2.1 Twenty Years with KCK

An introductory talk to celebrate the history of KCK, an interdisciplinary research centre within heterogeneous catalysis since 1995, was given by the director of KCK, Professor Magnus Skoglundh (Chalmers University of Technology). The diversity of the centre was emphasised: it was originally composed of Chemical Engineering, Chemical Reaction Engineering and Applied Physics departments at Chalmers University of Technology, and recently it was further expanded by Eva Olsson’s microscopy group. The research is focused on catalysis for emission control with a growing interest in energy related areas. KCK is financially supported by Chalmers University of Technology, the Swedish Energy Agency and the member companies: AB Volvo, ECAPS AB, Haldor Topsøe A/S, Scania CV AB, Volvo Car Corporation AB and Wärtsilä Finland Oy.

On a similar note, Pär Gabrielsson’s (Haldor Topsøe, Denmark) talk on ‘The Impact of KCK from an Industrial Perspective’ stressed the role played by KCK on students’ education and how it prepares them for employment in the catalysis and aftertreatment industry. This is confirmed by statistics, with 70% of PhDs employed by industry of which 45% are member companies. The remaining 30% of PhDs are employed by other organisations.

2.2 Automotive Aftertreatment

Galen Fisher (University of Michigan, USA) presented ‘Progress and Challenges in Automotive Emission Control’. Fisher is one of the members of the KCK’s international advisory board. His talk concentrated on current challenges facing the automotive emission control industry such as improving the low-temperature activity of three-way catalyst (TWC) and nitrogen oxides (NOx) traps. Moving the TWC design from a supported metal to a metal core surrounded by an inert shell was shown to prevent poisoning and metal sintering (1). Johnson Matthey was cited in relation to the development of palladium/cerium based low-temperature NOx adsorbers, characterised by lower nitrous oxide (N₂O) production compared to platinum-based catalysts and preferential storage of nitrogen oxide (NO) vs. nitrogen dioxide (NO₂) (2). Fisher discussed how the new aftertreatment technologies use layering/zoning strategies as well as diffusion effects to decrease emissions.

Jonas Jansson (AB Volvo, Sweden) presented ‘Exhaust Aftertreatment for Heavy Duty Diesel Engines – Current Trends and Future Challenges’. The evolution of the aftertreatment systems for heavy duty diesel vehicles at Volvo was discussed. The original configuration diesel oxidation catalyst (DOC) + diesel particulate filter (DPF) + selective catalytic reduction (SCR) has been recently substituted by close-coupled DOC + SCR on filter (SCRF^®) (or passive NOx adsorber (PNA) + SCRF^®), allowing an enhancement of the light-off performances. The location of the catalysts and of the urea tank depends on the geographical area where the vehicle is commercialised.

2.3 Advanced Characterisation

Stig Helveg (Haldor Topsøe) presented ‘Electron Microscopy Advances for Catalysis’. Helveg introduced the cutting-edge technology of in situ and operando transmission electron microscopy (TEM) imaging (3). A nanoreactor was designed at Haldor Topsøe in collaboration with TU Delft, The Netherlands, and was functionalised with a micrometre-sized gas-flow channel, transparent windows to allow the electron beam to reach the sample and with a heating device (4). This device allows the collection of images at 1 bar, solving the pressure gap issue typical of traditional TEM imaging. The time resolved TEM images and measurement of the outlet gas composition by mass spectrometry (MS) results in a powerful way of studying correlations between a catalyst structure and its activity. The research of oscillatory catalytic reactions, such as carbon monoxide oxidation, was reported as an example of successful application of this technique (5). In this case a link between catalyst activity and shape of platinum nanoparticles has been found (shape dynamics from squared to circular). Sintering mechanisms and kinetics can also be investigated with the same technique.

Anders Nilsson (Stockholm University, Sweden) presented ‘Fundamental X-ray Studies of Catalytic Reactions’. The understanding of the nature of the interaction between water and metals, which is of interest in heterogeneous catalysis, was described (6). Professor Nilsson developed a library of X-ray absorption spectroscopy (XAS) and X-ray Raman scattering (XRS) spectra that spans the liquid part of the water phase space and several important aqueous solutions. This was used as a reference to identify hydroxyl species involved in catalytic reactions such as hydrogen oxidation in fuel cell applications.

Per-Anders Carlsson presented ‘Studies of Catalysts at Work’. This talk focused on the use of synchrotron facilities (European Synchrotron Radiation Facility (ESRF), France; MAX IV, Sweden and PETRA III, Germany) to examine catalytic reactions. Some examples were given of various spectroscopic techniques (extended X-ray absorption fine structure (EXAFS), high-energy X-ray diffraction (HEXRD), Fourier transform infrared (FTIR) and MS) to distinguish the adsorbed species and simultaneously coordinate catalytic activity to changes in the catalyst oxidation state (7, 8) (Figure 1). The possibility of exploiting the structure gap, from ideal surfaces to big particles, small clusters and single atoms, to improve the understanding of catalytic reactions was also mentioned. Active areas of interest are total methane oxidation and partial selective methane oxidation to methanol.

2.4 Reaction Engineering and Molecular Modelling

Louise Olsson (Chalmers University of Technology) presented ‘Studies of Aging Mechanisms for NH₃-SCR Catalysts using Experiments and Kinetic Modelling’. Sulfur poisoning and regeneration on copper-SSZ13 were studied and performed in collaboration with Cummins Inc. A three-site kinetic model was necessary to describe ammonia storage and oxidation during temperature programmed desorption (TPD) experiments (9). A connection was also found experimentally between the rate of SCR reaction and Cu loading, that was introduced in the kinetic model. A sulfur exposure study showed that sulfur dioxide (SO₂) can be adsorbed on Cu sites (S1-SO₂), resulting in a decreased catalytic activity. The experimental observation of more NH₃ stored in the presence of sulfur was elucidated with the formation of adsorbed ammonium-sulfur species (S1-(NH₃)₂-SO₂). The gradual decomposition of these species leads to catalyst regeneration and also provides an alternative route to the SCR reaction. This mechanism was successfully included in a kinetic model.

Henrik Grönbeck (Chalmers University of Technology) presented ‘Catalysis from First-Principles Calculations’. A recent work combining X-ray photoelectron spectroscopy (XPS) measurements and first-principle calculations suggests that the most active phase for methane oxidation on Pd-based catalyst is a double layered PdO(101) structure (10). Density functional theory (DFT) calculations show that CH₄ repulsion from the surface is quite strong when only one monolayer of PdO is present, but it can be overcome after a second monolayer is created therefore explaining the better activity observed experimentally. A micro-kinetic model for CH₄ oxidation was also built from first principles, able to predict reaction orders in methane, water, and oxygen as well as apparent activation energies in good agreement with a range of experimental findings (11). Interestingly, different reaction steps were found to be limiting depending on the temperature: water inhibition, CH₄ desorption, CH₃ dissociation or CH₄ dissociation with increasing temperature. Different activation energies depending on the temperature were found also experimentally, which supports the modelling results.