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10.1002/cctc.202001799
ChemCatChem
COMMUNICATION
Selective C-O Bond Cleavage of Bio-Based Organic Acids over
Palladium Promoted MoOx/TiO2
Ayad Nacy,[+][a] Lucas Freitas de Lima e Freitas,[+][b] Sandra Albarracín-Suazo,[a] Génesis Ruiz-
Valentín,[a] Charles A. Roberts,[c] Eranda Nikolla*[b] and Yomaira J. Pagán-Torres*[a]
[a]
Dr. A. Nacy, S. Albarracín-Suazo, G. Ruíz-Valentín, Prof. Dr. Y. J. Pagán-Torres
Department of Chemical Engineering
University of Puerto Rico-Mayagüez Campus
Mayagüez, PR 00680 (USA)
E-mail: yomairaj.pagan@upr.edu
[b]
L. F. de L. e Freitas, Prof. Dr. E. Nikolla
Department of Chemical Engineering and Materials Science
Wayne State University
Detroit, MI 48202 (USA)
E-mail: erandan@wayne.edu
[c]
[+]
Dr. C. A. Roberts
Toyota Research Institute – North America
Ann Arbor, MI 48105 (USA)
The authors A. Nacy and L. F. de L. e Freitas contributed equally to this article.
Supporting information for this article is given via a link at the end of the document.
Abstract: Hydrodeoxygenation chemistries play a key role in the
upgrading of biomass-derived feedstocks. Among these, the removal
of targeted hydroxyl groups through selective C-O bond cleavage
from molecules containing multiple functionalities over heterogeneous
catalysts has shown to be a challenge. Herein, we report a highly
selective and stable heterogeneous catalyst for hydrodeoxygenation
of tartaric acid to succinic acid. The catalyst consists of reduced Mo5+
centers promoted by palladium, which facilitate selective C-O bond
cleavage, while leaving intact carboxylic acid end groups. Stable
catalytic performance over multiple cycles is demonstrated. This
catalytic system opens up opportunities for selective processing of
some of these challenges, a thermocatalytic one-step process to
produce SA from TA over a MoOx/carbon black (BC) catalyst was
developed.[7] Characterization studies revealed the presence of
a partially reduced MoOx/BC surface that promoted C–O bond
cleavage. Despite the high SA yield (87%) reported, the need for
catalyst pretreatment and reaction initiators (HBr and acetic acid)
to activate the C–O bond cleavage added complexity to the
process. Production of dimethyl succinate via deoxydehydration
(DODH) of tartaric acid or diethyl tartrate was also demonstrated
over a multicomponent, complex catalytic system comprised of a
homogeneous KReO4, Pd/C, H3PO4, and activated carbon
yielding 88% of methyl succinate under hydrogen atmosphere.[8]
In this case, the complex reaction pool presented significant
challenges for product separation.
biomass derived sugar acids with
functionality.
a high degree of chemical
Herein, we report on a highly active, selective and stable
heterogeneous catalytic system comprising of supported
reducible metal oxide species coupled with a hydrogenating metal
for selective HDO of TA to form SA with 92% yield (SA selectivity
of 93% and TA conversion of 99%) upon 16 hours of reaction. We
show that the dominant catalytic pathway involves sequential
HDO of TA to malic acid (MA) and MA to SA. In this catalytic cycle,
C-O bond cleavage was catalyzed by reduced Mo5+ sites formed
in-situ in the presence of Pd and hydrogen. The catalyst showed
stability upon multiple reuse cycles.
Currently, fossil fuels represent the primary source of
energy, fuel, and commodity chemical production.[1] However,
escalating concerns about the environmental effect of their
utilization and their inevitable depletion have urged the discovery
and development of environmentally benign processes.[2]
Succinic acid (SA) is a highly desired drop-in bio-based building
block, with an estimated market value of USD 130 million/year (in
2018).[3] SA is mainly produced via thermocatalytic processing of
petroleum-based n-butane.[3b, c] This process involves complex
purification steps and is highly dependent on the crude-oil cost.[3c]
Table 1 summarizes the TA HDO performance of various
catalysts containing hydrogenating noble metals (e.g., Pd (Entry
1), Rh (Entry 2), and Pt (Entry 3)) coupled with MoOX supported
on TiO2. The Pd-containing catalyst resulted in 80% SA selectivity
at a TA conversion of 65% and the highest SA formation rate of
13.6 x 10-7 mole gcat-1 s-1. High amounts of fumaric acid (FA) were
detected in the case of the Pt-containing catalyst (Entry 3, Table
1) potentially suggesting strong adsorption of carboxylic acid
groups on the Pt surface, blocking hydrogenation sites. The effect
of the nature of the dispersed metal oxide species (MoOx, WOx,
ReOx, VOx) in the presence of Pd (the best performing
hydrogenating metal) on the catalytic performance is shown in
Entries 1, 4, 5, and 6 of Table 1, respectively. We find that the
Recently, bio-based SA was manufactured via fermentation of
4]
glucose using engineered micro-organisms.[3c,
This route
suffered from significant drawbacks, including low productivity,
high nutrient requirements, the formation of organic acid
byproducts, along with a costly downstream recovery and
purification of the final product.[3c, 4-5] Synthesis of SA from tartaric
acid (TA) was reported via a two-step process that involved the
deoxydehydration (DODH) of TA to maleic acid (ME) in 3-
pentanol (both as reductant and solvent) with NH4ReO4, followed
by hydrogenation of ME to SA over Pt/C in water. While the
system yielded 86% SA, it required the utilization of two precious
metal catalysts and multiple processing steps.[6] To overcome
1
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