Understanding catalyst inhibition from biogenic impurities in transfer hydrogenation of a biorenewable platform chemical
Graphical Abstract
Introduction
Current efforts to develop biomass-based renewable energy technologies are focused on utilizing non-edible lignocellulosic biomass to produce platform chemicals [1], [2]. A myriad of novel processes and routes for sustainable production of high-value chemicals and fuels from biomass can be unraveled by working towards a smart integration of bio and chemo-catalysis [3], [4], [5]. In this regard, our group has developed a C10 platform chemical, 6-amyl-α-pyrone (6PP) [6], which is a 2-pyrone molecule obtained from the fermentation of waste lignocellulosic biomass such as sugarcane bagasse [7]. Coconut flavored 6PP is a well-studied metabolite produced by the filamentous fungus Trichoderma species [8]. In our earlier works, we have demonstrated the valorization of 6PP to produce food additives and aroma compounds such as non-2-en-4-one and δ-decalactone (DDL) [9], [10], [11]. In addition, we have explored simple reaction routes for the synthesis of jet and diesel range (C14–C15) hydrocarbon fuels from 6PP [6].
A major bottleneck in the integration of fermentation and catalytic processes is observed by Miller and co-workers in the valorization of lactic acid [12]. The authors have reported reduced activity of the Ru catalyst for lactic acid hydrogenation in the presence of ppm quantity of biogenic impurities such as cysteine (Cys), methionine (Met), etc. [12]. Low concentrations of salts and carbohydrates do not alter the catalyst activity [12]. Traces of biogenic impurities (100 ppm) are present with the reactant molecule even after purifying the fermentation media by adapting recommended bio-separation methods like solvent extraction [13]. For the valorization of fermentation-derived 2-pyrones, Dumesic and co-workers have confirmed reduced catalytic activity in the hydrogenation reaction of triacetic acid lactone (TAL) on Pd/γAl2O3 catalyst [13]. Significant deactivation of the catalyst surface has been observed in the presence of sulfur-containing amino acids such as Met, whereas alanine (Ala) with an alkyl group in the side chain is observed to cause mild deactivation [13]. The same group has also examined the role of biogenic impurities on cyclohexene hydrogenation reaction [14], wherein the reaction rate measurements and adsorption isotherms of representative amino acids (Cys, Met, Tryptophan, or Trp) and vitamins on Pt, Pd, and Ni catalysts showed a linear correlation between the adsorption strength and the loss of catalyst activity. Likewise, Matthiesen and co-workers have observed strong catalyst deactivation from biogenic impurities in electrochemical hydrogenation of muconic acid to trans-3-hexenedioic acid on Ni surface [15]. In addition, Beckham group has observed inhibition from biogenic impurities in muconic acid hydrogenation, wherein the reaction rate over Rh is significantly reduced with biomass-derived muconic acid feed [16]. Despite the deactivation of catalyst surface in the presence of biogenic impurities that have been observed in several studies, a systematic understanding of the physico-chemical principles underlying these interactions for is still missing.
In our previous theoretical work on biogenic impurities, attempts have been made to understand the covalent and non-covalent interactions of amino acids with the heterogeneous Ni catalyst surface using a combination of density functional theory (DFT) and molecular dynamics (MD) simulations [17]. In this study, we aim to obtain a similar understanding of the interaction of biogenic impurities on Pd (111) surface using a combination of model experiments and in silico studies. We have also extended this work to include large proteins like albumin to understand if any specific amino acids in protein dictate its interactions with the catalyst surface. This fundamental understanding is expected to provide desired mechanistic insights for developing stable catalyst materials that can function in a complex reaction environment. The development of stable catalysts can further pave a path to explore opportunities offered by 2-pyrone molecules and can lead to the opening of new avenues [18], [19], [20] to engineer reaction routes for bio-renewable products, which may be added to the portfolio of a futuristic biorefinery.
Section snippets
Experiments
6PP, cyclohexane, Met, Ala, Cys, cystine (Cys-dimer), arginine (Arg), and bovine serum albumin (BSA) used in this study are purchased from Sigma Aldrich Chemicals Pvt. Ltd. (India). 10 wt% Pd/C catalyst is supplied by Alfa Aesar (India). Formic acid and methanol are obtained from Merck India. The Pd/C is oven dried at 110ºC for 3 h before use . Catalytic transfer hydrogenation (CTH) of 6PP is carried out in an Anton Paar reactor (Model: Monowave-50), equipped with a stainless-steel heating
Density functional theory simulations
Periodic plane-wave DFT code available in Vienna Ab initio Simulation Package (VASP 5.4.1) is used to simulate the interaction of Cys on Pd (111) surface [21]. The exchange and correlation functional suggested in the generalized gradient approximation (GGA) framework of Revised-Perdew-Burke-Ernzerhof (RPBE) approach is applied [22], [23]. Ultra-soft pseudopotentials (USPP) are adapted to define the core electron-nuclei interactions [24]. Kohn Sham equations are solved using the plane-wave basis
Results and discussion
Scheme 1 shows the proposed metabolic pathways through which 6PP is thought to be produced from lignocellulosic biomass [36], [37], [38]. 6PP is further valorized to produce DDL via hydrogenation reaction, as shown in Scheme 1 (c) [9]. Herein, CTH of 6PP is carried out using formic acid as an in situ hydrogen source in cyclohexane solvent. The reaction parameters (time, temperature, solvent, catalyst loading, etc.) for the CTH are optimized and discussed in our previous report [9].
In order to
Conclusions
In the present study, an attempt is made to understand the role of biogenic impurities in the CTH of 6-amyl-α-pyrone to produce δ-decalactone by combining experiments, DFT, and MD simulations. The experiments using model impurities indicate different levels of catalyst inhibition. For example, Ala does not affect the catalyst activity or product selectivity, whereas the presence of trace (100 ppm) amount of sulfur-bearing amino acids (Cys and Met) is sufficient to inhibit catalyst activity. The
CRediT authorship contribution statement
Haseena K V: Data curation, Methodology, Writing – original draft, Writing – review & editing. Madhulika Gupta: Writing – review & editing, Methodology. Adarsh Madhu: Writing – review & editing. Atul Narang: Supervision. Md. Imteyaz Alam: Supervision, review & editing. M. Ali Haider: Conceptualization, Supervision, Writing – review & editing.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
The authors would like to acknowledge the Department of Science and Technology (DST) SERB (grant no. CRG/2019/0006176) for the financial support. High-Performance Computing (HPC) Facility at IIT Delhi is acknowledged for providing computational resources. HKV would also like to acknowledge the Council of Scientific and Industrial Research (CSIR) for the Senior Research Fellowship (09/086(1326)/2018-EMR-I) and Gandhiyan Young Technological Innovation Award (GYTI) by SRISTI.
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