1. Supported by a generous gift from The University of Wisconsin-Madison Graduate School and National Science Foundation through the University of
Wisconsin-Madison Materials Research Science and Engineering Center (DMR-0520527) and Nanoscale Science and Engineering Center (DMR-0425880).
Introduction Results and discussion
Additional information
Hypothesis
Conclusions
Next Steps
Method
Acknowledgements
The photo catalytic reduction of N2 to NH3 is typically hampered by
poor binding of N2 to catalytic materials and by the very high energy of
the intermediates involved in this reaction. The manufacture of
nitrogen fertilizers use about 2% of the world's annual energy
consumption which is not sustainable
in the long term. Our goal is to find a
simple way to reduce nitrogen
with minimum energy usage.
It was demonstrated that illuminated
hydrogen-terminated diamond yields
facile electron emission into water,
thus inducing reduction of N2 to NH3
at ambient temperature and pressure.
The result was not efficient which raised
the question:
How could we have a better efficiency ?
Does the pressure or the temperature affect the efficiency?
3 H2 (g) + N2 (g) 2 NH3 (g)
What would happen if we increase the pressure ?
By the law of equilibrium, the reaction would shift to the right which
leads to our supposition to have more Ammonia at higher-pressure.
Hydrogen termination of diamond samples:
Electrochemistry-grade boron-doped diamond was loaded in a
hydrogen plasma chamber constructed from a quartz tube repeatedly
evacuated and purged with hydrogen gas.
Photo catalytic measurements of nitrogen reduction to ammonia:
were performed using a 450 W high-pressure Hg/Xe lamp located
approximately 2 inches from the pressure chamber, which contained
the diamond sample and the H-cell containing 70 ml of NanoPure
saturated with N2.
70 ml of pure
water poured
into the H-cell
Sample Calculation:
Concentration of Ammonia at 0h:
H0= H0,1 – H0,0= 0.035 − 0.004 = 0.031
C0= (3.249 × 0.031) − 0.0227 = 0.078019 mg/l
Concentration of Ammonia at 2h
H2= H2,1 −H2,0= 0.047 − 0.003 = 0.044
C2= (3.249 × 0.044) − 0.0227 = 0.120256 mg/l
[NH3] in 70ml water between 0h-2h
[NH3]= (C2 − C0) × 70 = 2.9565 μg
As shown on the graph, the concentration of ammonia and impurities
increases as the pressure increases. The impurities are coming from the
saturated water that contained 99% of nitrogen and 1% of impurities.
This graph above shown the result of the dark reaction, which was done
without the presence of ultra-violet light. We observed a reaction going
through other than the reduction of nitrogen, which leads us to conclude
that some impurities might be present and affect the reaction. The
concentration of unknown increases as the pressure increases.
We can see on the graph that the concentration of ammonia increases as
the pressure increases. We found the concentration of ammonia by
subtracting the reaction with the UV light from the dark reaction.
Reduction of stable species, such as N2, via solvated electrons
presents interesting challenges and potential opportunities. The
present work provides a step toward the mechanism of these complex
processes as the pressure changes. Overall, it is found that the
reduction of N2 to NH3 respects the law of equilibrium. As we suppose
at the beginning the concentration of ammonia increases as the
pressure increases. The results supports our hypothesis. The question
remaining is:
Could we do another control reaction in addition to the dark
reaction ?
The next step is to do an additional control reaction in which we will
saturate water with argon instead with nitrogen; then we will be exactly
sure of the amount of ammonia product.
Andrew Greenberg
Sheri Severson
Cheri Barta
Anne Lynn Gillian-Daniel
Hamers’ group
Irradiating H-capped diamond with UV
light liberates electrons in water that
selectively convert N2 to NH3.
0
1
2
3
4
5
6
7
8
9
10
0 100 200 300 400 500 600
[NH3](μg)
Pressure (psi)
[NH3] + Impurities Vs. PressurePressure
(psi)
[NH3]
+
Impuritie
s (μg)
14.696 1.36759
100 1.81944
250 4.77603
350 5.91318
490 8.57736
450 W high-
Pressure
Hg/Xe lamp
(Daiel Instrument,
model# 66921)
mounted in an
Oriel lamp
housing located
approximately 10
inches from the
pressure
chamber
Pressure
(psi)
Impurities
(μg)
14.696 0.482299
100 0.68229
250 0.90972
350 1.13715
490 1.39201
Pressure
(psi)
[NH3]
(μg)
14.696 0.8853
100 1.36458
250 3.86631
350 4.77603
490 7.18535
H2 NH3
H0/H2: height of the curve at 0h/2h.
C0/C2: concentration of ammonia at
0h/2h.
Curve of absorbance of
ammonia at 2hours
reaction when the
pressure is 150psi.
Curve of absorbance of
ammonia at 0h.
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
0 100 200 300 400 500 600
Impurities(μg)
Pressure (psi)
Impurities Vs. Pressure
0
1
2
3
4
5
6
7
8
0 100 200 300 400 500 600
[NH3}(μg)
Pressure (psi)
Concentration of Ammonia Vs. Pressure