Using temporal analysis of products and flux response technology to determine diffusion coefficients in catalytic monoliths

Abstract

The importance of accurately measuring gas diffusivity in porous materials has led to a number of methods being developed. In this study the Temporal Analysis of Products ( To be submitted to Chem. Eng. Sci.

Flux Response Technology (FRT) Applied in Zero Length Column Diffusivity and Adsorption Measurements

“…These values are less than the literature value of 30.6 kJ mol −1 reported for tracer measurements of CO 2 diffusion in ZSM-5 at similar CO 2 molar concentration (Pitale et al 1988). This is an expected result as recent studies have shown that differences exist in diffusion parameters of complex zeolite systems where the substructure (defect structure) of the crystals offers a second diffusional resistance-a consideration detected by longer range (macro) measurements (Chmelik et al 2011;Maguire et al 2013).…”

Prerequisites for kinetic modeling of TPD data of porous catalysts—Exemplified by toluene/H-ZSM-5 system

“…Completely identical values were not expected, as the vacuum system concerns a single mobile component and the flow-through system contains an inert carrier gas (He) with a potential slight effect on the transport processes. An example with a similar order of magnitude for mesopore diffusion coefficients in the flow and vacuum systems is provided by Maguire et al (2013). The diffusion coefficient, D m , for mass transport in the evacuated packed crucible is in a meaningful order of magnitude for effective Knudsen diffusion.…”

Forty years of temporal analysis of products

“…While powdered catalysts have been the most commonly studied using TAP, the same methodologies have also been employed to characterize monolith catalysts for diffusivity 60,126 as well as mechanistic and kinetic studies. For instance, the transient catalytic process of NOx storage and reduction on monolith washcoated with Pt/Al 2 O 3 and Pt/Ba/ Al 2 O 3 have been studied (which were compared to analogous powdered catalysts) with the reactor configurations reported in Fig.…”

“…63,64 Inversely, a fully oxidized surface can be reduced by using pulses of hydrogen, hydrocarbons or another reducing agent. 60,99 Multi-pulse experiments (oxidizing and reducing) can also be conducted on fresh catalysts, 125 as a way to assess the initial state of a catalyst. This process can be performed with great precision as the pulse intensity (i.e.…”

“…17 Pulse experiments can also be applied to determine the effective Knudsen diffusion coefficient within fixed beds and wash-coated monoliths. 17,60 For this purpose, the average residence time for small, single pulses of non-adsorbing gases (less than 2 × 10 15 molecules) within the isothermal fixed bed reactor is measured. 17 2.4.2 Multi-pulse experiments.…”