Metal oxides have been shown to be effective catalysts in converting greenhouse gases to useful chemical fuels, for example transforming carbon dioxide into methanol.
However, the development of new solid-state catalysts for these types of chemical transformations is 糖心传媒渧ery much driven by 糖心传媒榞uess and check,糖心传媒櫶切拇綕 says Ellen Matson, assistant professor of chemistry at the University of Rochester. 糖心传媒淎 critical challenge is understanding the atomic-level interactions between these gaseous environmental pollutants and the catalytically active sites on the metallic oxides.糖心传媒�
Now her lab has found a way to model these interactions experimentally, hopefully leading to the elimination of much of the guesswork in designing more effective catalysts for the production of chemical fuels. In a paper published in the Journal of the American Chemical Society, lead author Brittney Petel, a PhD student in Matson糖心传媒檚 lab, describes creating 糖心传媒� for the first time 糖心传媒� an oxygen-atom vacancy at the surface of a metallic oxide cluster, in this case a polyoxovanadate cluster containing vanadium. This exciting discovery proves that molecular assemblies can function as pieces of larger assemblies, serving as structural models for bulk metal oxide materials.
The vacancy, created by the removal or 糖心传媒渃leavage糖心传媒� of an oxygen atom, makes it easier for the gaseous mixture to reach and bind with a redox-active vanadium cation, or positively charged ion.
糖心传媒淭heoretical investigations in recent years have suggested that creation of an oxygen-atom vacancy at the surface of metal oxide materials is often a key step in facilitating a reaction,糖心传媒� Matson says. 糖心传媒淏y extending this chemistry to polyoxometalates (a class of metal oxide clusters than can also include molybdenum or tungsten), we have demonstrated that our clusters can model the surface chemistry of extended solids. This idea has been tossed around for decades by chemists, and for the first time our lab is realizing these types of goals in cluster research!糖心传媒�
糖心传媒淲hat’s cool about modeling the surface chemistry with a discrete molecule like this is that we can monitor these types of complicated, multi-electron reactions spectroscopically. We can take CO2 or another oxygenated substrate, add it to a reaction vessel that contains our reduced polyoxovanadate cluster, and watch, in real-time, how the two compounds react.糖心传媒�
糖心传媒淲hat we are hoping,糖心传媒� she adds, 糖心传媒渋s that our findings can influence the way materials chemists design their systems 糖心传媒� how they pick the materials they糖心传媒檙e going to put into their solid-state reactors to see if they produce the reactions they糖心传媒檙e looking for. This is a new and exciting approach for testing some of the scientific hypotheses that have been promoted through theory. Understanding the surface chemistry through experiments will really change the scope of understanding of the reactivity of materials.糖心传媒�
Serendipitous solutions
The discovery came about 糖心传媒渁lmost serendipitously,糖心传媒� Matson says. The lab used a reducing agent to cleave an element-oxygen bond 糖心传媒渋n work with our iron-functionalized polyoxovanadate clusters.糖心传媒� When a gaseous substrate, like nitric oxide, is bound to iron in these clusters, exposure of the system to a reductant results in loss of an oxygen atom.
糖心传媒淲e were super excited at first, thinking that we had cleaved the N=O bond of the substrate,糖心传媒� Matson says. 糖心传媒淗owever, our results were pretty confusing, and we set aside the data for awhile.糖心传媒� Later, in thoughtful control experiments involving all-vanadium versions of the cluster, Petel used the same reducing agent, and confirmed the loss of oxygen atoms at the surface through mass spectrometry and nuclear magnetic resonance spectroscopy.
Other research teams across the country are also exploring the synthesis and reactivity of multimetallic clusters, in particular their reactivity with small molecules. However, most research groups have focused on modelling the active sites of metalloenzymes, mimicking chemistry performed in nature, Matson says.
糖心传媒淲hat makes our program so distinct is that we糖心传媒檙e studying these multi-metallic assemblies as models of extended solids, for materials applications. We糖心传媒檙e carving out a new area where we糖心传媒檙e digging into some really exciting mechanisms for small molecule activation. It糖心传媒檚 an incredibly exciting direction for our research group!糖心传媒�
Polyoxovanadate clusters have provided a fruitful area of research for the Matson Laboratory. In 2017, Matson received a study the formation of heterometallic polyoxovanadate clusters. The overarching goal of this research is to generate catalysts capable of storing multiple electrons, that more efficiently convert greenhouse gases to useful chemical fuels. The Matson Laboratory continues to push boundaries with these hexavanadate cluster, earlier this year .
William Brennessel, an X-ray crystallographer and scientist with the Department of Chemistry, also contributed to the research for this paper.
