Selective Decarbonylation of Fatty Acids to Long-Chain Alkenes via PtSn/SnO_x-Induced C–O Activation

Abstract

Long-chain olefins are an important class of chemicals and platform intermediates. A green and promising route for synthesizing long-chain olefins is the one-step decarbonylation and dehydration of biomass-derived fatty acids under hydrogen-free conditions. Major impediments for synthesizing olefins from fatty acids are (1) the difficulty in selectively cleaving C–O bonds (461.5 kJ/mol) of fatty acids and (2) the tendency to break the weaker C–C bonds (384.9 kJ/mol) to generate alkanes. Traditional homogeneous catalysts use a sacrificial anhydride to activate the C–O bonds of fatty acids. In this work, we prepared a bimetallic PtSn/SiO2 catalyst achieving quantitative conversion of stearic acid and a heptadecene yield of 73% at 320 °C without exogenous hydrogen after 4 h of reaction. The PtSn/SiO2 catalyst allowed changing the adsorption mode of carboxylic acid-containing molecules on SnO x while activating the C–O bond in the form of acyl adsorption. Reaction kinetics indicated that the direct decarbonylation of carboxylic acid to olefins was the primary reaction. In situ infrared (IR) spectroscopy measurements also supported this finding, indicating that carboxylic acids were adsorbed on SnO x surface species and dissociated into acyl and OH– over oxygen vacancies. In a subsequent step, C–C is broken on the active center of the Pt1Sn1 alloy to generate CO and alkyl cations, followed by deprotonation of the alkyl cations and binding with OH– to generate alkenes and water. The route described herein provides a competitive and green approach for long-chain olefin production from inexpensive biomass resources.

Greening the Synthesis of Biorenewable Fuels and Chemicals by Stoichiometric Reagentless Organic Transformations

“…In 2021, Zhao et al reported the preparation of 1-heptadecene in a 73% yield from stearic acid without any exogenous hydrogen under optimized conditions (320 °C, 4 h). The bimetallic PtSn/SiO 2 catalyst influenced FFA adsorption on the SnO x sites via the acyl group for selective decarbonylation . FAEs can be catalytically decarbonylated into long-chain alkenes, where the alcohol byproduct is recycled to form more starting material …”

“…The bimetallic PtSn/SiO 2 catalyst influenced FFA adsorption on the SnO x sites via the acyl group for selective decarbonylation. 130 FAEs can be catalytically decarbonylated into long-chain alkenes, where the alcohol byproduct is recycled to form more starting material. 131…”

Catalytic cracking of yeast-borne single-cell oil for the production of small-chain olefins over a PtSn/alumina catalyst

“…The production of long-chain olefins from fatty acids over supported catalysts has been widely reported, but the selective conversion to C 2 –C 4 olefins has rarely been explored. 19…”

“…The production of long-chain olefins from fatty acids over supported catalysts has been widely reported, but the selective conversion to C 2 -C 4 olefins has rarely been explored. 19 In general, upgrading of triglycerides is accomplished by subsequent catalytic cracking and deoxygenation to reduce the chain length. 20 The conversion of fatty acids into olefins involves several reaction steps, like hydrodeoxygenation, decarboxylation, catalytic cracking or dehydrogenation.…”

“…Therefore, multifunctional solid acid catalysts have been applied to facilitate a multistep reaction to produce olefins. 19,21,22 The reports on producing linear α-olefins from vegetable and lipid oils mainly involve catalysis by alkali metals, metal oxides or carbon-based supports. [22][23][24][25] Among them, Al 2 O 3 is a better choice because of its large surface area, acid resistance and cost advantages compared to other aluminosilicates.…”