Method for preparing nanoparticles interferes with the efficiency of  converting carbon dioxide into CO

 There is strategic interest in processes for transforming carbon dioxide (CO2), a greenhouse gas, into chemical products of aggregate commercial value, since the high concentration of carbon dioxide in the atmosphere is one of the main causes of global warming. The capture and transformation of CO2 into valuable products would be a way of avoiding its emission into the atmosphere.

One of the ways of transforming CO2 into chemical products occurs through the reaction of carbon dioxide with hydrogen gas – with the use of catalysts.  Nickel and palladium are two metals widely used as catalysts in hydrogenation reactions. An article published in June in the scientific magazine ChemCatChem, published by Wiley-VCH, presented the results of a study carried out in the Nanomaterials and Catalysis Laboratory of the Chemistry Institute of the University of São Paulo (IQ-USP) in collaboration with several groups in Brazil and abroad, which investigates the structure and the performance of catalysts of alloys formed by nickel and palladium.

“This is very fundamental research,” says Dr. Liane Marcia Rossi, full professor of the IQ-USP and coauthor of the article. “We studied the combination of these two metals, which can form metallic alloys, in order to understand the level of performance gained with a bimetallic catalyst.” The work was done within the scope of the FAPESP Shell Research Centre for Gas Innovation (RCGI), with the support of the São Paulo Research Foundation (FAPESP).

The conclusion was somewhat surprising, because the study indicated that, depending on the method of preparation, one may or may not form an alloy between the two metals. “Our results show that the synthesis protocol plays a decisive role in the performance of the materials obtained in the catalysis,” the authors wrote in the article.

By using an electron transmission microscope at the Brazilian National Nanotechnology Laboratory (LNNano), researchers saw that two preparation protocols, that is, two different ways of fomenting the blending of the metals, result in materials that have quite distinctly different structures – despite the fact that they contain the same elements: nickel and palladium.

When the particles, which measure between 3 and 6 nanometers, were prepared by a colloidal method and then immobilized on a base, the formation of an alloy containing the two metals was found. When a more traditional method was used, involving the direct deposition of the two precursors on the base, there was a formation of separate particles of the two metals, without forming an alloy. The material obtained by the most traditional method performed better in the catalysis, despite the fact that the system showed a structure that was not as organized as in the case of the alloys.

One of the objectives of the project was to achieve a better performance in the transformation of CO2 into carbon monoxide (CO), but mainly not to produce methane (CH4), which is another greenhouse gas that can be formed at the same time in this reaction between CO2 and H2. “Our goal is carbon monoxide (CO), which can be more easily transformed into valuable chemical products,” Dr. Rossi said.

According to her, the group will continue working to improve the nickel catalysts and develop nickel alloys with other metals. “We found that, actually, palladium is unable to contribute as much to improving the performance of the reaction being studied.” In the future, she also intends to develop studies for converting CO2 directly for products with aggregate value, without going through the carbon monoxide (CO) phase. Among the possible products to be made with carbon dioxide are hydrocarbons (fuels), olefins (raw material used in the production of plastics), alcohols (like ethanol and methanol), and others.

The work was highlighted on the cover of the magazine ChemCatChem, issue 11/2020, and the summary of the article Structure and activity of supported bimetallic NiPd nanoparticles: influence of preparation method on CO2 reduction can be read at