Temporal Analysis of Products (TAP), (TAP-2), (TAP-3) is an experimental technique for studying the

kinetics Kinetics ( grc, κίνησις, , kinesis, ''movement'' or ''to move'') may refer to: Science and medicine * Kinetics (physics), the study of motion and its causes ** Rigid body kinetics, the study of the motion of rigid bodies * Chemical ki ...

of physico-chemical interactions between gases and complex solid materials, primarily

heterogeneous catalysts In chemistry, heterogeneous catalysis is catalysis where the phase of catalysts differs from that of the reactants or products. The process contrasts with homogeneous catalysis where the reactants, products and catalyst exist in the same phase. P ...

. The TAP methodology is based on short pulse-response experiments at low background pressure (10⁻⁶-10² Pa), which are used to probe different steps in a catalytic process on the surface of a

porous material A porous medium or a porous material is a material containing pores (voids). The skeletal portion of the material is often called the "matrix" or "frame". The pores are typically filled with a fluid (liquid or gas). The skeletal material is usua ...

including

diffusion Diffusion is the net movement of anything (for example, atoms, ions, molecules, energy) generally from a region of higher concentration to a region of lower concentration. Diffusion is driven by a gradient in Gibbs free energy or chemical p ...

adsorption Adsorption is the adhesion of atoms, ions or molecules from a gas, liquid or dissolved solid to a surface. This process creates a film of the ''adsorbate'' on the surface of the ''adsorbent''. This process differs from absorption, in which a f ...

, surface reactions, and

desorption Desorption is the physical process where a previously adsorbed substance is released from a surface. This happens when a molecule gains enough energy to overcome the activation barrier of the bounding energy that keeps it in the surface. There ...

History

Since its invention by Dr. John T. Gleaves (then at

Monsanto Company The Monsanto Company () was an American agrochemical and agricultural biotechnology corporation founded in 1901 and headquartered in Creve Coeur, Missouri. Monsanto's best known product is Roundup (herbicide), Roundup, a glyphosate-based herbic ...

) in late 1980s, TAP has been used to study a variety of industrially and academically relevant catalytic reactions, bridging the gap between surface science experiments and applied catalysis. The state-of-the-art TAP installations (TAP-3) do not only provide better signal-to-noise ratio than the first generation TAP machines (TAP-1), but also allow for advanced automation and direct coupling with other techniques.

Hardware

TAP instrument consists of a heated packed-bed microreactor connected to a high-throughput vacuum system, a pulsing manifold with fast electromagnetically-driven gas injectors, and a Quadrupole Mass Spectrometer (QMS) located in the vacuum system below the micro-reactor outlet.

Experiments

In a typical TAP pulse-response experiment, very small (~10⁻⁹ mol) and narrow (~100 μs) gas pulses are introduced into the evacuated (~10⁻⁶

torr The torr (symbol: Torr) is a unit of pressure based on an absolute scale, defined as exactly of a standard atmosphere (). Thus one torr is exactly (≈ ). Historically, one torr was intended to be the same as one "millimeter of mercury ...

) microreactor containing a catalytic sample. While the injected gas molecules traverse the microreactor packing through the interstitial voids, they encounter the catalyst on which they may undergo chemical transformations. Unconverted and newly formed gas molecules eventually reach the reactor's outlet and escape into an adjacent vacuum chamber, where they are detected with millisecond time resolution by the QMS. The exit-flow rates of reactants, products and inert molecules recorded by the QMS are then used to quantify catalytic properties and deduce reaction mechanisms. The same TAP instrument can typically accommodate other types of kinetic measurements, including atmospheric pressure flow experiments (10⁵ Pa), Temperature-Programmed Desorption (TPD), and Steady-State Isotopic Transient Kinetic Analysis (SSITKA).

Data analysis

The general methodology of TAP data analysis, developed in a series of papers by Grigoriy (Gregory) Yablonsky ,D. Constales, G. S. Yablonsky, G. B. Marin, J. T. Gleaves, Chem. Eng. Sci 56 (2001) 133–149 is based on comparing an

inert gas An inert gas is a gas that does not readily undergo chemical reactions with other chemical substances and therefore does not readily form chemical compounds. The noble gases often do not react with many substances and were historically referred to ...

response which is controlled only by

Knudsen diffusion In physics, Knudsen diffusion, named after Martin Knudsen, is a means of diffusion that occurs when the scale length of a system is comparable to or smaller than the mean free path of the particles involved. An example of this is in a long pore wi ...

with a reactive gas response which is controlled by diffusion as well as adsorption and chemical reactions on the catalyst sample. TAP pulse-response experiments can be effectively modeled by a one-dimensional (1D) diffusion equation with uniquely simple combination of boundary conditions.

References

{{DEFAULTSORT:Temporal Analysis Of Products Inorganic reactions