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CO2 is the end-product of the largest-volume and most globally applied chemical reaction: the combustion of hydrocarbons and biomass. It has long been considered an irrelevant waste. A long latency period ensued, during which the increasing body of scientific evidence for the relationship between increasing CO2 emissions and climate change only slowly built up momentum, due in part to both the long time-scales of global natural carbon cycles and to innate resistance from the current energy-supply infrastructure. CO2 emissions eventually became a societal concern and elicited political actions aimed at curbing emissions. By then, the image of CO2 was mostly that of a “devil” molecule. Not surprisingly, the main focus of the discussions to go beyond the necessary CO2 emission reduction and prevention was on the methods to capture and sequester CO2 rather than on its reuse (with the exception of a limited group of scientists). For example, until the most recent (4th) version of the Intergovernmental Panel on Climate Change (IPCC) report published in 2007, the possibility of reusing CO2 was not among the cited mitigation policies.

Duncan Graham-Rowe, in a March 2008 article in New Scientist called “Turning CO2 back into hydrocarbons”, remarked that it was time to stop considering CO2 as a devil molecule and to start considering it as a resource. There are several simple reasons: (i) with the increasing socio-political pressure on reducing CO2 emissions and the creation, in several countries, of carbon-emission taxes, CO2 becomes an interesting raw material with a cost of zero, or even negative costs; (ii) visible CO2 management strategies can become a positive part of a company′s public image; and (iii) recycling CO2 rather than storing it [carbon capture and recycle (CCR) vs. carbon capture and sequestration (CCS)] avoids the cost induced by transporting CO2. The cost factor is critical because it can amount to up to ca. 35–40 % of the total CCS costs when the capture site is located more than ca. 100–150 km away from the storage site (a common situation in, for example, many European countries), and CCR thus becomes a valuable economic alternative to CCS.

Scientific and industrial initiatives towards the chemical utilization of CO2 have thus increased substantially over the last few years. This special issue of ChemSusChem, which complements the August 2010 special issue on Carbon Capture and Storage, is dedicated to recent advances in the field of CO2 conversion into chemicals and fuels, with particular attention to industrial perspectives and large-volume options. The aim of this special issue is to provide a panorama of the possibilities for chemical utilization of CO2, new trends, and research areas, from both fundamental and applied perspectives.

We have collected an array of invited and contributed papers that address the challenges of CCR. The issue includes 12 contributions, including two Reviews and two Minireviews, one Highlight and one Concept Paper, five Full Papers, and one Communication. Most of the papers feature content presented during the “CO2 Forum 2010 (Large-volume CO2 recycling)” held on September 27–28, 2010 at the CPE Lyon School of Engineering (France) and/or at the workshop “CO2: From waste to value” organized on March 30, 2011 in Brussels (Belgium) by the European Commission. These contributions, in particular the introductory Review on “Emerging Large-Scale Technologies Around Carbon Dioxide Recycling With Industrial Potential”, also reflect the intense, active discussions heard during these meetings. The increasing support for climate-safer actions, the possibility of increasing carbon taxation, and an overall possibility of tapping into CO2 as a zero- or even negative-cost chemical feedstock are indeed stimulating existing or emerging routes for the chemical utilization of CO2 (see Review by Müller, Leitner et al.) some already industrialized or with substantial industrial potential (see Review by Quadrelli et al.).

Among the routes for CO2 utilization, mineral carbonation (see Wang and Maroto-Valer) is explored as a possible link between long-term CO2 disposal by CCS (see Vitillo et al.) and synthesis of marketable materials by CCR. In organic chemistry, CO2 is emerging as a precursor to carbonates (see Ballivet-Tkatchenko et al.), acrylates (see Kühn et al.), carboxylic acids (see Highlight by Martìn and Kleij), and polymeric materials. In this context, CO2 is emerging as a valuable, eco-friendly chemical per se, possibly as a “green” carbonyl alternative to toxic phosgene for some synthetic routes. Furthermore, because carbonates, both inorganic and organic, are generally stable materials they become relevant in carbon-management strategies aimed at contributing to medium- and long-term storage policies.

CO2 recycling could also have a very meaningful impact on CO2 emissions if fuels, rather than only chemicals, could be obtained by means of direct CO2 conversion. Fuels from CO2, rather than chemicals from CO2, are expected to play a major role in CO2-emission management strategies for two main reasons: firstly, because the volume of the world-wide fuel market is about two orders of magnitude larger than that of chemicals; secondly, because CO2 emissions are mainly associated to energy use.

