Environmentally benign solid catalysts for sustainable biodiesel production: A critical review

Versatile bio-derived catalysts have been under dynamic investigation as potential substitutes to conventional chemical catalysts for sustainable biodiesel production. This is because of their unique, low-cost benefits and production processes that are environmentally and economically acceptable. This critical review aspires to present a viable approach to the synthesis of environmentally benign and cost-effective heterogeneous solid-base catalysts from a wide range of biological and industrial waste materials for sustainable biodiesel production. Most of these waste materials include an abundance of metallic minerals like potassium and calcium. The different approaches proposed by researchers to derive highly active catalysts from large-scale waste materials of a re-usable nature are described briefly. Finally, this report extends to present an overview of techno-economic feasibility of biodiesel production, its environmental impacts, commercial aspects of community-based biodiesel production and potential for large-scale expansion.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.BT/Biocatalysi

Valorization of Small Alkanes by Biocatalytic Oxyfunctionalization

The oxidation of alkanes into valuable chemical products is a vital reaction in organic synthesis. This reaction, however, is challenging, owing to the inertness of C−H bonds. Transition metal catalysts for C−H functionalization are frequently explored. Despite chemical alternatives, nature has also evolved powerful oxidative enzymes (e. g., methane monooxygenases, cytochrome P450 oxygenases, peroxygenases) that are capable of transforming C−H bonds under very mild conditions, with only the use of molecular oxygen or hydrogen peroxide as electron acceptors. Although progress in alkane oxidation has been reviewed extensively, little attention has been paid to small alkane oxidation. The latter holds great potential for the manufacture of chemicals. This Minireview provides a concise overview of the most relevant enzyme classes capable of small alkanes (C<6) oxyfunctionalization, describes the essentials of the catalytic mechanisms, and critically outlines the current state-of-the-art in preparative applications.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.BT/Biocatalysi

Production of Bio-alkanes from Biomass and CO₂

Bioelectrochemical technologies such as electro-fermentation and microbial CO2 electrosynthesis are emerging interdisciplinary technologies that can produce renewable fuels and chemicals (such as carboxylic acids). The benefits of electrically driven bioprocesses include improved production rate, selectivity, and carbon conversion efficiency. However, the accumulation of products can lead to inhibition of biocatalysts, necessitating further effort in separating products. The recent discovery of a new photoenzyme, capable of converting carboxylic acids to bio-alkanes, has offered an opportunity for system integration, providing a promising approach for simultaneous product separation and valorisation. Combining the strengths of photo/bio/electrochemical catalysis, we discuss an innovative circular cascading system that converts biomass and CO2 to value-added bio-alkanes (CnH2n+2, n = 2 to 5) whilst achieving carbon circularity.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.BT/Biocatalysi

Peroxygenase-Catalysed Sulfoxidations in Non-Aqueous Media

Chiral sulfoxides are valuable building blocks in asymmetric synthesis. However, the biocatalytic synthesis of chiral sulfoxides is still challenged by low product titres. Herein, we report the use of peroxygenase as a catalyst for asymmetric sulfoxidation under non-aqueous conditions. Upon covalent immobilisation, the peroxygenase showed stability and activity under neat reaction conditions. A large variety of sulfides was converted into chiral sulfoxides in very high product concentration with moderate to satisfactory optical purity (e. g. 626 mM of (R)-methyl phenyl sulfoxide in approx. 89 % ee in 48 h). Further polishing of the ee value via cascading methionine reductase A (MsrA) gave>99 % ee of the sulfoxide. The robustness of the enzymes and high product titer is superior to the state-of-the-art methodologies. Gram-scale synthesis has been demonstrated. Overall, we demonstrated a practical and facile catalytic method to synthesize chiral sulfoxides.BT/Biocatalysi

Water-Soluble Anthraquinone Photocatalysts Enable Methanol-Driven Enzymatic Halogenation and Hydroxylation Reactions

Peroxyzymes simply use H2O2 as a cosubstrate to oxidize a broad range of inert C-H bonds. The lability of many peroxyzymes against H2O2 can be addressed by a controlled supply of H2O2, ideally in situ. Here, we report a simple, robust, and water-soluble anthraquinone sulfonate (SAS) as a promising organophotocatalyst to drive both haloperoxidase-catalyzed halogenation and peroxygenase-catalyzed oxyfunctionalization reactions. Simple alcohols, methanol in particular, can be used both as a cosolvent and an electron donor for H2O2 generation. Very promising turnover numbers for the biocatalysts of up to 318 »000 have been achieved. BT/Biocatalysi

Chemoenzymatic Hunsdiecker-Type Decarboxylative Bromination of Cinnamic Acids

In this contribution, we report chemoenzymatic bromodecarboxylation (Hunsdiecker-type) of α,ß-unsaturated carboxylic acids. The extraordinarily robust chloroperoxidase from Curvularia inaequalis (CiVCPO) generated hypobromite from H2O2 and bromide, which then spontaneously reacted with a broad range of unsaturated carboxylic acids and yielded the corresponding vinyl bromide products. Selectivity issues arising from the (here undesired) addition of water to the intermediate bromonium ion could be solved by reaction medium engineering. The vinyl bromides so obtained could be used as starting materials for a range of cross-coupling and pericyclic reactions.BT/Biocatalysi

Selective Peroxygenase-Catalysed Oxidation of Toluene Derivates to Benzaldehydes

Biocatalytic oxidation reactions of toluene derivates to the corresponding aldehydes are typically challenged by regio- and chemoselectivity issues. In this contribution we address both challenges by a combined reactant- and reaction engineering approach. We demonstrate that the peroxygenase-catalysed transformation of ring-substituted toluenes proceeds highly regioselectively in benzylic position. Furthermore, neat reaction conditions not only enable attractive product concentrations (up to 185 mM) but also result in highly chemoselective oxidations to the aldehyde level.BT/Biocatalysi