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ABSTRACT
HETEROGENEOUS CATALYSTS FOR HYDROGEN PRODUCTION FROM
METHANE AND CARBON DIOXIDE
By
Julia M. Pusel
May 2015
Several heterogeneous catalysts were studied for synthesis gas production through
dry reforming of methane (DRM). This process uses carbon dioxide in lieu of the steam
that is traditionally used in conventional methane reforming to produce hydrogen that can
then be repurposed in more chemical processes. The monometallic catalysts explored
were Ni/Al2O3 and Ni/CeZrO2 followed by their bimetallic versions PtNi/Al2O3 and
PtNi/CeZrO2 at 800°C. In addition to these catalysts, platinum supported Zeolitic
Imidazolate Framework (ZIF)-8 was also investigated in comparison with PtNi/CeZrO2 at
490°C. The studies suggest that these catalysts are suitable for promoting the dry
reforming of methane for hydrogen production.
Keywords: Pt/ZIF-8, PtNi/Al2O3, PtNi/CeZrO2, Ni/Al2O3, Ni/CeZrO2, hydrogen,
carbon dioxide, methane, methane reforming, dry reforming, carbon dioxide reforming,
synthesis gas, gas chromatography, catalysts, plug flow reactor, greenhouse gases.
HETEROGENEOUS CATALYSTS FOR HYDROGEN PRODUCTION FROM
METHANE AND CARBON DIOXIDE
A THESIS
Presented to the Department of Chemical Engineering
California State University, Long Beach
In Partial Fulfillment
of the Requirements for the Degree
Master of Science in Engineering
Committee Members:
Sepideh Faraji, Ph.D. (Chair)
Gregory Smith, Ph.D.
Ted Yu, Ph.D.
College Designee:
Antonella Sciortino, Ph.D.
By Julia M. Pusel
B.S., 2007, Rose-Hulman Institute of Technology
May 2015
UMI Number: 1585646
All rights reserved
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UMI 1585646
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ACKNOWLEDGEMENTS
I would like to thank California State University, Long Beach for giving me the
opportunity to study Chemical Engineering at the graduate level. I would also like to
thank all of the professors that have shared their knowledge with me and helped to make
me a better engineer. I would especially like to thank my Research Advisor, Dr. Sepideh
Faraji, for her patience with me as I transitioned into a new job and by supporting my
research and my thesis through the challenges of living outside the local area and
balancing a full time job. I would also like to acknowledge the department’s Graduate
Advisor, Dr. Roger C. Lo and the chairman of the Department of Chemical Engineering,
Dr. Larry Jang for their continued support as I pursued my degree. Finally, I would like
to recognize and thank my family: my mother for always demanding that I do my best
and instilling in me the love for higher education since I was a child; my father for
always supporting my mother and I during our pursuit of education; and my husband for
his love, support, and engineering perspective during late night study sessions.
iii
TABLE OF CONTENTS
Page
ACKNOWLEDGEMENTS .........................................................................................
iii
LIST OF TABLES .......................................................................................................
v
LIST OF FIGURES .....................................................................................................
vi
LIST OF ABBREVIATIONS ...................................................................................... viii
LIST OF EQUATIONS ...............................................................................................
ix
CHAPTER
1. INTRODUCTION ............................................................................................
1
2. BACKGROUND INFORMATION .................................................................
4
The Utility of Hydrogen Production ..........................................................
Hydrogen Production .................................................................................
Catalyst Selection.......................................................................................
4
5
6
3. EXPERIMENTAL ............................................................................................
8
Setup ..........................................................................................................
Gas Chromatograph ...................................................................................
Procedure ...................................................................................................
Test Runs ...................................................................................................
Calculations................................................................................................
8
10
12
16
20
4. RESULTS AND DISCUSSION .......................................................................
22
Four Catalysts in Equal Quantities at the Same Temperature ...................
The Effect of Catalyst Mass .......................................................................
New Catalyst, Pt/ZIF, Compared to Traditional Bimetallic Catalyst ........
22
24
31
5. CONCLUSIONS...............................................................................................
35
REFERENCES ............................................................................................................
36
iv
LIST OF TABLES
TABLE
Page
1. First Run............................................................................................................
16
2. Second Run .......................................................................................................
17
3. Third Run ..........................................................................................................
17
4. Fourth Run ........................................................................................................
17
5. Fifth Run ...........................................................................................................
18
6. Sixth Run ..........................................................................................................
18
7. Seventh Run ......................................................................................................
18
8. Eighth Run ........................................................................................................
19
9. Ninth Run ..........................................................................................................
19
10. Tenth Run........................................................................................................
19
11: Eleventh Run...................................................................................................
20
12: Side-by-Side Comparison of All Test Runs ...................................................
21
v
LIST OF FIGURES
FIGURE
Page
1. Land air temperature anomalies, for global, north hemisphere and south
hemisphere for the period of 1850 to 2007 ................................................
3
2. Schematic of experimental setup consisting of plug-flow reactor, gas
chromatograph, fume hood, and a variety of gas feeds .............................
9
3. Image of laboratory setup at Cal State - Long Beach .......................................
10
4. Temperature profile for plug-flow reactor furnace ...........................................
14
5. Methane conversion of 4 different catalysts, in equal quantities, at 800°C
through a plug flow reactor utilizing the FID sensor in the GC ................
23
6. Methane conversion of 4 different catalysts, in equal quantities, at 800°C
through a plug flow reactor utilizing the TCD sensor in the GC ...............
24
7. Carbon Dioxide conversion of 4 different catalysts, in equal quantities, at
800°C through a plug flow reactor utilizing the FID sensor in the GC .....
25
8. Carbon Dioxide conversion of 4 different catalysts, in equal quantities, at
800°C through a plug flow reactor utilizing the TCD sensor in the GC....
