We Cannot Continue to Rely on Platinum and Palladium
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We Cannot Continue to Rely on Platinum and Palladium

Author: Vera KoesterORCID iD, R. J. M. (Bert) Klein Gebbink

Professor R. J. M. (Bert) Klein Gebbink is Vice Dean of Education and Professor at Utrecht University, The Netherlands. Here, he talks with Dr. Vera Koester for ChemistryViews about his fascination with manganese and iron catalysts, as well as his deep interests in sustainability and education, while addressing the associated challenges.

 

Can you tell us a bit about your research?

My research group has been working in the field of homogeneous catalysis for a long time. Over the years, our focus has shifted more and more towards sustainable and circular chemistry. At the core of our work is the design of molecular catalysts for selective transformations.

Over the years, the focus has moved from using catalysts based on noble metals to using more abundant metals as the catalytic sites in these compounds. In the past, we worked with palladium and rhenium compounds, but these days we are working with iron and manganese. Very abundant and very cheap metals, and also metals with low toxicity.

 

How do you choose your research topics? Do you begin with iron and manganese catalysts and then explore what reactions they can catalyze, or is it vice versa, starting with a specific reaction and then selecting the catalysts accordingly?

It is a bit of both. At the moment we focus a lot on molecular oxidation catalysis. There, it is simply the fact that iron and manganese are by far the most active and proficient catalysts with the kind of ligands that we are using. Consequently, that is the flow that you follow.

For other projects, we have set different targets. If, for instance, you say, we want to explore a new type of reaction or develop a new protocol, then you pick up what is already existing and develop from there. In doing so, you find yourself sometimes using other metals. However, the focus is really to stay away from the “normal” metals as much as possible.

 

How did that start?

It started from my interest in metalloenzymes. I did my Ph.D. with Roeland Nolte in Nijmegen, The Netherlands, and the topic was trying to make supramolecular models for the active site of metalloenzymes. If you look at metalloenzymes, none of these use a noble metal. They all use non-noble metals for various reasons. That is how I got into studying iron compounds, copper compounds, and later on, also manganese compounds.

Two aspects are coming together here: First, a fundamental interest in how a metalloenzyme works and whether we can understand metalloenzymes better by making very small mimics for these active sites.

Second, a sustainability aspect: realizing that, hey, we can’t just keep on using platinum and palladium for the next century, because then we run out of it, basically. We have to come up with something else.

 

What are the largest challenges in this field of chemistry for you?

The largest challenge is controlling the chemistry. Of course, with palladium and platinum, as a field, we believe that we have a pretty good control. The underlying chemistry is relatively well-defined, reactions occur at a manageable pace—though they can be fast, they are not too fast—and ligands tend to remain pretty nicely bound to these larger and heavier metal ions.

When you move to the smaller metal ions, especially those in the first row of the transition metal series, the kinetics of ligand exchange speed up enormously. You always have to ask the question: What is it that I have in my flask? While you might have a well-defined crystal structure, in many cases, it doesn’t accurately represent what’s present in the solution—unlike our experiences with platinum.

Then, the redox chemistries are faster and more diverse. Just having a good idea of what you have in the flask and what this thing is actually doing, is much more complicated.

And then the next step, studying that, is even more complicated because everything is paramagnetic. One of my current students, who has been working on his project in manganese chemistry for about two years now, was complaining to me: Within our larger research unit, everybody can use NMR and they all know what their molecules look like in solution. However, when it comes to his manganese compounds, every attempt to use NMR results in absolute nothingness; there’s no useful data to be found.

 

So what techniques do you use?

We use advanced mass spectrometry a lot because it provides a reasonably representative understanding of the ions that we have in our solutions. Electron paramagnetic resonance spectroscopy (EPR) we use occasionally, but its value lies more in investigating the electronic structure rather than the geometrical structure. Then X-ray crystallography comes into play, but it provides solid-state structural information, not solution-state data. And that’s about it, at least for manganese.

You can use optical spectroscopy, but, again, it is much less accurate, and our students are generally less well-trained in this technique. So, these are real challenges with the big question: What is it that I have in my flask?

 

Is the active site of an enzyme always the model for your catalysts?

Our research is going in different steps, starting with abstracting what you see in the active site of an enzyme. It is almost like distilling essential factors out of that to create a first model. We then assess whether this model is representative, both structurally and in terms of activity. Often, our structural analogs align pretty OK with the active site of the enzyme with good geometrical and spectroscopic similarity, but then lack the proper reactivity. This leads us to focus on improving activity by moving away from structural mimicry.

