Researchers from Brookhaven National Laboratory (Upton, US) have developed a catalyst to produce methanol, an essential chemical compound for many industrial processes, from carbon dioxide (a greenhouse gas).
The catalyst is made of copper, cerium oxide and titanium oxides; its use could help reduce the impact of carbon dioxide on the environment, by converting it into a valuable chemical.
What Is Methanol?
Methanol (CH3OH) is the simplest alcohol molecule. Unlike ethanol, the alcohol used in drinks, methanol is very toxic – therefore, it is not used in the food industry.
Despite this, however, methanol is a very important chemical compound, with many industrial applications.
Methanol is used, for instance, in the production of biodiesels – fuels derived from either animal fats or vegetable oils. CH3OH is also essential for the chemical synthesis of many important compounds we use in everyday life, such as plastics and resins. Methanol is converted either into formaldehyde or acetic acid, which are then employed in the production of these chemicals.
How Is Methanol Produced?
At the industrial level, methanol is generally produced by the reaction of a mixture of carbon monoxide (CO) and dioxide (CO2) with hydrogen (H2). The CO/CO2 mixture is used as it is obtained by reaction of natural gas (methane, CH4) with oxygen. The catalyst used for this reaction is a composite material made of copper (Cu) and zinc oxide (ZnO) on aluminum oxide (Al2O3) as a substrate.
There is interest, however, to produce CH3OH from carbon dioxide alone; the reaction to obtain methanol would be:
CO2 + 3H2 → CH3OH + H2O
Why Use Carbon Dioxide?
CO2 is a greenhouse gas, whose emissions in the atmosphere have increased remarkably in recent years, due to human activities. According to some theories, higher CO2 concentration is responsible for the increase in the Earth average temperature (global warming). Moreover, higher carbon dioxide content in the oceans is also causing an increase in its acidity (ocean acidification).
The use of CO2 to make methanol would, therefore, be a way to mitigate the effect of this gas on the environment and, at the same time, produce a very valuable chemical compound.
For the reaction between CO2 and H2 to take place, however, an appropriate catalyst is necessary. This is because CO2 is not a very reactive molecule. Because of this, the catalyst employed for the CO/CO2 mixture (Cu/ZnO/Al2O3) is not very effective if only CO2 is used in the chemical reaction.
Several studies were performed to develop new catalysts for methanol synthesis and/or to optimize the ones already existent.
Interesting results were obtained by the researchers of the Brookhaven National Laboratory (Upton, US); the work was done in cooperation with the University of Seville (Spain) and the Universidad Central de Venezuela (Caracas, Venezuela).
The results of this study were published in Science in August 2014.
Innovative Catalyst Formulation
Dr. José Rodriguez , leading scientist in this research, explains to Decoded Science how the catalyst was formulated.
“We tested a catalyst completely different from the ones developed before; we used cerium oxides (ceria) nanoparticles to create oxide-metal interfaces with unique chemical properties, an approach which was never used before for this reaction, but which was used for other industrial processes.
Ceria were combined with copper (Cu); as cerium has two possible oxidation states – +3 and +4 – the oxides present were both Ce2O3 and CeO2 (CeOx, x = 1,5 or 2). We used a copper substrate in which 20 % of the surface was covered with CeOx.”
According to Dr. Rodriguez:
“This catalyst worked much better; indeed, replacing ZnO with CeOx led to a reaction rate about 14 times higher. We performed some theoretical calculations on this system; results showed that the reaction follows a different path, with lower activation energy and, hence, it is faster. Experimental data – i.e. detection of intermediate chemical species – also confirmed this.”
Once they got these promising results, Dr. Rodriguez and his coworkers decided to improve the system even more. To do this, they added titanium dioxide (TiO2) to the catalyst.
“We codeposited Cu and CeOx in the form of nanoparticles on the surface of TiO2; what we saw was that the system Cu/CeOx/TiO2 was very efficient. In fact, with this catalyst the reaction between CO2 and H2 was about 87 times faster than with the “standard” Cu/ZnO catalyst.
It is important to highlight, however, than using just CeOx and TiO2 the catalyst did not work at all, and almost no reaction took place. Therefore it is essential to combine the three components (Cu, CeOx and TiO2) properly.”
Producing Methanol: Important Progress
As Dr. Rodriguez says:
“These results are important, as they show that there is a way to reuse carbon dioxide in a productive manner. In additionto mitigating CO2 effects on the environment, we could also make essential chemicals from it, benefitting the economy and society as a whole.”
Decoding Science. One article at a time.