25
9. Hydrogen to Carbon Monoxide ratio of 4 different catalysts, in equal
quantities, at 800°C through a plug flow reactor utilizing the FID
sensor in the GC .........................................................................................
26
10. Hydrogen to Carbon Monoxide ratio of 4 different catalysts, in equal
quantities, at 800°C through a plug flow reactor utilizing the TCD
sensor in the GC .........................................................................................
26
11. Methane conversion of Ni/Al2O3, in different quantities, at 800°C through
a plug flow reactor utilizing the FID sensor in the GC ..............................
28
12. Methane conversion of Ni/Al2O3, in different quantities, at 800°C through
a plug flow reactor utilizing the TCD sensor in the GC ............................
28
vi
FIGURE
Page
13. Carbon Dioxide conversion of Ni/Al2O3, in different quantities, at 800°C
through plug flow reactor utilizing the FID sensor in the GC ...................
29
14. Carbon Dioxide conversion of Ni/Al2O3, in different quantities, at 800°C
through a plug flow reactor utilizing the TCD sensor in the GC ...............
29
15. Hydrogen to Carbon Monoxide ratio of Ni/Al2O3, in different quantities, at
800°C through a plug flow reactor utilizing the FID sensor in the GC .....
30
16. Hydrogen to Carbon Monoxide ratio of Ni/Al2O3, in different quantities, at
800°C through a plug flow reactor utilizing the TCD sensor in the GC....
30
17. Methane conversion of 2 catalysts, in equal quantities, at 490°C through a
plug flow reactor utilizing both the FID and TCD sensor in the GC .........
33
18. Carbon Dioxide conversion of 2 catalysts, in equal quantities, at 490°C
through a plug flow reactor utilizing both the FID and the TCD sensor
in the GC ....................................................................................................
33
19. Hydrogen to Carbon Monoxide ratio of 2 catalysts, in equal quantities, at
490°C through a plug flow reactor utilizing both the FID and TCD
sensor in the GC .........................................................................................
34
vii
LIST OF ABBREVIATIONS
CH4
Methane
CO
Carbon Monoxide
CO2
Carbon Dioxide
DRM
Dry Reforming of Methane
FID
Flame Ionization Detector
GC
Gas Chromatograph
H
Hydrogen
MOF
Metal Organic Framework
Syngas
Synthesis Gas
TCD
Thermal Conductivity Detector
ZIF
Zeolitic Imidazolate Framework
viii
LIST OF EQUATIONS
Page
DRY REFORMING OF METHANE ..........................................................................
2
STEAM REFORMING OF METHANE .....................................................................
2
MOLAR FR FACTOR ................................................................................................
20
CONVERSION OF METHANE .................................................................................
20
METHANE DECOMPOSITION ................................................................................
27
ix
CHAPTER 1
INTRODUCTION
Hydrogen is a valuable gas for use in chemical processes across a number of
different industries. Because of this, efficient hydrogen production methods are of
substantial interest. Additionally, increased awareness in the rising concentrations of
greenhouse gases in the Earth’s atmosphere encourages the utilization and research of
methods that will help mitigate environmental impact. The greenhouse gas effect is a
phenomenon where atmospheric gases, namely water vapor, carbon dioxide, and
methane, absorb outgoing infrared radiation that results in the rising of the earth’s
temperature [1]. Catalytic reforming of methane with carbon dioxide, also known as dry
reforming, is one potential solution to these challenges to the industry because it utilizes
some of the most abundant greenhouse gases in our atmosphere as reactants to produce
hydrogen. Dry reforming of methane (1) utilizes carbon dioxide and methane and
converts them into carbon monoxide and hydrogen gas, also known as synthesis gas
(syngas) [2]. Dry reforming is preferable over traditional steam reforming (2) for two
reasons. First, dry reforming is preferable because it utilizes the carbon dioxide present
in natural gas fields and lowers the CO/H2 syngas ratio for the subsequent reaction to the
desired products [3]. Second, there is no need to separate CO2 from the product as would
be needed during traditional steam reforming. During steam reforming, the two products
resulting from the reaction are CO2 and H2 and therefore the CO2 would need to be
1
removed from the hydrogen before the hydrogen was usable. The separation of CO2 is a
costly and energy intensive process and therefore not desirable [4].
CH4 + CO2 ↔ 2 CO + 2 H2
(∆Hº = 247 kJ/mol)
(1)
CH4 + 2 H2O ↔ CO2 + 4 H2
(∆Hº = 165 kJ/mol)
(2)
Commercialization of dry reforming would be an ideal solution to help mitigate
the greenhouse gases in the atmosphere while promoting industrial chemical processes.
One challenge to this solution has been finding a catalyst that has both high activity and
high stability. Various studies exploring different types of catalysts that could be suitable
for dry reforming of methane have been conducted [5].
Carbon dioxide is not only naturally occurring in the atmosphere but also a result
of the burning of fossil fuels, changes in land-use, and other industrial processes. It is the
principal anthropogenic gas that is thought to affect the Earth’s radiative balance and
because of this there is thought to be a close correlation between carbon dioxide and the
rise in the Earth’s temperature [1].
2
FIGURE 1. Land air temperature anomalies, for global, north hemisphere and south
hemisphere for the period of 1850 to 2007.
