Lauren M. Best

Glenn Research Center, Cleveland, Ohio

Ana B. De La Ree

United Negro College Fund Special Programs Corporation, Cleveland, Ohio

Robyn L. Bradford

Central State University, Wilberforce, Ohio

Aloysius F. Hepp

Glenn Research Center, Cleveland, Ohio

Characterization of Catalyst Materials for 

Production of Aerospace Fuels

NASA/TM—2012-217403

April 2012

AIAA–2011–5741
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Lauren M. Best

Glenn Research Center, Cleveland, Ohio

Ana B. De La Ree

United Negro College Fund Special Programs Corporation, Cleveland, Ohio

Robyn L. Bradford

Central State University, Wilberforce, Ohio

Aloysius F. Hepp

Glenn Research Center, Cleveland, Ohio

Characterization of Catalyst Materials for 

Production of Aerospace Fuels

NASA/TM—2012-217403

April 2012

AIAA–2011–5741

National Aeronautics and

Space Administration

Glenn Research Center

Cleveland, Ohio 44135

Prepared for the

9th International Energy Conversion Engineering Conference (IECEC)

sponsored by the American Institute of Aeronautics and Astronautics

San Diego, California, July 31–August 3, 2011
Acknowledgments

This research was supported by NASA’s Fundamental Aeronautics (Subsonic Fixed Wing) and the Exploration Technology 

Development and Demonstration In-Situ Resource Utilization (ISRU) programs for in-house work. The NASA Education Office 

supported Dr. Ana De La Ree through the UNCFSP-UNEEC Energy and Environmental Studies Cluster. The Ohio Space Institute, 

the Ohio Space Grant Consortium, and the NASA Glenn Academy for Space Exploration supported the summer internship for 

Robyn L. Bradford. Gratitude is to be given to the NASA Glenn Research Center and the University of Akron’s cooperative 

education program for Lauren M. Best’s contributions to this research. Special thanks are to be given to the following person’s 

for their participation: Jennifer Klettlinger, Richard González-Arroyo, Dr. Michael Hoops, Dr. Michael Kulis, Dr. Conrad Jones 

and the Alternative Fuels Research Laboratory team. Acknowledgements are also extended to Sasol North America, Inc. for the 

gift of high surface area alumina support. 

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Trade names and trademarks are used in this report for identification 

only. Their usage does not constitute an official endorsement, 

either expressed or implied, by the National Aeronautics and 

Space Administration.

This work was sponsored by the Fundamental Aeronautics Program 

at the NASA Glenn Research Center.

Level of Review: This material has been technically reviewed by technical management. 
NASA/TM—2012-217403 1

Characterization of Catalyst Materials for Production of Aerospace Fuels

Lauren M. Best

National Aeronautics and Space Administration

Glenn Research Center

Cleveland, Ohio 44135

Ana B. De La Ree

United Negro College Fund Special Programs Corporation

Cleveland, Ohio 44315

Robyn L. Bradford

Central State University

Wilberforce, Ohio 45384

Aloysius F. Hepp

National Aeronautics and Space Administration

Glenn Research Center

Cleveland, Ohio 44135

Abstract

Due to environmental, economic, and security issues, there 

is a greater need for cleaner alternative fuels. There will 

undoubtedly be a shift from crude oil to non-petroleum 

sources as a feedstock for aviation (and other transportation) 

fuels. Additionally, efforts are concentrated on reducing costs 

coupled with fuel production from non-conventional sources. 

One solution to this issue is Fischer-Tropsch gas-to-liquid 

technology. Fischer-Tropsch processing of synthesis gas 

(CO/H2) produces a complex product stream of paraffins, 

olefins, and oxygenated compounds such as alcohols and 

aldehydes. The Fisher-Tropsch process can produce a cleaner 

diesel oil fraction with a high cetane number (typically above 

70) without any sulfur or aromatic compounds. This process is 

most commonly catalyzed by heterogeneous (in this case, 

silver and platinum) catalysts composed of cobalt supported 

on alumina or unsupported alloyed iron powders. 

Physisorption, chemisorptions, scanning electron microscopy 

(SEM), and energy dispersive spectroscopy (EDS) are 

described to better understand the potential performance of 

Fischer-Tropsch cobalt on alumina catalysts promoted with 

silver and platinum. The overall goal is to preferentially 

produce C8 to C18 paraffin compounds for use as aerospace 

fuels. Progress towards this goal will eventually be updated 

and achieved by a more thorough understanding of the 

characterization of catalyst materials. This work was 

supported by NASA’s Subsonic Fixed Wing and In-situ 

Resource Utilization projects. 