While our initial inspiration always stems from enzymes, the actual structure of our catalyst may be several steps away from what the enzyme’s active site looks like.

 

In the future, do you think that we can manage to go towards less toxic metals in catalysis?

I think we have to. We have to do it because of the toxicity, which I think will remain an issue, but also because of availability. I think in the near future, it will be quite difficult to ensure a sufficient supply of precious metals. So far, we have been relying on the fact that all of these precious metals are close together in Nature because they form ores and it’s relatively easy to harvest them. That is why we have platinum mines, that is why we have rhodium mines.

Often, we use them as nanoparticles, and these nanoparticles are spreading on the Earth’s crust. Where initially platinum, rhodium, and the others were, found in “hot spots” so to say, for example, in South Africa, now we are very slowly spreading them.

There is this interesting urban legend that has been around for quite some time that says that the amount of rhodium and platinum that you can find in the dust that you can collect from the highway is higher than the percentage of rhodium and platinum that is found in mines these days.

 

What do you think of the concept of circularity?

Circularity is, I think, the next step in sustainable chemistry. The concept of sustainability is broad and widely accepted, emphasizing that the chemistry we develop should prioritize sustainability in various aspects. The next step in this development is to go circular.

This even involves the element of carbon. What do we do with the carbon that we put, let’s say in step one, into our chemical factories? We give it to the consumers as a product, in whatever form, and what happens next? I think there are a lot of incentives in this area now. We need to close the loop on the elements, the cycle of goods. We need to do a better job of managing the supply of our resources, and I think the concept of circular chemistry is very nice in this context.

One of my colleagues from Amsterdam, Chris Slootweg, was one of those who advocated for these ideas some years ago, and many have now taken them up: We need to think of materials and molecules circularly from the start. This is circular by design. I think this will be the future of chemistry, that we know how to keep a good hold on the resources that we have on this planet. They are plentiful, but there’s also a limit. That is why we need to think about circularity, how to manage circularity, how to design for circularity, and actually, that is one of the reasons why in Utrecht, together with Bert Weckhuysen and some other colleagues like Pieter Bruijnincx, we recently started a new institute. It’s the Institute for Sustainable and Circular Chemistry. We deliberately combined the two buzzwords “sustainable” and “circular” in the name.

 

We have been talking about circularity for quite a while now. How far away are we still?

We are still at the very beginning. In the Netherlands, for example, the recycling of goods works very well in some respects. The recycling of paper and glass, for example, is, as in many other countries, in the process of forming a relatively closed loop. The percentage of recycling, at least what consumers bring back, for paper and glass is over 90 %, which is a lot.

For the recycling of plastics, it looks a little different. At least plastics are collected. What is then done with the collected plastic? Sometimes it is just added to furnances to keep the temperature. That’s not circular.

A circular economy can come about in many ways. Now, if you can capture the CO2 that comes out of the ovens really well and recycle it efficiently, then burning plastic can also be a form of circular economy. A question is, how much energy do you need to do that? There are some really big challenges there.

 

Are we too slow to adopt it?

I don’t think we are slow. I think we’re relatively fast in conceptualization because there are several principles for circular chemistry now. So I think that within a relatively short amount of time, we can develop concepts, put things in writing, and say this is what we need to do and these are the principles that can help us do it.

But then the real stuff starts, you know. Just because you have the idea, that doesn’t mean you can actually make and market the product or molecule that you have in mind. And then consumer adoption is the next big thing. I think that’s one of the biggest challenges overall in sustainability—convincing consumers of what we’re facing.

I think policy and governments have an instrumental role to play in opening the doors. A society has to be pushed in a certain direction because sustainability might be a little bit more expensive. With bio-based materials, initially, you thought, okay, there’s a large group of people who are willing to pay a bit more for a bio-based product. No. The product has to be better, and it has to be cheaper. That’s what we learned. That’s why these are real challenges. We can come up with fantastic molecules or fantastic ideas but also the whole cycle needs to work.

 

Education

Let’s move on to education. How can we get chemistry students to internalize the principle of “My molecule not only has to have a great function or, I don’t know, be great, but it also has to be sustainable”?