3
CHAPTER 2
BACKGROUND INFORMATION
The Utility of Hydrogen Production
Hydrogen, in its monatomic form, is the most abundant chemical element in the
universe and contributes to approximately 75% of normal matter by mass [6]. Despite its
abundance, naturally occurring monatomic hydrogen is relatively rare on Earth. This is
because the gas is so light that it gains enough velocity to leave our atmosphere from
collisions with other gases [7]. In hydrogen’s elemental form, however, it is a versatile
and valuable substance that can be used in a variety of chemical processes, many of
which have industrial application. Hydrogen’s versatility comes from the fact that it
contains only one proton and one electron and is therefore able to readily either donate or
accept an electron in order to react with or saturate other molecules. In the petrochemical
industry, hydrogen is used to process lower grade hydrocarbons into more valuable
hydrocarbons through hydrodealkylation (removal of functional groups),
hydrodesulfurization (removal of sulfur), and hydrocracking (molecule saturation) [8].
Often, refineries have their own supplementary supply of hydrogen from the hydrogen
plant in order to provide for the aforementioned processes [9]. Industrially produced
hydrogen can also be reacted with elemental nitrogen in order to produce ammonia,
which is a valuable substance to the agricultural and chemical industries. Furthermore,
the creation of saturated fats, such as margarine, is made possible through the
4
hydrogenation of unsaturated fats and oils. These applications illustrate the demand in
today’s industry for an economical solution to hydrogen production [7].
Hydrogen Production
A common method for the production of hydrogen in today’s industry is through
reforming. Reforming is a technique used in chemistry or chemical engineering to
rearrange the molecular structure of lower grade or undesirable hydrocarbons in order to
alter their properties into a more desirable state. There are two types of reforming:
thermal and catalytic. Thermal reforming achieves results by exposing the reactants to
high temperatures and pressures. In catalytic reforming, similar results are achieved
using a catalyst. A catalyst is a substance that improves the reaction rate of a chemical
reaction without itself being changed or consumed [10]. The process of catalytic
reforming is a strongly endothermic conversion, meaning the process requires a great
amount of heat in order for the reaction to proceed [11]. During the reaction, the
hydrocarbons are converted with either carbon dioxide (dry reforming as seen in reaction
1) or steam (steam reforming as seen in reaction 2) in order to produce syngas [2].
Syngas is simply a mixture of carbon monoxide and hydrogen. The product of interest in
the syngas production is hydrogen [12]. It should be noted that dry reforming presents a
more economical solution than steam reforming which also includes added environmental
benefits such as upgrading of biogas (a renewable resource composed mostly of methane
and carbon dioxide) and the utilization of two greenhouse gases [4].
The catalysts and energy required to perform dry reforming can become costly
when used industrially. The goal of this research was both to test the hydrogen yields of
different catalysts as well as to explore the possibility of producing hydrogen with a
5
catalyst at lower temperatures to determine the feasibility of significantly reduced
production costs when applied commercially.
Catalyst Selection
For dry reforming the Noble Metals (Rh, Ru, Pt, and Pd) in addition to the nonnoble metal, Ni, are most commonly used for active components. In addition, the catalyst
supports used are: Al2O3, SiO2, ZrO2, and La2O3 [5]. Supported noble metal catalysts
exhibit considerable catalytic activity and are less sensitive to carbon deposition but nonnoble metal catalysts are more available and cost effective [5]. Carbon deposits present a
problem where the catalytic pores are blocked leading to the deactivation of the catalyst
through active site blockage. Fortunately, by using adequate promoters and modifying
catalysts supports, carbon formation upon the catalyst can be mitigated. Various
promoters and supports have been investigated [13]. As previously mentioned, it is
commonly known that noble metals inhibit coke formation. Furthermore, it was found
that adding noble metals to Nickel based catalysts can promote the reducibility of Ni and
stabilize its degree of reduction during the catalytic process [13]. Additionally, it was
found that the catalytic activity for the auto thermal reforming of methane was increased
when small amounts of Platinum (Pt) were added to the catalyst Ni/Al2O3 [13]. A
catalyst with increased stability, activity, and reduced carbon formation is a feasible
choice for utilization during hydrogen production by dry methane reforming [13]. The
two monometallic Nickel based catalysts chosen for this experiment were Ni/Al2O3 and
Ni/CeZrO2. Additionally, their bimetallic versions were also investigated: PtNi/Al2O3
and PtNi/CeZrO2 .
6
A fifth catalyst based on a new support, Zeolitic Imidazolate Framework (ZIF)-8,
was also investigated (Pt/ZIF). Zeolites, an aluminosilicate-based material, are an
essential synthetic product with valuable uses as catalysts in the petroleum refining
industry. ZIFs are a new class of porous crystals whose three-dimensional structure
consist of tetrahedral metal ions connected by imidazolates at a 145° angle [14]. ZIFs,
although a subfamily of metal-organic frameworks (MOFs), are quite chemically stable.
ZIF-8, in particular, is both chemically and thermally stable. ZIF-8 can withstand boiling
in water, alkaline solutions, and refluxing in organic solvents without losing crystallinity
or porosity. Furthermore, ZIF-8 is thermally stable up to 500°C [14]. Additionally, ZIFs
have an affinity for capturing carbon dioxide and can separate carbon dioxide from gas
mixtures and store carbon dioxide within the framework [14].
7
CHAPTER 3
EXPERIMENTAL
Setup
The laboratory and equipment used during this experiment were acquired and set
up by Dr. Sepideh Faraji and her students during Summer 2011. A plug flow reactor in
which the reagents flow at an assumed constant velocity through the reactor with no
upstream or downstream mixing was used [15]. The reactor received a feed from up to
four gas lines: methane, carbon dioxide, argon, and mix gas. The methane and carbon
dioxide feeds were the reactants during the experiment. These two lines were fed in
equal proportions through the plug flow reactor, in which the gases passed through the
catalyst at a constant temperature. The purpose of the argon gas line was to purge the
system of residual gases before starting the calibration and test runs. Finally, the mix gas
feed was used to calibrate the gas chromatograph (GC) before each test run. For this
reason, the mix gas consisted of set percentages of each of the gases that would be
measured by the GC during the reaction: the two reactant gases, methane and carbon
dioxide; and the two product gases, carbon monoxide and hydrogen. The gases used
during this experiment were obtained from Airgas and the flow rates of the different
feeds were controlled with a Porter Model CM-400 Mass Flow Controller manufactured
by Parker Hannifin Corporation. An Omega model CN7200 microprocessor-based
temperature process control unit controlled and monitored the reactor’s furnace
temperature.
