Kinetics of the Interconversion of Parahydrogen and Orthohydrogen Catalyzed by Paramagnetic Complex Ions

Matsumoto, Mitsuru; Espenson, James H.

doi:10.1021/ja0524292

Cited by 51 publications

(51 citation statements)

References 68 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…Because para hydrogen is NMR-inactive, 23 the para hydrogen molecule has a spin of zero; the ortho hydrogen molecule has a spin of one. In the quantitative estimation of the hydrogen molecule by NMR, the estimated quantity should be corrected in terms of the ortho and para ratio of hydrogen.…”

Section: Exposure Pressure Dependency Of Dissolved Hydrogen In Nbrmentioning

confidence: 99%

Evaluation of hydrogen dissolved in rubber materials under high-pressure exposure using nuclear magnetic resonance

Fujiwara

Nishimura

2012

Polym J

View full text Add to dashboard Cite

Hydrogen molecules dissolved in rubber due to high-pressure hydrogen gas exposure have been analyzed using 1 H nuclear magnetic resonance (NMR) with solution and solid-state probes. To analyze the characteristics of dissolved hydrogen in rubber materials and to compare them with gaseous phase hydrogen, we measured the NMR spectra of gaseous phase hydrogen and evaluated the chemical shifts and pressure dependency. Measurement using a sealed tube and liquid phase probes enabled the simultaneous analysis of dissolved hydrogen in rubber and gaseous phase hydrogen eliminated from the rubber. Two peaks at 4.3 and 4.8 p.p.m. were observed in the 1 H MAS NMR of the rubber samples after high-pressure hydrogen exposure. Using information from the chemical shift of the free hydrogen gas and the time dependency of hydrogen quantification in the rubber, both of these peaks were confirmed to be attributable to dissolved hydrogen. Their differences in relaxation time confirmed that their mobilities were different. In conclusion, the hydrogen dissolved in acrylonitrile butadiene rubber exists in two different forms with different mobilities. The ratio of those two hydrogens differs and is affected by the exposure pressure and elimination process time.

show abstract

Section: Exposure Pressure Dependency Of Dissolved Hydrogen In Nbrmentioning

confidence: 99%

Evaluation of hydrogen dissolved in rubber materials under high-pressure exposure using nuclear magnetic resonance

Fujiwara

Nishimura

2012

Polym J

View full text Add to dashboard Cite

show abstract

“…This active interest in p − H 2 polarization has also prompted a number of theoretical studies investigating the mechanism of ortho and para interconversion in a variety of chemically relevant conditions [8,13,110,151].…”

Section: Applicationsmentioning

confidence: 99%

MRI of Heterogeneous Hydrogenation Reactions Using Parahydrogen Polarization

Burt

2008

View full text Add to dashboard Cite

The power of magnetic resonance imaging (MRI) is its ability to image the internal structure of optically opaque samples and provide detailed maps of a variety of important parameters, such as density, diffusion, velocity and temperature. However, one of the fundamental limitations of this technique is its inherent low sensitivity. For example, the low signal to noise ratio (SNR) is particularly problematic for imaging gases in porous materials due to the low density of the gas and the large volume occluded by the porous material. This is unfortunate, as many industrially relevant chemical reactions take place at gas-surface interfaces in porous media, such as packed catalyst beds. Because of this severe SNR problem, many techniques have been developed to directly increase the signal strength. These techniques work by manipulating the nuclear spin populations to produce polarized (i.e. non-equilibrium) states with resulting signal strengths that are orders of magnitude larger than those available at thermal equilibrium. 2This dissertation is concerned with an extension of a polarization technique based on the properties of parahydrogen. Specifically, I report on the novel use of heterogeneous catalysis to produce parahydrogen induced polarization and applications of this new technique to gas phase MRI and the characterization of micro-reactors. First, I provide an overview of nuclear magnetic resonance (NMR) and how parahydrogen is used to improve the SNR of the NMR signal. I then present experimental results demonstrating that it is possible to use heterogeneous catalysis to produce parahydrogen-induced polarization.These results are extended to imaging void spaces using a parahydrogen polarized gas. In the second half of this dissertation, I demonstrate the use of parahydrogen-polarized gasphase MRI for characterizing catalytic microreactors. Specifically, I show how the improved SNR allows one to map parameters important for characterizing the heat and mass transport in a heterogeneous catalyst bed. This is followed by appendices containing detailed

