Pieter C. A. Bruijnincx

The Catalytic Valorization of Lignin for the Production of Renewable Chemicals

Biomass is an important feedstock for the renewable production of fuels, chemicals, and energy. As of 2005, over 3% of the total energy consumption in the United States was supplied by biomass, and it recently surpassed hydroelectric energy as the largest domestic source of renewable energy. Similarly, the European Union received 66.1% of its renewable energy from biomass, which thus surpassed the total combined contribution from hydropower, wind power, geothermal energy, and solar power. In addition to energy, the production of chemicals from biomass is also essential; indeed, the only renewable source of liquid transportation fuels is currently obtained from biomass.

Paving the Way for Lignin Valorisation: Recent Advances in Bioengineering, Biorefining and Catalysis

Abstract Lignin is an abundant biopolymer with a high carbon content and high aromaticity. Despite its potential as a raw material for the fuel and chemical industries, lignin remains the most poorly utilised of the lignocellulosic biopolymers. Effective valorisation of lignin requires careful fine‐tuning of multiple “upstream” (i.e., lignin bioengineering, lignin isolation and “early‐stage catalytic conversion of lignin”) and “downstream” (i.e., lignin depolymerisation and upgrading) process stages, demanding input and understanding from a broad array of scientific disciplines. This review provides a “beginning‐to‐end” analysis of the recent advances reported in lignin valorisation. Particular emphasis is placed on the improved understanding of lignins biosynthesis and structure, differences in structure and chemical bonding between native and technical lignins, emerging catalytic valorisation strategies, and the relationships between lignin structure and catalyst performance.

Catalytic Lignin Valorization Process for the Production of Aromatic Chemicals and Hydrogen

With dwindling reserves of fossil feedstock as a resource for chemicals production, the fraction of chemicals and energy supplied by alternative, renewable resources, such as lignin, can be expected to increase in the foreseeable future. Here, we demonstrate a catalytic process to valorize lignin (exemplified with kraft, organosolv, and sugarcane bagasse lignin) using a mixture of cheap, bio-renewable ethanol and water as solvent. Ethanol/water mixtures readily solubilize lignin under moderate temperatures and pressures with little residual solids. The molecular weight of the dissolved lignins was shown to be reduced by gel permeation chromatography and quantitative HSQC NMR methods. The use of liquid-phase reforming of the solubilized lignin over a Pt/Al(2)O(3) catalyst at 498 K and 58 bar is introduced to yield up to 17 % combined yield of monomeric aromatic oxygenates such as guaiacol and substituted guaiacols generating hydrogen as a useful by-product. Reduction of the lignin dissolved in ethanol/water using a supported transition metal catalyst at 473 K and 30 bar hydrogen yields up to 6 % of cyclic hydrocarbons and aromatics.

Formation, molecular structure, and morphology of humins in biomass conversion: influence of feedstock and processing conditions.

Neither the routes through which humin byproducts are formed, nor their molecular structure have yet been unequivocally established. A better understanding of the formation and physicochemical properties of humins, however, would aid in making biomass conversion processes more efficient. Here, an extensive multiple-technique-based study of the formation, molecular structure, and morphology of humins is presented as a function of sugar feed, the presence of additives (e.g., 1,2,4-trihydroxybenzene), and the applied processing conditions. Elemental analyses indicate that humins are formed through a dehydration pathway, with humin formation and levulinic acid yields strongly depending on the processing parameters. The addition of implied intermediates to the feedstocks showed that furan and phenol compounds formed during the acid-catalyzed dehydration of sugars are indeed included in the humin structure. IR spectra, sheared sum projections of solid-state 2DPASS (13) C NMR spectra, and pyrolysis GC-MS data indicate that humins consist of a furan-rich polymer network containing different oxygen functional groups. The structure is furthermore found to strongly depend on the type of feedstock. A model for the molecular structure of humins is proposed based on the data presented.

New insights into the structure and composition of technical lignins: a comparative characterisation study

Detailed insight into the structure and composition of industrial (technical) lignins is needed to devise efficient thermal, bio- or chemocatalytic valorisation strategies. Six such technical lignins covering three main industrial pulping methods (Indulin AT Kraft, Protobind 1000 soda lignin and Alcell, poplar, spruce and wheat straw organosolv lignins) were comprehensively characterised by lignin composition analysis, FT-IR, pyrolysis-GC-MS, quantitative 31P and 2D HSQC NMR analysis and molar mass distribution by Size Exclusion Chromatography (SEC). A comparison of nine SEC methods, including the first analysis of lignins with commercial alkaline SEC columns, showed molar masses to vary considerably, allowing some recommendations to be made. The lignin molar mass decreased in the order: Indulin Kraft > soda P1000 > Alcell > OS-W ∼ OS-P ∼ OS-S, regardless of the SEC method chosen. Structural identification and quantification of aromatic units and inter-unit linkages indicated that all technical lignins, including the organosolv ones, have considerably been degraded and condensed by the pulping process. Importantly, low amounts of β- ether linkages were found compared to literature values for protolignin and lignins obtained by other, milder isolation processes. Stilbenes and ether furfural units could also be identified in some of the lignins. Taken together, the insights gained in the structure of the technical lignins, in particular, the low β-O-4 contents, carry implications for the design of lignin valorisation strategies including (catalytic) depolymerisation and material applications.

