoO 
(Refs. 1 to 3). 
Confirmation of the identity of the nanoparticles and substrate materials was made by scanning 
transmission electron microscopy (STEM) and energy dispersive spectroscopy (EDS) (Fig. 5). Note that 
the darker features are predominantly Co-containing while lighter-shaded areas contain both Al and Co. 
 
 
 
Figure 4.—(a) Bright field TEM images of Co-containing NP/Al2O3 sample shown in Figure 3(b) on left and 
(b) at higher magnifications on right. 
 
 
 
Figure 5.—(a) Scanning transmission electron microscopy (STEM) image (left) and on right, corresponding 
energy dispersive spectra (EDS) of (b) regions 1 (top) and (c) 3 (bottom). 
  
NASA/TM—2016-219138 5 
Discussion 
Earlier use of TOPO and related compounds was reported for industrial extractions (Ref. 4) such as 
reprocessing of nuclear fuels (Ref. 5); early reports for producing quantum dots or semiconductor 
nanoparticles of III-V compounds are found in 1996 (Ref. 6). Our work indicates that TOPO not only 
plays an important role (well known in field of colloidal chemistry) in synthesizing Co nanoparticles 
uniform in size and morphology, but also could potentially play a vital role for the fabrication of highly 
disperse Co NP/alumina-catalyst structures.  
One of the current problems when preparing catalysts by conventional methods previously described 
occurs as the Co agglomerates or ripens during calcination resulting in catalysts with poor dispersion 
(Refs. 1 to 3). The use of TOPO as a capping group for the synthesis of Co nanoparticles dispersed onto 
alumina circumvents these issues as its extremely low-volatility (Refs. 4 to 6) allows sufficient time for 
the metallic Co to bind to the alumina support before the TOPO is released in the calcination process. The 
low volatility of TOPO dictates that the calcination temperature has to be a minimum of 230 °C for its 
effective removal. 
Conclusions 
Co-containing NPs have been synthesized in the presence of the highly coordinating ligand 
TOPO. Nanoparticle formation can be quenched in toluene. Alumina substrates can also support these 
Co-containing nanoparticles. Typical crystallite sizes for both supported and unsupported Co-containing 
NPs are below 10 nm as compared to 50 to 200 nm for conventionally-processed FT catalysts. This 
method shows great potential for production of highly dispersed catalysts that are either supported or 
unsupported. Further process improvement(s) should enable finer control of size and distribution. 
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Synthesis and Characterization of Cobalt Containing Nanoparticles on Alumina A Potential Catalyst for Gas to Liquid Fuels Production

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