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Researchers at the University of Aberdeen use CI Microbalances for a wide variety of applications

Researchers in both the School of Engineering and the School of Natural & Computing Sciences at the University of Aberdeen have been working with CI Microbalances for around 20 years. Prof James Anderson, head of the Surface Chemistry & Catalysis Group, supervises students from both this group and the Materials & Chemical Engineering Research Group. Three microbalances, located in the Surface Chemistry & Catalysis group laboratory, are used by PDRAs, PhD Students, visiting research students (Erasmus), undergraduate (BSc), postgraduate (MChem) researchers and previous PhD students. Current PhD Student Greg A. Mutch writes: Our research focuses on chemical engineering, surface chemistry and catalysis. Typically we couple microbalances to high vacuum/high temperature equipment and FTIR spectrometers to perform gravimetric analysis and in-situ quantitative spectroscopy in the presence of reactive gases, probe molecules or reactants. In the past we have studied a wide range of catalytic reactions, typically looking at acid sites on the surfaces of oxides, but currently we have three major projects that use the microbalance rigs.

• Quantification of carbonation extent and diffusion rates in calcium loopingapplications for climate change mitigation through carbon capture.
• Determination of absorption coefficients to affect quantitative spectroscopic investigation of the catalytic reactions.
• Investigation of the water adsorption capacity of metal-organic frameworks (MOF’s).

In the first project we look at the reaction between calcium oxide and carbon dioxide under different thermodynamic conditions to understand losses in capacity during calcium looping cycles and through complimentary spectroscopy, the reactions occurring purely on the surface, or in the bulk of the materials. We are interested in looking at the effect of water on these carbon capture processes also. In the second project we have directly interfaced a microbalance with a reaction cell placed in the beam path of an FTIR spectrometer to allow us to produce absorption coefficients for adsorbed molecules – simply put we can relate what we “see” in the spectra with a mass change recorded by the microbalance, allowing us to produce a coefficient that we can then use to quantify products formed in catalytic reactions. In the third project we measure the water adsorption capacity of MOFs under different humidities as part of our investigations on the stability of MOFs. We correlate spectroscopic and diffraction studies that identify adsorption mechanisms and structural stability with the amount of adsorbed water. We have recently published a review article on quantitative spectroscopy:

• “Quantitative determination of surface species and adsorption sites using Infrared spectroscopy” Catalysis Today 259 (2015) p19-26, doi:10.1016/j.cattod.2015.03.039 We have published original research articles using data obtained from the microbalances:
• “Quantitative determination of acid sites on silica-alumina” Applied Catalysis A: General 390 (2010) p127-134 doi:10.1016/j.apcata.2010.10.001
• “On determination of acid site densities on sulphated oxides” Catalysis Letters 83 (2002) p59-63 doi:10.1023/A:1020657515516
• “Modification of the acid properties of silica-zirconica aerogels by in situ and ex situ sulfation” 210 (2002) p218-228 doi:10.1006/jcat.2002.3656
• “Influence of Si/Zr ratio on the formation of surface acidity in silica-zirconia aerogels” Journal of Catalysis 192 (2000) p344-354 doi:10.1006/jcat.2000.2850

We are in the process of publishing multiple articles in the newest areas outlined above. When using our high temperature gravimetric rig, we typically study powdered samples suspended in a small fritted quartz bucket. However when using our quantitative spectroscopy rig we press powdered samples into self-supporting wafers to permit spectroscopic investigation. The majority of our experiments run at a mg scale. The experiments vary depending on application from a few hours to a number of days or weeks. Spectroscopic experiments can be relatively quick, whereas solid state diffusion and water adsorption experiments can run from 1 day to a number of weeks. We use a wide variety of gases – CO for probe molecule studies of transition metal catalysts, basic probe molecules such as ammonia and pyridine to look at acid sites on solid oxides, CO2for carbonation of carbon capture sorbents, H2O vapour to look at water adsorption in MOFs and a variety of hydrocarbon vapours to determine absorption coefficients for organic molecules. Weuse Lab Weigh Software to monitor in real-time but often use specialist software for interpretation and presentation purposes. On being asked why the University of Aberdeen chooses to work with CI’s microbalances rather than others on the market, Greg Mutch responded:

“The ease of integration with other equipment is a real advantage for us as we often look to study materials under harsh conditions, at high temperature, under vacuum and in the confines of FTIR spectrometers.”

Regarding technical support from CI Precision, he says,

“On the odd occasion we have had to call for support the staff have been very friendly – particularly a certain Martyn Wright!”

Asked whether he would recommend CI Microbalances to others, he replied,

“Yes, we find them useful, reliable and of wide potential application. Quantification of FTIR spectroscopy is at the forefront of the application of the technique, without microbalances we would not be able to perform these measurements.”

For more information about CI Microbalances, thermo-gravimetric kits and accessories from CI Precision, or to discuss your specific application, please telephone +44 (0) 1722 424100, or e-mail sales@ciprecision.com