Nomenclature

BET Brunauer, Emmett, and Teller surface area analysis 

method (physisorption)

C constant related to the energy of adsorption

CO carbon monoxide

CO2 carbon dioxide

CSTR continuously-stirred tank reactor

EDS energy dispersive spectroscopy

FT(S) Fischer-Tropsch (synthesis)

GRC NASA Glenn Research Center

GTL gas-to-liquid

P pressure

P0 vapor pressure of liquefied gas at the adsorbing 

temperature

SEM scanning electron microscopy

TCD thermal conductivity detector

TPR temperature-programmed reduction (chemisorption

analysis method)

Va STP volume of gas adsorbed at pressure P

Vm STP volume of gas needed to form an adsorbed 

monolayer

Introduction

For much of the last 2 centuries, fossil fuels, most notably 

petroleum, have facilitated the rapid growth and development 

of the modern transportation system used throughout the 

world today. At the conclusion of the twentieth century, the 

reality of society’s over-reliance and misuse of non-renewable 

resources became evident. As a result, throughout scientific 

and political arenas, new and affordable renewable energies 

have become key to the future preservation of an energyintensive society. Space and aviation vehicles require high 

energy density liquids for propulsion (and power), thus 

differentiating them from conventional “green” energies 

available for terrestrial and marine propulsions (electric, 

nuclear, etc.). At the NASA Glenn Research Center (GRC), 

research is focused on alternative fuels derived from FischerTropsch synthesis (FTS) and other gas-to-liquid (GTL) 
NASA/TM—2012-217403 2

processes for aerospace propulsions. There are many 

objectives branching from FT research, including analysis of 

specific promoters for particular fuel compositions, 

optimization of the synthesis of FT catalysts, and end product 

improvement to enable the goal of reduced reliance on nonrenewable sources for aerospace fuels. 

The FTS reaction can be described as a series of chemical 

reactions used to convert synthesis gas (CO/H2) into useful 

hydrocarbon products. The process generally includes the 

following two highly exothermic reactions:

(2n+1)H2 + nCO => CnH2n+2 + nH2O (1)

2nH2 + nCO => CnH2n + nH2O (2)

The hydrocarbon product stream is a very complex mixture, 

containing paraffins, olefins, and oxygenated compounds such 

as alcohols (Ref. 1). Fischer-Tropsch synthesis is an essential 

component of GTL technologies and is a noteworthy 

alternative fuel source, since the resultant alkanes and alkenes 

can be converted into useful aviation fuel (C8 – C18

hydrocarbon chains). There are several key advantages to FTderived fuels. Since products do not contain sulfurs, heavy 

metals, or aromatics, emissions are greatly reduced; FT fuels 

are much more environmentally friendly than those derived 

from petroleum (Ref. 2).

FTS is based on a radical mechanism. In order for the FT 

reaction to proceed, a metallic catalyst must be used to facilitate

the reaction between CO and H2. The reaction is a surfacecatalyzed polymerization reaction that links –CH2 monomers 

from CO and H2 (Ref. 3). The overall performance of the 

reaction is based on many factors, but most importantly the 

synthesis gas and catalyst composition, and the operating 

temperature. For the GTL processes, the feed gas is most 

commonly obtained from methane, but can be acquired from 

coal and crude oil via steam reforming or partial oxidation or 

through biomass derivatives (Refs. 4 and 5).

As a result of decades of research, it is now known that the 

most active metals for FT synthesis are nickel (Ni), ruthenium

(Ru), cobalt (Co), and iron (Fe) (Ref. 6). However, the most 

common metals used for commercial applications of FT 

synthesis contain Co and Fe since they are less expensive than 

Ru and Ni, which predominately produces methane. Typical 

FT synthesis is catalyzed by cobalt on alumina (Al2O3), which 

may include additional transition metal promoters (ex. Pt, Ag, 

Pd, Mn, etc.), or unsupported alloyed iron powders. The main 

difference between the iron and cobalt catalysts involves the 

formation of oxygen-containing products. When reacted, the 

oxygen from the synthesis gas is converted to water with 

cobalt catalysts and CO2 with iron (Ref. 7). Since cobalt does 

not have significant water-gas-shift (WGS) activity (iron has 

considerable WGS activity), the synthesis gas ratio of H2:CO 

must be higher than 2:1. This ratio is typical of syn-gas 

derived from natural gas (CH4). As natural gas availability is 

currently the main driving force behind FT synthesis, cobalt 

catalysts are primarily used. Cobalt is also more rugged and 

can be used for multiple GTL conversions; which further 

reduces the cost of feedstock production. Moreover, Co has a 

much lower yield of oxygen-containing products including 

ketones, alcohols, and aldehydes which further promotes the 

use of this metal (Ref. 8).