8
The resulting product exiting the reactor consisted of a mix of carbon monoxide
and hydrogen gas. The carbon monoxide and hydrogen gas products passed through a
valve where the gas stream was routed directly to the fume hood or to the GC, where the
percentage of each gas in the stream was measured. The GC utilized for this experiment
was a Model 8610C Gas Chromatograph manufactured by SRI Instruments. The GC
worked in conjunction with PeakSimple, a computer program, to sample and record the
data from the gas injections. After leaving the GC, the gas stream flowed to the fume
hood for proper ventilation. This process is shown in Figure 2.
FIGURE 2. Schematic of experimental setup consisting of plug-flow reactor, gas
chromatograph, fume hood, and a variety of gas feeds.
Additionally, an image of the actual laboratory setup at California State
University, Long Beach can be seen in Figure 3.
9
Mass Flow
Controller
Feed
Valves
GC display
and control
computer with
PeakSimple
Plug-Flow
Reactor
Gas
Chromatograph
Temperature
Controller
FIGURE 3. Image of laboratory setup at Cal State - Long Beach.
Gas Chromatograph
Chromatography is a laboratory technique used to separate mixtures. The product
of interest is mixed with a fluid, known as the mobile phase, and travels through the
stationary phase where the elemental structures in the product of interest separate because
their different physical properties cause them to travel at different speeds [16]. In gas
chromatography (GC), the mobile phase is a gas. It is known as the carrier gas and is
usually helium or another type of inert gas [17]. For the purpose of this work, however,
helium as the carrier gas may have caused difficulties with the GC. This difficulty is
caused because the product of interest in our reaction is hydrogen and the thermal
conductivity of hydrogen is very close to that of helium. The fidelity of the GC may not
10
be sufficient to determine the hydrogen and helium as two separate gases leading to false
positives for hydrogen production. In order to avoid this, the carrier gas chosen was
ultra-high purity argon. The carrier gas then moves the products through the stationary
phase, or a packed column in the case of a GC. The compounds in the product interact
with the walls of the column and elute at different times. This is known as the retention
time for each compound and will correlate to a peak location on the resulting graph that is
produced by the GC. The retention time, or location, of the peak is what differentiates
compounds and allows one to determine which peak represents each compound. The
areas under each peak are then calculated to find the percent composition of each
compound in the feed [16].
Gas Chromatographs typically have two types of detectors, a flame ionization
detector (FID) and a thermal conductivity detector (TCD) [16]. An FID is more sensitive
to hydrocarbons and is compatible with helium, nitrogen, and argon as carrier gases [18].
TCDs are universal detectors that can detect nearly any compound such as air, hydrogen,
carbon monoxide, and many other compounds. TCDs tend to work best with helium,
nitrogen, argon, or even hydrogen as carrier gases [19]. For these reasons, during the
experiment the FID will be used as the primary detector with TCD data collected as a
backup for data comparison.
The GC was set to take a sample of the product gas every thirty minutes. This
injection was analyzed by both detectors and then translated into PeakSimple
Chromatography Software that displays the amount of a component versus retention time,
graphically. This information was used to determine the percent composition of the
syngas produced.
11
Procedure
The first run was conducted using the catalyst Ni/Al2O3. A personal gas monitor
was used to ensure the laboratory conditions were safe. Then, the hood was turned on. A
glass tube approximately 18” in length was cleaned on both the inside and the outside
with acetone and then blown dry with clean air.
The mass balance was tared with a weigh paper and then 0.0045 g of catalyst was
weighed onto the paper. The glass tube was packed with quartz wool and centered in the
tube.
The pre-weighed catalyst was loaded into the tube so that it was suspended in the
middle of the tube upon the quartz wool. The glass tube was carefully placed through the
reactor so that the catalyst would be situated in the center of the reactor. The tube was
then fixed to the copper tubing on each side of the reactor. The glass tube was sealed
with rubber O-rings and the fixtures were tightened carefully so as to not exceed a
pressure that would crack the glass tube.
Each side of the reactor (top and bottom) was packed with fiberglass around the
openings, with the exception of the glass tube near the catalyst to ensure that minimal
heat would escape from the furnace while also not insulating the catalyst bed from the
heat.
The ultra-high purity argon cylinder and hydrogen cylinder were opened so that
they may flow into the GC. This is needed for proper operation of the GC. The reason
argon was chosen over helium as the carrier gas is due to the difficulty of hydrogen
detection in the GC in the presence of helium versus argon. The GC was then turned on.
12
The computer and Peak Simple software were turned on to ensure proper connection to
the GC.
The mix gas cylinder was opened and the mix valve on the front of the instrument
was routed to the bypass line, which feeds directly to the GC for calibration prior to
execution of the reaction. The regular argon cylinder was also opened and the argon
valve on the front of the instrument was routed to the reactor. The argon was used to
purge the system of any residual gases prior to the test.
Thus far, ultra high purity argon and hydrogen were going directly to the GC, mix
gas was flowing through the bypass line into the GC, and the regular argon was flowing
through the reactor and into the hood in order to purge the system without disrupting the
GC calibration.
