Solvation science into focus at historic Solvay conference.

Three members of the Cluster of Excellence RESOLV attended last October the renowned Solvay-Conference on Chemistry in Brussel, an event open to invited scientists only. Prof. Dr. Martina Havenith, speaker of RESOLV at RUB, Prof. Dr. Frank Neese, director at the Max-Planck-Institute for Energy Conversion, and Prof. Dr. Benjamin List, director at the Max-Planck-Institute for Coal Research, both based in Mülheim an der Ruhr, were among the fifty attendees.

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2016 Solvay Conference group picture ©InternationalSolvayInstitutes

Belgian chemist and industrialist Ernest Solvay, the founder of the chemical company Solvay S.A., initiated the first series of international conferences on physics in 1911, while the first meeting on chemistry occurred in 1922. Since then the Solvay-Conferences on Chemistry and Physics had been held every three years. The conferences have become extremely famous after the 1927 physics meeting on ´Electrons and Photons´, when Albert Einstein and Niels Bohr, among others, met to discuss the newly forged quantum theory.

The 2016 meeting evolved around the theme ‘Catalysis in Chemistry and Biology’. We briefly interviewed Havenith, List and Neese about their experience in Brussels.

 

What was your impression of the conference?

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Discussing at the 2016 Solvay Conference ©InternationalSolvayInstitutes

Martina Havenith: It was very impressive for many different reasons. First of all, it’s rare to see five Nobel prize winners together! – and it’s even rarer that they are listening to your ideas and discussing the future direction of chemistry. Besides, it was an intimate meeting, and we had much more time than usual for discussions. It was also remarkable to witness the special engagement of an industrial family into science. And it was impressive to read the names of Albert Einstein and Marie Curie in a guestbook!

Benjamin List:  One of the best conferences I have ever attended!

Frank Neese: The conference was unlike any other I have ever attended. There obviously is an impressive history associated with Solvay conferences and it was a major honor to be invited to participate. It takes place in a fairly unique setting in a beautiful historic hotel in Brussels with a closed circle of only invited international speakers and an outstanding accompanying program. The format is also different from usual: The talks are just ten minutes long and the discussion takes first place among the members of the session, only later it involves the other guests.

 

What was the take-home message? How was solvation science portrayed?

Martina Havenith: This meeting focused on the main challenges in catalysis. It was not about the details of the field but it rather provided a big picture of what we have learned in the past and what is still unclear. Most interesting for RESOLV: In the end it was noted that the solvent has not yet been taken much into consideration, but in the future we should have a closer look into it and its important role in catalysis.

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Session begins at the 2016 Solvay Conference ©InternationalSolvayInstitutes

Benjamin List: I was able to identify three unifying principles of catalysis – including heterogeneous, homogenous organic and metal catalysis, and biocatalysis: 1. Turnover frequency (an index of a catalyst’s activity: The larger the frequency, the more active the catalyst); 2. Confinement (a well-defined and confined local environment of a catalyst’s active site); and 3. Solvation! Everybody in the field is aware of the unique relevance of solvation to catalysis – understanding this defines one of the grand challenges of the field.

Frank Neese: It became very evident that an open dialogue among the various disciplines of catalysis, in particular homogeneous and heterogeneous catalysis, is really needed. At the end of the day, the problems are the same (what are the intermediates? How is selectivity controlled? How is the energy loss minimized?). Yet vocabulary, cultures and challenges of the various disciplines are vastly different, hence there hardly can be any 1:1 transfer from one field to the other. However, it was interesting to see how biochemists have achieved the most detailed understanding of individual reaction mechanisms in biological catalysis. That’s partially because they are willing to devote their entire career to study few reaction mechanisms and to involve experts from neighbouring disciplines in the endavour. Clearly, quantum chemistry has evolved as a very powerful partner of experiment and it’s becoming a universal tool for catalysis research as a whole.


About the author

EF3Emiliano Feresin is a science journalist, currently responsible for the outreach activities within the RESOLV cluster at RUB. Born and raised in Italy, he holds a Diploma and a PhD degree in chemistry. Driven by an innate curiosity for scientific stories, he completed his education with a master degree in science communication. Along the path he has written for outlets like Nature and Chemistry World and learned that the reader has always the last word.

 

 

Embedding nanoparticles into porous materials for greener chemistry.

Chemical and pharmaceutical industries are constantly seeking new ways towards sustainable chemistry that allows for less waste production and reduced energy consumption during industrial processes. One way, which I investigated in my PhD research, would be to use nanoparticles to speed up chemical reactions – a process called catalysis.

