Chemocatalysis relies on know-how generated over almost two centuries. Jöns Jakob Berzelius for the first time coined the phrasing ‘catalyzed processes’ in 1836 to describe chemical reactions that are accelerated by ‘magic’ substances. Since these early years catalysis has clearly shaped our society and provided us with the means and goods to enjoy a more prosperous life. Three key examples may illustrate the vast impact of catalytic technologies on our daily life. The first is the discovery of catalysts for the synthesis of ammonia from nitrogen and hydrogen, which has led to the manufacturing of fertilizers. In this manner famines, at least in most parts of the world, have been wiped out. Another breakthrough technology, well-known to almost everyone, is the catalyst for treating the exhaust gases of our cars and trucks, drastically reducing the emissions of greenhouse gases such as nitrogen oxides. A third showcase example is the catalyst technology to convert for example crude oil, created by biomass decomposition over millions of years, into transportation fuels and building blocks for the chemical industry. This development has led to a society heavily dependent on fossil resources. Fortunately, our know-how on chemocatalysis can now be used in an elegant way to foster the transition towards a more sustainable society, with a broader portfolio composed of fossil as well as renewable resources, including, but not limited to biomass. A biorefinery that supplements its manufacture of low-value biofuels with high-value biobased chemicals can enable efforts to reduce nonrenewable fuel consumption while simultaneously providing the necessary financial incentive to stimulate expansion of the biorefining industry. To catalyze research efforts in this area the US Department of Energy (DOE) published in 2004 a group of fifteen chemical opportunities from carbohydrates, including the biotechnological and chemocatalytic research needs required for their production.1
Historically the Netherlands has a vast reputation in catalysis. The Netherlands Institute for Catalysis Research (NIOK) was founded in 1991. NIOK unites full- and part-time professors, lecturers, and PhD students originating from eight Dutch Universities. NIOK has a longstanding tradition as a key initiator of large multidisciplinary research programs. NIOK members, amongst others, published in 2001 the technology roadmap Catalysis, Key to Sustainability, which initiated the launch of a large research program ACTS (Advanced Chemical Technologies for Sustainability), an initiative of the Dutch government, academia, and industry on precompetitive and industrially relevant research, with the aim to anticipate on the needs of the future society. In 2006 NIOK further implemented the catalysis roadmap by entering the field of catalytic biomass conversion.
Since 2007, renewable chemocatalysis has been united in the Netherlands in the research consortium CatchBio. Figure 1 outlines the main philosophy behind the CatchBio program: Fostering the recirculation of CO2, one of the major greenhouse gases. The CatchBio consortium unites chemical industry, universities, and knowledge institutes. The Netherlands is an ideal place for creating the kind of innovation required. The relatively large private sector combined with the considerable expertise in chemistry and chemical engineering both in academia and industry creates a favorable position. The consortium is determined to build further on this strong foundation and to face the challenges of the future together. These challenges are serious, as the gradual shift towards biomass as a renewable feedstock necessitates novel conversion processes that are suitable for this alternative feedstock supply. At the same time this transition must take place as smoothly as possible, by designing alternative manufacturing routes that seamlessly fit into the existing production infrastructure of the chemical industry.2 The Netherlands have a long tradition in public-private funded R&D. CatchBio builds further on this practice by uniting ten Dutch universities and research institutes, global companies such as Shell, BASF and SABIC, and small and medium enterprises (SMEs) such as the renewable chemicals producer Avantium.
The Catchbio consortium is organized along five classes of biomass based feeds: i) sugars, ii) (hemi)cellulose, iii) lignin and humines, iv) vegetable oils, and v) proteins (this feedstock approach is summarized in Figure 2). The ultimate goal in CatchBio is to rely on the nonedible parts of the biomass, which is where the challenging and complex chemistry comes in. Researchers in CatchBio aim to valorize these feeds towards biofuels, building blocks for bulk chemical intermediates and to highly functionalized fine chemicals. This Special Issue of ChemSusChem is dedicated to state-of-the-art chemistry within the field of chemocatalytic biomass conversion, specifically focusing on the joint research efforts in The Netherlands within the public–private research consortium CatchBio.