The system was checked for leaks using gas leak detection fluid and any
questionable joints were tightened. The flow rates were then adjusted using a Porter
Model CM-400 Mass Flow Controller. The mix gas and argon flow rates were set to 5.00
mL/min. The gas factors were also set on the flow controller as follows: Ar = 1.443,
CO2 = 0.745, CO = 1.001, CH4 = 0.731, H2 = 1.021.
The GC was checked to ensure the Carrier 1 and Hydrogen 1 lights were green
indicating positive gas flow to the GC. The carrier was set to 30 psi and the hydrogen
was set to 20 psi. The mix gas was set to flow for 20 minutes to allow the percentages of
each gas to reach equilibrium before they were injected into the GC.
The reactor’s furnace was then turned on using the Omega CN 7200 temperature
process control unit. The controller was set to the following temperature profile: ramp up
13
from ambient temperature (25°C) to 800°C over 2 hours, hold 800°C for 15 hours, then
shut off. The temperature profile can be seen in Figure 4.
FIGURE 4. Temperature profile for plug-flow reactor furnace.
The GC was programmed to take an injection every 30 minutes. Four injections
were needed of the mix gas for calibration and so the reactor’s furnace was set to heat to
the desired temperature over a span of two hours so that the GC could be calibrated in the
same amount of time. The regular argon flushed the reactor during the time that the
furnace was heating and the GC was calibrating.
Once the calibration was complete, the reaction began. The mix gas cylinder was
turned off and mix valves were closed on the instrument. The regular argon cylinder was
14
turned off and the argon valves were closed on the instrument. The three-way valve on
the exiting stream of the reactor was switched to route the gas to the GC.
The methane and carbon dioxide cylinders were turned on and their
corresponding valves on the instrument were opened. Both the methane and carbon
dioxide feeds were routed to the reactor. The methane and carbon dioxide flows were
adjusted on the flow controller to 5.00 mL/min.
The flow measurements taken at the hood were 4.52 mL/min for methane and
4.63 mL/min for carbon dioxide. Although the flow controller was set to 5 mL/min, the
actual flow rates measured at the hood were slightly less than 5 mL/min. This could have
been due to imperfections in the joints of the laboratory setup resulting in some loss of
flow.
The GC was set up to take twenty-eight injections over the next fourteen hours or
one injection every thirty minutes. Peak Simple was closely monitored to ensure that the
program was recording the areas of the correct curves during each injection. An FID was
used to measure the amount of methane, carbon dioxide, and carbon monoxide in the
stream. A TCD was used to measure the hydrogen gas in the stream.
After the twenty-eighth injection, the GC was set to automatically stop. After the
GC was turned off, the ultra-high purity argon and hydrogen cylinders were closed. The
temperature controller for the furnace was then turned off and the reactor was allowed to
cool. The remaining cylinders were closed and the valves on the instrument were also
closed so that nothing more would flow into the reactor.
After the reactor was cooled to room temperature, the fiberglass was unpacked,
and the glass tube was removed. The catalyst and quartz wool were removed and
15
disposed of properly. The glass tube was cleaned inside and out with acetone in
preparation for the next run.
All steps were repeated for each catalyst run. The catalysts, amounts, and flow
rates for each run are recorded in the tables below.
Test Runs
A total of eleven runs were performed during the course of this research. The first
four were to compare two monometallic catalysts to their bimetallic versions. A crack
developed in the glass tube during the course of the third run that resulted in a leak. This
catalyst had to be re-run. In addition, the effects of varying the amount of Ni/Al2O3 were
to be investigated. Four additional runs were performed to investigate this concept. The
data from the initial four milligram run would be used. In addition, a second run was
performed with four milligrams of catalyst, followed by two runs with eight milligrams
of catalyst, and one run with ten milligrams of catalyst. Finally, PtNi/CeZrO2 was
compared to Pt/ZIF at the reduced temperature of 490°C. As mentioned previously, ZIF8 is thermally stable only up to a temperature of 500°C [14]. In order to ensure that the
catalyst was acting at its full potential during the test, 490°C was not exceeded.
TABLE 1. First Run
Catalyst
Ni/Al2O3
Mass
0.0045 g
Flow Rate of CH4
4.52 mL/min
Flow Rate of CO2
4.63 mL/min
Reaction Temperature
800°C
16
TABLE 2. Second Run
Catalyst
PtNi/Al2O3
Mass
0.0042 g
Flow Rate of CH4
4.61 mL/min
Flow Rate of CO2
4.69 mL/min
Reaction Temperature
800°C
TABLE 3. Third Run
Catalyst
Ni/CeZrO2
Mass
0.0040 g
Flow Rate of CH4
4.58 mL/min
Flow Rate of CO2
4.65 mL/min
Reaction Temperature
800°C
(Leak during run)
TABLE 4. Fourth Run
Catalyst
PtNi/CeZrO2
Mass
0.0040 g
Flow Rate of CH4
4.63 mL/min
Flow Rate of CO2
4.67 mL/min
Reaction Temperature
800°C
17
TABLE 5. Fifth Run
Catalyst
Ni/Al2O3
Mass
0.0080 g
Flow Rate of CH4
4.50 mL/min
Flow Rate of CO2
4.57 mL/min
Reaction Temperature
800°C
TABLE 6. Sixth Run
Catalyst
Pt/ZIF
Mass
0.0115 g
Flow Rate of CH4
4.52 mL/min
Flow Rate of CO2
4.59 mL/min
Reaction Temperature
490°C
TABLE 7. Seventh Run
Catalyst
Ni/Al2O3
Mass
0.0039 g
Flow Rate of CH4
3.38 mL/min
Flow Rate of CO2
3.40 mL/min
Reaction Temperature
800°C
18
TABLE 8. Eighth Run
Catalyst
Ni/Al2O3
Mass
0.0080 g
Flow Rate of CH4
3.50 mL/min
Flow Rate of CO2
3.20 mL/min
Reaction Temperature
800°C
TABLE 9. Ninth Run
Catalyst
Ni/Al2O3
Mass
0.0101 g
Flow Rate of CH4
3.30 mL/min
Flow Rate of CO2
3.10 mL/min
Reaction Temperature
800°C
TABLE 10. Tenth Run
Catalyst
Ni/CeZrO2
Mass
0.0040 g
Flow Rate of CH4
4.58 mL/min
Flow Rate of CO2
4.65 mL/min
Reaction Temperature
800°C
(re-do of leaky run)
19
TABLE 11. Eleventh Run
Catalyst
PtNi/ CeZrO2
Mass
0.0102 g
Flow Rate of CH4
4.63 mL/min
Flow Rate of CO2
4.67 mL/min
Reaction Temperature
490°C
Calculations
The first calculation performed for each test run is the calibration of the gas
chromatograph. Four calibration injections were taken prior to each test run. As with the
actual run, the first injection is disregarded. The average area under the curves for the
second through fourth injection is calculated for each compound. The average area is
then divided by its corresponding known percentage from the mix gas tank to find the
slope. The values for each curve obtained during the test runs are divided by the slope in
order to ensure the results are calibrated. From this result the molar FR factor (3) can be
calculated and then used to calculate the methane conversion (4) value.