Currently, there are two standard sets of FT operating 

conditions, high temperature and low temperature. Typically, 

for high temperature (300 to 350 °C) conditions, the alloyed 

iron catalysts are used for the production of low molecular 

weight olefins, whereas the low temperature (200 to 240 °C) 

reactions use cobalt catalysts to promote the production of 

high molecular weight saturated paraffins or waxes (Ref. 9).

At GRC, cobalt FT catalysts are used in the Alternative Fuels 

Research Laboratory in three continuously-stirred tank 

reactors (CSTRs) for the production of FT hydrocarbons, one 

for Fe and two for Co. 

Before catalysts are tested or run in FT reactors, they are 

typically characterized by various analytical techniques: 

scanning electron microscopy (SEM) and energy dispersive 

spectroscopy (EDS); temperature programmed reduction 

(TPR, or chemisorption); and Brunauer, Emmett, and Teller 

surface area analysis (BET, or physisorption). The main goal 

of characterization is to indicate promising FT synthesis 

catalysts that promote products within the transportation fuel 

and additives range (C8 – C18). Additionally, the use of 

transition metals as promoters is used to enhance the catalytic 

properties of the FT catalysts, most commonly ruthenium, 

platinum, and rhenium. Promoters are very valuable to the FT 

process and have been shown to increase catalytic activity and

the reducibility of cobalt oxide, improve mechanical 

properties, and stabilize high surface area catalysts (Refs. 10

and 11). Promoter alternatives include silver, nickel, 

palladium, and manganese. However silver and manganese are 

especially investigated due to their low cost versus the 

platinum-group metals. For this paper, platinum and silver 

promoted and unpromoted catalysts will be compared.

Experimental

Synthesis of Unpromoted Co/Al2O3 FT Catalysts

For catalyst synthesis at GRC, procedures were 

modified based on a description in a U.S. patent by 

Espinoza, et al. (Ref. 12). A summarized procedure list 

can be found in Table I.

TABLE I.—SUMMARY OF TARGET LOADING 

OF UNPROMOTED CATALYSTS

Step 1 First Co loading > Rotavap

Step 2 Second Co loading > Rotavap

Step 3 Calcination

Step 4 Characterization
NASA/TM—2012-217403 3

Cobalt nitrate (Co(NO3)2·6H2O) is dissolved in distilled 

deionized H2O. The Co solution was then added to a dispenser 

titration burette and added dropwise to the alumina (Al2O3) 

(Figure 1), stirring constantly for 30 min without heat. The 

cobalt nitrate/alumina mixture is heated and stirred in a water 

bath at 80 °C, under vacuum for water extraction via 

Rotavapor 210 and Vacuum Pump V-700 (BÜCHI 

Labortechnik) until it is bright pink and powder dry (Figure 2). 

Repeat the above steps for a second Co impregnation onto the 

alumina. The catalyst is then removed and prepared for 

calcination. Calcination is the thermal treatment applied to 

solid materials to cause a phase transition or removal of any 

volatiles. In this case, when the catalyst is calcined, the 

nitrates present are removed through the release of nitric oxide 

(NO). This calcination furnace is composed of a sealed long 1-

in. OD stainless steel tube packed with glass wool. The 

catalyst is loaded into the reactor with a thermocouple in place 

to monitor the internal temperature of the material. Air is 

flowed through the tube at about 5 mL/min to ensure that the 

volatiles are carried out of the reactor. Additionally, air is used 

to make certain the catalyst does not burn. The stainless steel 

tube is placed into a Blue M tube furnace (Thermo Scientific 

Lindberg/Blue). Then, the cobalt nitrate/alumina powder is 

heated to an internal temperature of 350 °C for 4 hr where the 

temperature is programmed and controlled by the CN3251 

Controller Box (Omega). The catalyst is then characterized 

with SEM/EDS, BET, and TPR. 

Synthesis of Promoted Co/Al2O3 FT Catalysts

Promoted FT catalysts are prepared by adding promoter salt 

solutions to an uncalcined, unpromoted Co/Al2O3 catalyst, in 

this case [Pt(NH3)4][NO3]2 or Ag(NO3). Target loadings of 

Figure 1.—Impregnation of Co on alumnia dropwise from 

burette. 

promoters are usually between 0.5 and 1 percent of the 

catalyst mass, however up to 2 percent and even 5 percent 

have been used. The promoter solution is then added dropwise 

to the unpromoted catalyst, stirring constantly for 15 min 

without heat. The catalyst is then placed on the Rotavapor 

where it is heated in a 70 °C water bath. At this stage, the 

catalyst is pink and powder dry; it is placed in the calcination 

reactor where it is calcined using the unpromoted catalyst 

specifications. The finished catalyst is a fine black powder, 

shown in Figure 3. It should be noted that more than one 

promoter can be added to catalyst. One would simply repeat 

Step 3 before calcination is completed. A summary of the 

promoter addition procedure is given in Table II.