To develop processes for the efficient utilization of biomass resources, it is important to understand how catalysts can be used to alter the high degree of oxygen functionalities in biomass-derived molecules.3 Consider, for example, lignin. Waste from the paper industry, wood waste, wheat straw, and other nonfood biomass streams all contain lignin. It is abundant and cheap. This makes lignin an ideal starting material for catalytic conversion with a focus on the manufacture of valuable and useful aromatic platform chemicals, which can be used as the building blocks for example biomass based bottles. Lignin is a natural amorphous polymer that acts as the essential glue that gives plants their structural integrity. It is a main constituent of lignocellulosic biomass (15–30% by weight, 40% by energy), together with cellulose and hemicelluloses. The complicated lignocellulosic structure serves to protect the plant species from microbial attack and provides resistance to the elements, yet it also makes the material recalcitrant to chemical reaction or fermentation to useful products. In particular, the nature of biomass feedstocks (CnHmOo), which contain a high oxygen content and various ether linkages that make them more hydrophilic, differs significantly from hydrophobic petroleum feedstocks (CnHm). These differences have ramifications for the development of suitable catalysts. CatchBio researchers have developed catalytic technology that can dissolve almost all types of lignin. It can help convert 20% of lignin into interesting chemical building blocks, an outstanding yield. Lignin is a tough nut to crack, but its conversion into chemical feedstock is highly promising in the long run.5, 6
The most abundant constituents of biomass are (hemi)cellulose-derived sugars. Within CatchBio several research groups work in close collaboration with the industrial partners on valorizing these sugars towards valuable platform chemicals such as furfural,7 hydroxymethylfurfural (HMF),8 and levulinic acid (LA). These platform chemicals give access to a high variety of bulk chemicals with high value turnovers on the market. Alternative value chains involve biopolymers which are converted in one or several steps to functional materials.9 CatchBio researchers successfully applied the combination of high-throughput screening and detailed kinetic studies to determine the differences in reactivity between hexoses in the acid-catalyzed dehydration to HMF. The screening shows that different ketoses have different reactivity in the acid-catalyzed dehydration to HMF (Van Putten et al.).
Such acid-catalyzed conversions of the (hemi-)cellulose fraction of lignocellulosic biomass to these platform chemicals are, however, unavoidably accompanied by the formation of so-called artificial humin byproducts, in short referred to as humins. Humins are carbonaceous, heterogeneous, polydisperse materials of which the molecular structure is largely unknown. The challenge chemists are facing with humin formation is twofold, that is: to suppress humin formation or to valorize the humins themselves (Van Zandvoort et al.). The only application of humins so far is for generating heat via combustion. Interestingly, most conversions in the biorefinery involve a hydrogenation step. This requires import of hydrogen from external fossil sources, which is expensive and not sustainable. In this context, efficient conversion of humins to syngas (CO + H2) or hydrogen is interesting from an (socio-)economic perspective. Hydrogen generation from humins would allow complete usage of feedstock in sugar conversion processes by generating hydrogen from what is normally considered a waste byproduct (Hoang et al).
Pyrolysis is a heating process that cracks substances without using oxygen. Lignocellulosic biomass can be converted into bio-oil by fast pyrolysis. The bio-oil can then be gasified to give syngas, or can be separated to give phenolic compounds and/or carbohydrate fractions. Of the various thermochemical processes available for biomass conversion, pyrolysis is the preferred conversion method.10 Pyrolysis is an appropriate process for the conversion of large amounts of wood into bio-oil, from which biofuels and chemicals can be produced. However, some important bio-oil characteristics are disadvantageous, such as high water and oxygen content, corrosiveness, lower stability, high acidity, high viscosity, and low calorific value. Therefore, improvement of the bio-oil quality is a prerequisite before upgrading to biofuels can be envisaged. The conversion of woody biomass into pyrolysis oil takes just two seconds. Biomass is cracked into ‘oil gas’, which condensates to an oil. After further treatment, up to 20% of this oil can be mixed with crude oil in the existing refinery process. By making smart use of catalysts, researchers ultimately hope to enhance the pyrolysis oil quality to create ‘green crude oil’.11
Even closer to practical application is the conversion of fatty acids from nonedible vegetable oil and used cooking fats into diesel.12 All one needs are vegetable oil and fats and a catalyst; the simplicity gives this conversion process its competitive edge. There is no need for chemicals such as methanol or hydrogen. Furthermore, the process can be carried out on a range of scales, from small to industrial. CatchBio chemists study the role of feedstock, reaction conditions, and nature of the catalyst on the reaction pathways for deoxygenation of vegetable oils and its derivatives (Gosselink, Hollak et al.). Stellwagen et al. show how the performance of functionalized carbon nanofibers in the transesterification reaction illustrates the benefits of catalyst design in the acid-catalyzed biodiesel production.
