To provide a first comprehensive set of guidelines for measurements and reporting of diffusion properties of chemical compounds in nanoporous materials serving for catalytic, mass separation and other relevant purposes.
Diffusion is among the rate-limiting processes in the technological application of nanoporous materials. During their exploitation in mass separation and catalytic conversion, e.g., the gain in value-added products can never be faster than allowed by the rate of mass transfer within these materials. In the last decades, the advent of “microscopic” techniques of diffusion measurement, together with a concurrent refinement of the “macrosocopic” techniques, has revolutionized our knowledge. Rather than being controlled by the diffusional resistance of the genuine micropore network as so far generally assumed, diffusive mass transfer in nanoporous materials is now in many cases known to be subject to a hierarchy of resistances. Though nowadays (as detailed, e.g., in the textbook on “Diffusion in Nanoporous Materials” by J. Karger, D. M. Ruthven and D. N. Theodorou, Wiley-VCH 2012) techniques and methodologies to experimentally determine all these resistances are available, our knowledge of mass transfer in the nanoporous materials in technological use is generally rather limited, if not even totally wrong. This situation is mainly caused by the fact that transport resistances occur over essentially all length scales. The sensitivity of the measuring techniques must, correspondingly, be adjusted to these very length scales. Inappropriate use of these techniques will therefore lead to wrong conclusions, which (as a common case given the complexity of the given situations) the unexperienced user is scarcely able to avoid. In reviewing the literature (including some of our own earlier studies) we came across many instances in which experimental techniques have been applied incorrectly or the intrusion of an extraneous effect has not been properly accounted for. In many of these cases there are simple experimental checks that would have detected the error but these were often omitted.
The intention of the proposed work is to focus on the practical procedures for the most important experimental techniques, with emphasis on the conditions that must be fulfilled and any experimental checks that should be undertaken to ensure reliable results. The results of this study will be summarized as recommended protocols that could be applied routinely by anyone interested in measuring diffusivities, eliminating the need to undertake detailed preliminary studies of the underlying theory and practice. Thus, bringing together worldwide leading specialists in the different fields of diffusion measurement, the suggested initiative aims at the formulation of recipes for the application of the major techniques of diffusion measurement with nanoporous materials, including clear statement of the preconditions for their application and of the attainable information.
With such an initiative the task group will follow previous activities comprising groups from Germany with colleagues from France, UK and the US under the auspices of the German Science Foundation aiming at a clarification of the discrepancy so far often encountered in diffusion measurement. These efforts did, most distinctively, reveal the necessity to continue this initiative on an international (world-wide) level which, under the auspices of IUPAC, would find the most appropriate and favorable boundary conditions.
Jan 2015 – Project announcement published in Chem. Int. Jan 2016, p. 24; https://dx.doi.org/10.1515/ci-2016-0118
April 2019 update: A paper entitled “Diffusion in Nanopores: Inspecting the Grounds” is in preparation and will constitute the first manuscript of a special issue of the Adsorption Journal to appear mid 2020. This manuscript is the first step towards the project goal, namely the completion of a “Technical Report” providing guidelines for measurements and reporting of diffusion properties of chemical compounds in nanoporous materials for catalytic, mass separation and other relevant purposes.
September 2019 update: The occasion of this year’s three international conferences (“Fundamentals of Adsorption 13” in Cairns, Australia (26-31 May), 19th International Zeolite Conference in Perth, Australia (7-12 July), and the 8th Diffusion-Fundamentals conference in Erlangen, Germany (1-5 Sep)) was exploited for discussions among the participating group members, resulting in confirmation of and a clear agreement about our further steps, namely:
(i) The edition of a Thematic Issue of the Adsorption journal on “Diffusion in Nanoporous Materials”, with May 31st, 2020 as the deadline for contribution submission, and
(ii) The development of “a first, comprehensive set of guidelines for measurements and reporting of diffusion properties of chemical compounds in nanoporous materials serving for catalytic, mass separation and other relevant purposes” as emerging from this Thematic Issue, to be formulated as an IUPAC Technical Report for being published in Pure Appl. Chem. A first draft of this report is scheduled to be circulated among the IUPAC task group and the contributors to the Thematic Issue before September 2021, so that the 9th meeting in the Diffusion-Fundamentals (DF) Conference Series (Krakow, Poland, rescheduled September 21-24, 2022) provides the task group with an ideal opportunity for presenting and discussing these guidelines in contact with the relevant community. The final version of the Technical Report is scheduled to appear in 2022.
July 2020 update: Papers for the Thematic Issue “Diffusion in Nanoporous Materials” of the Adsorption Journal are being collected; this is the first step towards the completion of a Technical Report providing “Guidelines for measurements and reporting of diffusion properties of chemical compounds in nanoporous materials for catalytic, mass separation and other relevant purposes”. The deadline of paper submission has been deferred to the end of August and the intent is to complete the Issue by the end of 2020.
A forum for continuing this project activities aiming at the formulation of the “Guidelines for measurements and reporting of diffusion properties …” is being organized as a workshop part of the 9th Diffusion-Fundamentals conference in Krakow in September 2022 (https://diffusionfundamentals2021.confer.uj.edu.pl).
Sept 2020 update: The first papers in the Thematic Issue “Diffusion in Nanoporous Materials” of the Adsorption Journal are being release online ahead of print – see collection
Page last update 20 Oct 2020