Figure 2.—Catalyst drying before calcination on Rotavapor 210.

Figure 3.—Completed catalyst after calcination. 

Promoted and unpromoted catalysts both are black 

powders upon completion.
NASA/TM—2012-217403 4

TABLE II.—SUMMARY OF TARGET LOADING 

OF PROMOTED CATALYSTS

Steps 1 and 2 First Co loading > Rotavap > Second Co loading > Rotavap

Step 3 Promoter loading > Rotavap

Step 4 Calcine

Step 5 Characterization

Catalyst Characterization Methods

For FT synthesis, there are many factors that may affect the 

overall selectivity and conversion of CO during the reaction

and also the type of hydrocarbon product produced. The goal 

of FT synthesis research at GRC is to develop a heterogeneous

catalyst that can generate a specific type or range of 

hydrocarbons needed for an application (terrestrial 

transportation, aviation, etc.). When characterizing catalysts, 

the goal is to understand the surface of the catalyst at the 

microscopic and mesoscopic level at reaction specific 

conditions (Ref. 13). These studies would include analysis of 

the catalytic activity per unit area, the catalyst behavior based 

on the composition of the material, surface adsorption, and 

electron microscopy (Ref. 3).

Energy Dispersive Spectroscopy and Scanning 

Electron Microscopy 

Energy dispersive spectroscopy (EDS), based on x-ray 

florescence spectroscopy, is used to determine specific surface 

properties and elemental composition of a given material on 

the sub-micron scale (Ref. 14). As samples are excited with 

electrons in an electromagnetic field, x-rays are emitted. Since

each element has a different atomic structure, the x-ray 

emitted can be identified and the element can be determined.

X-ray florescence occurs when the vacated shell is filled with 

an electron from a higher shell. The energy gain by a specific 

signature or pattern from this transition is used to emit an xray photon, which is unique to that atom. EDS also competes 

with internal photoionization. Thus, the probability is the 

highest for elements heavier than magnesium (Ref. 13).

Emitted x-rays are analyzed by an energy dispersive x-ray 

detector that is located at a fixed point about the sample. The 

detector converts the photon, via the photoelectric effect, into 

an electron where the current is measured. The pulse height is 

then recorded (Refs. 13 and 14).

Scanning electron microscopy (SEM), in conjunction with 

EDS, allows the observation and in situ chemical analysis of 

heterogeneous materials at the micron level. There is a very 

wide range of magnification available on most SEM

microscopes. A material can be analyzed at magnifications as 

low as 10X to as high as 500,000X for some models (Ref. 15).

The instrument ordinarily operates at low vacuum pressures to 

permit the use of electron beams on the surface of the 

materials that are undergoing analysis (Ref. 15). A narrow 

electron beam in a raster scan pattern is produced over the 

surface of the material and backscattered; secondary electrons 

are produced by the primary beam and are used as the primary 

signals to form images. The contrast of the images is based on 

the orientation of the surface of the material to the detector

(typically using EDS technology) (Ref. 13). Bright sections of 

the material have the surface normal facing the detector, 

whereas the dark sections have the surface normal pointing 

away. The backscattered electrons carry information about the 

composition of the sample, since these electrons increase with 

an increase in atomic weight of the material (Ref. 14). Since, 

higher atomic weight elements are more efficient at scattering 

electrons throughout an area, these elements will appear 

brighter in SEM images (Ref. 16). Because such a narrow 

electron beam is used, SEM yields a three-dimensional 

analysis of the surface of the material which is very useful for 

structural analysis. 

Temperature Programmed Reduction 

Temperature-programmed studies involve assessments in 

which a chemical reaction is analyzed as the temperature is 

raised at a linear rate (Ref. 17). A TPR instrument consists of

temperature programmable equipment and a thermal 

conductivity detector (TCD) and is loaded with a catalyst in a 

sample tube. To remove the oxygen from the sample, an inert 

gas (usually He or Ar) is flowed through the catalyst until the 

TCD signal is constant. The instrument heats the sample as the 

temperature is increased at a rate of 1 to 20 °C/min. During 

this increase in temperature, the TCD measures the amount of 

H2 in the gas entering and leaving the instrument. For a typical 

TPR, one would use 4 to 10 percent H2 in N2 in Ar. When 

reduction occurs, H2 is consumed, which in turn increases the 

signal on the detector (Ref. 18). Total amount of H2 consumed 

can also be determined via the amount of water produced 

during the reaction. When a substance is reduced, the Gibbs 

free energy (by convection) is negative; the reaction is 

thermodynamically favorable and will release energy

(exothermic) (Ref. 19). Because the product of the FT catalyst 

reduction by hydrogen is water, and the free enthalpy is

always negative (by ΔG = ΔH – TΔS). From the TCD signal 

versus temperature plot, one can easily find the 

reduction/activation temperatures from peaks on the graph. If 

the catalyst contained multiple metals (i.e., a promoted 

catalyst), the plot should contain multiple peaks where the 

additional metals were reduced. This information can then be 

used to determine the multiple phases of the catalyst after the 

Co and promoter impregnation and can indicate the 

arrangement of the metals on the surface of the alumina

support. Additionally, the reduction temperature is used to 
NASA/TM—2012-217403 5

