The synthesis of copper-based aerogels and xerogels via the epoxide addition method using various Supports and templates to improve surface area and increase efficiency in preparation techniques
Aerogels and xerogels have desirable properties for heterogeneous catalysis. The epoxide addition sol-gel route has proven to be the most efficient and cost-effective method to produce transition metal aerogels and xerogels. Copper oxide and copper and zinc oxide catalysts are popular today because of their low cost and catalytic activity for reactions such as the oxidation of carbon monoxide and steam reformation reactions. Copper and zinc oxide catalysts are used commercially with an alumina support. The surface area can be increased if the copper and zinc oxide is in the form of an aerogel. If a copper and zinc oxide aerogel is used with minimal support material, then there is significantly more active catalyst surface area within the material. Silica acts as a robust support and is only needed in small amounts to form copper (II) oxide and zinc oxide aerogels. The silica support allows for uniformly high surface areas of all ratios of copper to zinc. The copper (II) oxide and zinc oxide aerogels with silica support can be reduced to copper and zinc oxide aerogels and used as heterogeneous catalysts in steam reformation. Xerogels are faster and cheaper to produce than aerogels, but they have lower surface areas. Incorporating dextran in copper xerogels can allow for improved surface area because the dextran prevents some pore collapse during the drying and annealing processes. Dextran can be used as a soft template because it can be cleanly burned away. The dextran takes up space within the xerogel structure, allowing for less shrinkage during drying. Then, during annealing, the dextran is cleanly burned off, which opens up more spaces within the final xerogel structure. Resorcinol-formaldehyde (RF) aerogels are a good choice for support of copper and zinc oxide aerogels because the RF reduces the copper (II) oxide during the annealing process, allowing for the elimination of a reduction step. The RF, copper, and zinc aerogels can gel together, with an epoxide inducing the gelation of the transition metal salt precursor solution and the acidity of the metal salt solution catalyzing the RF gelation. Methods of improving the catalytic potential of copper-based aerogels and xerogels produced via the epoxide addition method were investigated. Future work will be to directly study the catalytic activity of the materials produced using a fixed-bed reactor in conjunction with gas chromatography.