Gas-Phase Models for the Nickel- and Palladium-Catalyzed Deoxygenation of Fatty Acids

Author ORCID Identifier

Kevin Parker:https://orcid.org/0000-0002-8505-8468

Victor Ryzhov:https://orcid.org/0000-0001-6041-9821

Publication Title

ChemCatChem

ISSN

18673880

E-ISSN

18673899

Document Type

Article

Abstract

Using fatty acids as renewable sources of biofuels requires deoxygenation. While a number of promising catalysts have been developed to achieve this, their operating mechanisms are poorly understood. Here, model molecular systems are studied in the gas phase using mass spectrometry experiments and DFT calculations. The coordinated metal complexes [(phen)M(O2CR)]+ (where phen=1,10-phenanthroline; M=Ni or Pd; R=CnH2n+1, n≥2) are formed via electrospray ionization. Their collision-induced dissociation (CID) initiates deoxygenation via loss of CO2 and [C,H2,O2]. The CID spectrum of the stearate complexes (R=C17H35) also shows a series of cations [(phen)M(R’)]+ (where R’ < C17) separated by 14 Da (CH2) corresponding to losses of C2H4-C16H32 (cracking products). Sequential CID of [(phen)M(R’)]+ ultimately leads to [(phen)M(H)]+ and [(phen)M(CH3)]+, both of which react with volatile carboxylic acids, RCO2H, (acetic, propionic, and butyric) to reform the coordinated carboxylate complexes [(phen)M(O2CR)]+. In contrast, cracking products with longer carbon chains, [(phen)M(R)]+ (R>C2), were unreactive towards these carboxylic acids. DFT calculations are consistent with these results and reveal that the approach of the carboxylic acid to the “free” coordination site is blocked by agostic interactions for R > CH3.

First Page

5476

Last Page

5485

Publication Date

11-5-2020

DOI

10.1002/cctc.202000908

Keywords

Biomass conversion, Density Functional Theory calculation, gas-phase reactions, homogeneous catalysis, Mass spectrometry

Department

Department of Chemistry and Biochemistry

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