verify the activation energies and activation temperatures to be 

used in the FT reactors. At GRC, TPR is performed and 

analyzed on the AutoChem II 2920 (Micromeritics 

Instrumentation Corporation). 

Brunauer, Emmett, and Teller Surface Area Analysis 

Since catalysis in FT and many other reactions occur on the 

surface, the area available on the material available for 

reaction(s) is vital information for characterizing catalysts and 

the outcomes of FT synthesis, in particular. The Brunauer, 

Emmett, and Teller (BET) method is used to determine the 

surface area and is based on physisorption: the amount of gas 

that can physically adsorb onto a surface at a given pressure. 

The physisorption of a material is based on the interactions 

between the surface of the catalyst with the gas vapor pressure 

and the temperature. Because BET is very inexpensive and 

reliable, it is used in many research areas where the surface 

area of a material is needed. However, the test does not apply 

to all types of isotherms (Ref. 13).

In catalysis research, the surface area of the catalyst is very 

important with regards to the activity and stability of the 

material. The original BET theory is based on the original 

surface area of the Langmuir isotherm. Major advancements in 

adsorption models used the Langmuir isotherm, which 

described the accumulation of gas molecules in a monolayer 

on a surface to illustrate multilayer adsorption (Ref. 20). The 

supporting statements in BET theory state that the forces 

present in the condensation of gases are responsible for the 

multilayer binding on the surface of the catalyst. For an 

infinite number of layers, the BET characteristic equation can 

be found by summing the rate of condensation of gases onto 

an adsorbed layer and the rate of evaporation of the monolayer 

already of the surface (Ref. 18):

( ) 



 



−  = +

0 − 0

1 1

P

P

V C

C

V P P V C

P

a m m

(3)

In Equation (3), P0 and P are the saturation and equilibrium 

pressures of adsorbed gases at the temperature of adsorption. 

Va is quantity of adsorbed gas in units of volume and Vm is 

quantity of gas in the adsorbed monolayer. C is the BET 

constant, which is incorporates the heat of liquefaction of the 

monolayer and subsequent adsorbed gas layers on the surface. 

Equation (3) describes the equilibrium of the adsorption of gas 

on the catalyst surface at a constant temperature, and can be 

plotted in a linear relationship. 

The BET multilayer adsorption model is based on a series 

of assumptions. Firstly, as stated above, it is assumed that the 

gas molecules can adsorb onto the surface of catalyst in 

infinite layers. Second, there are no interactions between the 

gas layers; and third, the monolayer model applies to each 

individual layer (Ref. 20).

The most common procedure to measure the surface area of 

a catalyst is to observe how much N2 is adsorbed onto the 

material at low pressure and temperature (Ref. 21). The NASA 

catalyst synthesis group uses a FlowSorb III 2305 

(Micromeritics Instrumentation Corporation) for BET 

analysis. This instrument has the capability of reporting 

adsorption and desorption isotherms. A catalyst (or catalyst 

material, such as the alumina support) is loaded in a sample 

tube. A heating mantle is installed to raise the temperature of 

the sample to about 250 to 300 °C while the catalyst is 

exposed to flowing N2 to purge any air or water in the sample 

or tube. After degassing, the catalyst is prepared for analysis. 

A TCD is used to measure the thermal conductivity at the start 

of the experiment. Since the sample will not adsorb nitrogen at 

room temperature, the sample tube is immersed in a Dewar 

flask of liquid nitrogen (LN2). The sample almost immediately 

begins to adsorb nitrogen onto the surface. As the nitrogen 

molecules begin to adsorb on the surface, the thermal 

conductivity also changes. After the maximum amount of N2

is adsorbed, the Dewar is removed to investigate the 

desorption of the catalyst (Ref. 21). Since the same amount of 

nitrogen should be adsorbed and desorbed, these values should 

be very close in values. The amount of nitrogen consumed is 

then used to determine the surface area of the catalyst in m2

/g, 

based on the weight of the sample loaded in the instrument.