From a chemical perspective, the synthesis of fuels [i.e., the reduction of CO2 by cleavage of one or both C[DOUBLE BOND]O bond(s) and conversion into other C1 (CO, CH3OH) or Cn molecules] is crucially distinct from previous carboxylation examples, both in terms of energy balance and in terms of the applications of the resulting products. While the above-mentioned carboxylation reactions are generally not energy-intensive (because the CO2 moiety is incorporated intact into either the organic backbones of the organic products or into the inorganic frameworks of minerals), the reduction reactions are energy-intensive. Therefore, for this latter class of reactions [there included the electroreduction reactions (see Sridhar et al.)], the energy source (and more specifically within the present context of CO2 management, the need for renewable ones) is crucial. The involvement of an energy source also turns the molecules issued from CO2 reduction, such as formic acid (see DiBenedetto, Aresta et al. and the Minireview by Surya Prakash, Olah, et al.), into potential energy storage molecules, that is, CO2-based energy vectors for the storage of solar energy or other renewable energy sources.

An important part of CCR approaches lies in the capacity to exploit solar energy directly through biomass. CO2 biofixation through enzyme and hybrid technologies and by specific photobioreactor design (see Minireview by Su et al.) are necessary to meet the “fatter, faster, cheaper, and easier” microalgal biotech objectives of the National Algal Biofuels Technology 2009 Roadmap. From a strategic perspective, the chemical or biochemical reduction of CO2 into fuels or into large-volume chemicals such as light olefins (as discussed in the Concept paper by Centi and Perathoner) is a valuable opportunity to introduce renewable energy into the existing energy and chemical infrastructure (i.e., “drop-in” renewable energy), thus becoming a key pillar towards realizing a sustainable and resource-efficient chemical and energy production.

In summary, this issue of ChemSusChem dedicated to the recycling of CO2 into fuels and chemicals shows that the chemical transformations of CO2 comprise a dynamic field of research, in which many industrial initiatives also thrive. As is generally the case in such situations, many different options are being explored and it is not always straightforward to grasp the real opportunities and limitations of each option, but some indications about time frames associated with a CO2 utilization roadmap emerge:

• In a short-to-medium term, CO2 utilization as a raw material is expected to continue its progression, with several new products coming onto the market (e.g., polycarbonates).

Within the same timeframe, CO2 recycling can become an important component of the strategy portfolio necessary for curbing CO2 emissions: with very optimistic assumptions, CCR can offer a potential reduction equivalent of 250–350 million tonnes per year in the short-to-medium term, mostly driven by methanol, dimethylether, and dimethylcarbonate syntheses. This corresponds to about 10 % of the total reduction required globally, and is at a level comparable to the expected impact of CCS technologies.

• In the long term, CO2 recycling can become a key element of sustainable carbon-resource management in chemical and energy companies, combined with curbing consumption. CO2 can also become a strategic molecule for the progressive introduction of renewable energy resources into the chemical and energy chain, thus helping to slowly lessen our consumption of fossil fuels.

• A common element that emerges from these contributions is that CO2 is already at the heart of present strategies for sustainable chemical and process industries, where controlling both energy consumption and CO2 emissions is becoming a key priority. Similar actions are taking place in governmental bodies. For example, a resource-efficient Europe is the flagship initiative of the Europe 2020 Strategy, with CO2 management as its backbone.

Also on behalf of the editorial team of ChemSusChem, we hope that you enjoy this issue, and that the future will bring many exciting new contributions from the chemical sciences aimed at improving CO2 recycling and increasing its role in sustainable chemistry. In the International Year of Chemistry 2011, as launched by the United Nations Educational, Scientific and Cultural Organization (UNESCO) and by the International Union of Pure and Applied Chemistry (IUPAC), we believe that this issue of ChemSusChem celebrates how chemistry employs itself to address one of mankind′s current challenges and how it attempts to contribute to society by trying, with the means at its disposal, to turn a global problem into an opportunity.

Biographical Information

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Elsje Alessandra Quadrelli earned her B.Sc. in chemistry from the Scuola Normale Superiore di Pisa (Italy), and her Ph.D. from the University of Maryland (USA). She is currently a confirmed CNRS researcher in the field of catalysis and organometallic chemistry and head of the sustainable development chair of École Supérieure de Chimie Physique Électronique de Lyon (CPE Lyon, France); a chair sponsored by DOW Chemical. She co-chairs the decarbonated energies workgroup of the French competitive cluster AXELERA. Her current research interests are N2, SiH4, and CO2 activation by silica-supported organometallic complexes and by novel functional materials, such as metal organic frameworks. She organized the first “CO2 Forum (Large-volume CO2 recycling)” in Lyon (France) in 2010.

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Biographical Information

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Gabriele Centi completed his industrial chemistry studies at the University of Bologna (Italy) and is currently Professor of Industrial Chemistry at the University of Messina (Italy). He is a former President of the European Federation of Catalysis Societies, and was co-ordinator of the European Network of Excellence on Catalysis IDECAT. He is co-Chairman of the Editorial Board of ChemSusChem. His research interests lie in the development of industrial heterogeneous catalysts for sustainable chemical processes, environmental protection, and clean energy.

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