But CatchBio researchers study more options for valorizing the biomass. Dissolving, pyrolyzing, or electrochemically upgrading the biomass by means of a catalyst is one way to go. Gasification and consecutive Fischer–Tropsch synthesis (FTS), for converting a mixture of carbon monoxide and hydrogen into liquid hydrocarbons, is another. Currently, however, gas-to-liquid (GTL) technologies are only economically attractive at very large scales. Process intensification and new catalyst developments are a must if FTS technology is to be applied for biomass-to-liquid (BTL) conversions, where the availability of the feedstock near the chemical plant can be an obstacle. Within this context, Sartipi et al. have explored bifunctional cobalt-based catalysts on zeolite supports for the valorization of biosyngas through Fischer–Tropsch chemistry. By using these catalysts, waxes can be hydrocracked to shorter-chain hydrocarbons, increasing the selectivity towards the C5–C11 (gasoline) fraction.
Some processes in the fine chemicals industry are still inefficient in terms of energy consumption, raw materials utilization, and waste production. CatchBio develops improvements: more efficiency, less waste, and reduced use of harmful agents. An example is the conversion of bioalcohols into amines in a single step process, whereas previously a two-step conversion was required.13 The only waste product after the single step process is water. The resulting amines can be used to make polymers and drugs. Furthermore, the possibilities of specific biomass streams for fine chemical applications are being investigated. An example is the use of cashew nut shells.14 At present, the oil from these shells is used in polymers, but there might be even more value-added applications still. As shown by Perdriau and co-workers, hydroxystyrene derived from these shells can be converted into hydroxybenzaldehyde and hydroxybenzoic acid. These aromatic compounds can be further processed into pharmaceutical products, pesticides, or cosmetics.
It is important that newly developed sustainable processes really are a step forward when it comes to environmental impact and economic viability.15 The CatchBio consortium therefore includes the academic know-how needed to calculate the socio-economic impact of these processes throughout the entire production chain. For example, Patel et al. evaluate eight novel biobased processes being developed within CatchBio. In the assessment methodology, each of the chemical process options is evaluated in comparison to a conventional alternative based on indicators that represent economic feasibility, environmental impacts, hazards, and risk aspects.
By the end of 2016 CatchBio researchers aim to handover integrated process concepts to the industrial partners. To end up with these concepts a three-stage approach has been enrolled since the start of the consortium in 2007. In the first two phases a broad scientific basis has been created. PhD researchers have gained fundamental insights in the state-of-the-art chemistry needed to handle biomass in a chemical reactor. In phase 3 of the program, industry selected from this broad basis the most promising leads on the basis of predefined criteria: i) The selected catalytic system should be an improvement compared to the state-of-the-art with respect to properties such as conversion, activity, product stability, and robustness; ii) A socio-economic assessment of the catalytic system should give clear indications that the system contributes to reduced CO2 emissions; in-company economic assessments were included as well. The selected leads have been integrated in three program lines, for which post-doctoral researchers will be recruited to bring them towards integrated process concepts by the end of 2016. Figure 2 gives an overview of the set-up of the CatchBio program.
CatchBio’s main goal is to enable and support the paradigm shift the chemical industry is going through. Yet the deliverables can also be found at other levels. For academia, it is important to tap into the demand from industry and society. CatchBio creates and strengthens a network that benefits both industry and academia. Companies regard this public–private partnership as an important field of recruitment for their future staff. They wish to hire the smartest and brightest—and they find them within the CatchBio network. Candidates with a background in CatchBio are thoroughly trained in biobased thinking. Those new colleagues can inspire existing staff and spread a new way of thinking throughout the industry (Figure 3).
But the Netherlands remains after all a small country. Joining efforts in renewable catalysis is not only a Dutch demand. Teaming up across Europe and beyond is a prerequisite to give a boost to science and industry to make this transition towards a more sustainable society, partially based on biomass, really happen. Therefore, CatchBio set up collaborations with RWTH Aachen and the universities of St. Andrews and Edinburgh. This we consider the first step towards uniting renewable catalysis across Europe. One network to fulfill the societal demands for green chemical building blocks. With the huge shale gas reserves in the US an exciting time is ahead of us. What will probably become a challenging time for biomass-derived C1 and C2 building blocks, opens up new markets for biomass derived C3, C4 and aromatic building blocks.16