Methods

TPR Procedure

As stated previously, for TPR analysis was performed via 

an AutoChem II 2920 (Micromeritics Instrumentation 

Corporation). A sample, 0.1 to 0.2g by weight, is loaded into a 

quartz U-tube packed with glass wool at the bottom to hold the 

catalyst in place. The tube, with a thermocouple in place to 

measure the internal temperature of the catalyst, is then 

secured in the furnace vessel of the instrument. Argon is 

subsequently flowed through the instrument to remove any 

excess oxygen in the catalyst and to also stabilize the TCD 

before analyzing the sample. An ice-salt bath, at a temperature 

of –5 °C was installed at the cold trap of the instrument. The 

temperature is then ramped to 1000 °C at a rate of 10 °C/min 

while flow controllers inject 4 percent H2/Ar at a rate of 

30 cm3

/min. The TCD signal is recorded as a function of the 

temperature ramp throughout the analysis to determine the 

multiple activation temperatures of the catalyst. The TPR unit 

used for catalysis investigations is pictured in Figure 4.

SEM/EDS Procedure

FT catalysts were analyzed using S-3000N scanning 

electron microscope (Hitachi) for imaging and energy 

dispersive spectroscopy to determine the elemental 

composition and the surface properties of the material. The 

samples were prepared by placing some of the catalyst powder 

onto a strip of copper tape. Before the high vacuum mode is 

initiated, the strip is then inserted onto a sample holder and 

inserted into
NASA/TM—2012-217403 6

Figure 4.—Micromeritics AutoChem II 2920 used for TPR 

analysis.

the specimen stage of the SEM. The electron images were

viewed at 16.0 and 25.0 keV and at magnifications of 200X

and 250X. The working distances of the microscope varied, 

usually between 15 to 25 mm. Elemental composition data 

was attained using SEM Quant ZAF microanalysis software 

with a silicon drift detector used for EDS via the EDAX 

detecting unit (AMETEK). 

BET Procedure 

The FlowSorb II 2300 (Micromeritics Instrumentation 

Corporation), pictured in Figure 5, was used to obtain surface 

area measurements of the catalysts. Approximately 0.2g of 

catalyst is measured into an empty glass U-tube. It is 

imperative that the exact weight of the material is noted, since 

this value is crucial to the accuracy of the surface area 

measurement. The sample tube is inserted into the sample tube 

holder and secured by tightening connectors that seal via 

compressed O-rings, making a closed system assembly.

The catalyst must be degassed before it can be analyzed for 

surface area in order to remove any water vapor or other gases 

present during normal exposure to air. To achieve this, sample 

tube is attached to the degas section of the instrument via 

quick connect locking mechanisms. The sample is the heated 

via a heating mantle to a temperature of 250 °C for 

approximately 30 min while 30 percent N2/He is flowed. Once 

the catalyst is completely degassed, it is allowed to cool for 20 

min in the degas area in order to reduce the likelihood of 

thermal cracking. The sample is then moved to the test 

position to be prepared for analysis. It should be noted that 

30 percent N2/He is used exclusively for this entire 

experiment. To trigger the adsorption of nitrogen, a Dewar 

flask with liquid nitrogen (LN2) is installed on the sample tube

Figure 5.—Micromeritics FlowSorb II 2300 used for BET

analysis.

at the test position. This temperature and pressure change 

initiates this consumption of N2. This volume of nitrogen gas 

adsorbed onto Co/Al2O3 was used to find the amount of gas 

needed to form a single layer of N2 molecules over the 

surface. Once adsorption is complete, the Dewar of LN2 is 

removed. This removal changes the pressure again, triggering 

the desorption of nitrogen on the surface of the catalyst. The 

instrument will then display the surface area of the material. 

The sample tube is allowed to return to room temperature and 

the mass is recorded again for precision purposes. To 

determine the specific surface area in square meters, the 

displayed desorption reading is divided by the mass of the 

catalyst sample. 

Results and Discussion

Over 50 various heterogeneous FT catalysts have been 

synthesized and characterized at GRC. An analysis of the 

chemical composition and morphology were performed via 

BET, SEM and EDS. Many of the catalysts were sent off-site 

to Galbraith Laboratories, Inc., for inductively coupled plasma 

atomic emission spectroscopy (ICP-AES) elemental analysis

to be compared with in-house EDS weight percent data. The 

weight percents of the promoters and cobalt are of primary 

interest in this study, since these metals affect the reduction 

temperatures of the catalysts to the greatest degree. A 

complete listing of all relevant characterization data found 

during this inquiry is found in Table III. 
NASA/TM—2012-217403 7

TABLE III.—SAMPLES OF PROMOTED/UNPROMOTED Co/ALUMINA CATALYTS PREPARED AT GRC

Sample 

no.

