Catalysts are a vital part of any manufacturing process. They help to cut down on energy usage and in turn any related costs. Putting that in terms of numbers, 95% in volume of chemical products were produced using catalytic processes, and the total market size of catalyst manufacture is $16 billion . Among the various forms of catalysts available, nano catalysts are particularly unique. A nanosized catalyst is characterized by highly selectivity, high activity, low energy consumption and durability (i.e., being functional and reusable over a long period of time) . Nano catalysts are also exceptional because they combine the benefits of both homogeneous and heterogenous catalysts, while removing the problems that are associated with their use.
Homogenous catalysts are in the same physical state as the other reactants, therefore the catalytic activity is high. However, being in the same physical state means that after the reaction is complete it is difficult to separate the catalyst from the products. In the case of heterogenous catalysis where the reactants and the catalysts are in different physical states, separation of the catalyst from the products becomes easier, however, the drawback is that the catalytic activity of heterogenous catalyst is greatly reduced as the surface area of the catalyst with which the reactants come into contact is relatively smaller than when homogenous catalysts are used. Lower catalytic activity means that a high volume of the catalyst is consumed during the reaction. This leads to higher costs of production since most catalysts are expensive transition metals. The solution is to reduce the size of the active catalytic material therefore increasing the surface area to volume ratio. This is done by artificially synthesizing nano catalysts. One interesting thing to note here is that some materials such as gold can only act as catalysts on a nano scale .
One nanoparticle that has generated traction in recent years is iridium, one of the top nine rarest elements on earth. It is used is several applications, mostly during the process of commercial production of hydrogen and oxygen (water spitting) and in fuel cells. A unique aspect of iridium for its use as a nano catalyst is its wide range of oxidation states. It is also the most active catalyst in the platinum group elements. A method for the production of iridium nanoparticles involved iridium complex and carboxyl (COOH)‑carbon nanotubes as precursors, using a hydrothermal method where the iridium oxide nanoparticle is attached to carbon nanotubes .
The use of nano catalysts extends to the field of renewable energy where they are employed in the production of biofuels. In recent years the use of biofuel has drawn attraction due to its environmentally friendly nature. However, the conversion of oils to biofuel often involves processes such as pyrolysis, transesterification, supercritical fluids, and dilution, all of which require homogeneous catalysts. The problem with this ironically is that the use of homogeneous catalyst generates a lot of chemical wastewater, which is harmful for the environment. There are methods that involve the use of heterogenous catalysts, but they are inefficient. Therefore, scientists hypothesized that the use of nano catalysts would help solve the issue, as for example the use of potassium impregnated nano-magnetic ceria as a catalyst for the production of biofuels from rapeseed oil . A variety of concentrations of potassium ions were used to determine the ideal concentration in the CeO2 particle and the doping effect that the potassium ions might have on the catalytic activity of the particle.
In the experiment values of 15, 25 and-50 % potassium by weight were employed to impregnate CeO2 particle which where composited with Fe3O4 resulting in Fe3O4-CeO2 . These variants were used to convert rapeseed oil into fatty acid methyl esters and their yields were compared (Figure 1). The 25 wt % potassium impregnated Fe3O4-CeO2 exhibited the best results on the conversion of rapeseed oil to biodiesel.
Fig. 1. The efficiency of various catalyst for transesterification of rapeseed oil .
With rising concerns about the environment and diminishing fossil fuels, another alternative fuel is hydrogen. It has a high energy content and burns cleanly. Hydrazine borane (N2H4BH3) is a compound with a high hydrogen content, 15.4% hydrogen by weight, and a promising chemical hydrogen storage material. However, to utilize the hydrogen content of hydrazine borane, highly selective and efficient catalysts need to be designed. Recent studies have shown that Ni-based bimetallic catalysts alloyed with noble metals can act as potential catalysts for the specific dehydrogenation of hydrazine borane. Palladium has been chosen as the noble metal because of its availably and lower cost than other noble metals. Scientists have explored the possibility of NiPd nanoparticles, enhanced with oxides of molybdenum, acting as catalyst that could effectively release hydrogen from the compound. Existing catalysis methods involve the release of hydrogen in a sequence of three reactions:
N2H4BH3(s) + 3H2O(l) → N2H4(l) + H3BO3(l) + 3H2(g)
N2H4(l) → N2(g) + 2H2(g)
3N2H4(l) → 4NH3(g) + N2(g)
This is a problem mainly due to the third equation where ammonia is produced and is toxic to hydrogen fuel cells. Through the course of the experiment it was observed that the catalytic activity was affected by the molar ratios of Ni and Pd as illustrated in Figure 2 .
Fig. 2. Time course plots for hydrogen evolution from N2H4BH3 aqueous solution (200 mM, 5 mL) catalyzed by (a) Ni0.6Pd0.4-MoOx, Ni-MoOx, and Pd-MoOx NPs and (c) Ni0.6Pd0.4-(MoOx)0.8, Ni0.6Pd0.4, and MoOx with NaOH (0.75 M) at 323 K; The H2 selectivity and turnover frequency (TOF) values for hydrogen evolution from N2H4BH3 catalyzed by (b) Ni1-yPdyMo0.8 and (d) Ni0.6Pd0.4-(MoOx)z with different contents .
Nano catalysts are also being used in the purification of water. Previously water was decontaminated using photocatalysts, however its use was highly restricted due to the availability of an external source of light. Scientists have been able to find a substitute in the form of nano sheets of molybdenum sulfate, which is a piezo catalyst as well as a photo catalyst. Being a photocatalyst mean that the molybdenum sulfate has a low excitation energy, while being a piezo catalyst means that it can be activated by mechanical disturbances. When activated, the catalyst generates highly reactive oxygen species that kills Escherichia coli.
