This article will provide an overview of gold catalysts and their innovative role in industrial hydrogenation processes.
Gold nanoparticles. Image Credit: Georgy Shafeev/Shutterstock.com
The fundamental process of hydrogenation has been used as an organic chemical reaction to add hydrogen gas to a compound for various applications.
While this process occurs usually in the presence of catalysts such as nickel or platinum, the use of gold as an alternative has gathered significant attention from researchers as a potential method to propel innovative solutions.
Hydrogen is considered to be a high purity and premium product for a range of different applications, from a substitute for natural gas for heating to being used in engineering for innovative solutions in chemical production and photocatalytic energy capture.
The process of hydrogenation was initially used to recover oil from coal and the use of this process came to an end due to its high expense at the beginning of the 1950s before being recovered after the second oil crisis.
The Emergence of Gold Catalysts
Innovative catalysts to enhance the hydrogenation process have been researched such as gold nanoparticles for heterogeneous catalytic reactions. This emerging area of incorporating the element gold for selective hydrogenation is due to its desirable attribute for having the highest energy barrier for the dissociation of hydrogen.
Gold was originally thought to be an ineffective and inactive catalyst, possibly due to conventional catalyst preparation methods producing gold particles that were outside of the nanosize range that is required for effective activity. Larger gold particles have an inability to chemisorb reactant molecules, rendering this material to be thought of as a fairly inactive catalyst.
Promoting the Breakdown of Plastic with Nickel Catalysts and CO
However, researchers have previously tested the use of gold for heterogeneous catalysis with experiments carried out in the 1970s, illustrating the ability of gold to catalyze hydrogenation, oxidative dehydrogenation, hydrogen exchange, and hydrocracking. This activity of gold catalysts was considered to be poor in comparison to the more traditional catalysts such as platinum and palladium and so was not pursued as a serious catalytic contender.
Interestingly, the use of gold nanoparticles revived the notion of using gold as a catalyst, with significant discoveries being made in 1980. Researchers had found that the deposition of gold as nanoparticles through deposition-precipitation and co-precipitation, illustrated its activity for CO oxidation at various temperatures from ambient to -76°C.
This turn of events led to research into using gold as active catalysts for various applications with findings such as gold chloride being the most effective catalyst for ethyne hydrochlorination.
Gold Catalysts for Hydrogenation
As previously mentioned, the limited ability of gold for chemisorption such as to chemisorb hydrogen compared to platinum group metals has illustrated its inactivity as a catalyst for reactions including the dissociation of hydrogen.
While this can be seen to be true for gold in its enlarged state, research has signified the dependence on gold size which reflects its level of activity, with chemisorption of hydrogen being dependent on particle size. Additionally, with the decrease of particle size into the nanoscale, gold nanoparticles are considered to be very reactive with uses as radiolabels and for targeted cancer treatment.
Intriguing reports which support the hypothesis of gold catalysts showing hydrogenation activity have been uncovered when gold nanoparticles are supported on reducible oxides. Support for gold catalysts can come in various forms including ordered mesoporous carbon due to their role in the fine chemicals industry as well as novel energy technologies including biomass conversion and fuel cells.
Other researchers, including engineers, have undertaken the study of gold catalysts due to their selectivity in order to produce specific results within hydrogenation for innovative engineering solutions.
Professor Bert Chandler, from Penn State University, has commented on the new U.S. Department of Energy grant provided to this research team on gold catalyst used for hydrogenation, stating, “Hydrogenation reactions are pivotal components to a lot of green energy problems,” which can be applied to applications such as within energy transport, storage, low-carbon energy processing, energy efficiency in chemical production and photocatalytic energy capture.”
In this case, we don’t know how to make highly active and selective catalysts for some reactions. By working to understand how molecules react on gold catalysts, we believe we will be able to pose new solutions toward lessening the burden on the environment.
Professor Bert Chandler, Penn State University
The selectivity of gold to react with one molecule and not another is something researchers wish to exploit, making gold very valuable and “a very desirable characteristic in lots of separation and purification processes in chemical engineering,” commented Chandler.
His research team aims to focus on material synthesis and characterization in order to develop new catalytic reactions using gold, titanium dioxide, and other metal additives as hydrogenation catalysts. This will aid in understanding the surface chemistry of gold, a research area that consists of many contradictory findings of levels of inertness – this will assist in developing industrial separation and purification reactions.
The future outlook with the use of gold catalysts in hydrogenation can be seen to be promising, with researchers attempting to investigate its surface chemistry in order to tune this material and improve its selectivity in comparison to the more conventional active metals that are used as catalysts.
This is in line with other researchers who have investigated the use of gold catalysts using a support such as carbon to improve its active state for hydrogenation reactions.
While research in this field can be seen as challenging, the success of researchers such as Bert Chandler with the use of gold catalysts for hydrogenation may be useful for real-world applications such as the breakdown of waste plastics. This would be significant and critical for both the plastic pollution crisis as well as decreasing the environmental effect on human health from ineffective wastewater purification.
Additionally, further investigation of gold catalysts for the chemical compound, deuterium oxide, may also be revolutionary for this limited field as this innovative research may facilitate the production of smaller-scale and safer nuclear power plants.
The variation of applications for gold catalysts illustrates its utility and potentiality for a more sustainable future, with real-world applications that could revolutionize technology and advance environmental research for the better.
Further Reading and References
Juliusa, M., Robertsa, S. and Fletchera, J., 2010. A review of the use of gold catalysts in selective hydrogenation reactions Lynsey McEwana. Gold Bulletin, 43(4), pp.298-306. Available at: https://doi.org/10.1007/BF03214999
Psu.edu. 2021. Going gold: Engineers to investigate using gold as catalyst in hydrogenation | Penn State University. [online] Available at: <https://www.psu.edu/news/engineering/story/going-gold-engineers-investigate-using-gold-catalyst-hydrogenation/> [Accessed 27 December 2021].
Sun, Y., Cao, Y., Wang, L., Mu, X., Zhao, Q., Si, R., Zhu, X., Chen, S., Zhang, B., Chen, D. and Wan, Y., 2020. Gold catalysts containing interstitial carbon atoms boost hydrogenation activity. Nature Communications, 11(1). Available at: https://www.nature.com/articles/s41467-020-18322-x