Promoter ICP-AES element analysis EDS Surface area 

(m2/g)

Reduction 

temperature 

(°C)

1 None 21.6% Co/Al2O3 30.3% Co/Al2O3 126.3 350

2 None 9.31% Co/Al2O3 9.45% Co/Al2O3 142.4 335

3 None 31.7% Co/Al2O3 47.2% Co/Al2O3 108.7 436

4 Pt 21.5% Co/0.845% Pt/Al2O3 25.4% Co/2.57% Pt/Al2O3 123.7 254

5 Pt 20.9% Co/0.397% Pt/Al2O3 24.1% Co/1.49% Pt/Al2O3 106.6 349

6 Pt 24.8% Co/0.459% Pt/Al2O3 34.8% Co/2.30% Pt/Al2O3 115.9 265

7 Ag 21.0% Co/0.806% Ag/Al2O3 25.9% Co/1.31% Ag/Al2O3 118.2 275

8 Ag 23.6% Co/0.278% Ag/Al2O3 33.3% Co/2.19% Ag/Al2O3 109.4 369

9 Ag 22.9% Co/0.510% Ag/Al2O3 26.7% Co/1.63% Ag/Al2O3 117.6 337

When performing elemental analysis, it is important to 

understand that the amount of cobalt reported is representative 

of the amount of cobalt that has been distributed on the 

alumina, confirming a successful synthesis of a FT catalyst. 

When a promoter is added, the usual target loading is between 

0.1 and 0.5 percent of the total mass of the catalyst. Reported 

values from Galbraith were within 15 percent of the targeted 

initial loading. In this paper, ICP elemental analysis data will 

be used over EDS testing, since ICP is much more reliable, 

available, and accurate than that of EDS. Additionally, it 

should be noted that EDS detected other components in the 

catalyst that were not in the experimental design. These 

materials are most likely impurities in the support or chemical 

similarities of the components during characterization. These 

impurities are removed for the total weight percent of the 

metals in the sample. Since the platinum loading was very 

low, it was not detected during EDS analysis. 

The SEM images below are typical of the catalyst materials 

synthesized during this study. From Figure 6 and Figure 7, the 

surfaces look smooth and spherical particles look evenly 

dispersed throughout the alumina support. This smooth 

surface is desirable, since it reduces the surface area and 

provides a better plane for FT synthesis to occur. Figure 6 was 

viewed at working distance of 22.9 mm and at magnification 

of 250X. Figure 7 was recorded at a working distance of 

15.0 mm and at a magnification of 200X.

For unpromoted catalysts, the specific surface area of the 

catalysts generally decreases as the percent of cobalt increases. 

The starting surface area for the alumina support was 200 m2

/g 

(reported by Sasol, Inc.). With the addition of cobalt onto the 

support to create the FT catalysts, the surface area decreases 

with increased cobalt metal. This is aptly demonstrated by 

catalyst no. 3, which had an increase to 31 percent Co loaded 

on the alumina. The surface area dropped notably from 142.4 

to 108.7 m2

/g upon tripling the cobalt loading. Additional 

unpromoted catalysts would need to be investigated to provide 

a quantitative relationship. The promoted catalysts were also 

evaluated according to their corresponding surface areas. As 

depicted in Figure 8, there is a clear downward trend with 

regards to the weight percent

Figure 6.—SEM image of 21.6 percent Co/Al2O3 catalyst at 

250X magnification.

Figure 7.—SEM image of 21.5 percent Co/0.845 percent Pt/ 

Al2O3 catalyst at 200X magnification.
NASA/TM—2012-217403 8

Figure 8.—Percentage of cobalt versus specific surface area of 

promoted catalysts.

Figure 9.—Promoter weight percent versus the reduction 

temperatures of Pt and Ag promoted FT catalysts (with 

trendlines)

of cobalt and the specific surface areas of the promoted 

catalysts. This result, furthermore, agrees with the conclusion

above affirming that the addition of supplementary cobalt and 

promoters to the FT alumina support decreases the surface 

area. Additionally, the weight percent of the promoters was 

analyzed. It was expected that that with the higher amount of 

promoter present, the specific surface area will be higher 

because the metal promoter is not occupying the porous space. 

Rather, the promoter attaches to the surface. Unlike cobalt, the 

specific surface area is inversely proportional to the percent

loaded. For both platinum and silver, the surface areas of the 

FT catalysts increased as the amount of promoter loaded 

increased. The most plausible explanation for this 

phenomenon most likely involves the surface attachment of 

the particles on the surface of the alumina. Since the cobalt 

fills the majority of the porous spaces of the support, usually 

the promoter is given little space to fill inside the alumina, 

thus increasing the surface area of the catalyst. 

In addition to BET, TPR was performed on all catalysts 

above to determine the corresponding reduction temperatures. 