show abstract

“…Molecular hydrogen (H 2 ) exists as two nuclear spin isomers: the antisymmetric singlet nuclear spin state parahydrogen (pH 2 ) and the symmetric triplet spin nuclear state orthohydrogen (oH 2 ). The equilibrium distribution of the two isomers is a function of temperature.…”

Section: Introductionmentioning

confidence: 99%

“…At room temperature, the equilibrium composition is approximately 25 % pH 2 and 75 % oH 2 , a mixture typically referred to as normal hydrogen (nH 2 ). At lower temperatures the equilibrium distribution shifts to favour the lower energy pH 2 isomer, so that at its boiling point (20.3 K) the equilibrium composition of H 2 is almost 100 % pH 2 . However, as the conversion between oH 2 and pH 2 is forbidden, conversion between isomers is very slow unless a catalyst is used.…”

Section: Introductionmentioning

confidence: 99%

“…However, as the conversion between oH 2 and pH 2 is forbidden, conversion between isomers is very slow unless a catalyst is used. [1][2][3][4][5] The pH 2 isomer is useful for a wide range of applications, including: liquid fuels, [6][7][8] matrix isolation spectroscopy, 9,10 certain hyperpolarisation methods for nuclear magnetic resonance (NMR) spectroscopy, 3,4,11,12 and as a moderator for spallation neutron sources. 13,14 For many of these applications the proportion of the pH 2 isomer is of vital importance.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Quantitative In Situ Monitoring of Parahydrogen Fraction Using Raman Spectroscopy

Parrott

Dallin²,

Andrews³

et al. 2018

Appl Spectrosc

View full text Add to dashboard Cite

Raman spectroscopy has been used to provide a rapid, non-invasive and non-destructive quantification method for determining the parahydrogen fraction of hydrogen gas. The basis of the method is the measurement of the ratio of the first two rotational bands of hydrogen at 355 cm −1 and 586 cm −1 corresponding to parahydrogen and orthohydrogen, respectively. The method has been used to determine the parahydrogen content during a production process and a reaction. In the first example, the performance of an in-house liquid nitrogen cooled parahydrogen generator was monitored both at-line and on-line. The Raman measurements showed that it took several hours for the generator to reach steady state and hence, for maximum parahydrogen production (50 %) to be reached. The results obtained using Raman spectroscopy were compared to those obtained by at-line low-field NMR spectroscopy. While the results were in good agreement, Raman analysis has several advantages over NMR for this application. The Raman method does not require a reference sample, as both spin isomers (ortho and para) of hydrogen can be directly detected, which simplifies the procedure and eliminates some sources of error. In the second example, the method was used to monitor the fast conversion of parahydrogen to orthohydrogen in-situ. Here the ability to acquire Raman spectra every 30 s enabled a conversion process with a rate constant of 27.4 × 10 −4 s −1 to be monitored. The Raman method described here represents an improvement on previously reported work, in that it can be easily applied on-line and is approximately 500 times faster. This offers the potential of an industrially compatible method for determining parahydrogen content in applications that require the storage and usage of hydrogen.

show abstract

Kinetics of the Interconversion of Parahydrogen and Orthohydrogen Catalyzed by Paramagnetic Complex Ions

Cited by 51 publications

References 68 publications

Evaluation of hydrogen dissolved in rubber materials under high-pressure exposure using nuclear magnetic resonance

Evaluation of hydrogen dissolved in rubber materials under high-pressure exposure using nuclear magnetic resonance

MRI of Heterogeneous Hydrogenation Reactions Using Parahydrogen Polarization

Quantitative In Situ Monitoring of Parahydrogen Fraction Using Raman Spectroscopy

Contact Info

Product

Resources

About