Nanoparticles are tiny objects or combinations of several atoms that can be as small as 1 nm and show unique properties, different from the bulk material. Take gold, for example. We are used to its shapes and colors in jewelry, but gold nanoparticles show completely new properties, such as red color in solution or the ability to behave as a catalyst in an efficient and selective manner. Similarly, nanoparticles of Platinum (Pt) and Palladium (Pd) can also act as catalysts in various processes (i.e. hydrogenation, the reduction of organic compounds). Nanoparticles promise to be highly selective, to greatly increase the reaction rate and to lower energy consumption. However, one major disadvantage of nanoparticles is the tendency for aggregation and thus the loss of their unique catalytic properties.

MOFs support nanoparticles for catalysis

In my PhD, I successfully encapsulated catalytically active metal nanoparticles of Pt or a combination of Pt/Pd into stabilising support materials called metal-organic frameworks (MOFs), which prevent aggregation. Inside MOFs, the tiny metal particles could maintain their unique capacity to hydrogenate nitrobenzene-based compounds and additionally be very selective towards the target products. Moreover, I could show that the combination of bimetallic nanoparticles of Pt and Pd with MOFs can surpass the catalytic hydrogenation activity of the monometallic Pt nanoparticles. This alternative solution may help to reduce the costs for the use of noble metals, replacing parts of the expensive Pt by Pd.

Especially in view to catalysis, MOFs exhibit two beneficial properties: Storage capacity (sponge-like property) and molecular selectivity (sieve-like) – in fact, due to the unique microporous structure of the support, the embedded nanoparticles are only accessible by molecules that fit the dimensions of the MOF pores (see Figure 1). MOFs are porous materials, formed by interconnection of organic linker molecules and metal ions or clusters. Thereby, a three dimensional network with a huge inner surface area is formed, which simultaneously possesses enough space to accommodate small sized nanoparticles or other guest molecules and solvents (water, nitrogen, carbon dioxide). Hence, MOFs feature the ability to absorb and/or separate a certain amount of substances at the molecular level, very similar to sponges or sieves.

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Figure 1. Top: Schematic representation of encapsulated nanoparticles inside a MOF with shape-selective, catalytic properties. The smaller substrate A1 is able to infiltrate the framework and can be converted to the target product B at the embedded nanoparticles – the larger molecule A2 is instead unable to infiltrate the MOF. The MOF consists of metal clusters (blue tetrahedra) interconnected by organic linkers, building up a 3D structure, where metal nanoparticles are exclusively embedded. Bottom: hydrogenation of sterically different nitroarenes to the corresponding amines, where aniline is selectively produced (size selectivity).

In my work I choose the Zirconium-based metal organic framework named UiO-66, which appears in a 3-dimensional structures with tetrahedral and octahedral pore geometries. A major advantage of this particular MOF is its extraordinary high thermal and chemical stability against water, acids and several organic solvents. Therefore, UiO-66 represents an appropriate candidate for heterogeneous catalysis, while other MOFs would decompose during the applied catalytic conditions.

Low-cost bimetallic Pd/Pt into MOFs show promising catalytic activity

Following a template approach, we exclusively embedded preformed mono- and bimetallic Pt and Pd/Pt nanoparticles without undesired deposition at the outer surface of the porous material, which in fact represents the key feature for shape-selective catalysis. Then we elucidated the structural integrity of the material and the exact spatial distribution of the nanoparticles (fully embedded into the MOF crystals or not). For instance, powder x-ray diffraction (PXRD) measurements indicated the crystallinity of UiO-66, even after the encapsulation process; transmission electron microscopic (TEM) measurements showed the successful and exclusive encapsulation of the nanoparticles into the core of the MOF crystals.

Afterwards the materials were further studied for selective hydrogenation of nitrobenzene-based compounds to the respective anilines. Direct comparison of the embedded Pt and Pd/Pt NPs showed a much higher catalytic activity for the bimetallic species, while the shape-selective character, originating from the microporous MOF, was maintained. Hopefully, this may become another possible solution towards sustainable.

About the author:

picture2Christoph Rösler received his MSc in Inorganic Chemistry at RUB in 2012 – supervision of Prof. R. A. Fischer . During his Master thesis he visited the labs of Prof. H. Kitagawa at Kyoto University, designing metal nanoparticles, especially multiphase systems. Since 2013 he is a PhD student in the group of Prof. Fischer, tackling metal nanoparticle inclusion into metal-organic frameworks. He also investigated catalytic properties of NP@MOF composites at the the Instituto de Tecnología Química of Prof. A. Corma in Valencia.