In theory, the addition of promoters to an FT catalyst should 

reduce the reduction temperature, and therefore operation 

temperature, of FT synthesis. As seen from Table III, the 

reduction temperature of an unpromoted catalyst varies from 

350 to 425°C. Ideally, the aim is to reduce the temperature

needed for activation and operation. However, the addition of 

promoters drastically reduces this temperature. The trends 

between promoter weight percent and reduction temperature is 

shown in Figure 9. For both silver and platinum, as the weight 

percent of the promoter loaded is increased, the temperature is 

then decreased. Platinum seems to have a greater effect on the 

reduction, than that of its’ silver counterpart. Even with the 

addition of 0.3 percent of silver on the catalyst, the reduction 

temperature remains at 369 °C. The amount of silver needed 

must be increased close to 1 percent for any great effect to 

occur. However, platinum reduces at a lower temperature with 

the addition of only 0.5 percent of the catalyst weight. From the 

figure, it can be concluded that platinum promoted catalysts 

cause the reduction temperature to decrease a much faster rate 

than that of silver with smaller amounts of noble metal. 

Conclusion

Through this research, GRC’s Alternative Fuels group is

steps closer to finding novel aviation fuel range catalysts for 

use in the FT synthesis process. The data presented verifies 

that that production of promoted and unpromoted Co/Al2O3 is 

feasible at relatively mild reaction conditions. Our preliminary 

results are in accord with prior literature (Ref. 22); the 

available surface area of a heterogeneous material will impact 

catalytic activity simply by altering the number of active sites. 

The specific activity of a catalyst also depends upon the 

metal(s) and dispersion onto the support. 

In summary, initial results suggest that upon increase of 

cobalt on the alumina, the specific surface area of the catalyst 

decreases. This result coincides with other observations made 

in previous FT catalyst research. Moreover, since the specific 

surface area of the Co/Al2O3 was reduced, a smoother surface 

was created. However, this inclination is not the same for 

platinum and silver loadings, due to the surface attachment of 

the promoter onto the exterior of the support. Additionally, 

through TPR investigation, it was observed that promoting 

Co/Al2O3 with platinum reduced the reduction temperature to 

the greatest extent. Since the main goal behind promoting 

catalysts is to reduce the activation temperature of the catalyst, 

platinum and chemically-similar metals would be obvious 

candidate promoters for future catalysis investigations.

Future work involves the investigation of varying Co/Al2O3

loading and use of other promoters from the platinum-group 

and coinage metals to determine the impact on reactivity and 

product specificity through TPR and pulse re-oxidation 

techniques. Additionally, other catalyst supports (TiO2, SiO2, 

and doped-Al2O3) will be investigated to determine the ideal

80

90

100

110

120

130

140

20 22 24 26

Specific Surface Area (m2/g)

Weight Percent (Cobalt)

200

250

300

350

400

450

0 0.2 0.4 0.6 0.8 1

Reduction Temperature (°C)

Weight Percent (Promoters)

Silver

Platinum
NASA/TM—2012-217403 9

porosity of the material for FT synthesis. This data will then 

be collected to continue research into catalysts that 

specifically target aviation fuel production via FT synthesis. 

References

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Characterization of Catalyst Materials for Production of Aerospace Fuels 

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14. ABSTRACT

Due to environmental, economic, and security issues, there is a greater need for cleaner alternative fuels. There will undoubtedly be a shift 

from crude oil to non-petroleum sources as a feedstock for aviation (and other transportation) fuels. Additionally, efforts are concentrated on 

reducing costs coupled with fuel production from non-conventional sources. One solution to this issue is Fischer-Tropsch gas-to-liquid 

technology. Fischer-Tropsch processing of synthesis gas (CO/H2) produces a complex product stream of paraffins, olefins, and oxygenated 

compounds such as alcohols and aldehydes. The Fisher-Tropsch process can produce a cleaner diesel oil fraction with a high cetane number 

(typically above 70) without any sulfur or aromatic compounds. This process is most commonly catalyzed by heterogeneous (in this case, 

silver and platinum) catalysts composed of cobalt supported on alumina or unsupported alloyed iron powders. Physisorption, 

chemisorptions, scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) are described to better understand the 

potential performance of Fischer-Tropsch cobalt on alumina catalysts promoted with silver and platinum. The overall goal is to 

preferentially produce C8 to C18 paraffin compounds for use as aerospace fuels. Progress towards this goal will eventually be updated and 

achieved by a more thorough understanding of the characterization of catalyst materials. This work was supported by NASA’s Subsonic 

Fixed Wing and In-situ Resource Utilization projects. 

15. SUBJECT TERMS

Catalysis; Fisher-Tropsch process; Platinum; Silver; Fuels 

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