I think the education of our students is one of many starting points. I mean, the students that we’ve trained over the last decades are fantastic. They know how to make molecules, materials, and a lot more. But in their training, the real concepts of sustainability—and now, circularity—have not always been included, per se. I think we should include these concepts at the very beginning of our students’ education. They should be aware from the beginning that this is important for the survival of our planet.

For example, in Utrecht, in conjunction with our new institute, we will be launching a new master’s program next year that will focus exclusively on sustainable and circular chemistry. There, these concepts are in the minds of the students from day one. In addition to the typical chemistry courses, we will offer them courses in toxicology, life cycle assessment, and the like. We need to train the minds of our students, the future chemists, to really push this forward. This is about education and the next generation.

 

You are the Vice Dean of Education at Utrecht University. What does that mean?

I have been Vice Dean for Education for a year now. To give you a bit of an idea of the size of the faculty: The faculty itself has a total of 8,000 students. They are all in the natural sciences, from pharmacy to mathematics. One of the guiding principles that we as a faculty use is the Sustainable Development Goals of the United Nations. Of course, many of these relate to the natural sciences and also to the life sciences. So we are incorporating that more and more into the education of our students.

 

Does that mean, because you’re responsible for all of these subjects, that there’s more of an interdisciplinary look at studies?

I think that is a very nice question. Increasingly, we are including interdisciplinarity in our work. In the past, the Dutch education system was traditionally organized in a monodisciplinary way—chemistry, physics, biology—but now we see more and more that we mix these disciplines and even that we are creating an interdisciplinary natural sciences domain, for example. At the master’s level, this has been going on for some time, but also at the bachelor’s level, a group of students are already being trained from the beginning in this interdisciplinary way of thinking and collaborating with students from other disciplines. I think that’s very important.

The way we look at this now is that we want to offer both types of training because I think that we still need the hardcore experts, but we also need the people who can manage the overall problems.

 

Research Group and Hobby

In your research group, how do you teach young talents to be creative and have new ideas?

It may seem like a natural thing, but we’ve found, like many others, that you have to foster that. We try to have an open group atmosphere and open discussions. For the last couple of years, and this was the initiative of one of the assistant professors, every group meeting starts with an open discussion about a safety aspect that is unique to the lab. What’s interesting here is that students are a little uncomfortable at first when you start something like this. You have to be persistent, but after a while—and now we’re a couple of years down the road—you can see that they’re openly discussing safety, but they’re also more openly discussing other things in the group. I am very happy with this initiative. This open culture, where you discuss not only the chemistry projects that you do but also other aspects of science, will benefit many students and help their education, I think.

 

What inspires you most in chemistry?

I think those are the two topics that we were talking about: pushing sustainability and the education of young people forward. Those are the two things that motivate me a lot.

 

What do you do besides chemistry?

There are a number of things. To pick out one thing, I’m quite an avid cyclist …

On Friday morning, we leave with a small team of people for the north of Italy. As part of a big fundraising event to raise money for cancer research, we will cycle back from northern Italy to the Netherlands in eight days, trying to cross as many mountains as possible. In eight days, it’s 1,300 kilometers and over 19,000 altitude meters.

So that is one of my hobbies. It keeps you fit, but also keeps the mind sharp and it is a lot of fun.

 

Wow, very impressive and super cool. So You have been exercising quite a bit

I guess so, yesterday morning it was 130 kilometers …

 

Thank you very much for the interview and good luck on your bike tour.

Robertus (Bert) J. M. Klein Gebbink obtained his Ph.D. in supramolecular and bioinorganic chemistry under the supervision of Roeland Nolte from Nijmegen University, The Netherlands, in 1998. After completing postdoctoral studies at Stanford University, CA, USA, he accepted a senior postdoctoral position at Utrecht University with Gerard van Koten in 1999. In 2005, he became a Full Professor of Homogeneous and Bioinspired Catalysis at Utrecht University.

In the past years, he served as head of the chemistry department at Utrecht University and as the coordinator of the European initial training network NoNoMeCat on Non-Noble Metal Catalysis.

His research interests span the broader fields of homogeneous catalysis, organometallic chemistry, and bio-inorganic chemistry.

 

Selected Awards

  • VIDI personal grant from The Dutch National Science Foundation (NWO), 2004
  • MSCA-ITN-ETN Training Network NoNoMeCat, on Non-Noble Metal Catalysis, 2015
  • Rennes International Master Lectureship on Catalysis and Green Chemistry, 2023

 

Selected Publications

 

 

 

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