Future Challenges in Heterogeneous Catalysis: Understanding Catalysts under Dynamic Reaction Conditions

In the future, (electro-)chemical catalysts will have to be more tolerant towards a varying supply of energy and raw materials. This is mainly due to the fluctuating nature of renewable energies. For example, power-to-chemical processes require a shift from steady-state operation towards operation under dynamic reaction conditions. This brings along a number of demands for the design of both catalysts and reactors, because it is well-known that the structure of catalysts is very dynamic. However, in-depth studies of catalysts and catalytic reactors under such transient conditions have only started recently. This requires studies and advances in the fields of 1) operando spectroscopy including time-resolved methods, 2) theory with predictive quality, 3) kinetic modelling, 4) design of catalysts by appropriate preparation concepts, and 5) novel/modular reactor designs. An intensive exchange between these scientific disciplines will enable a substantial gain of fundamental knowledge which is urgently required. This concept article highlights recent developments, challenges, and future directions for understanding catalysts under dynamic reaction conditions

Peculiarities of self-diffusion of alkane molecules in kaolinite

Self-diffusion of alkanes in kaolinite has been explored by pulsed field gradient nuclear magnetic resonance. The concentration dependences of average self-diffusion coefficient (SDC) of liquid have been studied in the wide temperature interval (T=253-383 K). The translational mobility of alkane molecules in kaolinite was shown to have some specific peculiarities. An anomalous rise was found in the average self-diffusion coefficient of the liquid as its content in kaolinite decreased. To explain this we should introduce a new "gas-like" state for the diffusant, whose mobility exceeds that of pure liquid. The possibility of the existence of such a state is explained by kaolinite's ability to increase the specific surface area of the induced liquid. Analysis of a shape of the spin-echo diffusion attenuation leads one to suppose that there are heterogeneities in the medium's porous space. © 1991 Springer

Human exposure to persistent organic pollutants : Illustrated by four case studies in Europe

An extensive use of chemicals in countless consumer products has resulted in human exposure to several persistent organic pollutants (POPs). Sufficient knowledge about their chemical composition properties and environmental faith is required, to be able to proper risk assess and regulate the substances. Significant data gaps exist regarding knowledge of actual exposure to humans and toxicological effect data. The objective of this thesis was to add human exposure data of a few POPs from four case studies. The analytes discussed in this thesis are polychlorinated dibenzo-p-dioxins and furans (PCDDs/PCDFs), polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs) and hexabromocyclododecane (HBCDD). Three European populations were studied. Milk was analysed from a group of women, who were accidentally exposed to high levels of 2,3,7,8-TetraCDD (TCDD) in Seveso, 1976. Still today, twice as high TCDD levels were recorded in the milk, compared to background concentrations. Serum was analysed from mothers and their infants from The Netherlands. Cord serum contained equal amounts of POPs as in mother’s blood, indicating non-hindered placenta transfer. Serum analysed from Swedish men and women with a high fish intake had elevated PCB and PCB metabolite (OH-PCB) levels. Additionally, butter was collected worldwide and shown to be a suitable matrix for dairy product survey of POPs. The exposure levels in the four papers were compared to recently reported exposure levels in Europe. It is indicated in the thesis that the PCDDs/PCDFs and PCBs toxic equivalency (TEQ) levels are of concern, i.e. the ratio between threshold levels for adverse health effects and TEQ exposure levels is lower than requested margin of safety. Average levels of PBDE/HBCDD in the European population are estimated to be of no concern today, but for individuals with intakes at the 95th percentile are the current margins of safety small

Peculiarities of self-diffusion of alkane molecules in kaolinite

Self-diffusion of alkanes in kaolinite has been explored by pulsed field gradient nuclear magnetic resonance. The concentration dependences of average self-diffusion coefficient (SDC) of liquid have been studied in the wide temperature interval (T=253-383 K). The translational mobility of alkane molecules in kaolinite was shown to have some specific peculiarities. An anomalous rise was found in the average self-diffusion coefficient of the liquid as its content in kaolinite decreased. To explain this we should introduce a new "gas-like" state for the diffusant, whose mobility exceeds that of pure liquid. The possibility of the existence of such a state is explained by kaolinite's ability to increase the specific surface area of the induced liquid. Analysis of a shape of the spin-echo diffusion attenuation leads one to suppose that there are heterogeneities in the medium's porous space. © 1991 Springer

Peculiarities of self-diffusion of alkane molecules in kaolinite

Self-diffusion of alkanes in kaolinite has been explored by pulsed field gradient nuclear magnetic resonance. The concentration dependences of average self-diffusion coefficient (SDC) of liquid have been studied in the wide temperature interval (T=253-383 K). The translational mobility of alkane molecules in kaolinite was shown to have some specific peculiarities. An anomalous rise was found in the average self-diffusion coefficient of the liquid as its content in kaolinite decreased. To explain this we should introduce a new "gas-like" state for the diffusant, whose mobility exceeds that of pure liquid. The possibility of the existence of such a state is explained by kaolinite's ability to increase the specific surface area of the induced liquid. Analysis of a shape of the spin-echo diffusion attenuation leads one to suppose that there are heterogeneities in the medium's porous space. © 1991 Springer

Peculiarities of self-diffusion of alkane molecules in kaolinite

Self-diffusion of alkanes in kaolinite has been explored by pulsed field gradient nuclear magnetic resonance. The concentration dependences of average self-diffusion coefficient (SDC) of liquid have been studied in the wide temperature interval (T=253-383 K). The translational mobility of alkane molecules in kaolinite was shown to have some specific peculiarities. An anomalous rise was found in the average self-diffusion coefficient of the liquid as its content in kaolinite decreased. To explain this we should introduce a new "gas-like" state for the diffusant, whose mobility exceeds that of pure liquid. The possibility of the existence of such a state is explained by kaolinite's ability to increase the specific surface area of the induced liquid. Analysis of a shape of the spin-echo diffusion attenuation leads one to suppose that there are heterogeneities in the medium's porous space. © 1991 Springer