Zeolites can be extremely porous. Ten grams of them can have an inner surface area that is the same size as a soccer field. Because of their cavities, they are useful for catalyzing chemical reactions and thereby saving energy. A research team from around the world has made new discoveries about water molecules' role in these processes. Conversion of biomass into biofuel is one important application.Although biomass fuel is considered climate neutral, it is still necessary to produce the required chemical reactions.Johannes Lercher is a professor of Chemical Technology at TUM and Director of the Institute for Integrated Catalysis, Pacific Northwest National Laboratory, Richland, Washington. "If we want to eliminate fossil energy sources and make large-scale efficient use of biomass," he says.Lercher, who is part of an international research team has examined the role of water molecules within reactions in the pores of the zeolite, which have a size less than 1 nanometer.All it takes is acid!An acid easily donates protons. Hydrochloric acid is able to split into positively charged protons that attach to water molecules when it is added to water. The result is a positively charged hydronium Ion. This proton looks to be passed on to another molecule, such as an organic one.AdvertisementThe organic molecule attempts to stabilize itself when it is "forced to" accept a proton. An alcohol can create a molecule that has a double bond, which is a common reaction in the journey from biomass to biofuel. The zeolite walls help stabilize transitional states during conversion and reduce the energy required for the reaction to occur.Acids are made from zeolitesZeolites have oxygen atoms within their crystal structure that already contain a proton. Through interactions with water, they create hydronium ions similar to molecular acids.Hydronium ions are dispersed in water but remain tightly associated with the Zeolite. Pretreatment with chemicals can increase the number of active centers and thus establish a certain density for hydronium ions within the pores of the Zeolite.The perfect zeolite to match every reactionThe research team was able, by systematically changing the size of cavities, density of active sites, and water content, to determine the pore sizes, concentrations, and reactions that catalyzed the selected examples.Johannes Lercher says that it is possible to increase the reaction speed by making pores smaller and increasing the charge density. However, this can only be done to a certain extent. If the reactions become too complicated or the charges get too close together, the reaction rate will drop again. This allows us to determine the optimal conditions for each reaction.Lercher explains that Zeolites can be used as nanoreactors in chemical reactions where the reaction partners are able to fit into the pores. We are just at the beginning of a new development that has the potential to increase the reactivity and efficiency of molecules at low temperatures, as well as to save significant amounts of energy when producing fuels or chemicals.