20
(3)
(4)
TABLE 12. Side-by-Side Comparison of All Test Runs
Run
Ni/Al2O3
1
4 mg
800°C
PtNi/Al2O3
Ni/CeZrO2
4mg (leak)
800°C
3
4 mg
800°C
4
8 mg
800°C
11.5 mg
490°C
6
7
4 mg
800°C
8
8 mg
800°C
9
10 mg
800°C
10
Pt/ZIF
4 mg
800°C
2
5
PtNi/
CeZrO2
4 mg
(redo)
800°C
10.2 mg
490°C
11
21
CHAPTER 4
RESULTS AND DISCUSSION
Four Catalysts in Equal Quantities at the Same Temperature
The first evaluation compared the methane conversion results of the four different
catalysts at reaction temperatures of 800°C. Logically, a methane conversion of 100%, or
1.00, would be ideal. The conversion rate provides an idea of how much of the methane
feed was successfully converted into product during the reaction. The hydrogen to
carbon monoxide ratio was evaluated. As seen in Equation 1, a 1:1 ratio of hydrogen to
carbon monoxide was expected. For the first evaluation, two monometallic catalysts,
Ni/Al2O3 and Ni/CeZrO2, and their bimetallic versions, PtNi/Al2O3 and PtNi/ CeZrO2,
were used. Each run was performed at 800°C with approximately four milligrams of
catalyst at atmospheric pressure. For specific details on the amounts of catalysts used in
each of these test runs, refer to Chapter 3.
Because of the FID’s sensitivity for hydrocarbons and the TCD’s ability to detect
hydrogen, both the FID and the TCD were utilized to record data. To ensure accurate
data collection, data acquired by both sensors was compared. The first one or two
injections into the gas chromatograph were removed from data of interest. These first
injections were ignored due to inaccuracies of these first measurements compared to the
remainder of the experimental measurements.
22
Figure 5 and Figure 6 show the results for the methane conversion of the four
catalysts as measured by the FID sensor and TCD sensor, respectively. Both sensors
reveal that the NiAl2O3 had the highest methane conversion value of the four catalysts.
1.0000
0.9000
Fractional Conversion
0.8000
0.7000
0.6000
Ni/Al2O3
0.5000
PtNi/Al2O3
0.4000
Ni/CeZrO2
0.3000
PtNi/CeZrO2
0.2000
13.0
12.0
11.0
10.0
9.0
8.0
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0.0000
0.0
0.1000
Time (hours)
FIGURE 5. Methane conversion of 4 different catalysts, in equal quantities, at 800°C
through a plug flow reactor utilizing the FID sensor in the GC.
Figures 7 and 8 below show the carbon dioxide conversions from the FID and
TCD sensors respectively. Similar to the methane conversion charts, the carbon dioxide
chart from the FID sensor shows the catalyst NiAl2O3, as having the highest carbon
dioxide conversion rate. As expected, the hydrogen to carbon monoxide ratio was
approximately 1:1 slightly favoring hydrogen. Figure 9 and Figure 10 below show that
both FID and TCD sensors measured similar values for hydrogen to carbon monoxide
23
1.2000
Fractional Conversion
1.0000
0.8000
Ni/Al2O3
0.6000
PtNi/Al2O3
Ni/CeZrO2
0.4000
PtNi/CeZrO2
13.0
12.0
11.0
10.0
9.0
8.0
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0.0000
0.0
0.2000
Time (hours)
FIGURE 6. Methane conversion of 4 different catalysts, in equal quantities, at 800°C
through a plug flow reactor utilizing the TCD sensor in the GC.
ratio. This 1:1 ratio means that the amount of hydrogen produced by the reaction was
equivalent to the amount of carbon monoxide produced. Since hydrogen is the product of
interest, finding a catalyst whose results favor hydrogen would be preferred.
The Effect of Catalyst Mass
The second evaluation was performed to determine if increasing the mass of a
single catalyst while holding the flow rates of the reactants and temperature constant
would result in improved conversion. Four, eight, and ten milligrams of catalyst were
used for the tests. Given the results from the previous experiment, the catalyst chosen
was Ni/Al2O3 at 800°C. The results demonstrated no significant difference in the
methane conversion percentages between the varying amounts of catalyst as seen in
Figure 11. This could mean one of two things. First, the reaction might have reached an
24
1.0000
0.9000
Fractional Conversion
0.8000
0.7000
0.6000
Ni/Al2O3
0.5000
PtNi/Al2O3
0.4000
Ni/CeZrO2
0.3000
PtNi/CeZrO2
0.2000
13.0
12.0
11.0
10.0
9.0
8.0
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0.0000
0.0
0.1000
Time (hours)
FIGURE 7. Carbon Dioxide conversion of 4 different catalysts, in equal quantities, at
800°C through a plug flow reactor utilizing the FID sensor in the GC.
