Infrared Studies of Ammonia Borane

Kevin Meaux

Alternatives to fossil fuels to power transportation are sought

To use hydrogen for fuel, a more effective way of storing H2 is needed

High volumetric density, hydrogen mass %, stability, and reversibility are desired

Liquid and gaseous H2 are not dense enough

Metal hydrides and similar compounds offer potential solutions

Background

For Comparison…

Ammonia Borane (H3N:BH3)

description Nonhazardous stable white powder1

Melting point 104 ⁰C (377 K)Density 0.78 g/cm3

Mass % H 19.6% 1

Hydrogen Density 0.153 g H/cm3 H3N:BH3

[1] Marder, T., Angewandte Chemie International Edition, 2007, 46, 8116–8118.

Mass % H of LiAlH4

10.6%

Mass % H of NaBH4

10.7%

Density of L H2 0.068 g/cm3

Goal For effective use, more info is needed on

the dehydrogenation process of ammonia borane (AB)

Important first steps involve developing a working experimental setup to study this change

Analysis Method

Infrared Spectroscopy Schematic http://solidstate.physics.sunysb.edu/book/prob/node111.html

Using Transmittance Fourier Transform Infrared Spectroscopy

Characterizes a substance by the vibration of its chemical bonds

KBr and NH3BH3 are mixed in a 25:1 ratio KBr alone and the KBr/AB mixture are pressed into a tungsten mesh in different spots Have varied the referencesalt, absolute amounts,and ratios

Original Experimental Setup

The IR Cell

Image produced by Oleg Byl

sample

referencetungstenmesh grid

copper leadsfor resistive heating

Sample is under rough vacuum for analysis (~9E-2 torr)

Heated and then allowed to cool under argon (~5 torr)

New spectra is taken at room temperature and rough vacuum

10%

Our findings * Literature 2 Assignment

3386 NH anti sym stretch3309 3337 NH sym stretch

3259 3224 ???3197 3164 ???

2427 B10H stretch

2380 2415 B11H stretch

2350 2340 BH stretch2116 ???

1656 ???1604 1608 NH deformation

1591 ???1558 1558 ???1376 1343 NH deform

1301 NH rock1252 ???1165 1186 BH deform1060 1060 B10H deform

1052 B11H deform

987 B10N stretch

968 B11N stretch

783 ???725 ???

603 BH rock

Peak Comparison Table

*This table comparesreference IR peaks forammonia borane withdata gathered for 300K

[2] JJ. Smith, K. S. Seshadri, and David White: J. Mol. Spec., 1973, 45, 327-337.

The 1126,2225, and 2291 peaks shown forming at 433 K correspond to KBH4 3

The 1959/2029 peaks formed at 913 K arelikely the formation of B11O2/B10O2 anions 4

The other peaks observed at 433 K do not fit

with borazine, boron oxides, or boron nitride

Analysis

[4] I.C. Hisatsune and Noelia Haddock Suarez: Inorganic Chemistry, 1964, 3, 168-174.

[3] K. B. Harvey and N. R. McQuaker: Canadian Journal of Chemistry, 1971, 49, 3272-3281.

Current Sample Prep Idea Had problemswith KBr reactivity inpellet preparation Instead it is preparedon a KBr window Dissolved AB in THF Deposited solution on KBr disk Boiled off THF (67 C) Mounted disk onto mesh

Thermocouple

KBr Window

AB solution deposited on KBr disk

2.9 mg NH3-BH3 dissolved in 0.7 mL THF and deposited on KBr disk. KBr disk is mounted on tungsten mesh, on which thermocouple was spot-welded. Sample was heated under 0.1 torr pressure and spectra collected at room temperature.

Thermal Dehydrogenation of NH3-BH3

Wavenumber (cm-1)600 900 1200 1500 1800 2100 2400 2700 3000 3300 3600 3900

RT

375o C455o C515o C

120o C

100o C

150o C275o C

2328 2370 32843248

226313951563

1663670

1129

1399

1054877

1243

H3N:BH3 at Room Temperature*Evaporated THF solution on

KBr window Pressed KBr Pellet Literature 2 Assignment

  3386 NH anti sym stretch3284 3309 3337 NH sym stretch3248 3259 3224 ???

3197 3164 ???  2427 B10H stretch

2370 2380 2415 B11H stretch2328 2350 2340 BH stretch

2116  ???1663  1656 ???

1604 1608 NH deformation  1591 ???

1563 1558 1558 ???1395 1376 1343 NH deform

  1301 NH rock1243 1252  ???1129 1165 1186 BH deform1054 1060 1060 B10H deform

  1052 B11H deform  987 B10N stretch  968 B11N stretch

783  ???725  ???

670  603 BH rock

Analysis The new sample prep method shows more

clearly resolved peaks The accuracy of temperatures needs to be

verified The peaks are shifted somewhat from

literature values The spectra demonstrates dehydrogenation

with heating Neither the KBH4 nor BO2

- peaks are seen

Summary AB can be useful as a hydrogen storage

media

More work needs to be done in characterizing its dehydrogenation

Current method yields noisy spectra but shows potential

Will be dealing with the noise issues in the near future

Acknowledgements

This work was supported by the National Science Foundation under EEC-NSF Grant # 1062943

I would like to thank Dr. Trenary and Dr. Jash for their

guidance, as well as Dr. Takoudis and Dr. Jursich for administrating the UIC REU program