Abstract
The hydrogenation reaction of muconic acid, produced from biomass using fermentative processes, to bio-adipic acid is one of the most appealing green emerging chemical process. This reaction can be promoted by catalysts based on a metal belonging to the platinum group, and the use of a second metal can preserve and increase their activity. Pd–Au bimetallic nanoparticle samples supported on high-temperature, heat-treated carbon nanofibers were prepared using the sol immobilization method, changing the Pd–Au molar ratio. These catalysts were characterized by TEM, STEM, and XPS analysis and tested in a batch reactor pressurized with hydrogen, where muconic acid dissolved in water was converted to adipic acid. The synthesized Pd–Au bimetallic catalysts showed higher activity than monometallic Au and Pd material and better stability during the recycling tests. Moreover, the selectivity toward the mono-unsaturated changed by decreasing the Pd/Au molar ratio: the higher the amount of gold, the higher the selectivity toward the intermediates.
Highlights
The industrial success of emerging biomass conversion processes lies in the correct design and synthesis of a robust heterogeneous catalyst
Pd–Au bimetallic systems have been widely used in hydrogenation reactions, and compared to the monometallic Au and Pd material, the bimetallic samples always show the best performance in terms of conversion, selectivity, and stability [22,23,24,25,26,27]
The catalysts were characterized by transmission electron microscopy (TEM) (Transmission Electron Microscopy) and X-ray photoelectron spectroscopy (XPS) (X-Ray Photoelectron Spectroscopy) analysis
Summary
The industrial success of emerging biomass conversion processes lies in the correct design and synthesis of a robust heterogeneous catalyst. A synergistic effect is created, which generates distinctive and new properties, allowing an increase in the selectivity toward the desired products [16]. Pd–Au bimetallic systems have been widely used in hydrogenation reactions, and compared to the monometallic Au and Pd material, the bimetallic samples always show the best performance in terms of conversion, selectivity, and stability [22,23,24,25,26,27]. Considering the synergistic effect of a bimetallic catalyst for the enhancement in catalyst stability, in this work Pd–Au bimetallic NPs supported on a highly graphitized support (high-temperature, heat-treated carbon nanofibers (HHT CNFs)) were prepared using the sol immobilization method [30]. The Pd/Au molar ratio is a key parameter for the mono-unsaturated product: the higher the amount of gold, the higher the selectivity toward the intermediates
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