Controlling Platinum, Ruthenium and Osmium Reactivity for Anticancer Drug Design

Publisher Summary Transition-metal complexes provide enormously versatile platforms for drug design. Many variations in the metal itself, the types, and numbers of coordinated ligands and hence in the strengths of coordination bonds and in the kinetics of ligand-substitution processes are available. This chapter discusses the efforts towards the development of photoactive platinum anticancer agents and the ruthenium– and osmium–arene families of anticancer agents. The key to successful design of clinically useful drugs is effective activity while minimizing side effects. Both the thermodynamics and kinetics of ligand-exchange and redox processes must be carefully controlled. Such control is possible by systematic ligand variation. This way, photoactive platinum(IV) complexes can be designed that are stable and nontoxic in the dark. The strategy of activation by light to yield highly cytotoxic species at irradiated spots only allows for local, targeted treatment and holds the promise of less-invasive chemotherapy. Similarly, the work on the ruthenium– and osmium–arenes showed that thermodynamic and kinetic parameters, such as those associated with aquation, can vary over several orders of magnitude, thus allowing the chemist to fine-tune the properties of the agent for increased cytotoxicity.

Shale gas revolution: an opportunity for the production of biobased chemicals?

The current shale gas revolution is causing much excitement because it is leading to job creation, economic growth, and projected energy independence. Yet, at the same time, it causes concerns about the environmental impact, industrial competitiveness, and the resulting geopolitical changes. In the Netherlands and elsewhere, the topic features prominently in the media and political discussions, with pros and cons being extensively debated. Most of those involved do agree on one thing: the potential of the large-scale exploration of shale gas, and of related resources, such as shale and tight oil, to become a game changer for the chemical industry. Indeed, companies are rapidly adjusting to the change in energy flows, trying to take advantage of the cheap resources that now flow abundantly, at least in certain places on earth.

High performing and stable supported nano-alloys for the catalytic hydrogenation of levulinic acid to γ-valerolactone.

The catalytic hydrogenation of levulinic acid, a key platform molecule in many biorefinery schemes, into γ-valerolactone is considered as one of the pivotal reactions to convert lignocellulose-based biomass into renewable fuels and chemicals. Here we report on the development of highly active, selective and stable supported metal catalysts for this reaction and on the beneficial effects of metal nano-alloying. Bimetallic random alloys of gold-palladium and ruthenium-palladium supported on titanium dioxide are prepared with a modified metal impregnation method. Gold-palladium/titanium dioxide shows a marked,~27-fold increase in activity (that is, turnover frequency of 0.1 s−1) compared with its monometallic counterparts. Although ruthenium-palladium/titanium dioxide is not only exceptionally active (that is, turnover frequency of 0.6 s−1), it shows excellent, sustained selectivity to γ-valerolactone (99%). The dilution and isolation of ruthenium by palladium is thought to be responsible for this superior catalytic performance. Alloying, furthermore, greatly improves the stability of both supported nano-alloy catalysts.

Liquid-phase reforming and hydrodeoxygenation as a two-step route to aromatics from lignin

A two-step approach to the conversion of organosolv, kraft and sugarcane bagasse lignin to monoaromatic compounds of low oxygen content is presented. The first step consists of lignin depolymerization in a liquid phase reforming (LPR) reaction over a 1 wt% Pt/γ-Al2O3 catalyst at 225 °C in alkaline ethanol–water. The first LPR step resulted in a decrease in lignin molecular weight of 32%, 57% and 27% for organosolv, kraft and bagasse lignin, respectively. GC analysis of the depolymerized lignin reaction mixture furthermore showed the formation of alkylated phenol, guaiacol and syringol-type products in 11%, 9% and 5% yields from organosolv, kraft and bagasse lignin, respectively. The lignin-oil that was isolated by extraction of the ethanol–water solution was subjected to a subsequent hydrodeoxygenation (HDO) reaction in the second conversion step. HDO of the lignin-oil was performed in dodecane at 300 °C under 50 bar hydrogen pressure over CoMo/Al2O3 and Mo2C/CNF catalysts. GC analysis of the product mixture obtained after the two-step LPR–HDO process revealed the formation of, amongst others, benzene, toluene, xylenes and ethylmethylbenzenes. Of the total observed monomeric products (9%), 25% consisted of these oxygen-free products. Notably, such products cannot be obtained by direct HDO of lignin. HDO of the lignin-oil at 350 °C resulted in the conversion of all tris-oxygenated products, with 57% of the observed monomeric products now identified as mono-oxygenated phenolics.

Carbon Nanofiber Supported Transition‐Metal Carbide Catalysts for the Hydrodeoxygenation of Guaiacol

Hydrodeoxygenation (HDO) studies over carbon nanofiber‐supported (CNF) W2C and Mo2C catalysts were performed on guaiacol, a prototypical substrate to evaluate the potential of a catalyst for valorization of depolymerized lignin streams. Typical reactions were executed at 55 bar hydrogen pressure over a temperature range of 300–375 °C for 4 h in dodecane, using a batch autoclave system. Combined selectivities of up to 87 and 69 % to phenol and methylated phenolics were obtained at 375 °C for W2C/CNF and Mo2C/CNF at >99 % conversion, respectively. The molybdenum carbide‐based catalyst showed a higher activity than W2C/CNF and yielded more completely deoxygenated aromatic products, such as benzene and toluene. Catalyst recycling experiments, performed with and without regeneration of the carbide phase, showed that the Mo2C/CNF catalyst was stable during reusability experiments. The most promising results were obtained with the Mo2C/CNF catalyst, as it showed a much higher activity and higher selectivity to phenolics compared to W2C/CNF.