(169f) Chemisorption and Physisorption Rates On Catalysts Using Microfluidic ATR-FTIR Spectroscopy

We present a method to determine adsorption and desorption rates from liquids onto solid surfaces. In most experiments to determine these rates, diffusion to the surface readily becomes limiting, and the intrinsic rates are hard to determine. This is in stark contrast to high-vacuum surface science, where one can determine such rates using so called Transient Analysis of Products (TAP) reactors. In other words, the present study is a first attempt to create a TAP reactor for liquids. 

Diffusion limitations can only be overcome using miniaturization, which we present in this work Even in small channels, Taylor-Aris dispersion limits the resolution of a pulse or step change of concentration over a surface. We overcome this limitation by using a bubble between a concentration step-change, which remains a sharp transition even under flow. We measure the concentration on the surface using attenuated total reflection FTIR spectroscopy. This method has the advantage that both adsorbed and solution concentration can be distinguished and determined simultaneously. We report fast switching for non-adsorbing compounds and show intrinsic adsorption rates for heptylamine and cyclohexanone onto TiO2 catalysts. Especially heptylamine shows interesting non-langmuir behavior.