To prepare the nano sheets on molybdenum sulfate, a hydrothermal process was used. Ammonium molybdate (0.1 M) and thiourea (0.2M) were mixed and stirred, forming a clear solution. Afterwards the solution was mixed with 3-mercaptopropionic acid (0.1 M) and the resulting liquid was heated in an autoclave at 2200 C for 18 hours leading to a suspension of molybdenum sulfate nano sheets (Figure 3) .
Fig. 3: Formation of molybdenum sulfate nano sheets .
Another important use of nano catalysts is in the development of renewable energy technologies for reducing pollutants emission. Metal organic framework (MOF)-based nano catalysts have been employed for the conversion of CO2 to valuable substances (methane, methanol, formic acid, etc.) by photocatalytic reduction. Metal organic frameworks are crystalline porous solids composed of a three-dimensional (3D) network of metal ions held in place by multidentate organic molecules . MOFs nanomaterials, such as Zr-MOFs, Zn-MOFs, and Ti-MOFs, have been shown to exhibit great application prospects in the field of photocatalysis, due to their ultra-high specific surface area, porous properties, modified/regulated textures, and high capture capability for CO2 molecules .
Catalysts have been used since ancient times for various processes such as fermentation, however the modern iteration of catalysts is nano particles. What makes nanocatalysts unique is their high surface area to volume ratio, resulting in a higher amount of catalytic activity. Nano catalysts are versatile as seen in the presented examples, having applications in a variety of industries. What makes them even more unique is how selective they can be and how easily they can be attached to other molecules, such as graphene and palladium, to help enhance their properties. As mentioned, nanocatalysts also address some of the disadvantages possessed by traditional catalysts, such as difficulty of separation after the reaction and decrease of catalytic activity due to differences in physical states.
Dr. Raj Shah is a Director at Koehler Instrument Company in New York, where he has worked for the last 25 years. He is an elected Fellow by his peers at IChemE, CMI, STLE, AIC, NLGI, INSTMC, The Energy Institute and The Royal Society of Chemistry An ASTM Eagle award recipient, Dr. Shah recently coedited the bestseller, “Fuels and Lubricants handbook”, details of which are available at
A Ph.D in Chemical Engineering from The Penn State University and a Fellow from The Chartered Management Institute, London, Dr. Shah is also a Chartered Scientist with the Science Council, a Chartered Petroleum Engineer with the Energy Institute and a Chartered Engineer with the Engineering council, UK. An adjunct professor at the Dept. of Material Science and Chemical Engineering at State University of New York, Stony Brook, Raj has over 300 publications and has been active in the petroleum field for 3 decades. More information on Raj can be found at
Dr. Steve (Stephanos) Nitodas is currently a member of the Faculty of the Department of Materials Science and Chemical Engineering at Stony Brook University, NY. His expertise lies in the synthesis and applications of nanostructured carbon and polymer nanocomposites. He has served as Coordinator/ Principal Investigator in five (5) EU funded research projects of 4.2 million Euro total budget, and he has been involved as Co-Principal Scientist in thirteen (13) other funded research projects. Dr. Nitodas has worked for several years in the nanotechnology industry, possessing significant know-how related to transfer of knowledge from academia to the industry and the setup of startup companies.
Masrup Anon and Nathan Aragon are part of a thriving internship program at Koehler Instrument company and students of chemical engineering at State University of New York, Stony Brook, where Dr. Shah currently heads the External advisory board of directors.
- Bavykina, Anastasiya, et al. “Metal–Organic Frameworks in Heterogeneous Catalysis: Recent Progress, New Trends, and Future Perspectives.” Digital Object Identifier System, 2020, doi.org/10.1021/acs.chemrev.9b00685.
- Olveira, Sandro, et al. “Nanocatalysis: Academic Discipline and Industrial Realities.” Journal of Nanotechnology, Hindawi, 17 Feb. 2014, doi.org/10.1155/2014/324089.
- Ali, Imran, et al. “Advances in Iridium Nano Catalyst Preparation, Characterization and Applications.” Journal of Molecular Liquids, vol. 280, 2019, pp. 274–284., doi:10.1016/j.molliq.2019.02.050.
- Ambat, Indu, et al. “Nano-Magnetic Potassium Impregnated Ceria as Catalyst for the Biodiesel Production.” Renewable Energy, vol. 139, 2019, pp. 1428–1436., doi:10.1016/j.renene.2019.03.042.
- Yao, Qilu, et al. “Highly Efficient Hydrogen Generation from Hydrazine Borane via a MoOx-Promoted NiPd Nanocatalyst.” Renewable Energy, vol. 147, 2020, pp. 2024–2031., doi:10.1016/j.renene.2019.09.144.
- Chou, Ting-Mao, et al. “A Highly Efficient Au-MoS2 Nanocatalyst for Tunable Piezocatalytic and Photocatalytic Water Disinfection.” Nano Energy, vol. 57, 2019, pp. 14-21., doi:10.1016/j.nanoen.2018.12.006.
- Leus, Karen, et al., “A coordinative saturated vanadium containing metal organic framework that shows a remarkable catalytic activity”, Studies in Surface Science and Catalysis, 175, 2010, pp. 329-332. doi.org/10.1016/S0167-2991(10)75053-9.
- Liu, Chang, et al., “Recent Advances in MOF-based Nanocatalysts for Photo-Promoted CO2 Reduction Applications”, Catalysts, 9, 2019, pp. 658, doi:10.3390/catal9080658.