1.2000
Fractional Conversion
1.0000
0.8000
Ni/Al2O3
0.6000
PtNi/Al2O3
Ni/CeZrO2
0.4000
PtNi/CeZrO2
13.0
12.0
11.0
10.0
9.0
8.0
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0.0000
0.0
0.2000
Time (hours)
FIGURE 8. Carbon Dioxide conversion of 4 different catalysts, in equal quantities, at
800°C through a plug flow reactor utilizing the TCD sensor in the GC.
25
4.50
4.00
H2/CO Ratio
3.50
3.00
2.50
NiAl2O3
2.00
Pt/NiAl2O3
1.50
NiCeZrO2
1.00
Pt/NiCeZrO2
13.0
12.0
11.0
10.0
9.0
8.0
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0.00
0.0
0.50
Time (hours)
FIGURE 9. Hydrogen to Carbon Monoxide ratio of 4 different catalysts, in equal
quantities, at 800°C through a plug flow reactor utilizing the FID sensor in the GC.
5.00
4.50
4.00
H2/CO Ratio
3.50
3.00
Ni/Al2O3
2.50
PtNi/Al2O3
2.00
Ni/CeZrO2
1.50
PtNi/CeZrO2
1.00
13.0
12.0
11.0
10.0
9.0
8.0
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0.00
0.0
0.50
Time (hours)
FIGURE 10. Hydrogen to Carbon Monoxide ratio of 4 different catalysts, in equal
quantities, at 800°C through a plug flow reactor utilizing the TCD sensor in the GC.
26
equilibrium point at 800°C; or second, given that the flow rates of the reactants were held
constant, it is probable that the limiting factor in this test was the amount of reactant
provided and increasing the amount of catalyst did not increase the efficiency of the
conversion. It should be noted that the ratio of hydrogen to carbon monoxide is greater
than one for all ratios for all catalysts demonstrating each catalysts’ propensity of
hydrogen production over carbon monoxide. This also indicates that there were other
reactions occurring as well that were contributing to the hydrogen production, such as
steam reforming of methane (2) or methane decomposition (5) [4]. This means the
reaction mechanism is not as simple as what was expected.
CH4 + H2O ↔ CO + 3 H2
(∆Hº = 206 kJ/mol)
(2)
CH4 ↔ C + 2 H2
(∆Hº = 75 kJ/mol)
(5)
Additionally, as the amount of catalyst is increased from four to eight milligrams, the
hydrogen to carbon monoxide ratio also increases. This is demonstrated in both the FID
and TCD sensors as seen in Figures 15 and 16. Furthermore, when the amount of catalyst
is increased from eight to ten milligrams, the ratio of hydrogen to carbon monoxide
production increases yet again when analyzing the TCD data as seen in Figure 16. Figure
15 shows conflicting data from the FID sensor, which actually shows the hydrogen to
carbon monoxide ratio decreasing with the increase to ten milligrams of catalyst.
However, this could be due to the fact that the FID is not as suitable a detector for
measuring hydrogen as the TCD [19].
27
1.0000
0.9000
Fractionial Conversion
0.8000
0.7000
0.6000
4mg Run 1
0.5000
8mg Run 1
0.4000
4 mg Run 2
0.3000
8 mg Run 2
0.2000
10 mg Run 1
13.0
12.0
11.0
10.0
9.0
8.0
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0.0000
0.0
0.1000
Time (hours)
FIGURE 11. Methane conversion of Ni/Al2O3, in different quantities, at 800°C through a
plug flow reactor utilizing the FID sensor in the GC.
0.9000
0.8000
Fractional Conversion
0.7000
0.6000
4 mg Run 1
0.5000
8 mg Run 1
0.4000
4 mg Run 2
0.3000
8 mg Run 2
0.2000
10 mg Run 1
13.0
12.0
11.0
10.0
9.0
8.0
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0.0000
0.0
0.1000
Time (hours)
FIGURE 12. Methane conversion of Ni/Al2O3, in different quantities, at 800°C through a
plug flow reactor utilizing the TCD sensor in the GC.
28
1.0000
0.9000
Fractionial Conversion
0.8000
0.7000
0.6000
4mg Run 1
0.5000
8mg Run 1
0.4000
4 mg Run 2
0.3000
8 mg Run 2
0.2000
10 mg Run 1
13.0
12.0
11.0
10.0
9.0
8.0
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0.0000
0.0
0.1000
Time (hours)
FIGURE 13. Carbon Dioxide conversion of Ni/Al2O3, in different quantities, at 800°C
through plug flow reactor utilizing the FID sensor in the GC.
1.2000
Fractional Conversion
1.0000
0.8000
4 mg Run 1
0.6000
8 mg Run 1
4 mg Run 2
0.4000
8 mg Run 2
10 mg Run 1
13.0
12.0
11.0
10.0
9.0
8.0
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0.0000
0.0
0.2000
Time (hours)
FIGURE 14. Carbon Dioxide conversion of Ni/Al2O3, in different quantities, at 800°C
through a plug flow reactor utilizing the TCD sensor in the GC.
