Elemental Sustainability for Catalysis

Green Chemistry Centre of Excellence, Department of Chemistry, The University of York, Heslington, York, YOlO 5DD, UK Email andrew.hunt york.ac.uk 

Sustainable Catalysis With Non-endangered Metals, Part 1 

The factors that influence if elements are deemed as having a high associated risk of supply issues (or are deemed to be critical) can include but are not limited to  

Element Estimated continental crustal abundance symbol (uimg/kg) Resources remaining from traditional sources (Years) Main geographical location of known resource Estimated recycling rates f/of 

Critical elements of global importance Rare Earths / 100 + China 1 

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It is vital that we seek to maximise the metals catalytic activity and recover 100% of elements from catalytic processes at both the end of reaction and end of life (the only exception may be carbon that can be burnt for energy production at end of life). Development and application of Earth-abundant catalysts for a wider range of catalytic applications is possible in the midterm. However, the long-term and ideal scenario would be that even critical elements can be used as sustainable catalysts if total recoveiy from anthropogenic cycles is guaranteed. The concept of elemental sustainability for catalysis is likely to become increasingly important in the future. Now is the time for producers and users alike to progress to circular economies and embrace sustainable catalysis. 

A. J. Hunt and T. J. Farmer, Elemental sustainability for catalysis, in sustainable catalysis, ed. M. North, Royal Society of Chemistry, London, 2015. 

However, most of the available metal-based eatalysts for ROP and a-olefin polymerisation suffer from inherent toxicity, low abundance, high price and are listed as endangered elements, which is in contradiction with their application in green and sustainable procedures for polymer synthesis. In line with sustainable catalyst development, titanium is nontoxic (no known biological role), readily accessible and an abundant element (crustal abundance of 4136 ppm with the lowest supply risk searcity factor is about 2.5/8.5) making this element one of the most attraetive metals for use in sustainable polymerisation catalysis. 

All three metals have been used extensively in homogeneous catalysis of organic reactions. Early work focused on copper thus the catalysis-related literature for this element is abundant.4 Silver had sustained continuous interest,5 but never to the extent that copper experienced. Gold is the youngest member in the field of catalysis, but is currently (as of 2009) catching up at an incredible rate.6... 

Catalysis is thus a driver for sustainability and societal challenges [51] and for a sustainable energy [52, 53[. New demand for applications (e.g., the area of biorefineries [54, 55[) and new advances in both the ability to control catalyst characteristics through nanotechnologies [56, 57[ and to understand catalytic reactions [58-62] have greatly renewed the interest in catalysis and changed the research topics and approaches with respect to few years ago. We could thus conclude that catalysis is not only a key element for the sustainability of chemical processes but also that the recent advances in this area have further enhanced its critical role. 

Contained within this book are various chapters that review the possibilities for the sustainable use of catalysts in our chemical industiy. Earth abundant metals are discussed in Sustainable Catalysis With Non-endangered Metals, Parts 1 and 2, while the options for organocatalysis are discussed in Sustainable Catalysis Without Metals or Other Endangered Elements, Parts 1 and 2. The future chemical industiy cannot survive by the use of just one of the above catalyst classes, but will require the flexibility and versatility of both. An important aspect of sustainable catalysis that is also vital for the long-term security of elements is ensuring that we establish improved methods of catalyst recovery and reuse. 

There are many challenges to the science of catalysis that need to be met over the coming years. A sustainable future calls for the development of catalytic processes that do not rely on a net input of fossil resources. This can only be achieved if we discover new catalysts that can efficiently utilize the energy input from the sun or other sustainable sources to synthesize fuels as well as base chemicals for the production of everything from plastics to fertilizers. It also requires more selective processes with fewer waste products and catalysts made from Earth-abundant elements. This represents a formidable challenge. This textbook describes some of the fundamental concepts that will be needed to address this challenge. 

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