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Iso-potential operando spectroscopy

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“Measure what is measurable, and make measurable what is not so.” is a quotation often ascribed to Galileo Galilei. Whether this is true or not, it is true that a team of scientists at the Institute of Chemical Reaction Engineering at TUHH and REACNOSTICS made something measurable that has not been measurable before, the molecules adsorbed at the surface of a solid catalyst inside of a catalytic reactor. The team developed a new measurement method called “Iso-Potential Operando Spectroscopy” (IPOS) to perform spectroscopic measurements inside of catalytic reactors of arbitrary size and shape. The concept of IPOS is shown in the following figure.

Concept of Iso-Potential Operando Spectroscopy (IPOS), here shown with a DRIFTS cell from REACNOSTICS.

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In IPOS, a catalytic reactor is equipped with spatial profiling and the sampled reaction mixture is transferred into a spectroscopic cell containing a tiny amount (few mg) of the same catalyst as inside the reactor, just enough to measure the desired spectroscopic information but as little as possible to minimize conversion in the spectroscopic cell. Once the reaction fluid is separated from the catalyst in the reactor, the chemical composition x is fixed. The pressure p in the transfer system is kept very small (≤ 100 mbar) and the temperature T of the catalyst in the spectroscopic cell is set to the same value as measured locally in the reactor. In this way, the catalyst in the spectroscopic cell is exposed to the same chemical potential μ (same T, p, x = ‘iso potential’) as the catalyst locally in the reactor and should display the same adsorbates, redox state, crystal phases etc. By scanning the profile reactor now from inlet to outlet, the catalyst in the spectroscopic cell goes through the same chemical history as the catalyst in the reactor, and spatial reactor profiles of the respective spectroscopic information can be
measured. IPOS offers three distinct advantages: i) Any spectroscopic, microscopic, or imaging method, which can be applied at the temperature, pressure, and chemical composition conditions in the catalytic reactor, can be combined with any catalytic reactor, in principle even industrial production reactors. ii) The spectroscopic cell can be designed to meet the demands of the measurement method without that compromises have to be made resulting from the dual use as a catalytic reactor as in traditional operando spectroscopy. iii) The question of which reaction conditions to study is answered
automatically, as the reactor sets the reaction conditions inside the spectroscopic cell.


In a first application, we have applied IPOS as Iso-Potential DRIFT Spectroscopy to measure which adsorbates populate the catalyst surface on a Ni/g-Al2O3 catalyst during CO2 methanation inside of a catalytic reactor. This reaction plays a central role in converting CO2 from local emitters with green hydrogen to synthetic natural gas. Two surface adsorbates were observed, formate (*HCOOads) and carbonyl (*COads). While the formate band intensity correlates well with CO2 conversion identifying formate as reaction intermediate, the band intensity of *COads does not change, irrespective of position in the catalyst bed, identifying *COads as spectator species. The full paper was published in ACS Catalysis (ACS Catal., 14, 2024 8676-8693, DOI: 10.1021/acscatal.4c00536).


To perform high-quality iso-potential DRIFTS measurements, REACNOSTICS has developed a dedicated µ-DRIFTS cell ( If you are interested in applying this technology to your own catalytic reactions, contact us (

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