Bridging the Chemical and Biological Catalysis Gap: Challenges and Outlooks for Producing Sustainable Chemicals

Abstract

Recent advances in metabolic engineering have allowed for the production of a wide array of molecules via biocatalytic routes. The high selectivity of biocatalysis to remove functionality from biomass can be used to produce platform molecules that are suitable for subsequent upgrading over heterogeneous catalysts. Accordingly, the more robust continuous processing allowed by chemical catalysis could be leveraged to upgrade biologically derived platform molecules to produce direct or functional replacements for petroleum products. Herein, we highlight recent results that utilize a combination of chemical and biological catalysis, and using the perspective of heterogeneous chemical catalysis, we identify challenges that need to be addressed to bridge the gap between the two catalytic approaches. Specifically, studies are required to address the effects on catalyst performance of impurities that originate during bioprocessing. In addition, new generations of heterogeneous catalysts are required for stable operation under liquid phase reaction conditions in the presence of biogenic impurities. Finally, the design and syntheses of new catalysts are required to tailor the active sites and the environment around these sites to achieve selective conversion of the functional groups present in biologically derived platform molecules.

Catalyst stabilization by stoichiometrically limited layer-by-layer overcoating in liquid media

“…The shift to renewable substrates often involves liquid-phase catalytic processing. Such conditions are required because biomass-derived molecules usually have low volatility and are produced by biomass depolymerization or biological transformation in dilute aqueous or solvent streams [4][5][6]. Irreversible deactivation, including by sintering and leaching, tends to be more pronounced in liquid-phase conditions, which makes catalyst stability even more critical [1,2,7].…”

Improving Heterogeneous Catalyst Stability for Liquid-phase Biomass Conversion and Reforming

“…Though combining chemical catalysis with biological conversion can dramatically increase the number of molecules that can be produced from biomass, these molecules also tend to be produced in fairly dilute aqueous streams. [20] In addition, biological processes tend to introduce biogenic impurities including proteins and inorganic salts that can poison chemical catalysts. [20] Finally, even pyrolysis oils -a third major source of biomassderived molecules -which are much more concentrated -usually contain significant amounts of water and nonvolatile compounds.…”

“…[20] In addition, biological processes tend to introduce biogenic impurities including proteins and inorganic salts that can poison chemical catalysts. [20] Finally, even pyrolysis oils -a third major source of biomassderived molecules -which are much more concentrated -usually contain significant amounts of water and nonvolatile compounds. Therefore, platform molecules derived from biomass are often produced in dilute liquid, and often aqueous, streams.…”

Electrochemical Conversion of Biologically Produced Muconic Acid: Key Considerations for Scale-Up and Corresponding Technoeconomic Analysis

“…3,4 Recently, hybrid conversion technologies have been developed to streamline chemical and biochemical transformations and/or enable more complex transformations. [5][6][7][8][9] Along these lines, cellulose was converted to ethanol and styrene through fast pyrolysis and subsequent fermentation of the levoglucosan intermediate. [9][10][11] Metabolically engineered yeast and bacteria also enabled the production of triacetic acid lactone, 12,13 which can be further converted to fuel additives, food flavoring agents, insecticides, and cosmetics using acidic and precious metal hydrogenation catalysts.…”

“…9 In other instances, fermentation broths containing various biogenic impurities deactivated precious metal catalysts through reversible and/or irreversible poisoning. 7,15,16 Extensive separation and purification are therefore required to remove these compounds before downstream chemical conversion. 7,15,16 Streamlining the biological and chemical conversions in an integrated process currently remains a major challenge that will most likely require new catalysts and processes.…”