Investigation of Polyaniline-Supported Au-Pd Bimetallic Catalysts for Propanol Oxidation Reactions in Alkaline Media
Authors: Goodwin Nicole , Hatchett David 
Published: February 2020

Polyaniline (PANI) is extensively studied due to its unique electrochemical properties. Its conjugated structure makes PANI highly conductive. This conductivity can be fine-tuned by changing the electrolyte used for polymerization or the pH of its environment1. With a high chemical stability below 100°C, mechanical strength, and large surface area, the applications of PANI are numerous – from chemical sensing to corrosion inhibition coatings to light emitting diodes2. Another application for PANI is its use as a substrate for catalysts. Previous work has thoroughly investigated the electrochemical polymerization of PANI, electrochemical insertion of Pd and Au into PANI to form PANI/Pd3 and PANI/Au4composites, and the resulting composites’ catalytic activities for alcohol oxidation. Unfortunately, each of these composites has shown a significant amount of surface poisoning during alcohol oxidation, reducing its viability as an efficient catalyst.

In an effort to reduce surface poisoning, scientists have been examining the effects of adding a second metal to well-known, commonly-used catalysts. These bimetallic catalysts have been shown to reduce surface poisoning and increase catalytic activity. One possible explanation for this phenomenon is an electronic effect - the interaction of the two metals causes a shift in the electronic structure of the catalyst’s surface, resulting in a weakened interaction with poisoning species5. Another possibility is that it is due to a bifunctional effect. In one case different metals adhere to different functional groups in the molecule allowing for a more stable transition state and thus more efficient catalysis6. In the case of oxidation in alkaline media, hydroxide groups from the solvent adsorb to the secondary metal, then react with poisoning species on the primary catalytic metal to form molecules that are more easily removed from the catalyst surface7. Most likely some combination of these three phenomena results in reduced poisoning and increased efficiency.

This presentation will expand PANI research into the area of bimetallic PANI composites, specifically focusing on the simultaneous deposition of Au and Pd into PANI films. Three composites were prepared, each using a metal precursor solution with a different Au to Pd molar ratio (1:1, 2:1, or 1:2). Electrochemical data from metal deposition, surface oxide formation and reduction, and oxidation of 1-propanol provide insights into how metals interact with each other and their environment within the polymer. SEM/EDX data show morphology and composition of the composites. Overall the bimetallic composites show reduced surface poisoning and increased catalytic efficiency in comparison to their monometallic counterparts.

References

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