29
2.50
H2/CO Ratio
2.00
1.50
4mg Run 1
8mg Run 1
1.00
4 mg Run 2
8 mg Run 2
0.50
13.0
12.0
11.0
10.0
9.0
8.0
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0.0
0.00
10 mg Run 1
Time (hours)
FIGURE 15. Hydrogen to Carbon Monoxide ratio of Ni/Al2O3, in different quantities, at
800°C through a plug flow reactor utilizing the FID sensor in the GC.
3.00
H2/CO Ratio
2.50
2.00
4 mg Run 1
1.50
8 mg Run 1
4 mg Run 2
1.00
8 mg Run 2
10 mg Run 1
13.0
12.0
11.0
10.0
9.0
8.0
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0.00
0.0
0.50
Time (hours)
FIGURE 16. Hydrogen to Carbon Monoxide ratio of Ni/Al2O3, in different quantities, at
800°C through a plug flow reactor utilizing the TCD sensor in the GC.
30
New Catalyst, Pt/ZIF, Compared to Traditional Bimetallic Catalyst
The third experiment utilized a different type of catalyst support than used in the
previous two experiments, zeolitic imidazolate framework (ZIF). The platinumsupported ZIF is utilized at a lower temperature than the usual 800 °C because ZIFs are
only thermally stable up to 500 °C [14]. However, this upper reaction temperature
limitation could be considered a positive characteristic when evaluated with the
significant cost savings potential when applied commercially. Methane conversion and
hydrogen-to-carbon monoxide ratios of the reaction utilizing platinum supported ZIF-8
would be compared to the bimetallic catalyst, PtNi/CeZrO2. The catalysts were used in
equal amounts and were processed through the plug-flow reactor at the reduced
temperature of 490°C. Our goal is to find a low temperature catalyst with high surface
area for dry reforming of methane.
The methane conversion results of both PtNi/CeZrO2 and Pt/ZIF catalysts were
significantly lower than the percent conversion in any of the previous tests. The
temperature, which was reduced by 38.8%, yielded methane conversion values for
PtNi/CeZrO2 that were on average 62.2% lower than the conversion values for tests ran at
the full 800°C as seen in Figure 17. Because of the endothermicity of the dry reforming
reaction, an increase in temperature leads to an increase in methane conversion and
therefore a decrease in methane conversion at a lower temperature was expected [20].
However, it is important to note that while the overall conversion rate was lower due to
the lower temperature of the tests, the percent methane conversion from the ZIF catalyst
is very similar to the percent conversion of the PtNi/CeZrO2. The same observation is
made when comparing the percent carbon dioxide conversion of ZIF and PtNi/CeZrO2.
31
Figure 19 details FID sensor data demonstrating hydrogen-to-carbon monoxide
ratios that greatly favor hydrogen production in the reaction using ZIF-8 as the catalyst.
Additionally the hydrogen-to-carbon monoxide ratio for the PtNi/CeZrO2 yielded similar
results to all of the previous test runs of one-to-one. These results imply that even at
significantly lower production temperatures, ZIF is capable of converting methane and
favoring hydrogen production over carbon monoxide by an average factor of 2.4.
There are several reasons why achieving results with the ZIF-8 catalyst is
favorable. First, the Pt/ZIF reaction can be ran at a lower temperature resulting in
lowered production costs. Second, despite lower temperatures, the Pt/ZIF reaction favors
the production of hydrogen, the desirable product, over carbon monoxide. Lastly,
although less of the methane was converted during the run, the remaining methane is not
lost. It can be salvaged and continued to be fed through the reaction resulting in even
more hydrogen production.
32
1.0000
0.6000
Pt/ZIF FID
Pt/ZIF TCD
0.4000
PtNi/CeZrO2 FID
PtNi/CeZrO2 TCD
-0.2000
13.0
12.0
11.0
10.0
9.0
8.0
7.0
6.0
5.0
4.0
3.0
2.0
0.0000
1.0
0.2000
0.0
Fractional Conversion
0.8000
Time (hours)
FIGURE 17. Methane conversion of 2 catalysts, in equal quantities, at 490°C through a
plug flow reactor utilizing both the FID and TCD sensor in the GC.
0.8000
Fractional Conversion
0.7000
0.6000
0.5000
Pt/ZIF FID
0.4000
Pt/ZIF TCD
0.3000
PtNi/CeZrO2 FID
0.2000
PtNi/CeZrO2 TCD
13.0
12.0
11.0
10.0
9.0
8.0
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0.0000
0.0
0.1000
Time (hours)
FIGURE 18. Carbon Dioxide conversion of 2 catalysts, in equal quantities, at 490°C
through a plug flow reactor utilizing both the FID and the TCD sensor in the GC.
33
6.00
H2/CO Ratio
5.00
4.00
Pt/ZIF FID
3.00
Pt/ZIF TCD
PtNi/CeZrO2 FID
2.00
PtNi/CeZrO2 TCD
13.0
12.0
11.0
10.0
9.0
8.0
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0.00
0.0
1.00
Time (hours)
FIGURE 19. Hydrogen to Carbon Monoxide ratio of 2 catalysts, in equal quantities, at
490°C through a plug flow reactor utilizing both the FID and TCD sensor in the GC.
34
CHAPTER 5
CONCLUSIONS
Carbon dioxide reforming, or dry reforming, is an essential technique that should
be further utilized in today’s industry to not only synthesize a valuable substance, but
simultaneously present a potential carbon footprint reduction by using a greenhouse gas
as a reagent. Furthermore, several monometallic and bimetallic catalysts have been
shown to be suitable for the production of hydrogen through dry reforming. Finally,
zeolitic imidazolate frameworks show great promise as a next-generation catalyst for use
in carbon dioxide reforming. Not only does the lower reaction temperature result in
significant production savings when applied industrially, but the resulting product ratio
greatly favors hydrogen and should be exploited for commercial use in dry reforming.
35
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36
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